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Quaternary Science Reviews 19 (2000) 981}994

Late Quaternary vegetational and climate dynamicsin northeastern Brazil, inferences from marine core GeoB 3104-1

Hermann Behling*, Helge W. Arz, Ju Krgen Pa Ktzold, 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 Dansgaard-

Oeschger 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 paleoen-

vironmental 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 vegeta-

tional 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:#49-0421-

220-8330.

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 de-

posits (Haberle, 1997; Hoorn, 1997). Data on Late Quat-

ernary 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 interest-

ing region, concerning the origin and past #oristic con-

nections between the Amazonian and Atlantic rain forest

areas (Andrade-Lima, 1982; Cole, 1960; Prance, 1985).

In order to investigate vegetational and climatic chan-

ges in NE Brazil, the pollen and spore content of marinecore 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 77 - 3 7 9 1 ( 9 9 ) 0 0 0 4 6 - 3



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).

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 (Ceara H 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 As-

mus, 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 mountainoushinterland 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 cur-

rent (North Brazil Current, NBC). Starting at around

103S as a relatively weak current (North BrazilianUndercurrent" 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 seasonalamplitude 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

The modern vegetation in NE Brazil is primary

caatinga (IBGE, 1993), which is subdivided into several

physiognomic vegetation types, from grassland toxerophytic 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 for-

ests 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, includ-

ing 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 an-

nual 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 south-

easterlies bring relatively dry air masses from the high-pressure 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

982 H. Behling et al. / Quaternary Science Reviews 19 (2000) 981}994



Table 1

Location of terrestrial surface samples and the corresponding vegetation units from NE Brazil

No. Name Coord. (approx.) State Vegetation

River

1 Rio Jaguaribe I 4325N, 37345

W Ceara H Caatinga

2 Rio Jaguaribe II 4334N, 37346W Ceara H Caatinga

3 Rio (unclear) (between the sites 1and 4) Caatinga

7 Rio Mirim 5338N, 35323W Rio Grande do Norte Caatinga

4 Rio Potengi 5347N, 35315W Rio Grande do Norte Caatinga

13 Rio Sao Francisco 10316N, 36332W Sergipe Cerrado/Caatinga

12 Rio de Contas 14317N, 39300W Bahia Caatinga/Atlantic rain forest

11 Rio Jequitinhonha 15351N, 38355W Bahia Semideciduous forest/Atlantic

rain forest

Lake

6 Lagoa Grande 7304N, 41325W Piaum H Caatinga

5 Lago Bolim 6302N, 35311W Rio Grande do Norte Restinga

Forest soil

8 Picos 7304N, 41325W Piaum H Caatinga (secondary)

17 Picos 7304N, 41325W Piaum H Caatinga (secondary)

9 Mirim 5338N, 35323W Rio Grande do Norte Caatinga (secondary)

15 Campina Grande I 7313N, 35348W Paraiba Deciduous forest

16 Campina Grande I 7313N, 35348W Paraiba Deciduous forest

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 8 2660$50 2880

KIA-1857 20 5740$60 6450KIA-1856 52 9660$50 11,140

GrA-3719 87 12,580$100 14,760

KIA-1855 97 12,960$90 15,230

GrA-3720 172 16,120$160 19,150

KIA-651 209 20,540#350/ !330 24,280

GrA-3721 274 25,050$200 29,340

KIA-1853 292 27,820#290/ !280 32,340

KIA-1852 337 31,690#450/ !420 36,370

KIA-650 384 33,400#1840/ !149 38,100

GrA-3722 462 38,600#900/ !800 43,130

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 inten-

sity, and sea surface temperatures (Hastenrath, 1990; Raoet 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 V ICTOR H ENSEN cruise JOPS II,

Leg 6 Fortaleza } Recife, in March 1995 (Pa Ktzold 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 hand-

picked individuals of the foraminiferal speciesGlobigerinoides sacculifer (250}400 m). Carbonate hy-

drolysis and CO

reduction was performed in the

Geoscience Department of Bremen, Germany. The

AMS measurements were performed at the Leibniz-

Labor in Kiel, Germany (Nadeau et al., 1997) and the

Center for Isotope Research, Groningen, The Nether-

lands (Table 2).

3.3. Stable isotopes

Eight specimens of 350}400 m diameter (measured

along the longest axis) of the planktonic foraminiferal

species Globigerinoides sacculifer (without "nal chamber)

were used for stable isotope measurements. Sample prep-aration was performed employing an automatic carbon-

ate preparation system attached to a Finnigan MAT 251

mass spectrometer. Analytical internal longtime pre-

cision for O is better than$0.07.

H. Behling et al. / Quaternary Science Reviews 19 (2000) 981}994 983



Fig. 2. Age-depth curve for core GeoB 3104-1.

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 andIversen, 1989). Pollen preparation of marine samples

included addition of exotic Lycopodium spores to deter-

mine 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 statist-

ical calculation. Marine micro-foraminifera were also

counted on the pollen slides.

For identi"cation of pollen grains and spores, mor-

phological 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 micro-

foraminifera. 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 plainforests, mountain vegetation has not been "nished, be-

cause 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 in-

cludes also radiocarbon dates, the sum of micro-

foraminifera, pollen concentration, pollen in#ux record

and a cluster analysis dendrogram.

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-

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 paleoc-

limatic 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 O signal re#ects local variations in surface

water temperature and salinity. The global Holo-

cene/LGM amplitude in O 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 oscilla-

tions 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)

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 predomi-

nant 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




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 Piaum H State. Hedyosmum is not

known from NE Brazil. Fern spores seems to be extreme-

ly rare in the caatinga region.

