Paleo-environmental change in Amazonian and African rainforest during the LGM

18 Pages·2006·0.83 MB·English

Palaeogeography,Palaeoclimatology,Palaeoecology239(2006)510–527
www.elsevier.com/locate/palaeo
Paleo-environmental change in Amazonian and African rainforest
during the LGM
⁎
D. Anhuf a,b, , M.-P. Ledru c, H. Behling d, F.W. Da Cruz Jr. e, R.C. Cordeiro f,
T. Van der Hammen g, I. Karmann e, J.A. Marengo h, P.E. De Oliveira i,
L. Pessenda j, A. Siffedine f, A.L. Albuquerque f, P.L. Da Silva Dias k
aPhysicalGeography,UniversityofPassau,Innstr.40,94032Passau,Germany
b FAPESP/DAAD,InstitutodeEstudosAvançados,UniversidadedeSãoPaulo,Av.ProfLucianoGualberto,TravessaJ,374,
05508-900SãoPauloSP,Brazil
c CNPq/IRD,UniversidadedeSãoPaulo,DptodeGeociências/UR55,06708-900SãoPauloSP,Brazil
dGeosciences,UniversityofBremen,P.O.Box330440Bremen,Germany
e InstitutodeGeociências,UniversidadedeSãoPaulo,RuadoMatão,Travessa14,321,05508-900,SãoPaulo,SP,Brazil
f DepartamentodeGeoquímica,UniversidadeFederalFluminense,MorrodoValonguinhos/n,24020-007Niterói,RJ,Brazil
g FundaciónTropenbos-Colômbia,Carrera21//39–45,SantaFédeBogotá,ApartadoAéreo036062BogotaD.E.,Colombia
hInstitutoNacionaldePesquisasEspaciais(INPE)/CentrodePrevisãodeTempoeEstudosClimáticos(CPTEC),Av.DosAstronautas,
1758-Jd.Granja,12227-010,SãoJosédosCampos,SP,Brazil
iLaboratóriodeGeociências,UniversidadedeGuarulhos,PracaTerezaCristina1,07023-070Guarulhos,SP,Brazil
j CentrodeEnergiaNuclearnaAgricultura(CENA),UniversidadedeSãoPaulo,AvenidaCentenário303,13400-970Piracicaba,SP,Brazil
k InstitutodeAstronomiaeGeofísica,UniversidadedeSãoPaulo(USP),RuadoMatão1226,05508-900SãoPaulo,SP,Brazil
Received17June2004;receivedinrevisedform10October2005;accepted16January2006
Abstract
Thepaperprovidesnewandcomparativeinsightintotheecologicalhistoryofthetwolargestcontinentaltropicalforestareas
duringtheLastGlacialMaximum(LGM).Thetropicalforestregionsareofparticularinterestbecausetheypresentalargesource
ofheatandhavebeenshowntohavesignificantimpactontheextratropicalatmosphericcirculation.Theyarealsothemostintense
land-basedconvectivecenters.Thus,especiallyfromthetropicspaleoecologicalinformationisneededasbenchmarksforclimate
modeling. The African data for LGM climates were published earlier including the reconstructed paleoprecipitation patterns
deducedfrom SSTs.
The tropical South American LGM data were interpreted from pollen, geochemical, and δ18O (stable oxygen isotope)
data from Brazil and selected surrounding areas. The available terrestrial data are consistent with the SST derived
precipitation data for the tropical forests in Brazil and for Africa. However, the impact of LGM climate extremes was less
severe in the Amazon than in the Congo basin. The LGM humid forest area (including evergreen and semi-deciduous forest
types) in Africa was probably reduced by 84%. In contrast, the Amazon humid forest area probably shrank to 54% of their
present-day extension. Still, there are different interpretations with respect to the amount of reduction of the Amazon forest
⁎
Correspondingauthor.PhysicalGeographyUniversityofPassau,Innstr.40,94032Passau,Germany.Fax:[phone].
E-mailaddress:[email protected](D.Anhuf).
0031-0182/$-seefrontmatter©2006ElsevierB.V.Allrightsreserved.
doi:10.1016/j.palaeo.2006.01.017
D.Anhufetal./Palaeogeography,Palaeoclimatology,Palaeoecology239(2006)510–527 511
area during the LGM. Although direct information about LGM climates in Amazonia is still limited the more detailed map
obtained in the present work, however, allows a more reliable characterization of the last glacial tropical environment than
previously published for the Amazon region.
©2006Elsevier B.V. All rightsreserved.
