variability of the north atlantic thermohaline circulation during the last interglacial period studies of natural climate variability are essential for evaluating its future evolution greenland ice cores suggest that the modern warm period the holocene has been relatively stable for the past 9 000 years much less is known about other warm interglacial periods which comprise less than 10 of the climate record during the past 2 5 million years here we present high resolution ocean sediment records of surface and deep water variables from the bermuda rise spanning the last interglacial period about 118 000 127 000 years ago in general deep water chemical changes are coincident with transitions in surface climate at this site the records do not show any substantial fluctuations relative to the much higher variability observed during the preceding and subsequent cool climates the relatively stable interglacial period begins and ends with abrupt changes in deep water flow we estimate using 230 th measurements to constrain the chronology that transitions occur in less than 400 years

variations in mode of formation and temperature of oceanic deep waters over the past 125 000 years marked changes in the deep water temperature of the different oceanic basins during the past 125 kyr are revealed by a detailed comparison of the oxygen isotopic composition ofbenthicforaminiferafrom sediment cores taken from the norwegian sea and the pacific atlantic and southern oceans the last interglacial deep water temperatures were similar to the modern ones at the 5e 5d transition around 115 kyr bp the deep water temperatures dropped below approximately 0 c in the pacific and southern indian oceans in the atlantic ocean the deep water temperature dropped in 2 successive steps at 115 and 75ky bp the global ocean deep water temperatures were in the 0 to 1 c range for the whole of the last ice age isotope stages 4 2

abrupt changes in deep atlantic circulation during the transition to full glacial conditions 1 six ocean drilling program odp sites in the northwest atlantic have been used to investigate kinematic and chemical changes in the western boundary undercurrent wbuc during the development of full glacial conditions across the marine isotope stage 5a 4 boundary 70 000 years ago sortable silt mean grain size ss measurements are employed to examine changes in near bottom flow speeds together with carbon isotopes measured in benthic foraminifera and planktic foraminiferal fragmentation as proxies for changes in water mass chemistry a depth transect of cores spanning 1 8 4 6 km depth allows changes in both the strength and depth of the wbuc to be constrained across millennial scale events ss measurements reveal that the flow speed structure of the wbuc during warm intervals interstadials was comparable to modern holocene conditions however significant differences are observed during cold intervals with higher relative flow speeds inferred for the shallow component of the wbuc 2 km depth during all cold stadial intervals including heinrich stadial 6 and a substantial weakening of the deep component 3 4 km during full glacial conditions our results therefore reveal that the onset of full glacial conditions was associated with a regime shift to a shallower mode of circulation involving glacial north atlantic intermediate water that was quantitatively distinct from preceding cold stadial events furthermore our chemical proxy data show that the physical response of the wbuc during the last glacial inception was probably coupled to basin wide changes in the water mass composition of the deep northwest atlantic

high resolution record of the environmental response to climatic variations during the last interglacial glacial cycle in central europe the loess palaeosol sequence of dolni věstonice czech republic abstract high resolution multidisciplinary investigation of key european loess palaeosols profiles have demonstrated that loess sequences result from rapid and cyclic aeolian sedimentation which is reflected in variations of loess grain size indexes and correlated with greenland ice core dust records this correlation suggests a global connection between north atlantic and west european air masses herein we present a revised stratigraphy and a continuous high resolution record of grain size magnetic susceptibility and organic carbon 13c of the famous of dolni vestonice dv loess sequence in the moravian region of the czech republic a new set of quartz osl ages provides a reliable and accurate chronology of the sequence s main pedosedimentary events the grain size record shows strongly contrasting variations with numerous abrupt coarse grained events especially in the upper part of the sequence between ca 20 30 ka this time period is also characterised by a progressive coarsening of the loess deposits as already observed in other western european sequences the base of the dv sequence exhibits an exceptionally well preserved soil complex composed of three chernozem soil horizons and 5 aeolian silt layers marker silts this complex is at present the most complete record of environmental variations and dust deposition in the european loess belt for the weichselian early glacial period spanning about 110 to 70 ka allowing correlations with various global palaeoclimatic records osl ages combined with sedimentological and palaeopedological observations lead to the conclusion that this soil complex recorded all of the main climatic events expressed in the north grip record from greenland interstadials gis 25 to 19

a centennial scale record of vegetation and climate variability from 312 to 240 ka marine isotope stages 9c a 8 and 7e from tenaghi philippon ne greece abstract based on a new centennial scale resolution pollen record from the terrestrial site of tenaghi philippon ne greece we report a series of high amplitude millennial scale forest expansion events during the interval from 312 to 240 ka equivalent to isotopic substages c a of marine isotope stage mis 9 mis 8 and the onset of mis 7e pollen based indices support the climatic interpretation of the forest expansion events as indicators of abrupt increases in temperature and moisture availability in the mediterranean region long term changes in vegetation cover and composition during the studied interval permit the definition of glacial substages early middle and late analogous to the glacial substages of the last climatic cycle within this framework forest expansion events occurred during the early glacial equivalent to mis 9c a and the later part of the middle glacial mid to late mis 8 but are absent from the early part of the middle glacial early mis 8 forest expansion events are also detected during the lateglacial and onset of mis 7 associated with a millennial scale climate oscillation across the glacial interglacial transition i e termination iii t iii a peak for peak match between forest expansion events and antarctic temperature maxima suggests interhemispheric coupling of millennial scale climate variability via global oceanic circulation change and synergistic variability in atmospheric circulation consistent with the bipolar see saw the resolution of our record mean 290 yr also permits the characterisation of climate evolution over the course of interstadial episodes following forest expansion events and highlights differences in the characteristics of early and middle glacial interstadials saw tooth vs plateau profile these differences point to an influence of long term boundary conditions especially global ice volume on the characteristics of millennial scale events

millennial scale variability in western tropical atlantic surface ocean hydrography during the early pliocene abstract we use high resolution oxygen isotope data 18o from planktonic foraminifera in the western tropical atlantic ocean ocean drilling program leg 154 site 925 to investigate millennial scale climate variability during an interval of relative climate warmth the early pliocene for this purpose we have chosen a 100 kyr long time interval from 4 13 to 4 24 ma and subsampled it to obtain an average time step of 800 yr we reconstruct changes in upper ocean hydrography using the 18o values of globigerinoides sacculifer a mixed layer dweller and neogloboquadrina dutertrei a thermocline dweller their oxygen isotopic difference 18o is taken as a measure of the mixed layer to thermocline thermal gradient time series analysis indicates that significant concentration of variance exists in the g sacculifer and n dutertrei at sub milankovitch periods of between 8 and 4 kyr and in the 18o record between 13 and 8 kyr wavelet analysis illustrates that the suborbital variance is only present in the record when the amplitude of the precessional signal is large between 4 24 and 4 20 ma in this particular portion of the record however we observe positive 18o excursions in the individual 18o time series thus the suborbital periods evident in the spectra may reflect harmonics associated with asymmetrical time series because the excursions only occur when precession forcing is also strong we suggest that there is a relationship between the proxy records and climate although we cannot conclude that it is cyclical in nature the 18o record on the other hand is characterized by positive as well as negative excursions we observe significant concentration of variance close to half precession during the portion of the record when precession forcing is also strong which we believe reflects a close although nonlinear response of the western tropical surface ocean to low latitude insolation forcing

changes in meridional temperature and salinity gradients in the north atlantic ocean 30 72 n during the last interglacial period eight deep sea sediment cores from the north atlantic ocean ranging from 31 to 72 n are studied to reconstruct the meridional gradients in surface hydrographic conditions during the interval of minimum ice volume within the last interglacial period using benthic foraminiferal 18o measurements and estimates of sea surface temperature sst and sea surface salinity sss we show that summer ssts and ssss decreased gradually during the interval of minimum ice volume at high latitude sites 52 72 n whereas they were stable or increased during the same time period at low latitude sites 31 41 n this increase in meridional gradients of ssts and ssss may have been due to changes in the latitudinal distribution of summer and annual average insolation and associated oceanic and atmospheric feedbacks these trends documented for the eemian ice volume minimum period are similar to corresponding changes observed during the holocene and may have had a similar origin

persistent solar influence on north atlantic climate during the holocene surface winds and surface ocean hydrography in the subpolar north atlantic appear to have been influenced by variations in solar output through the entire holocene the evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon 14 and beryllium 10 and centennial to millennial time scale changes in proxies of drift ice measured in deep sea sediment cores a solar forcing mechanism therefore may underlie at least the holocene segment of the north atlantic9s 1500 year cycle the surface hydrographic changes may have affected production of north atlantic deep water potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally

late quaternary lithofacies provenance and depositional environments 12 30 cal ka north and south of the denmark strait this paper describes the lithofacies and chronology of cores from north and south of the denmark strait for a period when ice sheets flanked both sides of the strait a wide range of sediments have been recovered indicating a complex of depositional processes jm96 1229ggc1 1047 m water depth is from the base of the nw iceland slope at the southern edge of the blosseville basin whereas jm96 1226ggc4 retrieved sediments south of the sill in 1519 m of water additional information is based on jm96 1220ggc2 and 1221ggc2 which were recovered from the upper w iceland slope at 500 m water depth below the latra moraine of possible last glacial maximum age and upslope of jm96 1226 ams 14c dates indicate that jm96 1226 and 1229 span the last 10 to 27 32 ka bp whereas jm96 1220 and 1221 recovered sediments dated between ca 8 and 18 ka bp closely spaced radiocarbon dates on jm96 1229 indicate an erosional hiatus of 7 ky between 12 and 19 cal ka lithofacies descriptions are based on visual descriptions and x radiographs jm96 1229 consists of fine grained sediments sometimes graded with scattered ice rafted debris whereas jm96 1226 consists largely of beds of matrix supported diamicton provenance indicators mass magnetic susceptibility and geochemistry for jm96 1229 support the delivery of sediments from nw iceland but there is a substantial difference in these properties between sediments from the w iceland upper slope and the sediments in jm96 1226 south of the denmark strait this indicates that the diamictons on the floor of the strait did not derive entirely from the iceland ice sheet and adjacent upper slope the general absence of sediments 12 cal ka on the slopes and floor of the denmark strait indicates that denmark strait overflow waters inhibited sediment accumulation during the holocene between ca 12 and 30 cal ka however a combination of more proximal sediment sources ice sheets and reduced thermohaline activity resulted in the accumulation of sediments on the slopes and basin floors

