late pleistocene holocene climatic and vegetational history of the brazilian caatinga the fossil dunes of the middle sao francisco river palynological studies of a peat bog sequence with a basal date of 10 990 80 yr b p provide a history of vegetational and climatic changes in the icatu river valley located inside a large system of stabilized sand dunes at the middle sao francisco river at 10o24 0 s 43o13 0 w in northeastern brazil the present day vegetation of the valley is vereda a mauritia vinifera palm swamp forest bordered by a narrow strip of semi deciduous tropical forest the adjacent dunes are stabilized by arboreal caatinga and cerrado vegetation in some areas the palynological profile of the saquinho locality within this valley was divided into five pollen zones zone sa1 10 990 10 540 yr b p contains pollen of taxa found in present amazonian and atlantic forests as well as from montane taxa thus suggesting very humid climatic conditions synchronous with more reduced temperatures zone sa2 10 540 6790 yr b p has pollen spectra from a vegetation type dominated by mauritia suggesting progressive warming and high humidity levels the period between 8920 and 8910 yr b p has rapid sedimentation rate few thermoluminescence tl dates pronounced increase of mauritia and ilex pollen suggesting a very moist climate from 8910 to 6790 yr b p there is a progressive decline in forest taxa and a gradual increase of caatinga and cerrado taxa on the landscape zone sa3 6790 ca 6230 yr b p does not contain palynomorphs possibly indicating semi arid conditions zone sa4 ca 6230 ca 4535 yr b p marks the return of mosaic vegetation composed of gallery forest cerrado and caatinga taxa indicating moister climatic conditions a marked decline in moisture levels characterizes the period between 4240 yr b p and present as suggested by an increase in caatinga and cerrado species and a decline in gallery forest taxa zone sa5 ca 4535 yr b p present establishes the present vegetational and climatic pattern of the icatu river valley 1999 elsevier science b v all rights reserved

changes in itcz location and cross equatorial heat transport at the last glacial maximum heinrich stadial 1 and the mid holocene article history tropical paleoclimate records provide important insights into the response of precipitation patterns and the hadley circulation to past climate changes paleo records are commonly interpreted as indicating north south shifts of the intertropical convergence zone itcz with the itcz s mean position moving toward the warmer hemisphere in response to changes in cross equatorial temperature gradients though a number of records in tropical central and south america north africa asia and the indo australian region are consistent with this interpretation the magnitudes and regional variability of past itcz shifts are poorly constrained combining estimates of past tropical sea surface temperature sst gradients with the strong linear relationship observed between zonally averaged itcz position and tropical sst gradients in the modern seasonal cycle and in models of past climates we quantify past shifts in zonally averaged itcz position we find that mean itcz shifts are likely less than 1 latitude during the last glacial maximum lgm heinrich stadial 1 hs1 and mid holocene 6 ka climates with the largest shift during hs1 the itcz s position is closely tied to heat transport between the hemispheres by the atmosphere and ocean accordingly these small mean itcz shifts are associated with relatively large 0 1 0 4 pw changes in cross equatorial atmospheric heat transport ahteq these ahteq changes point to changes in cross equatorial ocean heat transport or net radiative fluxes of the opposite sign during hs1 the increase in northward ahteq is large enough to compensate for a partial or total shutdown in northward heat transport by the atlantic ocean s meridional overturning circulation the large ahteq response for small changes in mean itcz position places limits on the magnitude of past shifts in the globally averaged itcz large 5 meridional displacements of the itcz inferred from regional compilations of proxy records must be limited in their zonal extent and itcz shifts at other longitudes must be near zero for the global mean shift to remain 1 as suggested by our results our examination of model results and modern observations supports variable regional and seasonal changes in itcz precipitation this work thus highlights the importance of a dense network of tropical precipitation reconstructions to document the regional and seasonal heterogeneity of itcz responses to past climate changes

