absolute calibration of the greenland time scale implications for antarctic time scales and for δ14c abstract we propose a new age scale for the two ice cores grip and gisp2 that were drilled at greenland summit based on accelerator mass spectrometry 14c dating of foraminifera in core md95 2042 paleoceanography 15 2000 565 calibrated by means of recently obtained paired 14c and 230th measurements on pristine corals marine radiocarbon calibration curve spanning 10 500 to 50 000 years bp thousand years before present based on paired 230th 234u 238u and 14c dates on pristine corals geological society of america bulletin 2003 submitted for publication the record of core md95 2042 can be correlated very precisely to the greenland ice cores between 30 and 40 ka bp our scale is 1 4 ka older than the grip ss09sea time scale journal of quaternary science 16 2001 299 at the older end of marine isotope stage 3 we use published 230th dates from speleothems to calibrate the record using this scale we show a 14c record that is broadly consistent with the modelled record earth planet sci lett 200 2002 177 and with the data of hughen et al science 303 2004 202 but not consistent with the high values obtained by beck et al science 292 2001 2453 or by voelker et al radiocarbon 40 1998 517 we show how a set of age scales for the antarctic ice cores can be derived that are both fully consistent with the greenland scale and glaciologically reasonable

deglacial warming of the northeastern atlantic ocean correlation with the paleoclimatic evolution of the european continent abstract isotopic micropaleontologic and pollen analyses of deep sea cores from the bay of biscay and the northeastern atlantic ocean show that the deglacial warming of this oceanic area was closely correlated with the paleoclimatic evolution of the adjacent european continent temperatures were at least as warm as those of today in the bay of biscay between 13 300 and 11 000 b p coinciding with the combined bolling allerod warm continental events a major spread of polar water occurred between 11 000 and 10 000 b p during this event which coincides with the younger dryas continental cold event marine temperatures were almost as low as those of the last glacial maximum the final deglacial warming of the norteastern atlatntic ocean occurred during the following 3000 yr

constraints on the magnitude and patterns of ocean cooling at the last glacial maximum observation based reconstructions of sea surface temperature from relatively stable periods in the past such as the last glacial maximum represent an important means of constraining climate sensitivity and evaluating model simulations1 the first quantitative global reconstruction of sea surface temperatures during the last glacial maximum was developed by the climate long range investigation mapping and prediction climap project in the 1970s and 1980s refs 2 3 since that time several shortcomings of that earlier effort have become apparent4 here we present an updated synthesis of sea surface temperatures during the last glacial maximum rigorously defined as the period between 23 and 19 thousand years before present from the multiproxy approach for the reconstruction of the glacial ocean surface margo project5 we integrate microfossil and geochemical reconstructions of surface temperatures and include assessments of the reliability of individual records our reconstruction reveals the presence of large longitudinal gradients in sea surface temperature in all of the ocean basins in contrast to the simulations of the last glacial maximum climate available at present6 7

origin and consequences of cyclic ice rafting in the northeast atlantic ocean during the past 130 000 years deep sea sediment cores recovered from the northeast atlantic ocean were examined in order to elucidate the influence of the earth s orbital parameters on major ice rafting analyses of coarse grained ice rafted debris and planktonic foraminifers revealed a strong reaction to the precession signal since 130 000 yr b p dropstone layers have been deposited each half period of a precessional cycle 11 000 1000 yr ice rafting occurs during times of winter minimum summer maximum insolation and summer minimum winter maximum insolation in the first case high summer insolation forces meltwater discharge from the ice sheets into the polar seas which subsequently enhances formation of sea ice during the winter in the second case growth of continental ice enhances iceberg production which also leads to a salinity reduction of surface seawater both situations result in a southward penetration of polar water thus the marine record of dropstones documents ice rafting not only during weichselian stades but also during cold events within interstades the regularity of ice rafting yields a useful framework to calibrate and elucidate climatic changes not only in the region of the north atlantic ocean but also in remote areas such as the pacific ocean and the antarctic

isotope calibrated greenland temperature record over marine isotope stage 3 and its relation to ch4 large temperature variations on millennial time scales in greenland characterised the last ice age abrupt warmings known as dansgaard oeschger do events can be traced in the 18oice record of greenland ice cores however it has been shown that 18oice is not a direct temperature proxy measurements of the isotopic composition of gases trapped in the ice can be used to calibrate the paleothermometer here we present a continuous temperature record based on high resolution 15n measurements and firn model studies it covers a sequence of 9 do events 9 17 during the time period from 38 to 64 kyr bp for which temperature changes of 8 to 15 c were estimated the difference between the modern and the glacial 18oice t relationship can be explained by a combination of source temperature changes and changes in the annual distribution of precipitation a detailed comparison of the temperature evolution with reconstructions of the atmospheric methane ch4 concentration shows that ch4 rises lag temperature increases at the onset of do events by 25 to 70 yr within data resolution the strong correlation between greenland temperature and ch4 on millennial and submillennial time scales suggests that variations on these time scales were probably of hemispheric extent

rapid changes of glacial climate simulated in a coupled climate model abrupt changes in climate termed dansgaard oeschger and heinrich events have punctuated the last glacial period approximately 100 10 kyr ago but not the holocene the past 10 kyr here we use an intermediate complexity climate model to investigate the stability of glacial climate and we find that only one mode of atlantic ocean circulation is stable a cold mode with deep water formation in the atlantic ocean south of iceland however a warm circulation mode similar to the present day atlantic ocean is only marginally unstable and temporary transitions to this warm mode can easily be triggered this leads to abrupt warm events in the model which share many characteristics of the observed dansgaard oeschger events for a large freshwater input such as a large release of icebergs the model s deep water formation is temporarily switched off causing no strong cooling in greenland but warming in antarctica as is observed for heinrich events our stability analysis provides an explanation why glacial climate is much more variable than holocene climate

