Download Late Quaternary vegetational and climate dynamics in northeastern

Quaternary Science Reviews 19 (2000) 981}994
Late Quaternary vegetational and climate dynamics
in northeastern Brazil, inferences from marine core GeoB 3104-1
Hermann Behling *, Helge W. Arz, JuK rgen PaK tzold, Gerold Wefer
Center for Tropical Marine Ecology, Fahrenheitstra}e 1, 28359 Bremen, Germany
Geoscience Department,University of Bremen, Klagenfurter Strasse, 28359 Bremen, Germany
Abstract
Late Quaternary paleoenvironments from northeastern (NE) Brazil have been studied by pollen analysis of marine sediment.
The studied core GeoB 3104-1 (3340 S, 37343 W, 767 m b.s.l.) from the upper continental slope o! NE Brazil is 517 cm long
and '42,000 C yr BP old. Chronological control was obtained by 12 radiocarbon (AMS) dates from individuals of the
foraminiferal species Globigerinoides sacculifer. Modern pollen analogs were received from 15 river, lake and forest soil surface
samples from NE Brazil. Marine pollen dates indicate the predominance of semi-arid caatinga vegetation in NE Brazil during the
recorded period between '42,000 and 8500 C yr BP. The increased #uvial input of terrigenous material, with high concentrations
of pollen and specially fern spores, into the marine deposits, about 40,000, 33,000 and 24,000 C yr BP and between 15,500 and 11,800
C yr BP, indicate short-term periods of strong rainfall on the NE Brazilian continent. The expansion of mountain, #oodplain and
gallery forests characterize the interval between 15,500 and 11,800 C yr BP as the wettest recorded period in NE Brazil, which
allowed #oristic exchanges between Atlantic rain forest and Amazonian rain forest, and vice versa. The paleodata from core GeoB
3104-1 con"rm the, in general, dry pre-Last Glacial Maximum (LGM) and LGM conditions and the change to wet Lateglacial
environments in tropical South America. The annual movement of the intertropical convergence zone over NE Brazil, the strong
in#uence of the Antarctic cold fronts and changes of the high-pressure cell over the southern Atlantic, may explain the very wet
Lateglacial period in NE Brazil. The documented NE Brazilian short-term signals correlate with the documented DansgaardOeschger cycles and Heinrich events from the northern Hemisphere and suggest strong teleconnections. 2000 Elsevier Science
Ltd. All rights reserved.
1. Introduction
In South America, the region of northeastern (NE)
Brazil is still a white spot with regard to the paleoenvironmental history based on pollen analysis. NE Brazil
is well known for the occurrence of anomalous, strong
droughts (Hastenrath, 1990; Nimer, 1989), which have
strong social and economic consequences, so that a study
of the history of past environmental changes and their
causes is important. Pollen in marine deposits can be an
important archive to reconstruct past terrestrial vegetational and climate changes, in view of the di$culties in
getting long terrestrial records from lakes, especially as
strong droughts can destroy pollen in lacustrine deposits.
Pollen analysis of marine sediment cores can contribute
* Corresponding author. Tel.: #49-0421-220-8321; fax: #49-0421220-8330.
E-mail address: [email protected] (H. Behling).
signi"cantly to the understanding of past vegetational
and climatic changes on the South American continent as
is well demonstrated by studies of the Amazon fan deposits (Haberle, 1997; Hoorn, 1997). Data on Late Quaternary paleoenvironmental changes from NE Brazil are
also important for a better understanding of the natural
history of the neotropics (Absy et al., 1991; Behling and
Lichte, 1997; Behling and Hooghiemstra, 1998,2000;
Colinvaux et al., 1996; Ledru et al., 1998; Martin et al.,
1997; Van der Hammen and Absy, 1994). Further, from
the biogeographic point of view NE Brazil is an interesting region, concerning the origin and past #oristic connections between the Amazonian and Atlantic rain forest
areas (Andrade-Lima, 1982; Cole, 1960; Prance, 1985).
In order to investigate vegetational and climatic changes in NE Brazil, the pollen and spore content of marine
core GeoB 3104-1 was studied. Modern pollen spectra
was collected from terrestrial surface samples, from river
and lake sediments and forest soils, in order to create
a calibration data set.
0277-3791/00/$ - see front matter 2000 Elsevier Science Ltd. All rights reserved.
PII: S 0 2 7 7 - 3 7 9 1 ( 9 9 ) 0 0 0 4 6 - 3
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H. Behling et al. / Quaternary Science Reviews 19 (2000) 981}994
2. Study region
2.1. Modern physical setting
The location of the studied marine core GeoB 3104-1
(3340 S, 37343 W, 767 b.s.l.) is 90 km east of the city
Fortaleza (CearaH State) on the upper continental slope o!
