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

climate instability during the last interglacial period recorded in the grip ice core isotope and chemical analyses of the grip ice core from summit central greenland reveal that climate in greenland during the last interglacial period was characterized by a series of severe cold periods which began extremely rapidly and lasted from decades to centuries as the last interglacial seems to have been slightly warmer than the present one its unstable climate raises questions about the effects of future global warming

origin of the northern atlantic s heinrich events as first noted by heinrich 1988 glacial age sediments in the eastern part of the northern atlantic contain layers with unusually high ratios of ice rafted lithic fragments to foraminifera shells he estimated that these layers are spaced at intervals of roughly 10 000 years in this paper we present detailed information documenting the existence of the upper five of these layers in odp core 609 from 50 n and 24 w their ages are respectively 15 000 radiocarbon years 20 000 radiocarbon years 27 000 radiocarbon years about 40 000 years and about 50 000 years we also note that the high lithic fragment to foram ratio is the result of a near absence of shells in these layers although we are not of one mind regarding the origin of these layers we lean toward an explanation that the heinrich layers are debris released during the melting of massive influxes of icebergs into the northern atlantic these sudden inputs may be the result of surges along the eastern margin of the laurentide ice sheet

chronological discord between the last interglacial paleosol s1 and its parent material in the chinese loess plateau abstract an and porter geology 25 1997 603 reported six high dust influx events of millennial timescales recovered from the last interglacial paleosol s1 and correlated them to six cool events of millennial timescale in the north atlantic however the complexity of soil forming processes may have made the chronological correlation with the north atlantic records inadequate to examine the complexity of the s1 formation the s1 paleosol was traced laterally and identified based on the preserved characteristics observed in the field and analyzed in the laboratory our data show that from the northwest to the southeast the s1 paleosol gradually converges from three distinctive soil profiles into a single welded profile because the net rate of loess accumulation was attenuated to the southeast and pedogenic development intensified southeastward during the last interglacial three soil forming events within the s1 paleosol s1s1 s1s2 and s1s3 separated by two loess units s1l1 and s1l2 in the northwestern part of the loess plateau are stratigraphically coeval with a single soil profile in the southeastern margin of the loess plateau in the southeast the s1 paleosol developed into underlying older loess l2 e g at the lantian section the three paleosols s1s1 s1s2 and s1s3 are partially welded in the central part of the chinese loess plateau e g at the tianshui section where the lower portion of s1 paleosol developed in the underlying older loess unit l2 in the northwestern margin of the chinese loess plateau e g at the lanzhou section the preservation of the repeating soil loess sequence s1s1 s1l1 s1s2 s1l2 and s1s3 continuously documented the climatic events of the last interglacial our data also show that the magnetic signatures and particle size information are more or less acceptable climatic proxies only for the northwestern sections where the degree of pedogenesis was lower and the rate of eolian influx was greater during the last interglacial it appears that in all cases investigated the median grain size and the coarse fraction 63 m content define the upper and lower boundaries of the s1 paleosol reasonably well and can be used to estimate the time transgressive nature of the s1 paleosol relative to its parent material soil welding bioturbation and material translocation within the s1 soil profiles make it impossible to preserve the detailed and high resolution information of climate changes in those s1 profiles in the southeastern part including the popularly called central part of the chinese loess plateau

synchronous high frequency oscillations in tropical sea surface temperatures and north atlantic deep water production during the last glacial cycle stable isotopic measurements of g sacculifer and c wuellerstorfi in a core from the western equatorial atlantic imply that there are parallel suborbital oscillations in surface water hydrography and deep water circulation occurring during oxygen isotope stages 2 and 3 low values of g sacculifer 18o accompany high values of c wuellerstorfi 13c linking warmer sea surface temperatures ssts in the tropics with increased production of lower north atlantic deep water nadw the amplitude of the 18o oscillations is 0 6 or 2 3 c which is superimposed on a glacial interglacial amplitude of about 2 1 using the g sacculifer 18o data we calculate that surface waters were colder during stage 2 than calculated by climap 1976 1981 the longer period 2 kyr oscillations in air temperature recorded in the greenland and antarctic ice cores appear to correlate with oscillations in sea surface temperature in the equatorial atlantic the magnitude of these oscillations in tropical sst is too large to have resulted from changes in meridional heat transport caused by the global conveyor alone the apparent synchroneity of equatorial sst and polar air temperature changes as well as the amplitude of the sst changes at the equator are consistent with the climate effects expected from changes in the atmosphere s greenhouse gas content h2ovapor co2 and ch4

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

glacial millennial scale fluctuations in central african precipitation recorded in terrigenous sediment supply and freshwater signals offshore cameroon abstract evidence of rapid climatic oscillations like those observed in the greenland ice cores and sediments from high latitudes of the northern atlantic have been recognized in the pulses of terrigenous material to continental margin sediments off cameroon fe ca ratios used as a parameter to quantify the relative proportions of terrigenous fluxes versus marine carbonate monitor the variability of the west african monsoon they reveal the history of abrupt changes in precipitation over western and central africa during the past 52 kyr these rapid changes are particularly pronounced during the last glacial period and occur at timescales of a few thousand years stable oxygen isotope 18o records of globigerinoides ruber pink show high negative values reflecting periods of high monsoon precipitation the fe ca pattern is very similar to the dansgaard oeschger cycles from the greenland ice cores the good correspondence between the warm interstadials of the dansgaard oeschger cycles from the gisp2 ice core records and the high pulses of fe ca sedimentation in our core suggest a strong teleconnection between the low latitude african climate and the high latitude northern hemisphere climate oscillations during the last glacial this climatic link is probably vested in the west african monsoonal fluctuation that alters tropical sea surface temperatures thermohaline circulations and in turn net export of heat from the south to the north atlantic coupled with the variability of the low latitude southeast trade winds

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

electrical conductivity measurements from the gisp2 and grip greenland ice cores the direct current electrical conductivity of glacial ice depends on its acidity1 3 and can also indicate changes in climate as ice formed in cold dusty periods has a high concentration of alkaline dust1 4 5 which significantly reduces the conductivity6 7 compared to warmer less dusty periods here we present electrical conductivity records for the greenland ice sheet project 2 gisp2 and greenland ice core project grip ice cores drilled 28 km apart to enable direct comparison of the results the upper parts of both records are consistent with previous evidence from other greenland cores4 8 12 for a stable greenland climate during the holocene and a series of warm events punctuating the last glacial period however there is a significant discrepancy between the two records in the bottom 10 of the cores calling into question recent reports of climate variability in the last interglacial4 8 and the penultimate glaciation8 at this stage it is too early to say what exactly is causing the discrepancy although ice flow may have introduced some discontinuities into the records further work will be necessary to establish how much climatic information it will eventually be possible to extract from the lower parts of the two cores