Keywords:LastGlacialMaximum;Climatehistory;Vegetationhistory;Rainforest;SouthAmerica;Africa
Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 511
2. Studyregions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 512
2.1. Amazonia. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 512
2.2. Congobasin. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 514
3. The LGM intropical SouthAmerica. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 514
3.1. Amazon basin. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 514
3.2. Borderandsurrounding areas of theBrazilian Amazonbasin . . . . . . . . . . . . . . . . . . . . . . . . . 517
3.2.1. Cerrado-humid forest transitions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 517
3.2.2. Northernneotropicalsavannas:LlanosOrientales . . . . . . . . . . . . . . . . . . . . . . . . . . . 518
4. Summary of the resultsfor Amazonia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 518
5. Summary of results fromAfrica . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 518
6. Paleovegetation map ofAmazonia andAfrica. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 520
7. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 522
7.1. Interpretation of thepaleoecological conditions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 522
7.2. IntercomparisonoftheAmazonandtheCongobasins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 523
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 524
References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 524
1. Introduction periods of the past were selected worldwide (COH-
MAP, 1988). The Last Glacial Maximum (LGM)
Climate, climate changes, and climate predictability (18,000±1000 14C yr BP) and the mid-Holocene are
havebecomeincreasinglymoreimportantwithinsocial the two key periods adopted by the Paleoclimate
andscientificdiscussionssince1990.Climatechanges, Modeling Intercomparison Project (PMIP-IGBP-
induced naturally or by human activities, have direct PAGES) (Joussaume and Taylor, 1995). The LGM
implications on our environment and therefore on represents an experiment with enlarged ice sheets and
human society. The knowledge of an enhanced human low atmospheric CO . The mid-Holocene represents
2
influence on the atmosphere and the earth's climate by contrast an orbital forcing experiment, with the
since the beginning of the 20th century has led to perihelion in the northern summer/autumn and a
global collaboration to analyze the dimension, the greater-than-present axial tilt.
causes and the consequences of the anthropogenically Paleoclimate model reconstructions failed for
induced climatic change (Houghton et al., 2001) in South America mainly because of the scarcity of
order to predict the possible implications on future modern climate data and the sparse regional coverage
climate developments. This also includes a better of paleoclimate data (Farreira et al., 1999; Prentice et
understanding of natural variability and stability of the al., 2000). Special focus of this paper is the regional
climate system in general. In order to model the development of vegetation and climate of the
climate system of the earth, either forwards into the Amazon and adjacent areas during the LGM that is
future or backwards into the past, it is necessary to not represented in the models. Amazonia covers the
understand the Earth's system, especially the interac- largest continuous tropical lowland forest area.
tions between atmosphere, biosphere and ocean. Tropical forests contain as much as 40% of the
In order to verify the ability of global circulation carbon stored in terrestrial biomes and are home for
models (GCMs) to simulate the changes in regional up to 90% of all living species (Ozanne et al., 2003).
cli- mate under different boundary conditions, key As the Amazon basin provides 20% of the total fresh
512 D.Anhufetal./Palaeogeography,Palaeoclimatology,Palaeoecology239(2006)510–527
water worldwide, a reliable reconstruction of the Dry Corridor and between 0°N and 10°S, and the wes-
ecological conditions — prevailing under different tern and southwestern part (west of 70°Wand south of
climatic scenarios in the past — is essential in 10°S). The modern natural vegetation distribution was
achieving major progress in environmental modeling. adoptedfromthewidelyacceptedIBGEsystem(Fig.1)
As the number of well-dated paleoecological sites (Veloso et al.,1991).
hasincreased considerablyduringthelastfew years,at Annual rainfall in northern South America varies
least since the last COHMAP and BIOME (Prentice et greatly from less than 400 mm in Northeast Brazil and
al., 2000) evaluations, the paper provides a much some parts of the Caribbean coast of South America to
needed update of past ecological conditions and more than 3000 mm in the upper watershed of Rio
climates within the South American tropics and Negro.ThreecentersofabundantrainfallintheAmazon
subtropics for the last 21,000 years with special basin can be identified. One is located in Northwest
emphasisontheLGM.Themainprogressisinassessing Amazonia, with more than 3600 mm per year. Another
paleoprecipitationatthedifferentsites.Thecomparison regionwithabundantrainfallisthecentralpartofAma-
with available data from the African tropical forest zoniaaround5°Swith2400mmperyear.Athirdcenter
enablesthedescriptionofsimilaritiesanddifferencesin is found in the northeastern area close to the mouth of
the development of the ecological conditions for the theAmazonRivernearBelém,withmorethan2800mm
tropical continentalzones. per year. In the Rio Negro basin area, in northwestern
Amazonia, the rainfall is abundant throughout the year
2. Study regions reachingitsmaximumfromApriltoJune.Inthecentral,
the western and southwestern Amazon areas the rainy
2.1. Amazonia season is concentrated during the southern hemisphere
summer (November–March/April) providing almost
TheAmazonregionisofparticularinterestbecauseit 80% of the total annual amount (Rao and Hada, 1990;
representsalargesourceofheatinthetropicsandhasbeen Figueroa and Nobre, 1990; Marengo, 2003). The ex-
shown to have a significant impact on the extra tropical tremely high and localized values of precipitation in
circulation; also it is the largest and most intense land- narrowstripsalongtheeasternsideoftheAndeanslopes
based convective center (Grimm and Silva Dias, 1995; arethoughttobeduetoupslopecondensationandarain
MarengoandNobre,2001).DuringtheSouthernHemis- shadow effect on the lee side.