changes in north atlantic deep water formation associated with the dansgaard oeschger temperature oscillations 60 10 ka we closely comparedhigh resolution d 13 c records of benthic foraminifera cibicides wuellerstorfi a proxy for deep water ventilation with the dansgaard oeschger temperature oscillations our results reveal different perturbations of deep water formation in the north atlantic ocean associated with the millennial scale climate oscillations during the last glacial period the cooling episodes associated with the drastic heinrich events are related to large reductions of deep water formation and a northward migration of 13 c depleted southern source deep waters to 621n in the north atlantic ocean the inter heinrich events which are correlatedto the other coldstad ials are markedby significant changes of sea surface temperature aroundthe rockall plateau variations in the flux of icebergs to the north atlantic ocean but are not associated with such important reduction of deep water formation if changes in the thermohaline circulation thc are associatedwith these millennial scale climatic oscillation they affect only the deeper water masses below 2000 m of the north atlantic ocean we thus show that equivalent degree of cooling over greenland is obtained with different perturbations of deep water formation our results either question the role of the thc as the unique explanation for these millennial scale climate oscillations or call upon an amplifying mechanism not yet taken into account r 2002 elsevier science ltd all rights reserved

land sea correlations for the last glaciation inferred from a pollen and dinocyst record from the portuguese margin pollen and dinoflagellate cyst assemblages from core su 81 18 recovered off portugal 37 46 n 10 11 w 3135 m water depth have been used to document the short term environmental changes that occurred in southwest europe since 25 000 yr b p the relationship between the oceanic and continental environments has been further examined by the use of other marine proxies coarse sedimentary fraction foraminifera and by comparison with proximal land pollen records heinrich 2 h2 and heinrich 1 h1 events were the most extreme parts of the highly variable last glacial period with the maximum extension of dry steppe on land and the occurrence of cool and dilute waters at the core site our study shows that h1 and h2 are divided in two distinct phases one with neogloboquadrina pachyderma left coiling associated with the maximum input of ice rafted debris reflecting the in situ release of icebergs and the occurrence of cool and dilute seawater at the core site the other with dinoflagellate cysts of subpolar affinity bitectatodinium tepikiense reflecting a seasonal control marked by warm summer sst and cold winter sst

iceberg discharges into the north atlantic on millennial time scales during the last glaciation high resolution studies of north atlantic deep sea cores demonstrate that prominent increases in iceberg calving recurred at intervals of 2000 to 3000 years much more frequently than the 7000 to 10 000 year pacing of massive ice discharges associated with heinrich events the calving cycles correlate with warm cold oscillations called dansgaard oeschger events in greenland ice cores each cycle records synchronous discharges of ice from different sources and the cycles are decoupled from sea surface temperatures these findings point to a mechanism operating within the atmosphere that caused rapid oscillations in air temperatures above greenland and in calving from more than one ice sheet

position of the polar front along the western iberian margin during key cold episodes of the last 45 ka 1 this paper documents the migration of the polar front pf over the iberian margin during some of the cold climatic extremes of the last 45 ka it is based on a compilation of robust and coherent paleohydrological proxies obtained from eleven cores distributed between 36 and 42 n planktonic 18o globigerina bulloides ice rafted detritus concentrations and the relative abundance of the polar foraminifera neogloboquadrina pachyderma sinistral were used to track the pf position these three data sets compared from core to core show a consistent evolution of the sea surface paleohydrology along the iberian margin over the last 45 ka we focused on five time slices representative of cold periods under distinct paleoenvironmental forcings the 8 2 ka event and the younger dryas two recent cold events occurring within high values of summer insolation heinrich events 1 and 4 reflecting major episodes of massive iceberg discharges into the north atlantic and the last glacial maximum typifying the highest ice volume accumulated in the northern hemisphere for each event we generated schematic maps mirroring past sea surface hydrological conditions the maps revealed that the polar front presence along the iberian margin was restricted to heinrich events the sea surface conditions during the last glacial maximum were close to those at present day except for the northern sites which briefly experienced subarctic conditions

effects of the equatorial electrojet on magnetotelluric surveys field results from northwest brazil the distortion effect that the nonuniform equatorial electrojet eej currents might have on the plane wave assumption in magnetotelluric mt appli cations is investigated under experimental conditions a broad band 0 0006 2048 s mt survey consisting of 8 stations aligned at right angles to the magnetic equator and probing diverse geologic terrains was car ried out during the daytime under the presence of the eej nonuniform source and at nighttime when the eej flux almost vanishes a comparison between the daytime and nighttime soundings did not show any sig nificant divergence contrary to expectation from some theoretical calculations thus the results assure that the traditional plane wave formula employed in mt can provide reliable subsurface conductivity structures even under the influence of the eej at least up to periods of 2048 s an additional modelling exercise conside ring the two models most commonly used to simulate the eej sources was also performed it indicates that the line current model generates departures from the plane wave results not observed in practice and that the gaussian model only agrees with the experimental data within their error bars if the geoelectric section approaches its most conductive limit defined from a sta tic shift evaluation