40ar 39ar ages and 40ar concentrations of fine grained sediment fractions from north atlantic heinrich layers abstract new k ar ages based on 40 ar 39 ar incremental heating of 40 ar 39 ar based k ar age of 970 4 from orphan knoll in the southern labrador sea within the range found in eastern north atlantic heinrich layers thus the k ar data are robust in their indication of a dominant labrador sea ice rafted source to even the finest sediment fraction in the eastern north atlantic during the massive detrital carbonate bearing heinrich events of the last glacial cycle h1 h2 h4 h5 close correspondence of the radiogenic argon concentration 40 ar from the de carbonated a 40 ar 39 ar based k ar age of 433 5 million years for h11 in v28 82 is within the range of published data from background sediments in the eastern north atlantic and is consistent with published results across this interval in the driezack seamounts in contrast the 40 ar 39 ar based k ar age of h11 in the western atlantic core ew9303 jpc37 is 614 5 million years a brick red sample from approximately the interval of h3 of core ew9303 ggc40 yielded a 40 ar 39 ar based k ar age of 567 1 million years comparable to the published range of 523 543 ma from the 2 16 m fractions from that interval on the dreizack seamounts both jpc37 and ggc40 are located in the path of the north atlantic drift the older ages from western samples of h3 and h11 may result from dilution of a hudson strait source or an elevated age from southeastern laurentide sources

linking ocean and continental records of paleoclimate determining accord and discord in the records climate forcing at milankovitch and sub milankovitch frequencies are evaluated by linking climate proxy data from terrestrial and ocean records at two scales of temporal resolution 1 relatively coarse resolution over the last 500 ka and 2 higher resolution over the last 200 ka we determine that climate proxy data from hole 810c rep resent regional atmospheric and oceanic processes by comparison to core v21 146 both from the northwest pacific ocean we then compare records that represent regional deposition from china and the western pacific ocean to focus on determining milankovitch type periodicities grain size and magnetic susceptibility data from hole 810c and baoji china are contrasted using a time sensitive wavelet analysis the analyses indicate a general correspondence to milankovitch frequencies although there is no specific frequency that dominates throughout the records additionally the dominant 100 000 year frequency does not occur at the same time in the records these factors suggest that differ ences in the physical mechanisms of deposition may influence the preserved apparent periodicities in these environ ments lastly climate events over the last 200 000 years in marine and terrestrial records are correlated at a high resolution in the depth domain the last interglacial glacial boundary is consistently placed at the base of a cold period c20 in the terrestrial and marine records however the cold period in the ocean data 18 o is very subdued relative to terrestrial records additionally over the last 200 ka periods of minimum insolation intensity do not correspond lin early to periods of maximum grain size and ice volume variations revealed in the loess and ocean records respectively however during the warm interstadials of the last two glaciations peaks in insolation intensity compare favourably with the times of strongest pedogenic development in the continental records and minimum ice volume in the ocean records resume le forcage du climat a des frequences milankovitch et sous milankovitch est evalue en faisant un lien entre les donnees indirectes de sources terrestres et oceaniques a deux echelles de resolution dans le temps 1 une resolu tion relativement grossiere pour les dernieres 500 ka et 2 une plus haute resolution pour les dernieres 200 ka nous determinons que les donnees indirectes du trou 810c representent des procedes atmospheriques et oceaniques regionaux par rapport a la carotte v21 146 les deux provenant du nord ouest de l ocean pacifique nous avons ensuite compare les registres qui representent une deposition regionale en provenance de la chine et de l ouest de l ocean pacifique afin de se concentrer sur la determination de frequences de type milankovitch des donnees granulometriques et de suscep tibilite magnetique provenant du trou 810c et de baoji china sont mises en contraste au moyen d une analyse tempo relle des ondelettes les analyses indiquent une bonne correspondance generale aux frequences de milankovitch bien qu aucune frequence specifique ne domine a travers les registres de plus la frequence principale de 100 000 ans ne se presente pas au meme moment dans les registres ces facteurs suggerent que des differences dans les mecanismes phy siques de deposition peuvent influencer les periodicites apparentes preservees dans ces environnements finalement dans le domaine de la profondeur il y a correlation a haute resolution entre les registres marins et terrestres des evene ments climatiques au cours des derniers 200 000 ans la derniere limite glaciaire interglaciaire est constamment placee a la base d une periode froide c20 dans les registres marins et terrestres toutefois la periode froide dans les don nees oceaniques 18 o est tres attenuee par rapport aux registres terrestres de plus au cours des dernieres 200 ka des periodes d intensite minimale d insolation ne correspondent pas de facon lineaire aux periodes de granulometrie maximale et de variations des volumes de glace qui sont revelees respectivement dans les registres oceaniques et de loess toutefois au cours des rechauffements interstadiaires des deux dernieres glaciations des sommets dans l intensite d insolation se comparent favorablement avec les temps du plus fort developpement pedogenique dans les re gistres continentaux et avec le volume minimal de glace dans les registres oceaniques traduit par la redaction 848

clumped isotope paleotemperatures from mis 5 soil carbonates in southern hungary abstract quantitative paleotemperature reconstructions for the continents including east central europe over marine isotope stage 5 mis 5 and specifically the last interglacial lig mis 5e are scarce and mostly based on pollen assemblages here we provide soil and air temperature reconstructions for the summer season of mis 5e 5c using carbonate clumped isotope thermometry applied to soil carbonate concretions in the dunaszekcs loess paleosol record southern hungary the sediments making up the s1 pedocomplex investigated represent the mis 5 as demonstrated by bracketing k feldspar post ir irsl225 290 ages of 63 to 164 ka both the absolute ages and pedogenic susceptibility p curve indicate that all the subtages of mis 5 were found to be recorded in the sequence and soil carbonates found 1 m depth below the paleosurface of the s1 soil provide pristine undisturbed isotopic signals the soil carbonate concretions likely formed during mis 5e at a relatively shallow 20 50 cm depth but a later formation during mis 5c at 50 cm depth is also plausible clumped isotope based soil temperatures st 47sc ranged from 16 to 20 c and reconstructed summer season air temperatures sats for the lig are consistently lower than the modern values at the site by 1 5 c matching surprisingly well the soil bacteria membrane lipid based mis 5e air temperature estimates from a nearby serbian site at the same time the reconstructed sat values do not match the 2 4 c positive warm season anomalies modeled for east central europe between lig and present day in paleoclimate simulations st uncertainties of 1 6 c infiltration driven cooling of soil temperatures and the possibility of mis 5c formation of the investigated carbonates may account for this proxy model data discrepancy oxygen isotope compositions of summer season paleo rainwaters for mis 5e 5c as reconstructed using the st 47sc and 18osc data of soil carbonates were found in a range of 6 7 and 6 4 matching the modern mean summer season value of 6 2 0 94 within error

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

correlation of the eemian and the weichselian with deep sea oxygen isotope stratigraphy abstract the eemian interglacial was defined in the netherlands and is correlated all over northern europe it is now demonstrated that the eemian was the last interglacial in europe thus it is obvious that it should correlate with either the entire stage 5 in the deep sea oxygen isotope stratigraphy or with parts of stage 5 several observations prove that the eemian correlates with substage 5e the two other peaks in stage 5 correlates with the warm interstadials brorup and odderade in northern europe

millennial scale fluctuations in seasonal sea ice and deep water formation in the japan sea during the late quaternary abstract the east asian winter monsoon is characterized by cold dry air blowing from the siberian high to the surrounding lows this cold wind cools the surface water along the russian coast of the japan sea modern oceanographic observations indicate that sea ice formation along this coast during an extremely cold winter is an important process for deep water formation thus formation of both seasonal sea ice and deep water masses in the japan sea are closely related to the east asian winter monsoon two sediment cores were analyzed to reconstruct the history of sea ice expansion and deep water formation seasonal sea ice history was reconstructed from the occurrence of ice rafted debris ird in a core from the northeastern japan sea whereas the deep water ventilation history was estimated on the basis of records of a deep dwelling radiolarian species cycladophora davisiana in a core from the southwestern japan sea in the records of sea ice expansion and deep water ventilation for the last 160 ky clear fluctuations on a millennial timescale were observed during marine oxygen isotope stages 3 5 some of the peaks in sea ice formation and c davisiana abundance occurred contemporaneously indicating strong surface cooling along the russian coast by a strong winter monsoon decoupling of the two records might have occurred because of surface water stratification caused by the freshening of surface water in relation to high precipitation in summer synchronicity of high ird peaks with north atlantic heinrich events suggests that high latitude climate changes related to the bond cycle also occurred in the asian monsoon region on shorter timescales ird occurrence was not clearly related to dansgaard oeschger cycles which are revealed in the alternating dark and light layers in the late quaternary japan sea sediments therefore during the studied period strong east asian winter monsoons did not have a simple see saw like relationship with strong summer monsoons

