late quaternary climate variability and vegetation response in ziro lake basin eastern himalaya a multiproxy approach abstract pollen phytolith and stable carbon isotopic records provide new insights into the palaeoenvironmental and palaeoclimatic changes in ziro lake basin sub himalayan arunachal pradesh india since pre lgm time phytoliths record a minor change in grass woodland cover and appear to be more sensitive than pollen grains to climate fluctuations both pollen and non pollen palynomorph data suggest prevalence of a dense c3 species dominated moist semi evergreen forest in the area until the lgm which shows conformity with 13c data the phytolith assemblage indicates an alteration in forest cover with expansion of c4 grasses during the lgm the study further indicates a climatic amelioration with intensification of south west monsoon during 10 2 3 8 ka and an expansion of forest cover after 3 8 ka there was a rising trend of dryness shrinkage in forest cover and a slight increase in c4 species while c3 plants dominated ecosystem variability also points towards a hydrological transformation in the area since pre lgm time application of coexistence approach on pollen data reveals that prior to the lgm the mean annual temperature and mean annual precipitation were approximately 19 3 0 001 c and 1925 15 mm respectively between 10 2 and 3 8 ka mat was about 19 4 0 5 c while map was 1901 41 3 mm between 3 8 and 1 2 ka and onwards a slight increase in mat 0 3c was observed with further decrease in map to 1861 33 4 mm during pre and post lgm times mat was more or less similar in the ziro lake basin which increased gradually after 3 8 ka and was 1 2 c higher than today prior to the lgm map was higher than the present day by 94 mm between 10 2 and 3 8 ka by 70 mm and since 3 8 ka onwards by 30 mm showing a tendency of gradual decline suggesting a consequent increase in dryness

amazonia during the last glacial abstract new data on the vegetational history and quaternary geology of amazonia permit an improved reconstruction of past environments in amazonia during the last glacial period although limited data from rondonia carajas and guyana show that in certain areas savanna type vegetation and savanna forest had replaced the rain forest during the late pleniglacial ca 22 000 13 000 yr b p the amazonian forest may have been split up into one major west amazonian and several other medium size forest areas this suggests a decline in rainfall of 500 to 1000 mm a reduction of 25 to 40 temperatures may also have been 2 to 6 c 4 2 c lower than today possibly substancially influencing amazonian vegetation during the humid middle pleniglacial 55 000 26 000 yr b p rivers carried a lot of water and sediment resulting in the deposition of lower terrace sediments with one dry interruption around 40 000 yr b p carajas and katira in carajas there is evidence of dry periods ocurring at about 40 000 yr b p and during the early pleniglacial ca 60 000 yr b p rivers carried little water and incised into the low terrace sediments during the dry late pleniglacial water levels rose during the late glacial 13 000 10 000 yr b p or at the beginning of the holocene 10 000 yr b p sedimentation in and of the present inundation valleys commenced after that

variability of internal tides in the laurentian channel data from three sequential stations of thermistor chains and current meters along the main axis of the lower st lawrence estuary during the summer fall period in 1978 were analyzed to help understand generation and variability of the internal tide the lagrangian or direct tracing method has been developed to compute the displacements of internal tides which can overcome limitations of the eulerian method caused by the very small vertical temperature gradients internal tides of semidiurnal frequency were observed but diurnal tides were not in both the time domain and frequency band the surface diurnal tide behaves like a standing wave rather than a progressive one due to the nonlinear interaction of the internal tide generated locally near the sill with topography quarter diurnal and higher frequency oscillations were also generated the displacement of internal tides can reach 80 40 and 30 m during spring tides respectively at station 1 and at two downstream stations 3 and 5 the internal tides propagate seaward with attenuation downstream which mainly results from changing vertical stratification conditions but may also be partly attributed to wave breaking and turbulent mixing in the upper layer and bottom and lateral friction the amplitude ratio of s2 m2 is smaller 0 2 for the baroclinic current than for the barotropic current 0 24 at station 1 but becomes larger at stations 3 and 5 this implies the presence of the narrower response frequency band of the baroclinic tide to the barotropic forcing near the generation site the progressive semidiurnal and quarter diurnal internal tides were of the poincare type which implies a three dimensional structure the nutrient pumping due to the internal tides was confirmed to occur only near the generation region of the internal tide this convergence zone of higher primary productivity is considered to be equivalent to the rotor clouds in atmospheric mountain waves