NE Brazil (Fig. 1). The nearest distance to the modern
coast line is about 70 km. The continental shelf is here
relatively narrow and shallow, 30 km wide and 50 } 80 m
deep, and has a steep continental slope (Ponte and Asmus, 1978). The most important source for the #uvial
input of terrigenous material into the marine deposits,
including pollen and spores, is Rio Jaguaribe, which is
about 700 km long and #ows into the Atlantic Ocean
about 80 km south of the core site. The river catchment
includes the Rio Jaguaribe basin and the )200 km wide
relatively #at Atlantic coastal plain, the mountainous
hinterland of the Chapada do Araripe, and the Serra dos
Cariris Novos between 200 and 1000 m elevation. Trans-
portation of pollen and spores by wind to the Atlantic is
probably low, because of the main winds blow from the
Atlantic Ocean on to the land area (Nimer, 1989).
The surface hydrography of the core area is dominated
by the northward #owing South Atlantic boundary current (North Brazil Current, NBC). Starting at around
103S as a relatively weak current (North Brazilian
Undercurrent " NBUC), the NBC is mainly supplied
by South Equatorial Current (SEC) waters and its #ow is
closely connected to the shelf edge. A further con#uence
with the northern SEC branch at 3}53 S leads to an
intensi"cation of the NBC (Condie, 1991; Peterson and
Stramma, 1991; Stramma, 1991; Da Silveira et al., 1994).
The seasonal variability of NBUC and NBC transport is
related to the southeastern trade winds, with a larger
transport during austral spring and reduced transport in
austral fall (Johns et al., 1998). With annual means of
27.33C, sea surface temperature (SST) shows a seasonal
amplitude of ca. 23C. The average sea surface salinity
(SSS) is around 36%. Marine pollen transport by the
NBC, primarily from the eastern Brazilian coast and with
north}northwestward orientation, has to be taken into
consideration.
2.2. Vegetation and climate
Fig. 1. Location of the marine core GeoB 3104-1 and the terrestrial
surface samples from rivers (1}8), lakes (9}10), and forest soils (11}14) in
NE Brazil including the schematic surface circulation pattern o! NE
Brazil (SEC, South Equatorial Current; NBC, North-Brazil Current;
BC, Brazil Current).
The modern vegetation in NE Brazil is primary
caatinga (IBGE, 1993), which is subdivided into several
physiognomic vegetation types, from grassland to
xerophytic thorn shrub savanna, and shrub woodland
(Cole, 1986; Eiten, 1982). Main taxa belong to families of
Mimosaceae, Caesalpinaceae, Fabaceae, Euphorbiaceae,
Cactaceae and Poaceae (Hueck, 1966; Sampaio, 1995).
Patches of deciduous forest, gallery and #ood plain forests along rivers, and a few small islands of humid forests
in mountains over 500 m a.s.l. (Andrade-Lima, 1982)
characterize the semi-arid caatinga region. Along the
coast di!erent forms of coastal vegetation occur, including the Atlantic rain forest, which is restricted to a small
strip along the western coast starting from the city of
Natal southwards.
Characteristic of the caatinga region is the long dry
season (6}11 months), with the main annual rainfall of
less than 250}750 mm, occurring between November and
March. The average annual temperature is 24}263C. The
Atlantic rain forest region re#ects a humid climate with
'1250 mm annual precipitation and only a short annual dry period (Nimer, 1989).
The general atmospheric circulation of NE Brazil is
in#uenced continuously by the southeasterly air #ow
from the Atlantic Ocean (Nieuwolt, 1977). These southeasterlies bring relatively dry air masses from the highpressure cell over the southern Atlantic. The rainy season
is related to the annual movement of the intertropical
convergence zone (ITCZ) and occurs only when the
ITCZ moves over NE Brazil. Unusually strong droughts
H. Behling et al. / Quaternary Science Reviews 19 (2000) 981}994
occur when the ITCZ remains north of the equator.
Depending upon the meteorological conditions these
e!ect the behavior of cold fronts from the Southern
Hemisphere in eastern and southern Brazil (Ratisbona,
1976). Conditions in the South Atlantic Ocean determine
the strength of the subtropical high, the SEC/NBC intensity, and sea surface temperatures (Hastenrath, 1990; Rao
et al., 1993; Arz et al., 1998).
3. Material and methods
3.1. Fieldwork
The 517 cm long marine gravity core GeoB 3104-1 was
collected during the RV VICTOR HENSEN cruise JOPS II,
Leg 6 Fortaleza } Recife, in March 1995 (PaK tzold et al.,
1996; Arz et al., 1998) from the upper continental slope
(water depth: 767 m) o! Fortaleza.