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

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

river response to high frequency climate oscillations in southern europe over the past 200 k y a 200 k y chronology of river response to climate related environmental change has been established for northeast spain using newly developed luminescence dating techniques this constitutes the best documented record of late quaternary river behavior currently available for the north atlantic region and enables fluvial stratigraphies to be compared with high resolution ice core and marine oxygen isotope climate series pleistocene and holocene river aggradational episodes coincide with stadial or neoglacial events while phases of river incision occur during interstadial or interglacial periods alluviation and erosion cycles would appear to track variations in sediment supply controlled by vegetation cover and winter storm frequency

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

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

multidisciplinary tephrochronological correlation of marker events in the eastern tyrrhenian sea between 48 and 105 ka abstract the basal portion 2 92 5 08 m from core top of the cet1 core located in a bathyal area of the eastern tyrrhenian sea is the subject of a multidisciplinary investigation encompassing tephrostratigraphy quantitative analyses of planktonic foraminifera and calcareous nannofossil assemblages and 18o measurements supported by a 40ar 39ar age determination calcareous nannofossil assemblages allowed the attribution of the analyzed sediments to the biozone mmn21a and the succession spans from more than 48 to ca 105 ka although there are at least two stratigraphic gaps and minor resedimentation episodes a paleoclimatic reconstruction obtained via 18o and planktonic foraminifera data identifies several of the major climatic events that occurred in the investigated time span a total of 13 visible tephra layers and cryptotephras are recognized and correlated with their volcanic sources campanian volcanic zone and pantelleria volcano and when possible with well known and dated events or with widespread marker tephras using a combination of biostratigraphic oxygen isotope and tephrostratigraphic correlations we develop a chronostratigraphy for the main climatic events and tephra layers in the core and pinpoint tephra markers for the climatic events comprised between gs 22 and gi 24 in the eastern tyrrhenian sea

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

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

millennial scale climate change and oceanic processes in the late pliocene and early pleistocene we generated 200 500 year resolution records of oceanic processes in the north atlantic ocean drilling program site 983 60 24 n 23 38 w 1983 meters water depth for intervals in the latest pliocene 1 86 1 93 ma and the earliest pleistocene 1 75 1 83 ma in order to examine the linkages between millennial scale variations in the ocean and background glacial interglacial climate change within glacial intervals we find evidence for variations similar to those observed in the late pleistocene we find discrete ice rafted debris ird events that reoccur every 2 5 kyr these events are preceded by a short cooling and accompanied by a reorganization of glacial deep waters the timing of ird events in the late pliocene and early pleistocene intervals is similar to that of dansgaard oeschger cycles but we find no ird events comparable in timing to late pleistocene heinrich events although interglacial intervals are much more stable we do find evidence for low amplitude variations in deep water properties that reoccur every 2 kyr within interglacial intervals the similarity between our late pliocene early pleistocene records and late pleistocene records implies that the mechanism driving millennial scale variations cannot be uniquely attributed to the strongly nonlinear linkage between climate and insolation and the large ice sheets of the late pleistocene

continental oxygen isotopic record of the last 170 000 years in jerusalem abstract a long radiometrically dated oxygen isotopic record of continental climatic variations since the penultimate glaciation was obtained from a stalagmite deposited in a sealed cave in jerusalem this record shows that speleothems have the potential of assigning dates to long and short term climatic events with possible refining of milankovitch tuning of ice and marine records which themselves are not datable short term 1000 yr events are very significant in the region reaching 50 of glacial interglacial fluctuations the mediterranean sea was the most probable source of local precipitation throughout the last glacial cycle

sedimentology and flow behavior of a rain triggered lahar mangatoetoenui stream ruapehu volcano new zealand on october 28 1995 heavy rain triggered failure of approximately 3 3 10 5 m 3 of fall deposits on the mangatoetoenui glacier and generated a lahar event that flowed east northeast of ruapehu volcano down the mangatoetoenui stream and eventually entered the tongariro river 19 km downstream the lahar left multiple stacked deposits of at least three major flow surges or pulses which traveled down slope at calculated velocities of as much as 27 m s 1 and calculated maximum peak discharges of as much as 2900 m 3 s 1 the source area of the mangatoetoenui lahar is delineated by a thin furrowed lag of unsorted ash and lapilli margined by steep headwall scarps marking the edges of undisturbed fall deposits failure of fall deposits in the source area triggered debris flows down a north and south branch of the mangatoetoenui stream these two debris flows coalesced and ponded then flowed across seasonal snowpack covering the stream in the proximal zone to 5 km downstream of the source area the deposits of the individual constituent debris flows cannot be distinguished however in the medial zone between 5 and 16 km downstream of the source area and beyond the limit of the snowpack and the junction with perennial streamflow the depositional record of this lahar shows clear evidence for downstream transformation of individual peak flows from debris flow to hyperconcentrated flow transformation began at 5 km from source due to dilution 1 by each peak flow incorporating normal streamflow in the perennial mangatoetoenui stream and tributaries and 2 through deposition of part of each peak flow9s sediment load the hyperconcentrated flow deposits frequently may be subdivided into multiple units which is evidence that the lahar flowed as a series of surges or waves we consider that these were caused by episodic but contemporaneous inputs from a divergent flow from a single source area or by ponding and episodic release of debris within the channel estimated froude numbers for the mangatoetoenui lahar are greater than 3 implying supercritical flow and the development of fluid mechanical instabilities that enhanced these flow surges

the taylor dome antarctic 18o record and globally synchronous changes in climate abstract the 18 o 16 o profile of a 554 m long ice core through taylor dome antarctica shows the climate variability of the last glacial interglacial cycle in detail and extends at least another full cycle taylor dome shares the main features of the vostok record including the early climatic optimum with later cool phase of the last interglacial period in antarctica taylor dome 18 o fluctuations are more abrupt and larger than those at vostok and byrd station although still less pronounced than those of the greenland gisp2 and grip records the influence of the atlantic thermohaline circulation on regional ocean heat transport explains the partly north atlantic character of this antarctic record under full glacial climate marine isotope stage 4 late stage 3 and stage 2 this marine influence diminished and taylor dome became more like vostok varying degrees of marine influence produce climate heterogeneity within antarctica which may account for conflicting evidence regarding the relative phasing of northern and southern hemisphere climate change

modelled nucleation centres of the pleistocene ice sheets from an ice sheet model with subgrid topographic and glaciologic parameterizations abstract ice sheet inception at the onset of the last glacial epoch ca 115 kyr bp is not well understood to cause the northern hemisphere to descend into ice age conditions internal climate system feedbacks must have acted to amplify relatively low amplitude orbital cooling trends while a number of plausible internal mechanisms have been proposed for this internal amplification the dramatic continental ice sheet expansion that is recorded in the marine sediment record is an enduring mystery global sea level lowering of at least 20 m and as much as 75 m over 10 kyr appears typical of the early stages of glacial inception this rate of ice sheet growth has not been freely captured in either glaciologic or climatic models is it because we do not adequately understand the relevant internal feedbacks or fail to capture them in models is it simply related to technical model limitations e g topographic resolution this paper explores the premise that model resolution poses a critical limitation on simulations of ice sheet nucleation i present a series of ice sheet nucleation simulations in north america and eurasia based on an ice sheet model that includes parameterizations of km scale topographic detail snow ice accumulation and melt and glacier dynamics model climate is based on perturbations to modern observational climatology even with this topographic detail and with simulations long enough to allow ice to advect downslope and spread over the terrain it remains difficult to induce a large scale glacierization in both north america and eurasia severe climate perturbations are required cold temperatures need to be accompanied by substantial increases in precipitation in the north atlantic and polar regions in order to accrue continental ice at the rate demanded by sea level reconstructions the simulations presented here are too simple to separate climate perturbations from internal system feedbacks but with modern precipitation rates a combined climate cooling net positive feedback of more than 8 c is required to establish large scale ice sheets in

