Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
WHOI-73-28 LATE PLEISTOCENE-HOLOCENE CHEMICAL STRATIGRAPHY AND PALEOLIMNOLOGY OF THE RIFT VALLEY LAKES OF CENTRAL AFRICA By Robert E. Hecky and Egon T. Degens WOODS HOLE OCEANOGRAPHIC INSTITUTION Woods Hole, Massachusetts 02543 May 1973 TECHNICAL REPORT Prepared for the National Science Foundation under Grants GA-30641 and GA-35334. Reproduction in whole or in part is permitted for any purpose of the United States Govern ment. In citing this manuscript in a biblio graphy., the reference should be followed by the phrase: UNPUBLISHED M4JVUSCRIPT. Approved for Distribution iohn M. Hunt, Chairman Department of Chemistry Late Pleistocene Chemical of the Stratigraphy Rift Valley - Holocene and Paleolimnology Lakes of Central Africa Robert E. Hecky1 and Egon T. Degens2 Woods Hole Oceanographic Woods Hole, Institution Massachusetts 02543 3-Present address: Fisheries Research Board of Canada, Freshwater Institute, WINNIPEG 19, Manitoba 2Present address: Institut Geologisch-Pal&ontologisches der Universitt Hamburg, 2 HAMBURG 13, Von-Melle-Park 11. TABLE OF CONTENTS Page No, 2 ABSTRACT INTRODUCTION 6 MODERN LAKES WATER CHEMISTRY 7 LIMNOLOGY 8 Kivu 8 Tccnganyika 11 Edz1ard 13 Albert 14 Malci 15 16 GROSS STRATIGRAPHY AND CHRONOLOGY Kivu 16 Tanganyika 21 Ediard 22 Albert 23 Malcai 24 24 LAKE KIVU SEDIMENTS DEEP, NORTHERN BASIN >400 m water depth 24 Chemical Stratigraphy 24 Bios tratigraphy 40 Silicious microfossils 40 Organic matter 51 SHALLOW SOUTHERN BASINS <100 m water depth South Idjwi Basin Station Bukavu Basin Station 25’ 23’ 56 56 58 LAKE LEVEL OSCILLATIONS AND WATER BUET Kivu 62 Tanganyika 66 Edward 80 Albert 82 Malc&i 85 62 CONCLUSIONS 87 REFERENCES 88 -2- ABSTRACT The interaction Late Pleistocene tological of climate and Holocene and limnological and geology in Central is examined. Africa during The study is based on sedimen- work on the main lakes of the Western Branch of the East African Rift Valley, particularly Lake Kivu, Changes in sediment chemistry, mineralogy and diatom assemblage provide a detailed histogram of lake level oscillations... drop in lake level Kivu, Fluctuations Calculations indicate that the could be as high as 600 m for Tanganyika and 400 m for in water levels.are the means for reconstruction climatic events in tropical Africa of the last 15,000 years. climatic pluvial Bdlling, comparison between tropical times coincide with the prominent AllerØd, in equatorial that in Europe, e0g0 cool and dry periods Africa with ice ages in the Northern Hemisphere. accompanied by corresponding This may suggest activities. Paleo- zones reveals interstadials Climatic Optimum, and reversely, The African climatic cence0 and temperate of sequence .of pluvials periods and interpluvials of hydrothermal that rain water exercises activity control is and quies on hydrothermal. -3- INTRODUCTION Eastern Africa focus of intense tectonic dramatic topography, in large rifted crustal and volcanic Broad regional troughs blocks since Miocerie times Bishop, activity uplift can be traced across the African Cloos, continent which has produced a of the Red Sea as a juvenile has directed rift interest system and its rifts relationship Degens et al., elsewhere buried to the present 1971, 1939, This pattern oceanic rift and riftirig Recent charac with active status to the world-wide have been accompanied by profuse Active volcanoes spreading of the African system of mid-ocean in eastern Africa as volcanism which has deeply large areas of Precambrian basement under Tertiary, and Recent lava and ash, of rifting for nearly 3,000 km from the and future Uplift resulted downward movement of Zambesi River in the south to the Red Sea in the north. terization has been a has concomitantly formed by the relative along normal faults 1963 are still Pleistocene, a prominent feature of the landscape. The African sections: 1 valleys are generally the Nyasa section, or Gregory Rift 1965, rift and 4 These Rift 2 section, the Western Rift, the Lake Rudolf and Ethiopian valleys delimit drainage basins, lakes the size of which is partially over the respective grouped into four separate areas. the Eastern section Fig. regime a large area of the Nyasa Kivu, Edward, and Albert along the arcuate Western Rift valley Holmes, and they contain dependent on the climatic Lake Malawi occupies while Lakes Tanganyika, 3 1. are strung out Lakes Edward and Albert have recently been renamed as Lake Idi Amiri Dada and Lake Mobutu Sese Seko respectively, but they will be referred to in this paper by their former -.4- names to facilitate valleys referring have comparatively are presently tributary regions high rainfall of external Lake Malawi. of internal the Zafre literature. over their drainage, to three of the largest .rivers Edward and Albert, drainage shrinking between .the Eastern lake, and Western Rift duct of the same large-scale Lakes and the Zambesi Rift are large basins but it has been grad Livingstone Victoria, are lakes dot the vast area. is an exception, last 5,000 years The other large East African the Nile Lakes Kivu and Tanganyika, Rift and they The lakes of these rifts in the world, where only small saline for the These two rift catchment, The arid Eastern Rift and Ethiopian Lake Rudolf in the Ethiopian ually to the earlier and Kendall, occupies a gentle valleys, and likewise, 1968. downwarp it is a pro earth movements which led to the formation of the rifts, The antiquity their.geology present the interaction ficant of these rift earth historians of climate to be found. growing explosively; poorly understood. their tropical a unique.opportunity and geology on the continents portion of geological longer records basins, time. however, the correlative controversy the evidence for numerous Pleistocene glacial cycles differences a continuous holes and seismic presence records record from the continents for maximum climatic in the Albert of over 1.2 km of sediments record is over the correlation record so far examined has preserved. is preferred a signi of the oceans is continental continental setting to examine through which the To reconcile is required information, Basin have demonstrated Bishop, between found in the oceanic record and the concept of only five or so major glaciations tropical and Only in the oceans are substantially Knowledge of the history There is still position, such and a Borethe 1963; and Wong, unpublished. -5- Seismic profiles tude Table from the other lakes show accumulations 1; Degens et al,, stratigraphic sections but the aridity Thus far, sites Butzer lished. coring techniques 12 m core recovered and Richardson, information of exposed stratigraphic Albert which covers the past 1965 unpub of a and descrip see Bishop, of a 12 m core from Lake is also. presently under study This paper presents Institution 1971 to Lake Kivu and 1972 to Lakes Kivu. and piston cores of varying a 1972 expedition of Heidelberg cores up to 3 m in length from each of these to the description Livingstone, 25,000 years In addition torium f1r Sedimentforschung of gravity 1972; Richardson in the Albert basin have returned gravity from 1 m to 8 m. 30,000 years from the Woods Hole Oceanographic in 1970 to Lake Tanganyika, lengths a rather communication, Recent expeditions Edward and Albert is limited sections in reconstructing of the Western Rift is very The diatom stratigraphy Thomas Harvey, personal the greater record in the shallow lakes over the past rift from Lake Tanganyika 1963,.. for a summary. cores of that 1972; Richardson Published record, Rift have received have been successful view of the history known, of the modern lakes which can be brought to these By comparison the paleolimnology poorly suite a continuous of the sedimentary Such efforts et al,, and the shallowness Rifts, because of the abundance of human cultural and the accessibility coherent Thick found in the Eastern and Ethiopian of recovering of paleohistorians remote areas, 1973; Wongç unpublished. the lakes of the Eastern to the unsophisticated tions are also of the climate reduce the probability attention 1971, of similar magni University by the Labora has recovered a from Lake Malawi. the chemical stratigraphy of representative lakes along with the biochemical and diatom -6- stratigraphy still of Lake Kivu. in progress. struction stratigraphic climatic on these lakes. logy of the present Malawi Brooks, depauperate Verbeke, various lakes, such as the species 1950; Fryer, fauna in Kivu unusual aspects 1959 is also a miniscule fraction it does cover the and shows the effects In addition, recon 15,000 years lakes, evidence will have significance been proposed to explain cores are a provisional represents record in these transition the stratigraphic data, material Late Glacial-Holocene fluctuations on the other of these lakes for the past Although the available of the potential studies Based on the available of the history attempted. Microfossil of Pleistocene interpretations to theories which have of the biology flocks of and limno- in Tanganyika and and the immense methane reservoir Degens et al,, 1973; Deuser et al,, and 1973; 1957. MODERN LAKES To provide follow, a brief The information extracted synopsis presented from a diverse to the original see a framework for the historical Damas, 1937; Verbeke, for Lake Tanganyika et al.., in Table 1 and Table 2 and reviewed below was literature; Tallingff and the interested discussion 1963; Verbeke, 1957; for Lake Kivu 1955; Verbeke, to of the modern lakes is necessary. sources for a more detailed for Lake Albert Kufferath, of the limnology reconstructions Beauchamp, 1939; Capart,, 1971; and for Lake Ma1awi of the various lakes 1957; for Lake Edward: Damas, 1957; Degens. et al., reader is directed 1937; Schmitz and 1973; Deuser et al,, 1952; Coulter, Beauchamp, 1953; Eccles, 1973; 1963; Degens 1962, WATER CHEMISTRY The chemical composition Kivu, and Tanganyika Table magnesium values relative that these unusual of the area. of lake waters is remarkable 1 from Albert, for the high potassium to the other cations. ionic ratios find their The Virunga volcanic Kilham These rocks have K20 > by their Na2O, and the Ca and Mg contents than for average crustal material Higazy, These volcanic rocks are also rich rocks of Southwestern ultrabasic, and proposes in the volcanic origin between Edward and Kivu, and the Toro-Ankole field, are characterized 1971a which forms the drainage field, in the Edward basin, Edward, divide Uganda potassic rocks. are much higher 1954; Bell and Powell,, 1969. in TiO2 and P2O5, and have relatively great abundances of Sr, Ba, Rb and Zr, which are uncommon for such ultra- basic rocks. sedimentary These facts l97la and Degens et al, of these rocks by hot, quent loss of Ca by precipitation a straightforward in turn, Semliki taries taries take on these proportion the plateaus different tive to interpretations of composition cf. of salts intense the observed composition arise in and Tanganyika will, major tributaries, in Edward md Kivu, the These tribu of the water budget and an even to Albert escarpments Malagarisi Albert as their and Tanganyika. from the Precambrian granitic above the rift contribution will yield portion of the salts believe that CO2-charged ground waters with subse characteristics supply a considerable deriving 1973 manner for Kivu and Edward. and Ruzizi respectively, greater be important chemistry.. Kilham weathering will later and metamorphic rocks of are more dilute and Ruzizi by these tributaries Other tribu and of a quite in Table 1. The rela must be minor, as Albert -8- and Tanganyika strongly resemble Kivu and Edward in their major ion composition, Lake Malawi farther the aforementioned The volcanism, to the south and with no connections volcanic provinces, has a quite unusual petrology, different and hydrothermal spring water chemistry. activity so dominate the lakes in the Western Rift are less significant Nyasan Rift. valley, Hot springs are known along the rift with in the but they are unaccompanied by active volcanism Von .Herzen and Vacquier, 1967. lake is much more dilute that weathering Rift, in volcanic-derived CO2, The suggesting perhaps are lower because the ground waters rates are not enriched than those of the Western which of the region However, rainfall is generally higher, temperatures lower, and the lake volume smaller than Tanganyika, and the dilution may simply reflect composition of the waters is representative though Talling low, and Talling 1965 .1973, of fairly The ionic of most African waters, do note that According to Becky and Kilham African lakes are indicative times. lower residence the chloride is relatively low Cl/Na ratios humid conditions al in many in the drainage basin, LIMNOLOGY Kivu Damas first 1937 described Kivu which has since been studied al,, 1973. the unusual in ever increasing Below 70 m, temperature and salinity The density increase produced by higher sity decrease inherent hydrography salinities with the higher temperatures Degens et detail increase just of Lake with depth. offsets resulting the den in a stable -9. thermohaline r.’he greater density structure, diffusivity to salts yields a series of convecting cells of heat relative Turner, 1969, and the increases in temperature and salinity with depth occur in a steplike fashion. Density differences between these cells are minute and can often be resolved at a decimeter level density differential F, Newman, unpublinthed data,’ and the between even surface water and water below 350 m is not large, being on the order of .002 g/cm3 Schmitz and Kufferath, At present, 1955. Kivu would seem to be a delicately balanced system which has persisted for at least the 40 years of observation, The history of this phenomenon over longer periods is an important consideration present stratigraphic of t.he work. MeromixiS in Kivu greatly reduces the exchange of water between the upper 70 m of water which circulate water of greater depths. The effect at least seasonally and the anoxic of this lack of mixing is dramatic, Surface waters are depLeted as the nutrient values in Table 1 attest, in phosphorus and nitrogen by plankton production and subsequent sinking and decay below the thermohaloclines where regenerated nutrients are effectively trapped. Silicon, in Table 1, also increases the other nutrient with depth, but it gives a linear regression on Na,, indicating well as trapping canic al., has little and resolution production CO2 nutrients, to do with the observed trends. the deep waters also accumulate and predominantly biological .origin The loss of nutrients the primary productivity diatom As gases of vol H2S and CE4 1973, which are held in solution .by hydrostatic pressure, below 300 m contain two liters that Deuser et waters of gas for each liter of water, to the deep water trap profoundly influences of surface waters Table 2. Primary production -10- is less than one-fourth that of Edward and Albert, similar size and chemical composition, In addition dines, Kivu has a seasonal which is established thermocline 20 m depth during the warm, rainy seasons, ences between the epilimnion stratification can develop, temperatures tropical as the density Cool, dry seasons lead to full is increased after is reduced by the increased listed in Table 2 pertain offshore Coulter, by intense in the greater to 50 m, plankton blooms; the inshore waters none of which is considered Chaoborids 1957. The fish extinctions, judging from the abundance of shells esp. pelecypods, in the lake, a pelagic, planktopha- seem to have suffered The planktonic diatom flora Various possible unusual water chemistry, perspective on the limnology recent of species which are for the domination by the genus Nitzschia, is also shared by Tanganyika. insight, aspects which have are absent from the lake as they are from The molluscs, and an historical are often fauna is depauperate Tanganyika. overturns, The values part of the lake. with only 11 species, catastrophic of the whereas such events are uncommon Verbeke, is remarkable production communities of the lake. caused prior comment no longer extant Biological of plankton. The fauna and flora of Kivu have several gous species. a very stable and the transparency populations 1963, differ than at lower temperatures. only to the pelagic In Kivu as in Tanganyika characterized are slight, greater of mixing, waters at approx changes at these elevated circulation these periods to the deep thermohalo Although temperature and hypolimnion are relatively which are lakes of a causes, etc. Hustedt, a feature including 1949 which volcanism, have been suggested, of the lake should provide -11- Tanganyika Tanganyika is divided by a shallow 500 m into two basins, of which the southern mum depth of 1,470 m, It is thermally dine 100 m. lying at approx. depth in both basins, structural sill mean depth is the deepest with a maxi stratified with a perennial Although the thermocline the lower limit of detectable lies at the same dissolved oxygen is 200 m in the south basin of the lake and 100 m in the north, indicating that mixing phenomena for the basins .are somewhat different. differences across the seasonal and perennial thermoclines thermocline in the dry season, to maintain several years. unknown. plete.ly the thermal stratification The persistence Brooks 1950 deeper in 1895. suggests Beauchamp irregularly suggested littoral 1939 that cooler tributaries introduce waves, generated stresses, may account into the epilimnion is the lake might mix com-. Talling, currents intervals 1963 or seasonal to .the depths. of have cooling of which would con In offshore of the thermocline areas under meteoro for much of the mixing of hypolimnetic Coulter, Despite the perennial cient to prevent any significant constituents. e.g. and nocturnal by tilting is suffi stood somewhat of time when prolonged downslope density cooler waters 1963 over longer periods the thermocline Others combined over at least periods believed that over long periods waters might yield tinuously waters that Coulter, of stratification of cooler climate allowed mixing. logical are slight, This .minor density differential with the enormous volumes of water to be mixed internal Temperature from 2-3°C in the wet season to 0.5-1°C across the perennial ranging cient thermo- .1963, thermocline, mixing processes stratification Only those minor consitutents are suffi of the major chemical subject to biological uptake -12- and release mous store exhibit of nutrients in the greater offshore stratification. waters suggesting Alteration is similar an enor populations and others consider whereas the littoral the regions have been done in the lake, of the present is even to Kivu and the transparency that the offshore of the lake, to planktonic 1963 measurements areas are even less productive hydrographic greater mixing across the thermocline ductivity constitute at the southern end of the lake are eutro upweliing No primary productivity greater, Coulter to be ultra-oligotrophic, but the diatom flora Kivu. which are unavailable part of the lake. and areas of seasonal phic. The deep waters than regime which would permit could substantially alter the pro and evidence of such might be found in the strati- graphic record. The Ruzizi River is the major tributary its chemical composition, and most authors The lake has been closed in historical agree that without the Ruzizi ganyika would be closed and more saline Ruzizi coincided with the blockage drainage The acquisition of the formerly northward Moore 1903 originally ventured work has moved the date of the Virunga event substantially events Brooks, 1950, Hydrological in the Kivu basin and the status problem which will find resolution Tan- of the flowing of the Virunga volcanoes years B,P, based on the rugged appearance of the volcanoes, Pleistocene times, and the Kivu drainage, today. in the Kivu basin by the imposition which created Lake Kivu. to the lake and determines a date of 15,000 Subsequent back into the linkage via the Ruzizi between of Tanganyika in stratigraphic is a most interesting studies’ on the sedi ments of the two lakes, Biologically, Lake Tanganyika is exceptional among the East African lakes for the large number of endemic genera and species Brooks, -13- Although species 1950, the region, especially much more restricted. flocks among fish are present in other lakes of Malawi and Victoria at the generic In addition nearly all to fish, groups have a high degree of endemicity, lakes. diversification, istry responsible greatly to understanding and temporal isolating for the evolutionary in lake levels but temporal variability are thought to have played a role. tribute the major faunal which is not the case in the other of the lake is.most The antiquity level they are Stratigraphic and water chem studies will con importance of geographical the relative mechanisms to speciation in Tanganyika. Edward Lake Edward lies to the north of the Virunga volcanic runoff from that area via the Ruchuru River as well receives George to the east via the Kazinga Channel. is nearly identical meters, with that which has important to the seasonal thermocline, generally waters Below this depth,, However, depths greater efficient. great of Kivu and probably Tanganyika. consists The productivity primarily this must be considered anoxic,, nutrient-rich Consequently, and nutrient a eutrophic most regenera of Edward is four times as The diatom flora of the of Nitzschia fonticola discus dconasi of secondary importance.. which than 80 m occupy only side of .the basin, tion is quite areas In addition there is a feeble deep thermocline of the basin is mixed to the bottom seasonal1y offshore as from Lake The lake’s water chemistry consequences for productivity. a very small area on the western as that It of Kivu, but its mean depth is only forty lies between 70-80 m, are encountered. dam. with Stephano In view of the productivity, assemblage. -14- The fish fauna of the lake is depauperate northern neighbor, Albert. the basin indicate Brooks,, 1950 desiccation