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Transcript
ON CIRCULATION, PHOSPHATE-PHOSPHORUS CONTENT, AND ZOOPLANKTON VOLUMES IN THE UPPER PART OF THE PACIFIC OCEAN’ Joseph L. Reid, Jr. Scripps Institution of Oceanography ABSTRACT The circulation of the Pacific Ocean may bc considcrcd to consist of two high-latitude cyclonic gyres, two subtropical anticyclonic gyres, and a series of subequatorial zonal flows in alternate directions. The phosphate-phosphorus at the surface is related to the surface divcrgcnce and is high in the cyclones, low in the anticycloncs, and high in regions of coastal and equatorial upwelling. The POa-P at 100 m is related to the depth of the pycnocline and is also high in the cyclones and low in the anticyclones, and high at the equator and at the poleward edges of the equatorial countercurrents. The zooplankton volume is distributed very much as is the P&P, particularly that at 100 m. It is also low in the anticyclones <and high in the cyclones, at the equator and at the poleward edges of the equatorial countercurrents. At the center of the subarctic cyclone, however, zooplankton is only moderate, but Pod-P concentration is high both at the surface and at 100 m. It is suggested that the surface divergence is too rapid for zooplankton to accumulate in the center of the cyclone, even though reproduction and growth may be prolific. In the California Current zooplankton volume appears to vary inversely with temperature, is found near the tip of Baja an d an area of minimum volume and maximum temperature California. It is speculated that this indicates a change from subarctic to subequatorial species. This, and the close relation of the plankton volume to the system of gyres, suggests that the gyres may rcprcscnt the principal plankton communities. INTRODUCTION An interesting correspondence may be noted between the maps of circulation, inorganic phosphate-phosphorus content in the upper levels, and zooplankton volume that appear in the NORPAC ATLAS (NORPAC Committee 1960). In extending the map of circulation to cover the rest of the Pacific ( Reid 1961)) it was found that there were enough available data to extend the other maps also. CoXrrespondcnce between the three quantities is then found over the entire Pacific. There are theories of the nature of ocean circulation that can account for the distribution of the P04-P. If correct, they must also be consonant with the observed distribution of zoopkankton volumes, and it is interesting to speculate fro,m the point of view of physical oceanography alone about the nature of the plankton communities, THE CIRCULATION The currents With certain limitations, the geopotential anomaly at the sea surface with respect to the l,OOO-dccibar surface (Fig. 1 reproduced from Reid 1961) represents the surface currents and may be used to illustrate the features of the circulation that are discussed here. Since only the geostrophic flow is represented in the figure, the current field is incomplete, and one must imagine enough cross-contour flow to avoid over-running the continents and to balance the apparent convergence at the equator. The two major features are the two huge subtropical anticyclones which include the western bo,undary currents, parts of the l This work was supported by the Marine Lift west wind drift, the eastern boundary curResearch Program, the Scripps Institution of Occarents, and the two westward-flowing equanography’s component of the California Coopcrative Oceanic Fisheries Investigations, a project torial currents a few degrees north and sponsored by the Marine Research Committee of south oI the equator. At higher latitudes, the State of California. I am particularly grateful there are the Antarctic Circumpolar Curto Mr Garth Murphy of the California Academy rent and the system containing the Alaska of Scicnccs for many helpful discussions and comments and for reading the manuscript, Current and the Oyashio Current. Both of 287 288 JOSEPH L. REID, JR. FIG. 1. Currents at the surface of the Pacific Ocean (gcopotential respect to the l,OOO-decibar surface, in dynamic meters ) . these systems are cyclonic (with the South Pole at the center of the southern one) and will be referred to, respectively, as the subantarctic and the subarctic cyclones. Equatorward of the subtropical anticyclones, the flow is zonal except at the eastcm and western boundaries. The flow is westward at the equator with countercurrents north and south of the equator. The southern coun tcrcurrent is better developed in the west and the northern better developcd in the east, somewhat in accordance anomaly at the sea surface with the mean position of the doldrums either edge of the ocean. with at Divergence and the depth of the mixed layer The circulation is wind-driven and partly balanced geos trophically. Stommel ( 1957 ) has surveyed the theories of such a system and prepared schematic illustrations of the movement. It is seen that within the winddriven anticyclonic gyres, surface waters converge and sinking occurs. Within the CIRCULATION, TABLE ---- 1. PO4-P, AND The inorganic ZOOPLANKTON phosphate-phosphorus -- --~~ -~~~ Vessel or cruise Period Aug. 1957-Jan. 1958 July 1950, Sept. 1950 Oct. 1928-Nov. 1929 Aug. 1934 JunoAug. 