the influence of changing orbital parameters and surface boundary conditions on climate simulations for the past 18 000 years abstract general circulation model experiments at 3000 year intervals for the past 18 000 years were made to estimate the magnitude timing and pattern of the climatic response to prescribed changes of orbital parameters date of perihelion axial tilt eccentricity and glacial age lower boundary conditions ice sheets land albedo sea ice and sea surface temperature the experiments used the community climate model ccm of the national center for atmospheric research ncar the response of monsoon circulations and tropical precipitation to the orbitally produced solar radiation changes was much larger than the response to changes of glacial age boundary conditions the continental interior of eurasia was 2 4 k warmer in summer and summer monsoon precipitation of north africa south asia was increased by 10 20 between 12 000 and 6000 yr bp before present when perihelion occurred during northern summer rather than in winter as now and the earth s axial tilt was larger than now southern hemisphe

lateglacial calendar year chronology based on annually laminated sediments from lake meerfelder maar germany abstract annually laminated sediments from lake meerfelder maar mfm in the eifel germany provide an independent calendar year timescale for the last glacial interglacial transition changes in varve thickness and varve facies reflect significant environment variations during this period the general micro facies pattern confirms that diatomaceous organic varves are favoured during warm climatic phases while cold periods generate higher allochthonous sediment fluxes an exception is the significant increase in diatom blooms at the beginning of the younger dryas six lateglacial biozones have been defined by litt and stebich quaternary international 1999 the sediment record comprises two tephra layers as chronomarkers the laacher see tephra 12 880 varve years bp is a continent wide correlation horizon while the ulmener maar tephra provides regional chronological links the beginning of the lateglacial warming is dated at 14 450 varve years vyrs bp which is regarded as the minimum age three abrupt cold spells interrupted the lateglacial interstadial at 13 800 vyrs bp oldest dryas 13 540 vyrs bp older dryas and 12 680 vyrs bp younger dryas the oldest dryas 130 years and the older dryas 190 years were rather short while the younger dryas lasted much longer 1090 years the mfm chronology was compared with ice core timescales from gisp2 and grip there is a good agreement between these timescales with the grip model age ss09 providing the best match to the mfm chronology

bio and chronostratigraphy of the lateglacial in the eifel region germany abstract in recent years enormous success has been achieved in varve counting of the eifel maar lakes but a detailed correlation with the biostratigraphy has been missing in this paper we present new palynological results of the lateglacial sequences from holzmaar lake and meerfelder maar lake based on annually laminated sediments in particular the meerfelder maar has great potential because in contrast to the holzmaar the sequence between the ulmener maar tephra 11 000 varve years bp and the laacher see tephra 12 880 varve years bp including the younger dryas is undisturbed and complete therefore we currently use the meerfelder maar chronology brauer et al 1999b as an independent varve calendar for the biostratigraphy of the lateglacial the palynological signals of both maar lakes are in good agreement and can easily be correlated with one another and with type sections type regions in northwestern germany and jutland the sequences of the eifel maar lakes have the quality of hypostratotypes with regional biozones based on an absolute time scale

a mid european decadal isotope climate record from 15 500 to 5000 years b p oxygen isotope ratios of precipitation delta18op inferred from deep lake ostracods from the ammersee southern germany provide a climate record with decadal resolution the record in detail shows many of the rapid climate shifts seen in central greenland ice cores between 15 000 and 5000 years before the present b p negative excursions in the estimated delta18op from both of these records likely reflect short weakenings of the thermohaline circulation caused by episodic discharges of continental freshwater into the north atlantic deviating millennial scale trends however indicate that climate gradients between europe and greenland changed systematically reflecting a gradual rearrangement of north atlantic circulation during deglaciation