holocene palaeoenvironmental reconstruction in norteastern brazi inferred from polen charcoal and carboon isotope records soils in the barreirinhas region maranhao state were sampled for 613 c analysis and buried charcoal fragments in the soils were radiocarbon dated three soil profiles collected in forested areas around the lagoa do caqo and one in a woody savanna mixture of non arboreal and arboreal species located approximately 10 km southeast of the lagoa were studied a high resolution pollen record was obtained from lake sediments showing that forest vegetation was predominant in the area in the early holocene from approximately 10 000 14c yr bp the pollen spectrum gradually changed suggesting the dominance of open savanna communities these were transformed to a more forested landscape woody savanna from approximately 7500 yr bp the lake sediments also record evidence of fire indicated by buried charcoal particles at several soil depths during the holocene the 613 c analysis of soil organic matter som indicates that from between approximately io0000 yr bp and 9000 yr bp to 4000 yr bp a woody savanna

fifty thousand year vegetation and climate history of noel kempff mercado national park bolivian amazon abstract pollen and charcoal records from two large shallow lakes reveal that throughout most of the past 50 000 yr noel kempff mercado national park in northeastern lowland bolivia southwestern amazon basin was predominantly covered by savannas and seasonally dry semideciduous forests lowered atmospheric co 2 concentrations in combination with a longer dry season caused expansion of dry forests and savannas during the last glacial period especially at the last glacial maximum these ecosystems persisted until the mid holocene although they underwent significant species reassortment forest communities containing a mixture of evergreen and semideciduous species began to expand between 6000 and 3000 14 c yr b p humid evergreen rain forests expanded to cover most of the area within the past 2000 14 c yr b p coincident with a reduction in fire frequencies comparisons between modern pollen spectra and vegetation reveal that the moraceae dominated rain forest pollen spectra likely have a regional source area at least 2 3 km beyond the lake shore whereas the grass and sedge dominated savanna pollen spectra likely have a predominantly local source area the holocene vegetation changes are consistent with independent paleoprecipitation records from the bolivian altiplano and paleovegetation records from other parts of southwestern amazonia the progressive expansion in rain forests through the holocene can be largely attributed to enhanced convective activity over amazonia due to greater seasonality of insolation in the southern hemisphere tropics driven by the precession cycle according to the milankovitch astronomical theory

relation between carbon isotopes of plants and soils on marajo island a large tropical island implications for interpretation of modern and past vegetation dynamics in the amazon region abstract we assess the relation between the contrasting vegetation types of rainforest open savanna and wooded savanna coexisting in close contact on marajo island at the mouth of the amazon river floristic and carbon isotopic characterizations of modern plants were combined with organic matter carbon isotope and grain size records of soil to characterize vegetation evolution at six locations on southeastern and northeastern marajo island and its relations to climate changes since the late pleistocene c3 plants contribute 100 of the biomass in the rainforest on post barreiras sediments site 1 no significant vegetation changes are evident in these places since at least 7860 cal yr b p rainforests on paleochannels sites 4 and 6 are protected from flooding by slightly elevated sandy levee and have flora very similar to site 1 these forests were formed since the early mid holocene after channel abandonment c3 grasses are predominant in open savanna areas sites 4 5 and 6 with less representation in wooded savannas sites 2 and 3 however c4 grasses despite having fewer species constitute significant biomass in the wooded 60 and open savanna vegetation areas especially during the dry season the reconstructions of past vegetation together with the distributions of modern vegetation allow prediction that climate changes to drier conditions can significantly influence the future marajo island landscape likely enabling expansion of c4 plants in the flooding zone and of trees in the rainforests

late quaternary vegetation and climate changes in central texas based on the isotopic composition of organic carbon stable carbon isotope analysis of organic carbon in alluvial deposits and soils of three streams in central texas reveals significant shifts in the ratio of c3 to c4 plant biomass production during the past 15 000 yr these temporal changes in vegetation appear to be in response to changes in climate during the late pleistocene c4 plants comprised only about 45 to 50 of the vegetative biomass in this area suggesting that conditions were cooler and wetter than at any time during the past 15 000 yr the time between 11 000 and 8000 yr b p is interpreted as transitional between late pleistocene conditions and warmer and drier holocene conditions based on a slight increase in the abundance of c4 plant biomass during the middle holocene between approximately 6000 and 5000 yr b p mixed c3 c4 plant communities were replaced almost completely by c4 dominated communities indicating prairie expansion and warmer and drier climatic conditions by 4000 yr b p the abundance of c4 plant biomass decreased to levels similar to the early holocene transitional period suggesting a return to cooler and wetter climatic conditions no significant shift in the ratio of c3 to c4 productivity has occurred during the last 4000 yr except for a slight increase in the abundance of c4 plant biomass around 2000 yr b p the results of this investigation correlate well with other regional late quaternary climatic interpretations for central and north texas the southern plains region and with other portions of the great plains