1956 Nov. 1928-Aug. 1929 May-Oct. 1932, Jan.-Feb. 1936, Jan.-Mar. 1938, Oct. 1950-June 1951 Downwind Oct. 1957-Feb. 1958 EASTROPIC Horizon Oct.-Dee. 1955 Hugh M. Smith Sept.-Dec. 1955 II Spencer F. Baird Oct.-Dec. 1955 Aug.-Sept. 1956 EQUibAC Hugh M. Smith II Or&m III S&.-Oct. 1956 II Satsuma July-Aug. 1956 Albatross C.C.O.F.I. Carnegie Chelan ( USCGS ) Chinook Dana Discovery II Shunkotsu May-June 1956 II II Stranger Umitaka Aug. 1956 Oct.-Nov. 1956 Gannet ( USS ) Hugh M. Smith Cruise 5 ,I 38 Muklui’ NORPAC Brown Bear ,, C.C.O.F.I. II Ryofu II Satsuma 11 Shiny0 11 Shumpu II Ste. Therese Aug. 1933 July-Aug. 1950 .-Mar. 1957 ;;y-Aug. 1957 +June-Oct. 1955 ( HMCS ) I, Tenyo Umitaka Yushio II OB ;‘955-1956 OB Cruise 3 April-May 1956 May-June 1958 Orsom III 56-5 Orsom III Astrolabc Oshoro Queenborough & Quickmatch William Scoresby TRANSPAC Umitaka ( Coral Sea ) Oct. Nov. 1956 May 1958 July+ug. 1956 March-April 1958 May-Aug. 1931 April-June 1958 May-Aug. 1952 July-Nov. 1953 Jan. 1959 Vityax 25 July-Oct. 1957 Vityax 26 Vityax 27 Warreen Nov. 1957-Feb. 1958 March-June 1958 May-Sept. 1948 Scot Shellback --_ Total - -- IN THE materials -. No. of stations used Om 1OOm 51 35 121 3 4: 146 289 PACIFIC Refcrcnco 52 Bruncau, Jcrlov, and Koczy (1953) 35 Univ. Calif. ( 1955) 121 Fleming and others ( 1945 ) 3 Barnes and Thompson ( 1938 ) Unpublished Univ. Calif. data 4: Carlsbcrg Foundation ( 1937) 148 Disc. Comm. ( 1941,1944,1947, 1957) 24 Unpublished Univ. Calif. data 68 18 King, Austin, ani Do;’ ( 19;; ) 17 Unpublished Univ. Calif. data 62 Austin (1957) 19 Legand ( 1957 ) 17 Unpublished Japanese Hydrographic Office data report 21 27 Unpublished Japanese Fishcries Agency of Japan data 37 40 Unpublished Univ. Calif. data 16 16 Unpublished Tokyo University of Fisheries data 4 4 Barnes and Thompson ( 1938 ) 14 14 Cromwell and Austin (1954) 42 43 Wilson and Rinkel ( 1957 ) 3 3 Unpublished Univ. Calif. data NORPAC Comm. ( 1960a) s”: 1;: II ,I 4 4 ,I II 40 I, ,I 4 4 II ‘1 I, II 45 44 24 66 22 16 65 19 - 79 10 57 3 18 27 81 11 58 3 12 28 II ,I ,I I, I, I, U.S.i.R. Acai: Sci. (1958) Data made available by World IGY Data Center A 15 18 Rotschi ( 1958 ) 43 43 Rots&i, Angot, and Logand (1959) 35 36 Hokkaido U. Fat. Fish. ( 1957 ) 12 12 C.S.I.R.O. (1960) 14 16 Disc. Comm. ( 1949) 59 56 Holmes & Blackburn ( 1960 ) 102 102 Unpublished Univ. Calif. data 56 56 13 13 Uniublishcd &S.I.<.O. aid Tokyo Univ. of Fish. data 82 75 Data made available by World IGY Data Center A 97 92 11 II 51 53 (1951, ;01. 3) 8 8 c.s.&o. -1,743 1,826 -____---- -- -.- 290 JOSEPH L. cyclonic gyres, surface waters diverge and upwelling of deeper waters to the surface occurs. The surface layer is thickest at the centers of the anticyclones, becoming thinner toward the centers of the cyclones and the coastal boundaries of the anticyclones. Although the currents ne,ar the equator are relatively narrow zonal features and in some cases flow upwind, they still show this relation of the depth of the mixed layer to the circulation, In westward flow the mixed layer is thickest on the poleward sides of the currents, and vice versa. This results in a series of zonal ridges and troughs in the depth of the mixed layer (Cromwell 1958). The observed distribution of P04-P in the upper layers of the Pacific is shown to bc consonant with these concepts and that of coastal and equatorial wind-induced upwelling (Reid, Roden, and Wyllie 1958; Cromwell 1953 ) . INORGANIC PHOSPHATE-PHOSPHORUS Nearly everywhere in the ocean, values of P04-P are lowest in the mixed layer with a sharp rise in the pycnocline to a maximum several hundred meters beneath the surface and a slight decrease from there to the bottom. Maps of the P04-P have been prepared from the materials listed in Table 1 and appear as Figures 2 and 3. Phosphate-phosphorus at the sea surface Where horizontal divergence occurs at the surface and regenerated materials are brought into the mixed layer, the surface concentration of P04-P may become high. Where convergence occurs, the deplc ted surface waters accumulate and surface concentrations may become low. Bohnecke, Hentschcl, and Wattenberg ( 1930) noted the enrichment of the surface waters within the cyclonic gyre between Greenland and Iceland, and proposed that it is caused by horizontal dithe gyre and upwGd vergence within movement of the deeper, nutrient-rich water. The distribution of PO*-P at the surface (Fig. 2) is seen to be consonant with this REID, JR. concept of surface divergence. Concentrations rare low in the anticyclones and high in the cyclones, the areas of coastal upwelling and at the equator. Coastal upwelling occurs along the California and Peru Currents as a consequence of the equatorward winds along these coasts, Downwelling occurs in part of the Alaska Current where the wind is poleward along the coast