binge purge oscillations of the laurentide ice sheet as a cause of the north atlantic s heinrich events ice rafted debris in sediment cores from the north atlantic suggests that the laurentide ice sheet lis periodically disgorged icebergs in brief but violent episodes which occurred approximately every 7 000 years here i propose that heinrich events i e what these episodes are called were caused by free oscillations in the flow of the laurentide ice sheet which arose because the floor of hudson bay and hudson strait is covered with soft unconsolidated sediment that forms a slippery lubricant when thawed the proposed heinrich event cycle has two phases the growth phase occurs when the sediment is frozen and the lis is stranded immobile on a rigid bed the volume of the lis slowly grows during this phase at a rate dictated by snow accumulation the purge phase occurs when the basal sediment thaws and a basally lubricated discharge pathway i e an ice stream such as those which occur in west antarctica today developes through hudson strait the volume of the lis rapidly equilibrates to the reduced basal friction during this phase by dumping icebergs into the labrador sea the periodicity t k sl2g 2 7000 years of the proposed heinrich event cycle is a function of the thermal conductivity and diffusivity of ice k and respectively the atmospheric sea level temperature sl in degrees celsius and the excess geothermal heat flux defined by g g k where is the atmospheric lapse rate and g is the geothermal heat flux agreement between the predicted t and the apparent periodicity implied by the marine record is the main virtue of the free oscillation mechanism i propose an alternative mechanism in which heinrich events are forced by periodic variations in external climate is implausible because periodic atmospheric temperature perturbations are strongly attenuated with depth in an ice sheet

comparison of changes in vegetation in northeast greece with records of climate variability on orbital and suborbital frequencies over the last 450 000 years abstract a new direct pollen orbital tuning procedure based on a correspondence between changes in certain vegetation elements and march and june perihelion configurations is applied to the tenaghi philippon record northeast greece the development of a refined chronological scheme allows comparisons to be made with records of climate variability from the north atlantic as well as of global sea level ice volume and atmospheric co2 content on orbital frequencies the comparison reveals a close correspondence between relative ice volume extent and tree population size during glacial intervals during interglacial and interstadial periods the degree of forest development is more closely associated with high latitude insolation and related climate regimes rather than extent of residual ice volume on suborbital frequencies the greek record shows similar repeat times in peaks of steppe vegetation with north atlantic ice rafting events but the amplitude of this variability in the two records is not always proportional overall what emerges is that the major shifts in the relative abundance of forest v open vegetation communities at tenaghi philippon on orbital and suborbital frequencies over the last 450 000 years are coherent with high latitude changes affecting atmospheric and oceanic circulation glacial decreases in atmospheric co2 content contributed to the elimination of tree populations by exacerbating water stress conditions during arid intervals but do not appear to be the primary driver of the observed vegetation changes at this latitude variations in co2 levels in the order of 40 ppmv between different interglacial interstadials periods with adequate moisture availability appear to have had a limited effect on the nature and size of tree populations

climate correlations between greenland and antarctica during the past 100 000 years the ice cores recovered from central greenland by the grip1 2 and gisp23 projects record 22 interstadial warm events during the part of the last glaciation spanning 20 105 kyr before present the ice core from vostok east antarctica records nine interstadials during this period4 5 here we explore links between greenland and antarctic climate during the last glaciation using a high resolution chronology derived by correlating oxygen isotope data for trapped o2 in the gisp2 and vostok cores we find that interstadials occurred in east antarctica whenever those in greenland lasted longer than 2 000 years our results suggest that partial deglaciation and changes in ocean circulation are partly responsible for the climate teleconnection between greenland and antarctica ice older than 115 kyr in the gisp2 core shows rapid variations in the 18o of o2 that have no counterpart in the vostok record the age depth relationship and thus the climate record in this part of the gisp2 core appears to be significantly disturbed

oxygen isotopes and sea level from the time that detailed oxygen isotope records derived from foraminifera living in the constant temperature environment of the abyssal ocean became available there has been a discrepancy between the ice volume record that these records imply and that derived from the altitude of dated coral terraces around the world here we re examine the data and conclude that the temperature of the abyssal ocean has been an actively varying component of the climate system

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

responses of the okhotsk sea environment and sedimentology to global climate changes at the orbital and millennial scale during the last 350 kyr abstract we measured productivity proxies chlorin carbonate and organic carbon opal and biogenic ba content and lithophysical proxies magnetic susceptibility water content density and coarse sediment fraction in sediment of central okhotsk sea core pc 7r the age model covering the last 350 kyr of this core was constructed by correlating the dated series of relative paleointensity lows recognized in geomagnetic intensity records marine isotope stage mis boundaries determined in broad variations of the lithophysical and productivity proxies and tephrochronology the orbital changes of the lithophysical and productivity proxy stacks lag behind northern hemisphere summer radiation by approximately 6 3 and 5 9 kyr respectively this lag is consistent with a milankovich model of climate control by solar radiation through the northern ice sheet volume and sea surface and surrounding land responses which are fast compared with sedimentological evidence productivity proxies of the okhotsk sea also demonstrate 52 abrupt pronounced productivity minima associated with regional climate coolings during the last 350 kyr which present useful indicators of millennial scale climate changes in this marginal sea based on the postulated synchronicity of dansgaard oeschger cycles in the northern hemisphere and the established simultaneity of 11 okhotsk sea coolings in the last 77 kyr with abrupt severe cold events in the greenland ice core and north atlantic heinrich events all of these may be regarded as heinrich equivalent event anomalies the okhotsk sea events have their counterparts in the records of north atlantic sediments the greenland ice sheet east asia summer monsoon and the antarctic ice sheet probably the arctic oscillation was the main factor determining orbital and millennial climate oscillations in the high latitude northern hemisphere including the okhotsk sea region

reconstruction of the grande pile eemian using inverse modeling of biomes and δ13c abstract a new method to reconstruct past climatic conditions between 130 and 100 ka bp from pollen and isotopic data is applied to a previously unanalyzed grande pile core gpxxi we applied the inverse mode to the biome4 vegetation model the method utilizes 13 c measured in parallel to the pollen samples as a constraint for the model first the biomes and the 13 c simulated by the model are compared with the biome allocation of the pollen data the 13 c to be simulated takes into account the degradation effect on the preserved organic matter this procedure allows the reconstruction of the mean annual temperature and precipitation as well as the mean temperatures of the warmest and coldest months we show that during the eemian sensu stricto the reconstructed precipitation is similar to modern values with low variability the cold stadials and the penultimate glaciation are characterized by very low precipitation amounts the temperature estimates however indicate differences with several oscillations identified the peak values are reached at about 124 125 ka bp but two other warm intervals are also identified the variations in temperature appear to be related to sea surface temperature oscillations in the north atlantic region and are also in agreement with the timing of ice sheet build up in the northern hemisphere seasonal variations are also identified in the estimated temperatures of the warmest and coldest months

dysaerobic conditions during heinrich events 4 and 5 evidence from phosphorus distribution in a north atlantic deep sea core abstract reactive phosphorus undergoes diagenetic transformation once transferred into marine sediments the degree of regeneration and redistribution of phosphorus depends on early diagenetic and environmental conditions which may be linked to larger scale phenomena such as bottom water circulation water column ventilation and organic carbon flux phosphorus phases of the

progress in paleoclimate modeling this paper briefly surveys areas of paleoclimate modeling notable for recent progress new ideas including hypotheses giving a pivotal role to sea ice have revitalized the low order models used to simulate the time evolution of glacial cycles through the pleistocene a prohibitive length of time for comprehensive general circulation models gcms in a recent breakthrough however gcms have succeeded in simulating the onset of glaciations this occurs at times most recently 115 kyr b p when high northern latitudes are cold enough to maintain a snow cover and tropical latitudes are warm enhancing the moisture source more generally the improvement in models has allowed simulations of key periods such as the last glacial maximum and the mid holocene that compare more favorably and in more detail with paleoproxy data these models now simulate enso cycles and some of them have been shown to reproduce the reduction of enso activity observed in the early to middle holocene modeling studies have demonstrated that the reduction is a response to the altered orbital configuration at that time an urgent challenge for paleoclimate modeling is to explain and to simulate the abrupt changes observed during glacial epochs i e dansgaard oescher cycles heinrich events and the younger dryas efforts have begun to simulate the last millennium over this time the forcing due to orbital variations is less important than the radiance changes due to volcanic eruptions and variations in solar output simulations of these natural variations test the models relied on for future climate change projections they provide better estimates of the internal and naturally forced variability at centennial time scales elucidating how unusual the recent global temperature trends are

late warming and early cooling of the sea surface in the nordic seas during mis 5e eemian interglacial abstract geochemical identification of a tephra layer found in two cores from the ne atlantic ocean and the se norwegian sea respectively and dated to 127 ka bp has enabled us to obtain a precise correlation across the iceland scotland ridge at the marine isotope stage mis 6 5 transition the direct distance between the two cores is only about 200 km south of the iceland scotland ridge sea surface temperatures rose abruptly at 130 ka bp at the onset of mis 5e and at least 2 3000 years earlier than north of the ridge maximum sea surface temperatures south of the ridge occurred during this initial phase of mis 5e when temperatures in the nordic seas were still low north of the ridge the sea surface warmed rapidly at 127 ka bp correlations between the north atlantic records and the eemian of northwest europe tentatively indicate that the initial phase of mis 5e correlates with the early part of the eemian characterised by a warm continental type of climate the period after the warming of the nordic seas corresponds to the slightly cooler and more oceanic middle eemian interval in europe the sea surface temperatures fell gradually north of the ridge during the later part of mis 5e and they were low during mis 5d 5a south of the ridge the temperatures remained relatively high the data shows that there was no outflow of deep water from the norwegian sea during the later part of mis 6 outflow began at the mis 6 5 transition simultaneous with the sea surface warming south of the ridge

testing provenance diagrams lessons from the well constrained cariaco basin abstract the fine grained sediments of the cariaco basin venezuela of the last 130 ky whose deposition history is well characterized were analyzed geochemically in order to test the validity of sediment bulk geochemistry as an indicator of detrital provenance several binary and ternary diagrams as well as the chemical index of alteration cia were tested for their capacity to discriminate the poorly contrasted detrital sources to the cariaco basin and to describe the temporal evolution of the contributions of these different sources most of the diagrams tested did not allow a good discrimination of sources or when sources were well discriminated did not allow an interpretation of the temporal variations consistent with the known history a relatively good discrimination of sources and a consistent interpretation of temporal variations were however obtained using hf vs th and la yb vs gd yb binary diagrams as well as ti zr th ti zr la and lu hf th ternary diagrams compared to the previous studies of the detrital content of the cariaco basin sediments the geochemical approach permitted the recognition of a sediment contribution eroded from the unare platform and gulf of cariaco during rapid sea level oscillations and the contribution of saharan eolian particles during the younger dryas preboreal and mis6 5 transition the choice of plotted elements was determined after considering carrier minerals so that different elements may be informative in different sedimentary contexts overall mineral sorting during transport appears as a major limit to quantitative estimation of the different contributions in particular mineral sorting leads to the selective enrichment of elements associated with clays al rb th and lree in sediments deposited in the basin unless the geochemical effect of mineral sorting can be measured it appears that quantitative provenance analysis should be performed on fractions of similar grain size instead of bulk sediment