paleo environmental change in amazonian and african rainforest during the lgm abstract the paper provides new and comparative insight into the ecological history of the two largest continental tropical forest areas during the last glacial maximum lgm the tropical forest regions are of particular interest because they present a large source of heat and have been shown to have significant impact on the extra tropical atmospheric circulation they are also the most intense land based convective centers thus especially from the tropics paleoecological information is needed as benchmarks for climate modeling the african data for lgm climates were published earlier including the reconstructed paleoprecipitation patterns deduced from ssts the tropical south american lgm data were interpreted from pollen geochemical and 18o 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 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

late quaternary vegetation dynamics in the southern amazon basin inferred from carbon isotopes in soil organic matter abstract carbon isotopes of soil organic matter som were used to evaluate and establish the chronology of the vegetation dynamics of an ecosystem presently composed of savannas surrounded by forests the study was carried out on a 200 km transect along highway br 319 on the border of amazonas and rondonia states in southern amazon brazil large ranges in 13 c values were observed in som collected from profiles in the savanna 27 to 14 and forest regions 26 to 19 reflecting changing distribution of 13 c depleted c 3 forest and 13 c enriched c 4 savanna vegetation in response to climate change these results indicate that from about 17 000 to 9000 14 c yr b p the study area was covered by forest vegetation between approximately 9000 and 3000 14 c yr b p savanna vegetation expanded at the expense of the forest although the expansion of savanna did not occur with the same intensity along the study transect this process was very clearly registered by 13 c enrichment in the som since 3000 14 c yr b p the carbon isotope data suggest that forested regions have expanded this study adds to the mounting evidence that extensive forested areas existed in the amazon during the last glaciation and that savanna vegetation expanded in response to warm and dry conditions during the early to middle holocene

holocene palaeoenvironmental history of the amazonian mangrove belt abstract wetland dynamic in the northern brazilian amazon region during the holocene was reviewed using palynological carbon and nitrogen isotopes records and c n ratio previously published the integration of 72 radiocarbon dates recorded in 34 sediment cores sampled along the marine and fluvial littoral and mainly influenced by the amazon river reveals that marine influence and mangrove vegetation were wider than today on the mouth of amazon river between 8990 8690 and 2300 2230 cal yr bp forming a continuous mangrove belt along the northern brazilian amazon littoral the establishment of this mangrove strip is a direct consequence of the marine incursion caused by post glacial sea level rise possibly associated with tectonic subsidence during the early and middle holocene in the late holocene in areas influenced by the amazon river discharge the mangroves were replaced by freshwater vegetation and the coast morphology evolved from an estuarine dominated into a rectilinear coast due to coastal progradation nevertheless the marine influenced littoral which is currently dominated by mangroves and salt marsh vegetation has persistently had brackish water vegetation over tidal mud flats throughout the entire holocene likely the fragmentation of this continuous mangrove line during the late holocene was caused by the increase of river freshwater discharge associated to the change from dry into wet climates in the late holocene this caused a significant decrease of tidal water salinity in areas near the mouth of amazon river these changes in the amazon discharge are probably associated with dry and wet periods in the northern amazon region during the holocene

dynamics of the last four glacial terminations recorded in lake van turkey abstract a well dated suite of lake van climate proxy data covering the last 360 ka documents environmental changes over 4 glacial interglacial cycles in eastern anatolia turkey the picture of cold and dry glacials and warm and wet interglacials emerging from pollen organic carbon authigenic carbonate content elemental profiling by xrf and lithological analyses is inconsistent with classical interpretation of oxygen isotopic composition of carbonates pointing to a more complex pattern in lake van region detailed analysis of glacial terminations allows for the constraining of a depositional model explaining different patterns observed in all the proxies we hypothesize that variations in relative contribution of rainfall snowmelt and glacier meltwater recharging the basin have a very important role for all sedimentary processes in lake van lake level of glacial lake van predominantly fed by snowmelt was low the water column was oxic and carbonates precipitating in the epilimnion recorded the light isotopic signature of inflow during terminations increasing rainfall and significant supply of mountain glaciers meltwater contributed to lake level rise increased rainfall enhanced density gradients in the water column and hindered mixing leading to development of bottom water anoxia carbonates precipitating during terminations show large fluctuations in their isotopic composition full interglacial conditions in lake van are characterized by high or slowly falling lake level rainfall and snowmelt feed the lake but due to re established mixing the isotopic composition of authigenic carbonates is heavier and closer to that of evaporation influenced lake water than that of runoff representing snowmelt and atmospheric precipitation

