millennial scale fluctuations of the european ice sheet at the end of the last glacial and their potential impact on global climate abstract reconstructing northern hemisphere ice sheet oscillations and meltwater routing to the ocean is important to better understand the mechanisms behind abrupt climate changes to date research efforts have mainly focused on the north american laurentide ice sheets lis leaving the potential role of the european ice sheet eis and of the scandinavian ice sheet sis in particular largely unexplored using neodymium isotopes in detrital sediments deposited off the channel river we provide a continuous and well dated record for the evolution of the eis southern margin through the end of the last glacial period and during the deglaciation our results reveal that the evolution of eis margins was accompanied with substantial ice recession especially of the sis and simultaneous release of meltwater to the north atlantic these events occurred both in the course of the eis to its lgm position i e during heinrich stadial hs 3 and hs2 31 29 ka and 26 23 ka respectively and during the deglaciation i e at 22 ka 20 19 ka and from 18 2 0 2 to 16 7 0 2 ka that corresponds to the first part of hs1 the deglaciation was discontinuous in character and similar in timing to that of the southern lis margin with moderate ice sheet retreat from 22 5 0 2 ka in the baltic lowlands as soon as the northern summer insolation increase from 23 ka and an acceleration of the margin retreat thereafter from 20 ka importantly our results show that eis retreat events and release of meltwater to the north atlantic during the deglaciation coincide with amoc destabilisation and interhemispheric climate changes they thus suggest that the eis together with the lis could have played a critical role in the climatic reorganization that accompanied the last deglaciation finally our data suggest that meltwater discharges to the north atlantic produced by large scale recession of continental parts of northern hemisphere ice sheets during hs could have been a possible source for the oceanic perturbations i e amoc shutdown responsible for the marine based ice stream purge cycle or so called he s that punctuate the last glacial period

episodic reductions in bottom water currents since the last ice age although north atlantic deep water formation was greatly reduced during the last glacial maximum bottom water currents were as vigorous as at present however they were weakened during periods of north atlantic surface freshening a strong correlation can be seen between bottom water current strength and greenland air temperature records thus confirming a close connection between ocean circulation and abrupt climate change past changes in the freshwater balance of the surface north atlantic ocean are thought to have influenced the rate of deep water formation and consequently climate1 2 although water mass proxies are generally consistent with an impact of freshwater input on meridional overturning circulation3 there has been little dynamic evidence to support this linkage here we present a 25 000 year record of variations in sediment grain size from south of iceland which indicates vigorous bottom water currents during both the last glacial maximum and the holocene period together with reconstructions of north atlantic water mass distribution vigorous bottom currents suggest a shorter residence time of northern source waters during the last glacial maximum relative to the holocene period the most significant reductions in flow strength occur during periods that have been associated with freshening of the surface north atlantic the short term deglacial oscillations in bottom current strength are closely coupled to changes in greenland air temperature with a minimum during the younger dryas cold reversal and a maximum at the time of rapid warming at the onset of the holocene our results support a strong connection between ocean circulation and rapid climate change

the deglacial evolution of north atlantic deep convection deepwater formation in the north atlantic by open ocean convection is an essential component of the overturning circulation of the atlantic ocean which helps regulate global climate we use water column radiocarbon reconstructions to examine changes in northeast atlantic convection since the last glacial maximum during cold intervals we infer a reduction in open ocean convection and an associated incursion of an extremely radiocarbon 14c depleted water mass interpreted to be antarctic intermediate water comparing the timing of deep convection changes in the northeast and northwest atlantic we suggest that despite a strong control on greenland temperature by northeast atlantic convection reduced open ocean convection in both the northwest and northeast atlantic is necessary to account for contemporaneous perturbations in atmospheric circulation

controls on sr ca in benthic foraminifera and implications for seawater sr ca during the late pleistocene changes in the sr to ca ratio of sea water have important implications for the interpretation of past climate it has proven difficult to interpret sr ca of foraminiferal calcite as a measure of seawater sr ca or as reflecting the influence of deep water carbonate ion saturation co 32 on the incorporation of sr into benthic foraminiferal carbonate here we address this issue by measurements of paired benthic foraminiferal sr ca and b ca a proxy for deep water delta co 32 for core tops from the global ocean and three down cores at different settings during the last glacial textendash interglacial cycle these new data suggest a significant control of deep water delta co 32 on benthic foraminiferal sr ca and that down core shell sr ca variations can be largely accounted for by past deep water delta co 32 changes we conclude that seawater sr ca has likely remained near constant on glacial textendash interglacial timescales during the late pleistocene in agreement with model results with due caution benthic sr ca may be used as an auxiliary proxy for deep water delta co 32 if seawater sr ca is constant