of Canada, and possibly at the southern tip of South America when the winds have a poleward component. Along the equator, as a consequence of the earth’s rotation, the trade winds drive the northern surface waters northward and the southern surface waters southward, and upwelling occurs ( Cromwell 1953). Averaged throughout the year, Hidaka’s (1958) wind stress calculations show that this effect should be stronger in the eastern half of the ocean than in the western half. Certainly the PO,-P concentration does decrease toward the west. Phosphate-phosphorus at 100 m Since the concentrations of POa-P are higher beneath the mixed layer, the variation in depth of the pycnocline over the ocean affects the distribution of POh-P on any surface of constant depth near the pycnocline. Where the pycnocline is shallow, the P04-P at 75 m (for example) is high. Where it lies deeper than 75 m, the POb-P at 75 m is low, This effect is to be seen on any levels from 50 m down at least 200 m. In Figure 3, the effects of the variations of depth of pycnocline are quite apparent. The cyclones and anticyclones seen on the map of currents are clearly defined over most of the area as regions of high and low P04-P, respectively. In these data, the distribution between 15” N and 15’S is more irregular, but zones of high P04-P arc seen at the equator, at about lOoN, and at about 7”s. These three zones correspond respectively to the Equatorial Current, to the boundary between the North Equatorial Current and Countercurrent, and less clearly to the southern boundary of the South Equatorial Countercurrent. CIRCULATION, Pod-P, AND ZOOPLANKTON The two maps of Pod-P are similar, although consumption occurs at the surface and regeneration at 100 m. The major difference occurs in the western subequatorial region. The processes that enrich the surface in the region between the Tropics arc more effective in the eastern part, and the surface concentration decreases to the west. The westward currents near the equator, however, continue at least as far as New Guinea, and in the areas of shallow pycnoCline, which are associated with their equatorward boundaries, the Pod-P at 100 m remains fairly high. POSSIDLE AND EFFECTS CIRCULATION OF PHOSPHATE-PHOSPHORUS UPON LIFE IN THE OCEAN Phosphate-phosphorus When one considers that the concentration of Pod-P in the Pacific is much higher than in the Atlantic and that the Pacific is not reported to be more productive, one wonders why Pod-P is examined at all with Hentschel and respect to zooplankton. Wattenberg (193U) included a map of the central and southern Atlantic showing PObP distribution in the upper 50 m that is quite similar in pattern to the Pacific map, but the values are lower. The average concentration in the Atlantic appears to be about half of that in the Pacific. The reason for selecting Pod-P for analysis is that data are available for the entire Pacific whereas data on other nutrients are very scanty. Variations of Pod-P may or may not be important in themsclvcs. They may bc important as indicators of variations of other nutrients, such as nitrate, that are affected by the same processes, b,ut are not present in excess. Circulation The effect of horizontal and vertical movement of the water, beyond its effect on the nutrients, must be considered. The volume of the plankton in the ocean probably f‘ar exceeds the combined volume of the free-swimming and bottom organisms, The movement of the biomass is mostly a consequence of the motion of the water rather than of any swimming effort, and the IN THE PACIFIC 291 distribution in space of the biomass is severely limited by the currents. Temperature, which may also limit any particular organism, varies over the greater part of the ocean largely with latitude (though there are notable extensions of cold water equatorward in the eastern boundary currents and of warm water poleward in the western boundary currents). The gyres are relatively narrow zonal features, and therefore the temperature variation within each gyre is small compared with the differences between adjacent gyres. Each of the gyres also acts in a way to hold a substantial part of the organisms within it instead of carrying them to areas with different properties. Convergence in the anticyclones helps to balance the outward diffusion, and the subarctic and subantarctic cyclones have substantial continental boundaries on one edge that help to confine some of the individuals. It is plausible to expect that these areas of semi-enclosed circulation and relatively narrow range of properties are distinguished also by the planktonic faunas that inhabit them, Since plankters cannot move against the currents, they require a system of currents that will allow them to remain These within a tolerable environment. gyres, each of which covers only about 20 to 25 dcgrecs of latitude, may be such systems. The cxtrcmc ranges of temperature at a depth of 50 m in the Pacific arc from about -1 to 10°C in the subarctic cyclone, from about 8 to 25°C in the northern subtropical anticyclone, and from about 19 to 29°C in the subequatorial system. These extreme ranges include seasonal variations, It may not be necessary for an organism inhabiting a gyre to be able to reproduce throughout the extreme areal and seasonal range of temperature, but only to survive it (Damas 1905; Svcrdrup, Johnson, and Fleming 1942). If reproduction occurs in one season only, then the effective range of tempcrature is reduced, and if it occurs in only one limb of a gyre the range is reduced even further. Damas (1905) has suggested the impor- 292 FIG. 2 (a). 