paleoenvironmental reconstruction of the lower mogi guacu river basin sao paulo state brazil morphopedosedimentary records and fluvial processes abstract the mogi guacu river rises in bom repouso minas gerais state brazil in the mantiqueira ridge and flows into the rio pardo river at an elevation of 483 m in pontal sao paulo state brazil after running a 530 km long course especially along the lower mogi guacu basin the river morphology is extremely sinuous characterized by intense processes of channel migration avulsion abandonment and reactivation of the channel producing an extensive alluvial plain composed of a series of associated relief forms and sedimentary facies among these forms point bar deposits by lateral accretion abandoned meanders paleo channels and fluvial terraces are notable features in this sense the objective of this work was to investigate whether these features could be linked to environmental changes to reach this goal soil properties of a catena of the jatai ecological station luiz antonio sao paulo state were analyzed in four sectors slope terrace i terrace ii and alluvial plain the results from grain size determination geochemical and isotopic studies dating paleopalynology coal fragments and micromorphology are presented in this paper from these analyses a paleo environmental evolution divided in three stages is proposed for the area 130 000 ybp upper pleistocene when the mogi guacu river base level was approximately 6 m above the present one a drier second phase 10 250 years bp lower holocene when an organic horizon was formed inside of an abandoned meander oxbow lake and a third phase 2096 ybp upper holocene of reactivation of a warm and humid climate that promoted the development of a two meters thick typic udifluvent in a sector where the mogi guacu river no more floods due to the incision of its thalweg reaching more than six meters depth in the last 130 000 years bp thus this paper used a fluvial geomorphologic approach and its interplay with climate to understand how the landscape was shaped from upper pleistocene to holocene however neotectonics might have played a relevant role as well not only in the mogi guacu river basin but also in the parana sedimentary basin

vegetation dynamics during the late pleistocene in the barreirinhas region maranhao state northeastern brazil based on carbon isotopes in soil organic matter abstract the study place is in the barreirinhas region maranhao state northeastern brazil a vegetation transect of 78 km was studied among four vegetation types restinga coastal vegetation cerrado woody savanna cerradao dense woody savanna and forest as well as three forested sites around lagoa do caco located approximately 10 km of the transect soil profiles in this transect were sampled for 13c analysis as well as buried charcoal fragments were used for 14c dating the data interpretation indicated that approximately between 15 000 and 9000 14c yr b p arboreal vegetation prevailed in the whole transect probably due to the presence of a humid climate approximately between 9000 and 4000 3000 14c yr b p there was the expansion of the savanna probably related to the presence of drier climate from 4000 3000 14c yr b p to the present the results indicated an increase in the arboreal density in the area due to the return to a more humid and probably similar climate to the present the presence of buried charcoal fragments in several soil depths suggested the occurrence of palaeofires during the holocene the vegetation dynamic inferred in this study for northeastern brazil is in agreement with the results obtained in areas of amazon region based on pollen analysis of lake sediments and carbon isotope analysis of soil organic matter som implying than similar climatic conditions have affected these areas during the late pleistocene until the present