phere summer when convection is best developed, the The coastal maximum is caused by nocturnal
Amazon basin is one of the wettest regions on Earth. convergence between the trade wind and the land
Amazonia, of course is not isolated from the rest of the breeze (Marengo and Nobre, 2001). Today's dry sector
worldandaglobalperspectiveisneededtounderstandthe in the eastern Amazon is related to the fact that as the
natureandcausesofclimatologicalanomaliesinAmazo- seabreezesqualllinespropagatetotheWest/Southwest,
niaandhowtheyfeedbacktoinfluencetheglobalclimate they travel over this region during the night, when the
system.Withamodernmeanprecipitationof2.0–5.9m/yr intensity ofthe systemisata relativeminimum (Cohen
(FigueroaandNobre,1990;MarengoandNobre,2001), et al., 1995). As the sun rises, the squall line intensity
Amazonia's climate is likely to limit the environmental peaks up and heavier precipitation is expected to the
response to a precipitation changethatwould drastically West. The LGM displacement of the coast due to
alterthevegetationofthegenerallydrierregionofequa- generally lower sea levels of the order of 120 m would
torialAfrica(Anhuf,2000).Nevertheless,anAmazonian have had a significant impact on the horizontal distri-
“DryCorridor”existsnowadaysbetweenBelém(1°28′S, butionofprecipitationinviewofthismechanism.Thus,
48°27′W)andSantarém(2°25′S,54°42′W)withamean the area directly influenced by the sea breeze climates
annual precipitation below 1.75 m/yr (Figueroa and would have been located 200 to 500 km to the
Nobre, 1990; Van der Hammen and Absy, 1994). But Northeast.
eventhisdrierareaiscoveredwithevergreenandsemi- ThenortheasternAmazon,the“DrySector”,andthe
deciduousforeststoday. northwesternAmazonregionaswellasthenortheastern
To describe the situation within the Amazon basin BraziliancoastbetweenFernandodeNoronhaandSal-
during the LGM we subdivide the region into five dif- vadorreceiveaconsiderablepartoftheirrainduringthe
ferentareas.ThenortheasternAmazoncoversthesector northern hemisphere summer (April to September)
east of the “Dry Sector”, the “Dry Sector” itself, the (Uaupés 50%, Belém 44%, Santarém 50%, Salvador
northwesternpartoftheAmazon(westofthedrysector 64%, and Recife/Olinda 73% (Ratisbona, 1976)). Al-
and north of the equator), the central part (west of the thoughthetimingoftheannualcycleofrainfallislargely
D.Anhufetal./Palaeogeography,Palaeoclimatology,Palaeoecology239(2006)510–527 513
Fig.1.VegetationmapofBrazil(adaptedfromIBGE,1993).
controlled by the sun, rainfall in different parts of the andBras(1993).Allofthemindicatetheactiveroleof
basin is triggered by different rain producing mechan- the evapotranspiration from the tropical forest in the
isms(GarreaudandWallace,1998;Fischetal.,1998). regional hydrological cycle, although the latter study
Regional water balances are calculated based on indicates a lesser role. The aerological estimates of the
stream flow data, observed precipitation and evapo- evapotranspiration over the eastern and central parts of
transpiration measurements. Studies on recycling of the basin averaged 3 to 3.5 mm/day. The different esti-
water in the hydrological cycle of the Amazon basin matesofmoisturerecyclingintheAmazoniavaryfrom
have been performed during the last two decades by 25% to 75% related to the percentage of total annual
Lettau et al. (1979), Salati (1987), Salati et al. (1979), rainfall of the Amazon basin originating from water
Salatiand Voce(1984), Salatiet al.(2001), and Eltahir vapor import from thetropical Atlantic.