size sorting in marine muds processes pitfalls and prospects for paleoflow speed proxies the basis for and use of fine grain size parameters for inference of paleoflow speeds is reviewed here the basis resides in data on deposited sediment taken in conjunction with flow speed measurements in the field experimental data on suspended sediment transport and deposition and theoretical treatments of the generation of size distributions of deposits from suspension controlled by particle settling velocity and flow speed in the deep sea sorting events occur under resuspension deposition events in benthic storms at flow speeds below 10 15 cm s 1 size in the noncohesive sortable silt 10 63 m range is controlled by selective deposition whereas above that range removal of finer material by winnowing also plays a role the best particle size instruments to measure a flow speed related grain size employ the settling velocity method while laser diffraction sizers can yield misleading results because of particle shape effects potential problems including source effects downslope supply on continental margins spatial variability of flow over bedforms and influence of ice rafted detritus are examined a number of studies using the sortable silt flow speed proxy are reviewed and inverse modeling of grain size distributions is examined outstanding problems are that corroboration is sparse because almost no studies have yet used the full range of proxies for flow rate and water mass identification and that the sortable silt mean size is not yet properly calibrated in terms of flow speed

changes in northeast atlantic hydrology during termination 1 insights from celtic margin s benthic foraminifera abstract using benthic foraminiferal based proxies in sediments from the celtic margin we provide a well dated record across the last deglaciation of the channel river dynamics and its potential impact on the hydrology of intermediate water masses along the european margin our results describe three main periods 1 during the last glacial maximum and before 21 ka bp the predominance of meso oligotrophic species suggests well oxygenated water masses after 21 ka bp increasing proportions of eutrophic species related to enhanced riverine supply occurs concomitantly with early warming in greenland air temperatures 2 a thick laminated deposit occurring during a 1500 years long period of seasonal melting of the european ice sheet eis is associated with early heinrich stadial 1 period 18 2 16 7 ka bp the benthic proxies describe low salinity episodes cold temperatures severe dysoxia and eutrophic conditions on the sea floor perhaps evidence for cascading of turbid meltwaters 3 during late hs1 16 7 14 7 ka bp conditions on the celtic margin s seafloor changed drastically and faunas indicate oligotrophic conditions as a result of the ceasing of eis meltwater discharges while surface waters were cold due to laurentide ice sheet lis icebergs releases increasing benthic mg ca ratios reveal a progressive warming of intermediate water masses whereas oxygen proxies indicate overall well oxygenated conditions in addition to the well known effect of eis meltwaters on surface waters in the celtic margin our benthic record documents a pronounced impact on intermediate water depths during hs1 which coincided with major amoc disruptions

patterns of ice rafted detritus in the glacial north atlantic 40 55 n the observation by heinrich 1988 that during the last glacial period much of the input of ice rafted detritus to the north atlantic sediments may have occurred as a succession of catastrophic events rekindled interest on the history of the northern ice sheets over the last glacial period in this paper we present a rapid method to study the distribution of these events both in space and time using whole core low field magnetic susceptibility we report on approximately 20 cores covering the last 150 to 250 kyr well defined patterns of ice rafted detritus appear during periods of large continental ice sheet extent although these are not always associated within their maxima most of the events may be traced across the north atlantic ocean for the six most recent heinrich layers hl two distinct patterns exist hl1 hl2 hl4 hl5 are distributed along the northern boundary of the glacial polar front over most of the north atlantic between 40 and 50 n hl3 is more restricted to the central and eastern part of the northern atlantic the nd sr isotopic composition of the material constituting different heinrich events indicates the different provenance of the two patterns hl3 has a typical scandinavia arctic icelandic young crust signature and the others have a large component of northern quebec and northern west greenland old crust material these isotopic results obtained on core su 9008 from the north american basin are in agreement with the study by jantschik and huon 1992 who used k ar dating of silt and clay size fractions of an eastern basin core me 68 89 these data confirm the large spatial scale of these events and the enormous amount of ice rafted detritus they represent