the 14c dates and 13c 12c ratios of soil organic matter as a means of studying the past vegetation in intertropical regions examples from colombia south america abstract the 14 c ages and 13 c 12 c values were obtained on soil organic matter of various soils sampled in the guasca valley adjacent to the high plain of the sabana de bogota in the colombian cordillera oriental a soil distribution is observed as a function of climatic and altitudinal changes in the lowest parts of the valley planosols are found from the bottom of the valley to 2700 2800 m at altitudes up to 2900 m brunizems and ferrisols occur above 3000 m andic soils are almost everywhere present in more humid mountain zones at present the landscape is widely open without any natural forest nevertheless it was proved by pollen analytical data that at altitudes up to 3000 m the andean forest replaced a paramo formation 13 000 yr ago to conciliate the facts with the known evolution of the vegetal population a first hypothesis consists of admitting that open landscapes were due to a recent anthropogenic destruction of the forest the forest degradation hypothesis was tested by determination of the 13 c 12 c ratio because the trees have a 13 c of 25 to 28 influence of plants with c 3 photosynthesis pathway whereas herbs characteristic of open vegetation such as tropical grasses may have a 13 c of 23 to 16 due to a c 4 photosynthetic cycle the organic matter dated at 13 000 30 000 yr has 13 c close to 25 in the andic soil zone this indicates that at elevations of around 3000 m a cold paramo vegetation was probable for organic matter dated at 12 000 6000 yr 13 c shows a variation from 23 to 21 that does not indicate forest conditions it is uncertain that a forest stage occurred in the past for the planosols brunizem and ferrisol organic matter dated at 13 000 20 000 yr has a 13 c 23 compatible with the paramo vegetational phase occurring at that time for organic matter dated at 9500 yr and less 13 c varies from 20 to 17 these values do not confirm the evidence of forest conditions but rather the existence of open vegetation typified by a mixture of c 3 plants shrubs and rare trees and tropical graminaea thus the 13 c values prove that the valley has known drier and warmer influences that prevented the forest from developing during the holocene to explain the origin of the open landscapes of the valley the hypothesis of recent human deforestation must be discarded moreover the valley appears as a persistent dry enclave in the oriental cordillera

mid to late holocene fluvial activity behind pre columbian social complexity in the southwestern amazon basin the scale spatial variability and implications of pre columbian human induced changes in the amazon basin are controversial while some scholars believe that large settlements and complex societie

astronomical forcing of contrasting rainfall changes in tropical south america between 12 400 and 8800 cal yr b p abstract today precipitation over tropical south america is largely controlled by the seasonal movements of the inter tropical convergence zone itcz during the summer the itcz is shifted southward due to the warming of the continent paleoclimate data from southeastern amazonia and the central andes indicate that these two areas evolved similarly during the last 30 000 yr however between 12 400 and 8800 cal yr b p eastern amazonia received substantial moisture whereas the bolivian altiplano was arid this suggests that the itcz during summer was then farther north than it is today

a multi proxy evidence for the transition from estuarine mangroves to deltaic freshwater marshes southeastern brazil due to climatic and sea level changes during the late holocene abstract the present study investigates a paleo estuary at the doce river delta southeastern brazil through a multi proxy approach that links palynology diatoms sedimentology and geochemistry analyses i e total c total n 13 c and 15 n these analyses temporally synchronized with five radiocarbon ages revealed environmental changes from marine to continental over the last 7550 years the studied sedimentary succession recorded the upward transition from estuarine channel until 7550 cal yr bp to estuarine central basin 7550 to 5250 cal yr bp deposits the latter containing increased mangrove vegetation marine and marine brackish water diatoms the range of geochemical values 13 c 30 10 15 n 2 8 and c n 4 40 also indicate marine estuarine organic matter and c 3 terrestrial plants to that time interval a following period recorded two phases lake ria 5250 to 400 cal yr bp and fluvial channel 400 cal yr bp until modern age during this stage mangroves were replaced by trees shrubs and herbs grasses due to the disconnection with the marine realm as a result the corresponding sediments contain only organic matter sourced from freshwater and c 3 terrestrial plants 13 c 29 26 15 n 0 8 and c n 10 45 the equilibrium between fluvial sediment supply and relative sea level changes during the holocene controlled the morphologic and vegetation changes in the studied littoral the estuary became established during the early holocene as a resulted of a eustatic sea level rise when the fluvial sediment supply to the coast was relatively lower due to a dry period however during the late holocene the climatic force was more significant to the development of coastal morphology due to a wet period that caused an increase in sandy sediment supply to coastal system then the increase of fluvial discharge associated to a relative sea level fall caused a marine regression and shrinkage of mangroves during the late holocene the evaluation of mangrove dynamics according to climatic and sea level changes mainly during the late holocene is essential for the understanding of their survival ability under future scenarios with a probable accelerated sea level rise and intensification of extreme climatic events in southeastern brazil for the next century

rainfall redistribution over low hills due to flow perturbation abstract a simple potential flow model is developed for airflow over low hills the model readily allows incorporation of simple rain microphysics so that drop trajectories can be traced in the region of a hill complex rainfall intensity variations are found in the horizontal and in the vertical and a straightforward modification to the model allows for time dependence to be studied the model is shown to serve as a useful diagnostic tool to describe rain drop redistribution due to perturbed airflow in particular increased rainfall is predicted in the lee of hill peaks and depleted rainfall is predicted on ridges the redistribution effects dominate at low levels in contrast to predictions based on seeder feeder enhancement comparison with field measurements shows good qualitative agreement over low hills and in some cases close quantitative agreement redistribution of rain appears to be a significant process that should be considered in rainfall interpolation and prediction schemes involving hilly terrain