paleohydrology of the santiaguillo basin mexico since late last glacial and climate variation in southern part of western subtropical north america abstract stratigraphy geochemistry and radiocarbon dating of a succession of sediment in the santiaguillo basin central northern mexico help reconstruct the millennial scale dynamics of hydrological variability that occurred in the southern part of western subtropical north america since the late last glacial runoff was generally above average during the late last glacial from 27 to 18 ka following this interval runoff decreased and deposition of authigenic carbonate and aeolian transported sediment increased until 4 ka heinrich 1 and 2 and younger dryas were intervals of reduced runoff and increased aeolian activity the wetter climate of central northern mexico and arid conditions in north northwestern mexico during the late last glacial were probably related to formation of tropical cyclones in the eastern north pacific during the autumn with restricted rainfall swaths and an absent weaker north american monsoon enhanced north american monsoon and tropical cyclones with expanded rainfall swaths brought more summer and autumn precipitation to a broader region extending from the central northern mexico to the continental interiors of southwestern us during the early holocene

strong hemispheric coupling of glacial climate through freshwater discharge and ocean circulation the climate of the last glacial period was extremely variable characterized by abrupt warming events in the northern hemisphere accompanied by slower temperature changes in antarctica and variations of global sea level it is generally accepted that this millennial scale climate variability was caused by abrupt changes in the ocean thermohaline circulation here we use a coupled ocean atmosphere sea ice model to show that freshwater discharge into the north atlantic ocean in addition to a reduction of the thermohaline circulation has a direct effect on southern ocean temperature the related anomalous oceanic southward heat transport arises from a zonal density gradient in the subtropical north atlantic caused by a fast wave adjustment process we present an extended and quantitative bipolar seesaw concept that explains the timing and amplitude of greenland and antarctic temperature changes the slow changes in antarctic temperature and its similarity to sea level as well as a possible time lag of sea level with respect to antarctic temperature during marine isotope stage 3

n2o and ch4 variations during the last glacial epoch insight into global processes 1 greenhouse gas measurements along polar ice cores provide important insight into the former composition of the atmosphere its natural variations and the responses to fast climatic changes in the past we present high resolution nitrous oxide n2o and methane ch4 records measured along two ice cores from central greenland covering part of marine isotope stages 3 and 4 in the last glacial epoch the n2o data confirm the hypothesis that n2o shows variations in phase to fast climatic changes observed in the northern hemisphere the so called dansgaard oeschger d o events variations exist not only for events with a long duration 1500 years and more but also for the shorter ones the comparison with ch4 unveils interesting differences between the response of ch4 and n2o to d o events while the average amplitudes of ch4 oscillations associated with d o events are similar to those of the northern hemisphere summer insolation the magnitude of the n2o concentration change instead correlates with the duration of the d o events the records give further insight into the timing of concentration changes at the beginning of d o events they show that for long lasting events the n2o concentration starts to increase before both the sharp increase in the ch4 concentration and the temperature reconstructed for greenland

rapid environmental changes in southern europe during the last glacial period oxygen isotope records from greenland ice cores1 2 indicate numerous rapid climate fluctuations during the last glacial period north atlantic marine sediment cores show comparable variability in sea surface temperature and the deposition of ice rafted debris3 4 5 in contrast very few continental records of this time period provide the temporal resolution and environmental sensitivity necessary to reveal the extent and effects of these environmental fluctuations on the continents here we present high resolution geochemical physical and pollen data from lake sediments in italy and from a mediterranean sediment core linked by a common tephrochronology our lacustrine sequence extends to the past 102 000 years many of its features correlate well with the greenland ice core records demonstrating that the closely coupled ocean atmosphere system of the northern hemisphere during the last glacial4 extended its influence at least as far as the central mediterranean region numerous vegetation changes were rapid frequently occurring in less than 200 years showing that the terrestrial biosphere participated fully in last glacial climate variability earlier than 65 000 years ago our record shows more climate fluctuations than are apparent in the greenland ice cores together the multi proxy data from the continental and marine records reveal differences in the seasonal character of climate during successive interstadials and provide a step towards determining the underlying mechanisms of the centennial millennial scale variability

vegetation response to abrupt climate changes in western europe from 45 to 14 7k cal a bp the bergsee lacustrine record black forest germany

short term soil formation events in last glacial east european loess evidence from multi method luminescence dating here we provide a robust luminescence chronology for stayky ukraine a reference profile in european late pleistocene loess stratigraphy based on optically stimulated luminescence osl dating on quartz 4 11 m 63 90 m and post infrared infrared stimulated luminescence pir irsl on polymineral fine grains for the bug loess unit the equivalent of marine isotope stage mis 2 results are in agreement between methods demonstrating that the suite of embryonic soils previously interpreted as reflecting climate variability similar to greenland interstadials gi actually date to 29 27 15 ka with most emplaced around or after 20 ka this temporal span is further confirmed by age depth modelling of available data apart from gi 2 no interstadial type climate events are recorded in greenland ice core data for that time interval as short term pedogenetic phases are also documented in records from central western europe there is a need for more research into the european mid latitude terrestrial environments response to mis 2 hydroclimate variability the dating of vytachiv paleosol previously debatably linked to various gi events within mis 3 resulted in ages of 40 4 ka and 53 4 ka at the lower transition and 26 2 ka to 30 2 ka in the overlying loess these ages indicate that the truncated vytachiv paleosol is either not continuous or that it encompasses a broader age range within mis 3 than previously considered in both cases data would not allow for an unambiguous linking of this paleosol with specific gi events as previously attempted the pir irsl290 dating of the loams immediately underneath pryluky unit in the range of 120 ka to 168 ka and of the pryluky mollisol from 90 ka to 126 ka confirm the broad correspondence of this unit with mis 5 although poor dose recovery results open the possibility for further testing on the degree these ages provide overestimated results quartz data severely underestimate the pir irsl290 ages for these samples the application of pir irsl290 dating for the underlying dnieper till previously linked to the saalian glaciation resulted in natural signals at the level of laboratory saturation yielding minimum ages of c 700 ka for the same sample the natural sar osl signals for 4 11 m quartz were found significantly below laboratory saturation level resulting in finite ages of 250 270 ka interpreted here as underestimates while coarse quartz 63 90 m signals reached about 85 of the laboratory saturation level these data suggest extreme caution must be taken when dating such old samples using quartz osl results from our high resolution luminescence dating raises important implications for the chronological representativeness of stayky as a key loess site in eastern europe beyond mis 2