paleoenvironmental changes associated with the holocene marine transgression yellow sea hwanghae benthic foraminiferal and stable isotopic data from two radiocarbon dated cores from the yellow sea record paleoenvironmental changes largely associated with the holocene marine transgression the holocene marine transgression began significantly earlier 12 9 ka in the central part of the yellow sea as recorded in 278 cm long core cc 02 water depth 77 5 m compared with 7 9 ka in a tidal flat on west coast of korea as recorded in 350 cm long vibra core dh4 1 water depth 1 8 m the benthic foraminiferal assemblages in the lower part of cc 02 and the entire marine sequence of dh4 1 are dominated by assemblages characteristic of shallow 50 m waters ammonia ketienziensis ishizaki astrononion italicum cushman and edwards and hanzawaia nipponica asano after 7 5 ka in the central yellow sea much higher 18o 1 6 to 1 8 and 13c 0 1 to 0 7 values of a ketienziensis reflect a change to more open ocean higher salinity environments with deeper waters dominated by the hwanghae cold water as in the present day

insights into north atlantic deep water formation during the peak interglacial interval of marine isotope stage 9 mis 9 foraminifera abundance and stable isotope records from odp site 984 61 25 n 24 04 w 1648 m in the north atlantic are used to reconstruct surface circulation variations and the relative strength of the north atlantic deep water nadw formation over the period spanning the peak warmth of marine interglacial stage mis 9e 324 336 ka this interval includes the preceding deglaciation termination 4 t4 and the subsequent glacial inception of mis 9d the records indicate a greatly reduced contribution of nadw during t4 as observed in more recent deglaciations in contrast with the most recent deglaciation the lack of a significant nadw signal extended from t4 well into the peak interglacial mis 9e and persisted nearly until the transition to the subsequent glacial stage mis 9d although nadw formation resumed during mis 9e only depths greater than 2000 m appear to have been ventilated the poorly ventilated intermediate depth of site 984 2000 m may have resulted on one hand from a general reduction of deep water ventilation by nadw during the study interval or on the other hand from different pathways of the spread of newly formed nadw that bypassed the study location the intermediate depths may have also been invaded by southern sourced waters as the formation of intermediate depth nadw weakened the absence of any significant nadw signal at the water depth of site 984 during the climatic optimum contrasts sharply with subsequent interglacial peaks mis 5e and the holocene despite the perturbed intermediate depth circulation oceanic heat transport northeastward was not interrupted and may have contributed to the relatively mild interglacial conditions of mis 9e

interglacials of the last 800 000 years interglacials including the present holocene period are warm low land ice extent high sea level end members of glacial cycles based on a sea level definition we identify eleven interglacials in the last 800 000 years a result that is robust to alternative definitions data compilations suggest that despite spatial heterogeneity marine isotope stages mis 5e last interglacial and 11c 400 ka ago were globally strong warm while mis 13a 500 ka ago was cool at many locations a step change in strength of interglacials at 450 ka is apparent only in atmospheric co2 and in antarctic and deep ocean temperature the onset of an interglacial glacial termination seems to require a reducing precession parameter increasing northern hemisphere summer insolation but this condition alone is insufficient terminations involve rapid nonlinear reactions of ice volume co2 and temperature to external astronomical forcing the precise timing of events may be modulated by millennial scale climate change that can lead to a contrasting timing of maximum interglacial intensity in each hemisphere a variety of temporal trends is observed such that maxima in the main records are observed either early or late in different interglacials the end of an interglacial glacial inception is a slower process involving a global sequence of changes interglacials have been typically 10 30 ka long the combination of minimal reduction in northern summer insolation over the next few orbital cycles owing to low eccentricity and high atmospheric greenhouse gas concentrations implies that the next glacial inception is many tens of millennia in the future

millennial scale fluctuations in north atlantic heat flux during the last 150 000 years abstract surface water and deep ocean palaeoclimate records obtained from north atlantic core su90 03 40 n 32 w exhibit pronounced fluctuations at sub orbital time scales surface temperature variability in the mid latitude atlantic over the last 150 kyr is dominated by forcing at precession 21 kyr and semi precession harmonics 11 kyr abrupt changes in sea surface temperatures show that the northward transport of heat by the north atlantic current was curtailed during ice rafting events sea surface temperatures were about 12 c colder than modern values during the most intense cooling episodes associated with major ice rafting events heinrich events 1 4 6 and 11 and 10 c below modern values during the later part of isotope stage 3 40 30 ka during these cold intervals the north atlantic current was displaced to south of 40 n as the cold meltwaters penetrated southwards into what is now the subtropical ocean these changes in surface ocean heat exchange were most probably allied to a latitudinal migration and increase in zonality of atmospheric circulation patterns concurrent shifts in ird concentration sea surface temperatures and benthic 13 c values provide evidence of coupling between sea surface processes and the deep water circulation and suggest that decreases in surface temperature and salinity during ice rafting events culminated in a significant reorganisation of north atlantic deep water production

stratigraphy and distribution of tephra layers in marine sediment cores from the faeroe islands north atlantic the stratigraphical position of eight discrete tephra layers is investigated in four marine sediment cores from north and south of the faeroe islands the tephras are correlated to the marine oxygen isotope stratigraphy and the interstadial stadial cycles dansgaard oeschger cycles of the greenland ice cores a very prominent volcanic event occurred during interstadial 23 in marine oxygen isotope stage mis 5c correlating with a cold event within this otherwise warm interval two tephra horizons in mis 5a correlate with the beginning and end of interstadial 21 respectively the most widely distributed ash is the well known ash zone 2 from the lower part of mis 3 in the two cores from north of the faeroe islands it consists of two discrete layers a lower one composed of rhyolitic and basaltic tephra and an upper layer composed exclusively of basaltic glass the two tephra falls coincide with the two warm intervals of dansgaard oeschger cycle no 15 a hitherto unknown basaltic tephra was recorded just above heinrich event h4 in the lower part of the warm interstadial 8 and dated to ca 33 14c ka bp another frequently recorded layer termed the fugloyarbanki tephra is likewise basaltic it is dated to 23 1 14c ka bp it was deposited after the peak warm phase of interstadial 3 at the mis 3 2 transition finally a tephra dated ca 15 4 14c ka bp was found in two cores from north of the ridge it was deposited at the beginning of the deglaciation between the last glacial maximum and heinrich event h1

high resolution climate records from the north atlantic during the last interglacial the two deep ice cores recovered by the grip1 and gisp22 projects at summit greenland agree in detail over the past 100 000 years3 and demonstrate dramatic climate variability in the north atlantic region during the last glacial before the current period of holocene stability this glacial climate instability has subsequently been documented in the marine sedimentary record of surface ocean conditions in the north atlantic4 before 100 kyr ago the two ice core records are discrepant however casting doubt on whether the oxygen isotope fluctuations during the last interglacial eemian seen in the grip core1 5 represent a true climate signal here we present high resolution records of foraminiferal assemblages and ice rafted detritus from two north atlantic cores for the interval 65 kyr to 135 kyr ago extending the surface ocean record back to the eemian the correlation between our records and the greenland ice core records is good throughout the period in which the two ice cores agree suggesting a regionally coherent climate response during the eemian our marine records show a more stable climate than that implied by the grip ice core suggesting that localized phenomena may be responsible for the variability in the latter record during the eemian

western north atlantic evidence for millennial scale changes in ocean circulation and climate two late quaternary series of high resolution percent carbonate data from western north atlantic sediment drifts bermuda rise and bahama outer ridge show millennial scale oscillations superimposed on the familiar longer period oscillations of orbital origin the dominant high frequency oscillation in these records has a quasi period of about 4000 years these percent caco3 changes most likely result from the influence of climate change on the flux of terrigenous material from eastern canada the resuspension of continental margin sediment by deep eddy kinetic energy and carbonate dissolution sediment is transported to the bermuda rise by deep recirculating gyres and to the bahama outer ridge by the deep western boundary current system stable isotope results on foraminifera across several of these oscillations from interstadial climate conditions and from a glacial inception display variability similar to that of percent caco3 oxygen isotope ratios of planktonic foraminifera suggest large variations in near surface temperature and or salinity and carbon isotope ratios of benthic foraminifera indicate that there were significant oscillations in the flux of north atlantic deep water nadw these data support models which couple surface ocean conditions in the north atlantic production of nadw north atlantic heat flux and evidence for temperature oscillations in ice cores

comparison of oxygen isotope records from the gisp2 and grip greenland ice cores recent results1 2 from the greenland ice core project grip summit ice core suggest that the climate in greenland has been remarkably stable during the holocene but was extremely unstable for the time period represented by the rest of the core spanning the last two glaciations and the intervening eemian inter glacial here we present the complete oxygen isotope record for the greenland ice sheet project 2 gisp2 core drilled 28 km west of the grip core we observe large rapid climate fluctuations throughout the last glacial period which closely match those reported for the grip core however in the bottom 10 of the cores spanning the eemian interglacial and the previous glacia tion there are significant differences between the two records it is possible that ice flow may have altered the chronological sequences of the stratigraphy for the bottom part of one or both of the cores considerable further work will be necessary to evaluate the likelihood of this and the extent to which it will still be possible to extract meaningful climate information from the lowest sections of the cores

a north atlantic tephrostratigraphical framework for 130 60 ka b2k new tephra discoveries marine based correlations and future challenges abstract building chronological frameworks for proxy sequences spanning 130 60 ka b2k is plagued by difficulties and uncertainties recent developments in the north atlantic region however affirm the potential offered by tephrochronology and specifically the search for cryptotephra here we review the potential offered by tephrostratigraphy for sequences spanning 130 60 ka b2k we combine newly identified cryptotephra deposits from the ngrip ice core and a marine core from the iceland basin with previously published data from the ice and marine realms to construct the first tephrostratigraphical framework for this time interval forty three tephra or cryptotephra deposits are incorporated into this framework twenty three tephra deposits are found in the greenland ice cores including nine new ngrip tephras and twenty separate deposits are preserved in various north atlantic marine sequences major minor and trace element results are presented for the new ngrip horizons together with age estimates based on their position within the ice core record basaltic tephras of icelandic origin dominate the framework with only eight tephras of rhyolitic composition found new results from marine core md99 2253 also illustrate some of the complexities and challenges of assessing the depositional integrity of marine cryptotephra deposits tephra based correlations in the marine environment provide independent tie points for this time interval and highlight the potential of widening the application of tephrochronology further investigations however are required that combine robust geochemical fingerprinting and a rigorous assessment of tephra depositional processes in order to trace coeval events between the two depositional realms