deglacial sea level record from tahiti corals and the timing of global meltwater discharge the timing of the last deglaciation is important to our understanding of the dynamics of large ice sheets1 and their effects on the earth s surface2 3 moreover the disappearance of the glacial ice sheets was responsible for dramatic increases in freshwater fluxes to the oceans which probably disturbed the ocean s thermohaline circulation and hence global climate4 7 sea level increases bear witness to the melting of continental ice sheets but only two such records from barbados8 9 and new guinea10 11 corals have been accurately dated but these corals overlie active subduction zones where tectonic movements are large and often discontinuous especially in new guinea so the apparent sea level records may be contaminated by a complex tectonic component here we date fossil corals from tahiti which is far from plate boundaries and thus is likely to be tectonically relatively stable and remote from the locations of large former ice sheets the resulting record indicates a large sea level jump shortly before 13 800 calendar years bp which corresponds to meltwater pulse 1a in the barbados coral records8 9 the timing of this event is more accurately constrained in the tahiti record revealing that the meltwater pulse coincides with a short and intense climate cooling event12 15 that followed the initiation of the bolling allerod warm period12 16 but preceded the younger dryas cold event by about 1 000 years

geomorphic expression of abrupt climate change in southwestern north america at the glacial termination eolian and subaqueous landforms composed of gypsum sand provide geomorphic evidence for a wet episode at the termination of glacial climate in southwestern north america drying of pluvial lake estancia central new mexico occurred after ca 12 000 14c yr b p thereafter eolian landforms on the old lake floor constructed of gypsum sand were overridden by rising lake water modified by subaqueous processes and organized into beach ridges along the lake s eastern shore preservation of preexisting eolian landforms in the shallow lake suggests abupt changes in lake level and climate available radiocarbon ages suggest that the final highstand recorded by beach ridges may have developed during the younger dryas yd stade the beach ridges provide information about lake surface area which was 45 of the lake area reached during the maximum highstands of the late pleistocene a similar proportional response has been reported for yd climate changes outside the north atlantic region

absolute dating of the late glacial period in switzerland using annually laminated sediments abstract results of a high resolution late glacial ams 14 c chronology from rotsee central switzerland have given evidence that the atmospheric radiocarbon concentration was not constant between 13 000 and 9500 yr b p this resulted in three marked phases of constant radiocarbon age at 12 700 at 10 000 and at 9500 yr b p new results of a late glacial varve chronology from soppensee central switzerland suggest that the younger two phases of constant 14 c age each had a duration of ca 400 calendar years the length of the late glacial chronozones has been calculated on the basis of these replicate varve counts and a comparison with their estimated duration in radiocarbon years shows that the estimated duration of the chronozones bolling ca 800 calendar yr vs 1000 14 c yr and younger dryas ca 900 calendar yr vs 1000 14 c yr agree with the expected time span whereas the estimated duration of the allerod chronozone ca 400 calendar yr vs 1000 14 c yr is substantially shorter than expected furthermore a tentative comparison of varve ages and 14 c ages suggests that the varve chronology is more than 1000 yr offset toward older ages from the radiocarbon chronology during the late glacial period

a calendar age estimate of the younger dryas holocene boundary at krakenes western norway the younger dryas holocene transition yd h in the sediments of krakenes lake western norway is well marked both lithologically and palaeobiologically at 756 5 cm in the investigated core a ser

terrestrial laser scanner imaging for the cyclostratigraphy and astronomical tuning of the ypresian lutetian pelagic section of smirra umbria marche basin italy abstract terrestrial laser scanner imaging is applied together with calcimetry and lithofacies logging for the cyclostratigraphic characterization of the ypresian lutetian pelagites exposed in the smirra section umbria marche basin italy the necessary chronostratigraphic framework is provided by detailed bio and magnetostratigraphic analyses which allow locating the ypresian lutetian boundary in this section terrestrial laser scanner intensity is compared to carbonate content values obtained through calcimetric analyses carried out on samples taken from the same section and is found to represent a good proxy for lithology in these pelagic homogenites time series analysis highlights milankovitch frequencies particularly evident in the high resolution terrestrial laser scanner intensity series the recognition of distinctive low frequency 1 myr features in the amplitude oscillations of short eccentricity as well as its 400 kyr modulation long eccentricity promote a tuning of the smirra series using the most recent astronomic solution la2010 nominal which provides insights on the ages of the y l boundary and of the main biostratigraphic and magnetostratigraphic events in the umbria marche basin results confirm the value of high resolution mm scale terrestrial laser scanning for scrutinizing pelagite successions in search of low frequency cycles that may help in the refinement of the astrochronological time scale