variability of el nino southern oscillation activity at millennial timescales during the holocene epoch the variability of el nino southern oscillation enso during the holocene epoch in particular on millennial timescales is poorly understood palaeoclimate studies have documented enso variability for selected intervals in the holocene but most records are either too short or insufficiently resolved to investigate variability on millennial scales1 2 3 here we present a record of sedimentation in laguna pallcacocha southern ecuador which is strongly influenced by enso variability and covers the past 12 000 years continuously we find that changes on a timescale of 2 8 years which we attribute to warm enso events become more frequent over the holocene until about 1 200 years ago and then decline towards the present periods of relatively high and low enso activity alternating at a timescale of about 2 000 years are superimposed on this long term trend we attribute the long term trend to orbitally induced changes in insolation and suggest internal enso dynamics as a possible cause of the millennial variability however the millennial oscillation will need to be confirmed in other enso proxy records

nonlinear transfer function modelling of beach morphology at duck north carolina abstract this paper presents a simple nonlinear data based modelling approach for predicting the beach profile volume at duck north carolina usa the state dependent parameter form of the general transfer function sdp tf model is used to describe nonlinearity influencing these morphological data in two case examples case 1 investigates the nonlinearity associated with the dependency of wave forcing on the preceding beach volume case 2 investigates the ability to model the variables within the well known diffusion equation for beach volume using this data based approach the results of this study show that the sdp tf approach can be used successfully to develop statistically robust models for describing nonlinearity in beach morphological systems furthermore these models are shown to predict the beach volumes over both short 1 month ahead and long 2 years ahead time periods and thus show great potential for practical applications in coastal zone management and engineering

stepped surfaces and palaeolandforms in the northern brazilian nordeste constraints on models of morphotectonic evolution abstract from the parnaiba basin to the borborema plateau northeastern brazil the crystalline and sedimentary highlands and plains of the huge jaguaribe piranhas amphitheatre are intersected seawards by offset elements of a marginal scarp which overlooks coastal lowlands along the equatorial atlantic transform margin its stepped surfaces are classically related to regional uplift induced by the break up of the gondwana supercontinent supposed to have triggered the formation until the plio pleistocene of successively younger planation surfaces below a culminating cretaceous surface a reinterpretation of this topography combined with analyses of palaeolandforms surface deposits drainage anomalies and structural controls on landforms is used to obtain ages for significant features of the stepped patterns and to propose a morphostratigraphic scheme for the whole area it is shown that the regional morphology is widely controlled by structures formed during early cretaceous continental rifting and later aptian oceanic opening exhumed pre cenomanian palaeolandforms planation surfaces residual cretaceous fault scarps are identified this study points out the value of the morphostructural approach for revisiting classical problems of geomorphology such as the meaning of stepped landforms identification of palaeosurfaces of cretaceous age at various levels and the age and origin of planation surfaces its results are considered as constraining elements for a further tentative reconstruction of the morphotectonic evolution of this margin

weathering intensity and pedostratigraphy of the middle to upper pleistocene loess palaeosol sequence of wels aschet upper austria abstract on top of a fluvioglacial terrace near wels aschet a complex loess palaeosol sequence has been investigated to date the terrace is classified as a classical gunz unit older deckenschotter sedimentological and mineralogical analyses were carried out on the basis of palaeopedological field data the results show that in terms of mineralogical composition the palaeosols can clearly be differentiated and are characterised throughout by interglacial weathering intensity bulk mineralogical as well as clay mineralogical data allow a five stage ranking of weathering intensity based on indicator minerals from the bulk mineralogical perspective slightly weathered loess still contains carbonate minerals and primary chlorite whereas the intensely weathered soil horizons are characterised by the total or near absence of carbonate minerals and primary chlorite micas and feldspars in clay mineralogical results chlorite and the relation of 14 a and 18 a vermiculites as well as mixed layer minerals play an important role in determining the weathering stage primary chlorite can be present in slightly weathered loess loams and vermiculite 14 a is dominant there stage 1 and 2 from weathering stage 3 onwards the amount of vermiculite 18 a increases considerably and dominates the following stage 4 most intensive weathering causes the absence of illite stage 5 generally the studied interglacial palaeosols belong to at least stage 3 with the applied methodology four interglacial palaeosols have been demarcated as well as a highly weathered palaeosol within the terrace gravels of the gunz in wels aschet pedostratigrapy points to a classification of the older deckenschotter in mis 14 at minimum however since this glacial period was of low intensity and the weathering intensity of the basal palaeosol was significantly enhanced a correlation of the gunz terrace with mis 16 also seems possible