stratigraphic the fauna was more diverse and was of Nilotic during origin, the Pleistocene, been from Lake Victoria, Albert Fossil-rich when compared to its beds exposed in in the early Pleistocene Extinction is attributed Most recent faunal invasions and recolonization is precluded by the cataracts to have by the Nile fauna in Lake on the Semliki River, Albert Lake Albert receives a large portion of its total Lake Edward via the Semliki River, in proportions Talling to Edward, but the nutrients and Talling, but impoverished These nutrient The major constituents 1965, in silica, relations flora between the lakes, are strikingly Albert waters from are similar different are very rich in phosphate whereas the opposite may account inflows is true in Edward, for the differences as sediment assemblages in the diatom from Albert are domi’ nated by Stephanodiscus aslraea as opposed to the Nitzschia fonticola in Edward. This is consistent S. astraea is a low silica production efficient nutrient regeneration. in Albert, stratification lations of nutrients This stratification inshore waters. ephemeral specialist is also high in Albert, stratification lived with Kilham’s l97lab hypothesis among planktonic and .again this diatoms. is related that Primary in part There is no well defined seasonal but Talling 1963 reports a peculiar short- of sufficient magnitude to allow detectable and depletion of oxygen in the deepest waters, evidently is initiated accumu by the sinking of cooler Contrary to the other lakes, stratification to then, Albert achieves it does ‘have in the cool-dry season, the and is most thoroughly mixed during the warm-wet seasons, to be warmer than offshore when inshore waters tend waters. Malai’i Malawi is the least tioned above, Its nutrient nutrients its water chemistry chemistry generally is quite is most similar are low in the offshore thermocline deeper than in Tanganyika. than Tanganyika; 273 m, substantial areas This in conjunction dominant diatoms, The depth of detectable and, because the average has fallen more saline deep and oxygen 250 m depth is only of the lake are mixed to the sediment surface, Beauchamp,, 1953 should mean a fairly estimates under high pro are available, the conditions, to one genus. much younger than Tanganyika, there The lake has a perennial depth is much more variable Malawi has some species flocks most reasonable all the Melosira nyassensis and Stephanodiscus astraea, suggest mesotrophic restricted from the other lakes, to Tanganyika in that Although no primary productivity ductivity. As men with the apparent mobility of the thermoclines the strong wind regime largely different waters, as in Tanganyika,, but its is also greater at least studied of the lakes considered, Brooks, phases occurred The lake is generally with a Middle Pleistocene 1950, below its outlet among the fish, but these are considered origin considered As is the case in Tanganyika, in modern times; in the past. the lake and it is conceivable However, to be that according to Brooks are no faunal elements as there are in Tanganyika which require suggest such a phase, or -16- GROSS STRATIGRAPHY AND CHRONOLOGY Ki vu The gross stratigraphy lS,, and 13’ are presented tive of the greater are from different of sediment cores from stations in Fig, 2.. These are considered number of cores collected depths and basins. 10, 4’, representa in 1971 and 1972 as they Stations 10 and 4 Fig, are 1 from the deep northern basin of the lake where depths exceed 400 m, 10 has three distinct finely loci, units. laminated with alternating particularly generally very high, dark brown material is almost entirely are carbonate, 90-95%, The second unit is also finely is not present. of organic-rich material of pure diatomite stratigraphic a meter of this alternating volcanic material organic, of this was recovered section is of the consist Several intervals are also. found. ash, terminates section laminated with alter with diatomites, cm thick while the The brown material layers. The laminations up to several unit, has a gel-like The .water content of this dark grey and yellowish-white upper section At several from 24-29 cm and .100-138 cm,, the white laminae are The brown material white laminations From 0-138 cm the sediment is dark brown and white layers, absent and the resulting consistency. nating sedimentary Core The third the core at 320 cm, at a nearby station: Over towards the bottom of the second unit, from 260 to 320 cm,, numerous thin intercala tions 3 cm of ash. occur in the top unit from 75 to 78 cm, of ash occur, The massive Also, ash was not encountered from the north basin, out rapidly. bathymetric Capart suggesting that from Verbeke, study of the lake, in numerous other 5 m cores it .is of local occurrence 1957, identified and pinches as a consequence of a detailed three sublacustrine volcanic -17- cones in the north basin in the vicinity of our station the deepest members of a set of volcanic cones along the northern shore of the, lake, which erupted underwater, 1955, 1963, DeNaeyer, with the activity subsequent sedimentation sublacustrine is an 8 m section. shortening gases on retrieval cones. and the fine structure section has essentially 10, and core- were along bedding intercalations >0.5 The as the second unit cm are more frequent, unit of core 10 is absent,. stratigraphy indicates 13’ and 15’ are significant lower water levels in the past, and second units of station 10 present, because their Station in 86 m of water at the southern end of the main lake. dark grey, texturally stiff, and structureless, but it terminated crumbly texture similar lost on retrieval, bottom unit, in.a third This unit was except for the top 30 cm, which were white because of a high calcium carbonate also a thin white band at.195. 13 was This core had the unit which extended from 160 cm to the bottom at 421 cm, than its of station Numerous gas spaces between sections. only one unit... .It is laminated Cores from stations first extent, of the sediment was not disturbed. in core 10, but major diatomite The first limited of the section by expanding of core were present upon opening,. but .the separations planes origin with over 10 m of sediment, past the core catcher probably occurred, associated A subaerial kilometers’ to the southeast The corer penetrated or extrusion 10 is probably seems to be ruled out by their Core 4’, from several These are although they are now exposed The ash at station of these 10. content, There was The very .bottom of the core had a dry,, to a soil. Some of this material may have been Organic and water content were low throughout this The stratigraphy present level suggests .that the lake stood much lower during the deposition of this third unit, was probably lower than the coring site before.then, and it -18- than its present level during the deposition of this was probably lower than the coring site before Station 90 m. organic then, from the main lake and station The first 35 m deep, and structureless, and water content that aragonite The high carbonate very From lSO.to...260 cm the sediment has frequent bottom of the core the sediment has a light reveals 13’ by a 150 cm are dark brown to black, thin laminae of calcium and magnesium carbonates, material and it was in the Bukavu Basin of Lake Kivu at a depth of l5 This basin is separated shallow sill, third unit, are relatively Below 260 cm to the grey appearance low, Microscopic needles are a primary constituent and low organic content suggest and organic examination of the sediment, a shallow environment and lower water levels. Several other cores recovered evidence of A core from station .9 in a depth of 338 m had the same lower lake levels, two upper stratigraphic tured clay-rich from Kivu contained facies units as core 10, but it terminated which extended from 337-357 cm, The lower 20 cm almost bridge the stratigraphic gap between core 10 and 4’. virtually in depths greater absent in the present >60% from sediments lake, are restricted that the silts and clays derived to depths of less 338 m suggests than 40 m, of station 369 cm clays from..the rivers Verbeke in a clay-rich, 10 are present of station 1957 are generally Presence of the clay-rich a profound drop in water level, of water also terminates two units depths, Clays are than one hundred meters and sediments with the clay content to much shallower in an unstruc reports restricted sediments at Station .unstructured 9 1’ in 229 meters sediment, The top from 0-180 cm, but from 180 cm to become much more important, From station 12’ in 254 m of -19- water a 257 m core was recovered, present, and this From .150 to 190 cm a clay facies was underlain by an .even coarser, 190-250 cm, suggesting that the mouth. of a larger by at the time of deposition. laminated and diatomaceous, mica-rich that bed from creek was very close The bottom .7 cm of.this which indicates was core were finely a much higher lake level had preceded the shallow water phase. The most dramatic evidence for a much lower lake level at station 14, where a 6 m core was taken in 310 m of water. cm of this core contained stratigraphic units correlative two units of station 10, well-rounded of metamorphic provenance, pebbles 5,5 cm in diameter. fragments Below 90 cm the core consisted the seismic profiles tural is a beach deposit. Degens et al., Further 1973, These sediment depths .contrast of shell for a level comes from show that age of 10,000 years. These dates indicate part the struc sharply with the greater for the cores from Lake Kivu are listed Sediment from a depth of 170 cm in station The bottom of 10 is correlated of core 9 by microfossil overlying at found in the deep northern basin, Radiocarbon dates age of 6,200 years, sorted, of which was support These records is only a thin veneer of sediments than 0,5 km of sediments Table 3, of poorly than 300 m,, which are .found mostly in the southern there basement, with the upper the largest former lake stand at more than 300 m below the present of the lake, The top 90 The lack of graded bedding and the presence suggest that this depths of less was found and chemical criteria, in 10 is assigned an with the dated bottom and it is assigned an The base of core .9 has an age of 10,700 years, a sedimentation rate of 0,3 mm/yr for sediments between 9 and 170 cm and 0,4 mm/yr for sediments between 170 and 320 cm. -20- A date of 11,200 years B,P, was obtained Such an age is reasonable 10 is absent, as the distinctive and microfossil that there indicate brownish upper unit of core and chemical data to be presented is explained either of the corer, covered the brown unit, dates from 4’ indicate superpenetration by a depositional seems most likely. a very high sedimentation Although the high rate is surprising, The hiatus The other rate of 3-4 mm per 10,000 years it is similar rate measured on a 1 meter core from 310 m n and Vacquier, later As all ‘other cores in the basin re year, or nearly 10 times the rate for the past 10. 4’, is no temporal overlap between cores 10 and 4’, absence of the upper units or superpenetration from the top of station at station to the high Lake Malawi Von Herzen 1967, Other samples for dating were chosen in order to estimate date of the former lowered lake levels rise, The dates from core l3 of the relatively core, i.e., laminated inorganic, for the surface indicate shallow water facies sediments sediments, of the subsequent very rapid deposition at the bottom of the 13’ and .5,2 mm/yr at station in 15’ were deposited and the uppermost unlaminated error and core.l5’ 1,6 mm/yr at station sediments and the rapidity at 0,15 mm/yr, An assumption of atmospheric sizable contribution 13’ and 15’ seem to show that between the initiation 11,070 years B,P, CO2 to the alkalinity data to estimate The assuming no zero for the CO2 in the modern lake may be unfounded, we have no pertinent 15’. at a lower rate of 2,6 mm/yr bration of volcanic the the possible equili as there is a of the lake, error, but The dates from as much as 1,000 years may have elapsed of predominantly and biogenic biogenic sedimentation sedimentation over 15’ over 13’ 9,725 years B,P.. -21- This implies until that the Bukavu basin was separated approximately the Bukavu basin, 10,000 years B,P,.. .As the Ruzizi exits the lake from Kivu had no surface outlet until timing of these rising lake levels with dates established on other African lakes Kendall, 1969, and this in the ‘sediments assuming that suggests was quite climatic from the main lake up and eventual that..the that after tIme. overflow are consistent Butzer et al,, 1972; organic carbon incorporated near equilibrium with the atmospheric reservoir, events in East Africa were contemporaneous. the carbon dates are affected The If by "old" carbon, then the dates given are maximum estimates. Tan ganyika The stratigraphy and radiocarbon cores have been previously short presented review will be given here. in length are available the north basin, Sedimentation station 3. A series from various and only a cores up to 250 cm depths in the lakes, A core from 3, are depicted in Fig, 2, 12, and 0,4 mm/yr at Rates which were 10 times lower are found on the sill Both cores have two stratigraphic laminated, in color and the laminations less thick are present through both sections quent in the southern basin core, contain 1971, of gravity are about 0,5 mm/yr at station is dark .grey in color and finely higher of the Tanganyika Degens et al,, 12, and one from the south, rates the two basins, lighter chronology sedimentation rates a much greater regular, Turbidites in both cores, These thrbidites of clays, The upper one while the lower section in the deep basin. admixture units, between is up to 3 cm but are more fre explain in part the All the Tanganyika cores principally kaolinite with -22- some illite and chlorite, from station 19 over the sill stratigraphic blue-grey than the deep...cores units in 550 m.ofwater not encountered and’grey in color, the present regime. greater two additional These were in.-..the deep basin cores, dominated the clays, combined with the absence of pyrite in these sediments were laid down under suggested that conditions, oxidizing recovered and montmorillonite The change in the clay mineralogy these lower units A 200 cm core from Kivu. which implies a hydrography markedly different from A date from the bottom of core 19 gave an age of than 28,200 years B,P. Edward The sediments At station 5 laminated, but the thickness variable; see of Lake Edward varied 120 m, and station similar throughout visually laminae diatomites to that of station the cores very, fine volcanic over as much as 10 cm bands, present, of the light Also discrete but these coarser strata finer material. a result These two cores bands of coarser ash were were not directly associated homogeneous brown color and still in the deeper cores, very organic. to these depths brings fine lamination present at greater sufficient with the and had a quite of their high pigment content, no trace of the lamination present At several ash was disseminated other cores from Edward were from depths of 80 m or less. ing of waters was quite 4’ in Kivu, These two deep cores were very organic pronounced green color, with depth, 4, 102 m, the sediments were numerous bands, 1-2 cm thick,. were encountered, are strikingly intervals Fig. 2, quite dramatically The three These showed They were of a Presumably turbulence seasonal mix to destroy the depths below the more permanent deep -23- The role of organisms thermocline. but Verbeke of less states 1957 than 40 m, in sediment mixing cannot be ignored, that the benthic A radiocarbon fauna is restricted to depths date from the deepest core indicates a rate of 0,9 mm/yr. sedimentation Albert The sediments of Lake Albert the other lakes considered Fig, are quite 2, different The core from station mum depth of the lake is a nearly uniform grey sediment, the most abundant component, There is a slight site. The core from station 5 at the maxi and clays are color change over the length of the core as it becomes darker towards the top, near the base of the core yields from those of a sedimentation A carbon date from rate of 0,7 mm/yr at that 3,, water depth 47 m, is more noteworthy, From the top to 185 cm the sediment is dark grey to black in color, from 185 to 460 cm it is a uniform light grey, 480 is very sandy, and the core terminates 481 cm, T. Harvey personal at 660 cm in his 12 in core taken bracket the layer indicate is studying the diatoms of Albert 7,500 years B,P, fossil at’this site, at station The shallowness layer His carbon dates which Harvey an age of Thus, sedimentation years B,P, have been quite variable Harvey also finds the rates of this at assigned to 340 cm by a micro- 0.25 mm/yr from 13,000-7,500 5, a similar 3 and has informed us that with his well dated core. from 7,500 to the present, material layer is 13,000 years old, could be provisionally correlation encountered from Albert. that this The sediment from 460 to in a dry, brittle communication and rates and 0,45 mm/yr and much lower than in his core to be labile, lake.and the large fetch of the wind allows mix ing to the bottom throughout much of the year, which results in fairly -24- well .oxidized sediments. time may indicate,fairly topography of the sites The variable sedimentation the different in space and which combine with the strong bottom currents to yield rates rates, Malcmi A 252 cm core from 553 m of.water made available similar by G, Miller of Heidelberg, to. those of Tanganyika in that and diatomaceous laminations The sediments are often apparent,. especially available core, but the possibility mm/yr 15 at Malawi was appear to be the sediment is fine and organic, are also frequent, for this of station below 143 cm, Mica-rich turbidites No carbon dates are yet of rather high rates in the lake is demonstrated by Von Herzen and Vacquier 3 1967, LAKE KIVU SEDIMENTS DEEP NORTHERN BASIN >400 in water depth Chemical Stratigraphy Nineteen trace metals tuents of the sediments, determined Details in separate reports radiocarbon from stations Degens and Kulbicki, chronology, 10 and 4’ are considered, to give a nearly mentary events in the northern basin years, of the method as well as the raw l973ab; 1970. The cores their Fe2O3,, SiO2, A12O3, CaO, MgO, and TiO2, were by uv.spectroscopy. data are presented Baradat, as well as the major chemical consti because of complete record of sedi of Kivu through the past 14,000 However, as we have constructed the chronology, a gap between -25- 10,000 and 11,000 years B,P. this gap are present supports results, in nearby core 9. such an interpretation. graphy are presented which exhibit stratigraphy Fortunately, Other evidence presented The highlights in Fig. 3; the distribution large variation we recognize is presented. oscillating Mn.. ,of only those On the basis elements of this in the cores, by high but variable chemical The lowest Al.and The second unit from 710 cm to 500 cm has declin ing Al and the Mn fluctuations frequency.. later of the chemical strati five geochemical units from 710 cm to 1,200 cm is characterized strongly about 700 years of are reduced in intensity and eventually From 500 cm to 410 cm, Fe accompanied by Ni is prominent in the sediment, A similar facies is present from 320-275 cm in core 10, From 275 to 130 cm and from 90-35 cm in the latter core the CaCO3 content is high1 while from 130 to 90 cm and 35-0 cm CaCO3 is again absent, organic matter and Pb are greatly Spencer et al, analysis to interpretation, unstructured to a simplified Factor analysis were found to explain varimax factor just detectable limits, the efficacy matrix which is more amenable rotation Table 3 presents matrix for each element which was present the identification ments are not depicted in Fig.. behavior of the other elements, Spencer, data of cores 10 and 4’, and five 82% of the variance, concentrations.. of factor raw data which sedimentary with orthogonal was performed on the elemental factors within yield, elevated. have demonstrated for reducing the large, analyses generally 1966 1968 and These factor loading of the factors.. 