the late glacial pedogenesis interrupted by aeolian activity in central poland records from the lake gościąz catchment abstract an interdisciplinary study was undertaken to reconstruct the late glacial fluvioglacial and aeolian sediment transformations with a particular focus on soil forming processes the studies included complex pedological research physical and chemical properties x ray diffraction xrd analysis of clay minerals and optically stimulated luminescence osl dating on soil deposit sequences developed within the aeolian landscape of inland dunes in the lake go ci z catchment central poland late glacial buried bwb soil horizons are known as finow soils this paleosol was identified in the central part of inland dunes in vertical perspective developed from aeolian material deposited on fluvioglacial sediments the average content of silt and clay in this paleosols ranged from 7 3 to 41 1 and from 6 7 to 12 6 respectively in other soil horizons within profiles the average content of these granulometric fractions was about 3 and 1 5 respectively the dominance of dioctahedral vermiculite and the higher content of free iron oxides especially oxalate form and aluminium within bwb horizons indicates their pedogenic origin the osl dates suggested that finow soil fossilization began along with the development of aeolian processes in the late glacial cold periods the older dryas and the younger dryas while finow soil development took place in the warmer periods of the late glacial bolling allerod these results were consistent with data from germany other stands in northern poland and the tomsk priobye region se western siberia

surface temperature in nw europe during the younger dryas agcm simulation compared with temperature reconstructions during the younger dryas yd the climate in nw europe returned to near glacial conditions to improve our understanding of climate variability during this cold interval we compare an agcm simulation of this climate performed with the echam model with temperature reconstructions for nw europe based on geological and paleoecological records maps for the mean winter summer and annual temperature are presented the simulated winters are consistent with reconstructions in the northern part of the study area a strong deviation is noted in ireland and england where the simulation is too warm by at least 10 c it appears that the n atlantic was cooler than prescribed in the yd simulation including a southward expansion of the sea ice margin the comparison for the summer shows a too warm continental europe in the simulation supposedly these anomalously warm conditions are caused by the agcm s response to the prescribed increased summer insolation the region of maximum summer cooling is similar in both the simulation and reconstruction i e s sweden we suggest that this is due to the local cooling effect of the scandinavian ice sheet compared to the present climate a considerable increase of the annual temperature range is inferred especially for regions close to the atlantic ocean

reef drowning during the last deglaciation evidence for catastrophic sea level rise and ice sheet collapse elevations and ages of drowned acropora palmata reefs from the caribbean atlantic region document three catastrophic metre scale sea level rise events during the last deglaciation these catastrophic rises were synchronous with 1 collapse of the laurentide and antarctic ice sheets 2 dramatic reorganization of ocean atmosphere circulation and 3 releases of huge volumes of subglacial and proglacial meltwater this correlation suggests that release of stored meltwater periodically destabilized ice sheets causing them to collapse and send huge fleets of icebergs into the atlantic massive inputs of ice not only produced catastrophic sea level rise drowning reefs and destabilizing other ice sheets but also rapidly reduced the elevation of the laurentide ice sheet flipping atmospheric circulation patterns and forcing warm equatorial waters into the frigid north atlantic such dramatic evidence of catastrophic climate and sea level change during deglaciation has potentially disastrous implications for the future especially as the stability of remaining ice sheets such as in west antarctica is in question

deglacial changes in ocean circulation from an extended radiocarbon calibration temporal variations in the atmospheric concentration of radiocarbon sometimes result in radiocarbon based age estimates of biogenic material that do not agree with true calendar age this problem is particularly severe beyond the limit of the high resolution radiocarbon calibration based on tree ring data which stretches back only to1 2 about 11 8 kyr before present bp near the termination of the younger dryas cold period if a wide range of palaeoclimate records are to be exploited for better understanding the rates and patterns of environmental change during the last deglaciation extending the well calibrated radiocarbon timescale back further in time is crucial several studies attempting such an extension using uranium thorium dated corals3 4 5 and laminae counts in varved sediments6 7 8 9 show conflicting results here we use radiocarbon data from varved sediments in the cariaco basin in the southern caribbean sea to construct an accurate and continuous radiocarbon calibration for the period 9 to 14 5 kyr bp nearly 3 000 years beyond the tree ring based calibration a simple model compared to the calculated atmospheric radiocarbon concentration and palaeoclimate data from the same sediment core suggests that north atlantic deep water formation shut down during the younger dryas period but was gradually replaced by an alternative mode of convection possibly via the formation of north atlantic intermediate water