514 D.Anhufetal./Palaeogeography,Palaeoclimatology,Palaeoecology239(2006)510–527
2.2. Congo basin March to June, the southwestern monsoon establishes
resulting in the first “long” rainy season. During the
In contrast to the Amazon basin, the Congo basin ITCZ's northernmost position in July and August the
receiveslowerannualprecipitation,ingenerallessthan equatorial east African highlands remain almost dry
2000 mm/yr (UNESCO, 1978). Higher rainfall, com- beforethesecond“short”rainyseasonstartsinOctober,
parable to that of the western Andean ridge, are regis- lasting until the end of November, caused by the
teredonly inareaswithconsiderabletopographic relief southward shift ofthe ITCZ.
like the east African ridge, the southern side of Mount West Africa and the Congo basin receive the water
Cameroon and along the Guinean Highlands between vapor from theeast and southeast Atlantic when this is
Greenville(5°01′N,9°03′W)andCapePalmas(4°25′N, coolest(australwinter)andthewatervaporpoolofEast
7°50′W). The amount of precipitation as well as the AfricaoriginatesinthewesternIndianOceanwhenitis
duration andtheannualdistributionof rainfall depends warmest at theend of theaustralsummer.
onthemajorwatervaporsourcesforAfrica,theSouth–
East Atlantic along the west coast of Africa and the 3. The LGM in tropical South America
Indian Ocean along the east side of thecontinent.
InAfrica,thehumidtropicalforestswhichdominate 3.1. Amazon basin
the floristic Guinea region, are subdivided into ever-
green forests (Fig. 2), in which the annual dry season The Amazon rainforest evolution during the glacia-
does not exceed two months, and into semi-deciduous tionsoftheQuaternaryhasbeenstronglydebatedduring
forests with no more than three to four dry months the last decade. The discussion — whether there was
(Anhuf, 2000). The Sudan region is dominated by dry fragmentationoftheforestornot—openednewideas
forests and savannas, comparable to the Cerrado in onhowglobalclimaticchangescouldimpactthetropical
South America. Most trees shedtheirleaves duringthe rain forests. Two types of hypothesis emerged: 1) The
arid season when it lasts for more than four months. Amazonianrainforestwasfragmentedinrefugiaislands
Thegeneralatmosphericcirculationoverbothequa- or its areal extension remained relatively stable. 2) Its
torial areas is controlled by the seasonal movements of floristic composition was submitted to species re-
theITCZ.EquatorialAfricaconsistsofthreemainareas: associations because of connections with the Andean,
thesoutherncoastofwestAfricabetween5°Nand9°N, Tepuyan, and Atlantic rainforest ecosystems. Both
the Congo basin between 5°N and 6°S, and the hypotheses came to the conclusion that the forest was
equatorial east African highlands between 11°S and different from the one we observe today and that it
14°N. experiencedtransformationsindistributionandfloristic
Thelargeamountsofwatervaporthatmaintainhigh composition during the last glaciation. It also empha-
rainfall quantities along the west African coast and sizeddifferencesintheexpressionoftheclimaticsignal
withintheCongobasinoriginatemainlyfromthesouth- betweenwesternandeasternAmazonbasin(Colinvaux
easternAtlanticOcean.However,rainfalltotalsinequa- etal.,1996;VanderHammenandHooghiemstra,2000;
torial Africa are relatively modest compared to other Colinvaux and De Oliveira, 2001; Van der Hammen,
equatorialregionswithinthetropicsbecausethecoastal 2001;HafferandPrance,2001).
areasadjacenttotheCongobasinareoftencooledbythe Only seven pollen records located in the Amazonian
Benguelacurrentreducingtheinflowofwatervaporinto rainforestareaincludingtheAmazonfandatebacktothe
the continent. The seasonal movements of the ITCZ last glacial maximum (Table 1): Katira (9°S, 63°W),
createamajordryseasonduringDecember,January,and Carajás(6°S,50°W),HillofSixLakes(0°16′N,66°4′W),
February when dry northeasterly trade winds prevail Maicurú(0°30′S,54°14′W),LagunaBellaVista(13°37′S,
overtheregion.WhentheITCZreachesitsnorthernmost 61°33′W),LagunaChaplin(14°28′S,61°04′W),ODPsite
positioninJulyandAugustashortdryseasonatthecoast 932(5°13′N,47°2′W(Absyetal.,1991;VanderHammen
cansometimesbeobserved. and Absy, 1994; Siffedine et al., 2001; Colinvaux et al.,
Generally exceptional low rainfall characterizes the 1996; Haberle and Maslin, 1999; Mayle et al., 2000;
equatorialregionofeastAfrica.Twomonsoonsystems Santos et al., 2001; Colinvaux and De Oliveira, 2001;
dominate the climate system. During the northern he- Bushetal.,2004).
misphere winter (December to March) the dry north- A14CyrBPdateof18,500atKatiraisrelatedtohigh
eastern monsoon passing over northeast Africa or the frequencies of grass pollen and an almost total
coolSomalicurrentbringingmostlydryairmassesinto disappearance of arboreal pollen, while the 13C values
the equatorial region of the highlands. In spring, from indicatethedominanceoftropicalgrassesandcolluvial
D.Anhufetal./Palaeogeography,Palaeoclimatology,Palaeoecology239(2006)510–527 515
a.
c
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i
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or
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u
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al
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.