3, this table will in greater the than scores permit, Also, as all the ele allow insight into the -26- The high loadings of A12O3, Ti02, Ga, Cr, Cu,, Zn, and V suggest that this linite is the detrital and illites first three component consisting and weathered volcanic elements with detrital are generally residuals of clays is not surprising, Cowgill kao The movement of the ash, minerals of weathering primarily & Hutchinson, as they 1970 and the movement of the other four elements with this group can be traced to the unusual volcanic rock sequence of the basin.. The rocks of the area are thought 1954 atite Higazy, magma with crustal istics to have resulted rock, These distinctive imparted by the volcanic process are brought association lesser mobilization The high negative loading is with SiO2. the SiO2 of factor The positive gical origin, growth, the sediments, is certainly factor as both elements are essential The negative incorporated relationship but it will be shown later carbonate deposition As a general factor rule, indicates The their not detrital, primarily micronutrients by diatoms, with a biolo for algal with the organic matter of between the carbonate phase This is partially that temporal and spatial changed high biological accompanied by low carbonate deposition 2 suggests The highest posi is in line mutual dilution, have probably though, factor.. being contributed and. the biogenic phases suggestsa true, with this of V and Mo on this and they are probably factor of Ca, Sr, and Ba on factor As this 2 is biogenic, loading character than the other metals, that the carbonate phase is involved loading geochemical and erosion process, of Cr, Zn, Cu and V with this by weathering of a carbon to the lava and ash of the area to the sediment by the weathering strong tive from the reaction fundamentally productivity patterns of in the lake, has probably been to the coring sites, and the -27- observed hints loading on factor 2 is the result, The negative loading of Mn at a manganous carbonate phase which, it will be seen, was reason able for an early period of the lake’s history.. Factor 3 has high positive Zn, and Cu, The close association ments has previously 1970, been noted availability of a sulfide factor depositional of these for Fe, Ni, Co, elements in lacustrine determined by redox phenomena and the 3 might be characterized’as and co-precipitation, the redox potential of the environment, almost entirely Manganese also has a sizable waters of this region This is consistent and Fyfe, 1973 Table 1 to factor loading 4 with a very high on this remains in solution, factor, solutions Christ seem to show that Mg in while Ca is removed, with its known chemical behavior, magnesium bicarbonate Experiments and Hostetler, aqueous Mg2+ is very unreactive in itself of a magnesium carbonate phase; crystallization crystallization is catalyzed may be a primary determinant the salinity by increasing of the lake, as attractive, low although the possibility in Kivu, and factor 4 would The specificity of factor involving because the loading it must be admitted of such compounds. is more compatible salinity hypothesis that strength. however,, Thus, of Mg deposition Mg does not make an alternative formation increasing ionic because Mg2+ concentration In fact, inhibits with 1970; and Sayles of its highly hydrated structure. then reflect sedi 1966; Cowgill and Hutchinson, phase for precipitation Magnesium responds loading. loadings MacKereth, Their behavior is largely Therefore, >0,400 or chlorite for SiO2 and A12O3 is very a low loading The relatively with a carbonate phase. sepiolite 4 for does not rule out high loading of Mn The only appreciable negative -28- loading is that ductivity tation of Mo, which may result, from decreased planktonic or at least dilution would be consistent with the hypothesized Only one element, this makes it difficult by the Mg-rich phase, Pb, has significant to establish shows that the Pb concentration from 85 cm to 120 cm with lesser carbon and pyrite material suggesting Pb becomes available above and below that, 1970 in rather discrete volcanic provided by factor through nearly 14,000 years discussed this period, mica, constituted continual of its In Kivu sediments to its concentration analysis, it is now possible of the north basin of Lake Kivu history. earlier, Between 13,700 years and which, based on the may have been as much as 300 Al203 was between 10 and 20% average and detrital or the 1954, the lake stood at a much lower level below the present level, throughout rock Higazy, the hydrogeochemistry stratigraphy Cowgill but they did not observe the pulsing 3 to 4 times enriched relative gross pulses. which suggested Pb is always at least With the insight and studied were enriched up to 5,800 ppm which we find. <10 ppm in neighboring that But the upper unit very high Pb content 12,500 years, Organic perhaps by chelation found that the sediments they and precipitation, to characterize Fig.. 3 from 0-30 cm does not show the Pb enrichment, in lead when compared to source materials leaching 5, and of the factor, or as a sulfide, of organic-rich and Hutchinson on factor low, but has extreme values with organic.matter,, in humic.compounds, that loading are also high between 85 cm and 120 cm, suggesting the Pb is removed either incorporation pulses Either interpre high salinity, the identity is generally pro components, especially over 50% of the sediment by weight. = in 12% kaolinite and Although A12O3 is -29- abundant, levels its quite markedly, value fluctuates and. distances from source rivers reflecting and streams to the coring site, Lake Kivu during this period was a closed basin lake; levels, reflecting Langbein, short-term 1961,, changing water and astatic and evaporation balances of precipitation would be expected, The waters of a closed Lake Kivu would have been saline alkaline; and, except for their distinctive source rocks, bicarbonate-carbonate waters Ca precipitates sition in offshore they would have strongly peripherally as it enters and alkalinity increase aspect the exception and Ca depo Na, K, and Mg would accumulate from the Eastern water depth, of Rudolf, sediment surf ace diurnally, tocene Kivu suggests that water level would The closed basin lakes of East Africa, level, but the greater with Lake Kivu, even had 100 m of water over the lakes are usually mixed prolonged 1961. Rift Valley lakes in one signi are shallow or even ephemeral, The shallow This explains when the lake was down Langbein, when it stood 300 m below its present 4’ coring site, the lakes, with time, but a fluctuating wastage by deflation Lake Kivu would differ In these alkaline is low Kilham and Hecky, in press. Ca content of core 4’, ficant resembled the sodium lakes of the Eastern Rift Valley, areas and somewhat higher K and Mg derived from the negligible allow salt water oxygenated to the water depth of the Late Pleis stratification might have occurred as it does in the deep, modern lakes, The oscillating stratification Mn reflects leads to deoxygenation After deoxygenation,, redox potentials the stratification history, of deep waters in productive lakes, in deep waters and sediments decline; and, as they do, many elements become reduced and the solubility Prolonged of their -30- compounds may change, Mn and Fe as well as many other transition are chiefly affected, Mn will be reduced first or silicate and will enter deep waters, to drop, Fe2+ can become available, concentration solubility from its sedimentary oxide If the redox potential In the alkaline, saline of these two reduced species would probably with respect pH values than deep waters continues Kivu,,. the increase to the carbonate phase was exceeded, behavior would also be pH dependent, metals until Thus their Surface waters would have higher and, therefore, more CO3 available to remove Mn or Fe, Kivu during this period was a closed system, so that simply changing the Mn from an oxide to carbonate would not produce ,the oscilla tions, Two scenarios redistribution, are offered which could bring about the required One is largely not mutually exclusive, temporal In the first and one spatial, and they are case stratification occurs; diffuses from the, sediment and accumulates waters, Subsequent mixing because of weakening or obliteration stratification would deposit as a carbonate The second case involves Mn2+ diffusing across the thermocline and precipitation, would lead to resolution shallow water permits Fluctuations record the position Garrels of the of Mn2+ oxida and MacKenzie, from sediments, Precipitation mixing in deep water because of the lower pH, while precipitation incorporation water sediments become impoverished enriched, low pH deep MnCO3, as the slow kinetics tion should favor precipitation 1971. in relatively Mn2+ in the sediments, in Mn while shallower in Mn content of the thermocline. was above the thermocline; In this at the 4’ site case deep sediments in this in are’ case would When Mn is high, the 4’ site and, when Mn is low, it was below the thermo- dine, Thermal stratification cation meromixis would be much more stable case Fe2+ and sulfide rather constant at 13,500, seems most likely, production throughout.this 13,200, period, The first in which In fact showing enrichment in the core by .a bed, almost 1 cm thick, stratifi and longer lived, should have occurred, and 12,500 years BP, the chemical composition as a salinity Fe is. only 3 times, of these is represented of nearly pure manganosiderite; of this material is not known, since our routine 5 cm spacing between samples missed this bed, If the depth of mixing of the epilimnion period is considered sampling interval mentation level, site rate’, to be more or less then these High water levels and Mn-depleted fluctuations sediment would accumulate, which implies that with no significant Mn occurred, values sediment, our there are no significant was more persistent, The redox potential, to liberate of Mn on factor could be generated as suggested Subsequently to water levels would is presented might be reconstructed, stratification, stratification sufficient Lower water the lake may have been completely In the discussion loading years well above the 4’ This interpretation when the lake was shallowest content of deposited what higher, of Mn can be related would place the thermocline 4, which shows how lake levels 13,500 years, over several low water is on the order of 10 years because of the high sedi bring Mn-rich sediment to the site, Fig, constant during this Prior in to by the A12O3 oscillations, mixed throughout the lake level was some and redistribution however, only infrequently of. dropped to Fe2+, of the factor 4, the Mg factor, by fluctuating analysis a rather was noted, lake levels high positive Such a covariance in a closed, alkaline, -32- lake saline Periods of Mn deposition and higher salinities. favor precipitation scale, Increasing be particularly high, i.e., dine could alter cient to modify salinity siderite x-ray above, a slight Mn deposition contains ionic strength never on a massive, the correlation would not have to shift without ensued, a period of generally The A12O3 and Mn contents increases, ash are present, to volcanism rather Therefore, detrital this that even higher, increases than changes in lake level. and the increases from greater Iron shows an appreciable and pyrite formation. higher Mn will continue lake level and a more stable the more reducing conditions, discussed halocline. later, to migrate also suggest a stable Between 11,700 years Thin laminae of to the TiO2 peaks, increase in sediments suggesting The availability to shallow stratification The fossil thermocline more strongly of sulfide metals, while the environments. A presumably engendered diatoms in these and 11,500, are accom in A12O3 are related in the deep waters will trap Fe and other transitional more soluble sediment inputs of unweathered between 12,000 and 11,700 years B,P,, reducing conditions rising No extreme fluctuations observed correspond higher Mn results material. deposited indicating of the deposited High A12O3 values panied by TiO2 values which are relatively in Mn occur, by analyses, and the iron content volcanic of note the the mangano Itis Beginning at 12,500 years B,P,, decrease a volume change suffi involving significantly. of the thermo in the position on average between 50 and 80% MnCO3 as ascertained diffraction lake levels should and alkalinity although of magnesium carbonates, By the models presented lake levels at 4’ imply falling strata, or possibly Fe deposition to be a weak decreased -33- slightly rise, in relation This implies to other components, a less stable and biogenic sedimentation deposition to open the lake to the south, are inferred, The core from station however,, the bottom of this interval .greater High lake levels, and a stable but stratification core is assigned an age of 10,000 years of sediments deposited in the north basin record, at station between 10,000 and 11,000 years B.P, formed at the base of core 4’ to 10 begins with Fe and Ni similarly B,P,, which leaves a gap of 1,000 years geochemistry was relatively decreased, not sufficient high; continued stratification, After 11,500 years B,P, pyrite as detrital and water levels 9 in the critical resembles high Al and low Fe, closely The time those A lower lake level stand is inferred, The beginning of CaCO3 deposition in offshore when the lake rose above the Ruzizi outlet, vation than now, decreased, As the lake overflowed, the HCO31 -CO32 removal of CO2 caused its precipitation. nickel results and a hydrography similar thermocline catastrophic by the CaCO3,, The decrease in iron and The lake had open drainage i.e,, a deep, perennial events occurred in the lake’s basin, which indicates sedimentation but it up to 5,000 years B,P,, when stratification From 5,500 to 5,000 years B,P,, sharply, alkalinity as it entered, to Edward and Tanganyika, with no salinity ele where high pH values because of photosyn thetic from dilution is effected which stood at a higher Ca was no longer removed peripherally was mixed into the open lake, waters of ash, increasing TiO2 and A12O3 deposition volcanic activity At 5,000 years B,P,, organic carbon and Pb increase, rose in the basin and CaCO3 deposition ceases while The organic carbon emerges as the contri- -34- bution of other sedimentary is reduced, Rather, production In contrast, especially to be discussed of terrestrial the Pb increase with the biostrati organic matter was relatively by a factor of nearly 100 sug a large input at that time, CaCO3 is not being deposited either, The lake is presently with CO2 Degens et al,, have been.accomplished, Surface waters at the station but the trend.is water’ acidic with depth. noticeably become anoxic, Therefore CaCO3 particles and incorporation is only possible in depths above the first Kivu’s today exhibit shoreline surface charged No pH measurements on the deepest the deep water redissolve, Verbeke, today, and the deep waters meromictic, 1973,. 10 site have pH values between .9 and 10, but the pH drops below 7 as the waters 1957; sediments. halocline, regions The absence of carbonate to that existing and extremely alkaline today, Many areas of pavement of CaCO3 have carbonate-rich from 130 cm to 90 cm implies It ,does not mean a lower lake surface waters, ments.. of the core from 400 cm to l200 into falling of CaCO3 into the sediment a nearly continuous and cores from shallower meromixis similar level CaCO3 and diatoms, carbon does not.mean higher productivity, dropped and the contribution increased. gests The higher organic planktonic graphy, constituents, as the carbonate-free cm, because.the sedi Al203 content is low. The warm, saline, to hydrothermal springs became significantly sediments deep waters of.the Degens et al,, stronger present 1973, 5,000 years B,P, are a good marker of spring activity, years indicate that the springs were present lake are attributed and this spring activity High Pb values for the, and peaks ,prior to 5,000 but on a reduced scale, -35- The Pb derives from intense leaching ash by warm, ground waters charged with volcanic should enrich the lake waters in all of the metals and their of the metal-rich differ are split phase, and it contained metals which were either were not incorporated their highest loadings on factor with the detrital more resistant part of a widely recognized of metals Spencer 1968 conditions, which migrates covariant together time, quite Pb exists different virtually behavior alone in the last hydrothermal metals increased, ment. The removal was effected process Pb was the first sedimentation. precipitated spheres sulfide and failure by sequestration Degens et al. to form sphalerite to find these dominate after indicating a the input of all the to be removed and added to the sedi "1 micron in diameter which covered the sphere. factor, activity, with organic material 1972 for Zn in Lake Kivu, but with a different fied resinous under.oxid.izing from the other metals, With the increased and subsequent suite In Kivu the oxides and heavy metal carbonates predominate prior to 11,500 years B,P., while the sulfides that Zn, 3 while Zn and Cu also had significant This represents and reducing to leach Fe, Ni, and Co had factor, loadings,, et al,, The first into the lake sediments, loadings on this fate Factor analysis among three factors, contained those metals which were associated Cu, and Cr had their highest This leaching markedly. factor ing or, if leached, lavas and but the geochemical the metals, sedimentation showed that the heavy metals CO2 volcanic describe result, They identi which chelated crystallites a similar Zn and 5 to 50 in size These spheres were found in the water column, spheres in the sediment suggested that were buoyant and were being lost to the lake, they Such is not the case with -36- the chelated lake. Pb,, however, and it is rapidly Cowgill and Hutchinson similarly during weathering petrologic provenance lavas and ash. to soils similar was observed, in Kivu indicates above mechanism rather being sedimented, entry to the in a basin which has a to Kivu, i,e,, Both Zn and Pb were greatly after Zn and Pb behaved very found that and sedimentation and rock; no difference weathering factor 1970 deposited abundantpotassic enriched in mobilization alkalic in sediments relative between Zn and Pb during The high loading of Zn on the detrital that it is being lost from the basin by the than being totally deposited in the lake, but it is being removed in a manner similar Pb is to that of Zn. The abs’ence of Fe and other metals Zn from the sphalerite organic not, resins no organic as sulfides specific, reasons, chelator excluding coordinate was present or in shallow waters metabolic free energy; demonstrates as oxides. at depth, sulfide in surface production waters, that plankton production thermal pulses; the These metals for which Precipitation of sulfide of these metals by sulfate- as a hydrogen acceptor in They are dependent on organic matter as a source of and, thus, organic production that would have to be removed in deep waters These organisms use sulfate oxidation, 1972 with. those metals which could properly. in deep waters would depend on the production reducing bacteria. associated spheres suggested to Degens et al, were highly for structural frequently this in turn in deep water will be tied to Evidence to be presented sharply fell during these hydro should also have affected The magnitude of this decrease 9,000 years B.P,, CaCO3 rose from nearly later microbial can be estimated activity in Fig. 3, At 0 to 30% of the sediment by dry -37- weight, This necessarily approximately this amount,, one-third i,e,, decreased to maintain also decreased at this 5,000 years H.P., at least supply of metals, migrated a one-third production been destroyed, hydrothermal sufficient salts of cooling The therinohaline unless surface constant, of heat and salt i,e,, 1957 and aridity Assuming to the hotter waters leach then the maintenance is dependent source of denser water must exist, If the lake became closed, waters and/or could lead to a breakdown, thermal density decreases, diluted stratification in the Kivu system are or concentrating Hutchinson, waters must be constantly as coolness or out the Ruzizi River, contribution is relatively to offset a sublacustrine as they years B,P, and which occurs today had the deep waters of crenogenic meromixis i to meet the greater The deep waters were no longer acid because that the relative waters production’ to the deep waters The density changes involved and a combination heuristically in a major 4,000 years H.P., CaCO3 was again being deposited from 5,000-4,000 or diluting in sulfide did not increase were more efficient, which was present increase Diatoms to the organic matter. in the deep north basin. mixing processes CaCO3 disap As Fe did not rise by 5% at reduction to shallow oxygenated sediments Approximately heating and the only relative and these metals were lost they could coordinate small, At 5,000 years H.P., by organic carbon, Sulfide Iron did decrease by but there was no response by the Fe, time, component is registered had occurred, a zero sum. from 15% to 10%. peared from the sediments, the other major components by all on two processes: and ii surface by runoff and loss at the effluent, surface waters would become more saline; are correlated in the African climate, and, surface -38- cooling might be expected also, breakdown of the convecting Such a state water cells The depth of the well-mixed hilated, would grow from above in a gradual extended over many years, process catastrophic, near atmospheric equilibrium cells, If the the mixing of the immense reserves into the surface that Kivu was without of CaCO3 deposition, and saline layer are anni waters need not be as it was prior a surface outlet during this Despite the fact that the lake was closed to 9,000 years B,P,, Ca was deposited deep north basin because the source of Ca was the sublacustrine not surface activity, of Evidence from other cores and lakes will be presented below, which indicates interval as density differences cascade of collapsing gases and heavy metals hydrothermal of events would lead to a in the springs,, runoff as was the case previous to the onset of spring The occurrence of high Pb concentration CaCO3 deposition means that the hydrothermal within the period springs of simply changed in water chemistry. The above results if mixing was propagated and/or hotter water, sharply with what would happen would contrast from below by the injection These circumstances substances equilibrium. of the deep waters could be introduced case rapidly into the consequences for the biota, no. evidence in the stratigraphic record the fossil record, the biota coincides stratification for a situation whether such short-term This evidence will be discussed later, this, but events could be resolved with the onset of intense than the termination There is like What evidence there is for conditions rather cells In this surface waters with catastrophic it is questionable saline would lead to convecting growing from below and not in atmospheric toxic of less hydrothermal deleterious activity of the thermohaline in to and structure, -39- Events similar to those that happened at 5,000 years B,P, occurred again at 1,200 years H.P. High TiO2, A12O3, and Mn content volcanic ash are found in sediments immediately underlying depleted sediments, suggesting The Fe and Ni subsequently that the productivity duction was not as drastically similarity of surface spring activity relationship between volcanism in both cases, may be involved also, The strong As the water of these Degens et al,, namely climatically 1973, climatic determined availability of water for deep percolation through the porous lavas and ash of the Virunga system might regulate the volcanic with hot magma, would be transformed