correlated millennial scale changes in surface hydrography and terrigenous sediment yield inferred from last glacial marine deposits off northeastern brazil abstract the stable isotope composition of planktonic foraminifera correlates with evidence for pulses of terrigenous sediment in a sediment core from the upper continental slope off northeastern brazil stable oxygen isotope records of the planktonic foraminiferal speciesglobigerinoides sacculiferandglobigerinoides ruber pink reveal sub milankovitch changes in sea surface hydrography during the last 85 000 yr warming of the surface water coincided with terrigenous sedimentation pulses that are inferred from high xrf intensities of ti and fe and which suggest humid conditions in northeast brazil these tropical signals correlate with climatic oscillations recorded in greenland ice cores dansgaard oeschger cycles and in sediment cores from the north atlantic heinrich events trade winds may have caused changes in the north brazil current that altered heat and salt flux into the north atlantic thus affecting the growth and decay of the large glacial ice sheets

coupling of millennial scale changes in sea surface temperature and precipitation off northeastern brazil with high latitude climate shifts during the last glacial period 1 high resolution records of alkenone derived sea surface temperatures and elemental ti ca ratios from a sediment core retrieved off northeastern brazil 4 s reveal short term climate variability throughout the past 63 000 a large pulses of terrigenous sediment discharge caused by increased precipitation in the brazilian hinterland coincide with heinrich events and the younger dryas period terrigenous input maxima related to heinrich events h6 h2 are characterized by rapid cooling of surface water ranging between 0 5 and 2 c this signature is consistent with a climate model experiment where a reduction of the atlantic meridional overturning circulation amoc and related north atlantic cooling causes intensification of ne trade winds and a southward movement of the intertropical convergence zone resulting in enhanced precipitation off northeastern brazil during deglaciation the surface temperature evolution at the core site predominantly followed the antarctic warming trend including a cooling prior to the younger dryas period an abrupt temperature rise preceding the onset of the bolling allerod transition agrees with model experiments suggesting a southern hemisphere origin for the abrupt resumption of the amoc during deglaciation caused by southern ocean warming and associated with northward flow anomalies of the south atlantic western boundary current

extreme block and boulder transport along a cliffed coastline calicoan island philippines during super typhoon haiyan abstract this paper presents data and analysis for block and boulder transport during super typhoon haiyan along a 4 5 km long low 5 12 m cliffed coastline in calicoan island eastern samar philippines wave runup exceeding 15 2 m elevation above mean sea level drove large limestone clasts with volumes up to 83 m3 up to 280 m inland a few very large clasts with volumes 65 132 m3 were not transported by the waves when combined with recent transport reported in may et al 2015 cox et al 2016 and other literature it is becoming increasingly clear that the largest blocks transported by storms overlie much of the tsunami transport range increasing the difficulty in attributing the transport source without additional evidence comparison of present results with a global database of storm boulder transport shows a mass elevation envelope outside of which no transport is observed initiation of motion criteria were extended to include non rectangular cross sections which significantly reduces inferred velocities particularly for overturning motion these new relations were applied to the largest observed sliding and overturning boulders while considering coefficient uncertainties and resulting velocity uncertainty was large enough that direct inference of wave heights would be problematic estimates of initiation velocities for cliff edge boulders computed using lifting joint bounded relations were unreasonably large when compared to those for sliding and overturning boulders suggesting that processes other than bernoulli lift forces dominated at cliff edges

interhemispheric atlantic seesaw response during the last deglaciation the asynchronous relationship between millennial scale temperature changes over greenland and antarctica during the last glacial period has led to the notion of a bipolar seesaw which acts to redistribute heat depending on the state of meridional overturning circulation within the atlantic ocean here we present new records from the south atlantic that show rapid changes during the last deglaciation that were instantaneous within dating uncertainty and of opposite sign to those observed in the north atlantic our results demonstrate a direct link between the abrupt changes associated with variations in the atlantic meridional overturning circulation and the more gradual adjustments characteristic of the southern ocean these results emphasize the importance of the southern ocean for the development and transmission of millennial scale climate variability and highlight its role in deglacial climate change and the associated rise in atmospheric carbon dioxide

