rapid flooding of the sunda shelf a late glacial sea level record the increase in sea level from the last glacial maximum has been derived from a siliciclastic system on the tectonically stable sunda shelf in southeast asia the time from 21 to 14 thousand calendar years before the present has been poorly covered in other records the record generally confirms sea level reconstructions from coral reefs the rise of sea level during meltwater pulse 1a was as much as 16 meters within 300 years 14 6 to 14 3 thousand years ago

quaternary oceans and climate change lessons for the future there is much interest in ice age studies in recent decades in the context of global warming the relevant findings are these large regular changes in climate occurred within the last million years especially in the northern north atlantic extreme conditions were similar suggesting strong negative feedback at the edges of the range of variation the nature of the periods of climate variation suggests orbital forcing by modulation of internal oscillations involving lagged negative feedback on ice buildup transitions from cold to warm were rapid and they were not readily reversed indicating that ice dynamics underlies abrupt climate change accelerated rates of ice decay upon warming correspond to a sea level rise of one to two m century millennial scale abrupt disturbances known as dansgaard oeschger and heinrich events occur when large ice masses are present in the northern hemisphere they may be considered experiments on the ocean s response to massive meltwater input when using results from ice age studies to project future developments one must be aware that the future will be largely outside of experience with regard to the recent geologic past also there are as yet no generally accepted explanations for striking changes in the past such as the rapid rise of carbon dioxide during deglaciation demonstrating a profound lack of understanding of climate dynamics this is so far the lesson from ice age studies they say much about the deficiencies in our level of understanding and not so much about what is ahead

moisture supply for northern ice sheet growth during the last glacial maximum during the last ice age the barents sea ice sheet began to grow 22 kyr ago1 only 8 kyr before it began to disintegrate2 this implies that the ice must have grown very rapidly from the coast to the edge of the continental shelf such rapid growth of a large ice sheet requires significant amounts of moisture3 but the origin of this moisture has been unclear particularly as the climap climate reconstruction suggests4 5 that the greenland iceland norwegian gin seas were perennially ice covered during this period here we present data from deep sea sediment cores from the fram strait which suggest that relatively warm water from the north atlantic ocean was advected into the gin seas in two short term events 27 22 5 and 19 5 14 5 kyr ago we suggest that the resulting seasonally ice free waters were an important regional moisture source for the barents sea ice sheet and that the gin seas played a much more active role in climate during the last glaciation than has previously been supposed

remote sensing of hydrogen in earth s mantle hydrogen1 in earth s interior is known to play a key role in a number of processes consequently inferring the distribution of hydrogen is a critical step in our study of dynamics and evolution of earth usually hydrogen distribution is inferred from two types of samples at the surface first a magma may contain hydrogen water and under some conditions the water content of the magma can be quenched upon cooling in these cases measurements of the water content of the magma provide us with some constraints on the hydrogen water content of the source region if we know the partitioning of hydrogen between magmas and the source rocks and the degree of melting second hydrogen content of some xenoliths transported by magma can be measured they provide a direct clue as to the hydrogen content in a region from which a xenolith has been carried however these direct petrologic approaches have two major problems firstly the sampling is limited by the distribution of volcanoes and even if there are volcanoes that carry rocks from earth s interior the depth extent that volcanoes sample rocks is limited usually 200 km secondly there is no guarantee that the hydrogen content that one measures on these samples actually represents the hydrogen content in a region where these samples came from for example hydrogen is known to diffuse very easily so hydrogen dissolved in minerals could diffuse out during the transport of a rock or conversely a piece of rock may acquire extra hydrogen during its ascent also hydrogen atoms dissolved in minerals may precipitate in the mineral to form fluid inclusions or micro scale hydrous minerals in summary the direct method to infer the distribution of hydrogen from rock samples has major limitations and an alternative approach i e remote sensing hydrogen content from geophysical