Table1 A
SitesprovidingdatedinformationofLGMecologicalconditionsbasedonpollenorplantmacrofossildatawithintheAmazonBasin(01–08)andfromtheAmazonfan(09) nh
u
f
Number Site Location Elevation Actualclimate Actualvegetation 1800014Cyears 1800014Cyears Reference et
a
(a.s.l.) BPclimate BPvegetation l.
/
01 LagunaelPinal 4°08′N/71°23′W 180 1200–2000mm Grasssavannaand Lessrainfall savanna Behlingand Pa
(Colombia) 4–5drymonths galleryforestswith thantodayor Hooghiemstra,1999 lae
o
Mauritiapalms longerdryseason g
e
02 LagoaPata 0°16′N/66°41′W 250–300 N3000mm Tropicalrainforest 5°Ccooler, Rainforest Colinvauxetal.,1996, og
r
LagoaGragao nodryseason drier:Lake expansionof Santosetal.,2001, ap
h
LagoaVerde leveldecrease Araucaria+ Bushetal.,2004 y
,
(SeisLagos) Weinmannia P
a
03 Maicuru 0°30′S/54°14′W 550 2000–2500mm Forest ? Hiatus ColinvauxandDe la
e
o
3monthslittlerain Oliveira,2001 c
04 Carajas 6°20′S/50°25′W 700 1500–2000mm Tropicalrainforest, N30%lessrain HiatusSavanna Absyetal.,1991, lim
a
3monthslittlerain Edaphicsavannas expansionbefore Sifeddineetal.,2001 to
lo
andafter g
y
05 Katira 9°S/63°W b200 2000–2500mm Tropicalrainforest Verydry Drygrasssavanna VanDerHammen ,P
1000–1500mm at18500yearsB.P. andAbsym,1994 ala
06 Forest(46) 8°21′S/63°57′W 80–150 1800–3500mm Forest WetterCooler? Forest Freitasetal.,2001 eo
e
3–4monthslittle co
rain log
07 NoelKempff 13°37′S/61°33′W 210 1500mm Tropicalrainforest/dry ? Hiatus Mayleetal.,2000 y2
3
LagunaBella deciduousforest 9
Vista (2
0
08 NoelKempff 14°28′S/61°04′W 210 1500mm Tropicalrainforest/dry ? Savanna Mayleetal.,2000 06
)
LagunaChaplin deciduousforest 5
1
09 ODP932 5°13′N/47°2′W –3334 ∼2700mm(Belém) Tropicalrainforest HaberleandMaslin, 0–
5
Nodryseason (Belém) 1999 2
7
D.Anhufetal./Palaeogeography,Palaeoclimatology,Palaeoecology239(2006)510–527 517
sedimentation indicates even an incomplete vegetation al., 1996) but possibly with more deciduous species
cover (Absy and Van der Hammen, 1976; Van der (Van der Hammen and Hooghiemstra, 2000).