a high resolution record of vegetation and climate through the last glacial cycle from caledonia fen southeastern highlands of australia a blocked tributary has provided a rare site of long term sediment accumulation in montane southeastern australia this site has yielded a continuous detailed pollen record through the last ca 140 000 years and revealed marked vegetation and environmental changes at orbital to sub millennial scales radiocarbon and optically stimulated luminescence osl or optical ages provide some chronological control for the last ca 70 000 years most of the sediment is inorganic but with well preserved pollen that accumulated under unproductive and probably largely ice covered lake conditions the lake was surrounded by low growing plants with an alpine character exceptions include three discrete periods of high organic sedimentation in the basin and forest development in the surrounding catchment the two major periods of forest expansion are related to the last interglacial and the holocene with the third shorter period considered to represent an interstadial in the early part of marine isotope stage mis 3 the latter part of the last glacial period is characterised by abrupt sub millennial amelioration events that may relate to documented global oscillations emanating from the north atlantic there are systematic changes through the record that can be partly attributed to basin infilling but the progressive reduction and regional extinction of some plant taxa is attributed to a long term trend towards climatic drying copyright 2007 john wiley sons ltd

the last interglacial climate during the last 10 000 years the holocene has been relatively mild and stable in contrast the climate during the last interglacial is often portrayed as more variable but as kukla discusses in this perspective evidence for a more stable last interglacial is emerging furthermore the transition to the next glacial proceeded in stages and was not uniform across europe

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

palaeocurrent reconstruction sediment and thorium focussing on the iberian margin over the last 140 ka sedimentological data in particular sediment grain size from core md95 2040 2465 m water depth and a nearby core omii 9k 1833 m water depth presently under the influence of lower north atlantic deep water and deep intermediate water respectively have been used to reconstruct changes in the vigour of near bottom water flow on the iberian margin the pattern of the palaeocurrent index indicates faster flow during the warm periods and slower in cold this also holds in the younger dryas but there is an added effect of brief collapse of the circulation in termination 1b due to meltwater input the cold periods are generally characterised by elevated clay percentage terrigenous material 2 m diameter and overall sediment accumulation fluxes in comparison warm periods of higher flow have lower depositional flux and a tendency to silt terrigenous material 2 63 m dominance consistent with the higher flow speed and suppression of clay deposition this is in contrast with a recent 230thxs based study of two cores md95 2040 and 2039 j thomson et al earth planet sci lett 165 1999 255 270 which concluded that increased glacial sediment and th focussing was caused by stronger currents the crucial factor is that the controlling speed is that of the flow at the depositional site rather than that of the erosional or transporting flow to the site high glacial maximum fluxes of carbonate 6 g cm 2 ka 1 are largely composed of fine 63 m non coccolith material suggesting a significant detrital component it is proposed that the sediment and th arrive on the lower slope via different routes sediment down slope in bottom nepheloid layers and turbidity currents th scavenged from the water column by organic matter and are rapidly mixed on the bed removal of this material from a large area and its deposition in a small one adjacent to oporto seamount together with a small amount of direct down slope supply accounts for the properties of the deposits allowance for erroneous fluxes due to possible coring expansion stretching of the upper part of md95 2040 does not invalidate these conclusions

sea surface temperature variability in the north atlantic during the last two glacial interglacial cycles comparison of faunal oxygen isotopic and mg ca derived records climate variability in the northeast atlantic was investigated on glacial interglacial and millennial time scales during the last 200 000 years using sea surface temperature sst records derived from planktonic foraminiferal diversities and from mg ca measurements on globigerina bulloides paleoceanographical interpretations are supported by species composition analyses benthic and planktonic isotopic data as well as records of iceberg rafted debris ird differences of climate development are recognized for both interglacial and glacial periods temperature estimates indicate slightly warmer conditions up to 2 c during marine oxygen isotope stage mis 5e than during the holocene in contrast to the last glaciation when the sst minimum coincided with a minimum in solar insolation immediately before termination i during the penultimate glaciation a long sst minimum occurred at times of intermediate solar insolation well preceding the onset of termination ii this discrepancy between two glacial terminations may be explained by an inherently different orbital configuration characteristic for each glacial interval despite these differences between the two glacial trends the superimposed shorter lived climatic events reveal the same order of principal steps implying their common causal nature a direct comparison of faunal ssts with those retrieved from mg ca analysis shows that mg ca derived temperatures follow the general glacial interglacial trend however the latter appear to be largely overestimated supported by 18o data in g bulloides which show little response to millennial scale variability there seems to be a need for species dependent calibration experiments that also consider the different oceanographic settings this particular species can live in

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

interglacial and glacial climate oscillations in a marine shelf sequence from northern denmark a multidisciplinary study abstract a 22 5 m long marine shelf sequence in northern denmark covers the climatic shifts from glacial environments through interglacial and into early glacial conditions the interglacial was interrupted by two cool intervals also the early glacial succession experienced oscillations of the climate and a period with ameliorated temperature conditions has been separated as an interstadial these results are based on a multidisciplinary high resolution study of lithology foraminifera ostracods macrofauna diatoms and stable isotopes in a silty clay sequence from a borehole at norre lyngby 70 5 48 0 m depth the lithostratigraphy and the variations in depositional environment in the area is supported by a reflection seismic profile across the core site the chronostratigraphy is discussed on the basis of biostratigraphical correlation and seismostratigraphy as well as optically stimulated luminescence osl dating and amino acid measurements the biostratigraphy and the osl dates suggest an eemian age for the interglacial while amino acid results point to an older age if the interglacial is confirmed as eemian we believe that the succeeding interstadial period is likely to be correlated with the brorup interstadial the climatic changes in this eastern part of the north sea region are closely linked with changes in the north atlantic circulation pattern and the environmental fluctuations at norre lyngby are therefore believed to reflect fluctuations in the past regional climatic and oceanic system