evaluating climatic response to external radiative forcing during the late miocene to early pliocene new perspectives from eastern equatorial pacific iodp u1338 and north atlantic odp 982 locations orbital scale climate variability during the latest miocene early pliocene is poorly understood due to a lack of high resolution records spanning 8 0 3 5 ma which resolve all orbital cycles assessing this variability improves understanding of how earth s system sensitivity to insolation evolves and provides insight into the factors driving the messinian salinity crisis msc and the late miocene carbon isotope shift lmcis new high resolution benthic foraminiferal cibicidoides mundulus 18o and 13c records from equatorial pacific international ocean drilling program site u1338 are correlated to north atlantic ocean drilling program site 982 to obtain a global perspective four long term benthic 18o variations are identified the tortonian messinian miocene pliocene and early pliocene oxygen isotope lows 8 7 5 9 4 9 and 4 8 3 5 ma and the messinian oxygen isotope high moh 7 5 9 ma obliquity paced variability dominates throughout except during the moh eleven new orbital scale isotopic stages are identified between 7 4 and 7 1 ma cryosphere and carbon cycle sensitivities estimated from 18o and 13c variability suggest a weak cryosphere carbon cycle coupling the msc termination coincided with moderate cryosphere sensitivity and reduced global ice sheets the lmcis coincided with reduced carbon cycle sensitivity suggesting a driving force independent of insolation changes the response of the cryosphere and carbon cycle to obliquity forcing is established defined as earth system response esr observations reveal that two late miocene early pliocene climate states existed the first is a prevailing dynamic state with moderate esr and obliquity driven antarctic ice variations associated with reduced global ice volumes the second is a stable state which occurred during the moh with reduced esr and lower obliquity driven variability associated with expanded global ice volumes

late quaternary paleosol sediment sequences and landscape evolution along the andean piedmont bolivian chaco abstract as part of the bolivian chaco the andean piedmont is situated in the transitional zone between the tropical humid climate regime to the north amazonia and the subtropical semiarid regime to the south gran chaco in this zone which is sensitive to climatic changes late quaternary landscape and climate history was reconstructed based on detailed sedimentological pedological and geochemical analyses of paleosol sediment sequences along the andean piedmont the determination of characteristic lithofacies allowed correlation between the investigated profiles and their interpretation in terms of paleoenvironmental conditions i e geomorphic stability soil formation or geomorphic activity fluvial or fluvio aeolian sedimentation erosion etc coarse fluvial deposits gravels sands form the base of the investigated profiles and have likely been deposited in a braided river environment with low vegetation cover and intensive discharge events before and during the last glacial maximum well developed paleosols formed in the upper part of these sediments during the lateglacial documenting geomorphic stability high vegetation cover and wet conditions overlying palustrine sediments dated to the early holocene indicate a dramatic change in seasonality i e increased winter precipitation and decreased summer precipitation subsequent erosion followed by accumulation of fluvial and fluvio aeolian sands points to much drier conditions during the mid holocene since 2 9 cal ka bp soil formation indicates a return to geomorphic stability and wetter conditions characteristic of the present day climate interrupted by short arid intervals

the role of late pleistocene holocene tectono sedimentary history on the origin of patches of savanna vegetation in the middle madeira river southwest of the amazonian lowlands abstract savanna patches are features of the amazonian landscape that have been long under intense debate but there are still questions about the main factors that have determined their establishment and evolution within the rainforest matrix in particular their geological substrates were poorly documented the aim of this work is to reconstruct the tectono sedimentary history of four savanna patches in the middle madeira river southwest amazonia and discuss its potential control over the development of the savanna communities the approach consisted in the integration of geomorphological sedimentological chronological and floristic data the results revealed that the savanna substrates are sandy deposits aged between 118 9 and 35 6 ky overlain by late pleistocene to holocene muddier successions