Hammen and Absy, 1994). The Hill of Six Lakes has Analysis of Amazonian evaporation dependent veg-
been intensively investigated since 1996 by Colinvaux etation and lakes also show a strong decrease in preci-
and his colleagues showing that forest taxa dominated pitationduringtheLGM,e.g.thetropicalcloudforestof
the vegetation cover also during the LGM (Bush et al., the Eastern Cordillera in Bolivia. Siberia, nowadays
2004).Mayleetal.(2000)reportfromLagunaChaplin within the tropical cloud forest zone, is located at an
thatsavannacommunitiesdominatedtherespectivearea altitude of 2920 m in Bolivia (17°50′S, 64°43′08″W)
continuously between 40,000 and 2240 14C yr BP. Ha- (MourguiartandLedru,2003a).TheLGMisrepresented
berle andMaslin (1999) publishedresults fromadeep- by2mofsedimentand3radiocarbondates23,660±100,
sea core from the Amazon fan covering the last 21,900±90,19,150±7014CyrBPandshowslowarbo-
50,000 years. During the LGM the authors attested the realpollenfrequencies,4%to10%,highquartzcontent
lowest pollen concentration values within the whole toover30%andlowtotalorganiccarbon(TOC)ofless
time span, a significant increase of wind-transported than 0.5% suggested an open landscape and a dry, cold
pollenfromAndeantaxalikeAlnusandPodocarpusbut climate. More to the North, paleoenvironmental data
atthesametimethepollenfromPoaceaeandAsteraceae fromLakeHuiñamarca,isactuallyconnected toL.Titi-
remained low. The authors pointed out that no general caca today as a sub-basin, (16°20′S, 68°57′45″W, at an
change in Amazon ecosystems were detected but they altitudeof3810mandunder19mdepthofwater),with4
also did not contradict to the possibility of a moderate radiocarbon dates (21,000±260, 19,625±220, 19,090±
extensionofsavannaecosystemsupto32%oftheentire 200, 18,185±180 14C yr BP) within 2 m of sediment
catchment area. The respective core represents only a depositionreveallowTOCvaluesand highpercentages
single late Quaternary fan record from the entire for Isoetes, a submerged ferninoligotrophicwaters, for
Amazon basin. Thus, it is advisable to be cautious in Valeriana,aherbfrommesicwetlandsofthehighAndes,
interpretingthesedataparticularlywhendatingisbased and low algal frequencies (Mourguiart and Ledru,
on an age model derived from δ18O records and 2003a).LakeHuiñaimarca attests ofatleast a reduction
geomagnetic field excursiondata. of ∼18 m of water which was not perceptible under
All the following records show a hiatus in sedimen- 120 m depth of water in Lake Titicaca (Mourguiart and
tationbetweenrespectively23,000and13,00014CyrBP Ledru, 2003b). These data confirm a relatively low
(Carajás), 30,000 and 16,000 14C yr BP or between reductioninwaterlevelintheAndesofBoliviacompared
25,690 and 17,410 14C yr BP (Maicurú), and 38,600 tootherregionsoftropicalSouthAmerica.
and11,03014CyrBP(LagunaBellaVista).Thishiatus
isassociatedwithalackofdepositionoforganicmate- 3.2. Border and surrounding areas of the Brazilian
rialduringthousandsofyears(Ledruetal.,1998)and/ Amazon basin
orstrongerosiveconditions. Presence of tropical semi-
deciduousdryforestattheCerrado-rainforestboundary 3.2.1. Cerrado-humid forest transitions
innortheasternBolivia(BellaVista:Mayleetal.,2000) Carbonisotopes(12C,13C,14C)ofsoilorganicmatter
was documented at ca. 30,000 yr BP after which a were used to evaluate and establish the chronology of
hiatus was recorded lasting until the beginning of the past vegetation of patches of Cerrado surrounded by
Holocene. rainforestinthestatesofRondôniaandAmazonas.Large
At Lagoa da Pata, geochemical analysis showed a ranges in δ13C values were observed from profiles ob-
sand layer intercalated by two organic-rich levels. This tainedintheCerradoarea(−27‰to−14‰)andinthe
sandy facies with lower carbon and water content and forest(−26‰to−19‰)reflectingchangingdistribution
high bulk density is interpreted to reflect sudden and of13C-depletedC3forestand13C-enrichedC4grassland
torrential rains, typical of seasonal climates and vegetation. At the base of the soil profiles, between
different from today. After this probably drier episode, 17,000and900014CyrBP(km46:16,940±14014Cyr
dated at ca. 18,000 14C yr BP, increase in lacustrine BP),δ13CvaluesreflectC3plantsdocumentingpresence
productivity associated to lake level rise is recorded of forest (Freitas et al., 2001). This corresponds to the
documented by an increase in the chlorophyll edgeofthepredictedforestpatchintheLGMvegetation
derivates and the carbon flux. The C/Nvalues dropped mapofVanderHammenandHooghiemstra(2000)and
indicating an increase in algae organic matter VanderHammen(2001)andthecorrespondingsavanna-
contribution characteristic of open water. However, forest gradient Katira–Porto Velho–Humaitá. δ13C data
rainforest survived near Lagoa da Pata (Colinvaux et also indicate that savanna grasses (C4 plants) have
518 D.Anhufetal./Palaeogeography,Palaeoclimatology,Palaeoecology239(2006)510–527
influencedsignificantlythecompositionofthevegetation elements. Between 28,000 and 17,000 14C yr BP the
reflectingdrierclimatesafter9000 14CyrBP(Pessenda arboreal pollen decreased to 4–10%. After 16,000 14C
etal.,1998).However,theisotopeanalysisbasedonthe yr BP, Siberia showed an increase of open forest-taxa
humin fraction do not give any evidences as to which again. Considering that the temperature decreases by
kind of forest persisted shortly after the LGM in that 5 °C (Stute et al., 1995) the zone of maximum preci-
specificareaofsouthernAmazonia. pitation was lowered by up to 500–600 m due to the
lowering of the respective condensation levels if
3.2.2.Northernneotropicalsavannas:LlanosOrientales precipitations were similar to the modern ones. The
TheLGMintheLlanosOrientalesinColombiainthe respective pollen record from Siberia represented an
Laguna El Pinal region (4°08′N/70°23′W) was charac- open landscape and a dry and cold climate during the
terizedbysavannavegetationandwithveryfewwoody LGM. The modern-day Andean cloud forest, provided
taxa. The respective vegetation reflects the driest that forest type had survived during the LGM, might
climatic conditions of the last 18,000 years (Behling havedescendedtoalevelofabout2000m(asl)during
and Hooghiemstra, 2001). that period according to the LGM cooling. Thus, one
wouldexpectAndeanforestpollen,especiallyallwind-
4. Summary of the results for Amazonia transportedpollentypes,tooccur intheSiberiarecord,
which would have been ca. 800 m above the proposed
Fromthepollenandfewgeochemicalrecordsinthe LGM Andean forest limit. However, Mourguiart and
AmazonbasinincludingtheAmazonfanthatdateback Ledru (2003b) did not find any pollen from this lower
totheLGMwehaveclearindicationofacoolerclimate cloud forest.