7 . ana contours. JOSEPII Distribution of Pot-P L. at the surface tance of the cyclonic gyre of the Norwegian Sea in maintaining organisms in a fixed region that in part of the year is favorable for reproduction. He speculates that gyral movement in the ocean may play a principal role in preserving species and in the creation of a special plankton in particular areas. Hclland-Hansen and Nansen ( 1909) have reviewed Damas’ findings in the light of their work on the physical oceanography of the area and have conftimed his relation of certain species to’ the water masses. Somme ( 1933)) although he disagrees with particulars of Damas’ findings, accepts in REID, JR. of the Pacific Ocean (ppd./L), station positions, principle the concept of maintenance of plankton population by systems rotating in fixed positions, and cites also Baffin Bay, the Gulf of Maine, and the area off the Lofoten Islands as areas where rotating systems could be shown to maintain particular populations. Sverdrup, Johnson, and Fleming (1942) concluded that current is one determining factor (p. 863) “. . . in maintuining an enThey cite not only demic population.” oscillating tidal currents and restricted flow in partially landlocked bays but (p. 864) ‘C . . . gyrating currents, sometimes circum- CIHCULATION, FIG. 2 (b). Distribution Pod-P, AND ZOOPLANKTON of PO,-P at the surface scribing relatively large areas in hydrographically closed systems of more or less permanence.” The data at that time limited the examples to small areas. ZOOPLANKTON VOLUME Since P04-P has been considered as a plant nutrient, it should be compared with productivity or with the standing crop of phytoplankton. Unfortunately, there are very few measurements of these quantities. The most readily available data on the biomass consist of measurements of the of the Pacific IN THE Ocean PACIFIC (,ug-at./L) 293. shaded by values. plankton volume collected by nets of relatively large mesh (0.25 to 0.55-mm aperture) from the upper few hundred meters of the ocean. Nets of this type sample mostly the larger zooplankton. A larger volume of smaller forms may escape the nets, so that these samples cannot represent the true biomass but only the volume of karger forms, The materials are specified and details of the nets are given in Table 2. About 1,000 of the samples were taken at stations where measurements of P04-P were made also. 294 FIG. 3 (a). Distribution positions, and contours. JOSEPH L. of POCP at a depth It is seen that the methods, equipment, laboratory techniques, and season of collection have varied. However, 1,365 of the 2,005 samples were collected with the CCOFI-POFI net. Of the others, 286 were collected with the Maruto,ku, modified Marutoku, or NORPAC nets, that differed from each other only in length. These 1,651 samples were all from measured quantities of water and will be referred to as the basic samples. In Table 3 the samples are divided by area, month, and depth of haul. ( The 51 Dnn.n samples and 65 of the REID, JR. of 100 m in the Pacific Ocean ( pg-at./L), station Vrsom III samples are not classified by depth in the table.) North of 20”N, 92.5% of the samples are from the basic group, and those basic samples collected in July, August, and September in hauls from depths of 150 or 140 m to the surface total 629, or 74.3% of all samples north of 20”N. Between 20”N and 20’S, 87.4% of the samples are from the basic group, but they are almost equally divided between hauls from 150 or 140 m to the surface and hauls from 300 m to the surface. Only 39.8% of CIRCULATION, FIG. 1 values. 3 (b). Distribution P04-P, AND ZOOPLANKTON of PO,-P at a depth of 100 all samples in this area were taken in July, August, or September, and the remainder includes samples from all the rest of the year. South of 20’S only 15% of the samples involved measurements of the amount of water filtered. Sampling extended throughout the year. Sampling in the northern of the three areas seems quite adequate for the preparation of a map, Sampling in the equatorial region is less satisfactory, but the seasonal variation may be less important there. South IN THE PACIFIC m in the Pacific Ocean (pg-z&./L) 2% shaded by of 20’S, the sampling is poor but it seems worthwhile to include what data are available. Flowrneters were not used with the 112 Discovery II N70V net hauls, and therefore the volumes south of 50’S and those necar Australia are uncertain. The 51 Dana hauls were not metered