late quaternary vegetation and climate change in the amazon basin based on a 50 000 year pollen record from the amazon fan odp site 932 hemipelagic sediments from the amazon deep sea fan odp site 932 5 12 7 n 47 1 8 w and continental shelf provide a 50 000 yr long pollen record of amazon basin vegetation the age model for hole 932a is constrained by eight magnetic remanence intensity features one paleomagnetic excursion and three ams14c dates alchornea melastomataceae myrtaceae and moraceae urticaceae are dominant taxa in the pollen record between 40 200 and 19 800 cal yr b p andean taxa such aspodocarpusandhedyosmum increase in abundance between 19 800 and 11 000 cal yr b p and prior to 40 200 cal yr b p the holocene pollen assemblage derived from amazon river and continental shelf sediments is dominated by secondary growth taxa such ascecropia climatic factors influencing the development of glacial and interglacial tropical vegetation are considered by comparing marine with terrestrial records of vegetation change this comparison shows that the amazon basin forests were not extensively replaced by savanna vegetation during the glacial period contradicting the refugia hypothesis

a mineralogical and organic geochemical overview of the effects of holocene changes in amazon river flow on three floodplain lakes abstract a synthesis of the impacts of the amazon river hydrological changes on the sedimentation process of organic matter om in three different floodplain lakes santa ninha maraca and comprido lakes is presented in this study today the santa ninha and maraca lakes are directly and permanently connected with the main channel of the amazon river in contrast to comprido lake which is indirectly and periodically influenced by the amazon river due to its greater distance from the main channel all three lake sediment records showed a reduced river inflow due to dry climatic conditions during the early and middle holocene followed by an increased fluvial input during the wetter late holocene in santa ninha and maraca lakes the reduced river inflow period was recorded by sediments with a low abundance of smectite on average 20 wt a clay mineral mainly transported by the fluvial system high total organic carbon toc contents on average 8 2 wt and a predominantly acidic soil om input evidenced by high concentrations on average 180 g gtoc 1 of branched glycerol dialkyl glycerol tetraethers gdgt during the late holocene a higher smectite abundance on average 43 wt and a lower toc content on average 1 4 wt pointed to greater dilution by riverine lithogenic matter this change was accompanied by a proportional increase in the aquatically produced crenarchaeol suggesting a higher lake water level in comprido lake a sedimentation gap occurred during the early and middle holocene the wetter late holocene since 3000 cal years bp was characterized by high toc values on average 9 wt and a sharp increase in soil om input as recorded by an increase in branched gdgt concentrations on average 81 g gtoc 1 but the smectite content was low on average 14 this combination suggests that the soil om input to comprido lake from the local catchment area became dominant during the wet climate late holocene due to the large distance of the lake from the amazon river main channel consequently our study shows that the sedimentation processes of om in amazonian floodplain lakes were strongly influenced by variations in the hydrodynamic regime of the amazon river during the holocene however the impacts of the variations on the three floodplain lakes were different depending on the distance of each lake from the main channel of the amazon river

spatial heterogeneity of land cover response to climatic change in the nilgiri highlands southern india since the last glacial maximum fourteen hillslope soil profiles were sampled under natural vegetation i e grassland or forest and plantations in the nilgiri highlands southern india delta 13c ratios were measured at different depths and 14c ages determined for six profiles in these highland soils where the turnover rate of organic matter is extremely low the 13c ratios of entire soil profiles have recorded signatures of past land cover by correlating the data with results previously obtained from peat bogs and with knowledge concerning the history of human settlement we distinguish three contrasting trajectories of palaeoenvironmental history and landscape change since the last glacial maximum in the central nilgiris between 18 and 10 ka bp forest expansion occurred due to the conjunction of a wetter climate the maximum of southwest monsoon related humidity occurring at ca 11 ka bp and higher temperatures since 10 ka bp the reversal towards grassland vegetation is attributed to drier conditions in the western nilgiris where strong southwest monsoon winds permanently restrict forest patches to sheltered valley sites steady but limited expansion of forest from 18 ka bp to the present is recorded and attributed to rising temperatures the southern and eastern nilgiris where the northeast monsoon contributes 20 of the annual rainfall are the less sensitive to fluctuations in the southwest monsoon in these areas rapid and extensive expansion of forest occurred mainly as a consequence of higher temperatures from 18 ka bp to the present massive deforestation by badaga cultivators and europeans planters followed after the 16th century ad as a result and in contrast with the western nilgiris where the land cover mosaic has remained remarkably stable in the last 18 ka bp the current landscape differs sharply from the land cover pattern detected by the soil record