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

a chronology for the long pollen record from lake wangoom western victoria australia as derived from uranium thorium disequilibrium dating the chronology of a long pollen record from lake wangoom one of the few long palaeoenvironmental records from southeastern australia is discussed in light of the acquisition of new uranium thorium disequilibrium utd dates of crucial importance has been the estimation of ages for two major pre holocene phases of forest expansion recorded in the sequence with implications for the timing of periods of high effective precipitation in the region the new utd ages indicate that the oldest forest phase falls within the penultimate interglacial whereas the later phase corresponds with the last interglacial this is older than indicated by previously reported utd and radiocarbon dates but confirms a chronology based on direct correlation with the pollen record from marine core e55 6 the new chronology of the lake wangoom sequence provides evidence that phases of sustained forest development in southeast australia relate to interglacial periods in comparison interstadial periods appear to be characterised by only minor arboreal development marked differences in the pattern of vegetation development evident in each of the interglacials are thought to reflect varying climatic and anthropogenic influences copyright 2002 john wiley sons ltd

rock magnetic properties of eemian maar lake sediments from massif central france a climatic signature the hypothesis of a climate variability within the last interglacial eemian suggested by oxygen isotope data of a greenland ice core grip was later supported by magnetic susceptibility organic matter and pollen signatures in the eemian lake sediments of the lac du bouchet france in the present paper we analyse in detail the rock magnetic properties of these sediments in order to determine the origin of the magnetic susceptibility variations furthermore in order to verify the empirical relation between magnetic susceptibility and climate we studied two eemian sequences from neighbouring lakes lac st front and ribains maar lake rock magnetic investigations mainly consisted of analyses of anhysteretic and isothermal remanent magnetizations along with hysteresis measurements carried out on pilot samples lac du bouchet susceptibility variations are at least partly affected by postdepositional magnetite dissolution lac st front sediments show a complex behaviour resulting in partly contradicting interpretations of rock magnetic parameters possible explanations may be the presence of a very fine grained magnetite or the presence of maghemite ribains maar lake sediments show a homogeneous magnetic mineralogy without major variations in most of the rock magnetic parameters susceptibility records of the three lakes were compared under the simplified assumption that magnetic susceptibility mainly reflects variations of the detrital titano magnetite input only a poor correlation between the three eemian susceptibility sequences is observed suggesting that local effects including dissolution and dilution effects may have altered the original detrital climatic signal the purely detrital origin of the lac du bouchet eemian susceptibility variations must thus be questioned but it nevertheless appears to be the only lake whose susceptibility variations can tentatively be correlated with the grip eemian oxygen isotope record

36cl dating of the classic pleistocene glacial record in the northeastern cascade range washington and are more degraded seventy six 36 cl dates for the moraines cluster in groups having mean ages 1 of 12 500 500 13 300 800 16 100 1100 19 100 3000 70 900 1500 93 100 2600 and 105 400 2200 years a still older highly weathered and eroded moraine is undated but likely is at least 165 000 years old the moraine ages and relative extent of the icicle creek glacier correspond closely to the ages and relative amplitude of july insolation minima at 47 5 n latitude they also are in accord with ages for glaciations in the european alps that were inferred by milutin milankovitch and colleagues in the 1920s based on calculations of summer insolation evidence that the greatest late pleistocene glacier advance occurred at the onset of the last glaciation during marine isotope substage 5d is consistent with a cooling climate and major glacier advances at that time elsewhere in north america and the eurasian arctic with a dramatic increase in global ice volume and with the shifting track of the jet stream over northwestern united states

geomagnetic paleointensity and environmental record from labrador sea core md95 2024 global marine sediment and ice core chronostratigraphy for the last 110 kyr piston core md95 2024 from the labrador rise provides a continuous record of rapidly deposited detrital layers denoting laurentide ice sheet lis instability the core also provides a high resolution record of geomagnetic paleointensity that is consistent with but at higher temporal resolution than previous labrador sea records correlation to the greenland summit ice cores grip gisp2 is achieved by assuming that labrador sea detrital layers correspond to cold stadials in the ice cores this allows a gisp2 official chronology to be placed on md95 2024 which is consistent with the inverse correlation between paleointensity and the flux of cosmogenic isotopes 10 be and 36 cl in greenland ice cores synchronous millennial scale variability observed from the md95 2024 paleointensity

seismic strain and seismogenic stress regimes in the crust of the southern tyrrhenian region abstract an investigation has been performed to identify and characterize the seismic deformation zones active over the last decades in the region of italy that has experienced the strongest seismicity during the last centuries the study is based on the estimate of hypocenter locations fault plane solutions seismogenic stress and seismic strain tensor orientations carried out using the entire dataset of the national and local seismic networks and the recently improved three dimensional 3d crustal velocity model of the study area a series of simulation tests have been performed to evaluate the significance of the earthquake space distribution obtained and whether it was influenced by network geometry problems related to the sea and the lack of ocean bottom seismometers in the sectors where hypocentral location was synthetically proved to be reliable space distributions of earthquakes located with epicenter and focal depth errors less than 3 and 4 km respectively have been compared with local geology in order to identify seismogenic faults the dataset of 32 fault plane solutions estimated with fault parameter errors less than 20 has been used to investigate space variations of seismogenic stress and seismic strain orientations over the study area stress was found to be uniform in the messina strait and southern calabria where inversion of the available set of 11 fault plane solutions showed clear evidence of an extensional regime the different orientations of the minimum compressive stress and strain found in this sector together with the information available on local geology and tectonics lead us to propose that the seismicity occurring over the last decades in the messina strait and southern calabria was not in general produced at the main faults but at minor faults activated by the main tectonic stress field acting in the area to the west in the sector including western etna the nebrodi chain and the western aeolian islands analysis of the available set of 16 fault plane solutions revealed a certain degree of stress heterogeneity with an apparent prevalence of north south compression this east to west change of stress strain regimes is evaluated in the light of current hypotheses regarding the geodynamics of the study region

high resolution palynological record off the iberian margin direct land sea correlation for the last interglacial complex abstract we present high resolution pollen dinocyst and isotopic data for the last interglacial complex from marine core md952042 southwestern margin of the iberian peninsula 37 48 n 10 10 w 3148 m direct land sea correlation from this core indicates that during this period north atlantic sea surface temperatures were in phase with iberian climate our palynological analysis suggests a younger dryas like event at the marine isotope stage mis 6 5 transition the analysis also indicates that the eemian spans from the lightest isotopic values of mis 5e ca 126 ky bp to the heavier isotopic values towards the mis 5e 5d transition therefore the eemian is not entirely equivalent to mis 5e pollen analysis identifies four climatic phases of low amplitude during the eemian a mediterranean climate in southwestern europe is gradually replaced by oceanic conditions the middle of the eemian is characterized by an increase in precipitation on the land and ocean associated with a slight cooling this seems to be the result of a displacement of the polar front as far south as southern europe during this period after the eemian three relatively short climatic phases on land melisey i st germain ia and montaigu cold event occurred contemporaneously with three shifts of sea surface temperatures the montaigu event first identified in terrestrial pollen sequences is therefore also recorded in core md952042 on the basis of pollen dinocyst and planktonic isotopic data our results also show that the warm periods of mis 5 are not characterized by similar climatic conditions on land

quantitative precipitation estimates for the northeastern qinghai tibetan plateau over the last 18 000 years quantitative information regarding the long term variability of precipitation and vegetation during the period covering both the lateglacial and the holocene on the qinghai tibetan plateau qtp is scarce herein we provide new and numerical reconstructions for annual mean precipitation pann and vegetation history over the last 18 000 years using high resolution pollen data from lakes dalianhai and qinghai on the northeastern qtp hitherto five calibration techniques including weighted averaging wa weighted average partial least squares regression wa pls modern analogue technique mat locally weighted weighted averaging regression lwwa and maximum likelihood ml were firstly employed to construct robust inference models and to produce reliable pann estimates on the qtp the biomization method was applied for reconstructing the vegetation dynamics the study area was dominated by steppe and characterized with a highly variable relatively dry climate at 18 000 11 000 cal a b p pann increased since the early holocene obtained a maximum at 8000 3000 cal a b p with coniferous temperate mixed forest as the dominant biome and thereafter declined to present the pann reconstructions are broadly consistent with other proxy based paleoclimatic records from the northeastern qtp and the northern region of monsoonal china the possible mechanisms behind the precipitation changes may be tentatively attributed to the internal feedback processes of higher latitude e g north atlantic and lower latitude e g subtropical monsoon competing climatic regimes which are primarily modulated by solar energy output as the external driving force these findings may provide important insights into understanding the future asian precipitation dynamics under the projected global warming