and were horizontal, and their values (in the central South Pacific and near New Zealand) are uncertain. For materials without flowmeters the standardized value has been obtained by assuming unimpeded passage of the water through the net. The effect of 296 JOSEPH -. Name of net Mesh at)e$c RElD, JR. Description of the materials used for the map of zooplankton volume ___--- -~~-. ____ -~- _- TABLE 2. -- L. Mouth diameter (cnl) Lyg;h m Open or Flowclosmg meter Shape ~- T’h”,“,;f -__ Period - ~. ~---. N”zbcr obscrvations Dep* ‘rzg; 51 200-O 204 300-O C.,C.O.F.I.0.55 front 100 5.0 Either Yes Conical Oblique P.O.F.I. net 0.25rear (after wetting) Hugh M. Smith, Cruise 5 (King and Dcmond 1953) June-Aug. 1950 Shellback (unpublished Univ. Calif. data) May-Aug. 1952 TRANSPAC (unpublished Univ. Calif. data) Cnpricorn (unpublished Univ. Calif. data) Troll (unpublished July-Nov. 1953 Dec. 1952Feb. 1953 March-April 1955 Univ. Calif. data) NORPAC B.C.F., Honolulu (NORPAC Cornm. 1960a, 1960b ) C.C.O.F.I. (NORPAC Comm. 1960a, 1960b) EASTROPIC (unpublished Univ. Calif. data) King, Austin, and Doty ( 1957) J;kh EQUAPAC Aug.-Sept. 1956 (unpublished Univ. Calif. data) Hugh M. Smith, Cruise 38 (Wilson Downwind C.C.O.F.I. data) (unpublished Gulf of California Tethys (unpublished Total, Marutoku C.C.O.F.I.-P.O.F.I. net 0.33 NORPAC Univ. Calif. data) (unpnblishcd B.C.F. La Jolla Univ. Calif. data) Total, Marutoku NORPAC 0.239 ClarkeBumpus NQRPAC Larvae net NORPAC 76 140-O 1, No Aug. 1957 74 140-O 17 140-O 45 0.80 Open Yes Conical Vertical Satsumn (NORPAC Comm. 1960a, 1960b) 60-O 200-O Aug. 1955 33 150-O Sept.-Oct. 1955 July-Sept. 1955 55 150-O 50 150-O Displacement volumeb Displacement volumeb Displacement volumeb II Yes Yes Yes Yes Yes (one ship only 1 Yes Yes No No Wet volume Wet weight Wet volume Yes Yes Yes 138 net 0.33 Yes No No 55 c.300-0 -- Yes 1,335 Umitakn Mamc (NORPAC Comm. 1960a, 1960b ) Tengo Maru (NORPAC Comm. 1960a, 1960b) Modified Marutoku net Yes II Oct. 1957Feb. 1958 1960 Wet volume’ Displacement volume” ,I II 140-O 26 22 June-July __ 81 Jan.-March 1957 net cZ&t Pcet-mP ..-. 191 140-O II 147 300-O I! 91 c.52-0 & Displacec.134-66 ment volumec 61 200-O Displacement volumec 77 140-O Displacement volumeb Aug. 1956 and Rinkcl 1957) -- 129 c.15&0 33 140-O July-Sept. 1955 Sept.-Dec. 1955 Sept.-Dec. 1955 Austin (1957) Units reported 45 1.65 Open Oshoro Maru (NORPAC 12.5 1.07 Opel1 Brown Bear (NORPAC Yes - Vertical Comm. 1960a, 1960b) No Conical Conical Vertical data) o Yes Conical data) e ------- June--July 1955 37 150-O Wet volume No Aug.-scpt. 1955 56 200-O Displacemcnt volume Yes May-June 1956 32 150-O Settling volume Yes July-Aug. 1956 43 150-O Displacement volume - Yes Oblique Comm. 1960a, 1960b) No 130 4.5 Open 0.33 EQUAPAC Shunkotsu Mn~u (unpublished 1.8 Open 45 net 0.33 EQUAPAC Sntsuma (unpublished Conical Vertical - - - _ - - _- -- .- - -_ CIRCULATION, Pod-P, AND TABLE KW Z z-=-- _ --. L L Mouth Mesh Nanlc of nct ayE%;, --.---- -_ - - ----- _ z -- - _ _ --- ZOOPLANKTON 2. IN (cm) - -- .- __ _ _-____-- Umitnkn Mnru (unpublished - - -. - - -. Cylindcr.55 Closing Cone 2.30 F. R. V. Warrsen Nov. 1956 data) c, * July-Aug. June-Aug. 1957 No 1956 Dcpth range (InI 17 150-O 39 42 150-O 150-O ConUnits current reported PO4-P data Displacement volume Weidisplacement volume Yes Yes No Cone Vertical with cylinder front 1956) (C.S.I.R.O. 32-52 (C.S.I.R.O. 1951, vol. 1) stas. 1-12, 1951, vol. 3) stas.14-45 Derwent ZZunter (C.S.I.R.O. 1959) B.A.N.Z.A.R.E. (Sheard 1947) stas. 206-213 April- July 1932 Dec. 1933 Feb.-Apr. 1936 Feb. Mar. 1938 Dee. 1938Jan. 1939 June 1951 May-Oct. 1938 May-Sept. 1948 Nov. 1957 ObliqueMar. 1930IMar. 1931 71 100-O Displacement volume Yes 15 100-O No 8 100-O Settling volumeh Displacement volume II 1, 7 100-O 11 c.125-0 Yes No No 112 net Orsom ZZZnet 0.36 Closing Yes 50 EQUAPAC Orsom ZZZ (Legand 1957 Annex I, column B ) Orsom ZZZ (Legand 1958, series I-XVII) Orsom ZZZ (Rotschi et al. 1959, Table 1) Orsom III N”%bcr obscrvations 141 70 F. R. V. Wnrreen Total, ---______ =-~~-~~~ net DZscovery ZZ (Foxton Total, N70V = Period Oshoro Maru (Hokkaido U. Fat. Fish. 1957) Hokusei Mnru (Hokkaido U. Fat. Fish. 1958) Total, NORPAC N70Vs 0.239 297 PACIFIC Continued .-_-- L~;g)th 0 en or FlowcFosmg meter Shape TE:lof L diamctcr THE Ho&. Sept.-Oct. at 10, 1956 50,150 200, 250 m Oblique Mar. 1957Mar. 1958 May-June 1958 net 15 200-O Wet volume Yes 10 300-O 200-O 150-O 100-O 300-O Wet volumeO No Wet volumec Yes Wet weight No 55 80 Kitahnrn 0.11 22.5 0.8 Open No Conical EQUAPAC Kngoshima ( unpublished data) * Vertical Dana net 1.0 Horiz. 150 or 200 Open No Conical Aug. 1956 23 200-O Oct. 1928Feb. 1929 51 50,100 Volume and per 300 m hour’s wire haul length tow at constant wire length Dana (Jcspersen 1935) - GRAND TOTAL --____- ---- -----~---____-~--- 2,005 a Fish eggs and larvae and all organisms greater than 5 cm wcrc removed before measurement. 