suborbital timescale variability of north atlantic deep water during the past 200 000 years we generated 200 kyr long proxy records of surface and deepwater variability from a subpolar north atlantic core v29 202 enabling us to assess the linkage between surface and deepwater changes on suborbital timescales in particular we used a benthic 13c record to evaluate the deep water response to dansgaard oeschger temperature oscillations and to heinrich events times of massive iceberg delivery to the north atlantic we found that the reduction of north atlantic deep water nadw production was generally associated with cold or dropping sea surface temperatures ssts as indicated by planktonic foraminiferal assemblages the nadw contribution to the site did not drop appreciably during heinrich events h4 through h2 probably because these events followed intervals of prolonged surface cooling already characterized by low rates of nadw production by contrast nadw reduction appears to have been synchronous with h5 sst rise associated with both dansgaard oeschger oscillations and heinrich events was usually accompanied by increasing nadw strength in a few cases the nadw recovery appeared to lag the sst rise however the apparent delay is most likely an artefact of the sedimentary record low concentrations of benthic foraminifera as a result of low benthic foraminiferal abundances during stage 6 the stage 6 benthic foraminiferal 13c record is of lower resolution than the younger part of the record the stage 6 proxy records for surface hydrography nevertheless reveal millennial scale oscillations similar to those seen in stage 3 the available 13c data suggest that nadw weakened in association with the cold portions of stage 6 sst oscillations we also sought to confirm a recent study which concluded that there was little nadw variability during the peak of the last interglaciation marine oxygen isotope substage 5e eemian isotope stage 5 was marked by a trend of increasing benthic 13c in v29 202 rising 13c through isotope stage 5 is also seen in tropical surface water records and at some deep atlantic sites and may reflect the common derivation of these water masses variations of 0 5 superimposed on this rising 13c trend within substage 5e in v29 202 are so far not evident in tropical feed waters and may therefore indicate that nadw production was weaker during the late than mid eemian an electronic supplement of this material may be obtained on a diskette or anonymous ftp from kosmos agu org login to agu s ftp account using anonymous as the username and guest as the password go to the right directory by typing cd apend type ls to see what files are available type get and the name of the file to get it finally type quit to leave the system paper 95pa02089 suborbital timescale variability of north atlantic deep water during the past 200 000 years by d w oppo and s j lehman diskette may be ordered from american geophysical union 2000 florida avenue n w washington dc 20009 15 00 payment must accompany order

comment on catastrophic ice shelf breakup as the source of heinrich event icebergs by c l hulbe et al hulbe et al 2004 argue that the original binge purge model of their coauthor macayeal 1993a 1993b is not appropriate for heinrich events but that a new ice shelf collapse mechanism may work we believe that thenew collapse mechanism disagrees with important dataand that macayeal s original model remains viable afterappropriate modifications we have enjoyed a fascinatingdiscussion with hulbe et al on this topic which isstimulating our thinking and research and we presentsome of the arguments here for a wider audience

how long and how stable was the last interglacial abstract surface ocean indicators in the north atlantic during marine isotope stage mis 5 correlate closely with the vegetational succession in northeastern france the melisey i silty layer which marks the end of the last interglacial biozone in la grande pile pollen record appears coeval with the polar front advance c24 registered in the core v29 191 by a sharply increased presence of ice rafted detritus and the cold water foraminifer neogloboquadrina pachyderma sinistral since this event is younger than the peak of mis 5d the last interglacial as recognized in northern france correlates not only with the mis 5e but also with a substantial part of mis 5d the last interglacial in la grande pile was twice as long as the holocene and the climate in its first half was apparently not less stable than during the current interglacial if the future natural climates were to develop as analogs of the past then the onset of the next glacial environments on land would be still many millennia ahead

magnetic susceptibility patterns and provenance of ice rafted material at feni drift rockall trough implications for the history of the british irish ice sheet abstract piston core enam 97 09 from feni drift atlantic margin west of ireland provides a record of ird input variability and provenance during the last 250 000 yrs the ird patterns can be related to late devensian detrital carbonate and meta sedimentary rock fragments represent two major ird types which were dominantly derived from irish inland ice and the irish sea ice stream respectively additional evidence for the latter source is based on heavy mineral data input from other circum north atlantic ice sheets notably the laurentide ice sheet is minor compared to british irish ird at least during periods of maximum expansion of the biis this is consistent with the marginal location of the core site with reference to the main north atlantic ird belt on the other hand laurentide ird presumably accounts for minor ird peaks at times of reduced ice volume in the british isles the main magnetic susceptibility peak during late isotope stage 2 termination i can be related to ird input from the laurentide ice sheet following early decay of the biis a similar pattern is observed during oxygen isotope stage 6 these observations are consistent with recent provenance studies indicating that only laurentide ird carries a strong magnetic susceptibility signal

the demise of the last interglacial recorded in isotopically dated speleothems from the alps abstract the transition from interglacial to glacial climate has attracted much attention in paleoclimatic research partly because orbital forcing dictates that such a return to a new ice age is inescapable albeit in the distant future only the detailed series of steps that leads to glacial inceptions remains poorly understood however and studies of past glacial inceptions are often compromised by incomplete records imprecise chronological control and or uncertainties associated with proxy transfer functions here we present results from u th dated speleothems from a cave in the austrian alps entrische kirche cave which grew continuously between ca 127 and 114 ka and intermittently also during subsequent stadials and interstadials the alpine setting of this cave is prone to periglacial and glacial processes as well as temperature and precipitation changes which are recorded in these cave deposits we use high resolution stable isotope data to constrain paleoenvironmental changes associated with the demise of the last interglacial unprecedented in detail for central europe peak interglacial conditions are characterized by high 18 o values and high growth rates from ca 127 to 124 ka a major drop in 18 o by 3 occurred at ca 118 ka which coincided with cold event c26 in the north atlantic this isotopic shift which occurred at or close to isotopic equilibrium cannot be explained by simple uniform cooling modelling suggests that enhanced seasonality dominated by significant changes in winter precipitation are required to reconcile the isotope data with the fact that calcite deposition continued across the mis 5e d transition i e no cave freezing this period of enhanced seasonality lasted for several millennia during which the catchment area of the cave remained geomorphologically stable and ice free eventually speleothem growth terminated at ca 114 ka which is in line with widespread ice rafting in the north atlantic cold event c24 and the onset of fully stadial conditions during mis 5d

evidence for last interglacial chronology and environmental change from southern europe establishing phase relationships between earth system components during periods of rapid global change is vital to understanding the underlying processes it requires records of each component with independent and accurate chronologies until now no continental record extending from the present to the penultimate glacial had such a chronology to our knowledge here we present such a record from the annually laminated sediments of lago grande di monticchio southern italy using this record we determine the duration 17 70 0 20 ka and age of onset 127 20 1 60 ka b p of the last interglacial as reflected by terrestrial ecosystems this record also reveals that the transitions at the beginning and end of the interglacial spanned only 100 and 150 years respectively comparison with records of other earth system components reveals complex leads and lags during the penultimate deglaciation phase relationships are similar to those during the most recent deglaciation peaks in antarctic warming and atmospheric methane both leading northern hemisphere terrestrial warming it is notable however that there is no evidence at monticchio of a younger dryas like oscillation during the penultimate deglaciation warming into the first major interstadial event after the last interglacial is characterized by markedly different phase relationships to those of the deglaciations warming at monticchio coinciding with antarctic warming and leading the atmospheric methane increase diachroneity is seen at the end of the interglacial several global proxies indicate progressive cooling after 115 ka b p whereas the main terrestrial response in the mediterranean region is abrupt and occurs at 109 50 1 40 ka b p

persistent suborbital climate variability in marine isotope stage 5 and termination ii new surface water records from two high sedimentation rate sites located in the western subtropical north atlantic near the axis of the gulf stream provide clear evidence of suborbital climate variations through marine isotope stage mis 5 persisting even into the warm peak of the interglaciation substage 5e we found that the amplitude of suborbital climate oscillations did not vary significantly for the whole of mis 5 implying that ice volume has little or no influence on the amplitude of suborbital climate variability in this region although some records suggest that longer suborbital variations 4 10 kyr during mis 5 are linked to deepwater changes none of the existing records is of sufficient resolution to assess if a linkage occurred for oscillations shorter than 4 kyr however when examined in conjunction with published data from the norwegian sea new evidence from the subpolar north atlantic suggests that coupled surface deepwater oscillations occurred during the penultimate deglaciation this supports the hypothesis that during glacial and deglacial times ocean ice interactions and deepwater variability amplify suborbital climate change at higher latitudes we suggest that during the penultimate deglaciation the north atlantic deepwater source varied between nordic sea and open north atlantic locations in parallel with surface temperature oscillations

freshwater pulses in the eastern arctic ocean during saalian and early weichselian ice sheet collapse abstract improved multiparameter records from the northern barents sea margin show two prominent freshwater pulses into the arctic ocean during mis 5 that significantly disturbed the regional oceanic regime and probably affected global climate both pulses are associated with major iceberg rafted debris ird events revealing intensive iceberg sea ice melting the older meltwater pulse occurred near the mis 5 6 boundary 131 000 yr ago its 2000 year duration and high ird input accompanied by high illite content suggest a collapse of large scale saalian glaciation in the arctic ocean movement of this meltwater with the transpolar drift current into the fram strait probably promoted freshening of nordic seas surface water which may have increased sea ice formation and significantly reduced deep water formation a second pulse of freshwater occurred within mis 5a 77 000 yr ago its high smectite content and relatively short duration is possibly consistent with sudden discharge of early weichselian ice dammed lakes in northern siberia as suggested by terrestrial glacial geologic data the influence of this mis 5a meltwater pulse has been observed at a number of sites along the transpolar drift through fram strait and into the nordic seas it may well have been a trigger for the north atlantic cooling event c20

global ice volume fluctuations north atlantic ice rafting events and deep ocean circulation changes between 130 and 70 ka multiproxy data from north atlantic deep sea sediment core neap18k provide a detailed record of climate through oxygen isotope stage ois 5 seven distinct large scale episodes of ice rafting c25 c19 were identified between 126 and 70 ka global ice volume reconstructions based on high resolution benthic 18 o records indicate that major ice rafting events were not confined to ice volume maxima at ois 5d and 5b but also occurred during periods of ice sheet growth and disintegration however iceberg discharges were restricted to times when sea levels were 40 65 m below present values ice rafting episode c25 the first large scale cooling of mid atlantic surface waters after the last interglacial occurred during the gradual buildup of continental ice sheets at the ois 5e 5d transition major ice sheet collapses allied to ice rafting events c24 and c21 were associated with rapid sea level increases of 20 and 40 m respectively suborbital climatic fluctuations in the neap18k sedimentary record denoted by prominent 7 5 4 5 and 3 k y cyclicities appear to correlate with both greenland atmospheric temperatures and changes in thermohaline circulation patterns inferred from benthic 13 c values and hence provide clear evidence of a highly interconnected north atlantic climatic regime during ois 5