land ice teleconnections of cold climatic periods during the last glacial interglacial transition independent calendar year chronologies are a basic requirement for the establishment of high resolution land ice teleconnections the annually laminated meerfelder maar record provides both an independent chronology established by varve counting and high resolution lithological proxy data for the period of the last glacial interglacial transition these data reveal a series of four periods of climatic deterioration coinciding with negative isotopic deviations in the grip record signal thus demonstrating the synchronicity of environment changes in western germany and temperature shifts in greenland the terrestrial data supports a further sub division of the event stratigraphy based on the grip core by introducing the cold event gi 1c2 between 13 500 and 13 400 calendar years bp multiproxy analyses reveal that the environmental response at meerfelder maar was not linear throughout the lateglacial but was modified by local processes a change in the response of the lake environment to climate deterioration was observed during sub stage gi 1b gerzensee oscillation the only event with gradual rather than abrupt transitions the two fold character of the younger dryas as seen in the grip record is more pronounced in the meerfelder maar record this lithological signal occurred with a delay of 60 years to the grip signal and has been linked to a shift in the catchment it is proposed that the trigger for this shift was a trend towards a more humid second half of the younger dryas

late glacial climatic oscillations as recorded in swiss lake sediments regional pollen assemblage zones for the late glacial period of the swiss plateau are introduced and defined they include four major zones artemisia juniperus hippophae betula pinus paz with several subzones pollen and oxygen isotope analyses on lacustrine sediments from several lakes in the area reveal four distinct phases of climatic oscillation in the time period of 13 000 9500 yr bp the first oscillation termed the aegelsee fluctuation occurs shortly before 12 000 yr bp and varve counts suggest its duration was ca 100 yr it is characterised by a short decrease in the oxygen isotopes as well as a short increase in nap associated with a depression in birch pollen values the second oscillation which occurs in the 18o record shortly before the deposition of the laacher see tephra ca 11 000 yr bp is termed the gerzensee fluctuation it occurs during a pine dominated phase and its vegetational effects cannot be determined palynologically the most prominent regressive phase is the younger dryas biozone ca 10 700 10 000 yr bp characterised by an increase in heliophilous nap and low 18o values the younger dryas biozone can often be subdivided palynologically into two parts a first part rich in grasses and juniper and a second part with higher filipendula and birch values during the preboreal biozone another distinct oscillation is evidenced only in the oxygen isotope ratios comparison of the swiss oxygen isotope profiles with the greenland dye 3 record suggests that not only the three major shifts in the 18o curves but also the minor ones are closely comparable suggesting some common climatic control

high resolution lacustrine record of the late glacial holocene transition in central europe abstract in this paper we present the high resolution record of proxy climatic data in central europe during the final stages of the last deglaciation derived from the annually laminated sediments of lake go ciaz central poland the isotopic palynological and other microfossil data confirm sudden changes of climate at the onset and termination of the younger dryas completed within 150 and 70 years respectively in close agreement with the previous estimates derived from the polar ice cores and marine sediments in the upper yd some amelioration of climate took place already about 600 years before the main yd preboreal transition counting of annual varves in the lake sediments allows a direct estimate of the duration of the younger sdryas in central europe it lasted approximately 1640 years substantially longer than suggested by previous estimates derived from laminated lake sediments and glacial varves but agreeing with the radiocarbon calibration data obtained for barbados corals the calendar ages of the boundaries of the yd 12 920 and 11 280 cal bp are tentatively set