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

marine core evidence for reduced deep water production during termination ii followed by a relatively stable substage 5e eemian we present oxygen and carbon isotope records of benthic foraminifera from the glacial stage 6 through interglacial substage 5e eemian sections of several cores from the subpolar north atlantic the cores range in water depth from 1451 to 2658 m in one core we generated estimates of sea surface temperature sst and of ice rafted detritus ird delivery for all of stage 5 we reconstruct bathymeric profiles of 13c for stage 6 termination ii and three time slices of substage 5e the 13c profiles indicate that local deep water geometry during stage 6 was similar to that of the last glaciation with glacial north atlantic intermediate water gnaiw overlying deeper waters partially of southern origin an anomalously large peak in ird coupled with planktonic 18o evidence for iceberg melting immediately precedes termination ii and is otherwise similar to stage 2 and 3 heinrich events during the termination low 13c values are observed in cores near and above 2 km providing evidence of reduced gnaiw production in association with deglacial melting in the shallowest cores low 13c values persist into early substage 5e indicating that the southward retreat of southern source waters was not completed until well after the beginning of the substage in contrast to termination i ssts remained cold until the end of the deglaciation this may be why there is little evidence from marine and terrestrial sequences for a pronounced climate reversal on termination ii despite what is now clear evidence of a significant reduction in ocean ventilation the faunal data suggest that ssts during early 5e were about 7 c warmer than during the glaciation sst rose several degrees from early to middle substage 5e peaked in middle substage 5e at about 10 c above glacial values and then gradually declined by about 5 c these changes were linked to variations in water mass configuration as interpreted from benthic 13c evidence most of the evidence suggests that oscillations superimposed on the gradual sst trend were 1 2 c in contrast to the larger sst changes 3 4 c documented for substage 5d

sclerochronology and geochemical variation in limpet shells patella vulgata a new archive to reconstruct coastal sea surface temperature 1 climate archives contained in shells of the european limpet patella vulgata accumulated in archaeological deposits can potentially provide much needed information about holocene environmental change in midlatitude coastal areas before reconstructing climate information preserved in these zooarchaeological records we studied the controls on oxygen and carbon isotope ratios 18o and 13c respectively in modern specimens we tested the hypothesis that p vulgata precipitates its shell in isotopic equilibrium with the ambient water by comparing 18oshell with predicted values predicted 18oshell was constructed using observed sea surface temperature sst records and the equilibrium fractionation equation for calcite and water we assumed a constant 18owater value of 0 10 vsmow based on published regional measurements comparison of 18oshell with predicted values revealed that 18oshell values were higher than expected by 1 01 0 21 consequently estimated sst calculated from 18oshell was 4 2 2 3 c lower than observed sst however because of the relatively uniform offset between observed and expected 18o an adjustment can be made to account for this predictable vital effect thus past climate can be reliably reconstructed using this temperature proxy once the offset is taken into account 13c values have a similar cyclicity to the 18o variation and therefore vary seasonally however 13c is slightly out of phase relative to 18o an overall negative shift in 13cshell over the lifetime of the individual indicates a vital effect associated with ontogeny further study of environmental and ecological factors that influence shell 13c is required to evaluate fully the potential of carbon isotope ratios as a useful environmental proxy

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

climatic instability ice sheets and ocean dynamics at high northern latitudes during the last glacial period 58 10 ka bp abstract oxygen isotope magnetic susceptibility and foraminiferal distribution data are presented for a high resolution core enam93 21 located at the northeast faeroe margin this core recorded a rapid succession of faunistic sedimentologic and isotopic variations which paralleled the greenland ice core isotopic records with their typical succession of abrupt temperature rises and gradual coolings the dansgaard oeschger cycles the most notable feature was the contemporaneous changes in surface and bottom water conditions and circulation that appeared tightly coupled with the rapid climate fluctuations warm episodes interstadials were appeared with higher sea surface temperatures and thermohaline convection in the norwegian greenland sea the polar front was located north of the enam93 21 site cold episodes stadials were associated with an increase in the input of melting fennoscandian icebergs low sea surface temperature and salinity and no thermohaline convection in the norwegian greenland sea intermediate waters changed to an estuarine mode at the faeroe margin with a reversed flow pattern through the faeroe shetland channel the polar front was located south of the enam93 21 site

determination of sediment provenance at drift sites using hydrogen isotopes and unsaturation ratios in alkenones the large 20 hydrogen isotopic gradient in surface waters of the northwest atlantic ocean is exploited to track changes in the source of alkenones to the bermuda rise sediment drift cultures of the predominant alkenone producing coccolithophorid e huxleyi were grown in deuterium enriched seawater and shown to possess alkenones with a d h ratio that closely tracked the water d h ratio r 2 0 999 n 5 isotopic enrichments with a fractionation factor between 0 732 and 0 775 a hydrogen isotopic depletion of 193 3 n 9 was measured in alkenones from suspended particles relative to seawater in the subpolar and subtropical northwest atlantic ocean this value was used to calculate the water d values in which alkenones from bermuda rise sediment were synthesized and by extension the water mass in which they were produced applying this technique we find that 60 to 100 of the alkenones in late holocene bermuda rise sediment were produced in deuterium depleted subpolar water to the northwest of the drift to reconcile values of the alkenone unsaturation ratio u k 37 a widely used proxy for sea surface temperature with the d values of alkenones in late holocene sediments from the bermuda rise at least three sources of sediment must be invoked a cold very isotopically depleted source almost certain to be the scotian margin a warm moderately isotopically depleted source likely to be the northwestern edge of the subtropical gyre and a cold isotopically enriched source which we hypothesize to be the subpolar waters overlying the main branch of north atlantic deep water flowing southwest from the nordic seas copyright 2005 elsevier ltd paleoclimate records with sufficient length and temporal resolution to study the occurrence and causal mechanisms of abrupt climate change are exceedingly rare rapidly deposited ocean sediments provide the best archive for studying these events through geologic time but such sites in the open ocean are limited to sediment drift deposits such as the bermuda rise in the northwest atlantic using multiple climate proxies in a single core is becoming more common in high resolution pa leoclimate investigations but a major potential concern for this approach arises from the possibility that the fine fraction of sediment e g 63 m and the climate proxies within it may represent conditions far from the deposition site here we propose and test the hypothesis that hydrogen isotope ratios of alkenones a class of lipids from phytoplankton may provide insight into the source of fine grained sediment because of their restricted sources broad geographic distri bution and excellent preservation properties alkenones are of particular interest in the emerging field of compound specific hydrogen isotopic analysis the sedimentary abundances ex tents of unsaturations and isotopic compositions of alkenones provide quantitative and near continuous records we isolated alkenones from cultured unicellular algae haptophyte emil iania huxleyi surface ocean particulate material and open ocean sediments to determine the extent and variability of hydrogen isotopic fractionation in the di tri and tetraunsat urated c37 compounds we then compared the d values of the alkenones in surface sediments between the bermuda rise and the scotian margin above which a large 20 d gradient exists we determined the fractionation between alkenones from suspended particulate samples and the water in which the phytoplanton lived and examined the variability of alkenone d values during the medieval warm period little ice age climate transition cf keigwin 1996 at the bermuda rise