climate swings come into focus the last glacial period was far from quiet during so called heinrich events large armadas of icebergs were shed from the ice sheet that covered much of north america the tracks of debris left by the melting icebergs can still be seen in sediment cores from the north atlantic in their perspective broecker and hemming 1 report from a recent miniconference that attempted to chart the climatic impacts of these events 1 http www sciencemag org cgi content short 294 5550 2308

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

paleoenvironments from robust loess stratigraphy using high resolution color and grain size data of the last glacial krems wachtberg record ne austria abstract the complex interplay of dust sedimentation pedogenesis and erosion reworking in the formation of loess paleosol sequences lps challenges paleoenvironmental proxies here we show that color and grain size are essential parameters characterizing loess profiles and support robust stratigraphies as a basis for reconstructions in the context of local geo ecological and large scale paleoclimatic evolution detailed paleoenvironmental records from the period since the arrival of anatomically modern humans to the last glacial maximum are scarce in the alpine surroundings the c 7 5 m thick lps krems wachtberg ne austria known for its well preserved upper paleolithic context at a depth of 5 5 m formed between 40 and 20 ka bp by quasi continuous dust sedimentation interrupted by phases of incipient pedogenesis and local reworking the new kw2015 composite is based on three sections studied and sampled at 2 5 cm resolution color and grain size data support a robust stratigraphy for reconstructions of the pedosedimentary evolution the marked transition from oxidized to reduced paleosols of kw2015 around 34 35 ka corresponds to the middle to upper pleniglacial transition as part of a general cooling trend from marine isotope stage mis 3 to 2 intensely modulated by millennial scale climatic fluctuations as recorded in the greenland ice core data the distinct response of kw2015 to these trends highlights that reconstructing lps evolution based on a robust stratigraphy is a prerequisite to paleoenvironmental proxy interpretation

modeling the distribution and seasonality of neogloboquadrina pachyderma in the north atlantic ocean during heinrich stadial 1

neotropical vegetation response to rapid climate changes during the last glacial period palynological evidence from the cariaco basin we present new palynological information from the anoxic cariaco basin off venezuela that provides insight into the response of northernmost south american vegetation to rapid climate changes between 68 and 28 ka specifically during north atlantic heinrich events hes and dansgaard oeschger cycles we defined three different vegetation modes 1 an interstadial mode characterized by the highest pollen concentration and the maximum extension of semi deciduous and evergreen forests 2 a stadial mode characterized by increases of salt marshes herbs and montane forests and 3 a heinrich event mode characterized by the lowest pollen concentrations abrupt increases of salt marshes and decreased forest abundance similarly indices of c4 c3 plants show increases during stadials with clear peaks during the onset of hes though grasslands did not become dominant during these periods we alternatively propose that these expansions of c4 plants are associated with the expansion of coastal salt marshes our vegetation record suggests the prevalence of humid conditions during interstadials dry and cold conditions during stadials and dry and cold conditions together with changes in sea level during hes this new palynological evidence supports previous interpretations that main environmental changes in northernmost south america were driven by latitudinal displacements of the intertropical convergence zone and sea level changes

high resolution record of northern hemisphere climate extending into the last interglacial period high resolution record of northern hemisphere climate extending into the last interglacial period

oceanic processes as potential trigger and amplifying mechanisms for heinrich events marine sediments recorded a series of heinrich events during the last glacial period massive ice surges thatdeposited prominent layers of ice rafted debris in the north atlantic here we explore oceanic mechanisms thatcan potentially trigger and amplify the observed ice calving events simulations of abrupt glacial climate changewith a coupled ocean atmosphere sea ice model show a substantial regional sea level rise in the north atlantic inresponse to a collapse of the atlantic meridional overturning circulation moc the increased heat uptake ofthe global ocean after the moc collapse leads to an additional rise in global sea level we hypothesize that thesesea level changes have the potential to destabilize northern hemisphere ice shelves and ice sheets and to triggerice surges sea level rise due to ice calving and subsurface ocean warming provides two positive feedbackmechanisms contributing to further destabilization of ice shelves and ice sheets