varve chronology and palynology of the lateglacial in northwest germany from lacustrine sediments of hamelsee in lower saxony abstract the hamelsee is a dolina from a collapse over permian salt that occurred at the end of the pleniglacial it is more than 21 m deep and contains 18 m of lacustrine sediments the lateglacial sediments in the central part of the lake consist of 2 7 m from 15 to 17 7 m of sapropelic and silty muds which are mostly laminated and partly bioturbated minor slumps occur mainly during colder phases the subdivision of the lateglacial is based on pollen zones multidisciplinary studies of the microfacies from thin sections geochemistry pollen analysis and rotifer analysis allow environmental and palaeoclimatological interpretations to be made the biozones of the lateglacial and their boundaries are marked by rapid climatic changes though covering comparatively short periods of time they are not monotonous but characterized by minor internal climatic fluctuations the sediments of the meiendorf and oldest dryas are not laminated the allerod sediment is seasonally varved without interruption and encompasses 625 yr the eruption of the laacher see volcano 12 900 cal bp had an impact on the climate during the following 10 yr the transition from the allerod to the younger dryas took some 50 yr and it occurred 200 yr after the eruption of the laacher see volcano the abrupt change at the end of the lateglacial 11 560 cal bp occurred within less than 10 yr however many proxies reacted with a time lapse of 15 to 30 yr

deglacial meltwater discharge north atlantic deep circulation and abrupt climate change high resolution paleogeochemical data from the north atlantic ocean indicate that in the interval 15 000 to 10 000 14c years before present b p north atlantic deep water nadw production was decreased or eliminated four times at about 14 500 and probably older 13 500 12 000 and 10 500 years b p each of these changes occurred at the same time as abrupt events of meltwater discharge to the surface ocean inferred from oxygen isotope studies of planktonic foraminifera and from glacial geological studies on land in addition each of these times may be associated with brief episodes of cooler climate in the north atlantic region the best example of which is the younger dryas cooling of 10 500 years ago these results support models linking meltwater discharge decreased nadw production and decreased north atlantic heat flux

late quaternary environmental and climatic changes in central europe as inferred from the composition of organic matter in annually laminated maar lake sediments 1 geochemical elemental analysis bulk 13ctoc thermal degradation techniques molecular analysis of n alkanes and microscopic investigations maceral analysis vitrinite reflectance were performed 1 to characterize the organic matter om in sediments from two maar lakes in the westeifel volcanic field germany and 2 to discuss paleoenvironmental processes which have controlled the accumulation and preservation of om the annually laminated sediments show a wide range of organic carbon contents between 0 3 and 21 4 toc and hydrogen index values between 80 and 501 mg hc g toc well developed laminations mirror suboxic to anoxic bottom waters diagnostic compounds in the pyrolysates and microscopic analysis permit discrimination between the principal om sources and their variations over time provide important evidence for the reconstruction of the environmental histories of the lakes and their watershed the significance of terrigenous om is reflected by the occurrence of methoxyphenols in the insoluble as well as mid and long chain n alkanes in the soluble om which are indicative of land plant or macrophyte input to the lakes the relative abundance of certain homologues together with the amount of terrigenous macerals can be used to show differences in higher plant input and vegetation changes through time during the pleniglacial and younger dryas period high reflecting reworked om was introduced by soil erosion in an environment with relatively open vegetation the alkylphenols in the pyrolysates originate partly from the microbial reworking of proteinaceous tyrosine moieties and or reflect a direct contribution from cyanobacteria we assume that variations in the carbon isotopic composition of om are mainly due to changes in the lake s primary productivity with the exception of the pleniglacial various forms of land use are reflected by increasing amounts of terrigenous particles as well as chemical plant markers from 500 varve years b p until present the organic geochemical and microscopic data correlate well with other proxy information about climate dependent fluctuations in the ecosystem of the studied sites

the atmospheric winter circulation during the younger dryas stadial in the atlantic european sector the younger dryas yd stadial signified an interruption of the warming during the transition from the last glacial to the present interglacial the mechanism responsible for this cooling is still uncertain so valuable information concerning climate variability can be obtained by numerical simulation of the yd climate we performed four experiments on the younger dryas climate with the hamburg atmospheric general circulation model here we use the results of these experiments which differed in prescribed boundary conditions to characterize the atmospheric winter circulation during the yd stadial in the north atlantic european sector the 10 year means of the following variables are presented sea level pressure 500 hpa geopotential heights and 200 hpa winds in addition we used daily values to calculate an index to assess the occurrence of blocking and strong zonal flow and to compute storm tracks our results show that the yd cooling in europe was present with a strong and stable westerly circulation without blocking this is in conflict with an earlier study suggesting frequent easterly winds over nw europe in our experiments the sea ice cover in the north atlantic ocean was the crucial factor forcing this specific yd circulation moreover the jet stream over the north atlantic was strengthened considerably causing an enhanced cyclonic activity over the eurasian continent the yd winter circulation was different from the circulation found in most simulation studies on the last glacial maximum since no glacial anticyclones were present and no split of the jet stream occurred