changes could fracture release or dislodge of volcanic ejecta system are undersaturated fore, supplies The water, confining Holmes, critical volume overburden and allow the The latest with water by mixing to this lavas from the Virunga 1965, p. 1024; and, there system, The chemical stratigiaphy of the deep, northern basin of Kivu the following about the lake history: i below its activity, to steam, and the consequent and lava, water may be especially pro seems to imply a causative and spring activity, springs has been shown to be meteoric processes and hence sulfide waters ash followed by evidence of increased i.e., hydrothermal CaCO3- more rapidly, by the second event, affected of the two events, increase Pb-rich, from information Prior to 12,500 years Lake Kivu stood as much as 300 m present level; the lake necessarily was closed and more saline and alkaline; ii water; Station 4’ site was under at least and, judging from the fluctuating depth of the perennial thermoclines marked the depth of the thermocline one hundred meters of Mn deposition in the modern lakes, at 4’ and the it may have through much of that time; -40- iii thermocline at 12,500 years B,P, water levels moved well above the 4’ site was some volcanic but not quite formation dropped sharply there around 10,700 years H.P. to the low level it occupied prior the lake achieved the elevation v increased; in the area around 12,000 years H.P.; activity the lake level iv the deep waters and sharpened; and sediment became more reducing and pyrite the began to rise; to 12,500 years H.P.; of the Ruzizi outlet 9,500 years B,P, and began to freshen; vi at 5,000 years H.P. hydrothermal dramatically following complex hydrography or coinciding similar spring with increased to that extant activity increased volcanic activity; a in the lake today was estab lished; vii terated, the thermohaline probably viii density by the lake level a wetter hydrothermal and volcanic thermohaline structure structure falling obli was subsequently below the Ruzizi outlet; and climate reopened the lake and another pulse of activity 1,200 years H.P. reestablished which has persisted the up to the present. Bios tratigraphy Siliceous micro fossils. of the north basin cores, analyses Characterization 10 and 4’, is based on siliceous for both cores and synoptic hexosainines for core 10, of the biostratigraphy determination Diatom frustules of amino acids and are by far the most abundant microfossils in cores from all of the Rift Valley lakes, preservation vary from lake to lake and within basin of Kivu preservation is excellent microfossil Fig. lakes, 3, States of but in the north Very few species -41- attain relative abundances greater shore planktonic variability populations is greatly in large, reduced relative of the diatom stratigraphy information derived of this lakes; to more temperate as hydrographic lakes. paper, Analyses only a brief outline from diatom analyses will be necessary, of the diatom stratigraphy presentation deep tropical in of f- of other Kivu cores and the other lakes is still For the purposes in progress, than 5%, as might be.expected of the A more detailed will be given when all the work on Kivu is completed, From the bottom of core 4’ to 130 cm in core 10, only 3 species comprise well over 90% of the flora Stephanodiscus astraea v, minutuja Grun,, at any sample level, Katz, and iVitzschia spiculum Hustedt, These three are Grun,, IVitzschia fonticola mong the other diatoms only Nitzschia acicularis W. Smith achieves abundances over 5% for short periods of time, Transmission in Figs. 5-7, stratification electronmicrographs Comparative availability of nutrients of the water column appear to control tivity of these species, from 1 Understanding the distribution between relationships 4 the behavior of the species within conclusions the relative produc ecology has been achieved 2 core, simple in lakes, and sinking rates, the present elsewhere and An elaboration Hecky and Kilham, in prep,, are given here in order to interpret of the diatom species through time in the north basin, Stephanodiscus astraea is a low silica tonic diatom species. and, indirectly, of nutrients species productivity of the argument will be presented are presented in the modern lakes, distribution 3 and only the general of their of the species models of the three-dimensional the distribution of carbon replicas Kilham l97lab states specialist that among plank it only becomes promi -42- nent in the plankton of lakes as dissolved below 1 mg/l, In Lake Albert, silica which has very low silica S. astraea dominates the microfossil phorus, sediments, In Lake Edward, where dissolved N, fonticola predominates, much higher, Nitzschia species to the virtual 25:1 N, spiculuni Figs. nutrients phosphorus 5 and 6 are extremely is nearly vanishing in surface waters Surficial sediments of Lake thin long, thin morphology results to volume ratios, of the nutrient-depleted euphotic and maximize the surface area available the situation constituent blue-green of the phytoplankton algae slower sinking esp, The area can be achieved, Contrary to diatoms are not the most prominent in Kivu and Tanganyika today, rates or self-motility and other dominate, reduce phosphorus yet dissolved level, in the north basin surface waters, Rather, algal groups with This is especially studied, sion on Na through all depths. pro of sinking out uptake. in Kivu, which has been most extensively unaffected The low nutrient and high surface for nutrient Lyngbya sp, in Kivu to a negligible under nutrient and can be seen in Table 2, zone before reproduction in Edward ‘and Albert, These on photoplankton reduce the probability All while dissolved production in slow sinking rates These attributes morphology, Table 1. for other diatom species. which was remarked on earlier to width ratio of this in .Kivu surface waters which are unsuitable is of other species. Tanganyika waters, supply in Kivu and Tanganyika has a marked effect ductivity, length exclusion long, thin Nitzschia appear to be able to sustain conditions from surficial silica is quite representative low in offshore f all and high phos assemblages Tanganyika and modern Lake Kivu contain long, > concentrations Biological silica clear processes is virtually as Si gives a linear regres Diatoms must account for only a small -43- of the primary productivity proportion when 5, astraea is prominent, greater and the accomplished is due solely to the Nitzschia spp. diatom production versely, in the north basin today, proportion diatoms are accounting of primary production as dissolved Con, for a much Si is driven very low, In tropical for surface waters drainage basin, lakes two quantitatively can be identified. The salt derived from the weathering fallout dissolved from the water of tributaries is primarily and nitrogen as rich from regeneration are efficiently Silicate SiO2, In contrast, will be poor in silica. regenerated Runoff from constituents, in dissolved rocks will yield and weathering SiO2 and HCO31 as the most prominent derived from the of nutrients Hecky and Kilham, 1973, in the Kivu basin, present sources of rocks except in arid regions where atmos the basin can be characterized nutrients contribution becomes important are exclusively nutrient One, is surface runoff and the other is regeneration column and sediments, pheric significant Phosphorus from plankton detritus, yielding the very low turnover times for these elements which are often measured in lakes Rigler, 1964, judging from the vast eration however, is only slowly released, accumulations of SiO2 can probably time scale, inately Silica, of diatomites be considered Thus water masses receiving from regeneration processes in these lakes, negligible their and regen on an ecological nutrient content predom will be comparatively rich in P and N but poor in Si, The relative runoff and Si-poor and stratification, contribution deep water, Generally of these two types of water, will be determined primarily speaking, Si-rich by lake size as lake area and volume increase, -44- replacement times increase and the nutrient runoff to the lake decreases the lakes, production of large tropical extent lakes, as that diatoms with silica to low silica of regenerated nutrients mixing processes, periods In such lakes, of their areas is’ possible proportional dine, i.e.. This difference interfaces systems, but in aquatic only eddy diffusion differential in conjunction seasonal variation depends on occurs in deep water, across more is significant order approximation, to the density for most mixing will be inversely across a thermocline with meteorological in temperature, winds, in turn, gives an indication rainfall, etc,, This depth area constituting exhibit surface waters, which is mixed completely most of the year, Edward, which is likewise less thoroughly circulated than 10% of its a hi’gh productivity, will of the amount of deep, nutrient- rich water which will be mixed into the nutrient-poor Lake Albert, or halo stresses, determine the depth range or mobility of the thermocline, range, attuned The availability across very stable and chemoclines As a first 1973 surface waters as much of the regeneration thermoclines area. et al., should predominate. in all the lakes under consideration or less stable of time. Guillard to the euphotic in upwelling the productivity Therefore, independent of A continuum from molecular diffusion to advection tends to remove peri and is relatively uptake kinetics concentrations enter of the ocean, depends to a large processes; inputs over significant of surface Where tributaries and this from weathering. on regeneration tributary proportionally, can be intense, the nutrients pherally contribution total and they do, and Lake except for a small surface area, Productivity should should also -45- be reasonably Table 2. high in Malawi, as its The deep thermocline of Kivu have been nearly is fairly deep thermocline of Tanganyika and the thermohaloclines stationary over the periods of observation, thus mixing and productivity are low, shallow will engender fluctuations seasonal thermocline Formation and obliteration value determined by mixing across the perennial With the above considerations abundances for the period A12O3 content the presence the waters are relatively near-shore conditions relatively less what higher water levels The mobile thermocline tively efficient water levels rich in Si, or at least stratification This indicates of land-derived Mn reflects, and N. spiculum increased. interpretation, that N, fonticola subsequently becomes of low Si nutrient-rich of deep water to the phytoplankton As the time indicates and a nearby tributary and reduced influence and more stable agree with this at this and S. astraca increases, regeneration is prominent, value in the core and low lake levels which the fluctuating years H.P., N, fonticola around a low mean in mind, the changes in diatom of N, fonticola are implied, abundant, of the from 13,700 years H,P, to 5,000 years H,P, can is near its highest are indicated, and thermocline, At 13,700 years B,P,, N, fonticola be interpreted. mobile rising contribution The low Al203 and Mn These elements subsequently S. astraea returns to dominance, reflecting rela Around 13,000 This suggests as the relative is reduced, nutrients, permits water, some lower lake levels rise, and and better circulation, Again at 12,000 years H,P,, N, spiculurn became prominent, rather stable stratification, Geochemically the stabler made the deep water and sediments more reducing, implying stratification and Fe-deposition as -46- pyrite and organic carbon deposition sedimentary constituents. evidence for volcanism subiacustrine water at depth. activity relative of these during this period saline and the introduction surface resulting layer of water overlying sharp, stable would be favored. thermocline of climatic cooler, Prolonged.intervals of a relatively saltier warm, water, The and N, spiculum endured for nearly two hundred years as stratification B,P,, N, fonticola became less High water levels and a fairly increased stable Increased pyrite deposition deep thermocline and high runoff is similarly and became diluted subsequently in abundance, N, spiculum, recognized as the temperature waters increases. a strongly stable becaue thermocline only the availability production are suggested, reducing hypolimnion, implied A as the lake opened to be replaced by N, fonticola a general and the thermocline and density differential is becoming more of surface of the phytoplankton and deep result, between S. astraea and N, fonticola of Si, and do not necessarily and warming trend in the Reduced mixing and lower productivity shifts to S. relative From 9,000 years to 5,000 years B,P,, This reflects world-wide, stable be emphasized that implies at 9,000 years. S, astraea declines the total is a climatic change or reduced volcanic activity, At 11,500 years climate spring through this would reduce mixing, These conditions before N, spiculum declined astraea, of saline ‘lake was being freshened, of warm, wet years might favor the establishment with the could indicate However, Pb is low, and equally plausible and a closed, dilute to the other conditions The climate was becoming warmer and moister causation, time, The association high Ti02 volcanic increased It must reflect imply any changes in or even of the diatoms, Gross -47- productivity will be set by the supply of P and N, which will be utilized by non-siliceous algae as well as diatoms. A relative increase spiculum, however, does imply, under the model presented, phytoplankton production Hydrothermal ture approximately has decreased activity established overall low mixing rates, density struc a thermohaline 5,000 years H,P,,, and the consequences were rapid and extreme, for diatoms At a sediment depth .of 130 cm in core 10, there is a sharp contact both in lithology 5 mm, the sediment changes yellowish In the space of and biofacies, from a carbonate-rich, ment, dark greenish grey in color, and diatomite, as it reflects that finely laminated to olive in color, dark brown in color, and finally material, The diatoms change from Nitzschia spiculum in the first with a gel-like of Nitzschia such as N, palea Kitz, absolute abundances, siliceous scales Saedeleer identified fossil. scales Fig. 6, Even more striking as diatoms.are consistency, unit to purely This assemblage of short, is not nearly siliceous Fig. 6, as extreme as it was in the first algal de but the elimination the past event. of 5,000 years Among non species of the green algal genera Tetraedron and Cosmarium are prominent in these brown layers, fiable Stokes become the most abundant micro- species which are abundant throughout microfossils, and minute, wide Nitzschia and Paraphysomonas recurs within each brown layer the long, thin are the changes in Paraphysomonas vestita by R. W. Norris short W. Smith and scarce in the brown unit, of the chrysophyte, ash to an organic, Stephanodiscus astraea v, minutula in the second, to relatively N. accomodata Hustedt sedi to a thin layer of fine volcanic unlaminated and, wide species in N, remains is quite but incidence of identi low compared to the other sedimentary units. -48- The brown units phytoplankton are interpreted productivity. Planktonic Many of the species present, for an epiphytic substrates planktonic as nutrient as periods e,g,, occupying benthic motile, colorless reduced diatoms were virtually eliminated, N, palea, have a demonstrated existence habitats 1956 Gessner, and/or energy sources. species of greatly in Kivu, phagotroph which ingests and using organic Hustedt found these 1949 Paraphysomonas vestita is a and small algae bacteria The emergence of these and Leedale, 1961, microfossils in the sediment may simply be due to the elimination more.numerous producers,, i.e., counting 400 diatoms restriction suggests of this that flourished at each level they are remnants of a distinctive techniques them; but the and the Parccphysomonas phytoplankton which at the time, By the models discussed stable would not reveal of the throughout the standard enumeration element to the Nitzschia spp, Manton as the most prominent species these elements are ubiquitous the core, but at abundances so low that ability density stratified rapid onset of this and led to a constant implies the lake sufficiently activity that the hydro to trap CO2 and dissolve such low productivity displaced of an extremely reduced mixing and extremely As the chemical stratigraphy calcium carbonate at .that time, the pre-existing is expected, The deep water upwards advection of water low in Si but rich in N and P into the surface waters, Production discus astraea was deposited, between the cool, was intense and the layer of Stephano- As the warm, saline basin and rose near the surface, established the establishment interf ace could lead to greatly low productivity. thermal activity earlier, a sharp density dilute water filled difference the deep would be surface water from runoff and the -49- water, hydrothermal The exact depth of this mined by the relative stable two-layer the result, inputs would be deter interface of the two water sources, Initially system may have been present with very low productivity Diatoms, because of their sinking habit, again in the low nutrient environment, of an epiphytic would survive by attaching existence buoyant algae such as blue-greens, would be selected Only those diatom species capable flagellates, tc resources, as a great .proportion will be tied up in dissolved perhaps on microalgae, e.g,, unable to ingest the larger previously water, from below, of biogenic heating liferation and greater increased, conditions, two-layer This species would be conditions, system, warm salty water under cool, system proliferated because of the heating may have been significantly layers mixing resulted, surface waters, the salinity and euplanktonic bacteria Deuser reduced density diatoms reappeared. et al,, differences As the hydrothermal and productivity augmented because relationships between layers, of the surface waters Under the low nutrient the long, thin Nitzschia were expected The ecological Pro 1973, water mixed into the Fig. was joined by N, bacata and N, mediocris as new elements plankton, feeding The Tetraedron and Cosmariwn would not be by fermentative of multiple in the system diatoms which dominated the phytoplankton a multi-layer This heating The to utilize pm would be present, with the proposed oligotrophic From the initial dilute 10-20 more we have found up to 50 mg small flagellates, and subsequently. inconsistent ability of’ the nutrients organic material; The small P. vestita C per liter, larger, and green algae, Nitzschia spp. would also be favored because of their organic a of these three 7, N, spiculuin in the diatom is unclear, as -50- little is known about any of them, but they all morphology, occupation of planktonic of all other diatom species, determine whether this lutionary niches left greatest relative or absent, which should indicate to of new species or evo of immigration N, mediocris and within the lake, have their vacant by the exclusion record is insufficient The available is a result diversification the long, thin of Nitzschia spp, of this morphology probably Proliferation represents do exhibit N, bacata abundances in the core where CaCO3 is low that stratification was most stable character, N. spiculum has a maximum for the past 5,000 years at approximately 2,000 years B,P,, while CaCO3 was being of a thermohaline deposited and perhaps only a deep thermocline and was present. Another new element in the diatom plankton was a Chaetoceros sp. Fig, 7, This genus is rarely typically tinental marine, All previous recorded from inland waters, reports of significant waters have been from lakes much more saline Lake Kivu, where we have found it in surficial 1958, Its abundance through imately 4,000 years B,P, higher salinities Its presence in the modern lake may reflect conditions negative as salinity interaction indicating that eliminated during stratification, is probably combined with low nutrient adaptation abundance in con than the present sediments the past 5,000 years cf, Anderson, in Kivu peaked related conditions, by a strain changed slowly over time, as it is approx to somewhat Its persistence to the more dilute It exhibits a very strong with the stubby Nitzschja spp, of the brown layers, it,, as all the plariktonic the ultra-oligotrophic species of diatoms, periods of extremely is virtually stable -51- Although the lake has experience¬able because of climatic and volcanic to varying nutrient the Chaetoceros sp. can be interpreted diatom stratigraphy is entirely in reconstructing portions in part tools, of the lacustrine conditions conditions of salinity alone, witness the modern lake, The chemical waters, on quite surface waters, which are caused by lake level diatoms can yield by species shifts, and biological to.changes fluctuations information as seen above, evidence can full reflects of surface’water in the deep of CaCO3 in the deep waters diatoms yield information and respond principally different stratigraphy but the imprint the dissolution In contrast, The Together they provide as they yield evidence in the surface Only with the chemical stratigraphy of the lake, environment. the regimes. can and will be strongly modified by conditions water and burial tion, in.terms consistent the paleolimnology powerful paleoecological changes in hydrography, related diatom flora has responded primarily changes in salinity primarily in nutrient and ‘stratification. on relative biological Only by integration understanding of on chemistry In addi productivity of the chemical of the paleoenvironment be achieved., Organic matter, in core 10 and’throughout organic carbon is rather core 4’ Fig. 12% C on a dry weight basis, in core 10, organic.carbon through the upper section cm, with an average rises below 130 cm Values range from 1.5% to around 7,5%, Above 130 cm sharply to 16% and remains over 12% except for the interval Changes in sedimentary simply interpretable 3,. constant between 90 cm and 30 organic carbon in the north basin are not in terms of productivity, Much of the pattern can -52- be accounted mentary for by the varying constituents, example, i.e,, diatoms, at 130 cm, organic tion of Fig. 3 shows that contributions CaCO3 ‘ i... of ‘the ‘other principal and detrital carbon increases.from. the detrital minerals above, planktonic plankton production represented strongly reducing and more conducive as a salinity can easily stratification account sitating an increase organic carbon yields productivity in productivity. to be’greatly This couldbe that In this production in glucose. from terrigenous had a distinctive associated relative to an allochthonous fell, to other sediments, source which would origin. organic with relatively The enrichment contribution component remained which created a relative cellulose, sugars, was too high low planktonic Itis present during .deposition pattern.of in the brown They found the However, galactose case the land-derived and.phytoplankton are usually of the thatplanktonic the sugars a.terrigenous with the hypothesized the unusual phytoplankton layers in glucose as reflecting all the material is compatible enrichment suggests from.,other strata. large amounts of cellulose, layer. constant, carbon withoutneces characterization characterized enriched interpreted to attribute to this of organic material fell brown.layers in glucose phyto These events taken together In ‘fact, and compared them with sugars contribute ‘ in organic which also Mopper and Degens ‘1972 layers or vanish, The deep waters became more was established, information and total for preservation for the dramaticrise by Al203 all decrease diatoms ‘became scarce, probably also fell. For 5% to 15%, but inspec TiO2, CaCO3 and Fe2O3, the other major components, As discussed minerals0 sedi also possible of these brown but brown organic.sediments high allochthonous contributions -53.