new spatial mg ca temperature calibrations for three arctic benthic foraminifera and reconstruction of north iceland shelf temperature for the past 4000 years 1 we have developed cold end mg ca temperature calibrations for three common arctic benthic foraminifera islandiella norcrossi helenae melonis barleeanus and cassidulina neoteretis and compare the three calibrations in a late holocene downcore record 0 4000 cal yr b p the calibration and downcore trends for the three arctic species extend the observation that mg incorporation into benthic foraminifera is species specific for the calibration we use a set of ctd casts bottom water 18oseawater measurements and surface grab samples collected from the iceland margin cruise b997 and the greenland margin cruise bs1191 water depth of sites used ranges from 165 to 656 m while spatial bottom temperature ranges from 0 to 7 c mg ca values ranged from 1 02 to 1 47 for i norcrossi helenae 0 64 to 2 21 for m barleeanus and 0 93 to 1 38 mmol mol for c neoteretis we calibrated mg ca content against isotopic calcification temperature calculated using t 16 9 4 0 18ocalcite corrected for vital effect 18oseawater exponential calibrations for the three species are as follows i norcrossi helenae mg ca 1 051 0 03 exp 0 060 0 011 t m barleeanus mg ca 0 658 0 07 exp 0 137 0 020 t and c neoteretis mg ca 0 864 0 07 exp 0 082 0 020 t on the basis of mg ca in these benthic species the downcore record from core md99 2269 is reconstructed bottom temperature values are interpreted to reflect variable inflow of atlantic and arctic water to the north iceland shelf during the last 4000 cal yr b p all three reconstructions show a decline by 0 1 c per century from circa 1500 0 cal yr b p which coincides with an increase in arctic benthic foraminifera abundances and a rise in sea ice proxies in the same core intriguingly c neoteretis diverges periodically to higher average temperature atlantic water conditions than shown by m barleeanus or i norcrossi helenae which both show arctic water temperature circa 1500 4000 cal yr b p

late cretaceous to miocene volcanism sedimentation and upper crustal faulting and folding in the principal cordillera central chile field and geochronological evidence for protracted arc volcanism and transpressive deformation

thermohaline instability in the north atlantic during meltwater events stable isotope and ice rafted detritus records from core so75 26kl portuguese margin a benthic isotope record has been measured for core so75 26kl from the upper portuguese margin 1099 m water depth to monitor the response of thermohaline overturn in the north atlantic during heinrich events evaluating benthic 18o in ts diagrams in conjunction with equilibrium c fractionation implies that advection of mediterranean outflow water mow to the upper portuguese margin was significantly reduced during the last glacial 15 compared to 30 today the benthic isotope record along core so75 26kl therefore primarily monitors variability of glacial north atlantic conveyor circulation the 14c accelerator mass spectrometry ages of 13 54 07 and 20 46 12 ka for two ice rafted detritus ird layers in the upper core section and an interpolated age of 36 1 ka for a third ird layer deeper in the core are in the range of published 14c ages for heinrich events h1 h2 and h4 marked depletion of benthic 13c by 0 7 1 1 during the heinrich events suggests reduced thermohaline overturn in the north atlantic during these events close similarity between meltwater patterns inferred from planktonic 18o at site 609 and ventilation patterns inferred from benthic 13c in core so75 26kl implies coupling between thermohaline overturn and surface forcing as is also suggested by ocean circulation models benthic 13c starts to decrease 1 5 2 5 kyr before heinrich events hl and h4 fully increased values are reached 1 5 3 kyr after the events indicating a successive slowdown of thermohaline circulation well before the events and resumption of the conveyor s full strength well after the events benthic 13c changes in the course of the heinrich events show subtle maxima and minima suggesting oscillatory behavior of thermohaline circulation a distinct feature of thermohaline instability in numerical models inferrred gradual spin up of thermohaline circulation after hl and h4 is in contrast to abrupt wanning in the north atlantic region that is indicated by sudden increases in greenland ice core 18o and in marine faunal records from the northern north atlantic from this we infer that thermohaline circulation can explain only in part the rapid climatic oscillations seen in glacial sections of the greenland ice core record