the δ18o record along the greenland ice core project deep ice core and the problem of possible eemian climatic instability over 70 000 samples from the 3029 m long greenland ice core project grip ice core drilled on the top of the greenland ice sheet summit have been analyzed for 8o a highly detailed and continuous 8o profile has thus been obtained and is discussed in terms of past temperatures in greenland we also discuss a three core stacked annual 8o profile for the past 917 years the short term 50 years variability of the annual 8o signal is found to be 1 in the holocene and estimates for the coldest parts of the last glacial are 3 or higher these data also provide insights into possible disturbances of the stratigraphic layering in the core which seems to be sound down to the onset of the eemian spectral analysis of highly detailed sequences of the profile helps determine the smoothing of the 8o signal which for the holocene ice is found to be considerably stronger than expected we suggest this is due to a process involving diffusion of water molecules along crystal boundaries in the recrystallizing ice matrix deconvolution techniques were employed for restoring with great confidence the highly attenuated annual 8o signal in the holocene we confirm earlier findings of dramatic temperature changes in greenland during the last glacial cycle abrupt and strong climatic shifts are also found within the eem sangamon interglaciation which is normally recorded as a period of warm and stable climate in lower latitudes the stratigraphic continuity of the eemian layers is consequently discussed in section 3 of this paper in terms of all pertinent data which we are not able to reconcile

late glacial to holocene aeolian deposition in northeastern europe the timing of sedimentation at the iisaku site ne estonia abstract the late glacial and holocene aeolian inland dune complex at iisaku ne estonia has been investigated using an accurate and detailed compilation of the sedimentary properties and chronological framework the quartz grains forming the dunes are very variable reflecting aeolian weathering and periglacial conditions both prior and after deposition although the morphological forms and the sedimentary record point to a dune like environment the transport record reflects either a short transport time or and distance and a contribution from neighbouring sedimentary environments dune development in the area was strongly controlled by the formation of the baltic ice lake bil in front of the retreating glacier luminescence ages from the aeolian complex suggest continuous deposition between 13 3 1 2 to 10 5 0 7 ka however the chronology of sand deposition also suggests phases in this aeolian activity 1 at 13 3 1 2 ka and onwards possibly correlated with the existence of an island separating the bil and peipsi lake 2 between 12 7 0 8 12 5 0 8 ka representing the younger dryas cold reversal 3 between 11 5 0 7 10 9 0 8 ka indicating that aeolian deposition continued over the younger dryas holocene boundary and 4 early holocene sand drift at 10 5 0 7 ka

high resolution late glacial chronology for the gerzensee lake record switzerland δ18o correlation between a gerzensee stack and ngrip oxygen isotope variations were analyzed on bulk samples of shallow water lake marl from gerzensee switzerland in order to evaluate major and minor climatic oscillations during the late glacial to highlight the overall signature of the gerzensee 18o record 18o records of four parallel sediment cores were first correlated by synchronizing major isotope shifts and pollen abundances then the records were stacked with a weighting depending on the differing sampling resolution to develop a precise chronology the 18o stack was then correlated with the ngrip 18o record applying a monte carlo simulation relying on the assumption that the shifts in 18o were climate driven and synchronous in both archives the established chronology on the gicc05 time scale is the basis for 1 comparing the 18o changes recorded in gerzensee with observed climatic and environmental fluctuations over the whole north atlantic region and 2 comparing sedimentological and biological changes during the rapid warming with smaller climatic variations during the bolling allerod period the 18o record of gerzensee is characterized by two major isotope shifts at the onset and at the termination of the bolling allerod warm period as well as four intervening negative shifts labeled gi 1e2 d c2 and b which show a shift of one third to one fourth of the major 18o shifts at the beginning and end of the bolling allerod despite some inconsistency in terminology these oscillations can be observed in various climatic proxies over wide regions in the north atlantic region especially in reconstructed colder temperatures and they seem to be caused by hemispheric climatic variations