Terrestrial surface samples for modern pollen data
were collected from rivers, lakes and forest soils in NE
Brazil by Dr. Matthias Tintelnot (Senckenberg Institute
in Wilhelmshaven, Germany) and by the "rst author
(Table 1 and Fig. 1).
3.2. Radiocarbon dates
Each C AMS sample consisted of about 700 handpicked individuals of the foraminiferal species
Globigerinoides sacculifer (250}400 lm). Carbonate hydrolysis and CO reduction was performed in the
Geoscience Department of Bremen, Germany. The
AMS measurements were performed at the Leibniz-
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Table 2
List of AMS-radiocarbon dates from core GeoB 3104-1
Lab. number
Depth (cm)
C yr B.P.
Calibrated Age
(cal B.P.)
KIA-653
KIA-1857
KIA-1856
GrA-3719
KIA-1855
GrA-3720
KIA-651
GrA-3721
KIA-1853
KIA-1852
KIA-650
GrA-3722
8
20
52
87
97
172
209
274
292
337
384
462
2660$50
5740$60
9660$50
12,580$100
12,960$90
16,120$160
20,540#350/!330
25,050$200
27,820#290/!280
31,690#450/!420
33,400#1840/!149
38,600#900/!800
2880
6450
11,140
14,760
15,230
19,150
24,280
29,340
32,340
36,370
38,100
43,130
Labor in Kiel, Germany (Nadeau et al., 1997) and the
Center for Isotope Research, Groningen, The Netherlands (Table 2).
3.3. Stable isotopes
Eight specimens of 350}400 lm diameter (measured
along the longest axis) of the planktonic foraminiferal
species Globigerinoides sacculifer (without "nal chamber)
were used for stable isotope measurements. Sample preparation was performed employing an automatic carbonate preparation system attached to a Finnigan MAT 251
mass spectrometer. Analytical internal longtime precision for dO is better than $0.07.
Table 1
Location of terrestrial surface samples and the corresponding vegetation units from NE Brazil
No. Name
Coord. (approx.)
State
Vegetation
4325N, 37345W
4334N, 37346W
(between the sites 1and 4)
5338N, 35323W
5347N, 35315W
10316N, 36332W
14317N, 39300W
15351N, 38355W
CearaH
CearaH
Caatinga
Caatinga
Caatinga
Caatinga
Caatinga
Cerrado/Caatinga
Caatinga/Atlantic rain forest
Semideciduous forest/Atlantic
rain forest
River
1
2
3
7
4
13
12
11
Rio
Rio
Rio
Rio
Rio
Rio
Rio
Rio
Lake
6
5
Lagoa Grande
Lago Bolim
7304N, 41325W
6302N, 35311W
PiaumH
Rio Grande do Norte
Caatinga
Restinga
Forest soil
8
17
9
15
16
Picos
Picos
Mirim
Campina Grande I
Campina Grande I
7304N,
7304N,
5338N,
7313N,
7313N,
PiaumH
PiaumH
Rio Grande do Norte
Paraiba
Paraiba
Caatinga (secondary)
Caatinga (secondary)
Caatinga (secondary)
Deciduous forest
Deciduous forest
Jaguaribe I
Jaguaribe II
(unclear)
Mirim
Potengi
Sao Francisco
de Contas
Jequitinhonha
41325W
41325W
35323W
35348W
35348W
Rio Grande do Norte
Rio Grande do Norte
Sergipe
Bahia
Bahia
984
H. Behling et al. / Quaternary Science Reviews 19 (2000) 981}994
3.4. Pollen analysis
Along the pro"le 52 samples (4 cm and 1 cm thick)
were collected at 10 cm intervals for the pollen analysis.
All samples, including terrestrial surface samples, were
treated with standard acetolysis method, using sodium
pyrophosphate and heavy liquid separation (Faegri and
Iversen, 1989). Pollen preparation of marine samples
included addition of exotic Lycopodium spores to determine pollen concentration (grains/cm) and pollen in#ux
(grains/cm/yr). Samples were counted until a minimum
of about 300 pollen grains or 100}200 pollen grains for
samples with a low pollen concentration. Twelve samples
of the core contained insu$cient pollen grains for statistical calculation. Marine micro-foraminifera were also
counted on the pollen slides.
For identi"cation of pollen grains and spores, morphological descriptions published by Behling (1993),
Hooghiemstra (1984), Roubik and Moreno (1991),
Salgado-Labouriau (1973) and Behling's own reference
collection were used. The total pollen sum, on which the
percentage calculation is based, includes herbs, shrubs
and trees, but not, fern spores, moss spores and microforaminifera. A few reworked pollen grains and spores
were not counted. Identi"ed pollen and spore taxa have
been preliminary grouped into herbs, shrubs and trees,
exotic pollen taxa, ferns and mosses. The "nal grouping
of identi"ed taxa into di!erent ecological groups such as
caatinga, Atlantic rain forest, gallery and #ood plain
forests, mountain vegetation has not been "nished, because of lacking pollen records and additional surface
samples from di!erent vegetation forms in NE Brazil.