- Hutchinson, plankton production. probably Earlier deep water, Reducing sediments activity otherwise, The very fact that the lowered activity of the sulfate-reducing these sediments bacteria, As a substrate, organic matter which had already been subjected degradation in soils teria as plankton Separation all productivity record, activity of intense from nutritional activity does reduce.phytoplankton metals to eliminate ganic’ sediment constituents, a rising trends through concentration the cores, initiated changing diagenetic conditions and the thermocline becoming sharper, in the hypolimnion, would be expected. created by inor no amino acids demonstrated may reflect in the deep water, Better preservation and contin in part The climate which leads to stronger Hexosamines increase strati production amino acids exhibited but total This rise from is reduced. at 260 cm 8,500 years H.P. uing to the surface of the core. conditions the variability The individual activity. are given for core 10 Amino acid and hexosamine concentrations recognizable bac density the stronger and the input of toxic in Fig. 8 on a carbon basis hydrothermal ones is not possible but it is clear that imposed by spring even when spring for the sulfate-reducing the evidence is compatible with very low during periods of toxic effects the stratigraphic fication to bacterial detritus, In conclusion, phytoplankton black because are brown reflects terrigenous would not be suitable the Fe and would have been removed are characteristically of FeS precipitation, was sulfate-reduction of these sediments; from the hydrothermal with a low phyto- is consistent it was noted that less during deposition other heavy metals in.the This likewise 1957, p. 882, the is warming reducing of organic material even more sharply at 260 cm, but -54- they subsequently tinue to fall contribute towards the surface, biomass produced, of amino acids, information neglecting bacteria affected effects rapidly are more conducive therefore, Degens and Hecky, 1973, as ammonification by heterotrophic in oxidized sediments while reducing conditions to preservation. Chitinous particles relative activity. mental to zooplankton plankton, Better preservation to amino acids in deep in two ways, The first into surface The second would be indirect, eliminate and change in algal some zooplankters. activity as stratification species composition caused a drop sufficient In modern Lake Kivu calanoid at all seasons, dant only after seasonal mixing when productivity cladocerans as the waters could poison the zoo- zooplankters In Edward and Albert, could be detri would be direct, the predominant 1957, AA:HA ratio of amino acids would account but the hydrothermal of heavy metals in productivity appear to be across the contact which marks the onset of strong for the change in part, introduction can yield Mopper and Degens, 1972, threefold hydrothermal source Diagenesis will In Lake Kivu sediments the amino acid:hexosamine increases considerations, community through time, as hexosamines are enriched ocean sediments By trophic will be the most prominent of the plankton for amino acids, proceeds and bacteria but we concur with Kemp of these two components, on the balance be most critical cell walls, algal proteins A ratio diagenetic sediments, insects chitin will be more abundant and more resis to breakdown than bacterial i.e., less ‘that sharply at 130 cm and con Zooplankton, hexosamines to lacustrine and Mudrochova 1972 tant off and then decrease level to copepods are while cladocerans is highest are abun Verbeke, and copepods are abundant -55-. throughout the year, phytoplankton although their be that one or all of these .L.J. acteristics may explain of diatom frustules population than one-half in the percentage to benthic that of breakage zooplankton analyses view of the present to either toxic that LJ_ L11.L a shift in organisms, decreased substances are broken. only those frustule. Prepara and thus breakage was not rapid agitation. as the entire of zooplankton Therefore the The decrease an overall in the or a reduction the breakage of zooplankton Breakage core is finely of zooplankton. have been done on’the core, distribution Helow by counting can be explained by either element producing in the changed, bottom fauna be absent, decrease in the feeding activity cladocerans eJ.LL an entire for’samples, breakage must be due only to the activity that __....___-- LiL indicates which does include which requires microfaunal for cladocerans the Nitsschia spiculum frustules were identical cannot be attributed specific iL.A depicted in Fig, 8 were generated due to sample handling, laminated, are necessary occurred when the AA:HA ratio which were greater tion techniques ._1..__. and it may why clad.ocerans have never been found offshore 130 cm nearly 50% of all frustules phytoplankton, Lake Tanganyika. Observation The frequencies lakes have high productivity, characteristics -.-- ultraoligotrophic numbers wax and wane with and a diatom-dominated 4-,-. ., zooplankton The latter productivity. high standing crops, relative during feeding, No but it is tempting, in the lakes, in to conclude in the Kivu about 5,000 years ago as a response from hydrothermal quantity and nature of food sources, particles >15 pm more effectively activities Large cladocerans or a change in the harvest than small zooplankton large Hrooks, 1969, -56-- Most of the diatoms a reduction of this study would qualify in diatom production to explain of Kivu, As there are no planktivorous the paucity of cladocerans by predation, lakes would not be a factor, If conditions as they did 5,000 years H.P., of trophic status, duction is markedly increased, degree, These circumstances. is available from that in much better phytoplankton pro to a lesser in the AA:HA ratio, was highest based on the diatom evidence Only one analysis and the AA:HA ratio As the lake was time, circulation high ratio of amino acids. increase algal lake phase of 13,000 years H.P. vertical this reducing, saline zooplankton as an indicator is that would lead to an increase In the Kivu core, productivity in the shallow, could serve of eutrophication while reduction do not change markedly in a core the AA:HA ratio A characteristic plankton commonly observed in temperate which i of preservation in the offshore fish in Lake Kivu today, of large zooplankters 1969, and 5,000 years H,?, might be sufficient in itself Brooks, as large particles, In this production at that time, cannot be attributed case the high ratio and eutrophic is 20, and deep waters to better reflects less preservation extremely high conditions. SHALLOW SOUTHERN BASINS <100 m water depth South Idjwi Basin Station At the southern 13’ end of the main lake, there is a shallow, like basin which has a maximum depth of 220 in, and deep sills separate the deeper water of this main lake, basin from direct The 421 cm core from station a soil horizon which developed l3 in 86 shelf at 180 m exchange with the in of water ended in during the low lake stand, A radiocarbon -57- date near the bottom indicates at 12,130 years B,?. that lacustrine This correlates average sedimentation the core Fig, geochemistry 9 from this elemental 10, conditions, a gradual material that the same five factors at station on the detrital lowering of the lake after in in the core are given in factor 1 deep water by downcutting are 13’ as were operating followed by the return This is explained as indicated factor a relatively years and 5,000 years B,?,, of with the deep water record, indicates distribution as it indicates a much lower The chemical stratigraphy Factor scores for each level The loading instructive, analysis 1.6 should reveal the shallow water hydro- which was correlative the north basin, Fig, site rate, and this would be consistent After 11,000 years B,?, rate is observed, Varimax factor controlling A high sedimentation up to 11,000 years B,?,, with a near shore environment, was initiated well with the high stand hypothe sized from evidence in the north bas’in, mm/yr, was indicated sedimentation is especially stand between 10,000 to somewhat shallower at the Ruzizi which created it opened, The deposition of detrital by the Ti02 and Al203 content was very high initially, No diatoms were observed in the sediments below 330 cm, which also suggests a very rapid rate of deposition, The negative loading of over most of the core on factor that deposition of CaCO3 was high relative this correlates well with events of this basin. 2 means to diatom sedimentation, time period in the northern The very high values for Ca at 11,000 years H.P. support hypothesis that in the closed lower values prior to that tributions, lake Ca was removed peripherally, represent dilution and the The by the high detrital Mn has maxima with the Ca, confirming the precipitation con of -58- a manganous carbonate Fig, 9 does not increase, deep water during this of the core, it at least Mn is relatively time, weakly reducing thermocline conditions most of the Mn present phase, Negative and a sulfide independently is in the detrital in the of A12O3 and TiO2, suggesting was over the site were common, shown in high in the lowest portion The subsequent period of low deposition the seasonal during this as it was being removed’ as a sulfide but it oscillates is authigenic. Fe2O3 not in shallow water environments. suggests at this time, that and In the upper region of the core, The lake was dilute phase. and MnCO3 would not be expected. loadings facies on factor 3 are also low over most of the core, was never abundant at this by the behavior of Ni Fig, loaded through the core, 9. The Mg factor indicating site; this is likewise is demonstrated negatively that the lake waters over this site have always been dilute. The increase reflects trapped of Pb deposition the initiation factor of hydrothermal 5 activity. at 5,000 years H.P. Not all the Pb was in the deep waters of the north basin by organic chelation precipitation, but the amounts incorporated in the shallow-water ‘ments are much lower than in the north basin sediments. of the sediments reconstruction at station of the Bukavu Basin Station Ruzizi River, sill, sedi The geochemistry 13’ does not appear to conflict with the lake based on the north basin record, 15’ The Hukavu Basin is isolated by a shallow and approximately the only outlet, 30 exits from the main lake and station in deep at its maximum depth, from the southern 13’ The end of this basin, -59- The stratigraphic record in the Hukavu Basin should be the best for the opening of the lake and the existence ysis again implicates scores ical the same factors a light grey color; >5 mm/yr. the latter core, often The highlights saline waters during this of higher lake levels deposition fell at this an evaporating site because the Ca-source land a saline but it was probably not as saline of salinity, initial until alkalinity sedimentary Carbonate was farther as that was also as the smaller would remain high and Ca-removal would above the present at the coring site freshened. not due to overflow deep lake would have existed prior deposition in itself, the lake was considerably in The first in the Hukavu Basin prior to connection. decrease was perhaps in the Kivu area 100 pan. Connection with the main lake dilute body of water which existed with the main is about 10,000 years H.P. the waters with The gross stratigraphy the coring site. would not significantly body of water, rapid deposi- The lake was below If it were connected away and/or the waters were more dilute, was for 70% of the dry weight. approximating indication be peripheral of the chem for most of the sediments, covered the site, time, shallower conditions Regardless and factor from 290 cm to the bottom, accounting 60 m of water would overlay suggests cores, suggested extremely Clays and CaCO3 account Shallow and alkaline lake, of this and carbon dating predominating, the Ruzizi outlet 10, Factor anal are depicted in Fig, 11, The lowest portion tion, as for the other for each sample are given in Fig, stratigraphy of an outlet, evidence at the Ruzizi, lake level to overflow, allowed relative Therefore suggest that The decrease increases the Terraces a rather in CaCO3 in all the other components, such as A12O3, TiO2, and Ni in the detrital phase, -60- and Mo and organic carbon in the biogenic phase, due solely to the decrease depth increased, concentration of carbonate sedimentation A very strong negative and the detrital These increases correlation and biogenic at site Throughout the lower portion as a carbonate or oxide, shallow water stage. phases is evident from Fig, 11, it rises quite alkaline, sharply, At approximately and for several though Ca-deposition become diluted, conditions indicating and Ca-deposition A similar suggest slight These sediments served, completely during circulated, lake level was The low Mn Mn-deposition, in the record, rates are ob as the river downcut its outlet From 5,000 years H.P. the basin has been the sediments were not sufficiently reduction, This means that the main lake must have been below the sill water depths greater the same time, and MnO2 remained in the deep sediment, the high lake stage, to allow sulfate the lake had of Ca-deposition and slow accumulation resulted and lowered the lake level, was very low, even and decreased marks the highest conditions it begins to decrease This means that change in the nature are not diatomites, Oxidizing were still was a consequence of photosynthesis reducing conditions and the low Mn interval in the conditions hundred years Mn deposition recorded in the north basin at approximately values that 9,600 years B.?,, achieved high values, in offshore waters, were possible in CaO is recorded in Mn, and decrease again when CaO does also, than the other ele of the core it is probably present as oxidizing The initial as water between the CaO The Mn as usual appears to behave differently ments, are than 130 in during Even reduced the deep thermocline separating the high stand. the basins in at -61- Trace metals and freshening alkaline, in the carbonate of the lake, saline phase likewise In the aragonite deposited Sr and Ba are very high, phase, record the opening in the shallow, They drop sharply Mn does as a response to a change in the nature of carbonate tion. As Ca-deposition changed from being purely mediated by algal photosynthesis, aragonite personal to calcite, communication, the crystal lattice, ited, once again, deposition activity hydrocalcite increased a return the correlation line of evidence that implicates served changes is an attempt years B,?. This material The attempt atmospheric, Further futile. Stoffers, began to be depos as hydrothermal and made deposition Lead also increases at the same with the north basin, the springs Another as the cause of the ob- to date sedimentary organic carbon between gave an anomolously old date of 9,460 ± 240 This was the only attempt made to date sediments deposited ‘after the hydrothermal lake, to inorganic processes impossible. changed from This change in carbonate the input of Ca and alkalinity substantiating 115-170 cm. aragonite and the Ba and Sr increase, represents P. to being change excluded Sr and Ha from At 5,000 years H.P., in the deep north basin time, and protodolomite The structural sedimenta inorganic the carbonate mineralogy when springs determined the water composition confirms that the carbon from the springs and only partial dating of sediments As a result, equilibration of the is not with the atmosphere occurs. deposited in the past 5,000 years would be age assignments during this interval are only approximate. There is a pronounced maximum in Mg at a depth of 60 cm. its peak Mg is nearly equal in concentration to Ca, suggesting At that -62- authigenic dolomite may be present, must imply a substantial increase For reasons discussed in salinity, The lake dropped below the Ruzizi, and may have had only an intermittent main lake, Such a connection evaporative directly 1967, concentration to high magnesium calcite Liebermann, dried out during The shift from aragonite and dolomite once again excluded Sr and Ba from the carbonate phase. This Mg maximum is correlative CaCO3-rich sediments deposited in the north basin. The decline Ruzizi outlet, ion ratios actually did it overflow. but neither to to dolomite precipitation might be favorable There is no evidence that the basin this interval, from Kivu which The waters when subjected because of the unusual from solution connection with the allowed recharge of waters were already low in Ca and high in Mg. this earlier, between 3,500 years and 1,200 years H.P. The consequences overflow will be discussed with the in Mg is attributed to regaining the for Tanganyika of the intermittent later. LAKE LEVEL OSCILLATIONS AND WATER BUDGET Kivu The radiocarbon-dated logy of lake levels are considered i cores Table to be established, 4 allow an absolute The most reliable chrono datum points to be: The thick beach deposit level the lake recorded at station in the time interval ii the clay facies iii the initiation at station 14 which marks the lowest sampled; 9; of sedimentation at station 13’; -63- the first iv decline the terraces v hiatus correlate at -310 has not been directly is thought to have occurred, The clay facies in station This implies that 10,000 years B,?. dated as a depo but it is thought to reasonably age of 13,700 bedding. as much as 250 m, and there over 90% of the assemblages, that the age is too young, no source of "fossil" carbon. 