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

geomorphology and quaternary stratigraphy the roles of morpho litho and allostratigraphy abstract the subdivision and ordering of quaternary sediments and landforms is very often based on geomorphology quaternary landforms such as moraines river terraces palaeoshorelines and indeed any other landform can be arranged and ordered in time based on their relative position in the landscape morphostratigraphy is the subdivision of sedimentary units primarily on the basis of surface form whilst surface form is often used as a criterion for separating sedimentary units morphostratigraphy also usually incorporates lithological criteria to aid stratigraphical subdivision and morpho and lithostratigraphy are often interlinked in quaternary science however another approach allostratigraphy has increasingly been applied to subdivide and order quaternary sediment landforms allostratigraphy uses discontinuities to subdivide sedimentary successions allostratigraphy enables lateral variations in lithology to be included within the same stratigraphical unit furthermore it enables lithologically similar sediments stacked on top of each other to be divided into separate units based on discontinuities this paper examines the applications of morpho litho and allostratigraphy to subdivide sediment landform assemblages and critically reviews their role in quaternary stratigraphy

comparison of quartz osl protocols using lateglacial and holocene dune sands from brandenburg germany abstract we present the results obtained using various different protocols in the quartz optically stimulated luminescence dating of a late glacial and holocene aeolian dune sequence near eberswalde north of berlin germany the allerod finow palaeosol and the laacher see tephra layer serve as chronostratigraphic markers and further independent age control is provided by eight 14 c ages the application of the single aliquot regenerative dose protocol using blue light stimulation and the multiple aliquot regenerative dose and additive dose protocols using broad band blue and green light stimulation are discussed a comparison of radionuclide analyses using high resolution gamma spectrometry and neutron activation analysis is also presented it is concluded that the two dosimetry methods give indistinguishable results although the gamma spectrometry data are more precise in contrast the single aliquot regenerative dose protocol is between 2 and 10 times more precise than the multiple aliquot protocols and systematic differences in performance are also observed the uncertainties in the dosimetry calculations are the largest contributor to the overall age uncertainties the accuracy of the resulting ages is considered very satisfactory when tested against the independent age controls over the entire age range from the present to 15 ka

late quaternary vegetational and climate dynamics in northeastern brazil inferences from marine core geob 3104 1 abstract late quaternary paleoenvironments from northeastern ne brazil have been studied by pollen analysis of marine sediment the studied core geob 3104 1 3 40 s 37 43 w 767 m b s l from the upper continental slope off ne brazil is 517 cm long and 42 000 14 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 14 c yr bp the increased fluvial 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 14 c yr bp and between 15 500 and 11 800 14 c yr bp indicate short term periods of strong rainfall on the ne brazilian continent the expansion of mountain floodplain and gallery forests characterize the interval between 15 500 and 11 800 14 c yr bp as the wettest recorded period in ne brazil which allowed floristic exchanges between atlantic rain forest and amazonian rain forest and vice versa the paleodata from core geob 3104 1 confirm 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 influence 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

variability in the mean latitude of the atlantic intertropical convergence zone as recorded by riverine input of sediments to the cariaco basin venezuela abstract changes in the strength and position of the intertropical convergence zone itcz are an important component of climate variability in the tropical atlantic the cariaco basin located on the northern margin of venezuela is sensitive to tropical atlantic climate change and its sediments provide a record of past itcz behavior today the cariaco basin experiences two distinct seasons that reflect the annual migration of the atlantic itcz between january and march when the itcz lies south of the equator northeasterly trade winds sit directly over cariaco basin and strong coastal upwelling and dry conditions dominate beginning in june july as the itcz moves north local rainfall reaches a maximum and the upwelling diminishes or disappears here we summarize new and previously published data on the river derived terrigenous fraction of cariaco basin sediments as well as comparisons to other paleoclimate records which together suggest a coherent climatologic response in the tropical atlantic triggered by a pattern of itcz migration that mimics the seasonal cycle during periods of cooler north atlantic ssts on time scales ranging from the little ice age to the younger dryas to the cold stadials of the last glacial decreased detrital delivery to cariaco basin from local rivers suggests a southward shift in the mean latitudinal position of the itcz during warm interstadials and periods of holocene and deglacial warmth northward shifts in itcz position and its belt of convective rainfall are inferred from increased detrital delivery to the basin whether the rapid shifts in itcz position and precipitation recorded by cariaco basin sediments and other regional records reflect a response to forcing originating in the high latitude atlantic or to forcing potentially sourced in the tropics is a key question yet to be fully answered