TILIA, TILIAGRAPH and CONISS software was
used to plot the pollen data and to make calculations and
cluster analysis (Grimm, 1987). Downcore changes of the
most frequent and important pollen and spore taxa are
illustrated in the form of a pollen percentage diagram,
a summary percentage diagram. The latter record includes also radiocarbon dates, the sum of microforaminifera, pollen concentration, pollen in#ux record
and a cluster analysis dendrogram.
Fig. 2. Age-depth curve for core GeoB 3104-1.
rigenous input (Tintelnot, 1997; Arz et al., 1998, 1999).
Downcore variations in the sediment composition re#ect
repeated periods of increased terrigenous sediment input
which dilutes the marine biogenic signal (carbonate
sedimentation). Thus, sedimentation rates are generally
high (&14.5 cm/kyr), favoring a high-resolution paleoclimatic study (Fig. 3).
4.2. Oxygen isotope data (Fig. 3)
G. sacculifer is a planktonic foraminifera living in the
uppermost 80 m of the water column. Besides the e!ect of
the glacio-eustatic sea-level change } the so called `ice
e!ecta } its dO signal re#ects local variations in surface
water temperature and salinity. The global Holocene/LGM amplitude in dO of 1.2 is exceeded in our
isotope curve by about 0.7. Oxygen Isotope Stages
(OIS) 3 and 2 are characterized by several distinct oscillations with amplitudes as much as 0.6. These isotopic
shifts appears to line up with the changes in the sediment
composition (Fig. 2).
4.3. Modern terrestrial pollen data (Fig. 1, Table 1, Fig. 4)
4. Results
4.1. Stratigraphy (Fig. 2, Table 2)
The chronostratigraphy of core GeoB 3104-1 is based on
linearly interpolated C AMS dates (Table 2 and Fig. 2).
The AMS dates were corrected by a reservoir age of 400
yr (Bard, 1988). The radiocarbon stratigraphy is in good
agreement with the marine oxygen isotope stratigraphy
(Fig. 3).
During the Last Glacial period and the deglaciation
period, sedimentation processes on the upper continental
slope o! Brazil were strongly in#uenced by riverine ter-
Surface samples from rivers (Nos. 1}8), lakes (Nos.
9}10) and forest soils (Nos. 11}15) in NE Brazil (Fig. 1,
Table 1) show the pollen representation of the modern
vegetation (Fig. 4). We have to consider the human
in#uence on the vegetation when using these modern
pollen analogs. Di!erent herb pollen taxa, primarily
Poaceae, Cyperaceae, Borreria, Asteraceae are predominant in the surface sediments. Pollen grains of arboreal
taxa, such as Melastomataceae/Combretaceae, Arecaceae
(Palmae), Moraceae/Urticaceae, Mimosa and Fabaceae
are less frequent, except two forest soil samples (Nos. 11
and 12) which show a strong local input of Mimosa.
Remarkable is the presence of Hedyosmum pollen in one
H. Behling et al. / Quaternary Science Reviews 19 (2000) 981}994
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Fig. 3. Oxygen isotope curve (G. sacculifer) and sedimentation rates (see also Arz et al., 1998) from GeoB 3104-1. The marine isotope stages are
indicated at the top. C AMS dating levels are marked with black arrows.
forest sample near Picos in PiaumH State. Hedyosmum is not
known from NE Brazil. Fern spores seems to be extremely rare in the caatinga region.
It is interesting to note, that the presence of Borreria
pollen grains (indicator for open vegetation types) decreases in the river samples from north to south, while
fern spores (indicator for wetter conditions) increases
along the eastern coast southwards. Spores of tree ferns,
e.g. from Cyathea (indicator for permanent moist conditions), are not found in modern river surface samples
from northern NE Brazil, but only in the southernmost
samples (Nos. 7 and 8), where tree ferns grow in the
humid Atlantic coastal mountains.
4.4. Marine fossil pollen data (Figs. 5}7)
About 160 di!erent pollen and spore types, including
20 unknown types, were recognized. Fig. 5 show the most
frequent pollen and spore taxa. All pollen assemblages
are characterized by abundant herb pollen (60}75%),
primarily Poaceae, Cyperaceae, Borreria, Asteraceae.