geomorphological evidence and 10be exposure ages for the last glacial maximum and deglaciation of the velka and mala studena dolina valleys in the high tatra mountains central europe abstract 10be exposure age chronology of the last glaciation was established in a key area at the southern slopes of the high tatra mts western carpathians in situ produced 10be in moraine boulders glacially transformed bedrock surfaces and rockfall accumulations constrains the timing of the last glacial maximum lgm glacier expansion and provides chronological evidence for the post lgm decay of one of the largest paleoglaciers in the range the uncertainty weighted mean age of 22 0 0 8 ka obtained for the terminal moraine in the forefield of the velka studena dolina valley indicates that the oldest moraine was deposited close to the global lgm this finding confirms that well preserved moraines in the range were formed during the last glacial cycle and that glaciation on the southern flank of the range was more extensive than earlier in the last glacial cycle the maximum glacier extent correlates with late wurmian weichselian glacier phases in the alps the bavarian bohemian forest and the krkonose mts but probably postdates the period of maximum glaciation in the southern carpathians re advance moraines at the mouth of the velka studena dolina valley and in the middle part of the mala studena dolina valley were deposited no later than around 20 5 ka and 15 5 ka respectively the timing of these advances is broadly synchronous within the high tatra mts as well as with glacier advances in the alps bavarian bohemian forest and krkonose mts 10be exposure ages obtained from glacially transformed bedrock surfaces range between 20 5 1 7 ka and 10 7 0 3 ka constraining the onset and the final phase of the deglaciation surface exposure dating of four rockfall accumulations produced uncertainty weighted mean ages of 20 2 1 2 ka 17 0 0 7 ka 16 5 0 4 ka and 15 6 0 7 ka these ages indicate that activation of rock slope failures occurred under paraglacial conditions within a few centuries up to 1400 years after the formation of re advance moraines

the fluvial record of climate change fluvial landforms and sediments can be used to reconstruct past hydrological conditions over different time scales once allowance has been made for tectonic base level and human complications field stratigraphic evidence is explored here at three time scales the later pleistocene the holocene and the historical and instrumental period new data from a range of field studies demonstrate that croll milankovitch forcing dansgaard oeschger and heinrich events enhanced monsoon circulation millennial to centennial scale climate variability within the holocene probably associated with solar forcing and deep ocean circulation and flood event variability in recent centuries can all be discerned in the fluvial record although very significant advances have been made in river system and climate change research in recent years the potential of fluvial palaeohydrology has yet to be fully realized to the detriment of climatology public health resource management and river engineering

the climate and landscape of the middle part of the weichselian glaciation in europe the stage 3 project abstract oxygen isotope stage 3 ois 3 was a mild interval between the two cold maxima of the last weichselian glaciation marked by climate changes oscillating on a 100 1000 yr time scale between near interglacial and peak glacial conditions during ois 3 modern humans entered europe and somewhat later their neanderthal predecessors became extinct our understanding of this momentous event depends on an answer to the question did the unstable environmental conditions of the time play a significant role in early human history the stage 3 project is an interdisciplinary study with two main goals 1 to describe with existing data and to simulate the climates and landscapes of typical warm and cold phases between 45 000 and 30 000 yr ago and 2 to compare the results with the spatial and temporal distribution of human beings in this context this paper introduces the stage 3 project and provides background to a set of papers on the climate and landscape aspects of the project that will appear in quaternary research and to studies of their relevance to the early upper paleolithic of europe to appear in journals yet to be determined

palaeoceanographic reconstruction of surface ocean changes in the southern norwegian sea for the last 130 000 years based on diatoms and with comparison to foraminiferal records abstract fossil marine diatom assemblages in a sediment core from the central northern faroe slope in the norwegian sea were used to reconstruct palaeoceanographic changes in the surface water mixed layer from the last 130 000 years marine isotope stage mis 6 5 transition to mis 1 including the eemian and holocene interglacials and to compare the results with previously published results on planktic foraminifera representing the subsurface conditions of the thermocline diatom floras from mis 5 of the nordic seas have rarely been studied in detail before and never the entire period from pre eemian to present the composition of diatom species together with maxima in absolute abundance of diatoms indicate two periods of warmer sea surface temperatures correlating with the eemian and holocene interglacials respectively the eemian differs from the holocene in that the iceland faroe front never developed suggesting the cold east icelandic current originating from the east greenland current running north of iceland was reduced or more mixed with atlantic water than during the holocene and that the surface temperature and salinity gradients were weaker the northern faroe slope was in the early weichselian of mis 5d 5a mainly influenced by weaker inflow of atlantic water and stronger influence of the east icelandic current and by seasonal sea ice cover during the later part of the weichselian mis 4 mis 2 cold conditions prevailed with extensive sea ice cover except during the warmer interstadials the diatom floras were more sensitive to climate changes than the planktic foraminifera and indicate longer periods with warm surface conditions and increased influence of the warm atlantic surface water from the faroe current in mis 5 suggesting a shallower and much steeper thermocline during the transitional periods compared to today the diatoms are good indicators for atlantic water inflow and possible convection in the nordic seas not merely reflecting orbital variations in insolation as previously suggested

high resolution greenland ice core data show abrupt climate change happens in few years the last two abrupt warmings at the onset of our present warm interglacial period interrupted by the younger dryas cooling event were investigated at high temporal resolution from the north greenland ice core project ice core the deuterium excess a proxy of greenland precipitation moisture source switched mode within 1 to 3 years over these transitions and initiated a more gradual change over 50 years of the greenland air temperature as recorded by stable water isotopes the onsets of both abrupt greenland warmings were slightly preceded by decreasing greenland dust deposition reflecting the wetting of asian deserts a northern shift of the intertropical convergence zone could be the trigger of these abrupt shifts of northern hemisphere atmospheric circulation resulting in changes of 2 to 4 kelvin in greenland moisture source temperature from one year to the next