sudden changes in north atlantic circulation during the last deglaciation sudden changes in the flow of warm atlantic surface waters into the norwegian sea occurred frequently during the last deglaciation typically involving shifts in sea surface temperature of 5 c in fewer than 40 years these led to equally large and rapid changes in atmospheric temperatures and to shifts in atlantic deep thermo haline circulation and ice sheet melting rates

origin of the first global meltwater pulse following the last glacial maximum well dated sea level records show that the glacioeustatic rise following the last glacial maximum was characterized by two or possibly three brief intervals of rapid sea level rise separating periods with much lower rates these very high rates of sea level rise indicate periods of exceptionally rapid deglaciation of remaining ice sheets the laurentide ice sheet is commonly targeted as the source of the first and largest of the meltwater pulses mwp ia between 14 200 12 200 14c years b p and 13 700 years ago 11 700 14c years b p in all oceanic records of deglaciation of the former northern hemisphere ice sheets that we review only those from the gulf of mexico and the bermuda rise show evidence of low 18o values at the time of mwp ia identifying the southern laurentide ice sheet as a potential source for mwp ia we question this source for mwp ia however because 1 ice sheet models suggest that this sector of the ice sheet contributed only a fraction 10 of the sea level needed for mwp ia 2 melting this sector of the ice sheet at the necessary rate to explain mwp ia is physically implausible and 3 ocean models predict a much stronger thermohaline response to the inferred freshwater pulse out of the mississippi river into the north atlantic than is recorded this leaves the antarctic ice sheet as the only other ice sheet capable of delivering enough sea level to explain mwp ia but there are currently no well dated high resolution records to document this hypothesis these conclusions suggest that reconstructions of the laurentide ice sheet in the ice 4g model which are constrained to match the sea level record may be too low for time periods younger than 15 000 years ago furthermore 18o records from the gulf of mexico show variable fluxes of meltwater from the southern margin of the laurentide ice sheet which can be traced to the opening and closing of eastward draining glacial lake outlets associated with surging ice sheet behavior these variable fluxes through eastern outlets were apparently sufficient to affect formation of north atlantic deep water thus underscoring the sensitivity of this process to changes in freshwater forcing

late glacial erosion and pedogenesis dynamics evidence from high resolution lacustrine archives and paleosols in south bohemia czech republic abstract sediments from three paleolakes and two paleosol horizons in south bohemia czech republic provide evidence of climate change and landscape evolution in central eastern europe on millennial to centennial timescales over the late glacial 16 11 5 ky based on a combination of geochemical sedimentological and geophysical proxy indicators along with the pollen record and soil micromorphology we propose a relationship between vegetation cover soil development and erosional processes four major and two minor environmental stages identified in all investigated paleo lakes were broadly correlated with the late glacial climatostratigraphy short term decadal to centennial climatic deteriorations between the bolling and allerod and within the allerod have been correlated with the older dryas and the intra allerod cold period iacp respectively b horizons of two gleyic podzols discovered under aeolian sand dunes in the lake catchments were dated to the allerod interstadial and were parallelized with usselo soils pedostratigraphical marker horizons of west and northern central europe the upper parts of these soils have signs of colluvial processes according to the radiocarbon dating the erosion occurred at 13 155 150 cal yr bp and can be associated with the iacp event which is marked by a significant input of allogenic material into the lake basins we attribute the significant increase in the iron and consequent phosphorus content in the lake sediments during the allerod to the podzolization that occurred with the humid interstadial conditions

high resolution sediment and vegetation responses to younger dryas climate change in varved lake sediments from meerfelder maar germany abstract this work focuses on a 1900 year section of varved sediments from lake meerfelder maar mfm extending from the late allerod to the preboreal varve counting provides the chronological framework and determines the length of younger dryas to 1025 1090 years a strong relation between climate change environment response and depositional processes has been found in consequence varve microfacies variations are a sensitive proxy for environment changes these are reflected for example in erosion processes within the lake s catchment minerogenic input and lake productivity diatom blooms the observed varve changes have been quantified by multiproxy analyses of physical and chemical sediment parameters with a resolution of between 8 and 40 years depending on sedimentation rate in addition high resolution palynological investigations provide the biostratigraphical subdivision based on changes in the vegetation occurring during the same time interval varve observations reveal that environment changes at the beginning and the end of the younger dryas occurred within 20 50 years furthermore sediment and vegetation changes were synchronous within the actual precision of the mfm and grip chronologies divergence of only a few decades terrestrial responses in western europe occurred quasi synchronous to temperature changes in greenland