Less frequent are Alternanthera, Amaranthaceae/
Chenopodiaceae, Gomphrena/Pfaza-type, and a number
of other types occur in low percentages. Shrub and
tree pollen percentages are lower (15}25%) and primarily represented by Melastomataceae/Combretaceae,
Arecaceae, Moraceae/Urticaceae, Alchornea, Myrtaceae,
Malpighiaceae, Hedyosmum, Mimosa and many other
taxa which were found in trace amounts (not shown
in the pollen diagrams). Ferns are mainly represented by
indeterminate monolete and trilete spores, Anemia,
Cyathea and Selaginella. Remarkable is the evidence of
the Cyathea horrida-type (previously called Hemitelia),
which is not known from NE Brazil. Unclear is the origin
of exotic pollen grains primarily Pinus, and Quercus and
less frequent Abies, Betula, Corylus, Ephedra, Juglans and
Juniperus-type. Long-distance transport by marine currents or the contamination of the upper sediments may
be the reason for presence of these pollen grains.
Portions of herb, shrub and tree pollen percentages do
not show marked changes during the time, except the
increase of shrub and trees, mainly by Melastomataceae/
Combretaceae, Alchornea and Hedyosmum during the
Lateglacial. Stronger variations are found among
the fern spores. Monolete psilate spores show high percentages during the Lateglacial, and only at this period
di!erent tree fern taxa from Cyathea are abundant. The
Selaginella spore curve illustrates marked #uctuations
corresponding to the rates of pollen concentration and
in#ux.
The calculated pollen concentration (deposition of pollen grains per cm) and in#ux (deposition of pollen grains
per cm and year) show strong variations from very low
to high values in the core sediments (Figs. 6 and 7). The
accumulation rate of terrestrial pollen and spores in
marine sediments were very low for statistical counts in
eight samples from glacial periods (423, 403, 343, 303,
293, 223, 217 and 173 cm depth) and in four samples of
the mid and late Holocene age (33, 23, 13 and 3 cm
depth). Pollen concentration and in#ux are low during
most of the time, including the LGM, and higher during
short glacial periods about 40,000, 33,000 and 24,000
C yr BP. The highest rates occur during the Lateglacial
between 15,500 and 11,800 C yr BP. Values from the
early Holocene are low. The in#ux of fern spores (Fig. 6)
follows the pattern of the pollen in#ux. The in#ux
Fig. 4. Pollen percentage diagram, showing the most frequent pollen and spore taxa of modern terrestrial surface samples from rivers (1}8), lakes (9}10), and forest soils (11}15), in NE Brazil.
986
H. Behling et al. / Quaternary Science Reviews 19 (2000) 981}994
Fig. 5. Pollen percentage diagram, showing the most frequent pollen and spore taxa from the marine core GeoB 3104-1. The pollen sum, on which the percentage calculations are based, includes herbs,
shrubs and trees.
H. Behling et al. / Quaternary Science Reviews 19 (2000) 981}994
987
Fig. 6. Pollen in#ux diagram, showing the in#ux values of selected herb, shrub and tree taxa, and the in#ux of sums of groups.
988
H. Behling et al. / Quaternary Science Reviews 19 (2000) 981}994
Fig. 7. Summary percentage diagram, showing the sum of the pollen and spore taxa, micro-foraminifera, pollen sum values, pollen concentration and pollen in#ux record, and the cluster analysis
dendrogram.
H. Behling et al. / Quaternary Science Reviews 19 (2000) 981}994
989
990
H. Behling et al. / Quaternary Science Reviews 19 (2000) 981}994
variation of marine micro-foraminifera (Fig. 6) is not so
marked than the in#ux of pollen and spores.
5. Interpretation and discussion
5.1. The marine signal
According to the detailed C AMS stratigraphy and
oxygen isotope record, core GeoB 3104-1 represents undisturbed and continuously sedimented Last Glacial to
Holocene marine deposits. The sediment generally consists of nannofossil foraminiferal ooze (carbonate content
of 40 up to 70 wt%) with episodically increasing amounts
of terrigenous clays of #uvial origin. Terrigenous input
(XRF Ti}Ca ratio) coincides with the short glacial periods of high pollen and spore concentrations about
40,000, 33,000 and 24,000 C yr BP and between 15,500
and 11,800 C yr BP as shown in Fig. 8. During these
intervals the oxygen isotopes are most negative, which
can be interpreted in terms of increased sea-surface temperatures. Arz et al. (1998) additionally suggested for
these periods an increased mixing of the upper water
column, accompanied by intensi"ed SE trade winds and
accordingly an enhanced north}northwestward transport of the NBC. Although these hydrographic changes
are most simply explained by variations in the tropical/subtropical wind "eld, the timing of the signals (based
on the calendar year calibrated chronology, Arz et al.,
1998) imply strong teleconnections with the short-term
climate variations (Daansgaard-Oeschger and Bond
cycles) as reported from the North Atlantic high latitudes
(Daansgaard et al., 1993; Bond and Lotti, 1995).