the greenland ice core chronology 2005 15 42 ka part 2 comparison to other records a new greenland ice core chronology gicc05 based on multi parameter counting of annual layers has been obtained for the last 42 ka here we compare the glacial part of the new time scale which is based entirely on records from the northgrip ice core to existing time scales and reference horizons covering the same period these include the grip and northgrip modelled time scales the meese sowers gisp2 counted time scale the shackleton fairbanks grip time scale sfcp04 based on 14c calibration of a marine core the hulu cave record three volcanic reference horizons and the laschamp geomagnetic excursion event occurring around greenland interstadial 10 gicc05 is generally in good long term agreement with the existing greenland ice core chronologies and with the hulu cave record but on shorter time scales there are significant discrepancies around the last glacial maximum there is a more than 1 ka age difference between gicc05 and sfcp04 and a more than 0 5 ka discrepancy in the same direction between gicc05 and the age of a recently identified tephra layer in the northgrip ice core both sfcp04 and the tephra age are based on 14c dated marine cores and fixed marine reservoir ages for the laschamp event gicc05 agrees with a recent independent dating within the uncertainties

modeled seasonality of glacial abrupt climate events greenland ice cores as well as many other paleo archives from the northern hemisphere recorded a series of 25 warm interstadial events the so called dansgaard oeschger d o events during the last glacial period we use the three dimensional coupled global ocean atmosphere sea ice model ecbilt clio and force it with freshwater input into the north atlantic to simulate abrupt glacial climate events which we use as analogues for d o events we focus our analysis on the northern hemisphere the simulated events show large differences in the regional and seasonal distribution of the temperature and precipitation changes while the temperature changes in high northern latitudes and in the north atlantic region are dominated by winter changes the largest temperature increases in most other land regions are seen in spring smallest changes over land are found during the summer months our model simulations also demonstrate that the temperature and precipitation change patterns for different intensifications of the atlantic meridional overturning circulation are not linear the extent of the transitions varies and local non linearities influence the amplitude of the annual mean response as well as the response in different seasons implications for the interpretation of paleo records are discussed

abrupt temperature changes in the western mediterranean over the past 250 000 years a continuous high resolution western mediterranean sea surface temperature sst alkenone record spanning the past 250 000 years shows that abrupt changes were more common at warming than at cooling during marine isotope stage mis 6 sst oscillated following a stadial interstadial pattern but at lower intensities and rates of change than in the dansgaard oeschger events of mis 3 some of the most prominent events occurred over miss 5 and 7 after prolonged warm periods of high stability climate during the whole period was predominantly maintained in interglacial interstadial conditions whereas the duration of stadials was much shorter

irregular glacial interstadials recorded in a new greenland ice core the greenland ice sheet offers the most favourable conditions in the northern hemisphere for obtaining high resolution continuous time series of climate related parameters profiles of 18o 16o ratio along three previous deep greenland ice cores1 3 seemed to reveal irregular but well defined episodes of relatively mild climate conditions interstadials during the mid and late parts of the last glaciation but there has been some doubt as to whether the shifts in oxygen isotope ratio were genuine representations of changes in climate rather than artefacts due to disturbed stratification here we present results from a new deep ice core drilled at the summit of the greenland ice sheet where the depositional environ ment and the flow pattern of the ice are close to ideal for core recovery and analysis the results reproduce the previous findings to such a degree that the existence of the interstadial episodes can no longer be in doubt according to a preliminary timescale based on stratigraphic studies the interstadials lasted from 500 to 2 000 years and their irregular occurrence suggests complexity in the behaviour of the north atlantic ocean circulation

reconciling the greenland ice core and radiocarbon timescales through the laschamp geomagnetic excursion abstract cosmogenic radionuclides such as 10be and 14c share a common production signal with their formation in the earth s upper atmosphere modulated by changes to the geomagnetic field as well as variations in the intensity of the solar wind here we use this common production signal to compare between the radiocarbon intcal and greenland ice core gicc05 timescales utilising the most pronounced cosmogenic production peak of the last 100 000 years that associated with the laschamp geomagnetic excursion circa 41 000 years ago we present 54 new 14c measurements from a peat core tp 2005 from tenaghi philippon ne greece contiguously spanning between circa 47 300 and 39 600 cal bp demonstrating a distinctive tripartite structure in the build up to the principal laschamp production maximum that is not present in the consensus intcal13 calibration curve this is the first time that a continuous non reservoir corrected 14c dataset has been generated over such a long time span for this the oldest portion of the radiocarbon timescale this period is critical for both palaeoenvironmental and archaeological applications with the replacement of neanderthals by anatomically modern humans in europe around this time by placing our tenaghi philippon 14c dataset on to the hulu cave u series timescale of cheng et al 2018 via bayesian statistical modelling the comparison of tp 2005 14c with greenland 10be fluxes also implicitly relates the underlying u series and gicc05 timescales themselves this comparison suggests that whilst these two timescales are broadly coherent the intcal13 timescale contains erroneous structure circa 40 000 cal bp