neogene and quaternary development of the neotropical rain forest the forest refugia hypothesis and a literature overview abstract the upheaval of the northern andes in miocene and pliocene time changed the drainage system in northern south america significantly and caused the present day rain forest areas of choco and the lower magdalena valley became separated from amazonas plant diversity may have reached the highest level in the miocene or pliocene and excessive present day phytodiversity may be regarded as a legacy of the tertiary rather than an evolutionary product of the quaternary in the quaternary strong temperature oscillations related to the series of ice ages were superposed on the late tertiary forest dynamics which included river displacement and latitudinal migrations of the equatorial rain belt caloric equator with the rhythm of the precession cycle of orbital climate forcing the hypothesis that claims a permanent rain forest cover all over the amazon basin during the last glacial is in contrast with the forest refugia hypothesis which accepts replacement of rain forest by savanna or savanna forest during dry climatic intervals both scenarios have been evidenced by pollen records in this paper it is suggested that both hypotheses are not necessarily conflicting and apparently did occur in different parts of the amazon basin and in different periods depending on the climatological constraints a compilation of the most important literature concerning the vegetational climatic and environmental history of the rain forest areas of amazonas and choco and surrounding dry ecosystems has been included

late quaternary palaeosol records from subtropical 38 s to tropical 16 s south america and palaeoclimatic implications abstract loess and palaeosols in the subtropical lowlands of south america 23 38 s have a large potential to serve as archives of late quaternary environmental and climate changes at present mean annual precipitation generally decreases from n to s and from e to w though with a complex seasonal pattern with austral summer rainfall related to the monsoonal circulation and with austral winter rainfall related to the se trades in this paper we present results of multiproxy geochemical analyses from three representative eolian alluvial soil profiles along a s n transect aiming at the reconstruction of past climate changes i profile chasico at the southern border of the subtropics 38 s ii d4 in misiones at the northern border of the subtropics 27 s and for comparison iii laguna sucuara in the savannas of the bolivian lowlands 16 s our results show that before 16 ka bp conditions were likely very cold and dry except for in d4 loess or soils are not preserved due to rather scarce vegetation cover and resultant deflation in chasico accumulation of sands directly overlying the tertiary starts only during the late glacial indicating increasing temperatures and increased monsoonal precipitation coinciding with the tauca wet phase on the altiplano in d4 a palaeosol is preserved below the late glacial sediments and the deflation hiatus this palaeosol is dated to 40 ka bp and documents an earlier but less intensive southward reaching phase of monsoonal precipitation inca huasi on the altiplano whereas the seasonality during the late glacial seems to have been very pronounced conditions for organic matter production and preservation became much more favourable at chasico and d4 during the early holocene we suggest that extra tropical winter precipitation played a more important role than before and than today between 7 5 and 3 ka bp the expansion of c4 plants along the s n transect suggests increasing aridity probably due to a weakening of the extra tropical circulation in combination with a relatively weak monsoonal circulation only after 3 ka bp climate became more humid again due to the re strengthening of the monsoon

late quaternary vegetation and coastal environmental changes at ilha do cardoso mangrove southeastern brazil abstract a 190 cm mangrove sediment core from the ilha do cardoso state park state of sao paulo southeastern brazil was analyzed for pollen diatoms as well as carbon and nitrogen isotopes the goal was to determine the dynamics of the coastal terrestrial aquatic ecosystems vegetation history and climate change in this region of the brazilian atlantic rainforest during the late pleistocene and holocene the values for total organic carbon toc from 3 up to 40 c n ratios from 10 up to 130 and 15n 0 to 8 are associated with well preserved aquatic and terrestrial organic matter and possibly influenced by nitrogen cycling e g denitrification that caused 15n enrichment between 40 000 cal yr b p and 23 000 cal yr b p depleted 13c values 28 0 are also observed and indicate the predominance of c3 plants during this time interval the pollen analysis reveals the presence of the genera ilex alchornea weinmannia myrsine symplocos drimys and podocarpus on a site currently occupied by mangrove vegetation these data suggest that in the past prevailed a colder and more humid climate than today with a low relative sea level from 23 000 cal yr b p to 2200 cal yr b p a sedimentary hiatus likely occurred related to an erosive event associated to the post glacial sea level rise since at least 2200 cal yr b p sediments are marked by relatively low c n ratios from 2 to 27 exhibit more enriched 13c from 26 0 to 24 0 and 15n up to 7 values and are characterized by the presence of marine diatoms this indicates the return of the marine coastal line to its current position and consequently the development of mangrove