1959. The only possible Precipitation the lake surface would reduce the residence to incorporation and. Walton, 1959. to be reasonably discussed, earlier, of volcanic C02, the and this error anions so there was could arise all except from in the closed lake of Ca and invasion across time, All our 14C analyses fraction will be much less of old carbon than will the carbonates Therefore, accurate and it is There is no reason to assume rock exposed in the basin, ‘were performed on organic carbon, or graded from the atmosphere by weathering time for the HC031 -CO32 and Walton, extends astraea constitutes is not a turbidite, Prior to the injection There is no carbonate a long residence Broecker This deposit of the water was derived reactions, The clay facies and Stephanodiscus of a shallow water environment. alkalinity between 11,000 and is no evidence of coarser material Diatoms are abundant, indicative 9 has a date of 10,670 years H,?,, the lake dropped significantly by perhaps over 30 cm of depth, 15’; and the time not sampled by cores 10 and which means it was deposited during subject at station with the bottom of core 4’, which has a carbon-dated years B.?. 4’. deposition which surround the lake, The beach deposit sitional in aragonite Hroécker the dates on the cores are considered for the one from station 15’ which was -64- The initiation years H.P., of sedimentation at which time the lake level appears unlikely record at station to tell and the mineralogy It may have before 12,400 years H.P. sediments and sloping The terrace Olson and Hroecker, and is likely was a fossil too old, site, and this, 13 combined would favor erosion at +100 m has been dated at 1959, but the date is on shell A date of 9,500 years H,P, seems more This date is likely as the higher terrace, reasonable. from a beach at the present A date of 14,000 years H.P. suggested to them this beach. same factor to be in error by nearly the and an age of 11,000 years would be This would coincide with the high stand prior at 10,500 years. If the lake stood that high, connected with the Bukavu Basin, in so it is not as this high stand probably marked the opening of the lake. level of the lake. 100 The exposure of station duration, Olson and Broecker also dated shell material in level 15’, it sank down at 10,500 years B.?, The low stand was of short than soil development. appropriate, changed at station evidence of the subaerial with the unconsolidated material However, it in, if the lake overflowed into the Hukavu Basin prior to There is no noticeable rather exceeded -86 15’ extends only to 10,200 years B,P,, 10,000 years B,?, at that time, 13’ occurred at 12,130 that the lake overflowed before 9,500 years B,P,, when carbonate deposition possible at station but the Ruzizi outlet to the drop then it was was still nearly above the lake, The only unequivocal evidence for lower stands H.P. are the Mg-rich sediments not extreme, probable, and an intermittent The sill in station 15’, since 9,500 years The drop in level was connection with the main lake appears is at -30 in, so a drop of much more than 30 have been only temporary. in would -65- The reconstruction of lake levels is presented it is compared to a record of lake level for Lake Victoria. because of its more detail. A rather but the Kivu record, to 12,000 years H,?,, Butzer are slight Victoria being a shallow saucer, would be more comparable. exists, 1969 exhibits for a low stand in Victoria between at that time This is a result 12, where inferred by Kendall but the closed basin lakes changes in Victoria changes in Kivu, lake level rate prior There is no clear evidence record lower levels The level good, correlation high sedimentation 2,000 and 3,000 years B,?., valley changes in Fig. et al., in the Eastern Rift 1972; Hecky, 1971, compared with the tremendous with of the morphometry of the basins, and Kivu a deep cup. The hydrologic parameters changes in Kivu will be discussed later The volume changes which permit in connection these with Lake Tanganyika. Aside from the firm datum points core suggests somewhat higher levels and 13,000 years H.P. on the basis geochemistry. tive The prominent discussed above, at approximately of the fossil the station 12,000 years B.?, diatoms and sediment 12,000 years H,P. event is probably with the "BØlling" interstadial followed would then correlate of Europe. interstadial. which station the "Younger Dryas", is not identified in the European chronology, the Camp Century ice core lations with approximately These oscillations the Holocene, Dansgaard et al., and the The very low lake succeeding high lake with the "Aller$d" opening of the lake would initiate correla The lower lake which with the "Older Dryas" stadial, 9 records would represent 4’ and the The 13,000 year event but o8 fluctuations 1971 in reveal minor oscil a 940-year period which precede will be termed "Kivu Oscillations", the BØlling, because the Lake -66- Kivu record presents the most complete and readily the late ?leistocene yet available great detail nearly that climatic in tropical correlated Africa. history It confirms of in events between the equator and the poles were synchronous through the past 14,000 years, Tangcmyika The cores available The oldest sediments 19 separating recovered The sedimentation low, and the possibility are rare in the core, suggesting rates of a hiatus and one of these was chosen for detailed resolution for the chemical history diatom stratigraphy. The recovered station Station 15 which was radiocarbon an age of 4,000 years, presented in Fig. 13. performed, and abundant fossil to gain better analysis and is readily dated, with the In addition, dating, correlated in of water, with nearby The bottom of the core is assigned of the chemical stratigraphy the core from station organic carbon, are 2 in the south and CaCO3 analyses This core was somewhat longer and older and covers over 6,000 years. The CaCO3 stratigraphy in Fig. 15, where it is compared to that is .given in Fig. The Ti02 and A12O3 content of the core. variation, or non-deposition, and to allow correlation The highlights basin also had radiocarbon seems likely. 12 is in the north basin in 1,200 core is 195 cm long, station implied for this dissolution The cores from the deep basin have much higher rates diatoms, cores, are in a core taken from the sill the two basins. core are extremely Microfossils from Tanganyika are short gravity 14 and the organic of stations carbon 15 and 19, are nearly uniform over the length The A12O3 concentrations presented in Fig, as they are given on an expanded scale; 13 show some but the variability -67- reflects primarily diatoms, organic the sedimentation of the other components, carbon, and carbonates. to have been stable Likewise, for the Mn system. that the hydrogeochemistry 4,000 years. sharp rise higher very low concentrations, High Ca-deposition which they fell than those prior similar sharply to 3,000 years was recorded in the recent past. strates Only CaO concentrations H,?. while Ca-deposition very low organic The ionic was noted above, 1952; Coulter, one-half Fig. abrupt. the salts thermal activity Ca-deposition an appropriate delivered in Tanganyika are rel.ated e.g., period, 15 Heauchamp, the Ruzizi accounted but do have 1939; Capart, for up to We have seen that of enforced hydro which began in Kivu 5,000 years B.P. in Tanganyika; about from Kivu and Tanganyika investigators that Fig. river is the result delay which reflects Organic 1971. to the lake annually. of the present demon increased more than 1,000 years of surface waters have suggested 14 from much lower levels Degens et al., and most previous 1963 the high salinity and, salts similarity for Another sharp increase cores which cover longer periods carbon contents is a rather to rates which were still The record in the north does not extend over this other correlatable in the past rates were maintained changes, but they are somewhat less 4,500 years H.P., show approximately The south basin core carbon in the south basin core,increased later. there at 130 cm which extends 30 cm, representing time, after appear invariant of the lake has changed markedly From initially 600 years of deposition. a short conditions Lead is relatively except for a pronounced peak at 95 cm, especially The’ increases in to the events in Kivu, but with the large residence times of water it would take nearly 1,000 years for the -68- tributaries of Tanganyika evaporation losses, to renew the volume of the lake, The Ruzizi is more saline and hence it flows downslope on entering on surface waters. effect Only after across the thermocline. Thus the initial of the lake become affected input source with the deep water homogenization become noticeable becomes a broad diffuse than Tanganyika waters, the lake without immediate will any pulse in salts Ruzizi neglecting in surface waters by mixing point the thermocline nearly synchronously the source of salts and wide areas well after the initial increases. In Fig. 14 the CaCO3 content of station with the Tanganyika records. basin of Kivu occurred 10 in Kivu is juxtaposed The maximum in deposition during an interval in the north when the lake was closed. the Kivu basin is the primary source of the calcium in Tanganyika postulated, after then a hiatus a sufficient lag as a lower deposition seems consistent increase in CaCO3 deposition salinity with the available concentration, changes. source of the Ca. in Tanganyika. Further as the tremendous volume of the lake buffers The correspondence thermal activity indicts as the mechanisms different, of the effect on Tanganyika of the hydro from analyses of interstitial of a core from station Kivu water as the of the maxima in Ca-deposition in Kivu and the climatically-induced the Ruzizi is obtained waters are quite confirmation The in Tanganyika 2,000 years ago cannot be due The peak in Pb concentration the increases Such a CaCO3 stratigraphy, 2,000 years H,P, in Kivu and Tanganyika is fortuitous, eliciting as in the overflow from Kivu would be reflected sequence to evaporative If 2 have been analyzed intermittency waters. of’ The pore Greene and Jones, -69- 1970, and the results salinity are given in Fig. of the lake over the past ions which are most sensitive disproportionately other inflows dramatic, and a second interval similar pattern an interval of increase without although slowly, salts as Na does, of the Ruzizi and the Malagaris; That Mg and only emphasizes that by calculations presented later, cations in Table 1. of the lake is still cf, It appears increasing, which indicate tribu and this that more enter the lake via the Ruzizi than leave the lake via the Lukuga. As the lake is not in equilibrium, have little meaning. In general calculations of salt it is concluded that primary source of salts flowing into the lake between approximately B.?, the Ruzizi, are the primary source for these from Fig. 16 that the salinity is supported of the lake would of the Virunga, which is the second largest tary to Lake Tanganyika, the chemistry the period for As Tanganyika must become continue rocks of the volcanoes A is seen for Na, but the pause so evident the salinity through pat concentra to the surface, closed when the Ruzizi is not flowing, K do not increase and a similar of constant extending Mg and K is only a change in slope in Na, to increase, The two on the Na and Ca would be less Both Mg and K exhibit of increase, of increase is demonstrated. carry large amounts of these cations, Ca is buffered with a solid phase, tion, in the in Ruzizi waters when compared to The effect as the other rivers an interval increase to events in Kivu are K and Mg, which are to Tanganyika, i.e., A general 5,000 years over-represented tern, 16. This chronology constructed to the lake, and that residence the Ruzizi times is the Lake Kivu was not over 4,000 years and 1,000 years for the Ruzizi at Tanganyika agrees, well with that for the river at its source, -70- The initiation the salinity of the Ruzizi River, the deep waters shows. of hydrothermal of Tanganyika, activity which began to increase as the stratigraphy The immense volume of the deep waters very slowly. As the increases Kivu, mixing processes in the Kivu basin increased of interstitial allowed salinity were slow, unlike generally the salinity water to change the situation kept pace and no persistent in Lake chemocline developed. The Ruzizi River is also cooler than the surface waters Heauchamp, 1939 The increased and nearly isothermal salinity of the Ruzizi the cool water plume to greater libration, reduced, The thermocline As previously , Nitzschia sp. detail, relative it with the deep waters after depths of the lake, 5,000 years H.P. would carry and reduce somewhat thermal equi- would be sharpened and mixing and productivity discussed, such conditions Although the diatom stratigraphy is clear that would favor long, is not complete prior to 5,000 years H.P. in the north basin the In the south basin S, astraea remains prominent microfossil assemblage up to the present, the south, The depth of detectable Degens et al., 1971. of seasonally account for these differences, material. immediately distance south winds Coulter, from surface i,e,, 1963 in the mixing in and the presumably stratification would lead of organic waters would not begin until in surface waters, deep water salinity at 5,000 years B,P,, organic astraea in the south and better preservation Ca began to increase of these events, better from the Ruzizi, A more stable reducing conditions CaCO3 precipitation the Ruzizi-derived succession strong indicating 02 is also greater The greater effects to more strongly thin in any abundance of Nitzschia spp. was lower and Stephanodiscus was present. of The temporal beginning to increase carbon increasing at 4,000 years -71- B,?., and CaCO3 precipitation buffering beginning yika are closely.linked, separated from the former, Tanganyika, In view of this, lake. hydrology may allow insight Hydrological reconstructions basin geology as it affects In open lakes, of the latter require runoff, changes are subdued, proportional to surface area, An increase will cause lakes to rise until increased surface a reduction it is possible generate the lake levels given in Langbein within observed, primarily estimates Theeuws The only discharge of rainfall and run from the Thus, when Kivu was closed most probable climates the hydrological parameters to relations data. evaporation, for the Lake Kivu basin of the Kivu basin are given in abstracted newly generated for rainfall, 1920, lakes, 1961, These were partially represent in discharge and lower inputs will lead to following and the Lake Tanganyika basin exclusive tially knowledge In closed-basin in inputs limits, Morphometric and hydrological Table 5. from the, which will be directly area and lake level, to reconstruct, detailed losses by evaporation area equal the inputs; in surface into that of Lake and lake morphometry. response is mediated by changes in lake level, water from a closed basin is by evaporation, of Lake, for that period response to changes is reflected while water level cannot be a reconstruction although we do not have a record of climate, off the has shown that Lake Kivu and Lake Tangan- and that the history Kivu’s late ‘Pleistocene rates reflects to change which the immense size of the lake engenders, The above discussion latter at 2,000 years, from various sources For Lake Tanganyika, and inflow to the lakes which appear to agree fairly and par hydrological are those of well with subsequent measure- -72- ments 1952, Capart, Morphometric data are based on the map of Capart and Hutchinson 1949 1957; lated using 900 mm as the average of the Lake Kivu drainage volume of inflows Verbeke 1957. and dividing 50% larger were estimated rate, Data for the past than previously function trough-like Figs. city, morphology to some fractional relation, believed, equations 17, 18, A Tanganyika basins Hutchinson, Langbein, in Volume area is propor 1961, any significant of Kivu, which dictates the volume are double and one-half Rainfall and rapid infiltration i.e., For simpli assume a linear error The basin slope, The runoff coefficients exclusive is for Kivu interest coefficients, In most lakes, lakes, to the north of the basin effectively For Tanganyika, discharge rates Of special these two parameters change in area, 1957, p. 230. is steep, flow over a in both lakes because of their A V°’40’75 relating ganyika is nearly double that nearly twice as much. from Amenage that Evaporation 1961. of area as it will for other a given proportional indicate and runoff but this will not introduce Tanganyika, relief 10 years from power of volume, because most lakes have a cross-section, Langbein’s value into the total which was obtained from a graph in Langbein V. is a nearly linear curvilinear over the basin exclusive des Chutes de Mururu, which monitors Table 5 are the basin slope parameter tional this is calcu The data for Kivu are abstracted except for discharge dam on the Ruzizi, nearly area, annual rainfall less the Ruzizi, ment Hydro-Electrique The runoff coefficient p. 168. for Kivu and AV/iA, for Tan that to accomplish depth must decrease for the Kivu basin and the the world average respectively is quite ,high in the Kivu basin, into the porous lavas and ash ,reduce evapotranspiration of the Kivu basin, losses. much of the basin area is -73- in the semiarid plateau are extreme, region of Central The water budgets Tanzania, lower than those of Heauchamp 1939, which are often cited because he the mean depth of Lake Tanganyika. are estimated salt losses and storage times, are not completely valid, as the lakes in Table 6 Also given As mentioned earlier, via the Lukuga outlet. the interstitial these are probably not in any long-term It can be seen that the Kivu basin is currently twice as much Na and over three storage time are much for refill overestimated equilibrium, losses for the two lakes based on the data in The estimates Table 5 are given in Table 6, and evaporative contributing times as much K to Tanganyika as is lost These values water stratigraphy, support the interpretation Both water and salts given to have long times in Tanganyika and can be expected to respond slowly to changes in input, From Tables 5 and 6 it can be seen that 18% of the tributary the Lukuga using waters, either and its the Ruzizi accounts for volume discharge Theeuw’s estimates {l920} or Capart’s Thus, loss of the Kivu overflow will be sufficient to become closed, Within the past The question of interest and what possible l952}, to cause Tanganyika 14,000 years this has happened twice, is how far did the level effects from Kivu exceeds did it.have of Tanganyika drop, on the biota of the lakes, When Lake Kivu stood at -300 m, the lake had an area of 948 Fig. 19 and the tributary is possible bein 1961 2 With these values it to generate a family of curves giving possible of mean annual temperature sufficient area was 6,192 to maintain and mean annual precipitation combinations ,which will be a lake at a given level by using graphs in Lang and assuming different runoff values. Two sets of curves -74- 20, are given in Fig. a closed lake at the modern level, maintain ditions One set gives the combination which would maintain conditions tions. it is necessary Schumm 1965 to precipitation gives a family of curves This indicates sity have on runoff. arid climate, the effect that determines highly variable a selection it can than poro Temperature glacial 1967 the depression is less likely lower temperatures. Flint calculated firn line. 1959 Mt.. Kenya and 7°C for Mt. Kilimanjaro to be and the probable the elevation of the of 4°C under modern precipitation of.the by or precipi that maxima in the Ruwenzori and determined in mean temperature one- during the late Pleistocene changes in Africa Osmaston i.e., With a curve selected over wide areas than precipitation, line during polation A value of 0,20, of mean annual temperature the other parameter, have been estimated, require From this would be lower under a more. should be reasonable. magnitude of temperature would explain mean annual runoff but it would probably not approach the value for Tanganyika, runoff coefficient, decrease relating condi topography and substratum The runoff coefficient half the modern value, firn of possible is nearly 50% greater 0.08, because of these unique basin factors. tation set those con of "most likely" for numerous basins, coefficient just to From these, sets to pick a combination be seen that the modern runoff expected, and the other a lake at -300 m. and temperature sufficient under similar of these values to lower elevations conditions Drier conditions calculated requires a would a value of 5°C for assumptions, Extra an assumption about the lapse rate. A temperature decrease of 3°C in the Kivu basin in the late Pleistocene should be conservative. For a mean annual temperature of 17°C, only 70 cm/yr annual precipitation would be required to maintain -75- the lake at -300 m, coefficient higher, If the temperature then even less annual precipitation nearly the Kivu basin, and Coetzee conditions Pleistocene, Africa, summarize evidence extrapolation areas is reasonable. i Rainfall fell resulting of changes of similar magnitude, for the African Zinderen, Bakker climate of the Late were cooler and drier all over of changes from the Kivu basin to nearby are: to 60 cm/yr over the greatest of the modern value, the runoff coefficient lead to overestimation was exclusive can be estimated, conditions Assumptions which is two-thirds ii exhibited of Tanganyika and conclude that so that Present time. in the Tanganyika basin, which was closed, 1972 would be adequate. is 130 cm/yr, which shows that precipitation then the probable level basin, rainfall half the ,modern value at that If climatic were lower and/or the runoff part 90 cm/yr; was the modern value of tributary inflows of the this should and underestimation of volume changes in the lake; iii iv temperature mean annual temperature net.annual evaporation was 114 cm/yr the following where iV is the volume change, no I-EA1 I the volume of inflows, = 0 then ‘ i.e., can be evaluated: and A the lake area at equilibrium. A1 and 1961. with these .conditions, equation = evaporation, for the assumed precipitation from Langbein, For the lake at equilibrium volume changes, was 21°C cf. modern 24°C; and = 7,550 When E the net annual -76- This area can be converted to a depth by means of Fig, relates area and volume to depth. lake was lowered by over 600 be sufficient to split in The above conditions imply that the during the Late Pleistocene, the lake into separate basins. which would The relatively large lowering of the lake is imposed by the high basin slope, requires area. ‘ relatively great volume reductions The drop is nearly twice that only one-half that of Tanganyika. changes Kendall estimated investigators Valley Hutzer et al., Lake level interpreted of light depressions greater hard, bottom, 1949 returns several lakes in the Eastern reported as indicative Rift that echo sounding of alternating echoes were observed. diffuse He hypothesized of denser At depths echoes, He layers In depths of less than 150 m the bottom and no multiple had allowed the deposition than now possible. than the of this magnitude have been postulated than 850 m only a single appeared, greater and the higher lake levels in closed-basin Capart and dense sediments, a very soft It is drastically between 150 m and 850 m recorded multiple these multiple was relatively a change in surface 1972, before for Lake Tanganyika. in soft.sediments which in Kivu, which has a basin slope for Victoria have identified to effect 21, which trace was recorded, that oscillations sediments less than 550 in In depths indicating of lake level at depths much greater as many as eight traces while at depths between 550 and 850 m only two appeared. Support for such lowerings was also found by the identification drowned river courses extending down to 550 Livingstone 1965 recovered a 10.74 of many in. in core from 440 in of water at the southern end of the lake in an area where his echosounder recorded -77- one multiple echo in the neighborhood the fathometer cient range to reach bottom at the sampling no soil horizons being quite cm yielded A radiocarbon Livingstone ash layers, found one date for the ash at approximately an age of 11,690 years H.P. Extrapolation 575 of the inferred rate to the bottom of the core suggested an age of 22,000 sedimentation years