dating of seasonal snow firn accumulation layers using pollen analysis reliable chronologies in ice cores and snow pits from many alpine glaciers in latitudes between 60 n and 60 s are often difficult to establish owing to problems with annual layer counting problems arise from melting wind erosion and the negligible amount of precipitation in some seasons all of which tend to obscure the seasonal variations in 18 o and chemical concentrations that are typically used to date ice cores however alpine glaciers contain many species of pollen grains that peak at particular times of the year we used the peaks in betulaceae pinus artemisia and a combination of abies and picea pollen species to determine the four seasonal layers of a snow pit on belukha glacier in russia s altai mountains comparing the pollen dated profiles with wind and precipitation records allows us to determine where a seasonal layer is missing thus the pollen dating method described here may be a useful tool to measure the annual snow deposition on alpine glaciers even when some seasonal layers are eroded by wind or missing due to negligible precipitation

eemian and early weichselian 140 60 ka paleoceanography and paleoclimate in the nordic seas with comparisons to holocene conditions paleoceanographic and paleoclimatic time series were extracted from norwegian iceland and greenland sea the nordic seas sediment sequences covering the time intervals 60 140 ka and 0 15 ka on the basis of stable isotope stratigraphy planktonic foraminiferal faunas and sedimentological methods the proxy temperature records from the norwegian iceland sea display a number of high frequency and high amplitude variations within the last interglacial the eemian indicating marked changes in heat flux at high northern latitudes eemian holocene comparisons document that the climate of the norwegian iceland sea in the last interglacial was less stable than that of the present interglacial and that the distribution of surface water masses in the eemian differed from that of the holocene within the greenland sea uniform cold conditions prevailed throughout both interglacials cooling of the nordic seas as well as the initial growth of the surrounding ice sheets began within the eemian interval before the main increase in global ice volume heat flux to the nordic seas was significantly higher during the interglacials than at any time during the early weichselian 60 113 ka and no marked stadial interstadial changes in sea surface temperature and deep water ventilation are documented in the early weichselian records contrary to the pattern found in north atlantic sediment records however fluctuations in planktonic foraminiferal content planktonic 13c and ice rafting on suborbital timescales mostly comparable in number and age to the stadial interstadial fluctuations in the greenland ice cores are demonstrated in our records the ice rafted detritus records provide a more detailed account of ice sheet variability than previously known for the early weichselian period and demonstrate that glaciers advanced to sea level somewhere around the nordic seas several times during this interval

magnetic signature of european margin sediments provenance of ice rafted debris and the climatic response of the british ice sheet during marine isotope stages 2 and 3 1 mineral magnetic measurements are used to distinguish ice rafted debris ird sources and climate cycles spanning marine isotope stage mis 3 and mis2 in core md95 2006 from the barra fan ne atlantic distinct magnetic properties are displayed by ird from the laurentide ice sheet lis high susceptibility low isothermal remanent magnetization irm low coercivity and the verwey transition the british ice sheet bis high high irm medium coercivity and suppressed verwey transition and the ambient background sediment low and low irm a magnetic unmixing model quantifies proportions of the ird sources during greenland stadial gs 16 to gs3 57 3 to 22 6 ka b p spanning heinrich event h 5 to h2 the magnetic model suggests lis ird is only dominant within an interval during gs9 assigned to h4 prior to h4 low proportions of bis ird suggest the bis was not able to deliver significant amounts of ird into the marine system following h4 proportions of bis ird during stadials increase suggesting growth of the bis during the latter stages of mis3 with further expansion of the bis during mis2 lis ird within h2 is masked by bis ird input climatically driven anhysteretic remanent magnetizations reflect the short dansgaard oeschger cycles between h5 and h4 while the proportions of hard magnetic minerals reflect the longer term bond cycles

high resolution stratigraphic correlation of benthic oxygen isotopic records spanning the last 300 000 years abstract in order to compare the response of different oceanographic regions to global climate change very detailed stratigraphic techniques are required the global signal of ice volume changes recorded in the oxygen isotopic composition of foraminifera can provide the tool for developing the necessary high resolution stratigraphy in order to evaluate the resolution of a stratigraphy based on detailed isotopic records two techniques are used to correlate a set of benthic oxygen isotope records from seven piston cores taken in the north and south atlantic the indian and the equatorial and north pacific oceans the first technique was modified from the graphic correlation procedure of shaw 1964 this procedure requires the identification of isotopic events that are correlated from core to core detailed correlations for intervals of the cores between events are provided by a series of straight line segments connecting all common events the second technique developed by martinson et al 1982 uses inverse procedures to define a continuous non linear mapping function that correlates the isotopic records the mapping function maximizes the correlation coefficient between data sets being compared the techniques are independent in that they rely on different criteria for correlating the data series stratigraphic correlations obtained by these procedures are in excellent agreement the mean difference between the correlations is on the order of the sampling intervals of each core and when corrected for sedimentation rates suggests that benthic isotope records from the suite of seven cores can be correlated to a resolution of 2000 to 4000 yrs

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

a stratigraphic framework for abrupt climatic changes during the last glacial period based on three synchronized greenland ice core records refining and extending the intimate event stratigraphy due to their outstanding resolution and well constrained chronologies greenland ice core records provide a master record of past climatic changes throughout the last interglacial glacial cycle in the north atlantic region as part of the intimate integration of ice core marine and terrestrial records project protocols have been proposed to ensure consistent and robust correlation between different records of past climate a key element of these protocols has been the formal definition and ordinal numbering of the sequence of greenland stadials gs and greenland interstadials gi within the most recent glacial period the gs and gi periods are the greenland expressions of the characteristic dansgaard oeschger events that represent cold and warm phases of the north atlantic region respectively we present here a more detailed and extended gs gi template for the whole of the last glacial period it is based on a synchronization of the ngrip grip and gisp2 ice core records that allows the parallel analysis of all three records on a common time scale the boundaries of the gs and gi periods are defined based on a combination of stable oxygen isotope ratios of the ice 18o reflecting mainly local temperature and calcium ion concentrations reflecting mainly atmospheric dust loading measured in the ice the data not only resolve the well known sequence of dansgaard oeschger events that were first defined and numbered in the ice core records more than two decades ago but also better resolve a number of short lived climatic oscillations some defined here for the first time using this revised scheme we propose a consistent approach for discriminating and naming all the significant abrupt climatic events of the last glacial period that are represented in the greenland ice records the final product constitutes an extended and better resolved greenland stratotype sequence against which other proxy records can be compared and correlated it also provides a more secure basis for investigating the dynamics and fundamental causes of these climatic perturbations

high resolution climate record from the beijing area during the last glacial interglacial cycle the zhaitang loess section located in the western suburbs of beijing has yielded a very high resolution magnetic susceptibility record for the last glacial and interglacial period all substages can be clearly defined in marine isotope stage mis 5 s1 and even also in substage 5a demonstrating comparable detail with vostok and parts of the grip ice record rapid climate shifts during the eemian period may have extended to continental asia but exerted only a weak influence on the zhaitang record abrupt climate transitions 5b 5c 5d 5e recorded in this section from the ne edge of the plateau show more detrial than most other chinese loess records these three well defined peaks in substage 5a imply sensitivity of the east asian monsoon to rapid hemisphere scale climate change and the prospect of finding more information on orbital and non orbital events in the loess sequence

eemian climate fluctuations observed in a european pollen record recent ice core data from greenland1 2 suggest that the climate during the last interglacial period the eemian was more unstable than that of the holocene about 10 000 years ago to the present being characterized in particular by a series of cold episodes each lasting about 70 to 750 years subsequent analysis of a second greenland ice core3 4 however failed to corroborate the details of these eemian climate fluctuations a result that may be attributable to the effects of ice flow4 to resolve this discrepancy it is imperative to seek alternative sources of information about the eemian climate here we present climate reconstructions from pollen data from the annually laminated eemian lake sediment record at bispingen5 and from the eemian and holocene peat records at la grande pile6 the former record indicates that an initially warm period of 2 900 yr was followed by cooling and a series of colder episodes one of which had winter temperatures comparable to those at the end of the preceding cold stage the latter records show greater climate instability during the eemian than the holocene these results are in broad agreement with those from the grip ice core but contrast both with the gisp2 core3 4 and with recent high resolution marine records from the north atlantic7 8