wet to dry climatic trend in north western iberia within heinrich events abstract the direct sea land correlation applied to core md99 2331 retrieved from the north western iberian margin shows a two phase pattern within heinrich events 4 2 and 1 in the ocean and in the adjacent landmasses changes between wet cold and dry cool conditions in the iberian peninsula detected during these extreme events cannot be explained by a simple oceanographic mechanism related to changes in the strength of the atlantic meridional overturning circulation here we propose an additional atmospheric mechanism able to produce this scenario based on the comparison between the md99 2331 record and other available palaeoclimate sequences from the north atlantic region 18 75 n and 0 75 w the climatic asymmetry observed between mid and subtropical eastern north atlantic latitudes wet dry and the blake outer ridge dry wet during h4 h2 and h1 can be explained by changes in the position of the atlantic jet stream during the first phase of h4 h2 and h1 the atlantic jet stream was located further south following the southward displacement of the oceanic thermal front as far south as 35 37 n on the contrary during the second phase of h4 h2 and h1 the jet stream was located further north following the northward displacement of this thermal front as far north as 42 n from the atmospheric point of view these two phases are reminiscent of the present day negative and positive prevailing modes of the north atlantic oscillation nao respectively but high resolution studies of additional north atlantic key sites and climate simulations are needed to confirm the hypothesis of a nao like mechanism operating on millennial timescales

coherent patterns of ice rafted debris deposits in the nordic regions during the last glacial 10 60 ka we have synchronized records of ice rafted rock debris deposits of three sediment cores from the norwegian sea and the irminger basin during the last glacial period from 10 to 50 ka by combining the use of radiocarbon dates and adjustments of physical properties our synchronized records indicate that layers rich in ice rafted debris were deposited throughout the nordic regions at times near to synchronous with the major collapses of the laurentide ice sheet during the heinrich events there are also millennial scale coherent and near to synchronous deposits of ice rafted rock debris into the norwegian sea related to repetitive changes of the flux of icebergs from the fenno scandinavian the correlation with the cold phases of the dansgaard oeschger temperature record points to a close coupling between atmospheric temperature oscillations and variations of iceberg fluxes into the norwegian sea during the last glacial variations in atmospheric circulation patterns bringing moisture supply to high latitudes and the distribution of this moisture over the different northern hemisphere coastal ice sheets and ice shelves could be controlling both the timing of ice sheet advances and the flux of iceberg to the open ocean

biogenic alteration of volcanic glass from the troodos ophiolite cyprus alteration of basaltic glass through the entire volcanic sequence of the troodos ophiolite is partly bio mediated the following observations support this conclusion alteration textures resembling microbes in form and size altered glass locally shows high carbon concentrations at the alteration front and organic remains the absence of dna suggests that the bio alteration is a fossil process temperatures calculated from 18 o of carbonate assumed to have been in equilibrium with seawater yield 27 65 c and 18 o silicate versus h 2 o relationships indicate seawater alteration these data are consistent with biogenic alteration during an early stage of ocean floor alteration of the troodos oceanic crust some 70 90 ma ago

millennial scale iceberg discharges in the irminger basin during the last glacial period relationship with the heinrich events and environmental settings high resolution records of coarse lithic content and oxygen isotope have been obtained in a piston core from the irminger basin the last glacial period is characterized by numerous periods of increased iceberg discharges originating partly from iceland and corresponding to millennial scale instabilities of the coastal ice sheets and ice shelves in the nordic area a comparison with midlatitude sediment cores shows that ice rafted material corresponding to the heinrich events was deposited synchronously from 40 to 60 n there are thus two oscillating systems every 5 10 kyr massive iceberg armadas are released from large continental ice caps whereas more frequent instabilities of the coastal ice sheets in the high latitude regions occur every 1 2 3 8 kyr at the time of the heinrich events the synchroneity of the response from all the northern hemisphere ice sheets attests the existence of strong interactions between the two systems

contrasting impacts of dansgaard oeschger events over a western european latitudinal transect modulated by orbital parameters abstract terrestrial and marine proxies pollen planktic and benthic foraminiferal oxygen isotopes alkenone and foraminifer derived sea surface temperatures ssts ice rafted debris from images deep sea cores md95 2042 and su81 18 37 n 10 w md99 2331 and md03 2697 42 n 9 w and md04 2845 45 n 5 w show that western european and offshore environments were strongly affected by dansgaard oeschger d o and heinrich h events we concentrate here on latitudinal variability in the forest cover extent and composition of western europe during the succession of d o events showing new pollen records for core md04 2845 and for marine isotopic stages mis 3 and 4 of core md99 2331 in general cold ssts characteristic of greenland stadials were contemporaneous with the expansion of semi desert or steppic vegetation while greenland interstadials were synchronous with the expansion of forest our data reveal that the amplitude of atlantic and mediterranean forest expansions differs for any given d o warming during the glacial period 74 18 ka in the western mediterranean d o 16 17 and d o 8 and 7 corresponding to minima in precession were associated with strong expansion of forest cover contrasting with weak expansion of forest cover during d o 14 and 12 the opposite pattern is revealed at the atlantic sites further north the strongest greenland warmings are recorded for d o 19 11 and 8 this contrasting latitudinal climatic scenario is compared with other northern hemisphere records revealing similarities between the mediterranean climate and the asian monsoon regime which may relate to a summer atmospheric teleconnection between the two regions comparable to the present day situation parallels between mediterranean climate enhancement and peaks in global methane ch 4 during the last glacial period suggest a significant role of monsoon activity in determining ch 4 emission from wetlands