ocean ventilation and sedimentation since the glacial maximum at 3 km in the western north atlantic 1 stable isotope sedimentological and radiocarbon data from cores at 3 km water depth on the blake ridge western subtropical north atlantic reveal the history of deep water ventilation since the last glacial maximum lgm bulk sediment accumulation rates varied locally by a factor of 2 under the influence of bottom currents in this sediment drift environment but the sand flux mostly foraminifera was nearly identical at a given time this suggests that the rain rate of foraminifera mostly planktonic was constant that transport of foraminifera was negligible and that current controlled differences in clay and silt transport drive bulk accumulation in two of the cores flux peaks in the benthic foraminifera cibicidoides and uvigerina peregrina occurred during the younger dryas yd cold event and at 18 2 19 6 21 1 25 0 and 28 1 ka radiocarbon measurements on those benthic foraminifera show the ventilation age of bottom waters was 1000 years during the yd and for older events it was as great as 2000 years these results contrast with holocene ventilation which was 500 years and 700 years at 1500 years and 7100 years before present respectively

regional and global benthic δ18o stacks for the last glacial cycle although detailed age models exist for some marine sediment records of the last glacial cycle 0 150 ka age models for many cores rely on the stratigraphic correlation of benthic 18o which measures ice volume and deep ocean temperature change the large amount of data available for the last glacial cycle offers the opportunity to improve upon previous benthic 18o compilations such as the lr04 global stack not only are the age constraints for the lr04 stack now outdated but a single global alignment target neglects regional differences of several thousand years in the timing of benthic 18o change during glacial terminations here we present regional stacks that characterize mean benthic 18o change for 8 ocean regions and a volume weighted global stack of data from 263 cores age models for these stacks are based on radiocarbon data from 0 to 40 ka correlation to a layer counted greenland ice core from 40 to 56 ka and correlation to radiometrically dated speleothems from 56 to 150 ka the regional 18o stacks offer better stratigraphic alignment targets than the lr04 global stack and furthermore suggest that the lr04 stack is biased 1 2 kyr too young throughout the pleistocene finally we compare global and regional benthic 18o responses with sea level estimates for the last glacial cycle

a late eemian aridity pulse in central europe during the last glacial inception how do ice ages begin it s an obvious question to ask as we enjoy the relative luxury of an interglacial but a hard one to answer a look at past transitions may give some clues as to how this period will one day come to an end a climate reconstruction based on sediments found beneath a lake in the eifel mountains in germany provides evidence of an extreme climate event lasting 468 years right at the end of the last interglacial dust storms aridity bushfires and the loss of trees associated with a warm climate coincided with a southward shift of the warm waters of the north atlantic drift in terms of insolation the rate of delivery of the sun s radiation to earth conditions then were similar to those we have now investigating the processes that led to the end of the last interglacial period is relevant for understanding how our ongoing interglacial will end which has been a matter of much debate see for example refs 1 2 a recent ice core from greenland demonstrates climate cooling from 122 000 years ago3 driven by orbitally controlled insolation with glacial inception at 118 000 years ago4 5 6 7 8 here we present an annually resolved layer counted record of varve thickness quartz grain size and pollen assemblages from a maar lake in the eifel germany which documents a late eemian aridity pulse lasting 468 years with dust storms aridity bushfire and a decline of thermophilous trees at the time of glacial inception we interpret the decrease in both precipitation and temperature as an indication of a close link of this extreme climate event to a sudden southward shift of the position of the north atlantic drift the ocean current that brings warm surface waters to the northern european region the late eemian aridity pulse occurred at a 65 n july insolation of 416 w m 2 close to today s value of 428 w m 2 ref 9 and may therefore be relevant for the interpretation of present day climate variability

coherent deep flow variation in the iceland and american basins during the last interglacial the first direct evidence that the deepflow speed of north atlantic deep water nadw in the south iceland and north americanbasins declined dramatically over a period of a few hundred years at about 120 000 years ago is presented the flow rate inferred from silt grain size then rose into the subsequent cool period stage 5d these changes are clear and synchronous in records from both locations these circulation events are recorded less markedly in chemical and isotopic proxies for the nutrient status of water masses the congruence of flowvariation and hydrography at the two separated sites suggests they are primarily controlled by variation in the deep thermohaline circulation

initial mediterranean response to major climate reorganization during the last interglacial glacial transition abstract millennial scale dansgaard oeschger do variability at northern high latitudes has influenced climatic and environmental conditions in the mediterranean during the last glacial period there is evidence that the hemispheric transmission of the do variability occurred at the end of do event 25 however the exact timing and the trigger that activated the environmental response in the mediterranean remains incompletely understood here we provide evidence that the clear millennial scale teleconnection between greenland and the mediterranean started at 111 4 ka bp and was initiated by a sub millennial scale cooling in greenland gi 25b high resolution sediment proxies and the pollen record of lago grande di monticchio mon italy reflect climatic instability during the last millennium of the last interglacial which was characterised by a first and short cooling episode mon 1 at 111 44 0 69 ka bp coinciding with the greenland cold sub event gi 25b in duration and timing within dating uncertainties mon and greenland northgrip ice core also agree in recording a subsequent warm rebound phase that abruptly culminated in the stadial mon 2 gs 25 marking the transition into the last glacial period our results show that the gi 25b triggered an early environmental response at mon to centennial scale climate change in greenland as a prelude to the millennial scale teleconnection that was maintained during the glacial period

intermediate water links to deep western boundary current variability in the subtropical nw atlantic during marine isotope stages 5 and 4 records from ocean drilling program sites 1057 and 1059 2584 m and 2985 m water depth respectively have been used to reconstruct the behavior of the deep western boundary current dwbc on the blake outer ridge bor from 130 to 60 kyr b p marine isotope stage mis 5 and the 5 4 transition site 1057 lies within labrador sea water lsw but close to the present day boundary with lower north atlantic deep water lnadw while site 1059 lies within lnadw high resolution sortable silt mean inline equation grain size and benthic 13c records were obtained and changes in the dwbc intensity and spatial variability were inferred comparisons are made with similar proxy records generated for the holocene from equivalent depth cores on the bor during mis 5e inline equation evidence at site 1057 suggests slower relative flow speeds consistent with a weakening and a possible shoaling of the lsw sourced shallower limb of the dwbc that occupies these depths today in contrast the paleocurrent record from the deeper site suggests that the fast flowing deep core of the dwbc was located close to its modern depth below 3500 m during this interval the benthic 13c suggests little chemical stratification of the water column and the presence of a near uniform lnadw dominated water mass after 111 kyr b p the inline equation record at site 1057 increases to reach values similar to site 1059 for the rest of mis 5 the strengthening of flow speeds at the shallow site may correspond to the initiation of glacial north atlantic intermediate water formation also suggested by a divergence in the benthic 13c records with site 1057 values increasing to 1 2 coupled suborbital oscillations in dwbc flow variability and paleohydrography persisted throughout mis 5 comparison of these data with planktonic 18o records from the sites and alkenone derived sea surface temperature sst estimates from the nearby bermuda rise suggest a hitherto unrecognized degree of linkage between oscillations in subtropical north atlantic sst and dwbc flow

increasing vegetation and climate gradient in western europe over the last glacial inception 122 110 ka data model comparison high resolution terrestrial pollen and marine planktic and benthic isotopes coarse fraction and n pachyderma s analyses have been performed in the marine isotope stage mis 5 interval of images core md99 2331 retrieved in the northwestern iberian margin this study shows the occurrence of a zeifen interstadial stadial succession on land and in the ocean during the first part of mis 5e in northwestern iberia the eemian is marked from 126 to 122 ka by the development of deciduous quercus forest at the same time as mediterranean forest colonised southern iberia and deciduous quercus corylus forest occupied northernmost european regions from 121 to 115 ka carpinus betulus forest developed in nw iberia indicating a winter cooling by 2degreesc on land and an increase in annual precipitation by 100 200 min along with a sea surface temperature sst decreasing trend off iberia a similar cooling has been documented at the same time in northern germany 52degreesn by the replacement of deciduous forest by coniferous abies picea formations implying a southward displacement of the deciduous tree line between similar to60degreesn and 50degreesn as early as 120 ka the southward migration of the tree line between 72degreesn and 58degreesn simulated by the earth model of intermediate complexity mobidic from 122 and 120 ka and considered as a major process to initiate the last glaciation is therefore compatible with data between 115 and 110 ka the substantial ice accumulation in northern high latitudes mis 5e 5d transition was synchronous with successive drops c26 and c25 in northeastern atlantic sst in northwestern iberia abies pinus trees developed at the expense of quercus carpinus forest a tundra like environment occupied northern germany marking the end of the interglacial in northwestern europe at 115 ka and boreal forest likely colonised northeastern france the first displacement of the vegetation belts at 121 ka was enhanced at 115 ka indicating an amplification of the vegetation and climate gradients in northeastern atlantic and european borderlands probably related with the well developed ice caps at that time the comparison between the general trend in the estimated and simulated mobidic winter and summer temperatures for latitudes between 35 and 45degreesn shows that both follow quite straightforwardly the precession signal although the simulated and reconstructed temperatures agree better in the south than north of 40degreesn annual precipitation is exhibiting opposite trend in the data and in the model this contradiction is likely the fact that the zonal climate simulated by the model may not accurately represent the regional climate features as reconstructed from the pollen c 2004 elsevier b v all rights reserved

species composition and glacial interglacial variations in the ostracode fauna of the northeast atlantic during the past 200 000 years sediment core m23414 from the rockall plateau north atlantic covering the last two climatic cycles marine isotope stages mis 7 to 1 was investigated for glacial interglacial variations in the deep sea benthic ostracode fauna a highly diversified ostracode fauna including 98 species was found two climate related assemblages were identified associated with interglacial and peak glacial periods respectively the interglacial group occurs during the end of mis 7 5 and 1 and is composed of the genera henryhowella pelecocythere echinocythereis cytherella bradleya aversovalva and eucytherura the glacial group consists of the genera acetabulastoma which is known as sea ice indicator in the modern arctic ocean polycope bythoceratina rhombobythere and some species possibly belonging to the genus pseudocythere and is found during mis 6 4 and 2 these longer term variations within the ostracode fauna seem related to the particular glacial and interglacial climate conditions that affected both deep water production as well as primary production in the surface waters however a detailed comparison of ostracode abundances with the occurrence of events marked by increased ice rafted debris reveals also much shorter term climate related changes in the ostracode fauna thus the temporal fluctuations within ostracode assemblages reflect long and short term alterations of the deep sea environment that are clearly linked to climate changes