H.P. locality, in his core, but he did find several thick, did not have suff i On the basis for why the traces even at his site of this, Livingstone would only be found in depths the volcanic no explanation of less than 850 valleys in, remote, source must have been quite however, that the sublacustrine didsuggest, could offer for He might have been eroded by density currents, Our hydrological and therefore, either reconstructions our estimations explanations of his results tation in Kivu suggests rates would disagree are grossly are possible. rate for the past 11,000 years to the previously is extremely rich in diatoms, lake levels productive by the magnitude upwelling minimum. Therefore, site, with sedimen of the sedimentation deposited of sediment ages, that Capart and we suggest would. bring the 1963 as lake levels at the south end of the rose after reaching Livingstone’s the possibility their the bottom of his core may be younger than supposed multiple The ash layer echo, but the congruity with those of Capart is a supposition least, core A lowering of and may not record the events of the lowest lake stands. may explain sediments Livingstone’s as were the Kivu cores, system Coulter, lake near Livingstone’s in error or alternative Our experience that extrapolation could lead to gross overestimates with Livingstone; which Livingstone of much lower levels of that return admits, At the during the Late Pleistocene -78- is revived by the demonstration of such levels levels keep viable ration of the lake into two basins would allow allopatric account explain the very low sedimentation as a depositional probable qualified. of the vegetation. are implied, 1949 Little evidence in result from a level of that is assumed that the Ruzizi discharge to -75 lower, accumulated discovered as Capart in to overflow at the Fig. 21, If it without loss, nearly to cause Tanganyika to overflow, When first A,D., at which time its are assumed even lower levels longer times would be required blocked, even if no in, in lake level, 2,200 km3 be added to the lake 700 years would be required let was completely about the very thin sediment cover at depths Lukuga requires flow at the Lukuga, 19 on the is available If changes in precipitation from the last decline To recover lake was certainly to that loss of the Ruzizi of Tanganyika to fall It may well be that suggested. As the to effect level fell century have been insufficient over in 1854 A.D,, the Lukuga out and the lake did not overflow until about the modern level prevailed. junction at station for the loss of the Kivu overflow, of less than 150 speciation The lower lake stand rate It can be stated changes are assumed, to be responsible and sepa as the pollen data becomes complicated by cultural alone would cause the level climatic lake lowerings loss of the Kivu drainage between 4,000 and 1,000 is less easily temperatures, alteration These lower lake hiatus or even erosion by wave action. The more recent years B,?. that multiple flocks in the lake, for the endemic species would also sill the hypothesis in Kivu, 1878 markedly before minor oscillations Climatic oscillations to close the basin again, of the past This in con with the long response time of the lake suggests that 1878 -79- A.D. marked the first overflow at the Lukuga since approximately 4,000 years B,?. In view of the high probability of internal tion. drainage, the salinity The "thalassine" as an adaptation to previously lake receives even before the hydrothermal a disproportionate are relatively and salinity of all 120 mg/i. Tanganyika amount of salts soluble, to the lake, During arid periods Under the climatic assumptions lake’s volume, 6,000 kin3, was only one-third occurred, and salinity of the present lake would give a salinity Harvey, basin lakes Hutzer which means that be generated fore, it through available At -600 m, the high, communication concentration from correlation periods, with and the Eastern Rift closedof 4,2 g/l would Lower values are more likely, is clear that Tanganyika has not been more than slightly in pluviai loss Assuming a salinity a threefold a maximum salinity began, its more recent.history. 18,800 If the lake is assumed to have been 1972, before dilution approxi the present volume, which appears reasonable et al., to the Mala which placed Lake at 0.2 mg/l/yr. which is unusually personal the composition would be imposed if no salt would increase closed for 15,000 years, Lake Albert in salinity of 1,2 g/l, and as the rocks in incoming waters were probably similar increase 1950. began the Kivu drainage probably at -600 m, inflows were 8,3 km3/yr, A threefold Brooks, from the Ruzizi, mately 1 x 1012 g/yr of salt was added to the lake. km3. ques in the lake has been explained 50% of its salts activity and periods of the lake comesinto much more saline waters perhaps the drainage garasi stability aspect of the biota The present supplied of lower lake levels There brackish As long as the moist Kivu drainage is a saline Lake Tanganyika is not possible, -80- Truly saline periods must antedate and the Virunga event. the acquisition The seismic of the Kivu drainage work in Lake Kivu puts this well. back into the Pleistocene. Ec,ard A chemical stratigraphy based on a.core from station for the past 6,000 years in Lake Edward, 4, is presented in Fig. 22. The detrital components, TiO2 and A12O3, covary and reach maxima during where fine ash was noted in the gross stratigraphy. layers, deposition deposition of detrital material has been prominent throughout field the time represented activity water chemistry in the Virunga field while numerous explosion and these may have supplied the ash. well with the hydrothermal years H,P,, an interval 1,200 years B,?, spring indicating a different indicating that hydrothermal possible source. that the radiocarbon C02, and it may be slightly concentrations fore, have similar in a similar fashion, As this field, in Kivu, with peaks at 5,600 and greater activity since the ash, perhaps core begins with a Pb peak, may already have commenced, it date for this core includes Nickel also demonstrates the Ni to any particular is some volcanic of high ?b and ash concentrations; to attribute lava flows, the Toro-Ankole case the Pb precedes too old, during periods it is difficult activity activity to the The Pb maxima appear to correspond of reduced activity, In the latter by the has been copious are present.in craters Ash The Virunga volcanoes to the east and, southeast volcanic rocks and would affect The most recent Aside from the ash appears to be invariant. core, but the exact source is.uncertain. south and the Toro-Ankole intervals maximum there facies, -81- Diatoms comprise the bulk of the dry sediments, material, as might,be Mo values are indicative values contrasts strongly of detrital with the conditions runoff and springs and never stratified contributed In Edward it is possible on productivity, Calcium carbonate of any component in the core, approximately to dilution 200 years B,?,, by ash. creased dramatically of the core. bution of the copious the basin, previously, to the lake efficient springs mixing. effect. were injected under was the result. the most marked changes in depo A significant increase and subsequent decreases In the very recent.past, occurred can be attributed Ca-deposition again in to 43% and 54% CaCO3 by dry weight at the surface requires a much greater Ca contri The Ca is probably derived from surficial weathering This tremendous increase to the lake, In Edward the had a positive and low productivity demonstrates The high The shallower mean depth also that volcanic activity it, Low and hydrothermal of Kivu. and relatively In Kivu the hydrothermal the lake and stratified The high components. peripherally it with a chemocline. allows mixing to the sediment surface lake, nature of the sediment, of Edward through this period of volcanic nutrient-rich sition highly productive of the biogenic for Mo mark higher deposition productivity activity expected in this along with organic amounts of fresh ash which have recently been added to This would imply that the lake is somewhat more saline Manganese appears to covary with CaCO3 with slight at 2,000 years H,P, and quite Again, increased inputs seem to.be involved, to Lake Kivu,. where increased increased deposition sharp increases than increases at the top of the core, The situation supply by subsurface is analogous weathering of Ca and Mn in shallow waters, led to In Lake Edward -82-. such sediments need not be restricted lake is not strongly stratified to shallow waters, and the salts because the are added peripherally to surface waters, Albert Lake Albert is downstream from Lake Edward, and the connecting Semliki River accounts Talling, 1963, stratigraphies for a large proportion and thus a close correspondence reduced in Lake Albert, and the diatoms are highly sediments, significant, Oxidizing conditions fauna to efficiently quence, the Lake Albert stratigraphy tions in the inorganic The chemical presented in Figs. the lake, 58 in, than at station this alogy, feldspar organic materials, allows a clearer 23 and 24, of two cores Station Sedimentation tates an active As a conse insight into varia from Lake Albert are 5 is,from the maximum depth of have been higher at that 3, where a much longer record is available. layer, The core from station This layer is underlain U, Hriegel, have been identified station Station enriched in by X-ray miner and mixed with sands of high quartz personal edly marks a lower stand in Lake Albert communication, correlative 3 3 terminated Ca, Sr, Mg, and Mn are all and dolomite and calcite content all depths permit may be phases, stratigrphy carbonate-rich layer, fragmented and dissolution regenerate is somewhat closer to shore also, in a dry, components are carbon is low throughout Albert through benthic However, the sediments as the biogenic Organic to the lake between the chemical of the two lakes might be expected. of the two lakes are quite different, greatly of the inflows and This layer undoubt with that of Kivu., -83- The’ detail for this as desiccation period which Lake Kivu supplies caused one or more hiatuses, However, the occurrence then, Dating of this make ‘the age assignments core is by correlation, imprecise. Dilute from the very low rates of CaCO3 deposition, constituent station 5 cores indicate. of fluctuations centrations indicate in Mn concentration tepresent oxidizing Eh’.s sufficiently was seen.on reducing. through this period, low to liberate Fe; therefore, throughout that a manganese carbonate phase,was At 5,000 years B,?, as did all At station 5 the increases of carbonate carbonate this period, are gradual, The Mg content of this may be inthe richer does rise, clays, In both cores after increase. with the highest concentrations 3 the increase in higher values than those inthe This high carbonate from the earlier The waters were ionically and it is unlikely of the lake changed, At station and CaCO3 achieves years H,?, does’differ No effect was only weakly and organic carbon content near the top of the core, is abrupt, The high con involved,. dry layer at the bottom of the core. saline. interface the hydrogeochemistry and the carbonate is evidence Mn from the sediment.. the other lakes in the Western Rift valley, Pb shows a peak, as both the whereas the low concentrations the sediment-water The lake was dilute are implied Clays are by far the most, In both cores there conditions, hiatuses followed, conditions up to 5,000 years H.P., prominent, sedimentary 3 and station and possible Much higher lake levels and the lake overflowed at the Albert Nile, of the lake did not open a secondary CaCO3 and Mn at 400 cm may imply that until is not evidenthere, layer at 5,000 one in that Mg does not increase, 5,000 years H,?, but not highly but it levels The clay facies off at around 3%, in Albert differs from Much -84- that in Kivu and Edward, as montmorillonite nearly one-half the clay by weight. more Mg than the kaolinite lakes, is present The montmorillonite and illites in station 5, but this 3 contrasts rates precipitation is mediated by algal photosynthesis the water. nearshore, fore, as nutrient the hihest shore waters eventually rates and the nearshore position In large African Ca-deposition 1969. exceed that different constant there, There near- 5 does sedimentation the chronology, 3, while station vastly 5 yields ‘a nearly rate. 5,000 years H.P. significantly As the absolute in the station contribution carbon probably reflects increased from the Virunga hydrothermal the Toro-Ankole field increasing productivity made the sediments noted earlier productivity, center by a factor slightly ceased after 3, and it is true rise in organic Greater nutrient’inputs eutrophication of two. reducing, for station of fresh ash in of the lake, perhaps The higher organic content and the Mn fluctuations 5,000 years B.?. 24 obscures it somewhat. this and the weathering caused a natural 3 core after of the clays is thought to have remained the same while CaCO3 increased, Fig. is measured of station 3, so that differing at station Organic carbon rises station The CaCO3 driving up the pH of are greatest As we have reconstructed rates ..are evident 3. would be expected in shallower, of station are also involved, by different of station The CaCO3 content with noticeably lakes the highest productivity’ input and regeneration Kendall, in the other is best explained sedimentation for incorporates which predominate The sharp peak in CaCO3 in station the gradual rise and accounts This is quite which were clear for 5,, although the expanded scale of The effect of the hydrothermal waters on -85- the productivity recovered of.Lake Edward was not noticeable, sediments which predated the lake was quite productive increased nutrient source of salts graphic record ficantly station input. . the onset of spring previously The Semliki and nutrients 5 core may demonstrate on the phytopiankton and/or and was not as sensitive to the lake, 5,000 years ago. activity to is thought to be the primary suggests that nutrient increased as we may not have so that "overflow" the Albert from Lake Edward signi Diatom analysis the effect strati- of the Albert of the natural eutrophication of the lake. Malcaii Lake Malawi has no hydrological Rift valley and could not be directly Virunga hydrothermal for the past part of the same rifting phenomenon, scale. gesting in the Nyasan rift, center of the initiation to see If they have, it is not a localized of rifting activity of the sediment is pre 25. activity are quite variable, observed. of However, Malawi is the opportunity The chemical analysis The presence of several hydrothermal 5,000 years, and it offers but merely an expression in Fig. by the events in the that the Virunga hydrothermal on a much greater sented system, events have occurred becomes probable affected with the Western center which have dominated hydrogeochemistry the lakes of that rift if similar connection is present Pb peaks in the sediments in the basin. The detrital as would be expected from the frequent Mn and Fe2O3 have maxima together an oxidized phase, suggests that elements turbidites between 40 and 80 cm, sug but at other core intervals they do not covary, -86-. implying reducing concentrations, indicate conditions, carbon and CaCO3 achieve maximum while Pb is high between 120 and 150 cm, which may hydrothermal that Organic activity supplied increasing productivity. that time, which could be caused by relatively or greater input of allochthonous earlier. Alternatively atures, more Ca and nutrients, However, the C:N ratio reaches a maximum at lower algal.production organic material, the high C:N might. indicate and more rapid deamination thereby as was discussed, warmer bottom temper of amino compounds as suggested by Mopper and Degens 1972. Radiocarbon dates of a nearby core, Von Herzen and Vacquier, 1967 slight give an age of about 2,000 years for the topmost but consistent sediments of this same extent, order of 3 increase core have been "contaminated" the figures in would translate per thousand years. of the lithological similarity imply that core 15 collected 1,000 years noticeable old. in this about.1,200 in age with depth. years Assuming that the by dead carbon to the to sedimentation rates in the This rate is not unreasonable to Kivu core 4’, by the Heidelberg We tentatively that is less the hydrothermal to the last It is conceivable in view These high rates would expedition conclude that core corresponds ago. sediment and a Kivu event, correlations thermal events recorded in older East African rift than activity which started of hydro lake sediments reveal a synchronous pattern. There is already activity sufficient to allow a hypothesis African and Red Sea rift are considered of related system. proposed for mid-ocean ridges, evidence of periodic rifting activity hydrothermal all along the Such behavior would be similar where rifting complementary processes. and hydrothermal to that activity CONCLUSIONS The stratigraphic Africa provide insight determining times, for five rift into the interplay the hydrogeochemistry andHolocene saline, records of climate lakes of the lakes during Late Pleistocene The Late Pleistocene which marked the transition warmer and wetter Holocene appear.to temperate cooling European record is indicated, lakes were closed and more from this be. readily with aridity occurring Climatic period into the correlated and ice cores from Greenland. much higher modern precipitation in Central and geology in as a cooler and much more arid climate prevailed, oscillations saline valley with the Worldwide in continental as evaporation areas with from a cooler and more ocean was reduced, Volcanic and hydrothermal Virunga volcanic region 5,000 years H,P, water bearing the unmistakable Virunga rocks now dictates Rift valley lakes. activity Similar increased The copious chemical "fingerprint" the chemical composition hydrothermal Nyasan Rift at the same time, possibly sharply activity supply of.saline of the distinctive of all the Western may have begun in the marking a renewal of rifting activity. Water may be a necessary prerequisite processes, .and the African sequence of pluvials climatic may have caused corresponding geological record. periods in the of activity for volcanic and rifting and interpluvials and quiescence in the -88- A CX1VOWLEDGMENTS We thank Drs, Peter Scientifiques vateur en Afrique Centrale Coordinateur, logistics support discussions de Virunga during the expeditions, de Recherches Von der Hecke Conser- for valuable advice The study has profited B. N. Price, by the National and from S. Honjo, G, Muller, Science Foundation GA-3064l and GA-35334. Contribution tion, Parc National it was supported Institut and Jean Pierre with Drs, D, A, Livingstone, and G. Kulbicki; under grants and Irene Kunkel No, 3092 Woods Hole, Massachusetts of the Woods Hole Oceanographic 02543 Institu U.S.A., REFERENCES Anderson, G, C, 1958 Seasonal characteristics of two saline Washington. Limnol. Oceanogr. 3: 51-68, Baradat, lakes in J. 1970 Dtermination des lements traces et des lements majeurs par spectrometrie d’mission U.V. Mmoires du CNAM, Section Physique. Beauchamp, R. S. A. 1939 Hydrology of Lake Tanganyika, Hydrobiol. 39: 316-353. Beauchamp, R, 5, A. 1953 41: 226-239. Hydrological mt. data from Lake Nyasa. Rev. J. Ecol. Hell, K. and J, L, Powell 1969 Strontium isotopic studies of alkalic rocks: the potassium-rich lavas of the Birunga and Toro-Ankole regions, East and Central Africa, J, Petrol. 10: 536-572, Bishop, W. W. 1963 The later Tertiary and Pleistocene in eastern equa torial Africa, In African Ecology and Human Evolution, pp. 246275 Wenner-Gren, New York, -89- Broecker, W. and A. Walton 1959 The geochemistry of C14 in fresh-water systems, Geochim, Cosmochim, Acta 16: 15-38, Brooks, J, L, 1950 Speciation 30-60, 131-176, in ancient lakes. Quart, Rev, Bid, 25: Brooks, J, L. 1969 Eutrophication and changes in the composition of the zooplankton. In Eutrophication: Causes, Consequences, Cor rectives, pp, 236-255 G. Rohlich, ed., N,A,S., Washington, Hutzer, K, W., G. L. Isaac, J, L, Richardson and C. Washbourn-Kaman 1972 Radiocarbon dating of East African lake levels, Science 175: 1069-1076, Capart, A. 1949 Sondages et carte bathymtrique. Exploration hydrobiologique du Lac Tanganyika 1946-47, Inst. Roy, Sci, Nat, Belg, 2: 2 16 p. Capart, A, 1952 Le milieu gographique et gophysique. Exploration hydrobiologique du Lao Tanganyika 1946-1947, Inst. Roy. Sci, Nat, Helg. 1: 3-27. Christ, C, L, and P. Hostetler 1970 Studies in the system MgO-Si02C02-H20 II: the.activity product constant of magnesite, Am, J, Sci, 268: 439-453, Cloos, H, Coulter, 1939 Hebung, Spaltung, Vulkanismus. Geol, Rdsch. 30: 401-444, G, W. 1963 Hydrological changes in relation to biological pro duction in southern Lake Tanganyika. Limnol, Oceanogr. 8: 463-477, Cowgill, U, M, and G. E, Hutchinson 1970 Chemistry and mineralogy of the sediments and their source materials, an account In Ianula: of the history and development of the Lago di Monterosi, Latium, Italy, pp. 37-101 G. E, Hutchinson, ed,, American Philosophical Society, Philadelphia. Damas, H. 1937 La stratification thermique et chimique des lacs Kivu, Edouard et Ndalaga Congo Belge, Verh, Int, Ver, Limnol, 8: 51-68, Dansgaard, W,, S. J, Johnsen, H, B, Clansen and C. C. Langway, Jr. 1971 Climatic record revealed by the Camp Century ice core. In The Late Cenozoic Glacial Ages, pp. 37-56 K, K, Turekian, ed,, Yale University Press,, New Haven and London, Degens, E, T. and R. E, Hecky 1973 Paleoclimatic reconstruction of Late Pleistocene and Holocene based on biogenic sediments from the Black Sea and a tropical African lake. Symposium on Quantitative Study of Climatic Variations during Pleistocene, Gif-sur-Yvette, 5-8 June 1973, -90- Degens, E. T. and G, Kulbicki 1973 Data file on metal distribution in East African rift sediments, Woods Hole Oceanographic Institu tion, Techn. Rep. 73-15: 1-280. Degens, E, T,, R. P. Von Herzen and How-Kin Wong 1971 Lake Tanganyika: water chemistry, sediments, geological structure. Naturwissen schaften 58: 229-240, Degens, E. T., H. Okada, S. Honjo and 3. C, Hathaway 1972 Microcrys talline sphalerite in resin globules suspended in Lake Kivu, East Africa, Mineral, Deposita Berl, 7: 1-12, Degens, E, T., R. P. Von Herzen, How-Kin Wong, W. G. Deuser and H, W, Jannasch 1973 Lake Kivu: structure, chemistry and biology of an East African Rift Lake, Geol. Rdsch, 62: 245-277, Deuser, W. G., E, T. Degens, G, W. Harvey and M, Rubin In press Methane in Lake Kivu: New data bearing on its origin. Science. Eccles, D, H, 1962 significance An internal wave in Lake Nyasa and its probable in the nutrient cycle. Nature 194: 832-833, Flint, R, F. 1959 Pleistocene climates in eastern Bull, Geol. Soc. Amer. 70: 343-374, Fryer, G, 1959 440-451, Garrels, Gessner, Some aspects of evolution R, M, and F. T, MacKenzie 1971 Norton, New York, 397 pp. F. and southern Africa, in Lake Nyasa, Evolution 13: Evolution of sedimentary rocks Das Plankton des Lago Maracaibo, Ergeb, der Deutschen Venezuela-Expedition 1952, Vol. 1: 67-92. 