5.2. Modern and past pollen sources
Pollen grains and fern spores originate from di!erent
vegetation types on the NE Brazilian continent, such as
from coastal vegetation (Poaceae, Cyperaceae, Borreria),
caatinga (Poaceae, Borreria, Mimosaceae), Atlantic rain
forest } gallery forest and #ood plain forests (Alchornea,
Arecaceae), and humid mountain vegetation (Cyathea) or
in general moist forest (ferns and Hedyosmum).
The major source of the pollen grains and spores
deposited at the site GeoB 3104-1 was apparently the
terrigenous #uvial input, most likely from the nearest
major river, Rio Juagaribe. This is also indicated by
mineralogical studies of core sediments (Tintelnot, 1997).
Atmospheric pollen and spore transport was probably
low, because the main winds blow from the Atlantic on to
the land area. Changes in the rainfall regime on the NE
Brazilian continent, caused changes in discharge and in
the transport of sediment loads by the river into the
Ocean. Modi"cations in the marine currents such as the
NBC, probably in#uenced on a smaller scale the #uvial
deposits in the marine sediments. In this context it has to
be considered, that the continental shelf was exposed
during glacial low Atlantic sea-level stands, conditions
that favored #uvial transport to the upper continental
slope. The high sea-level stand during the Holocene,
when marine currents also in#uenced the coastal shelf,
apparently diminished terrigenous sediment transport to
the slope. This is probably the reason for the very low
pollen and spore content of the mid and late Holocene
deposits.
Pollen and spore concentration and in#ux from the
#uvial deposits in the marine sediments re#ect also alternations in the deposition rate of continental sediments.
This is in general related to modi"cations in the river
discharge by changes in precipitation on the continent.
Oscillations of Atlantic sea-level stands, and marine currents may also have in#uenced deposition rates of pollen
and spores. However, low deposition rates of pollen and
spores suggest low precipitation rates on the NE Brazilian continent during glacial times, including the LGM,
while high deposition rates suggest short periods with
higher rainfall rates about 40,000, 33,000 and 24,000
C yr BP. The highest precipitation rate is found during
the Lateglacial between 15,500 and 11,800 C yr BP.
5.3. Vegetation and climate changes
Pollen data from river surface samples, including two
from the Rio Jaguaribe itself (Nos. 1 and 2 in Fig. 4),
re#ect the modern pollen analogue, which was not possible to obtain from the upper Holocene marine deposits.
Those data indicate that herb pollen dominate in the
modern human in#uenced open caatinga vegetation.
Relatively high percentages of pollen grains of herbs
and lower percentages of shrubs and trees from the fossil
marine deposits clearly suggest presence of open vegetation types such as caatinga and coastal savanna (abundant Cyperaceae) in NE Brazil during the glacial and
early Holocene periods. Abundant taxa such as Borreria,
Alternanthera, Amaranthaceae/Chenopodiaceae, and
Gomphrena/Pfaza are light tolerant and have strong
preferences to vegetation forms with an open canopy
(Gentry, 1993). No marked changes between the proportions of herbs, shrubs and trees probably indicate similar
semi-arid conditions in NE Brazil during the glacial
period than present day.
Remarkable are the short periods of higher pollen
concentration and in#ux, which show abundant fern
spores deposits. There is an interesting gradient in the
river surface samples from north to south along the NE
Brazilian coast, re#ected in a decrease of Borreria pollen
and an increase of fern spores. This gradient re#ects the
change from dry vegetation types with an open canopy to
closed humid vegetation types. This observation seems to
be important for the interpretation of the marine pollen
record and suggest periods of moister conditions in NE
Brazil.
H. Behling et al. / Quaternary Science Reviews 19 (2000) 981}994
991
Fig. 8. Summary of palynological and paleoceanographic data, showing the total pollen in#ux, the fern spore in#ux, the XRF Ti-Ca ratio(scaled up
fourfold), and the stable oxygen isotope curve (G. sacculifer) from sediment core GeoB 3104-1. Arrows denote more humid periods in NE Brazil.
Selaginella grows on moist soil and may be used as
a good disturbance indicator for erosion during strong
rain fall. The high presence of Selaginella spores, together
with the high deposition rate of pollen, suggest strong
rainfall at about 40,000, 33,000 and 24,000 C yr BP
under in general dry climatic conditions. These wetter
periods were apparently too short for an expansion of
humid #ood plain or mountain forests. Only from 15,500
to 11,800 C yr BP is a longer wetter period found which
allowed an expansion of humid forests as indicated by
the expansion of rain forest (e.g. Alchornea) and humid
mountain forests (e.g. Hedyosmum, Cyathea). The annual
dry season must have been very short, perhaps less than
three months. There was probably a marked expansion
of small areas of gallery and #ood plain forests along
rivers and humid mountain forests in moist valleys.