It is interesting to note, that the presence of Borreria

pollen grains (indicator for open vegetation types) de-

creases in the river samples from north to south, whilefern spores (indicator for wetter conditions) increases

along the eastern coast southwards. Spores of tree ferns,

e.g. from Cyathea (indicator for permanent moist condi-

tions), 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/ Pfa za-type, and a number

of other types occur in low percentages. Shrub and

tree pollen percentages are lower (15}25%) and pri-

marily represented by Melastomataceae/Combretaceae,

Arecaceae, Moraceae/Urticaceae, Alchornea, Myrtaceae,

Malpighiaceae, Hedyosmum, Mimosa and many other

taxa which were found in trace amounts (not shownin 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 cur-

rents 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 per-

centages 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 pol-

len 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 24,000C 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




F i g .

4 .

P o l l e n

p e r c e n t a g e d i a g r a m , s h o w i n g t h e m o s t f r e q u e n t p o l l e n a n d s p o r e t a x a o f m o d

e r n t e r r e s t r i a l s u r f a c e s a m p l e s f r o m

r i v

e r s ( 1 } 8 ) , l a k e s ( 9 } 1 0 ) , a n d f o r e s t s o i l s ( 1 1 } 1 5 ) , i n N E B r a z i l .




F i g .

5 .

P o l l e n p

e r c e n t a g e d i a g r a m , s h o w i n g t h e m o s t f r e q u e n t p o l l e n a n d s p o r e t a x a f r o m

t h e m a r i n e c o r e G e o B 3 1 0 4 - 1 .

T h e p o l l e n s u m

, o n w h i c h t h e p e r c e n t a g e c a l c u l a t i o n s a r e b a s e d ,

i n c l u d e s h e r b s ,

s h r u b s a n d t r e e s .




F i g .

6 .

P o l l e n

i n # u x d i a g r a m , s h o w i n g t h e i n # u x v a l u e s o f s e l e c t e d h e r b , s h r u b a n d t r e e t a x a , a n d t h e i n # u x o f s u m s o f g r o u p s .




F i g .

7 .

S u m m

a r y p e r c e n t a g e d i a g r a m , s h o w i n g t h e s

u m

o f t h e p o l l e n a n d s p o r e t a x a , m i c r o

- f o r a m i n i f e r a , p o l l e n s u m

v a l u e s , p o l l e n

c o n c e n t r a t i o n a n d p o l l e n i n # u x r e c o r d

, a n d t h e c l u s t e r a n a l y s i s

d e n d r o g r a m .




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 un-

disturbed and continuously sedimented Last Glacial to

Holocene marine deposits. The sediment generally con-

sists 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 peri-

ods of high pollen and spore concentrations about

40,000, 33,000 and 24,000

C yr BP and between 15,500and 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 tem-

peratures. 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 trans-

port of the NBC. Although these hydrographic changes

are most simply explained by variations in the tropi-

cal/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 inthe 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 lowpollen 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 alter-

nations 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 cur-

rents 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 Braz-ilian continent during glacial times, including the LGM,

while high deposition rates suggest short periods with

higher rainfall rates about 40,000, 33,000 and 24,000C 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 pos-sible 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 vegeta-

tion types such as caatinga and coastal savanna (abun-

dant Cyperaceae) in NE Brazil during the glacial and

early Holocene periods. Abundant taxa such as Borreria,

Alternanthera, Amaranthaceae/Chenopodiaceae, and

Gomphrena/ Pfa za are light tolerant and have strong

preferences to vegetation forms with an open canopy

(Gentry, 1993). No marked changes between the propor-

tions 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 toclosed 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.




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 thanthree 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 moun-

tain 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 ground-

water (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.




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 thelonger period of 15,500}11,800 C yr BP. This Lateg-

lacial interval was the wettest period recorded, which

allowed marked expansion of moist gallery and moun-

tain 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 cli-

matic 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 con-ditions 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}21,500C yr BP) and Cromm Hnia (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 mark-

edly longer than the wet short-term periods from the

record GeoB 3104-1. Continuously wet climatic condi-

tions are reported from central Amazonia (Colinvaux

et al., 1996).

The wet Lateglacial period between 15,500 and 11,800C 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 re-

cords from central Brazil (Agua Emendadas, and

Cromm Hnia) suggest that dry conditions prevailed (Sal-

gado-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 in-creasing 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, (Be-

hling, 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"ca-

tions 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 perma-

nent annual movement of the ITCZ over NE Brazil. In

their comparative study based on pollen and lake levelrecords in tropical and subtropical South America Mar-

tin et al. (1997) conjectured later humid period for eastern

Amazonia (based for example on records from the

Caraja H 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 con-

trolled (precession), insolation changes over South Amer-

ica 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-scaleatmospheric 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 high-

pressure 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 fa-

voring 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 high-

land 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 south-

eastern 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 Lateglacialmay 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




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 vegeta-

tion types. Di! erent herb taxa are predominant, re#ect-

ing primarily open caatinga vegetation types. Marine

pollen data indicate the occurrence of caatinga vegeta-tion 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 Atlan-

tic Ocean, which contain high concentration of pollen

and especially fern spores during relatively short inter-

vals 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 tropi-

cal/subtropical wind "eld. Timing, duration, and ampli-tude 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 consis-

tent 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 Depart-

ment of Environment, Brazil. Dr. Matthias Tintelnot,from the Senckenberg Institute in Wilhelmshaven (Ger-

many) 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

preparation of the pollen samples, when the "rst author

had a the post-doctoral position there. The Leibniz-

Labor in Kiel (Germany), and the Center for Isotope

Research in Groningen (The Netherlands), is acknow-

ledged for the radiocarbon dates. We thank Dr. Henry

Hooghiemstra and one anonymous reviewer for con-

structive and valuable comments on the manuscript. The"rst author thanks the Deutsche Forschungsgemein-

schaft (DFG) for the current scholarship.

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