variations in terrigenous dilution in western mediterranean sea pelagic sediments in response to climate change during the last glacial cycle hemipelagic intervals in four giant calypso piston cores from the balearic abyssal plain western mediterranean sea were studied in order to determine fluctuations in the supply of terrigenous sediments to the basin during the last 130 000 years and possible climatic modulation of terrigenous sediment and particle flux carbonate records from hemipelagic intervals in these cores display distinct atlantic type cycles where glacial periods show on average 20 lower calcium carbonate contents than interglacial period equivalents the decrease in calcium carbonate seen during glacials may be the result of increased dilution by terrigenous aeolian and fluvial particles derived from aeolian and or fluvial sources higher glacial aeolian particle fluxes to the western mediterranean sea may have been caused by changes in the prevailing atmospheric conditions resulting in drier and colder climatic conditions in the source areas and more frequent and intense outbreaks of dust transport the colder and drier climatic conditions in combination with a lowered sea level would allow rivers to dump their sediment load closer to the shelf edge promoting enhanced fluvial input into the basin besides significant calcium carbonate variations that correlate with glacial interglacial cycles several short term abrupt changes in the calcium carbonate content are recorded which appear coincident with enhanced magnetic susceptibility values especially the events within marine isotope stage mis 3 the timing of these short term events may be linked with cooling events in the north atlantic particularly heinrich events and cold events within mis 5 these short term trends may possibly be explained by increased terrigenous particle transport due to drier and colder climate in the mediterranean borderlands our results further show that about 90 of the sedimentary sequence of the balearic abyssal plain consists of turbidites generally these appear not to have caused significant erosion and an almost complete continuous time stratigraphy is present in the intercalated hemipelagic intervals

evidence for northward expansion of antarctic bottom water mass in the southern ocean during the last glacial inception 1 we investigated deep water changes in the southern ocean during the last glacial inception in relationship to surface hydrology and global climatology to better understand the mechanisms of the establishment of a glacial ocean circulation changes in benthic foraminiferal 13c from three high resolution cores are compared and indicate decoupled intermediate and deep water changes in the southern ocean from the comparison with records from the north atlantic south atlantic and the southern ocean we show that the early southern deep water 13c drop observed at the mis 5 5 5 4 transition occurred before any significant reduction of north atlantic deep water ventilation we propose that this drop is linked to the northward expansion of poorly ventilated antarctic bottom water aabw mass in the southern ocean associated with an early cooling in the high southern latitudes the westerly winds and surface oceanic fronts would migrate equatorward thus weakening the upwelling of circumpolar deep waters reduced heat brought to antarctic surface waters would enhance sea ice formation during winters and the deep convection of cold and poorly ventilated aabw

cryptotephrochronology of the eemian and the last interglacial glacial transition in the north east atlantic the eemian interglacial and the onset of the subsequent glacial period serve as the most recent analogue for the natural operation of the climate system during the current interglacial pronounced climatic oscillations occurred during this period but their nature and pattern are poorly understood due to dating limitations and unknown phase relationships between different regions and archives tephrochronology offers considerable potential for precise correlation of disparate palaeoclimatic archives preserving evidence of these rapid climatic transitions through the tracing of common isochronous tephra horizons we outline the identification of three previously unknown cryptotephra horizons within a marine core from the rockall trough north east atlantic this sequence preserves a high resolution record of this interval and shard size geochemical heterogeneity and the co variance of shard concentrations with ice rafted debris data are utilized to demonstrate that primary airfall was the most likely transport and depositional pathway the main geochemical populations of these horizons have similar transitional alkali major and trace element compositions suggesting that they were derived from a common icelandic source potentially the oraefajokull volcanic system these tephra horizons represent additions to the north atlantic event stratigraphy for this period and tentative correlations to icelandic terrestrial deposits are proposed for two horizons

the impact of precession changes on the arctic climate during the last interglacial glacial transition three sensitivity experiments using an ocean atmosphere general circulation model oagcm are conducted to simulate the climate impact of precession the relative contributions of components of the hydrological cycle including the albedo of arctic sea ice advection of atmospheric water vapor and sea surface temperature to the summer arctic melt process are evaluated timing of the perihelion is varied in each experiment with meteorological spring sp winter wp and autumn ap perihelion corresponding to conditions at 110 115 and 120 ky bp respectively obliquity is unchanged at the 115 ky level which is lower than today the experiments are assessed relative to the present day control which has been shown to simulate current conditions based on observations in the sp experiment top of the atmosphere toa insolation is weaker than today between the summer solstice and autumnal equinox in the ap case representing the interglacial it is less intense between vernal equinox and summer solstice but stronger during the remainder of the year although the incident solar radiation is reduced in summer in the sp experiment increased melting of snow is found primarily as a result of feedbacks from the delayed seasonal cycle of hydrologic components this is in contrast to both the wp and ap cases in which the perennial snow cover is simulated at the time of the last glacial inception 115 ky bp the wp experiment shows lower insolation to the high northern latitudes in late spring and summer mainly as a result of lower obliquity than today dynamical ocean atmosphere interactions in response to precession maintain the reduced sea ice melting in late spring strengthen the annual equator to pole sea surface temperature sst gradient and increase atmospheric moisture convergence in glaciation sensitive regions in both the wp and

temperature and productivity changes off the western iberian margin during the last 150 ky abstract present day hydrographic conditions along the western iberian margin are characterized by seasonal upwelling with filaments that can penetrate more than 200 km into the open ocean and constitute areas of cold and highly productive waters in order to investigate spatial and temporal gradients in temperature and productivity conditions during the last 150 ky high resolution proxy records were generated in 3 cores su92 03 md95 2040 md95 2042 located along the iberian coast between 43 12 n and 37 48 n and forming a n s profile in all cores planktonic foraminifera census counts are used to reconstruct summer sea surface temperature sstsu and export productivity pexpsu using the modern analog technique simmax 28 sstsu and pexpsu values similar to the present are observed throughout the holocene and mis 5e periods for each site respectively indicating fairly stable conditions equivalent to the modern ones on glacial interglacial timescales sstsu increases by 2 3 c from the northern to southernmost site pexpsu on the other hand shows a decrease of 30 40 gc m2 yr from north to south at present time and during interglacial periods and no significant variation 90 100 gc m2 yr during glacial periods the northernmost core su92 03 reveals the coldest conditions with records more similar to md95 2040 than to md95 2042 the later of which is as at present more affected by subtropical waters core su92 03 shows higher interglacial productivity similar to open ocean mid to high latitude sites while the other two cores monitor higher glacial productivity conform with other upwelling sites off nw africa a boundary between differences in glacial interglacial productivity appears to be present in our study between 43 12 n and 40 35 n especially north of 40 n coldest sstsu and lowest pexpsu are found during heinrich events h 1 h8 and h10 h11 in contrast lowest pexpsu do not coincide with these events at site md95 2042 but appear to be related to the presence of relatively warm and nutrient poor subtropical eastern north atlantic central water advected with the azores current

orbital signatures and long term vegetation patterns in the mediterranean abstract an attempt is made to explore the relation between vegetation phases and orbital configurations by comparing long pollen sequences from the mediterranean region and astronomical curves on the basis of their independent chronologies three recurring patterns emerge from this comparison i all intervals with perihelion passage occurring during northern winter were associated with significant contractions of tree populations ii all temperate stage expansions of certain mediterranean vegetation elements occurred when perihelion passage was in summer and iii temperate stage forests reached maximum extent at times of autumn perihelion of these patterns the first corresponds to extreme dry cold episodes culminating at times of march perihelion and the second to maximum summer temperature and evaporation regimes following june perihelion the third associated with the occurrence of september perihelion appears to be more diffuse both in time and space possibly reflecting local variations in hydrological regimes the consistency of at least the first two cases provides some support for the notion that certain recurring vegetation patterns appear to be a result of climate changes linked to specific orbital signatures this could eventually lead to the development of improved terrestrial chronologies through astronomical tuning

consistently dated records from the greenland grip gisp2 and ngrip ice cores for the past 104 ka reveal regional millennial scale δ18o gradients with possible heinrich event imprint abstract we present a synchronization of the ngrip grip and gisp2 ice cores onto a master chronology extending back to 104 ka before present providing a consistent chronological framework for these three greenland records the synchronization aligns distinct peaks in volcanic proxy records and other impurity records chemo stratigraphic matching and assumes that these layers of elevated impurity content represent the same instantaneous event in the past at all three sites more than 900 marker horizons between the three cores have been identified and our matching is independently confirmed by 24 new and previously identified volcanic ash tephra tie points using the reference horizons we transfer the widely used greenland ice core chronology gicc05modelext to the two summit cores grip and gisp2 furthermore we provide gas chronologies for the summit cores that are consistent with the gicc05modelext timescale by utilizing both existing and new gas data ch4 concentration and 15n of n2 we infer that the accumulation contrast between the stadial and interstadial phases of the glacial period was 10 greater at summit compared to at ngrip the 18o temperature proxy records from ngrip grip and gisp2 are generally very similar and display synchronous behaviour at climate transitions the 18o differences between summit and ngrip however changed slowly over the last glacial interglacial cycle and also underwent abrupt millennial to centennial scale variations we suggest that this observed latitudinal 18o gradient in greenland during the glacial period is the result of 1 relatively higher degree of precipitation with a pacific signature at ngrip 2 increased summer bias in precipitation at summit and 3 enhanced rayleigh distillation due to an increased source to site distance and a potentially larger source to site temperature gradient we propose that these processes are governed by changes in the north american ice sheet nais volume and north atlantic sea ice extent and or sea surface temperatures sst on orbital timescales and that changing sea ice extent and ssts are the driving mechanisms on shorter timescales finally we observe that maxima in the summit ngrip 18o difference are roughly coincident with prominent heinrich events this suggests that the climatic reorganization that takes place during stadials with heinrich events possibly driven by a southward expansion of sea ice and low ssts in the north atlantic are recorded in the ice core records

formal subdivision of the quaternary system period present status and future directions abstract the quaternary system period and pleistocene series epoch were defined in 2009 by the global boundary stratotype section and point gssp for the gelasian stage age 2 58 ma which aligns with marine isotope stage mis 103 and approximates the gauss matuyama chron boundary contrary to earlier reports the vrica gssp 1 80 ma was repurposed in 2011 to define the calabrian stage effectively completing the lower pleistocene subseries subepoch the candidate for the middle pleistocene subseries and proposed chibanian stage gssp 774 ka is the chiba section japan it aligns with mis 19 and approximates the matuyama brunhes chron boundary 773 ka the upper pleistocene subseries with a base traditionally marked by the onset of the last interglacial is not yet defined by gssp the holocene series epoch was formally defined in 2008 by a gssp in the ngrip2 greenland ice core with an age of 11 700 yr b2k before 2000 ce and in 2018 was subdivided using climatic events at 8 2 and 4 2 ka into the greenlandian northgrippian and meghalayan stages ages and their corresponding lower early middle upper late subseries subepochs the northgrippian gssp 8236 yr b2k is defined in the ngrip1 greenland ice core and the meghalayan gssp 4250 yr b2k in a speleothem from meghalaya india this subdivision formally introduces the rank of subseries subepoch and incorporates by far the briefest of all stages into the geological time scale using ice cores and a speleothem for gssps is unique to the holocene the presently undefined term anthropocene is already used extensively and like holocene subdivisional terms its functionality will be enhanced by formal definition the anthropocene should not be confused with anthropogenic it reflects a tipping point in the earth system response to the marked intensification of human impacts not simply the fact of human impact the geological anthropocene as currently envisioned would start in the mid twentieth century holding the rank of series and terminating the holocene but not interfering with its subdivision other than to terminate the meghalayan stage