evidence for massive discharges of icebergs into the north atlantic ocean during the last glacial period sediments in the north atlantic ocean contain a series of layers that are rich in ice rafted debris and unusually poor in foraminifera1 here we present evidence that the most recent six of these heinrich layers deposited between 14 000 and 70 000 years ago record marked decreases in sea surface temperature and salinity decreases in the flux of planktonic foraminifera to the sediments and short lived massive discharges of icebergs originating in eastern canada the path of the icebergs clearly marked by the presence of ice rafted detrital carbonate can be traced for more than 3 000 km a remarkable distance attesting to extreme cooling of surface waters and enormous amounts of drifting ice the cause of these extreme events is puzzling they may reflect repeated rapid advances of the laurentide ice sheet perhaps associated with reductions in air temperatures yet temperature records from greenland ice cores appear to exhibit only a weak corresponding signal moreover the 5 10 000 yr intervals between the events are inconsistent with milankovitch orbital periodicities raising the question of what the ultimate cause of the postulated cooling may have been

were glacial iceberg surges in the north atlantic triggered by climatic warming high resolution physical mineralogical sedimentological and micropalaeontological studies were carried out on north atlantic cores from the reykjanes ridge at 59degreesn and from the region southwest of the faeroe islands all core sites are situated along the pathway of iceland scotland overflow water isow and the various parameters measured display similar features previously identified carbonate oscillations keigwin and jones 1994 j geophys res 99 12397 12410 in the time span back to the marine isotope stage 5 4 transition and late glacial lithic events bond and lotti 1995 science 267 1005 1010 such as the heinrich ice rafting events are all represented in the core records long term trends and higher frequency changes in isow intensity were reconstructed on the basis of various independent proxy records the long term trends in circulation match theoretical orbitally forced insolation changes our observed links between ice rafted detritus ird input variations in sea surface temperature sst and circulation at greater depth point to the need to re examine the origin of ird events we suggest that these events may have been triggered by enhanced partly sub surface heat transport to the north enhanced northward heat transport may have caused bottom melting of floating outlet glaciers and ice shelves leading to increased iceberg discharge and ice sheet destabilization this discharge resulted in lower sst s and a lower temperature over greenland thus as shown by our records this scenario implies a temporary de coupling of surface processes and circulation at greater depth a key feature is the occurrence of a saw tooth pattern in the marine data which is similar to the greenland ice core records moreover the warming theory of ird events would explain the observed out of phase relationship between the greenland and antarctic ice core records and also the rapid establishment of higher temperatures over greenland immediately after the cold phases stadials of the dansgaard oeschger cycles less

sedimentary record of rapid climatic variability in the north atlantic ocean during the last glacial cycle comparisons between a greenland ice core isotopic record and marine sediment grey level records of the north atlantic ocean show that rapid temperature variations witnessed by the ice core dansgaard oeschger events during the last glacial period can also be detected in marine sediments this shows that the resolution obtained in marine cores can be sufficiently high to record rapid climatic fluctuations several spectral analyses of those grey level marine records consistently indicate that significative fluctuations of the climatic response exist with periodicities of 5 to 1 kyr in addition to orbital forcing these high frequencies are close to those predicted by various dynamic ocean models

eemian climatic and hydrographical instability on a marine shelf in northern denmark abstract benthic foraminifera and stable isotope data from the last interglaciation eemian substage 5e from a borehole at skagen denmark provide evidence for major environmental and hydrographic changes during this period during the first millennium of the eemian water masses covering northern denmark became gradually warmer temperate conditions prevailed during most of the interglaciation but these were interrupted by two periods with decreased water temperatures the first cooling event s 1 was not very distinct at skagen but the second event s 2 seen in both the foraminiferal and oxygen isotope record represents a large shift to subarctic conditions carbon isotopes indicate a change in ocean circulation during both events no comparable climate variations are seen within the holocene record at the site the final cooling of the water masses associated with the substage 5e 5d boundary occurred within a few hundred years these last interglacial climatic changes were probably caused by variations in strength and or position of the north atlantic drift possibly as a result of varying vigor of the atlantic conveyor in addition minor variations in the fossil assemblages also indicate fluctuations in the inflow of atlantic water to the skagerrak kattegat area during the warm intervals of substage 5e

quantitative estimates of asian dust input to the western philippine sea in the mid late quaternary and its potential significance for paleoenvironment we present a new high resolution multiproxy data set of sr nd isotopes rare earth element soluble iron and total organic carbon data from international marine global change study core md06 3047 located in the western philippine sea we integrate our new data with published clay mineralogy rare earth element chemistry thermocline depth and delta c 13 differences between benthic and planktonic foraminifera in order to quantitatively constrain asian dust input to the basin we explore the relationship between philippine sea and high latitude pacific eolian fluxes as well as its significance for marine productivity and atmospheric co2 during the mid late quaternary three different indices indicate that asian dust contributes between similar to 15 and similar to 50 to the detrital fraction of the sediments eolian dust flux in core md06 3047 is similar to that in the polar southern pacific sediment coherent changes for most dust flux maximum minimum indicate that dust generation in interhemispheric source areas might have a common response to climatic variation over the mid late quaternary furthermore we note relatively good coherence between asian dust input soluble iron concentration local marine productivity and even global atmospheric co2 concentration over the entire study interval this suggests that dust borne iron fertilization of marine phytoplankton might have been a periodic process operating at glacial interglacial time scales over the past 700 ka we suggest that strengthening of the biological pump in the philippine sea and elsewhere in the tropical western pacific during the mid late quaternary glacial periods may contribute to the lowering of atmospheric co2 concentrations during ice ages

a high resolution opal and radiolarian record from the subpolar north atlantic during the mid pleistocene transition 1069 779ka palaeoceanographic implications abstract a high resolution record of radiolarian assemblages from site u1314 was studied to reconstruct hydrographic and climatic changes in the north atlantic ocean during the mid pleistocene transition period 1069 779 ka besides the faunal record absolute accumulation of radiolarians and total biogenic opal are used to determine changes in surface water productivity results show that the north atlantic arctic front shifted back and forth repeatedly at a glacial interglacial timescale bringing the site under the influence of both cold arctic glacial and much warmer atlantic interglacial waters during glacial intervals and ice rafted debris ird events the deep dwelling taxon cycladophora davisiana was the greatest contributor of the radiolarian assemblage suggesting cold surface conditions melt water discharge and changes in deep and intermediate circulation interglacial intervals were characterized by abundant shallow dwelling taxa like pseudodyctiophimus gracilipes and lithomelissa setosa increased opal accumulation and higher radiolarian diversities indicating a northward flow of warm atlantic surface waters to the site u1314 area a marked change in the structure of the radiolarian assemblage occurred after mis 22 860 ka with large taxa differences between warm and cold periods probably in response to changing ocean conditions due to the higher amplitude of glacial interglacial changes as the dominant periodicity of high latitude climate oscillations shifted from 41 kyr to 100 kyr thus we conclude that the radiolarian assemblage from the north atlantic have changed drastically along with variations in ocean circulation in response to orbital and millennial scale climatic variations that occurred in the early and mid pleistocene