1,Organisms greater than 5 cm length were removed bcforc measurement. c Organisms greater than 2 cm were removed before measurement. d Fish eggs and larvae and all organisms grcatcr than 2 cm were romovcd before mcasurcment. c Data kindly made available through the offices of Mr. Yutaka Nagaya of the Japanese Hydrographic 1 No flowmcter was used. s Details of net in Kemp, et al. (1929). h Settling volumes were multiplied by 0.3 (Sheard 1947, Tables I and II). ---__ Office. Yes 298 JOSEPH TABLE Depth in meters 2 3. The zooplankton -.----.~_______ Net type u3 *-“a $j E : A.2 ogj za 150-or 140-O 200-O 300-O 150-o 200-O 200-O C.C.O.F.I.-P.O.F.I. Marutoku + NORPAC C.C.O.F.I.-P.O.F.I. C.C.O.F.I.-P.O.F.I. Larvae Clarke-Bumpus Kitahara 0g z .dM : ; $ m fi 3 m & A.2 H ZZe o3 150-or 140-O 200-O 300-O 60-O 15&O 200-O 200-O Others C.C.O.F.I.-P.O.F.I. Marutoku + NORPAC C.C.O.F.I.-P.O.F.I. C.C.O.F.I.-P.O.F.I. C.C.O.F.1,P.O.F.I. Larvae Orsom III Kitahara Li “0 2 0 k L. REID, data grouped J 4 20 19 1 9 4 ---___~-4 20 13 16 49 8 8 8 9 4 5 4 by area, net type, and month _- JFMAMJ 11 JR. 31 75 3 AS 287 91 100 45 2 --- 0 N 25 27 28 5 10 -D --w----2 Totals --. -. _ 784 2 1 21 8 10 20 64 1 26 37 19 -- 2 __ - --_ 109 419 164 62 9 115 62 32 4 34 1: 62 47 38 63 ~. 33 __ 2 847 836 13 2,005 21 36 29 72 10 3 16 19 1 5 13 29 _______ 8 34 127 5 10 121 109 205 67 8 88 8 115 &7 9 2 11 3 7 2 4 1 6 15 957 C.C.O.F.I.-P.O.F.I. m d ’ 0 g “0.3 cn z.n 100-O 125-O 50 100, 3bo - N70V N70V Dana Orsom ZZZ 3 41-27 16 12 4 1 7 8 24 this treatment is to give values that are too low by an uncertain amount. The data that have been plotted and contoured on Figure 4 arc expressed in units of parts per 109 by volume ( cnG/l,OOO M” ) . The concentrations vary from about 10 to more than 1,600 parts per 109. Concentrations in terms of surface area vary from 1.5 m/km2 to more than 240. If the avcrage value is taken at about 50 parts per loo, the total amount of plankton in the upper 150 m of the Pacific is estimated to be a little more than lo9 tons (assuming the biomass to have a density of one ton/m”). This is about 3 times the estimated weight of the Pod-P in the upper 150 m or about 10 times the weight of all the human beings in the world. The smaller forms that escape the net (including phytoplankton) may exceed this amount. The total annual yidd of the commercial fisheries of the world is about 745 of this weight. The zooplankton volume is distributed very much as is the Pod-P. The volumes are high in the cyclones and in the eastern boundary currents, and low in the anticyclones. They are relatively high in a zone 5 17 3 12 2 1 12 11 3 9 101 11 35 1 23 38 T&l 170 I along the equator and in two zones north and south of the equator, corresponding to the equatorial divergence and to the two current boundaries mentio,ned before. The charts that Hentschel and Wattenberg ( 1930) prepared for net plankton and POh-P in the central and southern Atlantic indicate a close correspondence between the two quantities. Friedrich (1950) has filled in the plankton map in the north, and the high latitude values of the North Atlantic are seen to be as great as those in the South Atlantic. That the plankton volumes should be high in high latitudes and in eastern boundary currents could be anticipated from work in the Atlantic at least as early as that of Hentschel (1928). Hentschel (1936) went so far as to prepare a schematic chart of the zooplankton concentration in a theoretical ocean intermediate in size and shape bctwcen the Atlantic and Pacific, in which concentrations are high in high latitudcs and in the eastern boundary currents and in two tongues extending from the eastern boundary currents part way across the ocean in the North and South Equatorial CIRCULATION, PO4-P, AND ZOOPLANKTON Currents. Schumacher ( 1946) has related the zone of lowest zooplankton population in the South Atlantic to the convergence within the subtropical anticyclone. A number of authors have discussed plankton volumes in various parts of the Pacific. Graham ( 1941), in a discussion of the central equatorial Pacific based on CARNEGIE data, found relations between Pod-P and hydrographic features, Sheard (1947) treated the Australian-Antarctic quadrant. King and Dcmond (1953) and King and Hida ( 1957), in their discussions of zooplankton abundance in the central Pacific, found the highest volumes at the north edge of the (North) Equatorial Countercurrent where the pycnocline is shallow. They noted also a large-scale correspondence between the zooplankton volume and Pod-P distribution. Bogorov and Vinogradov (1955) mapped the values off the Kurile Islands. Holmes, Schaefer, and Shimada (1957) and Brandhorst (1958), in mapping the zooplankton volumes in the eastern tropical Pacific, related them to the thermocline topography. The continuous and systematic zooplankton measurements of the California Cooperative Oceanic Fisheries Investigations not only allow the area of the California Current to be included on the chart with more confidence than any other area, but allow seasonal and non-scasonal studies. Thrailkill’s work ( 1956, 1957, 1959, 1961) indicates that the volumes mapped ( Fig. 4) for the California Current region, which were taken in July and August 1955, are not at the seasonal peak of zooplankton volume, but at some time past it, and that the year 1955 was not especially high or low, but moderate for the decade 1950-1959. The correspondence between zooplankton volume and Pod-P in the California Current has been shown by Reid, Rodcn, and Wyllic ( 1958) to hold remarkably well in some data such as those taken in July 1950 by the California Cooperative Oceanic Fisheries Investigations. Even small-scale tongues of zooplankton and P04-P correspond quite closely. Any reasonable allowancc of time lag for growth renders this IN ‘ITIE 299 PACIFIC close agreement baffling. It was suggested, not that these zooplankton volumes grew large from the immediate product of the phytoplankton in the rich tongues of Pod-P, but rather that both zooplankton and Pod-P had reached high values upstream (farther north) and that the tongues of water forced offshore by the northwesterly winds merely retain both high zooplankton and high P04-P values. TRANSPORT OF THE PLANKTON How much does the volume of zooplankton at any place reflect that which can be sustained there by local growth, and how much does it reflect the influx of plankton that has grown in other areas? The question is readily answered over much of the Pacific. Zooplankton volumes are consistently low in the large areas within the anticyclones, and transport into these areas is slow and from markedly different environments. It is inferred that the zooplankton volumes are produced locally and represent an equilibrium between the nutrients available there and the needs of the plankton. Over the rest of the ocean the question cannot be answered so readily. Possibly the nutrients along the axis of the subarctic cyclone could sustain a larger volume of zooplankton than the divergence will allow to accumulate. Surface divergence takes place and PO,-P is high. Zooplankton volume is high over most of the cyclone, but a local minimum is seen along the axis (Fig. 4). The water brought up from below is high in nutrients but is presumably deficient in surface forms, If phytoplankton volume may double in a few days but zooplankton volume requires a longer time, the maximum volume of zooplankton may be produced only after a time lag in which the Pod-P has decreased and the population has moved some distance from the center of the divergence. Some part of the rich zooplankton in the northern part of the California Current is brought in by the west wind drift from the dense subarctic populations (Fig. 4). The volumes rise off Cape Mendocino and Cape 300 FIG. upper JOSEPH Distribution 4 (a). 150 m of the Pacific L. of zooplankton volume Ocean, station positions, Blanco and in the other upwelling regions along the coast, indicating that not only the high northern volumes, but even higher volumes ccan be sustained. This plankton is swept southward with the flow, and undoubtedly accounts for a great part of the south of plankton volume immediately Point Conccp tion. The monthly plankton volume ch‘arts of the area of the California Current from 1949 through 1958 (Thrailkill 1956, 1957, 1959, 1961) illustrate this point quite clearly. The volume declines very rapidly with distance to the south of Point REID, JR. (parts per log by volume) and contours. in approximately the Conception, and presumably, since more plankton flows in than flows out, the growth rate is negative and the population is not being sustained, except perhaps quite near the coast, by local growth. After reaching a minimum near the tip of Baja Cahfornia (Fig. 4) the nearshore values rise again, indicating that the growth rate has changed from negative to positive. Since there is no break in the Pod-P distribution (Figs. 2 and 3) or in the flow (Fig. I), but a strong rise in the temperature of the water, it is speculated that the decline CIRCULATION, FIG. upper Pod-P, AND ZOOPLANKTON 4. Variation in phosphate concentration of lake water 150 m of the Pacific Ocean, shaded by values. along southern and Baja California may represent the extinction of the more northerly forms by the rising temperature. South of this area, the zooplankton volume rises again. Since temperature continues to rise along the flow, it seems unlikely that the increase in zooplankton volume represents a recrudescence of the northern forms. It is suggested, therefore, that it represents the growth of warmer-water forms in the still relatively rich water from the north. An example of the introduction of such a warm- IN THE stored PAClFIC in an iodine-treated 1-L poly- water form from both the west and the south has been given by Berner and Reid (1961). In addition, the roughly inverse relation of zooplankton volume to temperature in the California Current may be taken to imply that the northern forms predominate there. This inverse relation is indicated by a comparison of the volumes at 16 stations between Point Conception and Punta Eugenia, averaged for each year in the months from February through August, with the 302 JOSEPH L. corresponding 10-m temperatures. This comparison was made by Reid, Roden, and. Wyllie ( 1958) in a paper dealing with the California Current only, and their graph is reproduced and continued in Figure 5. Although they were discussing a possible relation to nutrients, they stated ( p. 54) “In. deed, if there is no direct relation between zooplankton growth and temperature, the relation shown between the temperature as an indirect measure of nutrients and zooplankton as an indirect measure of phytoplankton is better than would be expected, and grcatcr irregularities almost certainly will be found in subsequent data.” However, when one considers the distribution of zooplankton volume in the area upstream from the California Current, it is possible to speculate, as in the above paragraph, about changes in the nature of the zooplankton as well. It is in the years of low temperature in the California Current (and presumably greater influx of subarctic water) that volumes are highest. High tcmpcraturcs arc usually accompanied by lower pl,ankton volumes, although there appears to be a minimum below which the values do not fall. This minimum may comprise the local forms only or it may be bolstered by incoming forms from the south and west ( Berner and Reid 1961) . Possibly if the temperature should rise even higher than the 1958 and 1959 extremes, warm-water forms would appear from the southeast in sufficient quantity to cause the volume to rise with temperature. In cold years the high volumes extend far to the south and in warm years they retreat to the north. Distributions in a cold year (1956) and a warm year (1958) are shown in Figure 6 (taken from the work of Thrailkill 1959 and 1961). A similar shift from cold- to warm-water forms may occur near 20”s along the coast of South America, but the data are less complete there. The data in the western Pacific are consistent with the location of a shift from warm- to cold-water forms off the coast of Japan, but with perhaps a mixing of the two forms for some distance along REID, JR. FIG. 5. Temperature (“C) at a depth of 10 m and zooplankton in the upper 140 m (parts per log by volume) averaged from February through August for each year from 1949 to the present (continued from Reid, Roden, and Wyllie 1958, who included data through 1956 only). the eastward Current. CONCLUSION extension AND of the Kuroshio SPECULATIONS The concentration of Pod-P at the surface and at 100 m is related to the circulation of the ocean. At the surface it is high in regions of horizontal divergence and low in regions of convergence. At 100 m the POh-P is low where the pycnocline is deep and high where it is shallow, and thus corresponds closely to the current systems. Zooplankton volume has been shown to vary almost everywhere with Pod-P. As a major exception, the center of the subarctic cyclone is high in Pod-P, but only moderate in zooplankton volume. The hypothesis is offered that the divergence rate is too great for a high zooplankton volume to accumulate even though growth may be rapid. Ekman ( 1953) maintains the generally accepted view that the main regions of pelagic fauna consist of a warm-water region and a northern and a southern coldwater region. The close correspondence of both the PO*-P (as an indicator of nutrients) and the zooplankton volume to the system of gyres suggests that the gyres themselves may offer a more effective classification. Their relatively narrow range of latitude 20 FIG. 6. I 1300 OCCUPIED I Zooplankton 0 STATIONS do0 in the upper I tr I 1100 :oo 2o” volume 140 m of the California 0 Current I 130° I OCCUPIED I2bO I 0: n -09 in 1956 and in 1958 (parts per log by volume). STATIONS 301-900 OVER 900 m 301-900 OVER 900 l 34- 100 #gJ 101-300 o-33 101-300 :: :: 34- 100 o-33 i0” 30’ 30 IO0 4c 40 o 0 I 110 !O” 304 JOSEPH results in their having a relatively narrow range of properties. Particular features (surface convergence in the anticycloncs, coastal boundaries along much of the cyclones) tend to confine the individuals within the gyres. The observed distribution of zooplankton volume lends considerable weight to Damas’ ( 1905) speculation that ( p. 22) “Le mkchanisme de la circulation joue done ici le r8lc principal pour la conservation de l’esp&ce et la creation d’un plankton speciil.” and (p. 23) “. . . la rotation supcrficielle des eaux est l’un des Uments le plus importants dc la persistence de la vie a la surface de l’ocdan.” As a result, it is speculated that the greater part of the zooplankton volume within a gyre may bc made up of forms that are found generally throughout the gyre, but only in much smaller quantities in the adjacent gyres. If this is so, the great zooplankton communities are: the subarctic and the subantarctic which are high in volume (and which may bc quite similar); the subequatorial, which is modcrate to high in volume; and the subtropical, which is low in volume. REFERENCES AUSTIN, T. S. 1957. 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