sediment color record from the northeast atlantic reveals patterns of millennial scale climate variability during the past 500 000 years a 500 000 yr long deep sea sediment color record from the northeast atlantic was investigated to reconstruct the evolution of late pleistocene climate variability on millennial time scales variations of the red green color intensity are probably caused by climatically induced changes in the ice rafted input of red colored iron bearing terrigenous material to the core site the resolution of the age model impedes the detection of distinct spectral features at sub milankovitch periodicities hence millennial scale climate variability is quantified as time dependent variance of the high pass filtered color time series the course of the estimated variance shows distinct patterns which can be linked to continental ice mass during the past 500 000 yr large amplitude millennial scale climate variability occurs only if continental ice mass exceeds a threshold level equivalent to sea level at approximately 40 of the lowering during the last glacial maximum

climatic variability during the last interglacial inferred from geochemical proxies in the lake el gygytgyn sediment record the last interglacial period lip is often regarded as a good analogue for potential climatic conditions under predicted global warming scenarios despite this there is still debate over the nature duration and frequency of climatic changes during this period one particularly contentious issue has been the apparent evidence of climatic instability identified in many marine cores but seemingly lacking from many terrestrial archives especially within the arctic a key region for global climate change research in this paper geochemical records from lake el gygytgyn north eastern russia are used to infer past climatic changes during the lip from within the high arctic with a sampling resolution of 20 90 years these records offer the potential for detailed high resolution palaeoclimate reconstruction this study shows that the lip commenced in central chukotka 129 thousand years ago ka with the warmest climatic conditions occurring between 128 and 127 ka before being interrupted by a short lived cold reversal mild climatic conditions then persisted until 122 ka when a marked reduction in the sedimentation rate suggests a decrease in precipitation a further climatic deterioration at 118 ka marks the return to glacial conditions this study highlights the value of incorporating several geochemical proxies when inferring past climatic conditions thus providing the potential to identify signals related to environmental change within the catchment we also demonstrate the importance of considering how changes in sedimentation rate influence proxy records in order to develop robust palaeoenvironmental reconstructions

contrasting ocean changes between the subpolar and polar north atlantic during the past 135 ka variations in the poleward directed atlantic heat transfer was investigated over the past 135 ka with special emphasis on the last and present interglacial climate development eemian and holocene both interglacials exhibited very similar climatic oscillations during each preceding glacial terminations deglacial ti and tii like ti also tii has pronounced cold warm cold changes akin to events such as h1 bolling allerod and the younger dryas but unlike ti the cold events in tii were associated with intermittent southerly invasions of an atlantic faunal component which underscores quite a different water mass evolution in the nordic seas within the eemian interglaciation proper peak warming intervals were antiphased between the nordic seas and north atlantic moreover inferred temperatures for the nordic seas were generally colder in the eemian than in the holocene and vice versa for the north atlantic a reduced intensity of atlantic ocean heat transfer to the arctic therefore characterized the eemian requiring a reassessment of the actual role of the ocean atmosphere system behind interglacial but also glacial climate changes key points reduced amoc during the eemian ba yd type warming cooling in termination 1 and 2 comparison of glacial inceptions reveals present climate status

late quaternary lacustrine deposits of the dead sea basin high resolution sequence stratigraphy from downhole logging data abstract sequence architecture and depositional sequences of the quaternary lacustrine succession deposited in the northern dead sea sub basin were examined using logging data collected during the 2010 2011 icdp campaign methods borrowed from sequence stratigraphy techniques were used to investigate the characteristics of sediments deposited in the central part of the northern lake high resolution wire logging data combined with a detailed lithological description of the icdp 5017 1 a deep borehole were used to examine depositional systems and related processes controlling their formation analysis of sedimentary stacking patterns and stratal surfaces within the late pleistocene holocene lacustrine succession revealed 10 depositional sequences it was possible to identify key stratal boundaries and to discern between three sedimentary stacking patterns interpreted here as representing lowstand systems tracts lst transgressive systems tracts tst and highstand systems tracts hst examined together they may be interpreted in terms of relative lake level changes on the basis of the stratigraphic analysis complemented with new age dating this article presents a record of the sediment accumulation pattern and a relative lake level curve reconstructed for the last ca 225 ka results show that stratigraphic units and depositional and erosional surfaces examined in the deep 5017 1 a borehole can be correlated to the proximal area of the basin this means that changes in relative lake levels were generally synchronous and uniform across the dead sea basin the creation of accommodation space in the northern dead sea was found to generally be in phase with paleoclimatic modulating lake levels and not due to tectonics

interglacial variability mis 5 and mis 7 and dinoflagellate cyst assemblages in the bay of biscay north atlantic the interglacial periods of the late quaternary are frequently investigated as they constitute potential analogues for our modem climate and may shed light on the key questions of natural climate variability and future developments the aim of this work is to reconstruct the paleoenvironmental history of marine isotope stages mis 5 and 7 in deep sea sediments of the northern bay of biscay north east atlantic ocean on the basis of a multiproxy compilation including analysis of dinoflagellate cyst assemblages we discuss the nature of the paleoenvironmental and paleoclimate changes that took place in this region recurrent successions of species marking the beginning and the termination of the interglacial complexes mis 5 and mis 7 revealed a coherent scheme of water mass migration during these key transitional periods moreover our data extend knowledge about the ecology of several dinoflagellate taxa in particular we discuss the ecology of spiniferites septentrionalis and note that this species can be used as a biostratigraphical tracer in north atlantic quaternary sediments until a major event of iceberg calving occurred during mis 6 dated to around 150 ka bp the dinocyst spinferites mirabilis appears to be an important proxy for recognizing warm intervals within interglacial complexes during mis 5e the last interglacial this species is represented by the highest percentages ever recorded in sediments from the north atlantic region peak occurrence of this species during mis 7 indicates that substage mis 7c the second warm interval of the penultimate interglacial represents the climatic optimum during the mis 7 interglacial complex

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

quaternary depositional patterns and sea level fluctuations northeastern north carolina abstract a detailed record of late quaternary sea level oscillations is preserved within the upper 45 m of deposits along an eight km transect across croatan sound a drowned tributary of the roanoke albemarle drainage system northeastern north carolina drill hole and seismic data reveal nine relatively complete sequences filling an antecedent valley comprised of discontinuous middle and early pleistocene deposits on interfluves lithologically similar marine deposits of different sequences occur stacked in vertical succession and separated by ravinement surfaces within the paleo drainage marine deposits are separated by fluvial and or estuarine sediments deposited during periods of lowered sea level foraminiferal and molluscan fossil assemblages indicate that marine facies were deposited in a shallow marine embayment with open connection to shelf waters each sequence modifies or truncates portions of the preceding sequence or sequences sequence boundaries are the product of a combination of fluvial estuarine and marine erosional processes stratigraphic and age analyses constrain the ages of sequences to late marine isotope stage mis 6 and younger 140 ka to present indicating multiple sea level oscillations during this interval elevations of highstand deposits associated with late mis 5 and mis 3 imply that sea level was either similar to present during those times or that the region may have been influenced by glacio isostatic uplift and subsidence

millennial scale climatic oscillations during the last interglaciation in central china repeated southward excursions of north atlantic polar water during the last interglaciation 18 o stage 5 130 74 ka are recorded by planktonic foraminifera and ice rafted detritus in north atlantic sediment cores and greenland ice sheet cores display quasi synchronous fluctuations comparable high frequency variations in the east asian winter monsoon climate are discernible in three loess paleosol profiles in central china that span the last interglaciation peak values of the 40 m quartz fraction and bulk sediment samples from the s1 last interglacial accretionary paleosol complex reflect major dust flux events when winter monsoon winds strengthened frequent oscillations of the dust flux and nine significant dust events are recorded six events falling between ca 110 and 70 ka are correlated with cold peaks c19 24 identified in north atlantic cores two comparable dust peaks occur within paleosol s1ss3 substage 5e the older of these dating to ca 121 ka may correlate with a brief cold event recently recognized in high resolution marine and terrestrial climate proxy records

the last climatic cycle at la grande pile vosges france a new pollen profile a new pollen diagram has been made from an old unanalyzed core from la grande pile gp xx correlations with the previous work of woillard 1975 1978 leads to the following conclusions the end of the eemian was marked by a minor climatic change prior to the melisey i stadial the ognon ii and ognon iii interstadials are not consistent and correspond to the level of reworking of mesophilous taxa during the last pleniglacial the limitations of the botanical interpretation of pollen spectra from the last pleniglacial are underlined lastly bruckenthalia and larix are identified for the first time at la grande pile the respective roles of these taxa following the eemian are additional arguments for correlating the st germain i and ii with the early weichsel interstadials in the north of middle europe

what level of resolution is attainable in a deep sea core results of a spectrophotometer study a minolta cm 2022 spectrophotometer has been used to characterize downcore fluctuations in sediment lightness and color in core neap15k a 7 m core collected from the northeast atlantic ocean high resolution data series measured using a 4 mm diameter measurement spot and a 1 cm sampling interval were generated along two independent tracks down the core to investigate the statistical significance of fluctuations across the 2 20 cm depth range this small scale variability is characterized by abrupt changes in the lightness and color of the sediment that are several orders of magnitude greater than the instrumental precision our results establish that significant information is preserved at the 1 cm scale in spite of bioturbation effects these findings demonstrate that high resolution studies using conventional paleoclimatic proxies have the potential to recover meaningful century scale climate records in regions of the ocean where sedimentation rates exceed 10 cm per thousand years the coherency of these downcore records also implies that the spectrophotometer is a powerful instrument for establishing precise centimeter scale stratigraphic correlations between cores

the role of the deep ocean in north atlantic climate change between 70 and 130 kyr ago the suggestion1 that changes in north atlantic deep water nadw production are linked through surface heat flux to the atmospheric temperature over greenland is supported by earlier indications2 3 that nadw production decreased during glacial times and by the subsequent finding4 6 that it declined during the younger dryas cool period at the end of the last glaciation changes in north atlantic surface temperatures have been found7 to mirror high frequency temperature changes recorded in greenland ice cores over the past 80 kyr but the connection to abyssal circulation has yet to be established except for one or two isolated oscillations8 9 here we present carbon and oxygen isotope analyses of benthic foraminifera in a high resolution north atlantic deep sea sediment core for the period 70 130 kyr ago these data allow us to reconstruct the history of nadw production which shows a close correlation with greenland climate variability for much of this time interval suggesting that the climate influence of nadw variability was widespread we see no evidence however for changes in nadw production during substage 5e the eemian interglacial period in contrast with recent ice core data10 which suggest severe climate instability in greenland during this time period our results may support suggestions based on data from a second ice core that this apparent instability is an artefact caused by ice flow11 alternatively the eemian climate instability may have had a different origin from the subsequent climate events