rapid early holocene deglaciation of the laurentide ice sheet the demise of the laurentide ice sheet during the early holocene epoch is the most recent and best constrained disappearance of a large ice sheet in the northern hemisphere and thus allows an assessment of rates of ice sheet decay as well as attendant contributions to sea level rise here we use terrestrial and marine records of the deglaciation to identify two periods of rapid melting during the final demise of the laurentide ice sheet when melting ice contributed about 1 3 and 0 7cm of sea level rise per year respectively our simulations with a fully coupled ocean atmosphere model suggest that increased ablation due to enhanced early holocene boreal summer insolation was the predominant cause of laurentide ice sheet retreat although the surface radiative forcing in boreal summer during the early holocene is twice as large as the greenhouse gas forcing expected by the year 2100 the associated increase in summer surface air temperatures is very similar we conclude that our geologic evidence for a rapid retreat of the laurentide ice sheet may therefore describe a prehistoric precedent for mass balance changes of the greenland ice sheet over the coming century

cenozoic uplift and erosion of structural landforms in ne brazil abstract we investigate the evolution of uplifted areas in ne brazil which have been considered as residual landforms the study focuses on the 130 km long 41 km wide pereiro massif pm the structural control and the age of this uplift are the problems addressed in this study we carried out topographic analysis geomorphological and geological mapping detailed structural analysis and optically stimulated luminescence osl dating to address these problems the pm is bounded and cut by a system of steeply dipping normal and strike slip faults which control the morphology of the massif and associated sedimentary basins the maximum uplift rate of the pm is 34 m my 1 as constrained by the age of flat topography capped by miocene laterite which represents the previous peneplain subsequently uplifted by ca 600 m the minimum uplift rate is 13 m my 1 as constrained by fission track dating of differential crustal block movements across a nearby fault in the quaternary erosion occurred mainly by fault controlled scarp retreat under semi arid conditions with the formation of colluvial deposits along fault scarps and alluvial deposits in the low plains these deposits are now dated between 46 and 0 4 ka with a peak in sediment deposition in the pleistocene holocene transition it is concluded that the pm is a system of horsts and grabens that have been active in the cenozoic

sensitivity of the atlantic intertropical convergence zone to last glacial maximum boundary conditions 1 recent paleoproxy records suggest that the mean latitude of the atlantic intertropical convergence zone itcz varied synchronously with north atlantic climate over a range of timescales throughout the holocene and last glacial maximum we show that the present day meridional mode of atmosphere ocean variability in the tropical atlantic is a potentially useful model for understanding these paleoclimate changes the tropical atlantic in a coupled atmospheric general circulation and slab ocean model responds to last glacial maximum conditions with a southward displacement of the itcz this response arises primarily through the land ice sheet that forces increased north atlantic trades analogous to the forcing on the present day meridional mode changes to sea ice coverage and to ocean heat transport associated with a weakened atlantic thermohaline circulation also cause a meridional mode response though through different mechanisms our results highlight the potential for tropical atlantic paleoclimate to be driven from the high latitude influences in particular land ice on glacial interglacial timescales