with average temperature 4.5±1 or 5±1 °C lower than IntheanalysisofthecoresobtainedbetweenBR319,
that of today for the region and the northeastern Brazil km 46 north of Porto Velho (8°21′S, 63°57′W) to the
(Stuteetal.,1995;VanderHammenandHooghiemstra, South including Katira (less than a hundred kilometers
2000;Bushetal.,2001).Thisfactmightberesponsible furthersouth),LagunaBellaVista,andLagunaChaplin
for the appearance of mountainous species like Alnus (14°28′S, 61°04′W) a clear change in the LGM vege-
and Podocarpus in lowland Amazonian forest sites tation cover appears. The records show forest in nor-
includingtheAmazonfanduringtheLGM(Haberleand thern Rondônia, savanna at Katira, a hiatus at Bella
Maslin, 1999). Vista but clear indication of savanna vegetation at the
Other observational evidences around the Amazon southernmost end at Laguna Chaplinofthis transect.
basin are available to give indirect information about the Nevertheless, an inconsistent picture of the LGM
climate in the Amazon region: Reconstructions of tem- vegetation conditions in the Amazon basin remains.
peraturesintheAndesbetween4000and1500maltitude The point of view that claims that the Amazon
above sea level (asl) have been presented by Van der lowland forests were not replaced by savanna during
Hammen and Hooghiemstra (2000). They found that the the LGM (Colinvaux and De Oliveira, 2001; Bush et
glaciallapseratewas0.76°C/100m,0.16°C/100msteeper al., 2002; Haberle and Maslin, 1999) can no longer be
than present day. However, temperature is one of the as- supported by the data. On the other hand, data support
pects to be considered with respect to the impact of the view that the Amazon evergreen forest border on
changingclimateonthevegetationinmountainousregions. the northern hemisphere was located probably about
Precipitationwithinthetropicsshowsacharacteristic 200 km further south and that the same border on the
vertical distribution as a function of height above sea southern hemisphere was located probably 300 km
level.Thezoneofmaximumprecipitationisgenerallynot further north during the LGM (Van der Hammen and
locatedinthetropicallowlands,butwithinthemountain- Hooghiemstra, 2000; Behling, 2002) The latter was
ousbeltbetween800and1500m(asl).Abovethelevelof also corroborated by paleovegetation simulations
maximum condensation precipitation decreases consid- (Cowling et al., 2001).
erablyandamuchweakersecondcondensationlevelcan
beobservedbetween2700and3200mwithinthetropical 5. Summary of results from Africa
cloudforestsbelt(Lauer,1989).
Thus, the pollen records from Siberia (2920 m) and TheavailableAfricansiteswithdatedpaleoenviron-
LakeHuiñaimarca(3810m)areofsomehelptorecons- mental information have been discussed in detail in
truct the tropical lowland vegetation. Before the LGM Anhuf (2000). Only the general picture of the LGM
(40,000–29,000 14C yr BP) the vegetation at Siberia environment in tropical Africa is summarized below
was dominated by an open forest with cloud forest (Table 2).
