ice rafting from the british irish ice sheet since the earliest pleistocene 2 6 million years ago implications for long term mid latitudinal ice sheet growth in the north atlantic region abstract the plio pleistocene intensification of northern hemisphere continental ice sheet development is known to have profoundly affected the global climate system evidence for early continental glaciation is preserved in sediments throughout the north atlantic ocean where ice rafted detritus ird layers attest to the calving of sediment loaded icebergs from circum atlantic ice sheets so far early pleistocene ird deposition has been attributed to the presence of high latitudinal ice sheets whereas the existence and extent of ice accumulation in more temperate mid latitudinal regions remains enigmatic here we present results from the multiproxy provenance analysis of a unique pleistocene holocene ird sequence from the irish ne atlantic continental margin there the challenger coral carbonate mound iodp expedition 307 site u1317 preserved an early pleistocene record of 16 distinctive ird events deposited between ca 2 6 and 1 7 ma strong and complex ird signals are also identified during the mid pleistocene climate transition ca 1 2 to 0 65 ma and throughout the middle late pleistocene interval radiogenic isotope source fingerprinting in combination with coarse lithic component analysis indicates a dominant sediment source in the nearby british irish isles even for the oldest early pleistocene ird deposits hence our findings demonstrate for the first time repeated and substantial i e marine terminating ice accumulation on the british irish isles since the beginning of the pleistocene contemporaneous expansion of both high and mid latitudinal ice sheets in the north atlantic region is therefore implied at the onset of the pleistocene moreover it suggests the recurrent establishment of climatically favourable conditions for ice sheet inception growth and instability in mid latitudinal regions even in the earliest stages of northern hemisphere glacial expansion and in an obliquity driven climate system

the younger dryas termination and north atlantic deep water formation insights from climate model simulations and greenland ice cores results from the gisp2 and grip ice cores show that the termination of the younger dryas yd climate event in greenland was a large and extremely fast climate change a reinitiation of north atlantic deep water formation following a shutdown and its associated winter release of heat to the atmosphere has been suggested as the most likely cause of this climate transition to test this idea two general circulation model experiments using genesis have been completed for yd time 12 000 calendar years ago one with low heat flux in the nordic seas 10 w m deep water shutdown and one with high nordic sea heat flux 300 w m active deep water formation comparison of greenland climate differences between these experiments with the ice core records shows that when deep water is turned on much of the yd termination warming is achieved the increase in precipitation is underestimated because of a model tendency to overestimate summertime precipitation which obscures the dominantly wintertime response to the specified forcing the winter storm track shift toward greenland contributes much of the climate change at the yd termination

hudson bay hudson strait jokulhlaups and heinrich events a hypothesis abstract abrupt temperature changes in the northern north atlantic occurred frequently throughout the last glaciation as shown by proxy records from greenland ice cores deepsea cores and norway speleothems many of these variations occurred in irregular sawtooth cooling cycles which sometimes ended with the deposition of thick layers of ice rafted debris ird in the deep ocean that are known as heinrich events the lithologies of most of the ird deposits are consistent with widespread surges of the laurentide ice sheet that may have resulted from the accumulation of deformable sediments in portions of the ice sheet bed an alternative conceptual model proposed here to explain the sawtooth coolings and the surges involves repetitive jokulhlaups from a hudson bay lake dammed by ice at the mouth of hudson strait the slow sawtooth coolings may be explained by storm track diversion due to progressive coverage of the lake by icebergs and the surges by abrupt losses of water pressure and buttressing ice shelves at all ice sheet fronts in the lake when the ice dams failed

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

mineral magnetic characteristics of podzolic soils developed on sand dunes in the lake gosciaz catchment central poland a number of samples from the a0 a2 b and c horizons have been collected from podzolic soils in the lake gosciaz catchment in central poland the catchment is very uniform consisting of 2 6 m high sand dunes with sparse stands of pine and a grass undervegetation radiocarbon dates of fossil soils covered by dune sand within the same type of environment as the lake gosciaz catchment indicate that the main dune forming phase is of older dryas age magnetic measurements have been carried out on bulk samples and on particle size fractions from the different soil horizons with respect to our mineral magnetic study it can be concluded that the soils are very uniform over the entire catchment relatively high concentrations of magnetic grains are found in the humus layer particularly in the 4 m size fraction as indicated by the highest x xfd sirm and hirm values the most likely mechanism for the magnetic enhancement in these podzolic top soils is continued burning processes low magnetic concentrations in the a2 horizon are due to eluviation and chelation local conditions can lead to a range of magnetic minerals precipitating in the b horizon

the role of ocean atmosphere reorganizations in glacial cycles abstract a case is made that glacial to interglacial transitions involve major reorganizations of the ocean atmosphere system such reorganizations constitute jumps between stable modes of operation which cause changes in the greenhouse gas content and albedo of the atmosphere only in this way can the rapidity of glacial terminations the hemispheric synchroneity and symmetry of mountain glaciation and the large polar air temperature and dustiness variations be accounted for if these reorganizations are driven in some fashion by orbitally induced seasonal insolation changes then the connection between insolation and climate is most likely through impacts of fresh water transport on the ocean s salinity distribution

flux of ice rafted detritus from sea ice in the fram strait abstract a three year particle flux record from the eastern fram strait between greenland and svalbard revealed a rather untypical seasonal flux pattern compared to other particle flux studies from the nordic seas in the eastern fram strait this pattern is characterised by a sudden four to six fold increase of the particle flux in january when no daylight is available to support any biological productivity comparison with sea ice distribution maps led to the conclusion that the sudden increase in the flux is due to ice rafted detritus released from sea ice which originated from the svalbard archipelago and from the northern barents sea detailed grain size analyses of the silt fraction indicated the 10 m fraction of the lithogenic matter to be clearly enriched due to ird input even more important is the observation that lithogenic material 40 m occurs exclusively during the ice rafting event and therefore appears to be a suitable indicator for ird transported on sea ice thus in addition to coarse ird e g 500 m which is mainly derived from icebergs the analysis of fine ird 40 m in deep sea sediments can be used to reconstruct paleo sea ice extensions

the hierarchical structure of glacial climatic oscillations interactions between ice sheet dynamics and climate abrupt climatic oscillations around the north atlantic have been identified recently in greenland ice cores as well as in north atlantic marine sediment cores the good correlation between the dansgaard oeschger events in the ice and the heinrich events in the ocean suggests that climate in the north atlantic region underwent several massive reorganizations in the last glacial period a characteristic feature of these events seems to be their hierarchical structure every 7 to 10 thousand years when the temperature is close to its minimum the ice sheet undergoes a massive iceberg discharge this heinrich event is then followed by an abrupt warming then by several other oscillations each one lasting between one and two thousand years these secondary oscillations do not have a clear signature in marine sediments but constitute most of the dansgaard oeschger events found in the ice here we use a simplified model coupling an ice sheet and an ocean basin in order to illustrate how the interactions between these two components can lead to such a hierarchical structure the ice sheet model exhibits internal oscillations composed of ice sheet growing phases and basal ice melting phases that induce massive iceberg discharges these massive fresh water inputs in the ocean stop for a moment the thermohaline circulation enhancing the temperature contrast between low and high latitudes just after this event the thermohaline circulation restarts and an abrupt warming of high latitude regions is observed for some parameter values these warmer temperatures have in turn some influence on the ice sheet inducing secondary oscillations similar to those found in paleoclimatic records although the mechanism presented here may be too grossly simplified it nevertheless underlines the potential importance of the coupling between ice sheet dynamics and oceanic thermohaline circulation on the structure of the climatic records during the last glacial period