Hedyosmum, in general an indicator for a cool and humid
climate (Reitz, 1965), was apparently frequent in mountain forests and gallery forests along the rivers during the
cold Lateglacial period. Tree ferns belonging to Cyathea,
which are con"ned to very humid habitats without
marked dry season (Golte, 1976), were abundant only
during this period and supports the interpretation of
a cold and permanent wet climate at that time. Cooling
of ca. 53C during the LGM is reported from NE Brazil on
the basis of studies on noble gases dissolved in groundwater (Stute et al., 1995).
During the early Holocene, Hedyosmum disappears
and Cyathea was rare, indicating a return to drier climatic
conditions in NE Brazil. Mangrove pollen, especially
Rhizophora, were only found in the early Holocene,
suggesting that mangrove vegetation was probably rare
or absent in the studied coastal region during glacial
times.
992
H. Behling et al. / Quaternary Science Reviews 19 (2000) 981}994
5.4. Biogeographic implications
During the recorded glacial and early Holocene
period, NE Brazil mostly experienced semi-arid climatic
conditions as similar to today. However, distinct and
short-term wetter periods have been evidenced about
40,000, 33,000 and 24,000 C yr BP and during the
longer period of 15,500}11,800 C yr BP. This Lateglacial interval was the wettest period recorded, which
allowed marked expansion of moist gallery and mountain forests. During this period #oral migration in both
directions between Amazon rain forest and Atlantic rain
forest may have taken place. It is possible that during the
Lateglacial period a number of present-day humid forest
refugia in the mountains (Andrade-Lima, 1982) were
connected to form a larger area during cooler and wetter
climatic conditions.
5.5. NE Brazil in the context to paleoenvironmental records
from adjacent regions
Evaluating the new results from NE Brazil, one has to
consider that the climate of adjacent regions are in#uenced by di!erent climate regimes. The inferred climatic sequence from core GeoB 3104-1 follows the
general trend of dry pre-LGM and LGM conditions, as
reported from terrestrial sites in southeastern Brazil such
as Catas Altas (Behling and Lichte, 1997) and Morro de
Itapeva (Behling, 1997). Periods with relatively wet conditions are inferred from pollen records of Carajas (ca.
40,000}22,800 C yr BP) in southeastern Amazonia
(Absy et al., 1991), Aguas Emendadas (26,000}21,500
C yr BP) and CrommH nia (32,000}ca. 20,000 C yr BP)
in central Brazil (Barberi, 1994; Ferraz-Vincentini and
Salgado-Labouriau, 1996), and Salitre and Serra Negra
(40,000}27,000 C yr BP) in southeastern Brazil (Ledru
et al., 1996; De Oliveira, 1992). These periods are markedly longer than the wet short-term periods from the
record GeoB 3104-1. Continuously wet climatic conditions are reported from central Amazonia (Colinvaux
et al., 1996).
The wet Lateglacial period between 15,500 and 11,800
C yr BP from NE Brazil is earlier than in the Carajas
mountains, which are characterized by forest expansion
since around 12,000 until ca. 8,000 C yr BP. The records from central Brazil (Agua Emendadas, and
CrommH nia) suggest that dry conditions prevailed (Salgado-Labouriau et al., 1998), but here the dry climate
during the early Holocene may have caused the erosion
or oxidation of deposits of Lateglacial age. Between
16,000 and 11,000 C yr BP, the Salitre record shows
a succession of di!erent forest types, which re#ects increasing moisture. A change from dry LGM conditions
to wetter Lateglacial conditions is also reported from
Morro de Itapeva in southeastern Brazil. Of interest is
the record from Lago do Pires in the Atlantic lowlands of
southeastern Brazil (17357 S, 42313 W, 390 a.s.l.) which
documents a wetter interval between 8800 to 7500 C yr
BP during the markedly dry early Holocene period, (Behling, 1995).
5.6. Possible factors for paleoenvironmental changes
in NE Brazil
There is a general change from a dry LGM to wetter
climatic conditions in tropical South America during the
Lateglacial, both north and south of the equator (Behling
and Hooghiemstra, 2000). This suggests that modi"cations of the annual movements of the ITCZ between both
hemispheres plays an important role in determining past
climatic changes. The very wet climatic regime in NE
Brazil during the Lateglacial, can be explained by permanent annual movement of the ITCZ over NE Brazil. In
their comparative study based on pollen and lake level
records in tropical and subtropical South America Martin et al. (1997) conjectured later humid period for eastern
Amazonia (based for example on records from the
CarajaH s mountains) between 12,400 and 8800 cal yr B.P.