precession phasing offset between indian summer monsoon and arabian sea productivity linked to changes in atlantic overturning circulation results from transient climate modeling experiments indicate an in phase relationship between insolation forcing and indian summer monsoonal precipitation this is in contrast to high resolution radioisotopically dated speleothem oxygen isotope 18o records of china which showed that east asian monsoon maxima lag northern hemisphere peak summer insolation by 2 700 years while an approximately 8 000 year time lag was derived from late pleistocene records of arabian sea sediments here we evaluate the precession phase of the arabian sea signal by comparing a new high resolution productivity and oxygen minimum zone omz intensity record from the arabian sea over the past 450 000 years with the results of a transient climate modeling experiment that includes glacial bound ice volume variations the well established tuning technique between radioisotopically dated north atlantic cold events and the occurrence of deep dwelling planktonic foraminifera in the arabian sea for the last glacial cycle was used to extend the arabian sea chronology independent of orbital tuning cross spectral analysis over the last 224 000 years reveals that arabian sea productivity maxima lag precession minima by 6 900 200 years i e in close agreement with previous reconstructions also our climate modeling simulations are in accord with previous studies indicating an in phase relationship between precession minima and maximum summer monsoon intensity we argue that the summer monsoon is most likely not the main driver of changes in arabian sea biological productivity and omz intensity at the precession frequency band but that changes in the intensity of the atlantic meridional overturning circulation amoc have played the prominent role in controlling the nutrient delivery into the euphotic layer of the northern indian ocean and hence the amount of primary productivity and intensity of the oxygen minimum zone in the arabian sea such a mechanism explains the large precession related time lag between minimum precession and maximum productivity and omz conditions in the arabian sea since intensified amoc occurred during precession maxima

north atlantic millennial scale climate variability 910 to 790 ka and the role of the equatorial insolation forcing abstract the mid pleistocene transition mpt was the time when quasi periodic 100 kyr high amplitude glacial variability developed in the absence of any significant change in the character of orbital forcing leading to the establishment of the characteristic pattern of late pleistocene climate variability it has long been known that the interval around 900 ka stands out as a critical point of the mpt when major glaciations started occurring most notably in the northern hemisphere here we examine the record of climatic conditions during this significant interval using high resolution stable isotope records from benthic and planktonic foraminifera from a sediment core in the north atlantic integrated ocean drilling program expedition 306 site u1313 we have considered the time interval from late in marine isotope stage mis 23 to mis 20 910 to 790 ka our data indicate that interglacial mis 21 was a climatically unstable period and was broken into four interstadial periods which have been identified and correlated across the north atlantic region these extra peaks tend to contradict previous studies that interpreted the mis 21 variability as consisting essentially of a linear response to cyclical changes in orbital parameters cooling events in the surface record during mis 21 were associated with low benthic carbon isotope excursions suggesting a coupling between surface temperature changes and the strength of the atlantic meridional overturning circulation time series analysis performed on the whole interval indicates that benthic and planktonic oxygen isotopes have significant concentrations of spectral power centered on periods of 10 7 kyr and 6 kyr which is in agreement with the second and forth harmonic of precession the excellent correspondence between the foraminifera 18 o records and insolation variations at the equator in march and september suggests that a mechanism related to low latitude precession variations advected to the high latitudes by tropical convective processes might have generated such a response this scenario accounts for the presence of oscillations at frequencies equal to precession harmonics at site u1313 as well as the occurrence of higher amplitude oscillations between the mis22 21 transition and most of mis 21 times of enhanced insolation variability

orbital and suborbital climate variability in the sulu sea western tropical pacific 1 a detailed record of planktic 18o from a sediment core in the sulu sea located between the south china sea and the western pacific warm pool reveals that for the past 400 kyr 1 kyr 1000 years 18o variability on orbital timescales is similar to that caused by changes in ice volume alone this result indicates that in the sulu sea temperature driven changes in planktic 18o on orbital times scales were generally compensated for by the effects of sea level and changes in seasonal monsoon intensity on the local freshwater budget as well as by other changes in the tropical hydrologic cycle and their attendant effects on surface water 18o increased freshening of the western tropical pacific warm pool is reminiscent of la nina conditions however we argue that the mean tropical climate state was not more la nina like than today on broader spatial scales suborbital variability occurred in the sulu sea throughout the past 400 kyr suggesting little sensitivity to ice volume or to glacial interglacial changes in tropical hydrology variations on 4 10 kyr timescales appear to be linked to those in the north atlantic region suggesting a common forcing of that variability we suggest that sulu sea salinity variations were a response to suborbital climate variability in the north atlantic region transmitted via changes in the intensity of the east asian summer monsoon we suggest that a north atlantic origin of that tropical suborbital variability can be reconciled with weak glacial amplification in the tropics if the tropical response is nonlinear

millennial scale oceanic climate variability off the western iberian margin during the last two glacial periods high resolution palaeoclimate records recovered from the iberian margin in core md95 2040 exhibit large fluctuations in oceanographic conditions over the last 190 ka large scale cooling of the surface ocean is indicated by the presence of the polar planktonic foraminifer neogloboquadrina pachyderma sinistral and in some instances the occurrence of ice rafted debris ird ice rafting episodes were prevalent in both of the last two glacials with greater intensity in stages 2 through 4 than in stage 6 the six youngest heinrich events are well defined during the last glacial but detrital carbonate is absent from heinrich layers hl6 hl5 and hl3 dansgaard oeschger stadial equivalent sub millennial ird deposition events have been detected in particular during stage 3 allowing a good match with the cooling displayed in the greenland ice core gisp2 sea surface temperature off portugal in stage 6 was in general warmer than during the last glacial pointing towards a weaker southward influence of polar water masses ice rafting occurred mainly in mid mis marine isotope stage 6 between 173 and 153 kyr as a group of poorly differentiated short duration quasi continuous events mainly marked by the high abundance of sinistral n pachyderma differences exist in ird composition relative to the last glacial with a reduced canadian derived detrital carbonate component combined with an important contribution of volcanic particles the lower magnitude and higher frequency of these events suggest that the higher temperatures would have induced iceberg waning closer to the source areas

the production of north atlantic deep water sources rates and pathways updating an earlier account by dickson et al 1990 this paper reviews the initial development phase of north atlantic deep water nadw production from the points where the dense inflows from nordic seas cross the greenland scotland ridge to the point off south greenland where the buildup of new production appears almost complete in particular three long term current meter arrays totaling 91 instruments and set at 160 km intervals south from the denmark strait sill are used to validate earlier short term arrays by others and in combination with these earlier arrays to describe the downstream evolution of mean speed depth and entrainment the variability of the overflow current in space and time and the likely contribution of the other three main constituents of nadw production at densities greater than 27 8 from the points of overflow 5 6 sv the transport within this range increases by entrainment and confluence with other contributory streams to around 13 3 sv at cape farewell while recirculating elements prevent us from determining the net southgoing transport a nadw transport of this order appears consistent with recent estimates of net abyssal flow passing south through the north and south atlantic

evolution of millennial scale climate variability during the mid pleistocene 1 we use the oxygen isotopic composition of planktonic foraminifera globigerinoides ruber white from ocean drilling program site 1058 in the subtropical northwestern atlantic to construct a high resolution 800 year climate record spanning the mid pleistocene climate transition 410 ka to 1350 ka we investigate whether or not millennial scale instabilities in the proxy record are associated with the extent of continental glaciation g ruber 18o values display high frequency fluctuations throughout the record but the amplitude about mean glacial and interglacial 18o values increases at marine isotope stage mis 22 880 ka and is highest during mis 12 these observations support that millennial scale climate instabilities are associated with ice sheet size time series analysis illustrates that these variations have significant concentration of spectral power centered on periods of 10 12 ka and 5 ka the timing of these fluctuations agrees well or coincides with the periodicities of the second and fourth harmonics respectively of precessional forcing at the equator an insolation based origin of the millennial scale instabilities would be independent of ice volume and explains the presence of these fluctuations before the mid pleistocene climate transition as well as during interglacial intervals e g mis 37 and 17 because the amplitude of the millennial scale variations increases during the mid pleistocene transition feedback mechanisms associated with the growth of large 100 ka paced polar ice sheets may be important amplifiers of regional surface water hydrographic changes

millennial and centennial scale vegetation and climate changes during the late pleistocene and holocene from northern new mexico usa abstract high resolution pollen and magnetic susceptibility ms data from a sediment core from an alpine bog 3100 m in the sangre de cristo mountains new mexico record variations in treeline elevation and in sedimentation for the last 14 ka cal yr bp strong correspondence between the paleovegetation and the ms profile suggests that both records can be used to reconstruct past climatic conditions the coldest conditions in this area occurred at the end of the late pleistocene during the pinedale glaciation and the younger dryas chron a general warming trend took place during the early holocene lasting until 5 6 ka when the warmest conditions occurred a progressive climate cooling is then observed until today millennial and centennial scale changes are also observed throughout the vegetation and ms records the higher amplitude millennial scale cold events appear to correlate with the timing and duration of episodes of enhanced sea ice drift in the north atlantic and the lower amplitude centennial scale cold events may correlate with periods of lower solar activity a solar climate connection is suggested from these records by a prominent ca 200 yr cycle in tree pollen abundance which may correlate with the 208 yr suess solar cycle this study shows an immediate response of the vegetation treeline to climate change at millennial and centennial scales probably related to variations in summer insolation and solar activity during the late pleistocene and holocene such high resolution studies are very important in order to predict future climate change and particularly in very arid areas where human activity and economies are strongly influenced by climate

reconciliation of late quaternary sea levels derived from coral terraces at huon peninsula with deep sea oxygen isotope records a major discrepancy between the late quaternary sea level changes derived from raised coral reef terraces at the huon peninsula in papua new guinea and from oxygen isotopes in deep sea cores is resolved the two methods agree closely from 120 ka to 80 ka and from 20 ka to 0 ka ka 1000 yr before present but between 70 and 30 ka the isotopic sea levels are 20 40 m lower than the huon peninsula sea levels derived in earlier studies new high precision u series age measurements and revised stratigraphic data for huon peninsula terraces aged between 30 and 70 ka now give similar sea levels to those based on deep sea oxygen isotope data planktonic and benthic 18o data using the sea level and deep sea isotopic data oxygen isotope ratios are calculated for the northern continental ice sheets through the last glacial cycle and are consistent with results from greenland ice cores the record of ice volume changes through the last glacial cycle now appears to be reasonably complete