response of interior north america to abrupt climate oscillations in the north atlantic region during the last deglaciation several broad scale climatic oscillations during the last deglaciation are well documented in regions around the north atlantic ocean this paper reviews empirical evidence for these deglacial climatic oscillations from non coastal north america and discusses implications for testing climatic simulations and for understanding the cause and transmittal mechanisms paleoclimatic interpretation of oxygen isotope records from several small sites in the eastern great lakes region indicates a classic deglacial climatic sequence that is comparable with records from europe and greenland the climatic events as interpreted from crawford lake oxygen isotopes include the bolling allerod boa warming at 12 700 14c bp a warm boa at 12 500 10 920 14c bp an intra allerod cold period shortly before 11 000 14c bp a cold younger dryas yd climate reversal at 10 920 10 000 14c bp the holocene warming at 10 000 14c bp a brief preboreal oscillation pb at 9650 14c bp and an early holocene cold event at 7500 14c bp 8200 cal bp some of these events were also evident from changes in upland and aquatic vegetation and sediment lithology the pronounced yd climatic reversal has been documented from pollen records along the ecotones at this time and from glacier readvances in the great lakes region along the rocky mountains from alberta to colorado the yd event is indicated by alpine glacier advance and or shift in timberline vegetation in minnesota and upper new york early holocene climatic instability is also suggested by oxygen isotope records and or varve thickness the regional variations in evidence for the yd and other events in north america suggest that climatic oscillations may have different expressions in paleo records depending on geographic location and characteristics of a particular site the extent and magnitude of these climatic oscillations across north america suggest that these oscillations are an expression of climatic change that was probably widespread rather than locally induced by a nearby glacier the location of these sites implies that climatic signals were likely carried over the northern hemisphere through the atmosphere as indicated by general circulation models we hypothesize that the lack of evidence for a cold yd in interior north america west of the great lakes region and east of the rocky mountains was caused by the trapping of cold arctic air mass north of the laurentide ice sheet and by uninterrupted northward expansion of warm caribbean air this strongly contrasted climate also produced non analogous biological assemblages

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

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

a geochemical criterion for the recognition of heinrich events and estimation of their depositional fluxes by the 230thexcess 0 profiling method abstract a core from the armorican seamount 46 23 8 n 12 32 8 w 3849 m in the deep ne atlantic southwest of the british isles exhibits unusual mg al ratios in the sediments deposited during the last glacial period high mg al ratio values are restricted within layers of 14 cm thick and mark the presence of ice rafted detrital material deposited by heinrich events h1 h2 and h4 these peaks in the ratio are caused by local increases in the dolomite quartz and feldspar content and concomitant dilutions in the phyllosilicate content which overall increase mg and decrease al the known times of the heinrich events provide a chronology for the core and indicate a considerably slower mean sediment accumulation rate during and after the glacial interglacial transition 2 2 cm ky 1 than in earlier glacial times mean 5 6 cm ky 1 within the glacial however 230 th excess 0 profiling demonstrates that accumulation fluxes were at least 7 higher than normal during the deposition of heinrich events up to 25 g cm 2 ky 1 versus a background glacial level of 3 7 g cm 2 ky 1 because of post depositional bioturbation peak fluxes are likely to have been even higher the 230 th excess 0 method also reveals the presence of event h3 which bears minor dolomite and is the least well developed of the last four heinrich events despite the marked compositional and flux variations the total mass deposited at this site is estimated at only 2 4 4 9 and 7 9 g cm 2 for events h1 h2 and h4 respectively these inventories were deposited over maximum periods of 2 0 1 1 and 0 7 ky respectively but delivery could have been much more rapid of the order of a few hundred years

ice sheet action versus reaction distinguishing between heinrich events and dansgaard oeschger cycles in the north atlantic 1 glaciers and ice sheets play an active role in the climate system and the global hydrological cycle the stability of continental ice sheets must be better understood for assessments of future sea level rise and to uncover the causes of millennial scale climate variability that characterized the last glacial period ice rafted debris ird in the midlatitude oceans and subpolar seas tells of widespread calving of icebergs from the northern hemisphere ice sheets during the last glacial period but the climatic implications of this ird are unclear does the sediment record indicate repeated dynamical collapse of the ice sheets with ice sheets actively forcing the climate system alternatively were ice sheet margins simply advancing and retreating in response to climate vacillations on the basis of simulations of iceberg delivery to the ocean during the last glacial cycle we argue that the marine record exemplifies both of these phenomena heinrich events were clearly episodes of internal dynamical instability of the laurentide ice sheet while millennial scale ird is more simply interpreted as a response of the circum atlantic ice sheets to dansgaard oeschger climate cycles ice sheets in different coastal regions respond differently to climate fluctuations but overall iceberg fluxes increase in cold periods peaking within a few centuries of climatic cooling regions with relatively warm wet climates scandinavia western north america and svalbard are the most sensitive to millennial climate variability with rapid response times and large millennial variability in iceberg fluxes

sea ice ice rafting and ocean climate across denmark strait during rapid deglaciation 16 12 cal ka bp of the iceland and east greenland shelves

anatomy of labrador sea heinrich layers abstract heinrich layers h layers are distinct decimetre to centimetre thick layers of ice rafted debris ird that were deposited in the north atlantic during the late and middle pleistocene h layers h layers are characterized by high detrital carbonate and low foraminifera contents in the labrador sea h layers reach metre thickness in some proximal core sites near the iceberg source of the hudson strait ice stream and show five distinct depositional facies involving sediment lofting and low density turbidity currents as sediment delivery processes besides ice rafting thick massive ice rafted layers type i h layers occur in the most proximal parts of h layer 3 and older h layers within 300 km distance from the assumed hudson strait ice stream terminus h layers somewhat more distal than type i h layers consist predominantly of stacked thin layers of graded muds containing ird type ii h layers the graded muds that are spiked with ird resulted from the deposition of fine grained lofted sediment that collected dropstones and grains under the iceberg route at greater distance from the hudson strait outlet on the slope and rise south of the strait h layers on the levees of tributary canyons to the northwest atlantic mid ocean channel namoc consist of alternations of thin mud turbidites with intercalated laminae of ird type iii h layers on the levees of namoc type iv h layers consist of layers of ird alternating with fewer fine grained spill over turbidites because the spill over frequency from the deep channel was less than that from the less deep canyons on the slope type v is made up of bioturbated hemipelagic muds with coarser ird and occurs in regions between canyons not reached by spill over turbidity currents and in distal regions of the open ocean or on seamounts transport of significant portions of the sediment in h layers by suspended sediment columns lofted from sand carrying fresh water turbidity currents type ii and by low density turbidity currents types iii and iv explains the high percentage of detrital carbonate in the fine 80 of the total detrital carbonate of the bulk sediment which cannot be derived from icebergs alone it also explains the low magnetic susceptibility and low grey levels on the colour scale compared to h layers in the north atlantic east of greenland the anomalously great thickness of individual h layers on the slope and rise off the hudson strait as documented in isopach maps reflects the combined effect of the various processes involved in their deposition four hypotheses for the origin of h events are discussed i the binge purge model ii the subglacial outburst flow model iii the external forcing model and iv the catastrophic ice shelf break up model

late quaternary paleochemistry of high latitude surface waters recent studies have stressed the role of high latitude nutrient levels and productivity in controlling the carbon isotopic composition of the deep sea and the co2 content of the atmosphere we undertook a study of the chemical composition of the polar planktonic foraminifer neogloboquadrina pachyderma s sinistral coiling from 30 late holocene samples and 49 down core records from the high latitude north and south atlantic oceans to evaluate the history of sea surface chemical change from glacial to interglacial time stable isotopic analysis of coretop samples from the atlantic pacific and southern oceans shows no significant correlation between the 13c of n pachyderma and either 13c or po4 in seawater conversely cd ca ratios in planktonic foraminifera are consistent with the po4 content of surface waters the level of maximum glaciation 18 000 yr b p identified by climap and 18o was chosen for mapping isopleths of 18o on n pachyderma s in the north atlantic reveal a pattern largely influenced by sea surface temperature s s t and generally support the s s t reconstruction of climap differences between the two suggest significantly lower salinity in north atlantic surface waters at high latitudes than in lower latitudes down core 13c records of n pachyderma confirm that low 13c values occurred in the northeast atlantic during the latest glacial maximum labeyrie and duplessy 1985 however a map of 13c for the 18 000 yr b p level for a much larger region in the north atlantic shows that minimum n pachyderma 13c occurred in temperate waters n pachyderma 13c decreased toward the southwest reaching a minimum of 1 at 37 n despite the variability seen in 13c records of n pachyderma none of our cores show significant temporal variability in cd ca from the combined cd ca and 13c data we can see no evidence for an upwelling gyre in the eastern north atlantic during the latest glacial maximum nor evidence that the southern and northern oceans had significantly different levels of preformed nutrients than today

late quaternary iceberg rafted detritus events on the denmark strait southeast greenland continental slope 65 n related to north atlantic heinrich events hu93030 007 lcf 65o01 39 0 n and 30o14 81 0 w is a 4 5 m long giant 11 cm diameter piston core from 1800 m water depth on the continental slope south of the denmark strait sill the core sampled acoustically stratified sediments at a site below the kangerlussuaq trough nine ams 14 c dates on planktic foraminifera indicate that the core spans 14 to 28 14 c ka the sediments consists of two principal lithofacies lithofacies i li comprises tan ochre intervals with abundant ice rafted sandstone siltstone clasts larger than 2 mm and with an average thickness of 47 cm it is also associated with peaks in carbonate content and toc lithofacies ii lii consists of fine grained dark gray hemipelagic sediment there are three distinct intervals of li dated between 14 3 and 15 5 lic 20 1 and 21 9 lib 24 7 and 25 8 lia ka the ages suggest that deposition of li is approximately coeval with heinrich events 1 and 2 in the north atlantic whereas lia appears younger than h 3 lithofacies i is derived from far travelled ice bergs from an unknown source but not from the northeastern laurentide ice sheet stable isotope studies on neogloboquadrina pachydermasinistral show little evidence for significant meltwater events associated with li but surprisingly light oxygen isotopic events are present in the benthic foraminiferal analyses cibicidoides wuellerstorfiand melonis zaandamae the ages of the hu93030 007 iceberg rafted detritus ird events are similar to ird peaks in cores north of denmark strait on the east greenland slope hu87033 009 lcf se baffin slope 62o30 99 0 n and 59o26 82 0 w 1437 m wd is situated in a similar position to hu93030 007 but with respect to the laurentide ice sheet its d 18 o record on planktic foraminifera is virtually identical to that of hu93030 007 the timing of ird events is similar in both these cores between 14 and 30 ka h 3 may be present in hu87033 009 as an ird event but in contrast to h 1 and h 2 it is not evident as a discernible detrital carbonate event 1998 elsevier science b v all rights reserved

explained and unexplained spatial and temporal variability in rates of marine sediment accumulation along the northeast margin of the laurentide ice sheet 14 ka abstract changes in sediment accumulation rate sar cm ky for fifteen ams 14c dated late quaternary sites from along the ne margin of canada between 66 and 54 n are examined these 15 cores cover the last deglacial cycle of sediment input from the decaying laurentide ice sheet and subsequent postglacial marine sedimentation on these arctic and subarctic shelves and basins it is shown that the spatial and temporal variability of the 15 sar time series do not simply parallel the known glacial chronology deglaciation of the shelves initially occurred after heinrich event 1 h 1 14 5 ka all dates are in 14c yr subsequently there were major ice advances during the younger dryas yd h 0 10 11 ka and the noble inlet glacial events 8 6 ka with final collapse of the ice sheet ca 8 0 ka a total of 73 radiocarbon dates were used which led to 58 sar estimates the median sar is 69 cm ky however the distribution is strongly positively skewed because of short lived intervals of very high sar 5000 cm ky ca 5000 kg m 2 ky 1 on the labrador shelf high sar are associated with ice retreat from the noble inlet maximum 8 6 ka whereas on the se baffin shelf there is little response in the sediment system to this event conversely during the younger dryas heinrich 0 yd h 0 event high sars occur on the se baffin shelf but along the labrador shelf the interval 10 11 ka is marked by modest sars both the 11 10 and 8 6 8 ka rapid sediment accumulation events are marked by considerable increases in the detrital carbonate content hence bear similarities to the major heinrich events in the nw labrador sea these unexpected spatial and temporal differences in sediment deposition probably reflect changes in sediment transport trajectories associated with differences in ice glacial or sea ice extent and atmospheric oceanic circulations

last glacial maximum surface water properties and circulation over laurentian fan western north atlantic abstract millennial scale events marked by the contribution of detrital sand are recorded in north atlantic sediments during the last glacial maximum lgm between heinrich events he 1 and 2 and left their imprint on laurentian fan lf 43 n sediments off eastern canada the lf counterpart of the well known detrital events consist of glacial red brick sediments resulting from subglacial flows separated by olive grey sediments appears at 21 4 19 9 and 19 5 18 65 cal kyr bp high resolution analyses of diatom assemblages and lithic grains coupled with planktonic oxygen isotopic records reveal that while the red sediment is almost barren of diatoms foraminifera and lithics 150 m they are abundant in the olive grey sediment diatom assemblages reveal three phases during these events 1 initial relatively warm temperate conditions followed by 2 very cold surface water and drifting ice and 3 a final phase characterized by relatively warmer waters and the appearance of detrital carbonate although these events possibly reflect the variability specific to the slope water region they are likely the response to atlantic meridional overturning circulation perturbations and ice sheet instability through a chain of mechanisms meltwater inputs into the north atlantic led ultimately to an increased volume of tropical waters and part of the heat stored in the subsurface was flushed by a brief convective episode that was not sustained accounting for the return of cold conditions after the events the sequence of mechanisms deduced from the paleo data here and elsewhere is consistent with previous modeling results these data suggest that the detrital events between heinrich event 1 and 2 may be synchronous across the north atlantic and that the lgm was probably not a time of prolonged steady state in the climate system

the presence of polynyas in the weddell sea during the last glacial period with implications for the reconstruction of sea ice limits and ice sheet history cores from a contourite drift on the continental slope in the nw weddell sea antarctica contain up to four sandy foraminifer rich layers wa1 4 with dispersed ice rafted debris ird interbedded with silty clayey sands and sandy muds accelerator mass spectrometry ams 14c dating on neogloboquadrina pachyderma from the foraminifer rich layers wa2 and wa3 yielded ages spanning the last glacial maximum lgm and marine isotope stage mis 2 20 319 28 543 cal yr bp and the middle part of mis 3 41 349 43 242 cal yr bp respectively we attribute the high abundances of planktonic and benthic foraminifera to deposition in a seasonally open marine environment given that the nw weddell sea shelf was covered by grounded ice at the lgm and probably during mis 2 and mis 3 and that diatom based reconstructions place the northern limit of winter and summer sea ice coverage to the north of the core sites during the last glacial period our results document the presence of a seasonal or perennial polynya in the nw weddell sea the polynya may have been formed by katabatic winds blowing off the antarctic peninsula ice sheet apis when it was grounded at the continental shelf break although polynya formation through upwelling of deep water cannot be ruled out in addition we argue that previously published data from the southern southeastern and southwestern weddell sea as well as the ross sea may indicate the widespread occurrence of polynyas along the antarctic continental margin during the last glacial period the widespread occurrence of polynyas could help explain how i aabw formation through brine rejection continued throughout the lgm and ii antarctic shelf benthos survived glacial periods the presence of polynyas through glacial periods also has implications for sea ice reconstructions from ice core records possibly biasing the signal towards a reduced sea ice cover finally we propose that the fringes of the apis which probably influence the presence or absence of polynyas in the nw weddell sea are sensitive to changes in antarctic temperature that may be related to a reduction in oceanic heat transport from the north atlantic

ice rafted debris associated with binge purge oscillations of the laurentide ice sheet the north atlantic sediment record suggests quasi periodic 7000 to 12 000 year period ice rafted debris ird depositions during at least the last glacial period the cause of these heinrich events as they are commonly known is not fully understood however they may point to surges of the ice stream that drained the hudson bay hudson strait region of the laurentide ice sheet we investigate a simple conceptual model of ice stream instability the binge purge model to suggest ways in which the ice stream could have entrained sufficient debris to account for the estimated mass of ird associated with a typical heinrich ird layer in the north atlantic 1 0 0 3 1015 kg we find that freezing of debris laden ice at the bed of the ice stream during the brief 750 years surge phase of the ice stream s hypothesized binge purge cycle can incorporate up to 5 1 1015 kg this amount is sufficient to meet the constraints of the north atlantic sediment record but by no means verifies the binge purge model as the cause of heinrich events

oceanic evidence for coherent fluctuations in fennoscandian and laurentide ice sheets on millennium timescales proxy temperature records from greenland ice cores1 2 and north atlantic sediment cores3 have provided evidence for a high degree of climate instability during the last glacial period much of this variability seems to be linked with the dynamics of the laurentide ice sheet that covered north america at this time3 which dis charged iceberg flotillas into the north atlantic that are now recorded in sediment cores as heinrich events4 how if at all this variability was manifested on the other side of the atlantic in the nordic seas and the ice sheets of northwest europe and scandinavia has been unclear here we present sediment micro fossil and oxygen isotope data from a sediment core in the norweg ian sea which reveal cooling events and iceberg discharges analogous to heinrich events we show that these climate fluctua tions in the norwegian sea were in phase or were phase locked with air temperatures over greenland suggesting that the rapid changes in heat fluxes in the north atlantic recorded in previous records3 were felt in this high latitude region the iceberg dis charges in our record seem to have come from the fennoscandian ice sheet implying that this and the laurentide ice sheets fluctu ated coherently on timescales shorter than those of milankovitch orbital cycles

meltwater and deglaciation se baffin shelf ne margin laurentide ice sheet between 13 5 and 7 ka from o and c stable isotopic data stable isotopic values on planktonic foraminifera in a suite of cores from basins across the se baffin shelf are used to extract a record of meltwater events during termination i deglaciation resolution and hatton basins lie on the se baffin shelf at water depths 500 m seaward of major conduits for ice drainage from the eastern sector of the laurentide ice sheet lis accelerator mass spectrometry 14c dates are used to constrain our chronology of events in ten cores in resolution basin three cores have 14c ams dates on foraminifera of 20 ka at their bases whereas hatton basin cores terminate in sediments 13 kyr sedimentation rates varied between 0 1 to 4 5 m ka stable oxygen and carbon isotopic ratios were obtained on 146 samples of the planktonic foraminifera neogloboquadrina pachyderma ehrenberg sinistral from seven of the ten cores no evidence was found to indicate that test morphology or size affected 18o between 7 and 13 5 ka the surface water on the shelf was on average 1 lower than the open ocean signal significant temporal variations were found in both 18o and 13c evidence for significant low 18o events occurred between 13 and 8 ka the 13c record from the planktonic foraminifera suggests a threefold division of events between 13 and 7 ka with positive values between 10 8 and 13 0 ka negative values between 9 and 10 8 ka and positive values from 7 to 9 ka the 18o data suggest the presence of meltwater on the shelf some 3 000 years prior to the first late glacial dates on terrestrial deglaciation at circa 10 4 ka hudson strait must be the real key to the importance of the calving process during deglaciation because it is potentially the largest marine outlet for the laurentide ice sheet and because it leads into the very center of the ice sheet the rates of calving through hudson strait during the period of initial 18o rise unfortunately are unknown w f ruddiman 1987 p 151

oceanographic regimes in the northwest labrador sea since marine isotope stage 3 based on dinocyst and stable isotope proxy records abstract sea surface temperature sst salinity and density gradients in the upper water column of the northwest labrador sea have been reconstructed based on high resolution analysis of a core hu2008 029 004pc spanning the last 36 ka raised off hudson strait the modern analogue technique was applied to dinocyst assemblages and combined with stable isotope data from neogloboquadrina pachyderma left coiled npl for this purpose three oceanographic regimes were identified broadly corresponding to the glacial deglacial and postglacial intervals the site remained under the direct influence of the laurentide ice sheet lis margin until the postglacial and did not record the bolling allerod warming and weakly recorded the younger dryas event the glacial regime lasted until 12 2 cal ka bp it was characterized by generally low concentrations of dinocysts within an assemblage indicative of quasi perennial sea ice the deglacial regime ca 12 2 8 3 cal ka bp was marked by increased biogenic fluxes and more diversified dinocyst assemblages and possibly an enhanced subsurface inflow of north east atlantic deep water warm summer 11 c but low winter 0 c sea surface temperatures sea ice cover during about 3 months per year and low summer salinity 28 suggest strong stratification in the upper water layer in relation to meltwater supply from the lis following the final drainage of glacial lake agassiz through hudson strait which is dated here at 8 3 cal ka bp and the subsequent lis collapse increased summer salinity up to 35 was accompanied by a reduced seasonal gradient of sea surface temperature from winter 3 8 c to summer 8 6 c suggesting enhanced penetration of north atlantic water weakened stratification of the surface water layer then allowed for winter convection and labrador sea water formation which is consistent with increased npl 13c values in response to higher ventilation of the subsurface water layer

dansgaard oeschger events is there a signal off the hudson strait ice stream abstract it is generally accepted that the dramatic heinrich h events were principally sourced from the major hudson strait drainage basin of the laurentide ice sheet but it is not known whether the higher frequency dansgaard oeschger d o events have an imprint on sediments deposited during the inter h intervals in ice proximal slope sediments this paper examines this question by an analysis of data from cores on the se baffin slope because the proxies for heinrich events are so massive in scale we removed the major h events h 1 h 2 and h 4 from the records so as to better examine the structure of data in the intervening hemipelagic sediments the period of interest extends between 15 and 40 cal ka interstadial events 2 8 resolution varies with the proxy to between 210 and 700 yrs per sample in hu87033 009 from the lower slope a total of twelve variables for example 18o mass magnetic susceptibility calcite dolomite ratio number of ird 2 mm show a variety of multi millennial oscillations although not all of the same amplitude nor frequency several parameters show little correlation with the gisp2 18o record however a comparison of cie sediment color l from hu87033 009 and hu97048 007 from the upper slope with the gisp2 oxygen isotope record suggests that a substantial correlation exists between the records such changes might be associated with either detrital carbonate content or foraminiferal concentrations analysis suggests however that the first possibility is correct hence suggestive of a glaciological response of the hudson strait ice stream with d o events in the nw labrador sea the sediment records from around h 3 time 30 cal ka show excursions which might be correlative within this event but its amplitude is not unusual compared to events both before and after this reaffirms the argument that h 3 represents a different glaciological response a significant issue discussed in this paper is the inherent ambiguity of correlating records whose errors in the time domain approach that of a dominating periodicity in this case ca 1 5 kyr

reef drowning during the last deglaciation evidence for catastrophic sea level rise and ice sheet collapse elevations and ages of drowned acropora palmata reefs from the caribbean atlantic region document three catastrophic metre scale sea level rise events during the last deglaciation these catastrophic rises were synchronous with 1 collapse of the laurentide and antarctic ice sheets 2 dramatic reorganization of ocean atmosphere circulation and 3 releases of huge volumes of subglacial and proglacial meltwater this correlation suggests that release of stored meltwater periodically destabilized ice sheets causing them to collapse and send huge fleets of icebergs into the atlantic massive inputs of ice not only produced catastrophic sea level rise drowning reefs and destabilizing other ice sheets but also rapidly reduced the elevation of the laurentide ice sheet flipping atmospheric circulation patterns and forcing warm equatorial waters into the frigid north atlantic such dramatic evidence of catastrophic climate and sea level change during deglaciation has potentially disastrous implications for the future especially as the stability of remaining ice sheets such as in west antarctica is in question

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

temporal correspondence between pluvial lake highstands in the southwestern us and heinrich event 1 pluvial lakes were abundant in the southwestern united states during pleistocene glaciations particu larly in the great basin many of these lakes occupied closed basins therefore fluctuations of their water surface elevations are valuable sources of paleoclimate information histories of the largest lakes are well constrained whereas dozens of smaller lakes that were present in this region have received relatively little scientific attention given their dimensions these smaller lakes were climatically sensitive and can offer important information about quaternary climate variability here we present new ages for the highstands of three previously undated small lakes based on radiocarbon dating of gastropod shells recovered from beach ridges these results are combined with other published and unpublished 14 c ages to yield an extensive compilation of highstand shoreline ages for lakes of all sizes throughout the southwestern us the results indicate that although some lakes reached highstands during the last glacial maximum the strongest temporal correspondence is between highstands and heinrich event h1 these results are consistent with speleothem based reconstructions of effective moisture in the southwestern us which show increased precipitation during stadials of the last glacial cycle copyright 2012 john wiley sons ltd

sedimentology and history of sediment sources to the nw labrador sea during the past glacial cycle abstract the paleoceanography and sediment dynamics of the northernmost labrador sea provides critical records of glacial history glacially dominated sedimentation and paleocirculation a reference core at 938 m on the se baffin slope was investigated with new oxygen isotope stratigraphy x ray fluorescence geochemistry and 18 14c ams dates and correlated to 14 regional deep water cores the reference core provides a paleoceanographic and sediment source record over the last 40 ka overlying a 3 m thick blocky mass transport deposit over mis 5 autochthonous sediment detrital carbonate rich sediment layers h0 h4 based on bulk geochemistry were derived principally from hudson strait shortly after h2 and h3 the shelf crossing cumberland sound ice stream supplied dark brown ice proximal stratified sediments minor supply of carbonate rich sediment from baffin bay allows chronologic integration of the baffin bay and labrador sea detrital carbonate records and implies an open seaway through davis strait the counterparts of h3 h4 and h5 events in the deep labrador basin are 4 10 m thick units of thin bedded carbonate rich mud turbidites from glacigenic debris flows on the hudson strait slope the behavior of the hudson strait ice stream changed through the last glacial cycle in h1 and h2 the ice stream retreated back across the shelf but did not deglaciate hudson bay in h3 h5 it remained at the shelf break long enough to supply thick turbidites and subsequent retreat after h4 and h5 deglaciated hudson bay the maximum extent of ice streams in hudson strait cumberland sound and lancaster sound was not synchronous

a 200 ka geomagnetic chronostratigraphy for the labrador sea indirect correlation of the sediment record to specmap abstract a chronostratigraphic framework for the last 200 ka based on relative variations of geomagnetic paleointensity has been derived for the labrador sea where 18o stratigraphies are compromised by lack of benthic foraminifera and environmental perturbations of the planktic record relative paleointensity records derived from three labrador sea piston cores are correlated to a recently developed 200 ka paleointensity composite sint 200 y guyodo j p valet earth planet sci lett 143 1996 23 36 the chronology for sint 200 was derived by correlating oxygen isotope stratigraphies from individual paleointensity records to the specmap chronostratigraphy the correlation of sint 200 to labrador sea paleointensity records allows the specmap chronology to be imported into the labrador sea although comparisons of the chronostratigraphy based on paleointensity correlations with those derived from ams 14c dates and 18o data indicate significant discrepancies support for the new chronostratigraphic framework is provided by 1 consistent correlation of labrador sea detrital layers to north atlantic heinrich layers 2 general consistency between planktic 18o values and the specmap reference curve and 3 feasible prediction for the age of ash layer 2 as the new chronostratigraphy is tied to specmap labrador sea sediment cores can now be directly compared with any specmap dated record

late quaternary stratigraphy and paleoecology of northwest labrador sea abstract sedimentological study of 20 piston cores from the northwestern labrador sea shows that thin bedded distal turbidites are important constituents of the quaternary strata on the continental slope and rise sedimentation on the outer shelf ca 500 900 m is dominated by ice rafting and hemipelagic deposition detailed study of two outer shelf cores reveals a stratigraphic record extending to oxygen isotopic stage 9 studies of foraminifera and dinoflagellates show that subarctic surface waters penetrated into the northern labrador sea during the early middle glacial stages and pollen data indicate that northward advection of warm air masses occurred at the same time microfossil data indicate that late glacial stages were characterized by year around sea ice cover and arctic surface water and by the dominance of cold dry arctic air masses transitions from glacial to interglacial stages are marked by the presence of low salinity melt water these data support models which postulate that open water in the labrador sea played an important role in supplying moisture to laurentide and greenland ice sheets

detrital carbonate rich sediments northwestern labrador sea implications for ice sheet dynamics and iceberg rafting heinrich events in the north atlantic much of the bed of the central and eastern sectors of the laurentide ice sheet was underlain by paleozoic carbonates we propose that pulses of detrital carbonate rich sediments in two cores from the northwestern labrador sea reflect episodes when an ice stream from the hudson strait extended to the shelf break and delivered sediment onto the slope and deep sea plain atomic mass spectroscopy 14 c dating of planktonic foraminifera in cores hu75 009 iv 55 2 4 km water depth and hu87 033 009 1 4 km water depth and 150 km north northwest indicates that the youngest event occurred between ca 14 and 15 ka and another occurred between 19 and 21 ka the two carbonate intervals in northwestern labrador sea cores are coeval with heinrich events 1 and 2 in the eastern north atlantic lat 45 50 n long 20 w where they are associated with an increase in lithic fragments and a drastic reduction in the numbers of foraminifera these changes have been linked with the massive production of icebergs associated with ice sheet surges our evidence indicates that heinrich events 1 and 2 are associated with the dynamics of the hudson strait ice stream and denote considerable glaciological instability

deglacial meltwater discharge north atlantic deep circulation and abrupt climate change high resolution paleogeochemical data from the north atlantic ocean indicate that in the interval 15 000 to 10 000 14c years before present b p north atlantic deep water nadw production was decreased or eliminated four times at about 14 500 and probably older 13 500 12 000 and 10 500 years b p each of these changes occurred at the same time as abrupt events of meltwater discharge to the surface ocean inferred from oxygen isotope studies of planktonic foraminifera and from glacial geological studies on land in addition each of these times may be associated with brief episodes of cooler climate in the north atlantic region the best example of which is the younger dryas cooling of 10 500 years ago these results support models linking meltwater discharge decreased nadw production and decreased north atlantic heat flux

the low latitude monsoon climate during dansgaard oeschger cycles and heinrich events during the last 100 000 years dansgaard oeschger cycles d o cycles and heinrich events have been the dominant signal of past climate variability over greenland and the north atlantic the succession of stadials cold and interstadials warm associated with these cycles has been documented in records from the entire northern hemisphere south america new zealand antarctica the south atlantic and the southern ocean evidently climate forcing in the d o band affects both hemispheres the origin and cause of these teleconnected patterns is still unknown even if a large proportion of the cooling in europe and northern asia during heinrich events is a meteorological response to cold surface water in the north atlantic resulting from the surge of the laurentian and scandinavian ice sheets but this does not imply that the d o cycles are a priori caused by the collapse of these large icesheets a severe challenge to a primary origin from the northern ice sheet and north atlantic comes from the observation that warming in antarctica and the circumpolar current leads the north atlantic changes by some 1500 years charles et al 1996 blunier et al 1998 in the second part of the paper we investigate new deep sea records from the low latitude monsoon system mainly corroborating the result of schulz et al 1998 that the indian monsoon showed d o variability the abundance of eolian dust indicating continental humidity aridity in core 70kl from the arabian sea shows humid intervals which seem to correlate with temperature maxima in the antarctic vostok ice core apparently the low frequency sub milankovitch variability of the monsoon is associated with the southern hemisphere the d o scale component in the monsoonal climate on the other hand shows a succession of short humid intervals the sequence is most closely comparable to the greenland temperature record and to the stadial interstadial succession in the pacific santa barbara basin odp 893 in order to understand the global forcing of climate change in the d o band it appears necessary to quantify the phase relationships not only between d o cycles in the polar ice cores bender et al 1994 blunier et al 1998 steig et al 1998 but also between the low latitude pacific indian ocean and the high latitude records

deep sea records from the southeast labrador sea ocean circulation changes and ice rafting events during the last 160 000 years 1 results from two deep sea cores from northeast of newfoundland at 1251 and 2527 m water depth respectively indicate that during the time period from 160 000 to 10 000 years bp ice rafting events in the labrador sea were accompanied by rapid variations in deep and surface water circulation twelve ice rafting events occurred each coinciding with high concentrations of detrital carbonate and oxygen isotopic depletion of both surface and bottom waters eleven of these can be correlated with the north atlantic heinrich events h1 h11 the remaining very conspicuous ice rafting event took place early in mis substage 5e at a time when the planktic faunal assemblage suggests marked warming of the sea surface in the shallower core benthic delta 13 c values rise from a minimum during the deglaciation to peak substage 5e values following the last ice rafting event indicating that the ventilation of intermediate depths was renewed after the deglaciation was complete and continued throughout substage 5e the benthic foraminifera suggest that this well ventilated water mass was comparable to the modern labrador sea water lsw the benthic faunas suggest that a relatively warm intermediate water mass entered the se labrador sea during heinrich events generally low benthic delta 13 c values indicate that this water mass was poorly ventilated and rich in inorganic nutrients isotope data and benthic faunal distributions indicate that north atlantic deep water nadw formed in the norwegian greenland sea reached the se labrador sea between the heinrich events

the abrupt termination of the younger dryas climate event previous studies on two deep greenland ice cores have shown that a long series of climate oscillations characterized the late weichselian glaciation in the north atlantic region1 and that the last glacial cold period the younger dryas ended abruptly 10 700 years ago2 here we further focus on this epoch defining event and present detailed heavy isotope and dust concentration profiles which suggest that in less than 20 years the climate in the north atlantic region turned into a milder and less stormy regime as a consequence of a rapid retreat of the sea ice cover a warming of 7 c in south greenland was completed in about 50 years

late quaternary stage 2 and 3 meltwater and heinrich events northwest labrador sea two major meltwater events are documented in cores from the nw labrador sea one occurred ca 20 000 14c yr b p in association with deposition of a major detrital carbonate unit both prior to and after this event 18o values of near surface planktonic foraminifera were 4 5 indicating fully enriched glacial values a younger event ca 14 000 14 c yr b p is characterized by a dramatic change in 18o from 4 5 to 2 0 and coincided with the retreat of ice from the outer se baffin shelf possibly into hudson strait these meltwater events coincide with heinrich h layers 1 and 2 from north atlantic sediments the 14 000 14c yr b p meltwater event indicates that the eastern margin of the laurentide ice sheet also underwent rapid retreat at approximately the same time as other ice sheet margins around the ne north atlantic a third major detrital carbonate event at the base of hu87 033 009 possibly correlative with heinrich layer 3 occurred ca 33 960 675 14 c yr b p however this is older than the accepted date for h 3 of 27 000 14c yr b p and may be h 4

reflection of scandinavian ice sheet fluctuations in norwegian sea sediments during the past 150 000 years the record of glacier fluctuations in western scandinavia as reconstructed from continental data has been correlated with records of ice rafted detritus ird from well dated sediment cores from the norwegian sea covering the past 150 000 yr b p the input of ird into the ocean is used as a proxy for ice sheet advances onto the shelf and thus for the calibration of a glaciation curve the marine results generally support land based reconstructions of glacier fluctuations and improve the time control on glacial advances the saalian ice sheet decayed very rapidly approximately 125 000 yr b p in the early weichselian a minor but significant ird maximum indicates the presence of icebergs in isotope substage 5b especially between 95 000 and 83 000 yr b p reduced amounts of calcareous nannofossils indicate that surface waters were influenced by meltwater discharges during isotope substages 5d and 5b an extensive build up of inland ice began again during isotope stage 4 but maximum glaciation was reached only in early stage 3 58 000 53 000 yr b p marine sediments have minimum carbonate content indicating strong dilution by lithogenic ice rafted material generally the ird accumulation rate was considerably higher in stages 4 2 than in stage 5 a marked peak in ird accumulation rates from 47 000 to 43 000 yr b p correlates well with a second middle weichselian ice sheet advance dated by the laschamp olby paleomagnetic event minimum ice extent during the alesund interstade 38 500 32 500 yr b p and several glacial oscillations during the late weichselian are also seen in the ird record of several late weichselian glacial oscillations on the shelf at least four correspond to the north atlantic heinrich events ice sheet behavior was either coupled or linked by external forcing during these events whereas internal ice sheet mechanisms may account for the noncoherent fluctuations

late quaternary sedimentation on the southwestern scotian slope eastern canada relationship to glaciationgeological survey of canada contribution 20070176 the sedimentary record on continental slopes has the potential to preserve a record of glacial retreat on the adjacent continental shelf the glacial history of the southwestern part of the scotian shelf is poorly known air gun and high resolution sparker profiles and numerous sediment cores up to 10 m long have been used to determine the character of sedimentation on the southwestern scotian slope since the last glacial maximum lgm seismic reflection profiles show that glacial till was deposited at shallow depths on the upper continental slope and correlation to dated piston cores farther downslope show that this till dates from the lgm slope sedimentation at this time was dominated by local ice and deposited as plume fallout and turbidites progressively increasing importance of red brown sediment derived from glacial supply to laurentian channel indicates retreat of ice from the shelf edge and diminishing supply of proglacial sediment from the calving embayment in the mid scotian shelf with the

shelf erosion and glacial ice proximity in the labrador sea during and after heinrich events h 3 or 4 to h 0 as shown by foraminifera

late pleistocene mountain glacier response to north atlantic climate change in southwest ireland stephan harrison neil glasser ed anderson susan ivy ochs peter w kubik 2010 late pleistocene mountain glacier response to north atlantic climate change in southwest ireland quaternary science reviews 29 27 28 3948 3955

synchronized terrestrial atmospheric deglacial records around the north atlantic on the basis of synchronization of three carbon 14 c 14 dated lacustrine sequences from sweden with tree ring and ice core records the absolute age of the younger dryas preboreal climatic shift was determined to be 11 450 to 11 390 80 years before the present a 150 year long cooling in the early preboreal associated with rising delta 14 c values is evident in all records and indicates an ocean ventilation change this cooling is similar to earlier deglacial coolings and box model calculations suggest that they all may have been the result of increased freshwater forcing that inhibited the strength of the north atlantic heat conveyor although the younger dryas may have begun as an anomalous meltwater event

molecular stratigraphy of cores off northwest africa sea surface temperature history over the last 80 ka the molecular stratigraphy of biogeochemical oceanic flux study core 31k 19 n 20 10 w and ocean drilling program hole 658c 20 45 n 18 35 w has been studied for c37 alkenone abundances over the past 80 ka at high resolution circa 200 500 years the derived uk37 sea surface temperature record for both cores shows a range of temperatures from about 18 c during the last glacial to 21 5 c during the early holocene both records also reveal changes in sea surface temperature as much as 2 4 c over a few hundred years which correlate well with similar abrupt climatic changes observed in cores from elsewhere in the ne atlantic associated with heinrich events our results indicate that meltwater produced by these ice rafting events was transmitted southward by the canary current where it had considerable impact on sea surface temperatures in the subtropical eastern atlantic

rapid fluctuations of the laurentide ice sheet at the mouth of hudson strait new evidence for ocean ice sheet interactions as a control on the younger dryas ice directional features and erratic lithologies of the last glaciation demonstrate that a major outlet glacier of the laurentide ice sheet flowed nne across outer hudson strait rather than se down the strait as previously hypothesized ice advanced more than 600 km from a labradorean source crossing hudson strait and outer frobisher bay and advancing onto hall peninsula the highest summits on loks land circa 400 m asl a large island at the se tip of hall peninsula were inundated by labradorean ice three distinct late wisconsin advances have been recognized the earliest most extensive advance crossed frobisher about 11 5 kyr b p and was maintained for circa 1 kyr differences in the extent of amino acid racemization in shells from interstadial and deglacial sites on eastern loks land limit the duration of the most extensive late wisconsin advance s to a brief interval of no more than 2 kyr radiocarbon dates on in situ shells and on shells incorporated in till indicate that frobisher bay was ice free from at least 10 5 to 10 2 kyr b p after which a second labradorean advance the gold cove readvance attained nearly the same extent as the earlier advance the readvance was short lived and the bay was deglaciated before 9 5 kyr b p a final readvance occurred during the cockburn substage 9 to 8 kyr b p but ice failed to cross frobisher bay the maximum extent of the labradorean advance coincides with the onset of younger dryas cooling based on a minimum cross sectional area and reasonable estimates of ice velocity the iceberg flux to the north atlantic ocean at this time was between 300 to 2400 km year 1 about the same as the freshwater influx from the diversion of lake agassiz drainage to the st lawrence the input of a significant volume of ice into the north atlantic via the labrador sea would have cooled sea surface and air temperatures increased sea surface albedo and diminished the effectiveness of wind mixing of surface waters thereby reducing the volume of water required to effectively cap the north atlantic we suggest that a combination of a massive iceberg flux and increased st lawrence discharge may have been required to initiate younger dryas cooling when the outflow of lake agassiz was again routed down the st lawrence at 9 5 kyr b p a second younger dryas event failed to occur because by that time labradorean ice had retreated within hudson strait and was unable to generate a substantial climate altering volume of icebergs the possibility of an iceberg flood in the north atlantic could be tested by measuring the concentration of ice rafted detritus ird traditionally defined as quartz feldspar grains 125 m in deep sea cores however sediment entrained by the labradorean ice is dominated by detrital carbonate and only a small fraction of the noncarbonate component is 125 m hence a revised definition of ird is required to evaluate the iceberg flood hypothesis

seismic stratigraphy of the gulf of cadiz continental shelf a model for late quaternary very high resolution sequence stratigraphy and response to sea level fall

mid depth oxygen drawdown during heinrich events evidence from benthic foraminiferal community structure trace fossil tiering and benthic δ13c at the portuguese margin abstract the distribution of trace fossils and benthic foraminiferal assemblages in two sediment cores from 2160 m water depth at the northern and 1100 m at the southern portuguese continental margin was used to reconstruct the bottom water oxygenation during the last 40 ka emphasis was given to the heinrich events during which enhanced meltwater flux associated with the iceberg surges reduced or even halted deep water formation in the north atlantic condensed trace fossil tiering structures and high proportions of low oxygen tolerant benthic foraminifera suggest a major drawdown of bottom water oxygenation during heinrich events using the benthic foraminiferal oxygenation index bfoi of kaiho 1991 1994 that links benthic foraminiferal communities to ambient bottom water oxygenation we extracted apparent oxygen concentrations from benthic assemblages bfoi values suggest low oxic conditions during heinrich events 1 and 4 with mean oxygen levels of 2 6 to 2 8 ml l 1 and high oxic conditions with 4 1 ml l 1 during heinrich event 2 at the shallower site high proportions of low oxygen tolerant foraminiferal species and bfoi minima are recorded a few centimetres below the maximum concentrations of ice rafted debris indicating that the original microhabitat depth of dysoxic species is preserved beneath the heinrich layers even though bioturbation continued during the events trace fossil tiering calibrated with the redox boundary in low oxic environments and dysoxic ichnotaxa commonly associated with black shales indicate oxygen levels lower than those implied by the bfoi oxygenation estimates derived from trace fossil tiering denote low oxic conditions during h1 13 3 ka with oxygen concentrations slightly above 1 ml l 1 and dysoxic conditions during h2 20 6 ka h3 27 ka and h4 33 5 ka with oxygen concentrations between 0 1 and 1 ml l 1 during the younger dryas bottom waters likely were low oxic negative excursions of benthic carbon isotope values provide independent control on the oxygen drawdown during heinrich events considering a bottom water oxygenation of 6 1 to 6 5 ml l 1 during the last glacial the benthic 13 c minima reveal an oxygen depletion to values between 3 4 and 5 0 ml l 1 during h1 through h4 at the shallower core site differences between estimates from benthic 13 c bfoi and trace fossil tiering suggest that benthic foraminiferal communities are rather robust to oxygen depletion if the level does not fall below 3 ml l 1 whereas burrowing organisms react sensitively to depth variations of the redox boundary in near surface sediments due to even small changes of bottom water oxygenation

quantitative assessment of carbonate dissolution in marine sediments from foraminifer linings vs shell ratios davis strait northwest north atlantic a new method to evaluate quantitatively the degree of calcium carbonate preservation and dissolution in high latitude marine sediments is proposed on the basis of relative abundance of caco 3 shells and organic linings of benthic foraminifers this method was applied to a late quaternary sequence from davis strait in the northwest north atlantic and shows that caco 3 dissolution in sediments has increased since the last glacial maximum ca 18 000 b p and peaked when subpolar interglacial conditions were established in surface waters the dissolution in davis strait sediments appears to be closely related to organic biogenic production in surface waters with a regional pattern of bottom water formation and circulation

calibration of the c 14 timescale over the past 30 000 years using mass spectrometric u th ages from barbados corals uranium thorium ages obtained by mass spectrometry from corals raised off the island of barbados confirm the high precision of this technique over at least the past 30 000 years comparison of the u th ages with 14c ages obtained on the holocene samples shows that the u th ages are accurate because they accord with the dendrochronological calibration before 9 000 yr bp the 14c ages are systematically younger than the u th ages with a maximum difference of 3 500 yr at 20 000 yrbp the u th technique thus provides a way of calibrating the radiocarbon timescale beyond the range of dendrochronological calibration

baffin bay paleoenvironments in the lgm and hs1 resolving the ice shelf question abstract core hu2008029 12pc from the disko trough mouth fan on the central west greenland continental slope is used to test whether an ice shelf covered baffin bay during the last glacial maximum lgm and at the onset of the deglaciation we use benthic and planktic foraminiferal assemblages stable isotope analysis of planktic forams algal biomarkers ice rafted detritus ird lithofacies characteristics defined from ct scans and quantitative mineralogy to reconstruct paleoceanographic conditions sediment processes and sediment provenance the chronology is based on radiocarbon dates on planktic foraminifers using a r of 140 30 14 c years supplemented by the varying reservoir estimates of stern and lisiecki 2013 that provide an envelope of potential ages hu2008029 12pc is bioturbated throughout sediments between the core base at 11 3 m and 4 6 m lgm through hs1 comprise thin turbidites plumites and hemipelagic sediments with greenlandic provenance consistent with processes active at the greenland ice sheet margin grounded at or near the shelf edge abundance spikes of planktic forams coincide with elevated abundance of benthic forams in assemblages indicative of chilled atlantic water meltwater and intermittent marine productivity ird and ip 25 are rare in this interval but brassicasterol an indicator of marine productivity reaches and sustains low levels during the lgm these biological characteristics are consistent with a sea ice covered ocean experiencing periods of more open water such as leads or polynyas in the sea ice cover with chilled atlantic water at depth rather than full ice shelf cover they do not support the existence of a full baffin bay ice shelf cover extending from grounded ice on the davis strait initial ice retreat from the west greenland margin is manifested by a pronounced lithofacies shift to bioturbated diatomaceous mud with rare ird of greenlandic origin at 467 cm 16 2 cal ka bp r 140 yrs within hs1 a spike in foraminiferal abundance and ocean warmth indicator benthic forams precedes the initial ice retreat from the shelf edge at the end of hs1 ip 25 brassicasterol and benthic forams indicative of sea ice edge productivity increase indicating warming interstadial conditions within the bolling allerod interstadial a strong rise in ip 25 content and ird spikes rich in detrital carbonate from northern baffin bay indicate that northern baffin bay ice streams were retreating and provides evidence for increased open water advection of atlantic water in the west greenland current and formation of an ird belt along the w greenland margin