(ca. 10,700 and 7700 C yr B.P.) and with an onset at ca.
13,000 C yr B.P. They suggest a somewhat northward
shifted summer ITCZ due to massive, astronomical controlled (precession), insolation changes over South America during this period. However, to what extend the
coastal area of NE Brazil was a!ected by such ITCZ
movements is unclear. Considering more global-scale
atmospheric changes, the correspondence of the repeated
humid periods over NE Brazil with the North Atlantic
Bond cycles (maximum cooling) would rather imply
a slightly southward displacement of the ITCZ during
the Northern Hemisphere stadials, directly a!ecting the
precipitation in the study area. Changes of the highpressure cell over the southern Atlantic were probably
also important. Intensi"ed SE trade winds and surface
currents during each of the humid periods (Little et al.,
1997; Arz et al., 1998) could have induced a stronger
moisture supply from the open Atlantic Ocean thus favoring orographic rains in the coastal area of NE Brazil,
a fact which is also observed on modern seasonal scale
(Rao et al., 1993). Furthermore, a strong northward shift
of Antarctic cold fronts over the eastern Brazilian highland to NE Brazil, could explain the higher precipitation
rates and a markedly shorter annual dry season during
the Lateglacial. The occurrence of a wet period during
the early Holocene (8800 to 7500 C yr BP) in southeastern Brazil (Lago do Pires record), may be the result
that polar cold fronts reached only so far north at that
time. The retreat of the Antarctic cold fronts from NE
Brazil to southeastern Brazil at the end of the Lateglacial
may explain the return to semi-arid conditions. The same
mechanism was suggested by Martin et al. (1993) for
South American climate changes during the last 7000 yr,
which they interpreted to be related to long-term El Nin o
H. Behling et al. / Quaternary Science Reviews 19 (2000) 981}994
activity. Questionable, is whether Antarctic cold fronts
could reach a latitude of ca. 43S, because cold fronts
penetrating as far north as the coastal areas of Brazil
would expect to rather be blocked by SW trade winds.
6. Conclusion
Pollen analysis of modern surface samples and the well
dated marine core GeoB 3104-1 located o! NE Brazilian
continental slope lead to conclusions that contribute to
the understanding of vegetational and climatic changes
on the adjacent continent. Pollen data from river and
lake surface sediments and forest soil surface samples
provide a modern pollen analog of NE Brazilian vegetation types. Di!erent herb taxa are predominant, re#ecting primarily open caatinga vegetation types. Marine
pollen data indicate the occurrence of caatinga vegetation in NE Brazil during the recorded part of the Last
Glacial and early Holocene period (42,000 } 8500 C yr
BP), re#ecting most of the time semi-arid conditions. The
increase of transport of terrigenous material to the Atlantic Ocean, which contain high concentration of pollen
and especially fern spores during relatively short intervals around 40,000, 33,000 and 24,000 C yr BP, indicate
periods of higher precipitation. The wettest climate is
found from 15,500 to 11,800 C yr BP. These climatic
changes can be explained by variations in the tropical/subtropical wind "eld. Timing, duration, and amplitude of these climatic events are comparable with the
Daansgaard-Oeschger and Bond cycles, well known
from higher North Atlantic high latitudes, suggesting the
presence of a teleconnection in the climate system. Only
the Lateglacial period allowed an expansion of mountain
forests, #oodplain forest and gallery forests along rivers,
suggesting cold and very wet climatic conditions with
short annual dry seasons. Floristic exchanges between
Atlantic rain forest and Amazon rain forest vice versa
was during the Lateglacial period possible. The consistent annual movement of the ITCZ over NE Brazil, the
strong in#uence of the Antarctic cold fronts and changes
of the high pressure cell over the southern Atlantic may
explain the very wet Lateglacial period in NE Brazil.
Acknowledgements
The authors thank the RV Victor Hensen cruise JOPS
II members for the collection of marine sediment cores.
This cruise was supported by the Federal Department for
Science and Technology in Germany, and the Department of Environment, Brazil. Dr. Matthias Tintelnot,
from the Senckenberg Institute in Wilhelmshaven (Germany) is thanked for some river surface samples from NE
Brazil. Elly Beglinger and Annemarie Phillip of the Hugo
de Vries Laboratory in Amsterdam are thanked for the
993
preparation of the pollen samples, when the "rst author
had a the post-doctoral position there. The LeibnizLabor in Kiel (Germany), and the Center for Isotope
Research in Groningen (The Netherlands), is acknowledged for the radiocarbon dates. We thank Dr. Henry
Hooghiemstra and one anonymous reviewer for constructive and valuable comments on the manuscript. The
"rst author thanks the Deutsche Forschungsgemeinschaft (DFG) for the current scholarship.
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