1956 limnol, Greene, C. and E, N, Jones 1970 Physical and chemical properties of Lake Tanganyika. Tech, Memorandum No, 2213-331-70, New London Laboratory Naval Underwater Systems Center, New London, p. 17, Guillard, R. R, L,, P. Kilham and T, A, Jackson In press Kinetics of silicon-limited growth in the marine diatom Thalassiosira pseudona-na HASLE and HEIMDAL = Cyclotella nana HUSTEDT. J. Phycol. Hecky, R, E, 1971 Paleolimnology of the alkaline, saline lakes on the Mt. Meru lahar, Ph,D, Thesis, Duke University, 209 pp. Hecky, R. E, and P. Kilham 1973 Diatoms in alkaline, saline lakes: ecology and geochemical implications, Limnol. Oceanogr,. 18: 53-71, Higazy, R. 1954 Trace elements of volcanic of southwestern Uganda and adjoining Bull. Geol, Soc. Am. 65: 39-70, ultrabasic potassic part of the Belgian rocks Congo. -91- Principles Holmes, A, W. 1965 1288 pp. Hustedt, F. 1949 of Physical Geology Ronald, New York, Süsswasser-Diatomeen, Explor. Parc Albert, Fasc, 8, Hruxelles, 199 pp. Miss, H, Damas 1935-1936, Hutchinson, G. E. 1015 pp. 1957 A treatise on Limnology, Vol. 1 Wiley, New York, Kemp, A. L. W. and A, Mudrochova 1972 Distribution and forms of nitrogen in a Lake Ontario sediment core. Limnol. Oceanogr. 17: 855-867, Kendall, R. L. 1969 An ecological Ecol, Monogr. 39: 121-176, Kilham, P. l97la planktonic history of the Lake Victoria basin, A hypothesis concerning silica and the freshwater diatoms. Limnol, Oceanogr. 16: 10-18. Kilham, P. 197lb Hiogeochemistry of African Lakes and Rivers. Thesis, Duke Univ., Durham, 199 pp. Ph,D, Kilham, P. and P.. E. Hecky In press Fluoride: geochemical and ecolo gical significance in East African waters and sediments. Limnol. Oceanogr. Langbein, W, B. 1961 Salinity and hydrology of closed lakes. Geol. Surv. Prof. Paper 412, 20 pp. Liebermann, 0. 1967 Synthesis of dolomite, U, S. Nature 213: 241-245. Livingstone, D, A. 1965 Sedimentation and the history of water level change in Lake Tanganyika, Limnol. Oceanogr. 10: 607-610, studies of Livingstone, D. A. and R. L, Kendall 1969 Stratigraphic East African lakes. Mitt. Int, Ver. Theor. Angew. Limnol, 17: 147-153, MacKereth, F, J, H. 1966 Some chemical observations on post-glacial lake sediments. Phil. Trans. Roy, Soc. L, H 250: 165-214. Manton, I. and G. F. Leedale 1961 Observations on the fine structure of Paraphysomonas Vestita with special reference to the Golgi apparatus and the origin of scales, Phycologia 1: 37-57, Moore, J. E. S. 1903 London. The Tanganyika Problem Hurst and Blackett, Mopper, K. and E. T. Degens 1972 Aspects of the biogeochemistry of Techn, carbohydrates and proteins in aquatic environments. Rep. Woods Hole Oceanogr. Inst. 72-68, 118 pp. -92- Olson, E. A. and W, S. Broecker 1959 Lamont natural ments V. Amer. J, Sci. 257: 1-28. radiocarbon measure Osmaston, H, A. 1967 The sequence of glaciations in the Ruwenzori and their correlation with glaciations of other mountains in East Africa and Ethiopia, In Palaeoecology of Africa, Vol. II, pp. 26-28 E. M. van Zinderen Bakker, ed., A. A. Balkema, Capetown. Richardson, J. L, and A, E, Richardson 1972 History of an African rift lake and its climatic implications. Ecol. Monogr. 42: 499-534. Rigler, F. H. 1964 The phosphorus fractions and the turnover time of inorganic phosphorus in different types of lakes, Limnol. Oceanogr. 9: 511-518. Sayles, F. L, and W. S. Fyfe 1973 The crystallization of magnesite aqueous solution, Geochim, Cosmochim. Acta 37: 87-99. Schmitz, D. M. and J. Kufferath 1955 Problèmes poss par la prsence de gaz dissous dans les eaux profondes du Lac Kiu, Bull, Sances Acad. Roy. Sci. Coloniales, N,S. 1: 326-356, Schumm, S. A. 1965 Quaternary paleohydrology, pp. 783-794. H. Wright and D. Frey, ternary of the United States from In The Quaeds,, Princeton. Spencer, D. W. 1966 Factors nan graptolite band. affecting element distributions Chemical Geology 1: 221-249. in a Silu- Spencer, D. W., E, T. Degens and G. Kulbicki 1968 Factors affecting element distributions in sediments, In Origin and distribution of the elements, pp. 991-998 L. H. Ahrens, ed., Pergamon, New York. Tailing, J. F. 1963 The origin of stratification lake. Limnol. Oceanogr. 8: 68-78. Tailing, J. F. and I. B. Talling 1965 The chemical composition of African lake waters. Int, Rev. Ges. Hydrobiol. 50: 421-463, Theeuws, P.. Turner, 1920 Le Lac Tanganyika in an African rift Mouvem, Gogr., XXXIII. J. S. brine 1969 A physical interpretation of the observations of hot layers in the Red Sea. In Hot Brines and Recent Heavy Metal Deposits in the Red Sea, pp. 164-173 E. T. Degens and D. A. Ross, eds., Springer Verlag, New York. Verbeke, J, 1957 Recherches cologiques sur la faune des grands lacs de l’est du Congo Belge. Exploration Hydrobiologique des Lacs Kivu, Edouard et Albert, Vol. 3, Fasc. 1, 177 pp. + 16 p1. -93- Von Henzen, R. P. and V. Vacquier 1967 Terrestrial heat flow in Lake Malawi, Africa,, 3. Geophys. Res, 72: 4221-4226. Zinderen Hakker Sr., E, M, van and J, A, Coetzee 1972 A ne-appraisal of late-Quaternary climatic evidence, from tropical Africa. In Palaeoecology of Africa, pp. 151-181 E, M, van Zinderen Hakker, ed., A, A, Balkema, Capetown. LIST OF FIGURES Fig. 1 Location map of Lakes Malawi, Albert, showing core sites stations 2 discussed in present work, occupied in 1972 are marked with prime distinguish Fig. Kivu, Edward and Tanganyika, e.g., Kivu 4’ to them from the 1971 sites, Gross stratigraphy and sedimentological description of sample material, Fig. 3 Chemical stratigraphy Basin, Only those elements in concentration of Kivu stations Kulbicki, on all elements has in the form of a Technical Report Degens .and 1973. A complete use in the reconstruction file The upper 4 m of the profile 10, and the lower.8 in from station 4’, about Fig. 4 4’. Nearby station 700 years of this Distribution 9 shifted direction bridges gap. deposited between 13,700 and 11,000 years H.P. manganese values go on account contents 10 and the top of shown in graph of manganese in Kivu sediments the time interval deposited not are from station There is a hiatus of about 1,000 years between the base of station station Deep Northern are shown which show wide ranges and are of particular of the paleoenvironment. been published 10 and 4’ of manganosiderite, in shallow water environments. are explained by oscillations the area of inanganosidenite of the present core site, during High which is Fluctuations in Mn of the thermocline deposition which away or in the High water stands are Fig. 4 cont. indicated by the emergence of sulfides assemblages. Mineral facies oscillations was ca, 300 approximately at -100 thermocline the high water mark stood The fluctuations in. diatom The water depth at low stand lower than today; before 12,300 years B,?. tions" and reconstructed are indicated. in and specific are referred Degens and Hecky, 1973; in water level to as "Kivu Oscilla they exhibit one major high between 12.9 and 13,100 years H.P. Fig. 5 Dominant diatoms of Lake Kivu sediments deposited 5,000 years H.P. prior to 2 micron scale, Stephccnodiscus astrea Nitzschia fonticola a-c d,g,h Nitzschia spiculum e ZVitzschia acicularis Fig. 6 f Dominant diatoms and a crysophyte in .brown layers 2 micron scale. lVitzschia accomodata a Nitzschia sp. b Nitzschia palea c Nitzschia bacata d,g Nitzschia subcommunis e Paraphysomonas vestita Fig. 7 Dominant diatoms years H,?. f,g of Lake Kivu sediments 2 micron scale Chaetoceros sp. a,b,g IVitzschia spiculum f deposited since 5,000 Nitzschia bacata c Fig. 7 cont. Nitzschia mediocris Fig, 8 Distribution carbon, of amino acids AA/HA ratios d,e A-A, hexosamines and percentages The AA/HA ratios, contents to organic are expressed relative of Kivu station Chemical stratigraphy Fig. 10 Factor scores of Kivu stations Basin and b 13 and 15 Fig. 11 Chemical stratigraphy Fig, 12 Reconstruction Chemical stratigraphy Fig. 14 CaCO3 stratigraphy Fig. 15 Organic 15 Interstitial 19 Lake Kivu: South . Mg/g C. Idjwi Basin. Deep Northern Idjwi and Bukavu Basin, of Tanganyika 15 Bukavu Basin. 12 Northern Basin, in Tanganyika sediments from stations sill, water analyses linear station of Kivu and Tanganyika sediments. Central Greene and Jones, Fig, 17 A-A and HA carbon 10 ,and 4’ of Kivu Station carbon content North, South a 13 of of lake level in Kivu for the last 15,000 years, Fig, 13 16 of broken frustules Nitzschia sp, in Kivu core 10. Fig, 9 Fig. HA, organic and 2 South, Lake Tanganyika, station 2; after 1970. volume/area function indicating trough like morphology. Fig. 18 Lake Tanganyika: like morphology. linear volume/area function indicating trough- Fig, 19 Lake Kivu: Fig. 20 Runoff coefficient: relationship evaporation A volume/area/depth for Kivu relationships. between precipitation and Tanganyika values for modern precipitation B. and evaporation. Fig. 21 Lake Tanganyika: Fig, 22 Chemical stratigraphy of Edward station 5. Fig. 23 Chemical stratigraphy of Albert station 3, Fig. 24 Chemical stratigraphy of Albert station 5. Fig. 25 Chemical stratigraphy of Malawi station 15 expedition, 1972. Indicated volume/area/depth relationships. Heidelberg and are r’ C 00 0 ,J 0 J 0’ 0 C 0 a,0 0 C ________ ftJi 1}HLftH1 I C C E -o C Cl 0 C 0 U C C N C- C, I IHHIflfl II’III uui 1 u ii i U;: U - C > ‘H I N °I J]Jwo H rfliIHO .5 - *C C U C C 2 - 0 - o N 0 0 If 0 O C C > o OD 0.- C 0 ° - ‘5> .E - > 5 00 0 [III JoF oIl .g’1 I.C N C": 0 0 I ‘I ‘ I 6 z H 0 C C 0 C 0 1 0 0 0 E I ‘ C’J I N , I io I ‘0 Cl C’ C 0 C 0 ioHo i C, 0 -o C C >, 0 0 >, - I Age C’ -I C’ 0 0 C 0 c- 0 0 Co 0 C C I CD o Depth m J 0 CD >1 1 Mn [ppm] Therrnoc//ne [-Icke] level f [high] Depth [low f 14 0 1 L 0/ JO 400 [mb r 0/ [mq/g C] 1 ‘° 10 20 30 [xlO3yr] 1 ‘3 2 3 0 Orq. C AA HA x io--- AA/HA N//zsc/i/c sp, Ratio broken frust. 200 400 100 300 1 2 3 10 20 30 50010001500 25 50 75 10 20 30 A1203 Mn Ni CaO ppm ppm % lyrs. B.P Lx io 3 5 8 11 12 Pb ppm hO2 % 0I 10 Factor Scores -2 +2 -2 0 +2 -2 Age 0 +2 -2 0 +2 years I. B.P. x103 -3 -5. -7 -9 - 10 volcanic ash layer - 11 - 11.5 - 12 - 12.5 - 13 - 13.5 - 13.7 St. 4 3 Factor 4 5 Factor Scores -2 0+2 -2 0 Age +2 -2 St. 13 -2 -3 -4 -6 St.15 -8 -9 - 1 2 Fcc/or 10 q,o’c CC- Q 0 0 C cn E 0 0 0 C E. añ [m] 5 10 15 +100 1972 level -100 -200 -300 +20 +10 1972 level -10 -20 water level 14C Age [years B.P L xiO3 ‘17 r yrs.8.P [x iO TK2 20 23 300 500 800 20 50 80 Mn Pb CaO ppm ppm 0/ /0 O CaCO3 B 4 IYearslO Lx 10 3J b 2 ‘S b 4 South North K/vu Tan qanyika [o,t] Organ/c Carbon [Years [ B.P.1jO x103 2 3 q3 4 7 8 [%} r.. ci0 a a E 0 0 D z 0 IC 0 0 c’J 0 c’J 0 0 D C- 0 0 0 0 0 CJ E 0 q,daü 0 0 c’J ___ [km 2] 2000- LA v=3.0 4 1500 - 1000 - Kivu 500 0 I 0 100 200 300 Volume 400 500 [km 3] Ikm2 Lx IO 3. zA -1.5 2Q L Tangany/ka 1- 0 I I 0 Volume I 2 Ikm1 L x1o4j [km2] 2000 q* 1000 0 100 300 200 Depth 400 [cm] 180 4 .3 [cm] .1 .2 180 .4 - .3 .2 - I:. 160 160 140 140- 120 120 L,j - + 100 Modern Precipitation and Evaporation q- zj, 100 80 80 A 60 I I I I 20 40 60 80 I 100 60 I I I 120 140 160 Mean Annual Preci/tat/on 40 - 0 I I I I I 20 40 60 80 100 Mean Annua/ Precioi/a [km2 [xio 0 200 400 600 800 Depth 1000 1200 14 H C CO ° 0 0 0 C - 0 0 c’J 9ñt’ r’--’--l E L C - J 0 i 0 - 0 Q Q 0 r4 0 0 0 0 J C 0. G 0 C. 0 c’J C r0 c..J cJ C C’.j C LI Q 0 C iC C I c’J tfl r t9L5t/ r 0 o_ 40 50 60 18 20 22 1500 2500 234 200 300 400 246 [yrs.B.P1 0 [x103 ] q Pb ppm Al2 03 Mn ppm MgO Sr ppm CaCO3 0/ /0 O 22 .2 .5 .8 3 4.5 6 [cm] 2 Pb ppm T102 % 41203 0I to Mn ppm Fe203 0/ /0 Mo ppm CaCO 01 Organic C 0/ /0 Table 1 Chemicà Compo1tionQf Lake and River Waters from Central Africa Na K Ca Mg SO4 Cl ECO2 SI P 35 in mole/Kg mg/i Tanganyika1 St. 3; surface 66.3 34.2 8.2 41.5 21 3.4 5.64 0.034. Tanganyika1 St. 3; 1460 m 663 328 52 410 23 25 638 8.8 166 Kivu1 St.4; surface 121 6 97 4 4 8 87 55 23 8 12 5 6.5 26 Kivu1 St. 4. 100 in 192 0 145 0 64 0 147 mt 25 0 29 3 11.9 601 Kivu1 St. 4; 200 m 244 6 178 8 83 1 132 mt 166 4 42 0 12.0 1046 1 Klvu1 St. 4; 350 in 465 2 315 2 110 9 344 nt 21 0 133 0 29.6 1702 7 Klvu1 St. 4; 440 487 4 338 0 112 6 417 mt 220 0 121 0 34.3 1754 9 U70 1002 46 88 Ruzizi River at Tanganyika2 948 630 84 670 238 Plalagarisi River at Tanganyika2 164 24 129 91 155 in Ruzizi River near Bukavu * nd**nd 131 0.045 178 1O46 9.0 n.d. 21 155 22.4 n.d 65 18 Lake Edward3 HO 90 12 4 47 8 36 43 9 85 Lake Albert3 91 65 9 8 32 1 33 36 5 7 33 Lake Malawi3 2 19.8 4.7 55 2.36k 1from mt. Degens et al., 197 .jnterference 6.4 2from Beauchamp, 1939 ** n.d. = not determined 4.3 0.4-0,9 Li 35.2 12O-15O n.d from Tailing and Tailing, 1965 determined on supernatant after setting Table 2 Tabulation of Limnological Data ALBERT1 EDWARD1 KIVU TANGAN 6,800 25 58 140 2,325 40 117 90 2,055 240 485 583 34, 28.5-29 27.4-28.2 26.8-27.2 25.2-26 24.0-24.5 23.0-23.5 26 24 WET SEASON DRY SEASON DEPTH OF THERMOCLINE m 26.6-27.2 26.6 25.0-25.2 24.7-24.8 22,56 23 23 WET SEASON DRY SEASON RANGE OXYGEN:MAXIMUM DEPTH LIMIT MIXING SEASONS TRANSPARENCY m SECCHI DISK PRODUCTIVITY NET rng 02 m2hr’ DIATOMS Astatic Astatic Astatic 58 15-20 40-50 25-30 80-117 20_306 Dec.-Aug. 2-6 Mar.-Apr.; July-Aug. Feb.-Mar.; June-July 1.4-3 1UOO Ntz4c.h..ô’i. 3.5-6.0 2308 AREA 2 MEAN DEPTH m MAXIMUM DEPTH m VOLUME Kni3 TEMPERATURE EPILIMNION °C WET SEASON DRY SEASON TEMPERATURE i-iYPOLIMNION °c 1OOO7 SphznodLw ct6-t-’LaQuJ. 2Capart,1952 3Coulter, 1963 7Calculated from Tailing, 1965 22.8 50 10 50 10 Ju 10 Un 40-50 20 70 1VLtz4c.hi.a 4po. . OJ1,tLcO&L NLtz4 chia o p. ‘Verbeke, 1957 1, 18, StephctnodL cs dama 4Beauchamp, 1953 8Calculated from Degens et al., 1973 5Hutchinson, 1957 NL Table 3 Varimax Factor Matrix of Kivu Sediments ELEMENT FACT. 1 FACT. 4 FACT. Vanadium 0.701 0.505 0.293 -0.018 -0.007 0 Molybdenum 0.029 0.641 0.391 -0.451 0.295 0 Lead 0.157 0.212 0.142 -0.086 0.882 0 Zinc 0.706 0.261 0.467 0.003 0.282 0 Copper 0.751 0.180 0.415 0.029 0.228 O Chromium 0.827 -0.225 -0.012 0.097 0.161 0 Nickel 0.217 -0.299 0.724 -0.003 0.352 0 Cobalt 0.387 -0.303 0.679 -0.015 0.022 0 -0.222 -0.922 0.154 0.045 0.049 0 Baryum 0.114 -0.821 0.175 0.022 -0.119 0 Gallium 0.829 0.179 0.223 -0.116 -0.032 0 Manganese 0.260 -0.511 -0.003 0.437 -0.240 0 Fe203 0.197 0.379 0.809 0.041 -0.041 0 Si02 0.218 0.775 0.313 -0.106 0.143 0 A1203 0.945 0.164 0.058 0.005 0.011 0 CaO -0.295 -0.900 -0.011 0.164 -0.026 0 MgO 0.044 -0.148 0.044 0.951 -0.017 0 TiO 0.878 0.007 0.186 0.177 -0.034 0 28.44 24.80 14.05 7.80 6.93 53.24 67.29 75.09 82.03 Strontium FACT. 2 FACI. 3 No. of Samples: 381 % Variance % Accumulated Variance 28.44 5 COM Table 4 Radiocarbon Dates of East African Rift Sediments f Locality Core Sample depth cm Lake Kivu 9 10 330-350 160-180 0- 84 195-230 350-400 10,670 ± 280 6,200 ± 215 11,200 ± 165 665-700 7428OO 170-210 168-205 340-382 115-170 190-250 425-480 13,150 13,560 11,950 11,070 12,130 9,460 9,725 10,170 41 13’ 15’ Lake Tanganyika 3 120-140 235-255 85-105 175-195 10- 30 180-200 15 19 yr B.P. 12,300 ± 330 12,650 ± *l9P ± ± ± ± ± ± ± ± 330 165 250 160 170 240 165 140 3,670 ± 120 6,350 ± 160 1,925 ± 100 3,750 ± 105 1,300 ± 95 >28,200 Lake Edward 5 460-505 5,665 ± 100 Lake Albert 3 5 140-180 450-495 2,660 ± 90 6,910 ± 115 Lake Malawi NY_19* 0- 8 46- 53 2,400 ± 200 2,540 ±140 2,670 ± 200 86- 94 Lake Green LV1 Nyamuragira volcano N745 15O m above Kivu water *level *Von Herzen and Vacquier, 1967 Charcoal in lava flow 13,300 ± 1150 515 ± 120 Table 5 Morphometric and Hydrological Parameters for Lakes Kivu and Tanganyika Kivu Area: Depth: Km2 Ab = catchnient A1 = lake less islands 2,060 32,600 At = tributary area 5,080 198,400 7 = mean 240 570 485 1 ,470 583 18,880 m Zmax Volume: V Basin slope Discharge: Km3 = Runoff: Volume Km3/yr over A1 cm/yr 3.2 cm/yr 0.66 2.7 160 53 130 90 volume on A1 Km3/yr 2.7 29 volume on At Km3/yr 6.6 180 coefficient r 0.4 volume 2.7 Km3/yr over A1 Air Temperature; Evaporation: 0.33-0.4 V/tA1 Precipitation: rate P 7,140 Tanganyikaexclusive of Kivu 231,000 cm/yr 134 °C gross rate Eg volume loss 19.5 cm/yr Km3/yr net rate EnEg-P net volume 106 Km3/yr 2.1 cm/yr -24 -0.5 0.08 14 44 24 135 44 45 15 Table 6 Calculations on Water and Salt Budgets of Lakes Kivu and Tanganyika Kivu Tanganyika Water Volume Precipitation + Runoff Residence time for water Runoff Refill time runoff alone km3 km3/yr yr km3/yr yr 517 18,800 5.3 110 44.0 430 2.7 190 18 1,000 Salts Total Na1 Na + loss at effluent kg kg/yr 13 x 1010 3.7 x 10 8 12 x io11 1.7 x 10 8* Storage time** yr 350*** Total kg 9.5 x 1010 6.3 x iO kg/yr 3.2 x i08 9.2 x K loss at effluent Storage time yr 300 7,000 6,800 *Based on calculated Lukuga discharge of 2.7 km3/yr and composition of river identical to that of lake. **Storage time assuming losses of salt to sediment and evaporation are negligible. ***Storage time for whole lake; multiple water layers of Kivu will have their own storage times. Woods Hale Oceanographic Institution WHOI-73-28 ------- LATE PLEISTOCENE-HOLOCENE CHEMICAL STRATIGRAPHY NW PALEOLIMNOLOGY OF THE RIFT VALLEY LAKES OF CENTRAL AFRICA. By Robert E. Hecky and Egon 1. Degens. 114 pages, 20 figures and 6 tab’es. May 1973. National Science Grants GA-30641 and GA-35334. Woods Hole Oceanographic Institution WHOI-73-28 The interaction of climate and geology in Central Africa durthy Late Pleistocene and Holocene is examined. Pileoclimatic comparison between tropical and temperate zones reveals that p1uva1 times coincide with the prominent interstadials n Europe, and reversely, cool and dry periods in equatorial Africa with ice ages n the Northern Hemisphere. 1. Paleocliniatology 2. Cheniçal Stratigraphy 3. Rift Vafley Lakes 4. Centra’ Africa I. Hecky, Robert E. II. LATE PLEISTOCENE-HOLOCENE CHEMICAL STP.ATIGRAPHY AND PALE0LIrIN0L0GY OF THE RIFT VALLEY LAKES OF CENTRAL AFRICA. By Robert E. Hecky and Egon T. Degens. 114 pages, 20 figures and 6 tables. May 1973. National Science Grants GA-30641 and GA-35334. The interaction of climate and geology in Central Africa during Late Pleistocene and Holocene is examined. Paleoclimatic comparison between tropical and temperate zones reveals that pluvial times coincide with the prominent interstadials in Europe, and reversely,- cool and dry periods in equatorial Africa with Ice ages in the Northern Hemisphere. Degens, Egon 1. III. GA-30641 IV. GA-35334 This card is UNCLASSIFIED I I -- Woods Hole Oceanographic Institution WHOI-73-28 I . 1. Paleocliniatology I 2. Chemical Stratigraphy LATE PLEISTOCNE-HOLOCENE CHEMICAL STRATIGRAPI-IY AND PALEOLIMNOLOGY OF THE RIFT VALLEY LAKES OF CENTRAL AFRICA. By Robert E. Hecky and Egon 1. Degens. 114 pages, 20 figures and 6 tables. May 1973. National Science Grants GA-30641 and GA-35334. I zones reveals that pluvial times coincide with the prominent interstadials in Europe, and reverse’y, cool Ij I The interaction of climate and geology in Central Africa during Late Pleistocene and Ilolocene is examined. Paleoclimatic comparison between tropical and temperate and dry periods in equatorial Africa with ice ages in Woods Hole Oceanographic Institution WHOI-73-28 I I 3. Rift Valley Lakes 4. Central Africa I I I Hecky, Robert E. I Degens, Egon 1. GA-3o64l the Northern Hemisphere. IV. GA-35334 I This card is UNCLASSIFIED - - LATE PLEISTOCENE-HOLOCENE CHEMICAL STRATIGRAPHY AND PALEOLIMOLOGY OF THE RIFT VALLEY LAKES OF CENTRAL AFRICA. By Robert E. Hecky and Egon 1. Degens. 114 pages, 20 figures and 6 tables. May 1973. National Science Grants GA-30641 and GA-35334. The interaction of cflmate and geology in Central Africa during Late Pleistocene and Holocene is examined. Paleocliniatic comparison between tropical and temperate zones reveals that pluvial times coincide with the prominent interstadials in Europe, and reversely,- cool and dry periods in equatorial Africa with ice ages in the Northern Hemisphere. BLOGRApHIC DATA SHEET 2 L Report No. 3. Recipient’s Accession No. - 4. Title and Subtitle 7. 5. Report Date May 1973 LATE PLEISTOCENE-HOLOCENE CHEMICAL STRATIGRAPHY AND PALEOLIMNOLOGY OF THE RIFT VALLEY LAKES OF CENTRAL AFRICA 6 Authors 8. Performing Organization Rept. No. Robert E. Hecky and Egon T. Degens . WHOI-73-28 9. Performing Organization Name and Address 10. Project/Task/Work Unit No. Woods Hole Oceanographic Institution Woods Hole, Massachusetts 02543 fl. Contract/Grant No. NSF GA-30641 12. Sponsoring Organization Name and Address - National Science Foundation GA-30641 and GA-35334 13. Type of Report & Period Covered echnical Sept 69 Sept 72 U. . 15. Supplementary Notes 6. GA-35334 - Abstracts The interaction of climate and geology in Central Africa during Late Pleistocene Paleoclimatic comparison between tropical and temperate zones reveals that pluvial times coincide with the prominent interstadials in Europe, and reversely, cool and dry periods in equatorial Africa with ice ages in the Northern Hemisphere. and Holocene is examined. 7. Key Words and Document Analysis. 1. F’a1eoc1imatology 2. 3. Chemical Stratigraphy Rift Valley Lakes Central Africa 4. l7a. Descriptors 17b. Identifiers/Open-Ended Terms 17c. COSATI Field/Group 18. Availability Statement FORM NTIS-35 REV. 3-72 THES FORM MAY BE REPRODUCED