simmax a modern analog technique to deduce atlantic sea surface temperatures from planktonic foraminifera in deep sea sediments we present a data set of 738 planktonic foraminiferal species counts from sediment surface samples of the eastern north atlantic and the south atlantic between 87 n and 40 s 35 e and 60 w including published climate long range investigation mapping and prediction climap data these species counts are linked to levitus s 1982 modern water temperature data for the four caloric seasons four depth ranges 0 30 50 and 75 m and the combined means of those depth ranges the relation between planktonic foraminiferal assemblages and sea surface temperature sst data is estimated using the newly developed simmax technique which is an acronym for a modern analog technique mat with a similarity index based on 1 the scalar product of the normalized faunal percentages and 2 a weighting procedure of the modern analog s ssts according to the inverse geographical distances of the most similar samples compared to the classical climap transfer technique and conventional mat techniques simmax provides a more confident reconstruction of paleo ssts correlation coefficient is 0 994 for the caloric winter and 0 993 for caloric summer the standard deviation of the residuals is 0 90 c for caloric winter and 0 96 c for caloric summer at 0 m water depth the sst estimates reach optimum stability standard deviation of the residuals is 0 88 c at the average 0 to 75 m water depth our extensive database provides sst estimates over a range of 1 4 to 27 2 c for caloric winter and 0 4 to 28 6 c for caloric summer allowing sst estimates which are especially valuable for the high latitude atlantic during glacial times an electronic supplement of this material may be obtained on adiskette or anonymous ftp from kosmos agu org login toagu s ftp account using anonymous as the username and guestas the password go to the right directory by typing cd append typels to see what files are available type get and the name of the file toget it finally type exit to leave the system paper 95pa01743 simmax a modern analog technique to deduce atlantic sea surfacetemperatures from planktonic foraminifera in deep sea sediments uwepflaumann josette duprat claude pujol and laurent d labeyrie diskette may be ordered from american geophysical union 2000florida avenue n w washington dc 20009 payment mustaccompany order

foraminiferal faunal estimates of paleotemperature circumventing the no analog problem yields cool ice age tropics the sensitivity of the tropics to climate change particularly the amplitude of glacial to interglacial changes in sea surface temperature sst is one of the great controversies in paleoclimatology here we reassess faunal estimates of ice age ssts focusing on the problem of no analog planktonic foraminiferal assemblages in the equatorial oceans that confounds both classical transfer function and modern analog methods a new calibration strategy developed here which uses past variability of species to define robust faunal assemblages solves the no analog problem and reveals ice age cooling of 5 o to 6oc in the equatorial current systems of the atlantic and eastern pacific oceans classical transfer functions underestimated temperature changes in some areas of the tropical oceans because core top assemblages misrepresented the ice age faunal assemblages our finding is consistent with some geochemical estimates and model predictions of greater ice age cooling in the tropics than was inferred by climate long range investigation mapping and prediction climap 1981 and thus may help to resolve a long standing controversy our new foraminiferal transfer function suggests that such cooling was limited to the equatorial current systems however and supports climap s inference of stability of the subtropical gyre centers

last glacial sea surface temperatures and sea ice extent in the southern ocean atlantic indian sector a multiproxy approach 1 on the basis of the quantitative study of diatom radiolarian and planktic foraminiferal assemblages we estimated summer sea surface temperature ssst and sea ice extent at 50 sediment core localities in the atlantic and western indian sector of the southern ocean to reconstruct the last glacial environment at the glamap 18 to 15 ka equal to 21 500 to 18 000 calendar cal years bp and epilog 19 5 to 16 0 ka equal to 23 000 to 19 000 cal years bp time slices stratigraphic identification of the time slices was accomplished by a combination of ams 14c measurements benthic isotope and siliceous microfossil abundance records while the ssst estimates reveal greater surface water cooling than reconstructed by climap 1981 reaching a maximum in the area of the present subantarctic zone the sea ice reconstruction indicates that climap overestimated the expansion of the antarctic sea ice field especially for austral summer during winter the sea ice field was expanded by 60 70 compared to the present last glacial summer sea surface isotherms indicate a northward shift of the zonal bands of the antarctic circumpolar current and a relative expansion of the cold water realm south of the subantarctic front by 5 in latitude this coincides with a northward displacement of the zone of enhanced biogenic silica deposition and iceberg occurrence as a result of northward expansion of antarctic cold waters and a relatively small displacement of the subtropical front thermal gradients were steepened during the last glacial in the area of the present subtropical front the northward displacement of antarctic cold waters and the related deflection of southern ocean waters along the eastern boundary of south america may have resulted in a weakened cold water route across the drake passage in contrast the transport of warm and salty surface water from the indian into the atlantic ocean via the warm water route was not blocked allowing continuous but reduced import of heat into the south atlantic

a hydraulic box model study of the mediterranean response to postglacial sea level rise 1 this paper quantifies the role of changing sea level in affecting mediterranean stratification using a new model of the strait basin system which allows for explicit time dependence during the last deglaciation fairbank s meltwater peak 1b leads to rapidly rising global sea levels and a freshening of the oceans and hence increasing influx of ever freshening atlantic water into the mediterranean basin owing to long residence times the salinity of the deep and intermediate water reservoirs would have decreased more slowly so that the basin was more stably stratified for a period with possible implications for sapropel formation our model is used to estimate the size of this reservoir effect in comparison to the freshwater influx from the opening of the black sea at the bosphorus it is found that this mechanism affects the stratification to a similar degree as the black sea opening other climatic mechanisms have also affected the freshwater budget of the mediterranean at this time but their sizes are more difficult to quantify

link between european and north atlantic abrupt climate changes over the last glaciation 1 sub millennial timescale climate variations correlated with those in the north atlantic area are identified in the loess sequence from nussloch germany exceptionally developed over the interval between about 38 000 and 18 000 years ago the dansgaard oeschger do events 8 to 2 as well as some less pronounced warming episodes recorded in the greenland ice have their counterpart in the nussloch loess stratigraphy and in the variations of the loess grain size index gsi the north atlantic heinrich events 3 and 2 are expressed at nussloch as maxima of the gsi record the similarity of the fine variations in the nussloch loess and the greenland ice records points to an intimate link of climate changes in western europe with those in the north atlantic

past extent of sea ice in the northern north atlantic inferred from foraminiferal paleotemperature estimates 1 using 150 core top samples we developed a conservative but fairly robust new measure to reconstruct past changes in maximum seasonal sea ice distribution in the northern north atlantic hitherto a major unknown the proxy is based on similarity maximum modern analog technique simmax estimates of threshold temperatures near the sea surface sst today almost 100 of all sites with sst 2 5 c during summer 0 4 for winters 1978 1987 and 0 75 c for little ice age winters lie seaward of the sea ice margin when applied to 60 sediment records of the last glacial maximum this proxy shows that peak glacial sea ice was far more restricted than in the classic climap project members 1981 reconstruction during glacial summer sea ice only covered the arctic ocean and western fram strait the northern north atlantic and nordic seas were largely ice free and thus formed a high latitude moisture source for the continued buildup of continental ice sheets in contrast sea ice spread far south across the iceland faeroe ridge during glacial winter with an inferred patch of sea ice also in the central east atlantic near the center of the azores high a broad ice free channel extended from 50 to 60 n forming an ideal site for large scale convection of glacial upper north atlantic deep water the extreme seasonality in glacial sea ice formation and melt in the nordic seas implies a major consumption of the regional energy income

modelling tempo spatial signatures of heinrich events influence of the climatic background state abstract different sea surface temperature sst reconstructions for the last glacial maximum are applied to a hybrid coupled climate model the resulting oceanic states are perturbed by north atlantic meltwater inputs in order to simulate the effect of heinrich events on the atlantic thermohaline circulation thc and sst the experiments show that both the atlantic sst signature of the meltwater event and the time span of thc recovery strongly depend on the climatic background state data model comparison reveals that the overall spatial signature of sst anomalies is captured much better in the glacial meltwater experiments than in an analogous experiment under present day conditions in particular a breakdown of the modern thc would induce a much stronger temperature drop in high northern latitudes than did heinrich events during the ice age moreover our results suggest that the present day circulation can settle into a stable off mode whereas the glacial thc was mono stable mono stability may serve as an explanation for the recovery of the thc after heinrich event shutdowns during the last glaciation

evolution of a periglacial landscape in the late devensian environments and palaeobotany of the mepal area cambridgeshire england the landscape evolution of the mepal area from late devensian block fen terrace times to the beginning of the flandrian a period of ca 8000 radiocarbon years is reconstructed stratigraphy is based on borehole transects and single boreholes centred on a depression between the block fen terrace and the isle of ely within the depression is a devensian late glacial sequence with the windermere interstadial represented by radiocarbon dated organic sediments pollen and plant macroscopic remains of the late glacial sediments are analysed plant communities with betula developed in the interstadial before and after the interstadial there is much reworked pollen in the inorganic sediments derived from local pre devensian pleistocene sediments including temperate ipswichian stage sediments and from mass wasting of the local jurassic bedrock periods of such mass movement occur before and after the deposition of the late glacial lake sediments deposition of aeolian sediment occurs later than the main period of mass movement but before the windermere interstadial the relationship of the aeolian sediments in time and space to permafrost indicated by local contraction polygons and cracks is discussed solifluction diverted the flow of the river great ouse from a northeast direction in block fen terrace times to a southwest direction as a channel developed to the west of the chatteris march island this led to a drainage divide in flandrian times copyright 2002 john wiley sons ltd

radiolarian based transfer function for the estimation of sea surface temperatures in the southern ocean atlantic sector a new radiolarian based transfer function for sea surface temperature sst estimations has been developed from 23 taxa and taxa groups in 53 surface sediment samples recovered between 35 and 72 s in the atlantic sector of the southern ocean for the selection of taxa and taxa groups ecological information from water column studies was considered the transfer function allows the estimation of austral summer sst december march ranging between 1 and 18 c with a standard error of estimate of 1 2 c sst estimates from selected late pleistocene squences were sucessfully compared with independent paleotemperature estimates derived from a diatom transfer function this shows that radiolarians provide an excellent tool for paleotemperature reconstructions in pleistocene sediments of the southern ocean

bioturbational mixing depth and carbon flux at the seafloor radiocarbon dating series bulk sediment and organic carbon flux from various atlantic deep sea regions reveal that the thickness of the bioturbated zone increases by 2 cm if food supply increases by 1 gcm 2yr 1 r 0 8 bulk sediment accumulation rates do not influence the depth of bioturbational mixing under normal pelagic sedimentary conditions we believe that this relationship between nutrient supply and benthic mixing can be used for a quantitative and time variable unmixing procedure to improve high resolution stratigraphic correlations and paleoclimatic interpretations of deep sea records

glacial north atlantic sea surface conditions reconstructed by glamap 2000 the response of the tropical ocean to global climate change and the extent of sea ice in the glacial nordic seas belong to the great controversies in paleoclimatology our new reconstruction of peak glacial sea surface temperatures ssts in the atlantic is based on census counts of planktic foraminifera using the maximum similarity technique version 28 simmax 28 modern analog technique with 947 modern analog samples and 119 well dated sediment cores our study compares two slightly different scenarios of the last glacial maximum lgm the environmental processes of the ice age land oceans glaciers epilog and glacial atlantic ocean mapping glamap 2000 time slices the comparison shows that the maximum lgm cooling in the southern hemisphere slightly preceeded that in the north in both time slices sea ice was restricted to the north western margin of the nordic seas during glacial northern summer while the central and eastern parts were ice free during northern glacial winter sea ice advanced to the south of iceland and faeroe in the central northern north atlantic an anticyclonic gyre formed between 45degrees and 60degreesn with a cool water mass centered west of ireland where glacial cooling reached a maximum of 12degreesc in the subtropical ocean gyres the new reconstruction supports the glacial to interglacial stability of sst as shown by climap project members climap 1981 the zonal belt of minimum sst seasonality between 2degrees and 6degreesn suggests that the lgm caloric equator occupied the same latitude as today in contrast to the climap reconstruction the glacial cooling of the tropical east atlantic upwelling belt reached up to 6degrees 8degreesc during northern hemisphere summer differences between these simmax based and published u37 k and mg ca based equatorial sst records are ascribed to strong sst seasonalities and sst signals that were produced by different planktic species groups during different seasons

overview of glacial atlantic ocean mapping glamap 2000 glamap 2000 presents new reconstructions of the atlantic s sea surface temperatures sst at the last glacial maximum lgm defined at both 21 500 18 000 years b p last isotope maximum and 23 000 19 000 years b p maximum glacial sea level low stand and orbital minimum of solar insolation epilog working group see mix et al 2001 these reconstructions use 275 sediment cores between the north pole and 60 s with carefully defined chronostratigraphies four categories of core quality are distinguished more than 100 core sections provide a glacial record with subcentennial to multicentennial scale resolution sst estimates are based on a new set of almost 1000 reference samples of modern planktic foraminifera and on improved transfer function techniques to deduce sst from census counts of microfossils including radiolarians and diatoms new proxies also serve to deduce sea ice boundaries the glamap 2000 sst patterns differ significantly in crucial regions from the climap 1981 reconstruction and thus are important in providing updated boundary conditions to initiate and validate computational models for climate prediction

environmental processes of the ice age land oceans glaciers epilog knowledge of the state of the earth at the last glacial maximum lgm an interval around 21 000 years ago is an important benchmark for understanding the sensitivity of global environmental systems to change much progress in understanding climates of the lgm has occurred in the 20 years since the end of the climap project of the 1970s climate long range investigation mapping and prediction here we review this progress based on presentations and discussion at a rst open science meeting of the epilog project environmental processes of the ice age land oceans glaciers held in delmenhorst germany may 1999 we outline key controversies and document protocols for epilog contributions so that a new synthesis of the lgm earth can emerge as an open project of the world s community of scientists 2001 elsevier science ltd all rights reserved

variability of north atlantic heat transfer during mis 2 1 short term changes in sea surface conditions controlling the thermohaline circulation in the northern north atlantic are expected to be especially efficient in perturbing global climate stability here we assess past variability of sea surface temperature sst in the northeast atlantic and norwegian sea during marine isotope stage mis 2 and in particular during the last glacial maximum lgm five high resolution sst records were established on a meridional transect 53 n 72 n to trace centennial scale oscillations in sst and sea ice cover we used three independent computational techniques simmax modern analogue technique artificial neural networks ann and revised analog method ram to reconstruct sst from planktonic foraminifer census counts simmax and ann reproduced short term sst oscillations of similar magnitude and absolute levels while ram owing to a restrictive analog selection appears less suitable for reconstructing cold end sst the simmax and ann sst reconstructions support the existence of a weak paleo norwegian current during dansgaard oeschger do interstadials number 4 3 2 and 1 during the lgm two warm incursions of 7 c water to occurred in the northern north atlantic but ended north of the iceland faroe ridge a rough numerical estimate shows that the near surface poleward heat transfer from 53 across the iceland faroe ridge up to to 72 n dropped to less than 60 of the modern value during do interstadials and to almost zero during do stadials summer sea ice was generally confined to the area north of 70 n and only rarely expanded southward along the margins of continental ice sheets internal lgm variability of north atlantic 40 n sst in the glamap 2000 compilation sarnthein et al 2003b pflaumann et al 2003 indicates maximum instability in the glacial subpolar gyre and at the iberian margin while in the nordic seas sst was continuously low

modeling the water masses of the atlantic ocean at the last glacial maximum 1 we produced gridded monthly sea surface boundary conditions for the atlantic ocean at the last glacial maximum lgm based on the sea surface temperature reconstruction of the glamap project we used an ocean general circulation model ogcm subject to these sea surface boundary conditions and a corresponding wind stress field from an atmospheric general circulation model to study the differences in the distribution of the main water masses between the lgm and the present our global ogcm is characterized by high vertical resolution low vertical diffusion and isopycnal mixing and hence allows for a realistic representation of the hydrology and circulation of the modern atlantic ocean according to a series of lgm experiments with an increasing sea surface salinity anomaly in the weddell sea the ventilated thermocline was colder than today by 2 3 c in the north atlantic ocean and in the experiment with the largest anomaly 1 0 beyond the global anomaly by 4 5 c in the south atlantic ocean its depth was reduced by 50 m on average most notably in the tropics in the north atlantic ocean the outcrop locations of the thermocline isopycnal surfaces migrated southward by 5 10 and the ventilation increased in the south atlantic ocean the mixed layer and thermocline water masses were dominated by cold water originating from drake passage and the import of warm water from the indian ocean was reduced to about 4 sv or 40 of its modern value antarctic intermediate water was colder by 3 4 c and could be traced as far as 10 n the meridional overturning rates of north atlantic deep water nadw and antarctic bottom water aabw in the atlantic ocean were similar to those of the present day experiment 9 10 sv and 4 sv respectively however nadw cooled by 2 5 c and aabw by 1 c aabw was near the freezing point of seawater at the surface and the saltiest water mass in the atlantic ocean even saltier than nadw we show that the differences between the lgm and the present day experiments can be traced back to the changes in the subpolar and interhemispheric sea surface density gradients

the last glacial maximum lgm in western south island new zealand implications for the global lgm and mis 2 abstract the morainic and outwash deposits of the larrikins la and moana mn formations in north westland are correlated with the m5 t5 and m6 t6 deposits in south westland the la m5 deposits resulted from two separate otira glaciation glacial advances la 1 m5 1 la 2 m5 2 of essentially similar extents pollen sequences in peats and coverbeds extending from before to after the kawakawa tephra 26 500 cal yr bp indicate an extensive period of cold with a slight amelioration beginning shortly before tephra deposition this amelioration which is supported by interpretation of coverbed sequences in south westland separates the la 1 m5 1 and la 2 m5 2 advances the three westland glacial advances la 1 m5 1 la 2 m5 2 and mn m6 culminated at ca 28 000 21 500 and 19 000 cal yr bp the last being followed by major rapid glacier retreat pollen and caco 3 records from dsdp 594 east of the south island reflect contemporary glacier fluctuations on the east side of the southern alps they show the last major cold period as lasting from ca 34 000 to ca 16 000 years ago a period starting before the culmination of the la 1 m5 1 advance and ending later than the beginning of glacier retreat from the mn m6 advance the period from the la 1 m5 1 culmination to the mn m6 culmination represents the lgm in new zealand a slightly longer lgm is recorded in chile and a long lgm may also be indicated in australia a long lgm in the southern hemisphere is supported by the global sea level curve and by the regional antarctic temperature criteria of the vostok ice core these different records indicate a southern hemisphere lgm beginning at least as early as 27 000 years ago much earlier than the ocean last isotope maximum lim from 21 500 to 18 000 years ago the beginning of mis 2 defined primarily from deep sea benthic 18 o at 24 000 years is well after the beginning of ice advances leading to the southern hemisphere lgm a review of global land and ocean correlations is desirable

glacial south atlantic surface temperatures interpolated with a semi inverse ocean model 1 to drive an atmospheric general circulation model sea surface temperatures ssts are needed as lower boundary condition these are well known for the modern ocean but for other time slices the database is very sparse and often complete global sst fields are not available to circumvent this problem the simple ocean model has been developed which estimates surface currents in a diagnostic manner from surface winds horizontal heat transports by advection and diffusion and surface heat fluxes are used to calculated ssts the unknown transports from the deep ocean are inversely estimated from sparse sst data the model can be understood as a method to estimate a global sst field from a sparse data set where it takes into account the wind driven surface circulation the simple model is applied to a set of last glacial maximum ssts reconstructed from a new south atlantic core data set the resultant completed sst field exhibits more structure than the climap reconstruction with larger glacial cooling in the central equatorial atlantic and off the shore of angola namibia and less cooling in the central south atlantic

oxygen 18 16 variability in greenland snow and ice with 10 3 to 105 year time resolution the 3 km long greenland ice sheet project 2 gisp2 ice core presents a 100 000 year detailed oxygen isotope profile covering almost a full glacial interglacial cycle measuranents of isotopic fluctuations in snow frost and atmospheric water vapor samples collected during summer field seasons up to 20 0 are compatible with the large and abrupt 80 160 changes observed in accumulated tim snow pit 15 80 profiles from the gisp2 summit area however show rapid smoothing of the 180 160 signal near the surface beyond about 2 m depth the smoothedi5180 signal is fairly well preserved and can be interpreted in terms of average local weather conditions and climate the longer climate fluctuations also have regional and often global significance in the older part of the record corresponding to marine isotope stages mis 5a to 5d the effect of orbital climate forcing via the 19 and 23 kyr precession cycles and the 41 kyr obliquity cycle is obvious from the end ofmis 5a at about 75 000 years b p till the end of the glacial at the younger dryas preboreal transition at 11 650 years b p the o180 160 record shows frequent rapid switches between intermediate interstadial and low stadial values fourier spectra of the oscillations that are superimposed on the orbitally induced changes contain a strong periodicity at 1 5 kyr a broad peak at 4 0 kyr and additional shorter periods detailed comparison of the gisp2 180 160 record with the vostok antarctica 15d record pacific ocean foraminiferal 180 160 grande pile france tree pollen and insolation indicates that a counterpart to many of the rapid 180 160 fluctuations of gisp2 can be found in the other records and that the gisp2 isotopic changes clearly are the local expression of climate changes of worldwide extent correlation of events on the independent gisp2 and specmap time scales for the interval 10 000 50 000 years b p shows excellent chronometric agreement except possibly for the event labeled 3 1 the glacial to interglacial transition evidently started simultaneously in the arctic and the antarctic but its development and its expression in greenland isotopes was later suppressed by the influence of meltwater especially from the barents sea ice sheet on deep water formation and ocean circulation meltwaters from different ice sheets bordering the north atlantic also influenced ocean circulation during the bolling allerod interstadial complex and the younger dryas and led to a distinct development of european climate and greenland 180 160 values the holocene interval with long term stable mean isotopic values contains several fluauations with periods from years to millennia dominant is a 6 3 year oscillation with amplitude up to 3 to 4 0 periodicities of 11 and 210 years also found in the solar modulated records of the cosmogenic isotopes 1obe and 14c suggest solar processes as the cause of these cycles depression of180 160 values cooling by volcanic eruptions is observed in stacked gisp215 80 records but the effect is small and not likely to trigger major climate changes

arctic ocean during the last glacial maximum atlantic and polar domains of surface water mass distribution and ice cover on the basis of 52 sediment cores analyzed and dated at high resolution the paleoceanography and climate of the last glacial maximum lgm were reconstructed in detail for the fram strait and the eastern and central arctic ocean sediment composition and stable isotope data suggest three distinct paleoenvironments 1 a productive region in the eastern to central fram strait and along the northern barents sea continental margin characterized by atlantic water advection frequent open water conditions and occasional local meltwater supply and iceberg calving from the barents sea ice sheet 2 an intermediate region in the southwestern eurasian basin up to 84 85 n and the western fram strait characterized by subsurface atlantic water advection and recirculation a moderately high planktic productivity and a perennial ice cover that breaks up only occasionally and 3 a central arctic region north of 85 n in the eurasian basin characterized by a low salinity surface water layer and a thick ice cover that strongly reduces bioproduction and bulk sedimentation rates although the total inflow of atlantic water into the arctic ocean may have been reduced during the lgm its impact on ice coverage and halocline structure in the fram strait and southwestern eurasian basin was strong

variation of foraminiferal sr ca over quaternary glacial interglacial cycles evidence for changes in mean ocean sr ca 1 records of sr ca changes in planktonic and benthic foraminifera from diverse hydrographic settings reveal coherent variability 5 1 between ocean basins and between surface and deep waters over the past 300 kyr there is a general increase in foraminiferal sr ca over the penultimate glaciation declining to minimum values during stage 5 and an increase in sr ca from stage 5 through stage 2 coincident changes in benthic foraminifera records from the atlantic and pacific basins imply that sr ca variations are not dominated by dissolution planktonic culturing data provide evidence that the downcore sr ca variations are not controlled by temperature changes and suggest only a small influence of salinity and ph variation common to the records is most readily explained by changes in mean ocean sr ca if fossil foraminifera reliably record higher glacial seawater sr ca coral sr paleothermometry would underestimate sea surface temperature during glacialepisodes

quaternary surface water temperature estimations calibration of a diatom transfer function for the southern ocean the quantitative diatom analysis of 218 surface sediment samples recovered in the atlantic and western indian sector of the southern ocean is used to define a base of reference data for paleotemperature estimations from diatom assemblages using the imbrie and kipp transfer function method the criteria which justify the exclusion of samples and species out of the raw data set in order to define a reference database are outlined and discussed sensitivity tests with eight data sets were achieved evaluating the effects of overall dominance of single species different methods of species abundance ranking and no analog conditions e g eucampia antarctica on the estimated paleotemperatures the defined transfer functions were applied on a sediment core from the northern antarctic zone overall dominance of fragilariopsis kerguelensis in the diatom assemblages resulted in a close affinity between paleotemperature curve and relative abundance pattern of this species downcore logarithmic conversion of counting data applied with other ranking methods in order to compensate the dominance of f kerguelensis revealed the best statistical results a reliable diatom transfer function for future paleotemperature estimations is presented