north atlantic circulation and reservoir age changes over the past 41 000 years 1 constraints on the timing of atlantic meridional overturning circulation amoc changes during the last deglaciation are fundamental to understanding the climate s rapid response to insolation forcing however uncertainty about high latitude north atlantic hlna radiocarbon reservoir ages has previously precluded robust age model development for this critical region hlna reservoir ages also serve as a proxy for amoc strength we present regionally averaged hlna reservoir ages for 0 to 41 thousand years before the present kyr bp based on over 500 radiocarbon dates from 33 north atlantic cores an early deglacial increase to 1000 14c yr reservoir ages between 18 5 and 16 5 kyr bp suggests reduced amoc before peak heinrich stadial 1 hs1 ice rafted debris ird a rapid decrease in reservoir ages coincident with the ird maximum at 16 kyr bp indicates strong stratification of the upper water column caused by massive freshwater release

the last glacial termination a major puzzle of paleoclimatology is why after a long interval of cooling climate each late quaternary ice age ended with a relatively short warming leg called a termination we here offer a comprehensive hypothesis of how earth emerged from the last global ice age a prerequisite was the growth of very large northern hemisphere ice sheets whose subsequent collapse created stadial conditions that disrupted global patterns of ocean and atmospheric circulation the southern hemisphere westerlies shifted poleward during each northern stadial producing pulses of ocean upwelling and warming that together accounted for much of the termination in the southern ocean and antarctica rising atmospheric co2 during southern upwelling pulses augmented warming during the last termination in both polar hemispheres

progressive reduction in ne atlantic intermediate water ventilation prior to heinrich events response to nw european ice sheet instabilities we present high resolution benthic 13c records from intermediate water depth core site md01 2461 1153 m water depth from the porcupine seabight ne atlantic spanning 43 to 8 kyr b p at an average proxy time step of 160 56 years this core provides information on the linkage between records from the portuguese margin and high latitude north atlantic basin allowing additional insights into north atlantic thermohaline circulation thc variability during millennial scale climatic events of the last glacial together these records document both discrete and progressive reductions in glacial north atlantic intermediate water gnaiw formation preceding heinrich h events 1 2 and 4 recorded through the apparent interchange of glacial northern and southern sourced intermediate water signatures along the european margin close coupling of nw european ice sheet nweis instability and gnaiw formation is observed through transient advances of scw along the european margin concurrent with pulses of ice rafted debris and meltwater release into the ne atlantic between 27 and 16 kyr b p when the nweis was at maximum extent and proximal to last glacial maximum convection zones in the open north atlantic it is such nweis instability and meltwater forcing that may have triggered reduced north atlantic thc prior to collapse of the laurentide ice sheet at h1 and h2 precursory reduction in gnaiw formation prior to h4 may also be inferred however limited nweis ice volume prior to h4 and convection occurring in the norwegian greenland sea require that if a meltwater trigger is invoked as appears to be the case at h1 and h2 the source of meltwater prior to h4 is elsewhere likely higher latitude ice sheets clarification of the sequencing and likely mechanisms of precursory decrease of the north atlantic thc support theories of h event initiation relating to ice shelf growth during cold periods associated with reduced north atlantic thc and subsequent ablation through subsurface warming and sea level rise associated with further reductions in meridional overturning

trophic control of benthic foraminiferal abundance and microhabitat in the bathyal gulf of lions western mediterranean sea surface sediment was sampled at two bathyal sites in the southwestern gulf of lions in the western mediterranean sea in february and august 1997 to study the distribution and microhabitat of living rose bengal stained deep sea benthic foraminifera both standing stock and diversity of the faunas and the microhabitat of distinct species mirror the trophic situation and the depth of the oxidised layer at the different sites our results suggest that the faunas do not comprise highly opportunistic species and are adapted to rather stable environments in the axial channel of the lacaze duthiers canyon organic matter fluxes are enhanced due to advective transport of organic matter resulting in elevated oxygen consumption rates in the surface sediment and a rather thin oxidised layer the corresponding benthic foraminiferal fauna is characterised by rather high standing stock and diversity and a well developed deep infauna in addition to freshly deposited phytodetritus more degraded organic matter seems to be an important food source in contrast at the open slope organic matter fluxes and oxygen consumption rates in the surface sediment are lower and the oxidised layer is much thicker than inside the canyon the corresponding benthic foraminiferal fauna comprises mainly epifaunal and shallow infaunal species with much lower standing stocks and clear differences between february and august in august standing stocks are higher and the average living depths of most species shift towards the sediment surface these differences can be attributed to patchiness or represent a seasonal trophic signal

a critical review of the glaciomarine model for irish sea deglaciation evidence from southern britain the celtic shelf and adjacent continental slope in support of their glaciomarine model for the deglaciation of the irish sea basin eyles and mccabe cited the occurrence of distal glaciomarine mud drapes onshore in the isles of scilly and north devon and of arctic beach face gravels and sands around the shores of the celtic sea glacial and sea level data from the southern part of the irish sea in the terminal zone of the ice stream and the adjacent continental slope are reviewed here to test this aspect of the model the suggestion that the glacial sequences of both the isles of scilly and fremington in north devon are glaciomarine mud drapes is rejected an actively calving tidewater margin only occurred early in the deglacial sequence close to the terminal zone in the south central celtic sea relative sea levels were lower and therefore glacio isostatic depression less than envisaged in the glaciomarine model geochronological sedimentological and biostratigraphical data indicate that the raised beach sequences around the shores of the celtic sea and english channel were deposited at or during regression soon after interglacial eustatic highstands evidence for ice rafting at a time of high relative sea levels is restricted to a phase s earlier than the late devensian these data indicate that the raised beach sequences have no bearing on the style of irish sea deglaciation copyright 2001 john wiley sons ltd

benthic foraminiferal successions across late quaternary mediterranean sapropels abstract benthic foraminiferal records across late quaternary mediterranean sapropels s6 s5 and s1 are reviewed and re considered in the light of recent advances in foraminiferal ecology it is suggested that the main factor controlling the foraminiferal successions that occur immediately before and after sapropel deposition is the amount of time involved in the onset of anoxic conditions and in the re oxygenation of the benthic environment faunas dominated by deep infaunal taxa such as globobulimina and chilostomella reflect a very gradual decrease or increase of bottom water oxygenation post sapropel faunas dominated by small biconvex trochospiral taxa which are inferred to have a much more opportunistic life strategy are typical of a very rapid re oxygenation of the benthic environment after sapropel deposition the time involved in re oxygenation depends upon the mechanism causing sapropel formation the faunal succession found above sapropel s5 suggests a basin with a strong density gradient in the upper part of the water column during sapropel deposition followed by a rapid turnover of the following column and quick re oxygenation of the benthic environment in contrast the faunal succession above sapropel s6 suggests a water column with a more gradual density gradient deeper in the basin a progressive deepening of the halocline and a very slow increase of bottom water oxygenation

high resolution evidence for linkages between nw european ice sheet instability and atlantic meridional overturning circulation published studies show that ice rafted debris ird deposition preceding heinrich h events h1 and h2 in the ne atlantic was derived from the nw european ice sheets nweis possibly offering clues about ice sheet sensitivity and stability and the mechanisms that caused periodic collapse of the laurentide ice sheet lis we present detailed lithological and geochemical records including radiogenic isotope fingerprinting of ird deposits from core md01 2461 proximal to the last glacial british ice sheet bis demonstrating persistent instability of the bis with significant destabilisation occurring 1 5 1 9 kyr prior to both h1 and h2 dated at 16 9 and 24 1 kyr bp respectively in the ne atlantic paired mg ca and 18o data from the surface dwelling globigerina bulloides and subsurface dwelling neogloboquadrina pachyderma sinistral are used to determine late glacial variability of temperature salinity and stratification of the upper water column a picture emerges that the bis was in a continuing state of readjustment and never fully reached steady state increased sea surface temperatures appear to have triggered the episode of nweis instability preceding h1 it seems most probable that the so called precursor events were not linked to the h events however if response to a common thermal forcing is considered an increased response time of the lis up to 2 kyr longer than the nweis may be inferred negative salinity excursions of up to 2 6 indicate significant incursions of melt water associated with peaks in nweis instability decreased surface density led to a more stable stratification of the upper water column and is associated with reduced ventilation of intermediate waters recorded in depleted epibenthic 13c cibicidoides wuellerstorfi we suggest that instability and meltwater forcing of the nweis temporarily weakened atlantic meridional overturning circulation allowing transient advance of southern sourced waters to this site prior to h events 1 and 2

terrigenous fluxes at the celtic margin during the last glacial cycle the sedimentary sections of three cores from the celtic margin provide high resolution records of the terrigenous fluxes during the last glacial cycle a total of 21 14 c ams dates allow us to define age models with a resolution better than 100 yr during critical periods such as heinrich events 1 and 2 maximum sedimentary fluxes occurred at the meriadzek terrace site during the last glacial maximum lgm detailed x ray imagery of core md95 2002 from the meriadzek terrace shows no sedimentary structures suggestive of either deposition from high density turbidity currents or significant erosion two paroxysmal terrigenous flux episodes have been identified the first occurred after the deposition of heinrich event 2 canadian ice rafted debris ird and includes ird from european sources we suggest that the second represents an episode of deposition from turbid plumes which precedes ird deposition associated with heinrich event 1 at the end of marine isotopic stage 2 mis 2 and the beginning of mis 1 the highest fluxes are recorded on the whittard ridge where they correspond to deposition from turbidity current overflows canadian icebergs have rafted debris at the celtic margin during heinrich events 1 2 4 and 5 the highresolution records of heinrich events 1 and 2 show that in both cases the arrival of the canadian icebergs was preceded by a european ice rafting precursor event which took place about 1 1 5 kyr before two rafting episodes of european ird also occurred immediately after heinrich event 2 and just before heinrich event 1 the terrigenous fluxes recorded in core md95 2002 during the lgm are the highest reported at hemipelagic sites from the northwestern european margin the magnitude of the canadian ird fluxes at meriadzek terrace is similar to those from oceanic sites 2002 elsevier science b v all rights reserved

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

breaking characteristics and geometric properties of spilling breakers over slopes abstract a two phase flow cfd model based on the reynolds averaged navier stokes rans equations coupled with the level set method lsm and k turbulence model is used to simulate spilling breakers over a sloping bed in order to validate the present numerical model the simulated results are compared with the experimental data measured by ting and kirby 1996 the simulated horizontal velocities and free surface elevations are in good agreement with the experimental measurements moreover the present model is able to model the prominent features associated with the breaking process such as the motion of air pockets in the water formation of a forward moving jet the splash up phenomenon and the mixing of air and water in the breaking region the numerical model has been utilized to study the influences of three important environmental parameters water depth offshore wave steepness and beach slope on the characteristics and geometric properties of spilling breakers over slopes a total of 39 numerical experiment cases are performed to investigate the characteristics of breaking waves such as breaking location incipient breaker height and water depth at breaking incipient breaker indices and geometric properties with different offshore wave steepnesses at different water depths over a wide range of beach slopes the geometric properties associated with breaking waves in shallow water are described using the wave steepness and asymmetry factors introduced by kjeldsen and myrhaug 1978 the computed results appear to give reasonable predictions and consistency with previous studies

european climatic response to millennial scale changes in the atmosphere ocean system during the last glacial period abstract pollen foraminifer dinocyst and coarse lithic high resolution analyses and 18 o measurements have been carried out for the last glacial section of marine core md95 2042 located near the southwestern margin of the iberian peninsula the pollen data indicate a high frequency of vegetational changes on the adjacent continent during this period suggesting a climatic variability very similar to that of the dansgaard oeschger cycles recorded by the greenland ice cores the detailed direct correlation of the terrestrial and marine proxy data from core md95 2042 indicates a three phase pattern of heinrich events in land and ocean environments the first and last phases of the h5 and h4 events are characterized by a mild and humid climate in southwestern europe probably associated with the european origin of the ice rafted detritus the middle phase exhibits a cold and dry climate in iberia linked with the maximum input of ice rafted detritus this phase seems to correspond with the laurentide ice sheet surges between the heinrich events several cold and dry periods on land are correlated with stades of the dansgaard oeschger cycles the impact of the dansgaard oeschger stades in southwestern europe seems to be preferentially connected to the cold winter air masses reaching this mid latitude region