an event stratigraphy for the last termination in the north atlantic region based on the greenland ice core record a proposal by the intimate group it is suggested that the grip greenland ice core should constitute the stratotype for the last termination based on the oxygen isotope signal in that core a new event stratigraphy spanning the time interval from ca 22 0 to 11 5 k grip yr bp ca 19 0 10 0 k 14 c yr bp is proposed for the north atlantic region this covers the period from the last glacial maximum through termination 1 of the deep ocean record to the pleistocene holocene boundary and encompasses the last glacial late glacial of the traditional northwest european stratigraphy the isotopic record for this period is divided into two stadial episodes greenland stadials 1 gs 1 and 2 gs 2 and two interstadial events greenland interstadials 1 gi 1 and 2 gi 2 in addition gi 1 and gs 2 are further subdivided into shorter episodes the event stratigraphy is equally applicable to ice core marine and terrestrial records and is considered to be a more appropriate classificatory scheme than the terrestrially based radiocarbon dated chronostratigraphy that has been used hitherto 1998 john wiley sons ltd

primary aerosol sea salt and soil dust deposited in greenland ice during the last climatic cycle comparison with east antarctic records ion chromatography data of ca mg cl and ca and coulter counter particle measurements are used to study the cycle of marine and continental primary aerosol reaching greenland in relation to climatic changes over the last 150 kyr a detailed comparison between greenland dome summit and antarctic vostok records provides new insight on a potential link between northern and southern patterns ca is a good indicator of continental input and is mainly emitted as caco3 an attempt is made to estimate the contribution of aluminosilicates using the concentration of insoluble particles greater than 0 5 m in diameter the relative abundance of non sea salt mg and ca and of aluminosilicate shows that the calcium content of continental background aerosol over greenland was much higher during the glacial age the neutralization capacity of carbonaceous aerosol is estimated the inverse relationship between 18o and continental input as well as the response of this input to the rapid climatic variations that have occurred during the second part of the glacial age are discussed in terms of source and transport modification in relation to the presence and the extent of the great laurentide ice cap the corresponding vostok profiles strongly suggest that some of the phenomena observed at high northern latitudes are of global concern the marine component of na nam is a good tracer of sea salt aerosol similarly to continental input it shows an inverse but more linear relationship with 18o the sensitivity of greenland and antarctic marine input to climate variations of small and large amplitude is compared and a corresponding estimation is made for the aeolian contribution the respective influence of atmospheric circulation and the water vapor cycle is discussed the chlorine to marine sodium weight ratio increases with temperature from values very close to the bulk seawater ratio during the last glacial maximum 18 20 kyr b p to values significantly higher during the holocene and warm eemian the corresponding excess of chloride hcl is discussed in terms of atmospheric transport taking into account the role of atmospheric acidity on sea salt fractionation processes owing to postdepositional phenomena similar vostok data must be considered cautiously nevertheless aerosol fractionation seems to have been much more important over the vostok site except during glacial extrema

continental biogenic species in the greenland ice core project ice core tracing back the biomass history of the north american continent ammonium nitrate and organic acid records from the greenland ice core project deep ice core are discussed all species have a continental biogenic source that is situated predominantly on the north american continent for species deposited in summit central greenland the record therefore can be used to trace back the biomass history of the north american continent difficulty in the interpretation of these records arises from their unknown transfer behavior in a more alkaline atmosphere which characterizes glacial time periods compared to interglacial stadials this may have implications not only for weak acids such as formate and acetate but also possibly for the transport and incorporation of hno3 into aerosols whereas ammonium is probably not affected by the alkalinity change of the atmosphere our approach is to compare samples with similar h concentrations throughout the record from the records we infer several significant fluctuations in the extent of the laurentide ice sheet during the last glaciation we find evidence against the occurrence of an extensive younger dryas event in north america