sea surface temperatures in the equatorial and south atlantic ocean during the last glacial maximum 23 19 ka 1 we used planktic foraminiferal assemblages in 70 sediment cores from the tropical and subtropical south atlantic ocean 10 n 37 s to estimate annual mean sea surface temperatures ssts and seasonality for the last glacial maximum with a modified version of the imbrie kipp transfer function method iktf that takes into account the abundance of rare but temperature sensitive species in contrast to climap project members 1981 the reconstructed ssts indicate cooler glacial ssts in the entire tropical subtropical south atlantic with strongest cooling in the upwelling region off namibia 7 10 c and smallest cooling 1 2 c in the western subtropical gyre in the western atlantic our data support recent temperature estimates from other proxies in the upwelling regions in the eastern atlantic our data conflict with sst reconstructions from alkenones which may be due to an environmental preference of the alkenone producing algae or to an underestimation of foraminiferal ssts due to anomalous high abundances of n pachyderma sinistral

terrestrial conditions at the last glacial maximum and climap sea surface temperature estimates are they consistent climap 1981 seasonal reconstruction of the earth s surface at the last glacial maximum geological society of america map and chart series mc 36 boundary conditions were used as inputs to the giss general circulation model and the last glacial maximum lgm climate was simulated for six model years the simulation was compared with snow line depression and pollen inferred temperature data at low latitudes specifically for hawaii colombia east africa and new guinea the model does not produced as much cooling at low latitudes as is implied by the terrestrial evidence an alternative experiment in which the climap sea surface temperatures were uniformly lowered by 2 c produces a better fit to the land data although in hawaii model temperatures are still too warm the relatively warm climap tropical sea surface temperatures also provide for only a slight decrease in the hydrologic cycle in the model in contrast to both evidence of lgm tropical aridity and the results of the experiment with colder ocean temperatures with the climap sea surface temperatures the lgm global annual mean surface air temperature is 3 6 c colder than at present if the ocean temperatures were allowed to cool in conformity with the model s radiation balance the lgm simulation would be 5 6 c colder than today and in better agreement with the tropical land evidence

timing of the last glacial maximum from observed sea level minima during the last glacial maximum ice sheets covered large areas in northern latitudes and global temperatures were significantly lower than today but few direct estimates exist of the volume of the ice sheets or the timing and rates of change during their advance and retreat here we analyze four distinct sediment facies in the shallow tectonically stable bonaparte gulf australia each of which is characteristic of a distinct range in sea level to estimate the maximum volume of land based ice during the last glaciation and the timing of the initial melting phase we use faunal assemblages and preservation status of the sediments to distinguish open marine shallow marine marginal marine and brackish conditions and estimate the timing and the mass of the ice sheets using radiocarbon dating and glacio hydroisostatic modelling our results indicate that from at least 22 000 to 19 000 calendar years before present land based ice volume was at its maximum exceeding today s grounded ice sheets by 52 5 x 10 exp 6 cu km a rapid decrease in ice volume by about 10 percent within a few hundred years terminated the last glacial maximum at 19 000 250 years

the reconstruction of late quaternary antarctic sea ice distribution the use of diatoms as a proxy for sea ice the study of annual diatom transfer from the southern ocean surface to the sea floor using time series sediment traps combined with the mapping of diatom assemblages from surface sediments results in the definition of a proxy for past variations of sea ice extent the application and robustness of the proposed proxy are demonstrated by the study of late pleistocene sediment cores recovered from different environmental regimes in the southern ocean relative amounts of the sea ice indicator diatoms fragilariopsis cylindrus and fragilariopsis curta of 3 in diatom assemblages preserved in sediments are representative of the presence of seasonal winter sea ice summer sea ice occurrence is signalled by a distinct drop in biogenic sedimentation rate as a result of strongly reduced biogenic export in the presence 3 of diatom assemblage of the deep temperature diatom fragilariopsis obliquecostata the spatial and temporal distribution pattern of the sea ice proxy indicates significant sea ice variations during marine isotope stages 1 and 5 in the present antarctic zone of the southern ocean during glacial maxima the antarctic winter sea ice was extended into the present polar front zone while the antarctic summer sea ice was most probably expanded into the area of the present winter sea ice edge during the short climatic optima at the onset of interglacial periods the winter sea ice extent was distinctly reduced