a high resolution absolute dated late pleistocene monsoon record from hulu cave china oxygen isotope records of five stalagmites from hulu cave near nanjing bear a remarkable resemblance to oxygen isotope records from greenland ice cores suggesting that east asian monsoon intensity changed in concert with greenland temperature between 11 000 and 75 000 years before the present yr b p between 11 000 and 30 000 yr b p the timing of changes in the monsoon as established with 230th dates generally agrees with the timing of temperature changes from the greenland ice sheet project two gisp2 core which supports gisp2 s chronology in this interval our record links north atlantic climate with the meridional transport of heat and moisture from the warmest part of the ocean where the summer east asian monsoon originates

the greenland ice core chronology 2005 15 42 ka part 1 constructing the time scale the greenland ice core chronology 2005 gicc05 is extended back to 42 ka b2k before 2000 ad i e to the end of greenland stadial 11 the chronology is based on independent multi parameter counting of annual layers using comprehensive high resolution measurements available from the north greenland ice core project ngrip these are measurements of visual stratigraphy conductivity of the solid ice electrolytical melt water conductivity and the concentration of na c a 2 s o 4 n o 3 n h 4 a n uncertainty estimate of the time scale is obtained from identification of uncertain annual layers which are counted as 0 570 5 years the sum of the uncertain annual layers the so called maximum counting error of the presented chronology ranges from 4 in the warm interstadial periods to 7 in the cold stadials the annual accumulation rates of the stadials and interstadials are on average one third and half of the present day values respectively and the onset of the greenland interstadials 2 3 and 8 based on 20 year averaged d 18 o

hydrological impact of heinrich events in the subtropical northeast atlantic reconstructing the impact of heinrich events outside the main belt of ice rafting is crucial to understanding the underlying causes of these abrupt climatic events a high resolution study of a marine sediment core from the iberian margin demonstrates that this midlatitude area was strongly affected both by cooling and advection of low salinity arctic water masses during the last three heinrich events these paleoclimatic time series reveal the internal complexity of each of the last three heinrich events and illustrate the value of parallel studies of the organic and inorganic fractions of the sediments

simulated global scale response of the climate system to dansgaard oeschger and heinrich events by using an earth system model of intermediate complexity we have studied the global scale response of the glacial climate system during marine isotope stage mis 3 to perturbations at high northern latitudes and the tropics these perturbations include changes in inland ice volume over north america in freshwater flux into the northern north atlantic and in surface temperatures of the tropical pacific the global pattern of temperature series resulting from an experiment in which perturbations of inland ice and freshwater budget are imposed at high northern latitudes only agree with paleoclimatic reconstructions in particular a positive correlation of temperature variations near greenland and variations in all regions of the northern hemisphere and some parts of the southern tropics is found over the southern oceans a weak negative correlation appears which is strongest at a time lag of approximately 500 years further experimentation with prescribed temperature anomalies applied to the tropical pacific suggests that perturbation of tropical sea surface temperatures and hence the tropical water cycle is unlikely to have triggered dansgaard oeschger d o events however together with random freshwater anomalies prescribed at high northern latitudes tropical perturbations would be able to synchronize the occurrence of d o events via the mechanism of stochastic resonance

timing of millennial scale climate change in antarctica and greenland during the last glacial period a precise relative chronology for greenland and west antarctic paleotemperature is extended to 90 000 years ago based on correlation of atmospheric methane records from the greenland ice sheet project 2 and byrd ice cores over this period the onset of seven major millennial scale warmings in antarctica preceded the onset of greenland warmings by 1500 to 3000 years in general antarctic temperatures increased gradually while greenland temperatures were decreasing or constant and the termination of antarctic warming was apparently coincident with the onset of rapid warming in greenland this pattern provides further evidence for the operation of a bipolar see saw in air temperatures and an oceanic teleconnection between the hemispheres on millennial time scales

heinrich events massive late pleistocene detritus layers of the north atlantic and their global climate imprint 1 millennial climate oscillations of the glacial interval are interrupted by extreme events the so called heinrich events of the north atlantic their near global footprint is a testament to coherent interactions among earth s atmosphere oceans and cryosphere on millennial timescales heinrich detritus appears to have been derived from the region around hudson strait it was deposited over approximately 500 250 years several mechanisms have been proposed for the origin of the layers binge purge cycle of the laurentide ice sheet jokulhlaup activity from a hudson bay lake and an ice shelf buildup collapse fed by hudson strait to determine the origin of the heinrich events i recommend 1 further studies of the timing and duration of the events 2 further sedimentology study near the hudson strait and 3 greater spatial and temporal resolution studies of the layers as well as their precursory intervals studies of previous glacial intervals may also provide important constraints

insights into continental temperatures in the northwestern black sea area during the last glacial period using branched tetraether lipids abstract in the continental realm continuous quantitative temperature reconstructions spanning the last glacial are rare especially in central and eastern europe here we provide a reconstruction from the northwestern black sea catchment spanning 40 to 9 ka bp from a study of the relative distribution of branched glycerol dialkyl glycerol tetraethers brgdgts in black sea lacustrine sediments first the origins of brgdgts are discussed the comparison of geochemical proxies from the same core supports a dominant terrestrial origin for brgdgts during the last glacial and a strong decrease in the soil derived brgdgt proportion toward the holocene since the lowering of soil vs lacustrine derived brgdgts is prone to bias the temperature signal that is reconstructed using a soil calibration a correction for in situ production is applied the corrected signal is compared to independent discrete temperature records from the study area the brgdgt temperature relative evolution reconstructed in this work provides additional insight regarding millennial scale climate variability in central and eastern europe notably the imprints of heinrich event cold spells and lateglacial climatic oscillations are consistent with other regional paleorecords from the northern hemisphere

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr