comments to westaway and bridgland causes consequences and chronology of large magnitude palaeoflows in middle and late pleistocene river systems of northwest europe westaway and bridgland earth surface processes and landforms 35 1071 1094 2010 discuss the causes the consequences and the chronology of large magnitude palaeoflows in pleistocene river systems of northwest europe based on their calculations these authors suggest that the combined effects of meltwater from alpine glaciers rainfall snowmelt and melting of permafrost during heinrich events hes explain the large magnitude discharges of the fleuve manche palaeoriver which punctuated the last glacial period this comment identifies some approximations and inconsistencies regarding i the timing of the last massive fleuve manche palaeoriver discharge and its relation to the de glacial pattern of the british irish ice sheet point 1 ii the palaeoclimatic conditions prevailing on land and the antagonistic forcing mechanism proposed by the authors to explain the large magnitude palaeoflows point 2 iii westaway and bridgland s 2010 revised interpretation of the deep sea records from the bay of biscay point 3 and iv the relationship between the offshore sedimentation since the middle pleistocene and the formation of the dover strait point 4 each point is discussed

initiation of the european deglaciation as recorded in the northwestern bay of biscay slope environments meriadzek terrace and trevelyan escarpment a multi proxy approach three cores retrieved on the northwestern slope of the bay of biscay are described and discussed in the light of the european last deglaciation history this integrated sedimentological and micropalaeontological study provides a detailed evolution scheme for the deep and sea surface conditions of the bay during the final deglacial step with a direct link with the continental palaeoenvironments as early as 15 ka 14c bp a european precursor melting event is recorded as a purge of the channel and irish sea palaeoriver systems pleni heinrich event conditions occurred in the bay of biscay between 14 4 and 13 ka 14c bp with a typical canadian signature only recorded at 14 ka 14c bp namely 1 ka later than the first evidence of melting of the british ice sheet our data demonstrate that following heinrich event 2 the last glacial maximum was characterised by a gradual warming accompanied by at least two pulses of the north atlantic drift these north atlantic drift heat northward penetrations are supposed to have primarily forced the heinrich event 1 collapse

onshore and offshore evidences for four abrupt warming episodes during mis 6 at the westernmost tip of continental europe did they control the migrations of neanderthals the total shell production typical of the pupilla association in the onshore site of nantois brittany france evidenced for the first time four brief abrupt warm and humid episodes during the upper saalian mis 6 loess deposition these warming events were also found in the marine deposits of the celtic sea md03 2692 core comparison with the variations of the sea level show that the warming episodes were not only of regional interest but corresponded to global events ruled by precession and insolation cycles other comparisons with biomarker records mollus s charcoal and rodents of the paris basin villiers adam and jersey island la cotte de saint brolade confirm the existence of these warmer events tentative correlations with the discontinuous neanderthal dwelling phases recorded in brittany suggest that these populations were mainly only present in westernmost europe during the warmer episodes

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

causes consequences and chronology of large magnitude palaeoflows in middle and late pleistocene river systems of northwest europe this study examines the record of high palaeoflow phases in river systems in northwest europe investigating their causes whether due to unique events such as the formation of the dover strait or as characteristic consequences of climate change examining their consequences with regard to landscape evolution and possible effects on climate and determining the chronology of key events large magnitude palaeoflows more than an order of magnitude larger than present day flood peaks are shown to be characteristic of rivers in this region at particular times within the pleistocene these events the most recent of which were during heinrich events 2 and 1 at 25 and 17 ka were evidently caused by the combined effects of glacial outwash rainfall snowmelt and melting of permafrost in some proportion they released such large volumes of water that the thermohaline circulation of the atlantic ocean and thus the climate may well have been affected these large magnitude palaeoflows are thus a significant aspect of the pleistocene earth system that has hitherto gone unquantified

sahel megadrought during heinrich stadial 1 evidence for a three phase evolution of the low and mid level west african wind system abstract millennial scale dry events in the northern hemisphere monsoon regions during the last glacial period are commonly attributed to southward shifts of the intertropical convergence zone itcz associated with an intensification of the northeasterly ne trade wind system during intervals of reduced atlantic meridional overturning circulation amoc through the use of high resolution last deglaciation pollen records from the continental slope off senegal our data show that one of the longest and most extreme droughts in the western sahel history which occurred during the north atlantic heinrich stadial 1 hs1 displayed a succession of three major phases these phases progressed from an interval of maximum pollen representation of saharan elements between 19 and 17 4 kyr bp indicating the onset of aridity and intensified ne trade winds followed by a millennial interlude of reduced input of saharan pollen and increased input of sahelian pollen to a final phase between 16 2 and 15 kyr bp that was characterized by a second maximum of saharan pollen abundances this change in the pollen assemblage indicates a mid hs1 interlude of ne trade wind relaxation occurring between two distinct trade wind maxima along with an intensified mid tropospheric african easterly jet aej indicating a substantial change in west african atmospheric processes the pollen data thus suggest that although the ne trades have weakened the sahel drought remained severe during this time interval therefore a simple strengthening of trade winds and a southward shift of the west african monsoon trough alone cannot fully explain millennial scale sahel droughts during periods of amoc weakening instead we suggest that an intensification of the aej is needed to explain the persistence of the drought during hs1 simulations with the community climate system model indicate that an intensified aej during periods of reduced amoc affected the north african climate by enhancing moisture divergence over the west african realm thereby extending the sahel drought for about 4000 years

deglacial chronology from county donegal ireland implications for deglaciation of the british irish ice sheet in the north of ireland ice advanced northwards onto the continental shelf from inland centres of dispersion at the last glacial maximum we constrain the timing of three subsequent events by accelerator mass spectrometry 14 c dating of marine microfaunas from muds at corvish county donegal early and rapid deglaciation of the continental shelf off northwestern ireland occurred before 17 1 k 14 c years bp when marine muds formed in trawbreaga bay ice subsequently readvanced into the bay some time between 15 0 and 14 0 k 14 c years bp and compressed contemporary sea stacks and beach cobbles into a ridge at ballycrampsey early deglacial muds were deformed during this ice readvance and redeposited with stratigraphically inverted 14 c ages between 16 0 and 15 2 k 14 c years bp the deformed mud is overlain by undeformed laminae deposited during the final deglaciation of the area after 14 1 k 14 c years bp the early deglaciation in the north at c 17 k 14 c years bp is correlative with deglaciation recorded in the irish sea basin western ireland and northeastern scotland indicating a response of the entire british irish ice sheet to early warming of the north atlantic ocean that resulted in a loss of up to two thirds of its mass subsequent ice sheet readvance between 15 0 and 14 1 k 14 c years bp in the north is part of a widespread response of the british irish ice sheet to heinrich event 1 during the killard point stadial high relative sea levels that accompanied deglaciation at 17 k 14 c years bp and again at 14 1 k 14 c years bp indicate substantial loading and attendant isostatic depression by the british irish ice sheet

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

palaeoclimatology and palaeohydrography of the glacial stages on celtic and armorican margins over the last 360000 yrs core md03 2692 was retrieved in a water depth of 4064 m on the celtic margin bay of biscay during the sedicar cruise onboard the rv marion dufresne ii it covers the last 360 ka in a total length of 39 m multidisciplinary analyses have been applied to this sequence with the aim of studying the palaeoclimatic and palaeoenvironmental signals of the last few climatic cycles the analyses undertaken include 1 non destructive logging with physical properties magnetic susceptibility sediment colour x ray radiography and measurement of the major elements by x ray fluorescence 2 analyses of planktonic and benthic foraminifera lithic grains and stable isotopic measurements oxygen and carbon we have focused on the longterm evolution of glacial stages with special attention to terminations and heinrich events the results obtained confirm the close correlation between deep sea sedimentation recorded on the celtic margin and changes in the terrestrial environment of the adjacent continent heinrich layers have been identified in mis 2 3 6 and 8 we note the occurrence of laminated facies within deglacial sequences deposited during termination i and mis 6 these facies are closely linked to disintegration phases of the british irish ice sheet bis the laminations contain lower ice rafted detritus ird concentrations than the equivalent heinrich layers and are linked to abrupt changes in sea surface palaeotemperatures we suggest that the laminations are formed by an annual cycle of meltwater and iceberg release from the disintegrating bis generating cascading plumes of dense turbid meltwater coeval with ird release d 2005 elsevier b v all rights reserved

strain induced phase changes within cold basal ice from taylor glacier antarctica indicated by textural and gas analyses this paper reports detailed textural and gas measurements conducted in cold basal ice 178c from the margin of taylor glacier an outlet glacier of the east antarctic ice sheet the analyzed samples were retrieved from a basal ice sequence excavated at the end of a subglacial tunnel dug near the glacier snout the basal sequence exhibits two contrasting ice facies defined as the englacial and stratified facies on the one hand analysis of ice crystal textures from the basal ice sequence provides evidence for localized ductile deformation especially within the stratified facies where significant dynamic recrystallization was detected on the other hand high resolution gas analyses reveal that strong changes in gas composition occurred at the structural interfaces of the stratified facies these gas composition changes are typical of melting refreezing processes but are not associated with any significant loss of gas volume given the specific subglacial thermal conditions at the margin of taylor glacier we interpret this phenomenon as resulting from microscopic phase changes involving selective gas redistribution through the pre melt phase it is argued that such processes may play an important role in the post genetic geochemical evolution of cold debris laden ice and may be enhanced through intense strain conditions

late quaternary sedimentation patterns on the meriadzek terrace bay of biscay esscamp 02 core 47 n 9 w abstract foraminiferal assemblage changes size and mineralogy of lithic grains oxygen isotopes caco 3 and dolomite content were studied along a 9 m long core from the meriadzek terrace to gain insight into climate productivity and sediment source changes at this part of the northeast atlantic margin during the late quaternary an age model has been generated on the basis of radiocarbon dating downcore foraminiferal assemblages and 18 o values high sedimentation rates at this site allow very detailed records for the last glacial period down to late isotopic stage 3 sea surface temperature sst inferred from the foraminiferal assemblages 18 o curve and the temperature estimation by the simmax analog technique reveal three distinctive periods during isotopic stage 2 with late stage 2 15 3 13 4 ka being the coldest period of the last 26 ka a northward retreat of the polar front at 13 4 ka based on the sst record coincides with the strongest peak of primary productivity as indicated by the foraminiferal fluxes levels rich in large lithic grains llg interpreted as ice rafted debris ird correspond to periods of low sst and are coeval with heinrich layers 1 2 and 3 however the hematite stained quartz found in the detrital fraction and the scarce dolomite and detrital carbonate content in our core point to an iceland and or fenno scandian rather than a laurentian or greenland origin of this material

european contribution of ice rafted sand to heinrich layers h3 and h4 abstract this paper reports the sr nd isotopic composition of the carbonate free sand 63 m 1 mm fraction of heinrich layers 3 and 4 from about 17 cores from the northern atlantic ocean 38 n to 68 n the results indicate that the transporting icebergs were calved from many ice sheets from around the north atlantic at least the fennoscandian icelandic and laurentide our isotopic data show a more distinctly european origin for ice rafted debris ird deposited during the atypical heinrich event h3 than for background ird in contrast heinrich layer h4 a representative of typical heinrich events h1 h2 h4 and h5 presents a clear dominant laurentide signal this result confirms that these typical heinrich events are associated with a massive discharge of icebergs from the laurentide ice sheet however the theory that the laurentide ice sheet set the events into motion alley r b macayeal d r 1993 ice rafted debris associated with binge purge oscillations of the laurentide ice sheet paleoceanography 9 4 503 511 cannot explain the fact that a european signal of an early h4 sample has been observed prior to the laurentide signature of a late h4 sample in the same core along the european margin this observation indicates that the european ice sheets may have surged before the north american ones and suggests that the laurentide ice sheet was not the sole motor behind the heinrich events moreover in the norwegian sea ird has a scandinavian origin in both h3 and h4

compositional variability of ice rafted debris in heinrich layers 1 and 2 on the northwest european continental slope identified by environmental magnetic analyses the composition of ice rafted debris ird within a sediment core from the european continental slope core omex 2k 49 5 n 13 26 w has been examined using environmental magnetic analyses the data demonstrate compositional variability of the ird within heinrich layers 2 h2 and 1 h1 and these differences are most readily explained by changes in the contribution of different ird sources to the core site some ird within the main heinrich layers show magnetic signatures that are similar to ird derived from the laurentide ice sheet found in cores from within the main north atlantic ird belt in contrast other ird rich layers both prior to and within the main heinrich layers demonstrate different magnetic behaviour suggesting a contribution from a non laurentide sourced ird most likely derived from ice streams discharging from northeast atlantic ice sheets such as the british and fennoscandian ice sheets these data are consistent with published compositional data from the same core and given the rapid highly sensitive and non destructive nature of the method suggest that environmental magnetic analysis has considerable potential for characterising ird materials within heinrich layers for the purposes of defining provenance

initiation of fennoscandian ice sheet retreat during the last deglaciation although the retreat history of the southern margin of the laurentide ice sheet during the last deglaciation has been well known for several decades1 3 and recently supported by evidence from accelerator mass spectrometer ams radiocarbon dating of meltwater in the gulf of mexico4 and the north atlantic subtropical gyre5 the retreat history of the fennoscandian ice sheet before 13kyr ago is still poorly documented from ams 14c dating and isotopic analysis of a rapidly deposited series of supra till sediments in the norwegian channel north sea we find that the southern margin of the fennoscandian ice sheet was in retreat by 15 kyr bp before present approximately 2 000 yr earlier than previously supposed oxygen isotope analyses in the channel sediments confirm earlier evidence from deep norwegian sea sediment cores for low salinity due to ice sheet discharge beginning 15 14 5 kyr bp ref 6 recent recalibration of the 14c timescale indicates that the onset of deglaciation within the norwegian sea occurred during an interval of rapidly increasing summer insolation beginning 18 000 calendar yr bp ref 7 suggesting that ice sheet retreat may have been caused by increasing insolation acting on a particularly climate sensitive ice sheet configuration fresh water and icebergs discharged into the norwegian sea at this time reached the north atlantic and may have contributed to a brief interval of extreme oceanic cooling8 and reduced production of north atlantic deep water9 10 these factors may also have helped to briefly reverse the deglaciation trend erie interstade already underway in north america

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

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

long term vegetation climate and ocean dynamics inferred from a 73 500 years old marine sediment core geob2107 3 off southern brazil abstract long term changes in vegetation and climate of southern brazil as well as ocean dynamics of the adjacent south atlantic were studied by analyses of pollen spores and organic walled dinoflagellate cysts dinocysts in marine sediment core geob2107 3 collected offshore southern brazil covering the last 73 5 cal kyr bp the pollen record indicates that grasslands were much more frequent in the landscapes of southern brazil during the last glacial period if compared to the late holocene reflecting relatively colder and or less humid climatic conditions patches of forest occurred in the lowlands and probably also on the exposed continental shelf that was mainly covered by salt marshes interestingly drought susceptible araucaria trees were frequent in the highlands with a similar abundance as during the late holocene until 65 cal kyr bp but were rare during the following glacial period atlantic rainforest was present in the northern lowlands of southern brazil during the recorded last glacial period but was strongly reduced from 38 5 until 13 0 cal kyr bp the reduction was probably controlled by colder and or less humid climatic conditions atlantic rainforest expanded to the south since the lateglacial period while araucaria forests advanced in the highlands only during the late holocene dinocysts data indicate that the brazil current bc with its warm salty and nutrient poor waters influenced the study area throughout the investigated period however variations in the proportion of dinocyst taxa indicating an eutrophic environment reflect the input of nutrients transported mainly by the brazilian coastal current bcc and partly discharged by the rio itajai the major river closest to the core site this was strongly related to changes in sea level a stronger influence of the bcc with nutrient rich waters occurred during marine isotope stage mis 4 and in particular during the late mis 3 and mis 2 under low sea level evidence of nothofagus pollen grains from the southern andes during late mis 3 and mis 2 suggests an efficient transport by the southern westerlies and argentinean rivers then by the malvinas current and finally by the bcc to the study site major changes in the pollen spore and dinocyst assemblages occur with similar pacing indicating strongly interlinked continental and marine environmental changes proxy comparisons suggest that the changes were driven by similar overarching factors of which the most important was orbital obliquity

radiocarbon constraints on readvances of the british irish ice sheet in the northern irish sea basin during the last deglaciation moraines deposited by the dundalk bay ice lobe record two readvances of the irish ice sheet into the northern irish sea basin during the last deglaciation these readvances overrode and incorporated fossiliferous marine muds from the floor of dundalk bay ams 14c dates from monospecific microfaunas obtained from these muds indicate that the earlier clogher head readvance occurred sometime between 15 0 and 14 2 14c ka bp thus identifying a previously unrecognized ice margin fluctuation in the irish sea basin that is correlative with a readvance in northwest ireland the younger readvance occurred after 14 2 14c ka bp and is equivalent to the killard point readvance identified elsewhere in the irish sea basin these readvances occurred during the oldest dryas cold interval and bracket heinrich event 1 raised marine muds that were deposited between ice readvances require that a substantial ice sheet remained on ireland throughout much of the last deglaciation with attendant isostatic depression of at least 110 m

glacial geology and chronology of bishop creek and vicinity eastern sierra nevada california the valley of bishop creek which drains part of the eastern flank of the sierra nevada california contains an unusually well preserved set of middle to late quaternary moraines these deposits have been mapped by previous investigators but they have not been quantitatively dated we used the accumulation of cosmogenic 36 cl to assign a chronology to the maximal glacial positions mapped in the valley our results indicate that the terminal moraines mapped by previous investigators as tahoe were all deposited between ca 165 and ca 135 ka during marine isotope stage mis 6 moraines mapped as tioga were deposited between 28 and 14 ka during mis 2 these can be subdivided into tioga 1 28 24 ka tioga 3 18 5 17 0 ka and tioga 4 16 0 14 5 ka advances no moraines dated to tioga 2 21 19 ka were found presumably because the tioga 3 advance either overrode or fluvially eroded them at 15 0 14 5 ka the tioga 4 glacier retreated abruptly to the crest of the range this was followed by the brief and fairly minor recess peak advance at ca 13 4 ka no holocene advances extended beyond the very restricted limits of ice during the matthes little ice age advance all preserved terminal moraines at lower elevations were deposited during either the tahoe or tioga stades the tahoe terminal moraines are extensive and voluminous whereas the tioga moraines are relatively narrow and have small volumes however this notable difference may be more a result of idiosyncrasies in the local glacial history than the result of differences in the length or intensity of glaciation between the two glacial episodes the history of glacial advances at bishop creek exhibits a strong correspondence to global climate cycles and to paleoclimate events in the north atlantic in particular

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

sea ice cover sea surface salinity and halo thermocline structure of the northwest north atlantic modern versus full glacial conditions abstract seasonal sea ice develops along the eastern continental margins in the northern north atlantic where freshwater and or meltwater outflow are responsible for relatively low salinity in surface waters and very pronounced water mass stratification sea ice constitutes a major parameter in the marine ecosystem since the duration and extent of its seasonal spreading constrain the plankton distribution and the related microfossil assemblages on the sea floor organic walled dinoflagellate cysts that are highly resistant to dissolution were recovered from surface sediments of the northern north atlantic and used to develop transfer functions best analogue method for the reconstruction of the seasonal spreading and duration of sea ice cover in addition to salinity and temperature of the warmest month of the year application of the best analogue approach to cores from the labrador sea reveals large variations in sea ice cover and sea surface conditions throughout the last glacial stage and during the early holocene isotopic analyses in epipelagic and mesopelagic planktonic foraminifers also suggest important changes in salinity and temperature gradients between the surface and sub surface water masses specific study of the last glacial maximum lgm time slice 16 20 ka on a 14 c time scale in the northwestern north atlantic shows much more extensive sea ice than at present with perennial sea ice lying along the continental margins of eastern canada seasonal spreading of the cover of sea ice offshore was accompanied by large seasonal contrasts in temperature with very cold winters but relatively warm summers a pattern linked to strong stratification between a buoyant low saline surface layer having a low thermal inertia and the underlying intermediate oceanic waters

holocene paleoceanography of the bay of biscay evidence for west east linkages in the north atlantic based on dinocyst data abstract paleoceanographical changes during the holocene were reconstructed from the study of core md95 2002 situated in the northern bay of biscay which is marked by the direct influence of the northeastern return branch of the north atlantic drift palynological data sea surface condition estimates based on dinocyst assemblages and stable isotope measurements in planktic and benthic foraminifera reveal a strong influence of freshwater meltwaters from both the proximal european sources and the more distal laurentide ice sheet which experienced delayed deglaciation the data also indicate the setting of a climate optimum between 7 and 5 5 ka followed by a cooling trend which is consistent with insolation changes and other regional records of climate changes superimposed on the long term trends the reconstructions of sea surface conditions evidence large amplitude changes at centennial to millennial time scales with seven episodes of cooling and low salinity since 11 ka that generally match episodes of dense sea ice cover in the labrador sea the west to east transfer of the sea ice and or meltwater signal across the north atlantic evidenced from core md95 2002 points to strong linkages between western and eastern north atlantic probably in relation to the north atlantic oscillation nao mode of variability

simulation of ocean ice sheet interactions during the last deglaciation 1 the last deglaciation between 21 thousand years bp kyr bp and 8 kyr bp was punctuated by a series of climatic oscillations both in the northern and southern hemispheres often attributed to changes in ocean circulation these oscillations are explored with an earth system model of intermediate complexity including a synchronous coupling between atmosphere ocean and ice sheet dynamics we focused more particularly on the impact of heinrich event 1 he1 on the deglaciation process representation for he1 was achieved by a parameterization of iceberg discharge included in the ice sheet model based on paleoceanographic evidence the model simulates the following sequence in response to the he1 1 the thermohaline circulation is drastically reduced as soon as he1 starts causing a sharp cooling in the north atlantic and a smooth warming in the southern hemisphere 2 circulation restarts abruptly at the end of he1 producing an intense warming in both hemispheres up to 10degreesc warming in the greenland north atlantic area with a rapidly decreasing amplitude as one moves southward 3 along with this warming the melting of the north american and eurasian ice sheets is enhanced producing a small freshwater discharge to the north atlantic but there is no significant impact on atlantic salinity and thermohaline circulation 4 a few decades after the post heinrich warm event both the southern atlantic and antarctica entered a prolonged cold period caused by the reactivation of the thermohaline circulation 5 finally about 1500 years later depending on sensitivity experiments meltwater flowing into the north atlantic through the hudson strait and the barents sea causes a gradual vertical stratification of the northern north atlantic the presented simulations are compared to paleoarchives by taking into account the limits inherent to the model structure one of the conclusions is that there is probably no direct link between the meltwater pulse 1a observed in sea level data and the onset of the younger dryas

reconstruction of sea surface conditions at middle to high latitudes of the northern hemisphere during the last glacial maximum lgm based on dinoflagellate cyst assemblages abstract a new calibration database of census counts of organic walled dinoflagellate cyst dinocyst assemblages has been developed from the analyses of surface sediment samples collected at middle to high latitudes of the northern hemisphere after standardisation of taxonomy and laboratory procedures the database comprises 940 reference data points from the north atlantic arctic and north pacific oceans and their adjacent seas including the mediterranean sea as well as epicontinental environments such as the estuary and gulf of st lawrence the bering sea and the hudson bay the relative abundance of taxa was analysed to describe the distribution of assemblages the best analogue technique was used for the reconstruction of last glacial maximum lgm sea surface temperature and salinity during summer and winter in addition to sea ice cover extent at sites from the north atlantic n 63 mediterranean sea n 1 and eastern north pacific n 1 three of the north atlantic cores from the continental margin of eastern canada revealed a barren lgm interval probably because of quasi permanent sea ice six other cores from the greenland and norwegian seas were excluded from the compilation because of too sparse assemblages and poor analogue situation at the remaining sites n 54 relatively close modern analogues were found for most lgm samples which allowed reconstructions the new lgm results are consistent with previous reconstructions based on dinocyst data which show much cooler conditions than at present along the continental margins of canada and europe but sharp gradients of increasing temperature offshore the results also suggest low salinity and larger than present contrasts in seasonal temperatures with colder winters and more extensive sea ice cover whereas relatively warm conditions may have prevailed offshore in summer from these data we hypothesise low thermal inertia in a shallow and low density surface water layer

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

the first estimation of fleuve manche palaeoriver discharge during the last deglaciation evidence for fennoscandian ice sheet meltwater flow in the english channel ca 20 18 ka ago the fleuve manche english channel palaeoriver represents the largest river system that drained the european continent during pleistocene lowstands particularly during the elsterian marine isotope stage 12 and saalian drenthe mis 6 glaciations when extensive ice advances into the north sea area forced the central european rivers to flow southwards to the bay of biscay ne atlantic numerous long piston cores and high resolution acoustic data from the northern bay of biscay have been correlated using a well constrained chronostratigraphical framework and for the first time allow the estimation of the discharge of the fleuve manche palaeoriver at the end of the last glacial period i e weichselian our results discussed in the light of relationships between river loads and drainage area characteristics strongly suggest that the bay of biscay collected sediment laden meltwater from the northern european lowlands and the southern part of the fennoscandian ice sheet at the end of the last glacial period and particularly during the paroxysmal phase of the european deglaciation ca 20 18 ka ago this demonstrates that the fleuve manche drainage area at that time was equivalent to those dating from the major elsterian and saalian drenthe glaciations based on our data we propose a revision of the palaeogeographical and palaeoglaciological evolution of the north sea area while showing that the british and fennoscandian ice sheets entered the north sea basin until ca 18 ka initiating isostatic adjustment of the basin this allowed the north sea fluvial system to flow southwards through the dover strait finally we discuss the fleuve manche freshwater discharge during the maximum european ice sheet retreat ca 18 ka the estimated discharge at this time appears important and sufficiently sustained to possibly contribute to the profound destabilisation of the thermohaline circulation recognised in the north atlantic from ca 18 to 16 ka

ice sheet variability around the north atlantic ocean during the last deglaciation millennial scale variability in the flux of ice rafted detritus to north atlantic sediments during the last glacial period has been interpreted to reflect a climate forced increase in the discharge of icebergs from ice sheet margins surrounding the northern north atlantic ocean 1 but the relationship between ice sheet variability and climate change is not clear as both the sources of ice rafted detritus and the ice marginal processes are varied and complex 2 4 terrestrial records are helpful in unravelling this complexity because they can demonstrate the scale of ice sheet oscillations and whether the ice sheet or sector was advancing or retreating with respect to climate change here we constrain the age and anatomy of a prominent readvance of the british ice sheet in the northern irish sea region at similar to 14 14 c kyr bp similar to 16 4 calendar kyr bp the analysis indicates that the british ice sheet participated in an iceberg discharge episode known as heinrich event 1 comparison with other terrestrial and marine ice sheet records suggests that the dynamic collapse of the laurentide ice sheet beginning at 14 6 15 0 c 14 kyr bp1 4 similar to 17 2 17 6 calendar kyr bp 5 initiated varied responses from other ice sheet margins around the northern north atlantic region these observations support the argument that the release of icebergs and meltwater during heinrich event 1 disrupted the north atlantic thermohaline circulation 6 8 leading to a delay or reversal of deglaciation of the northern hemisphere and at least as far south as 40 degrees s for two to three thousand years 5 9 10 suggesting a climate forcing and response similar to that of the ensuing younger dryas cold snap 11 12

palaeoceanographic and palaeoclimatic changes during the last 37 000 years detected in the se bay of biscay based on benthic foraminifera abstract benthic foraminifera assemblages from a sedimentary core pp10 12 701 mwd from the se bay of biscay allow us to trace palaeoceanographic and palaeoclimatic changes occurred in this region during mid mis 3 marine isotope stage 3 and mis 1 interval 37 2 4 ka bp results are based on 176 benthic foraminifera species considering their ecology the difference between autochthonous allochthonous preservation and oxygen rates thus evidencing climatic and oceanographic events mis 3 is characterised by waters with a dominance of cassidulina laevigata and uvigerina peregrina by the end of this interval waters became colder and less oxygenated indicated by the occurrence of melonis affinis these conditions persisted at the beginning of mis 2 the heinrich event 1 h1 is well registered in this core with three intervals h1a h1s s h1b where hyalinea balthica dominates during h1s s the coldest waters are registered and the environment was unstable these conditions continued during h1b when the occurrence of globobulimina affinis evidences some intervals with anoxia during bolling allerod b a waters were warmer and low ventilated indicated by bulimina gibba cassidulina laevigata dominates the younger dryas yd and the beginning of lower holocene evidencing the occurrence of cool waters with low oxygen and high organic matter content the lower to middle holocene transition is registered as a cold interval holocene cooling event hce 5 from the middle holocene onward water temperature were milder based on the dominance of uvigerina peregrina

metamorphic evolution of the kamuikotan high pressure and low temperature metamorphic rocks in central hokkaido japan the kamuikotan complex in the sorachi yezo belt located in central hokkaido japan has been extensively subjected to subduction related high pressure and low temperature metamorphism on the basis of geological petrological and geochronological data the coherent metamorphic rocks are divided into six units as follows susunai horokanai harushinai biei pankehoronai and shizunai based on their metamorphic mineral sequences the six units can be classified into the following three baric types high pressure 1 hp1 high pressure 2 hp2 and high pressure intermediate hi the horokanai and shizunai units belong to the hp1 type the harushinai and biei units belong to the hp2 type and the susunai and pankehoronai units belong to the hi type metabasites of the hp1 type are defined by the association of lawsonite na amphibole or epidote na amphibole glaucophane or crossite the hp2 type is characterized by the assemblage of pumpellyite na pyroxene chlorite and the representative low variance asssemblages are lawsonite pumpellyite na pyroxene chlorite and pumpellyite na pyroxene na amphibole chlorite in the hi type the most common low variance assemblage is pumpellyite epidote actinolite chlorite these results together with the previously published k ar and 40ar 39ar ages suggest that the kamuikotan metamorphic rocks gradually decreased in pressure during the cretaceous this tendency indicates an increase in the kamuikotan subduction geotherm during early cretaceous to early eocene time the increase in the paleogeotherm may result from the change of subduction rates and subducting slab ages

a salt oscillator in the glacial atlantic 1 the concept as shown by the work of dansgaard and his colleagues climate oscillations of one or so millennia duration punctuate much of glacial section of the greenland ice cores these oscillations are characterized by 5 c air temperature changes severalfold dust content changes and 50 ppm co2 changes both the temperature and co2 change are best explained by changes in the mode of operation of the ocean in this paper we provide evidence which suggests that oscillations in surface water conditions of similar duration are present in the record from a deep sea core at 50 n based on this finding we suggest that the greenland climate changes are driven by oscillations in the salinity of the atlantic ocean which modulate the strength of the atlantic s conveyor circulation

interhemispheric appraisal of the value of alkenone indices as temperature and salinity proxies in high latitude locations alkenone sediment data from the nordic seas and north atlantic are compared to those from sikes et al 1997 for the southern ocean to evaluate further uk37 and uk37 as proxies to estimate cold temperatures 10 c and the effect of salinity and temperature in the relative abundance of 37 4 to the total abundance of c37 alkenones 37 4 uk37 and uk37 are found to be equally viable as proxies but there are significant regional differences in their cold temperature dependence the measurement of 37 4 in cores from the north atlantic region can be used to identify situations when uk37 is not a reliable paleothermometer variations in salinity are probably responsible for changes in the sedimentary record of 37 4 and a preliminary calibration has been obtained for 37 4 f salinity this new relationship should be further confirmed through field or laboratory experiments but it paves the way to derive a molecular proxy to reconstruct paleosalinity in surface waters

two phase structure of tropical hydroclimate during heinrich stadial 1 and its global implications abstract previous studies have proposed that the two phase structure of heinrich stadial 1 hs1 is a ubiquitous feature however few studies have focused on the internal structure of hs1 over a tropical domain thus the interhemispheric ocean atmosphere teleconnections during hs1 are poorly defined here we present high resolution sedimentological geochemical and palaeoceanographic records from the core cg2 in the southern south china sea scs off the northern sunda shelf the core continuously spans 9 0 22 0 ky bp the records suggest two episodes of increased monsoon rainfall during the pre hs1 19 0 18 0 ky bp and in the early hs1 17 5 16 1 ky bp along with a weaker monsoon rainfall during the late hs1 16 1 14 7 ky bp in contrast a lower precipitation over the flores sea occurred during the early hs1 off the southern sunda shelf followed by an enhanced precipitation runoff during the late hs1 muller et al 2012 notably these two different precipitation phases characterise a southward intertropical convergence zone itcz shift over the sunda shelf during hs1 these changes are also consistent with other monsoon records as well as other available data from the tropical to high latitudes of both hemispheres supporting the global scope of the twofold hs1 we propose that the two episodes of intense monsoon rainfall over the northern sunda shelf during the pre hs1 and the early hs1 observed in our study are closely linked to two different melting events associated with european ice sheet eis retreat we further propose that the subsequent maximum atlantic meridional overturning circulation amoc reduction and the migration of the itcz to its southernmost position during the late hs1 are tightly connected with the destabilization of the marine terminating ice streams of the laurentide ice sheet lis in the north atlantic tropical positive feedbacks during hs1 in turn should have played an important role in sustaining the amoc reduction and northern hemisphere nh stadial conditions by continuously lowering the salinity of the low latitude currents in the atlantic ocean in addition the tropical itcz appears to have been a key bridge in promoting interhemispheric climate connections by which north atlantic cooling was rapidly linked to increased southern ocean surface westerlies this in turn drove upwelling and co2 ventilation from the southern ocean and thereby facilitated deglacial warming finally these findings show that tropical climate variation is an important component of deglacial climate changes understanding how it responds to millennial events like hs1 may help us better understand global teleconnections

were the north atlantic heinrich events triggered by the behavior of the european ice sheets theories explaining the origin and distribution of heinrich layers abrupt massive discharges of ice rafted detritus generally attribute these layers to the laurentide ice sheet however doubt has been cast by the discovery that sediments also originated from european ice sheets here we present isotopic sr nd fingerprints of heinrich layers obtained in cores from the european margin they reveal that for most of the heinrich layers the icebergs were calved first from the european ice sheets predating the laurentide surges accelerator mass spectrometry 14c ages reveal that the oceanic heinrich events were synchronous with their dust equivalents in the greenland ice cores implying a direct ocean atmosphere link the typical laurentide surge seems to have occurred over a short time span after about 1 5 k y of iceberg release from the european ice sheets this suggests that the laurentide ice sheet responded to a stimulus created by events in the european sector

external controls on turbidite sedimentation on the glacially influenced armorican margin bay of biscay western european margin abstract sequence stratigraphic models predict increased sediment delivery to deep water areas during sea level lowstand the armorican margin bay of biscay western european margin is an interesting area to test this hypothesis because the margin has a wide continental shelf still partly flooded during sea level lowstand and the armorican turbidite system has experienced fluctuating sediment fluxes since the last glacial period the stratigraphic response of the armorican turbidite system to sea level oscillations and climate changes was assessed for the last 35 000 years through the study of the guilcher crozon and audierne levees millennial timescale resolution chronostratigraphy allowed us to reconstruct the sediment accumulation and turbidite frequency thickness and grain size over this period of time we found that the armorican turbidite system was sediment starved during highstand conditions ca 8 0 ka and that glacial conditions favoured sediment delivery to the deep bay of biscay however contrary to what would be expected from sequence stratigraphic models the turbidite flux did not reach a maximum during the lgm lowstand ca 26 20 ka but at the onset of termination i between ca 20 and 17 ka this makes the armorican turbidite system a transgression dominated one this sediment pulse can be interpreted as a huge increase in the meltwater discharge of the fleuve manche palaeoriver in response to the decay of the british and fennoscandian ice sheets at that time despite the rising sea level a large deltaic system had to have developed on the outer shelf leading to the delivery of the fleuve manche sediment load into the canyon heads on the other hand our dataset suggest that the delivery of sediment into canyons was mainly forced by the winnowing and reworking of the sediment stored on the wide drowned shelf during the last glacial period between ca 35 and 20 ka and between 17 and 8 ka these findings illustrate the competing influences of accommodation and sediment supply on the armorican margin over the last 35 000 years with a shelf acting as a buffer for the sediment supply signal for most of the period except during the last deglaciation at that time the western european sediment routing system was reactive the climatic signal rapidly propagated from the southern limb of the european ice sheet to the armorican turbidite system finally our study demonstrates that precise reconstruction of turbidite flux in deep water areas added to knowledge about the morphology of the margin and the palaeoenvironmental changes fluvial system shoreline position etc are crucial for determining the response of turbidite systems to external forcing

contrasting sea surface responses between the western mediterranean sea and eastern subtropical latitudes of the north atlantic during abrupt climatic events of mis 3 abstract dinoflagellate cyst dinocyst analysis was conducted on two cores from the sw iberian margin and central alboran sea from which high quality records of marine isotope stage 3 have been previously derived our aim in this study is to compare the dinocyst signature between 50 and 25 ka bp with existing datasets of foraminiferal and geochemical proxies related to hydrological parameters quantitative reconstructions of sea surface temperatures ssts and salinities sss based on dinocysts are performed for the first time in this area the results are compared to ssts derived from planktonic foraminifera and alkenone measurements and to sss calculated from planktonic 18 o and foraminiferal sst significant oscillations related to dansgaard oeschger cycles are recorded in both cores dinocyst derived hydrological parameters exhibit synchronous fluctuations and similar values to those derived from the other methods in particular when considering quantitative reconstructions for february based on foraminifera and dinocysts our study shows that the influence of subpolar waters was felt during each greenland stadial gs off portugal and that the amplification of the heinrich stadial cooling in the alboran sea was related to the penetration of subpolar waters through the strait of gibraltar during greenland interstadials gi we provide evidence for the occurrence of warm and nutrient rich sea surface waters in the alboran sea probably due to gyre induced upwelling finally the difference between august and february dinocyst sst estimates suggests higher seasonal contrasts during gs compared to gi at the two core sites additionally precession appears to have an imprint on dinocyst derived long term seasonality record however this observation needs to be confirmed by longer records

tide and wave dynamics on a sand bank from the deep shelf of the western channel approaches abstract the sedimentary response of deep shelf sediments to the interplay of tides and waves based on the example of the celtic sea sand banks is described grab samples and 1500 km of multibeam and side scan data have been collected from the 300 km2 densely surveyed kaiser bank area the bank is 140 170 m deep 30 m high and 60 km long oriented perpendicular to the shelf edge and nearly parallel to the major axis of the tidal ellipse surficial sediments of the bank consist of medium to gravely biolithoclastic sands they are swept by tidal currents that reach 0 9 m s 1 m above the seabed and under the occasional influence of waves the mobile sands are commonly bedformed and rest on a highly backscattering lag the flanks below 140 m mainly exhibit transverse tidal dunes and sand ribbons whereas the top of the bank mostly displays discontinuous sand patches and wave ripples the sand patches are interpreted as the remnants of tidal bedforms reworked by waves calculations of the threshold of motion of four modal grain sizes under various conditions at the seabed show that tidal bedforms are active during spring tides sometimes associated with waves whereas only the largest annual waves may explain the observed wave ripples as in active tidal banks there is a reversal of tidal bedload transport from one bank side to the other the sedimentation rate is very low on the kaiser bank in addition there is a loss of sediment at both bank extremities and the tidal bedload cross bank transfer is very small probably controlled by shelf residual currents and long term drift of sediment resuspended by waves however the present day action of waves at the bank top is less intense than it was at lower sea levels during the holocene as evidenced by seismic studies

growth dynamics and deglaciation of the last british irish ice sheet the deep sea ice rafted detritus record the evolution and dynamics of the last british irish ice sheet biis have hitherto largely been reconstructed from onshore and shallow marine glacial geological and geomorphological data this reconstruction has been problematic because these sequences and data are spatially and temporally incomplete and fragmentary in order to enhance biis reconstruction we present a compilation of new and previously published ice rafted detritus ird flux and concentration data from high resolution sediment cores recovered from the ne atlantic deep sea continental slope adjacent to the last biis these cores are situated adjacent to the full latitudinal extent of the last biis and cover marine isotope stages mis 2 and 3 age models are based on radiocarbon dating and graphical tuning of abundances of the polar planktonic foraminifera neogloboquadrina pachyderma sinistral nps to the greenland gisp2 ice core record multiple ird fingerprinting techniques indicate that at the selected locations most ird are sourced from adjacent biis ice streams except in the centre of heinrich h layers in which ird shows a prominent laurentide ice sheet provenance ird flux data are interpreted with reference to a conceptual model explaining the relations between flux north atlantic hydrography and ice dynamics both positive and rapid negative mass balance can cause increases and prominent peaks in ird flux first order interpretation of the ird record indicates the timing of the presence of the biis with an actively calving marine margin the records show a coherent latitudinal but partly phased signal during mis 3 and 2 published data indicate that the last biis initiated during the mis 5 4 cooling transition renewed growth just before h5 46 ka was succeeded by very strong millennial scale variability apparently corresponding with dansgaard oeschger do cycles closely coupled to millennial scale climate variability in the north atlantic region involving latitudinal migration of the north atlantic polar front this indicates that the previously defined precursor events are not uniquely associated with h events but are part of the millennial scale variability major growth of the ice sheet occurred after 29 ka with the barra ice stream attaining a shelf edge position and generating turbiditic flows on the barra donegal fan at 27 ka the ice sheet reached its maximum extent at h2 24 ka earlier than interpreted in previous studies rapid retreat initially characterised by peak ird flux during greenland interstadial 2 23 ka was followed by readvance between 22 and 16 ka readvance during h1 was only characterised by biis ice streams draining central dome s of the ice sheet and was followed by rapid deglaciation and ice exhaustion the evidence for a calving margin and ird supply from the biis during greenland stadial 1 younger dryas event is equivocal the timing of the initiation maximum extent deglacial and readvance phases of the biis interpreted from the ird flux record is strongly supported by recent independent data from both the irish sea and north sea sectors of the ice sheet

high frequency environmental changes and deposition processes in a 2 kyr long sedimentological record from the cap breton canyon bay of biscay the core md03 2693 43 39 258 n 01 39 805 w 431 m water depth was collected on an abandoned meander of the capbreton canyon se bay of biscay filled over the last millennia by very high sedimentation rates mean sedimentation rate of 1 2 cm yr linked to its specific environmental location and fine grained clayed sediment decantation from the proximal canyon axis this archive thus permits to undertake the study of late holocene regional climatic patterns at a decadal temporal resolution in the present work we use data derived from planktonic foraminifera assemblages coupled to a multiproxy approach that associates grain size measurements x ray fluorescence xrf elemental analysis and stable oxygen isotope on globigerina bulloides shells to infer sea surface temperature sst and sea surface salinity sss changes over the last two millennia signals reconstructed in the bay of biscay show significant oscillations that are consistent with well known temperature anomalies such as the little ice a

depositional facies of late pleistocene heinrich events in the labrador sea late pleistocene heinrich ice rafting events produced layers rich in ice rafted debris in major parts of the north atlantic north of 40 n a high detrital carbonate content points to the hudson strait outlet of the laurentide ice sheet as a dominant source of the icebergs heinrich events were coupled with short term climate fluctuations during the last and penultimate glaciations and provide evidence for cryosphere hydrosphere atmosphere interaction in pleistocene climate change an unsolved problem with heinrich layers has been their high concentration of fine grained detrital carbonate 80 of the total detrital carbonate which cannot have been delivered by icebergs alone we propose combinations of different processes that deposited four sedimentologically different types of heinrich layers ice rafting alone for the coarser sand to gravel sized fractions and the fine fractions in distal regions type iv heinrich layers whereas nepheloid flows deposited the bulk of the fine sediment in regions proximal to the hudson strait type i heinrich layers on the labrador slope turbidity currents spilling over from canyons were also involved in transporting the fine grained carbonate rich material causing an alternation of mud turbidites and thin laminae of ice rafted debris in type ii heinrich layers on the levees of the northwest atlantic mid ocean channel the thickness relationship is reversed mud turbidites deposited by occasional spillover of currents from the channel are thin and alternate with thicker laminae of ice rafted debris type iii heinrich layers

a 1 2 ma record of glaciation and fluvial discharge from the west european atlantic margin abstract the correlation of continental sedimentary records with the marine isotope stratigraphy is a challenge of central importance in quaternary stratigraphy particularly in western europe where long records of glaciation on land areas are particularly rare here we demonstrate for the first time the interrelationship of events during the last 1 2 ma in an ocean sediment core from the bay of biscay ne atlantic sw of the channel the identification of discharge variations from tributary river systems to the fleuve manche palaeoriver during glacio eustatic sea level lowstands demonstrates the correlation of the marine sediment stratigraphy to the expansion and recession of the european ice sheets the amplitude and chronology of european ice sheet oscillations since the late early pleistocene is discussed and our results demonstrate that the first coalescence of the fennoscandian and british ice sheets in the north sea basin ca 450 ka ago caused a profound change in lowstand european drainage alignment this change caused a rerouting of fennoscandian and eastern british ice sheets derived meltwaters from northwards into the nordic seas to southwards into the eastern north atlantic thereafter besides allowing a thorough synchronisation of the european ice sheet palaeogeography with the well dated records of palaeoceanographical changes our results improve the stratigraphy of the english channel palaeovalleys and will provide important constraints on paleoclimatic scenarios considering the impact that such rerouting and meltwater surges might have on the stability of the oceanic conveyor belt

a new concept for the paleoceanographic evolution of heinrich event 1 in the north atlantic new records of planktonic foraminiferal 18o and lithic and foraminiferal counts from eirik drift are combined with published data from the nordic seas and the ice rafted debris ird belt to portray a sequence of events through heinrich event 1 h1 these events progressed from an onset of meltwater release at not vert similar19 ka bp through the conventional h1 ird deposition phase in the ird belt starting from not vert similar17 5 ka bp to a final phase between 16 5 and not vert similar15 ka bp that was characterised by a pooling of freshwater in the nordic seas which we suggest was hyperpycnally injected into that basin after not vert similar15 ka bp this freshwater was purged from the nordic seas into the north atlantic which preconditioned the nordic seas for convective deep water formation this allowed an abrupt re start of north atlantic deep water nadw formation in the nordic seas at the bolling warming 14 6 ka bp in contrast to previous estimates for the duration of h1 i e 1000 years to only a century or two the total combined composite h1 signal presented here had a duration of over 4000 yrs not vert similar19 14 6 ka bp which spanned the entire period of nadw collapse it appears that deep water formation and climate are not simply controlled by the magnitude or rate of meltwater addition instead the location of meltwater injections may be more important with nadw formation being particularly sensitive to surface freshening in the arctic nordic seas

late glacial warming prior to heinrich event 1 the influence of ice rafting and large ice sheets on the timing of initial warming high resolution faunal isotopic and sedimentologic data from north atlantic core v29 191 show that sea surface temperatures increased from 17 5 to 17 3 ka prior to the heinrich event 1 h1 ice rafting event ca 17 16 ka these new data support previous studies that showed that warming predated the extensive climatic warming ca 15 9 ka this relationship indicates that h1 occurred after warming had begun loss of latent heat during iceberg melting created near glacial sea surface temperatures during h1 and kept much of the subpolar north atlantic cold despite increasing northern hemisphere insolation the cold ocean conditions influenced proximal terrestrial climates and may also have affected remote regions

grain size and srnd isotopes as tracer of paleo bottom current strength northeast atlantic ocean abstract a crucial question in modern paleoceanographic research is how vigourous was the bottom current in the glacial north atlantic ocean distribution of sediment grain size can provide such information if the characteristics of the source functions are known the interest of this paper is to use the sr nd isotopic composition of lithic particles as a tracer of origin in order to determine possible changes in the source function over the last 185 kyr grain size distribution data are derived from a sediment core in the icelandic basin gardar drift the distribution pattern reveals a well sorted silt size modal size 20 m in the glacial deposits sr and nd isotopic composition measured on separate size fractions indicates a more constant local origin iceland for the silt fraction than for the fine fraction these data suggest that the increase in the silt fraction during glacial periods is related primarily to an increase in the bottom current strength rather than to changes in sediment supply i e ice rafting turbidity current the increase in vigour of the bottom current recorded during the isotopic stages 6 4 and the last post glacial periods could have been initiated by a southward shift of the zone of deep water formation in the northern part of the icelandic basin

evidence for heinrich event 1 in the british isles in the north irish sea basin isb sedimentary successions constrained by ams 14c dates obtained from marine microfaunas record three major palaeoenvironmental shifts during the last deglacial cycle i marine muds cooley point interstadial dated to between 16 7 and 14 7 14c kyr bp record a major deglaciation of the isb following the late glacial maximum lgm ii terminal outwash and ice contact landforms killard point stadial were deposited during an extensive ice readvance which occurred after 14 7 14c kyr bp and reached a maximum extent at ca 14 14c kyr bp at this time the lowlands surrounding the north isb were drumlinised coeval flowlines reconstructed from these bedforms end at prominent moraines killard point bride st bees and indicate contemporaneity of drumlinisation from separate ice dispersal centres substrate erosion by fast ice flow and subglacial sediment transfer to ice sheet margins in north central ireland bed reorganisation associated with this fast ice flow phase involved overprinting and drumlinisation of earlier transverse ridges rogen type moraines by headward erosion along ice streams that exited through tidewater ice margins this is the first direct terrestrial evidence that the british ice sheet bis participated in heinrich event 1 h1 iii regional mud drapes directly overlying drumlins record high relative sea level rsl with stagnation zone retreat after 13 7 14c kyr bp rough island interstadial elsewhere in lowland areas of northern britain ice marginal sediments and morainic belts record millennial scale oscillations of the bis which post date the lgm advance on to the continental shelf and pre date the loch lomond stadial younger dryas advance in the highlands of western scotland ca 11 10 14c kyr bp in western northwestern and northern ireland killard point stadial h1 ice limits are reconstructed from ice flow lines that are coeval with those in the north isb and end at prominent moraines on the scottish continental shelf possible h1 age ice limits are reconstructed from dated marine muds and associated ice marginal moraines it is argued that the last major offshore ice expansion from the scottish mountains post dated ca 15 14c kyr bp and is therefore part of the h1 event in eastern england the stratigraphic significance of the dimlington silts is re evaluated because evidence shows that there was only one major ice oscillation post dating ca 18 14c kyr bp in these lowlands in a wider context the sequence of deglacial events in the isb widespread deglaciation of southern part of the bis major readvance during h1 ice sheet collapse is similar to records of ice sheet variability from the southern margins of the laurentide ice sheet lis well dated ice marginal records however show that during the killard point readvance the bis was at its maximum position when retreat of the lis was well underway this phasing relationship supports the idea that the bis readvance was a response to north atlantic cooling induced by collapse of the lis 1998 john wiley sons ltd

multi process generated sediment waves on the landes plateau bay of biscay north atlantic detailed analyses of recently collected bathymetric and sparker seismic data support a new interpretation of the landes plateau field of sediment waves located on the aquitaine upper continental slope bay of biscay the wave geometry previously described as the result of a major sediment failure is interpreted as a structure with a complex origin including the interaction of depositional and gravity deformation processes depositional processes are mainly recorded by the upslope migrating pattern of the waves resulting from oblique or sigmoid downlap reflections on the upslope flank of the waves and by toplapping and truncated reflections on the downslope flank hemipelagic and turbiditic sedimentation may be involved in the wave building as well as contouritic processes that could be related to the existing northward polar current and internal waves gravity deformations are syndepositional discontinuous and of low amplitude affecting thick layers which alternate with undeformed layers they seem to correspond to gentle sediment creeping or stretching associated with minor listric or compaction like faults and possible limited back rotation of sediment blocks these multi process generated sediment waves could be rather common on the continental margins as they could have been mistaken with either depositional or deformational structures

what forced the collapse of european ice sheets during the last two glacial periods 150 ka b p and 18 ka cal b p palynological evidence article i nfo we present a new marine palynological record from the temperate north eastern atlantic core md03 2692 celtic armorican margin in the area of influence of the fleuve manche paleoriver during glacial times the runoff of this paleoriver was connected to the glacial history of european ice sheets including the british irish ice sheet biis our study conducted on dinoflagellate cysts assemblages over the last 200 ka associated with quantification of palynological remains reflecting continental influence pre quaternary dinocysts and micro algae pediastrum spp coenobia yields detailed insights into the sea surface paleoenvironments of this sector more specifically mechanisms responsible for the origin of unusual deposits of laminated sequences found at the end of marine isotope stage mis 2 and within mid mis 6 are here constrained we provide evidence of genetic similarities between fluvial discharges occurring before and during times of deposition of the laminated deposits our study clarifies the causes of the collapse of european glaciated systems at the end of mis 2 prior to the deposition of the laminated deposits pleni oceanic influence characterized by high concentrations of quaternary dinocysts prevailed and a dinocyst species tracing the penetration of the warm north atlantic drift into the bay of biscay is recorded however this scenario did not recur prior to the deposition of laminated sediments of mid mis 6 in addition contrary to the laminated deposits found at the end of mis 2 and directly associated with termination i mis 6 laminae appeared 20 ka earlier than termination ii our work shows that during the penultimate glacial stage the collapse of mid latitudes ice sheets around 170 ka b p may have immediately followed the mis 6 5 warming phase then the most important melting event around 150 ka b p may be linked to a peak in insolation at 65 n though less important than those during mis 6 5 and termination ii

morphosedimentary features and recent depositional architectural model of the cantabrian continental margin abstract multibeam bathymetry high sleeve airguns and very high resolution parametric system topas seismic records were used to define the morphosedimentary features and investigate the depositional architecture of the cantabrian continental margin the outer shelf down to 180 245 m water depth displays an intensively eroded seafloor surface that truncates consolidated ancient folded and fractured deposits recent deposits are only locally present as lowstand shelf margin deposits and a transparent drape with bedforms the continental slope is affected by sedimentary processes that have combined to create the morphosedimentary features seen today the upper down to 2000 m water depth and lower down to 3700 4600 m water depth slopes are mostly subject to different types of slope failures such as slides mass transport deposits a mix of slumping and mass flows and turbidity currents the upper slope is also subject to the action of bottom currents the mediterranean water mw that interact with the le danois bank favouring the reworking of the sediment and the sculpting of a contourite system the continental rise is a bypass region of debris flows and turbidity currents where a complex channel lobe transition zone cltz of the cap ferret fan develops the recent architecture depositional model is complex and results from the remaining structural template and the great variability of interconnected sedimentary systems and processes this margin can be considered as starved due to the great sediment evacuation over a relatively steep entire depositional profile sediment is eroded mostly from the cantabrian and also the pyrenees mountains source and transported by small stream river mountains to the sea it bypasses the continental shelf and when sediment arrives at the slope it is transported through a major submarine drainage system large submarine valleys and mass movement processes down to the continental rise and adjacent biscay abyssal plain sink factors controlling this architecture are tectonism and sediment source dispersal which are closely interrelated whereas sea level changes and oceanography have played a minor role on a long term scale

sea surface hydrographical conditions off south faeroes and within the north eastern north atlantic through mis 2 the response of dinocysts the last glacial period showing the progressive development of large boreal ice sheets was punctuated by large climatic excursions these excursions were triggered mainly by atmosphereoceanice coupled dynamics and are thus exemplary case studies of natural climate variability to characterize the sea surface palaeohydrographical changes accompanying these oscillations along the european margin we have integrated new palynological data dinocysts acquired on core md99 2281 60 degrees n faeroe margin during marine isotope stage 2 in a latitudinal transect including published cores md95 2002 47 degrees n celtic margin and md95 2010 66 degrees n voring plateau this transect is superimposed on the modern north atlantic drift pathway but also at the outskirts of glacial european ice sheets thus ideally located to track sea ice extent and ice sheet instabilities through time the results show a coherent and sensitive response of sea surface environments to the complex chain of abrupt events that punctuated the end of the last glacial period the last glacial maximum was marked by large seasonal contrasts of temperatures whereas heinrich events he were characterized by a sharp cooling and sea ice development a tripartite structure is identified within he1 with indices of melting at 19k cal a bp followed by a temperate phase synchronous of a relative stability of ice sheets and a terminal phase 17 515k cal a bp characteristic of the conventional laurentian he1 copyright c 2013 john wiley sons ltd

late devensian and holocene shorelines of the british isles and north sea from models of glacio hydro isostatic rebound sea level change around the british isles since the time of the last glacial maximum is largely due to of the crustal rebound from the glacial unloading of northern britain and the concomitant melt water loading of the adjacent seas and atlantic ocean minor but not insignificant contributions also result from the rebound caused by the unloading of the distant ice sheets including fennoscandia and north america observations of sea level change for this period constrain the glacio hydro isostatic rebound model parameters describing the effective lithospheric thickness or rigidity and the effective mantle viscosity as well as certain ice sheet characteristics such as the ice thickness at the time of the last glacial maximum the models permit palaeobathymetry and palaeoshorelines to be predicted for the british isles region including the north sea the resulting evolution of the coastlines exhibits a complex behaviour through time one that is quite different from the usual models in which sea level change is assumed to be a function of time only in part this is because of the delayed response of the mantle to the spatially variable and time dependent ice and water loads and in part because the unloading history of the british ice sheet is different from those of the major global ice sheets thus maximum emergence of the north sea occurred after deglaciation had started and lasted for an extended period from about 15 000 to 12 000 radiocarbon years bp during this relative sea level still stand shoreline features could have formed for example along the western edge of the norwegian trough when access to the firths of eastern scotland would have been via a long and shallow marine inlet shoreline retreat across the north sea became relatively rapid after about 10000 years the model predictions for the irish and celtic seas also suggest a complex behaviour with the formation of a wide land bridge between about 20000 and 13 000 years ago the model also suggests that as long as the scottish ice extended across the northern irish sea until about 14 000 years ago there would have been a large freshwater periglacial lake located further south both the predicted sea level height age relations and the shoreline positions are consistent with a large body of observational evidence but some discrepancies occur particularly in northern scotland and ireland where the ice heights may have been somewhat greater than assumed in the model

high frequency climate fluctuations over the last deglaciation in the alboran sea western mediterranean evidence from calcareous plankton assemblages abstract a high resolution study with a centennial scale resolution has been performed on the calcareous plankton assemblage coccolithophores and planktonic foraminifera at ocean drilling program site 976 alboran sea western mediterranean focusing on the interval between 20 and 9 ka in order to reconstruct changes in surface and subsurface water dynamics and productivity the biotic surface water proxies integrate the extremely detailed multi decadal scale geochemical data set and the pollen record already available at the core thus providing a complete paleoenvironmental paleoceanographic reconstruction the results highlight the sensitivity of the calcareous plankton in recording stadial interstadial phases and higher frequency climatic events that produced changes in sea water features wind induced upwelling and river discharge during the last glacial period favored nutrient availability and moderate productivity during heinrich stadial 1 hs1 the arrival of cold and fresher waters from iceberg melting in the north atlantic significantly hampered productivity at its lowest values of the whole investigated interval calcareous plankton behavior supports the hypothesis that hs1 is a composite event marked by three phases hs1a characterized by the coldest sst polar atlantic water inflow into the basin and a first step toward a dry climate on the continent hs1b recording enhanced freshwater inflow and drought on land and hs1c indicating reduced polar water influx the bolling allerod ba interstadial sees the highest rate of productivity in the entire interval and accompanies the deposition of organic rich layer 1 during the ba coccolithophore assemblage also marks higher frequency changes in hydrographic conditions apparently in relation with greenland interstadial i gi i high variability the younger dryas stadial yd is characterized by refunding cold and dry conditions although not as severe as during hs1 and by enhanced detrital input in surface water during drier conditions on land the holocene onset records climate amelioration both in the marine and continental environment although coccolithophore productivity is not as high as during the ba the rapid shifts in climate sensitive taxa support the hypothesis that each of the climate phases subphases is characterized by a complex pattern forced by strong interaction between ice sheet instability meltwater discharge entering the gibraltar strait north atlantic westerlies and moisture availability clearly impacting over surface water temperature productivity and land masses

new constraints on european glacial freshwater releases to the north atlantic ocean during the late quaternary both external and internal forcings have driven major climatic shifts from glacial to interglacial conditions nonlinear climatic steps characterized the transitions leading to these extrema with intermediate excursions particularly well expressed in the dynamics of the northern hemisphere cryosphere here we document the impact of these dynamics on the north eastern north atlantic ocean focussing on the 35 10 ka interval sea surface salinities have been reconstructed quantitatively based on two independent methods from core md95 2002 recovered from the northern bay of biscay adjacent to the axis of the manche paleoriver outlet and thus in connection with proximal european ice sheets and glaciers quantitative reconstructions deriving from dinocyst and planktonic foraminiferal analyses have been combined within a robust chronology to assess the amplitude and timing of hydrological changes in this region our study evidences strong pulsed freshwater discharges which may have impacted the north atlantic meridional overturning circulation

multidecadal ocean variability and nw european ice sheet surges during the last deglaciation a multiproxy paleoceanographic record from the atlantic margin off the british isles reveals in unprecedented detail discharges of icebergs and meltwater in response to sea surface temperature increases across the last deglaciation we observe the earliest signal of deglaciation as a moderate elevation of sea surface temperatures that commenced with a weakly developed thermocline and the presence of highly ventilated intermediate waters in the rockall trough this warming pulse triggered a series of multidecadal ice rafted debris peaks that culminated with a major meltwater discharge at 17 500 years before present related to ice sheet disintegration across the nw european region the impact of meltwater caused a progressive reduction in deep water ventilation and a sea surface cooling phase that preceded the collapse of the laurentide ice sheet during heinrich event 1 by 500 1000 years a similar sequence of rapid ocean ice sheet interaction across the european continental margin is identified during the bolling allerod to younger dryas transition the strategic location of our sediment core suggests a sensitive and rapid response of ice sheets in nw europe to transient increases in thermohaline heat transport

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

climate variability across the last deglaciation in nw iberia and its margin abstract the direct comparison between marine and terrestrial data from the nw iberian margin core md03 2697 allows us to accurately evaluate without chronological ambiguity the vegetation response to north atlantic climate events across the last deglaciation comparison of md03 2697 data with other marine and terrestrial records from a vast area stretching from the azores to western w france iberia and its margin the w mediterranean and nw africa reveals the importance of enhanced winter north atlantic westerlies episodes in driving a heterogeneous regional climatic signal during particular events of the last deglaciation heinrich stadial 1 hs1 oldest dryas is a complex event marked by three synchronous main phases a extremely cold relatively wet b cool dry c relatively warmer increasing moisture availability in regions directly influenced by the north atlantic while it is characterized by a single phase cold and dry in most inland and high altitude areas changes in the strength and position of north atlantic westerlies could explain the variability in moisture during hs1 from w pyrenees to w mediterranean the bolling allerod b a event is marked by a synchronous progressive increase of ocean and atmospheric temperatures and precipitation from the bolling to the allerod in w iberia and w pyrenees contrasting with the greenland temperature pattern mid to high latitudes thermal contrast and the gradual strengthening of the atlantic meridional overturning circulation amoc triggered the continuing enhancement of westerlies and moisture along this period finally the younger dryas yd stadial is characterized by a land ocean synchronous returning cold conditions but not so cold as hs1 and although dry conditions persisted during this period extreme winter precipitation occurrences might have affected the most coastal areas of north and central w iberia and pyrenees in contrast dry conditions persisted during the yd in the western mediterranean regions the westerlies migrated further north following the displacement of the polar front during the deglaciation precluding the input of moisture in the w mediterranean region which persisted very dry during the yd stadial

evolution of the danube deep sea fan since the last glacial maximum new insights into black sea water level fluctuations abstract the danube deep sea fan nw black sea is one of the most developed deep sea sediment depositional systems in europe although the morphology and the architecture have been widely described in the past years little is known about the stratigraphy of this depositional system for the late quaternary this results from the lack of significant stratigraphic markers the scarcity of radiocarbon ages and the difficulty in constraining reservoir ages recent robust quantification of reservoir ages has allowed the construction of a new stratigraphic framework for the black sea from the end of the last glacial period to the holocene thus giving the opportunity to correlate sedimentological and geochemical features previously described on the nw black sea margin with climatic events identified in the northern hemisphere based on this approach we propose an improved chrono lithostratigraphic framework for the danube deep sea fan channel levees since the last glacial maximum we show that the danube deep sea fan was active during the last glacial maximum until the younger dryas early holocene transition ca 11 700 cal a bp when the turbidite activity abruptly terminated in the whole system throughout this period the danube river was the main source of the deep depositional system except between ca 17 200 cal a bp and 15 700 300 cal a bp at that time the deposition of red turbidites in the deep basin concomitant with the deposition of the so called red layers onto the continental shelf and the upper slope emphasises the direct impact of the increased meltwater runoff of the dnieper river as far as the danube deep sea fan some significant changes in the location of the depocentre of the danube deep sea fan occurred through time the main change in depocentre location occurred at ca 28 000 cal a bp with the northward avulsion leading to the formation of the middle channel although the middle and northern channel became the preferential turbidite depocentres after this event the deposition of turbidites has persisted in the southern channel levee until 14 700 cal a bp indicating that the southern channel was definitely not abandoned after the upstream northward avulsion unsurprisingly water level fluctuations and river sediment flux acted as the main forcings on the evolution of the danube deep sea fan based on these results and on the morphology of the danube canyon we propose that i lowstand conditions 110 m prevailed during the last glacial maximum and possibly between 15 700 300 cal a bp and 14 700 cal a bp ii water level ranged from 110 and 70 m between 14 700 and 11 700 cal a bp and iii water level ranged from 70 and 30 m from 11 700 cal a bp and until the reconnection of the black sea lake with the global ocean at ca 9000 cal a bp

black sea lake reservoir age evolution since the last glacial hydrologic and climatic implications abstract chronologies of sediments that document the last glacial history of the black sea lake are hampered by issues relating to reservoir age regulated by basin hydrology reservoir ages represent a tool that could potentially be used to better understand the response of black sea lake hydrology to climate change therefore deciphering reservoir age evolution is crucial both for better constraining the basin chronological framework and for providing new insights into our understanding of black sea lake hydrology by tuning a meaningful new high resolution geochemical dataset obtained from core md04 2790 to a climate reference record here we propose a reliable chronology spanning the last 32 kyr bp the chronology is compared to a large ams radiocarbon dataset n 51 pairs of calendar and radiocarbon ages allowed us to compute reservoir ages and to then reconstruct a high resolution quantitative reservoir age record for the last glacial history of the black sea lake the main factor controlling reservoir ages in lakes is the hard water effect hwe which is regulated by basin hydrology therefore changes in the reconstructed reservoir age record have been qualitatively interpreted in terms of the hydrologic responses of the black sea lake to climate change our results allowed us to determine periods of complete isolation or outflow for the black sea lake during heinrich event 2 he2 and during the last glacial maximum lgm the basin was strictly isolated whereas prior to he2 and during he1 it outflowed into the marmara sea following the onset of the bolling allerod factors other than the hwe are thought to have influenced the reservoir age preventing conclusive interpretations we also determined an undocumented to date phase of black sea lake stratification during the full glacial he2 and lgm our results indicate that reservoir age is a powerful tool for investigating and better understanding past hydrologic changes in lakes and inland seas

norwegian sea warm pulses during dansgaard oeschger stadials zooming in on these anomalies over the 35 41 ka cal bp interval and their impacts on proximal european ice sheet dynamics abstract the last glacial millennial climatic events i e dansgaard oeschger and heinrich events constitute outstanding case studies of coupled atmosphere ocean cryosphere interactions here we investigate the evolution of sea surface and subsurface conditions in terms of temperature salinity and sea ice cover at very high resolution mean resolution between 55 and 155 years depending on proxies during the 35 41 ka cal bp interval covering three dansgaard oeschger cycles and including heinrich event 4 in a new unpublished marine record i e the md99 2285 core 62 69 n 3 57s e we use a large panel of complementary tools which notably includes dinocyst derived sea ice cover duration quantifications the high temporal resolution and multiproxy approach of this work allows us to identify the sequence of processes and to assess ocean cryosphere interactions occurring during these periodic ice sheet collapse events our results evidence a paradoxical hydrological scheme where i greenland interstadials are marked by a homogeneous and cold upper water column with intensive winter sea ice formation and summer sea ice melting and ii greenland and heinrich stadials are characterized by a very warm and low saline surface layer with iceberg calving and reduced sea ice formation separated by a strong halocline from a less warm and saltier subsurface layer our work also suggests that this stadial surface subsurface warming started before massive iceberg release in relation with warm atlantic water advection these findings thus support the theory that upper ocean warming might have triggered european ice sheet destabilization besides previous paleoceanographic studies conducted along the atlantic inflow pathways close to the edge of european ice sheets suggest that such a feature might have occurred in this whole area nonetheless additional high resolution paleoreconstructions are required to confirm such a regional scheme

early reactivation of european rivers during the last deglaciation during the last glacial maximum the sea level lowstand combined with the large extent of the fennoscandian and british ice sheets led to the funneling of european continental runoff resulting in the largest river system that ever drained the european continent here we show an abrupt and early reactivation of the european hydrological cycle at the onset of the last deglaciation leading to intense discharge of the channel river into the bay of biscay this freshwater influx probably combined with inputs from proglacial or ice dammed lakes dramatically affected the hydrology of the region both on land and in the ocean

hyperpycnites deposited 700 km away from river mouths in the central japan sea abstract relatively little is known about the characteristics of deposits and potential runout distances of hyperpycnal currents this study describes and discusses evidence of sediment deposition from sustained long duration quasi steady turbidity currents in the distal part of the toyama deep sea channel which extends ca 700 km from river mouths in the central japan sea the study is based on gravity cores and airgun seismic reflection profiles obtained from the channel distal reaches the silty turbidite beds of the channel s terminal fan show rhythmic layering that indicates sustained turbidity currents with distinct flow strength fluctuations some of the rhythmite beds show a fining upward internal trend net flow strength waning whereas others show an upward coarsening net flow strength waxing followed by fining seismic reflection profiles from the channel levees show large bedforms of climbing dune type attributed to the spillover of thick sustained turbidity currents the deposition of the terminal fan rhythmites and accretionary levee bedforms is attributed to turbidity currents generated by hyperpycnal river effluent a quantitative assessment of sediment concentrations in the coastal rivers indicates that their effluents could become hyperpycnal nearly every year or during every major seasonal flood the density of a river generated underflow would increase by the entrainment of saline water and seafloor sediment on the steep slope of the toyama bay resulting in robust long runout turbidity currents the estimated flow velocities of these currents were around 0 3 m s and their recurrence period for the last 1000 years was of the order of 70 years the estimated duration of hyperpycnal flows required for the deposition of rhythmite beds 700 km away from the river mouth is of the order of several days to 3 4 weeks the study provides new insights into the recognition and classification of hyperpycnites in distal zones of deep marine turbiditic systems

occurrence of pockmarks on the ortegal spur continental margin northwestern iberian peninsula a total of 445 pockmarks were observed on the upper continental slope of the northwest corner of the iberian peninsula the ortegal spur area by swath bathymetric and ultrahigh resolution seismic data the pockmarks are u v and w shaped and have terraces or indentations in cross section and are dish shaped circular to oval in plan view they occur on the surface of the seabed and buried within the plio quaternary and neogene sediments four types of pockmarks were identified and mapped on the basis of their plan view and cross section morphology regular irregular asymmetric and composite the concentration of pockmarks is attributed to seepage of fluids migrating up dip from deeper parts of the sedimentary basin a linear high density concentration with a nnw to n ne and ese trend of pockmarks is observed above inferred basement faults that do not affect the quaternary succession these pockmarks are thus caused by seepage of thermogenic gas and or other pore fluids from deeper late cretaceous units and their distribution may help to improve our understanding of the fluid system and migration regime in this part of the galicia continental margin

new data for the last glacial maximum in great britain and ireland abstract understanding the history of the british and irish ice sheet biis at the last glacial maximum lgm has been advanced by new approaches in particular by cosmogenic nuclide surface exposure dating aminostratigraphy of shelly glacial deposits ams radiocarbon dating and the evidence from continental margin marine cores all of which supersede the previously weak geochronologic control it was formerly believed that great britain and ireland was largely ice free between the last interglacial oxygen isotope sub stage 5e and the late devensian when the lgm occurred as such the biis was effectively out of phase with laurentide and scandinavian ice sheets as well as inferences of ice volume from oxygen isotope stratigraphy the biis during the late devensian maximum was also perceived as having been relatively stationary new evidence shows that the lgm was an important event during the evolution of an earlier biis when the extent of ice was greater repeated iceberg rafting events over the past 50 ka are shown by marine cores while the derivative inference of numerous corresponding glacial advances is supported by several clusters of 36 cl ages on glaciated surfaces and glacial boulders that are indicative of deglacial events between 40 and 12 ka these appear to be associated with heinrich events the earliest being inferred as heinrich 4 at about 40 ka during this advance the biis and scandinavian ice sheet sis were in contact and all of ireland was glaciated the ice sheet appears to have fluctuated several times between 40 and 25 ka although evidence for this is poorly preserved but the 36 cl and 14 c evidence is clear that the biis reached its lgm maximum size about 22 ka soon after heinrich event 2 when the biis and sis were not in contact one cluster of 36 cl and 14 c ages at 21 4 1 3 ka records an initial pulse of deglaciation that was followed by extensive deglaciation about 17 4 0 4 ka just before heinrich event 1 when the ice sheet readvanced contrary to previous views the biis probably existed throughout much of devensian time as a mobile and sensitive ice sheet during which the lgm advance was but one important event in places glacial deposits of the earlier devensian glaciation have previously been incorrectly identified as products of the later lgm glaciation

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

deglacial laminated facies on the nw european continental margin the hydrographic significance of british irish ice sheet deglaciation and fleuve manche paleoriver discharges we have compiled results obtained from four high sedimentation rate hemipelagic sequences from the celtic sector of the nw european margin ne atlantic to investigate the paleoceanographic and paleoclimatic evolution of the area over the last few climatic cycles we focus on periods characteristic of deglacial transitions we adopt a multiproxy sedimentological geochemical and micropaleontological approach applying a sampling resolution down to ten microns for specific intervals the investigation demonstrates the relationships between the bay of biscay hydrography and the glacial deglacial history of both the proximal british irish ice sheet biis and the western european continent we identify recurrent phases of laminae deposition concurrent with major biis deglacial episodes in all the studied cores evidence for abrupt freshwater discharges into the open ocean highlights the influence of such events at a regional scale we discuss their impact at a global scale considering the present and past key location of the bay of biscay versus the atlantic meridional overturning circulation amoc

geochemical and geophysical implications of the radiocarbon calibration abstract a precise and accurate chronological framework is crucial to study the dynamics of a variety of phenomena which occurred during the last 45 000 years although the 14 c dating method has been widely applied since the 1950s it is recognized that the atmospheric 14 c 12 c ratio has not been stable during the past in order to calculate accurate ages these fluctuations have to be corrected by means of a calibration curve obtained by comparing raw 14 c measurements with true calendar ages provided by independent dating methods the calibration curve obtained so far is characterized by a long term trend with raw 14 c ages being significantly younger than calendar ages during most of the last 45 000 years abrupt 14 c shifts which occurred over centuries to millennia are superimposed on this long term trend of decreasing atmospheric 14 c 12 c ratio to a certain extent it is possible to outline the different causes of atmospheric 14 c variations by considering complementary information obtained from other cosmogenic nuclides studied at different latitudes 1 most high frequency changes in the atmospheric 14 c 12 c ratio are linked to magnetic fluctuations of solar origin as revealed by studying the last three centuries for which direct observations of the sun are available a similar conclusion is derived by comparing 14 c 12 c events with 10 be and 36 cl concentration maxima in polar ice cores 2 the long term trend shift of 14 c ages is due to a long period of decreased shielding effect of the geomagnetic dipole field which occurred over the interval between 10 000 and 40 000 years bp this interpretation is supported by paleomagnetic measurements performed on volcanic and sedimentary rocks and by 10 be and 36 cl analysed in low and high latitude records 3 a prominent and rapid atmospheric 14 c 12 c excursion occurred between 13 000 and 11 500 cal yr bp thus corresponding to the younger dryas cold period by contrast with the 14 c variability mentioned above which is linked to 14 c production changes this so called 14 c age plateau is probably due to an abrupt variation in the rates of exchange within the global carbon cycle this interpretation is supported by independent geochemical proxies and by numerical modelling of the carbon cycle

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

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

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

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

2000years of frequent turbidite activity in the capbreton canyon bay of biscay abstract capbreton canyon extends from 200 m water depth near the aquitanian coast to 3000 m water depth before abruptly turning northward and merging with the cap ferret systems the capbreton canyon has been disconnected from the adour river input since 1310 ad despite this situation modern sedimentary activity is evident in the first kilometres from the head present sedimentation in the capbreton canyon was studied by combined analysis of acoustic data and cores cores from the topographic highs document moderate hemipelagic sedimentation and record the global climatic signal of the bay of biscay within the canyon at 80 km from the head on terraces bordering the thalweg at 1600 m water depth cores attest to recent turbidite activity massive medium sand is restricted to the thalweg floor where sediment transfer dominates fine grained turbidites are preferentially accumulated on the shallower terraces near the thalweg the accumulation rate is 3 and 1 cm year at 75 m and 125 m above the thalweg respectively on a higher terrace 225 m turbidite sequences are absent or too thin to be preserved from bioturbation the sedimentation rate is lower approximately 0 17 cm year but still 10 times higher than the hemipelagic sedimentation outside the capbreton canyon we demonstrate that frequent turbidity currents 1 year are currently responsible for very high accumulation of dominantly fine grained sediments on the terraces that are the nearest from the thalweg we assume an impact of nepheloid layers on the sedimentation of the highest terraces looking for any impact on sediment supply of the disconnection of the capbreton canyon head from the adour river mouth it appears that the impact on the sedimentation affected the nature of the particles which are less carbonate rich rather than the quantity of sediments this result suggests that the longshore drift at the canyon head and hydrodynamic events are major factors in the sedimentation of capbreton canyon

the fleuve manche the submarine sedimentary features from the outer shelf to the deep sea fans bathymetric seismic and coring surveys have been carried out since the beginning of the 1990s on the outer shelf the slope and the continental rise of the western approaches margin most of the sedimentary features studied belong to a sedimentary system built up since the oligocene and fed by a palaeoriver the fleuve manche that flowed in the english channel during eustatic lowstands a geomorphological map details the spatial distributions of the palaeovalleys on the outer shelf the drainage basin like organised canyons on the slope and the channel levee and lobe complexes on the rise the obvious channel canyon connections and the assessed palaeovalley canyon links demonstrate that the fleuve manche was the single source for terrigeneous fluxes of the armorican deep sea fan when it was one of two sources of the celtic deep sea fan amongst parameters controlling the sedimentation two factors play a major role i subsidence controlled the possibly messinian riverine incision the turbidite activities during lowstands as well as marine infilling of the seawards part of the fleuve manche ii quaternary sedimentary supplies were influenced by the melting ice sheets and the connections with the onshore catchment basins copyright 2003 john wiley sons ltd

the origin of heinrich layers evidence from h2 for european precursor events recent well dated isotopic sr nd fingerprinting of heinrich layer ice rafted detritus ird on the european margin indicates supply from european ice sheets as precursors to laurentide ice sheet lis supply f e grousset et al geology 28 2000 123 126 h snoeckx et al mar geol 158 1999 197 208 these precursorevents lead lis input by up to 1 5 ka f e grousset et al geology 28 2000 123 126 and have been interpreted to indicate lis collapse during heinrichevents stimulated by events originating on the european side of the atlantic f e grousset et al geology 28 2000 123 126 such phasing of ird supply from different sources within heinrich layers therefore has implications for the origin and mechanics of heinrichevents we present evidence here that the ird comprising heinrich layer 2 h2 20 21 14c ka bp on the european continental margin contains detrital campanian upper chalk deriving from bedrock sources eroded on the celtic shelf by the british ice sheet bis in addition to lithic material sourced from the lis high resolution radiocarbon chronology indicates chalk grain deposition as discrete pulses both before and coincident with supply of lis sourced detritus the specificity of the chalk fingerprint to the bis enables a 700 1000 yr lag between the bis and lis events to be identified this phasing indicates a more rapid response of the outlet lobes draining the smaller bis than those draining the lis and implicates external climatic forcing of heinrichevents it is unlikely that this precursorevent represents ird event 18 the recently identified 1 2 ka ird cycle event which immediately precedes h2 because the lag between precursor and main event is here less than 1 5 ka and because such pervasive periodicity is not apparent in european continental margin ird records the later synchroneity between the bis and lis input in h2 identifies glacio eustatic sea level rise associated with lis discharges as a possible feedback mechanism causing destabilisation of ice streams elsewhere during heinrichevents

laminated sediments preceding heinrich event 1 in the northern north sea and southern norwegian sea origin processes and regional linkage abstract rapidly deposited laminated sediments dated between 18 and 21 cal ka bp have been observed at several core locations in the northern north sea and the southern norwegian sea sedimentation rates range from 20 cm ka up to 2000 cm ka compared to a normal background sedimentation rate in the area of 5 10 cm ka dropstones in situ paired bivalves and grain size distribution indicate a hemipelagic origin for the laminae in core md99 2291 from the upper continental slope of southern norway ams radiocarbon dating and cyclic changes in the number of planktonic foraminifera and lithological parameters suggest that the laminations in the core are annual varves the laminated sediments are interpreted to be suspension plume deposits and two phases of plume deposition have been dated to 21 5 and 18 6 cal ka bp large fluxes of meltwater were generated during this period as reflected in oxygen and carbon isotopes records from cores in the area the meltwater and the laminated plume deposits are interpreted to be associated with the presence and disintegration of the norwegian channel ice stream observations from other regions demonstrate that laminated high rate deposition is very widespread on glaciated continental margins around 18 6 cal ka bp increases in sediment fluxes also occurred on the barra fan the north sea fan the lofoten contourite drift and the svalbard margin preceding increased sediment and meltwater fluxes on the greenland margin and the labrador sea associated with heinrich event 1 warm water inflow to the norwegian sea together with rising sea level probably triggered the destabilisation of the ice streams of the fennoscandian ice sheet while a similar response of the laurentide ice sheet was delayed by 500 1000 yr

activity of the turbidite levees of the celtic armorican margin bay of biscay during the last 30 000 years imprints of the last european deglaciation and heinrich events abstract high resolution sedimentological and micropaleontological studies of several deep sea cores retrieved from the levees of the celtic and armorican turbidite systems bay of biscay north atlantic ocean allow the detection of the major oscillations of the british irish ice sheet biis and fleuve manche palaeoriver discharges over the last 30 000 years which were mainly triggered by climate changes between 30 and 20 cal ka the turbiditic activity on the celtic armorican margin was weak contrasting with previous stratigraphic models which predicted a substantial increase of sediment supply during low sea level stands this low turbidite deposit frequency was most likely the result of a weak activity of the fleuve manche palaeoriver and or of a reduced seaward transfer of sediments from the shelf to the margin however two episodes of turbiditic activity increase were detected in the celtic armorican margin during heinrich events he 3 and 2 this strengthening of the turbiditic activity was triggered by the meltwater releases from european ice sheets and glaciers favouring the seaward transfer of subglacial material at least via fleuve manche palaeoriver at around 20 cal ka a significant increase of turbidite deposit frequency occurred as a response to the onset of the last deglaciation the retreat of the european ice sheets and glaciers induced a substantial increase of the fleuve manche palaeoriver discharges and seaward transfer of continentally derived material into the armorican turbidite system the intensification of the turbiditic activity on the celtic system was directly sustained by the widespread transport of subglacial sediments from the british irish ice sheet biis to the celtic sea via the irish sea basin a sudden reduction of turbiditic activity in the armorican system between ca 19 and 18 3 cal ka could have been triggered by the first well known abrupt sea level rise meltwater pulse at around 19 cal ka favouring the trapping of sediment in the fleuve manche palaeoriver valleys and the decrease of the seaward transfer of continentally derived material the maximum of turbiditic activity strengthening in the celtic armorican margin between ca 18 3 and 17 cal ka was induced by the decay of european ice sheets and glaciers producing the most extreme episode of the fleuve manche palaeoriver runoff and a great seaward transfer of subglacial material into the bay of biscay between ca 17 5 and 16 cal ka the turbiditic activity significantly decreased in both celtic and armorican turbidite systems in response to a global re advance of glaciers and ice sheets in europe the last episode of ice sheet retreat between ca 16 and 14 cal ka is well expressed in the celtic system by a new increase of the turbiditic activity the major episode of sea level rise at around 14 cal ka meltwater pulse 1a precluding the seaward transfer of sediments induced the end of turbiditic activity in both the celtic and the armorican system although two main phases of global sea level rise seem to have had an effect on the celtic armorican margin this work proposes the biis retreat and associated riverine discharges as the main trigger mechanisms of the turbiditic activity in this region during the last 30 000 years

southernmost evidence of large european ice sheet derived freshwater discharges during the heinrich stadials of the last glacial period galician interior basin northwest iberian continental margin abstract reconstruction of circum atlantic ice sheet motion and instabilities is crucial to understanding the mechanisms that triggered and or enhanced abrupt climate changes using enviromagnetic and geochemical data we provide a continuous and well dated record of the evolution of glacial interglacial sedimentation on the northwest iberian margin during the last glacial period covering the last six heinrich stadials the record shows european sediments that were related to meltwater pre events during the initial stages of hs1 hs2 and hs4 that corroborate the channel river depositional history the record also includes ird from the laurentide ice sheet and the european ice sheet during the final stages of these stadials i e heinrich events therefore this study provides insight into one of the potential forcing mechanisms for heinrich events and by inference for heinrich stadials