D.Anhufetal./Palaeogeography,Palaeoclimatology,Palaeoecology239(2006)510–527 519
Table2
SelectedsitesprovidingdatedinformationofLGMecologicalconditionsfortropicalAfricabetween10°Sand20°N(forfurtherinformationsee
Anhuf2000)
Number Site Location Elevation(m) DatedMaterial 14CyearsBP Author
01 74KL,ArabianSea 14°19′N/57°20′E −3416 Carbonates 20580−1280BP Sirockoetal.(1991)
02 LakeAbhé,Ethiopia 11°15′N/42°00′E 240 Diatoms,SLC 17,100±400BP Gasse(1977)
20,500±400BP
03 SacredLake,Mt.Kenya, 0°10′S/37°19′E 2400 P 15,695±70BP Olagoetal.(2000)
Kenya 20,265±80BP
04 LakeNaivasha,Kenya 0°45′S/36°20′E 1890 SLC 12,270±180BP Maitima(1991)
20,900±1700BP
05 Mt.Elgon-LabootSwamp, 0°57′N/34°37′30′′E 2880 P 13,776±80BP Hamilton(1982)
Kenya 23,073±120BP
06 CheranganiHills,Kaisungor 1°12′N/35°15′E 2900 P 17,000±300BP Coetzee(1967)
Swamp,Kenya
07 Karimu,Kenya 0°30′S/36°41′E 3040 P 17,900±150BP PerrottandStreet-Perrott
21,540±160BP (1982)
08 PilkingtonBay,Uganda 0°18′N/33°20′E 1134 P 14,730±200BP Kendall(1969)
09 LakeMobutu,Uganda 1°50′N/31°10′E 619 P 14,700±260BP Beuningetal.(1997)
20,120±200BP
10 Ahakagyezi(AH2),Uganda 1°07′S/29°54′E 1830 P 15,640±110BP Taylor(1990)
18,770±120BP
11 Sd-24LakeTanganyika, 4°30′S/29°20′E 773 P 16,817±156BP Vincens(1993)
Tanzania 32328±894BP
12 KamiranzowuSwamp, 2°25′S/29°18′E 1950 P 15,745±150BP Hamilton(1982)
Rwanda 22,120±250BP
13 K-Kuruyange,Burundi 3°28′S/29°34′E 2000 P 18,900±700BP BonnefilleandChalié
21,500±1250BP (2000)
14 Ijenda,Burundi 3°29′S/29°33′E 2150 P 21,870±470BP RocheandBikwemu
(1989)
15 LakeChesi,Zambia 9°05′S/29°45′E 928 LF 12,500±550BP Stager(1988)
33,900±2000BP
16 Walikale,Congo 1°15′S/27°50′E 662 P 17,650±1020BP Runge(1996)
18,310±860BP
17 Hv12945Imbonga,Congo 0°42′7ʺS/19°43′5′′E 20 P 19,920±765BP Preuss(1990)
18 Gama2Ngamakala,Congo 4°18′S/15°14′E 400 P 16,300±140BP Elengaetal.(1994)
22,170±600BP
19 GeoB1016Southeast- 11°46′S/11°40′5′′E −3410 P 12,000cal.BP ShiandDupont(1997)
Atlantic,Angolamargin 24,100cal.BP
20 GeoB1023Southeast- 17°09′S/11°01′E −1978 P 15,070±60BP Shietal.(1998)
Atlantic,Angolamargin 17890±80BP
21 KS12GulfofGuinea 3°52′06′′N/1°56′16′′W 0 P 17,000cal.BP LézineandVergnaud-
22,000cal.BP Grazzini,(1993)
22 BM6LakeBarombi- 4°39′N/9°24′E 300 P 20,240±1448BP Brenac(1988)
Mbo,EastCameroon 22,030±2140BP
23 GIK16856GulfofGuinea, 4°48′N/3°24′E −2860 P 18,300cal.BP DupontandWeinelt
NigerDelta (1996)
24 LakeBosumtwi,Ghana 6°32′N/1°23′W 100 P 18,880±190BP Talbotetal.(1984)
20,220±230BP
25 GIK16776Atlantic, 3°44′N/11°24′W −4242 P 12,000cal.BP Jahnsetal.(1998)
WestAfrica,Liberia 24,000cal.BP
26 M.16017−2Atlantic, 21°15′N/17°48′W − P 16,060±230BP Hooghiemstra(1988)
North-WestAfrica 20,060±300BP
Acronyms:P=Pollen,SLC=SeaLevelChanges,LF=LimnicFauna.
In the southeast of Ivory Coast, near the border to permanence of rain forest on the adjacent continent
Ghana, only small relicts of the semi-deciduous rain- duringtheLGM(LézineandVergnaud-Grazzini,1993).
forest existed during the LGM. Sediments of a marine In contrast, this forest type remained in the western
core situated off the Ghanaian margin recorded the highlands of Guinea as well as in the area of Cape