landscape sensitivity to rapid environmental change a quaternary perspective with examples from tropical areas abstract a millennial scale of rapid change during the quaternary is recorded in grip and gisp2 ice core records and is also found in tropical oceans rapid warming episodes followed by gradual cooling associated with sub milankovich cycles implies an asymmetry in the behaviour of climate that is likely to be reflected in landscape responses slope failures floods colluvial alluvial sedimentation may reflect short term changes in the record but reorganisation of slope and fluvial systems involves significant time lags or delays often on a millennial scale and requiring changes to the vegetation cover while some records of sedimentation indicate major landscape instability during last 20 ky or in the early holocene others indicate pulses of activity throughout the last glacial cycle lgc these differences may reflect regional patterns of climate change but also illustrate the importance of landscape sensitivity to our understanding of the impacts of rapid environmental change methodological problems arise in attempting correlations between site specific records of sedimentation and integrated signals of hydrologic change found in deltaic and off shore fans

geomorphic response to rapid climatic and hydrologic change during the late pleistocene and early holocene in the humid and sub humid tropics abstract the data base concerning late quaternary environmental change in the humid tropics is dependent on records from scattered sites the intensity and duration of wet dry oscillations remain speculative and the responses of hillslopes and river systems are based on over simplified models however available evidence indicates that prolonged aridity affected all but a few favoured core areas of equatorial climate after 20 000 bp lasting 5 7 ka dry conditions at the lgm were marked by semi arid landforms and reduced steam activity large palaeofloods occurred after 13 000 be but dry conditions returned after 11 000 bp before the early holocene pluvial led to abundant sedimentation lasting nearly 2 ka after 9500 bp in africa amazonia and australasia erosion channel cutting and flood deposition occurred at the pleistocene holocene transition followed by multiple shifts from lateral to vertical accretion fill cut episodes during the early holocene while thick overbank deposits formed during the later holocene re establishment of the lowland rainforests was delayed until after 9000 bp in africa australia and brazil and several wet dry oscillations followed in the mid holocene period hillslope activity at the lgm was marked by local sediment transfers and fan formation at the termination sediment fluxes increased rapidly but mass movement probably peaked after 10 000 bp sediment delivery to stream channels was not immediate and large sediment stores remain on the landscape today many in areas of potential sensitivity of erosion

southward migration of the intertropical convergence zone through the holocene titanium and iron concentration data from the anoxic cariaco basin off the venezuelan coast can be used to infer variations in the hydrological cycle over northern south america during the past 14 000 years with subdecadal resolution following a dry younger dryas a period of increased precipitation and riverine discharge occurred during the holocene thermal maximum since approximately 5400 years ago a trend toward drier conditions is evident from the data with high amplitude fluctuations and precipitation minima during the time interval 3800 to 2800 years ago and during the little ice age these regional changes in precipitation are best explained by shifts in the mean latitude of the atlantic intertropical convergence zone itcz potentially driven by pacific based climate variability the cariaco basin record exhibits strong correlations with climate records from distant regions including the high latitude northern hemisphere providing evidence for global teleconnections among regional climates

understanding the impacts of late quaternary climate change in tropical and sub tropical regions abstract the understanding of climate impacts on tropical rivers and catchments has developed in part from models developed for temperate landscapes and a common rhythm is often apparent when millennial scale studies are compared at this level issues arising from the complex response of rivers to internal and external factors appear less important than the climate driven signal understanding the fluvial record however depends on the availability and interpretation of other sources of proxy data such as pollen spectra lake levels and ocean cores in many rainforest areas few pollen records exist and many of these reveal a hiatus at the time of the last glacial maximum examples of fluvial archives from africa indonesia and tropical queensland australia are discussed in relation to independent records of vegetation change and inferences are made concerning critical episodes in fluvial history focusing on the transitions from oxygen isotope stage ois 3 towards glacial conditions in ois2 and the pleistocene holocene transition to modern climates links between climate vegetation change and fluvial activity are presented as descriptive models

optical dating of sediments a new method for dating sediments is proposed which determines the time since the sediment was last exposed to sunlight an argon ion laser is used to excite electrons from thermally stable light sensitive traps and the subsequent luminescence used as a measure of the past radiation dose two sample sequences spanning the periods 0 700 kyr and 0 6 kyr show steadily increasing luminescence with age an age of 62 8 kyr is obtained for a silt radiocarbon dated at 58 8 0 3 kyr problems were found with two much younger samples