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

the late weichselian glaciation of the franz victoria trough northern barents sea ice sheet extent and timing high resolution seismic profiles parasound 4 khz and three sediment cores from the franz victoria trough and the adjacent continental slope were studied in order to constrain the timing and extent of the northern svalbard barents sea ice sheet during the late weichselian glaciation stacked debris flow lobes and layers of glacimarine diamicton on the lower continental slope indicate that large quantities of glacially derived sediments were deposited by the northern svalbard barents sea ice sheet directly onto the upper continental slope at approximately 23 14 c ka a grounding line advance to the shelf break is supported by the identification of diamicton interpreted as till in the seismic profile near the shelf break after several ice sheet instabilities marked by significant input of ice rafted detritus to the continental margin the disintegration of the northern svalbard barents sea ice sheet termination ia is indicated by a distinct pulse of ice rafted detritus at 15 4 14 c ka and the transition to an isotopically defined meltwater signal the drastic change in sedimentary pattern on the upper continental slope dated to about 13 4 14 c ka is interpreted as grounding line retreat from the shelf edge a further stepwise retreat of the northern svalbard barents sea ice sheet is indicated by pulses of ice rafted detritus which appear to be contemporaneous with the onset of distinct ice rafting events in adjacent areas and pulses of glacimarine sedimentation in the southwestern barents sea q 2000 elsevier science b v all rights reserved

late glacial ice margins and deglacial chronology for southeastern baffin island and hudson strait eastern canadian arctic radiocarbon dates from marine piston cores and from onshore raised marine stratigraphic sections in the hudson strait region were used to reconstruct deglacial isochrons for 9900 9500 8800 8500 and 8000 bp at the culmination of the gold cove readvance 9900 bp labrador ungava ice flowed northeastward across hudson strait and outer frobisher bay and stood for the last time on the baffin island continental shelf subsequent retreat by calving was rapid and profound opening the entire hudson strait marine trough by 9500 bp at this time ice dispersal from foxe basin labrador ungava and local ice on meta incognita peninsula supported tidewater margins along much of the coastline with the exception of northernmost ungava peninsula where the ice margin stabilized onshore this onshore margin remained in place throughout the cockburn substage while a major northeastward readvance of ungava bay ice the noble inlet readvance from 8800 to 8500 bp crossed outer hudson strait grounding on the hudson st

abrupt changes heinrich events in late quaternary north atlantic marine environments a history and review of data and concepts in the last several years evidence has mounted that a series of abrupt changes in sediment delivery and palaeoceanography effected the north atlantic they are recorded in a variety of proxy records but most dramatically in changes of grain size and mineralogy associated with postulated iceberg rafting events specifically heinrich h events this review paper examines the evidence for such evidence prior to the development of the heinrich event concept 1988 1992 and then examines the explosion of data and correlations that stemmed from the acceptance and use of this paradigm specific attention is focused on ideas pertaining to the cause s of glaciological mechanisms sediment delivery and sediment source and major gaps in our understanding of the underlying glaciological glacial geological and glacial marine processes are stressed abrupt changes across boundaries associated with h 2 in the labrador sea are illustrated from core hu87033 009lcf the case is made that correlations between records need to be more rigorous especially within the range of radiocarbon dating but it appears that abrupt changes in the delivery of iceberg rafted debris which characterize these intervals are multisourced it is unclear how global climate can simultaneously influence the abrupt behaviour of ice margins in different parts of the world for marine based margins changes in relative sea level are one possibility a qualitative model is presented for triggering h events which includes global changes in mass balance changes in relative sea level at ice margins due to glacial isostasy and changes in the basal thermal regime of tidewater ice streams 1998 john wiley sons ltd

provenance of icebergs during heinrich event 3 and the contrast to their sources during other heinrich episodes the sources of ice rafted debris ird from heinrich layer 3 h 3 in the north atlantic were studied by means of pb isotopic analyses of single and multiple grain samples of ice rafted feldspars from core v28 82 49 27 n 22 16 w pb ratios of h 3 grains point to multiple continental sources and are similar to the isotopic composition of the background sediment this similarity as well as previous observations about the age and the sr and nd isotopic composition of the fine fraction of h 3 in cores of the same area are all consistent with the hypothesis that in the eastern north atlantic along the latitude band of maximum ird deposition 40 50 n h 3 is a product of foraminifera dissolution and or low productivity in contrast analyses of composite samples of h 1 h 2 h 4 and h 5 plot in 206pb 204pb versus 206pb 204pb coordinates along the churchill province line supporting the premise that the hudson strait was the major pathway of iceberg drainage during these four events since an advance of the laurentide ice sheet during h 3 is demonstrated by increases in detrital carbonate at the level of h 3 in cores from the western north atlantic the results obtained here suggest that if indeed that advance took place the iceberg discharge melted mostly in the western basin

clay mineral evidence of nepheloid layer contributions to the heinrich layers in the northwest atlantic abstract the clay fraction of four cores drilled in the north atlantic ocean was studied at a very high resolution over the last 150 ka in order to record the mineralogical signature of heinrich events factor analysis of clay mineralogy establishes that three independent factors represent the main variations a detrital factor illite chlorite kaolinite a smectite factor and a mixed layer factor ivml illite vermiculite mixed layered clay the clay mineral fraction of core su90 38 drilled in the northeastern atlantic basin did not record any heinrich event whereas large changes in the clay mineral fraction occurred during heinrich events h1 h2 h4 and h5 in the three cores from the northwestern atlantic basin cores su90 08 su90 11 and su90 12 heinrich layers are characterized by increases in the detrital factor in cores su90 08 and su90 11 and sharp increases in the mixed layer factor in cores su90 11 and su90 12 the geographical setting of the cores the pattern of surface intermediate and deep water circulation and the main sources of clay minerals allow recognition of two major mechanisms involved in the deposition of the heinrich layers 1 an increased supply of detrital clay minerals by the icebergs and 2 a specific input of illite vermiculite mixed layer clay minerals by a nepheloid layer

history of the greenland ice sheet paleoclimatic insights abstract paleoclimatic records show that the greenland ice sheet consistently has lost mass in response to warming and grown in response to cooling such changes have occurred even at times of slow or zero sea level change so changing sea level cannot have been the cause of at least some of the ice sheet changes in contrast there are no documented major ice sheet changes that occurred independent of temperature changes moreover snowfall has increased when the climate warmed but the ice sheet lost mass nonetheless increased accumulation in the ice sheet s center has not been sufficient to counteract increased melting and flow near the edges most documented forcings and ice sheet responses spanned periods of several thousand years but limited data also show rapid response to rapid forcings in particular regions near the ice margin have responded within decades however major changes of central regions of the ice sheet are thought to require centuries to millennia the paleoclimatic record does not yet strongly constrain how rapidly a major shrinkage or nearly complete loss of the ice sheet could occur the evidence suggests nearly total ice sheet loss may result from warming of more than a few degrees above mean 20th century values but this threshold is poorly defined perhaps as little as 2 c or more than 7 c paleoclimatic records are sufficiently sketchy that the ice sheet may have grown temporarily in response to warming or changes may have been induced by factors other than temperature without having been recorded

sea level fingerprinting as a direct test for the source of global meltwater pulse ia the ice reservoir that served as the source for the meltwater pulse ia remains enigmatic and controversial we show that each of the melting scenarios that have been proposed for the event produces a distinct variation or fingerprint in the global distribution of meltwater we compare sea level fingerprints associated with various melting scenarios to existing sea level records from barbados and the sunda shelf and conclude that the southern laurentide ice sheet could not have been the sole source of the meltwater pulse whereas a substantial contribution from the antarctic ice sheet is consistent with these records

the great salinity anomaly in the northern north atlantic 1968 1982 the widespread freshening of the upper 500 800m layer of the northern north atlantic which this paper describes represents one of the most persistent and extreme variations in global ocean climate yet observed in this century though a range of explanations have been advanced to explain this event including in situ changes in the surface moisture flux this paper describes the great salinity anomaly as largely though not entirely an advective event traceable around the atlantic subpolar gyre for over 14 years from its origins north of iceland in the mid to late 1960s until its return to the greenland sea in 1981 1982 the overall propagation speed around this subpolar gyre is estimated at about 3cm s 1 of the total salt deficit associated with the anomaly as it passed south along the labrador coast in 1971 1973 about 72 109 tonnes a deficit equivalent to about two thirds of this figure 47 109 tonnes ultimately passed through the faroe shetland channel to the barents sea arctic ocean and greenland sea during the mid 1970s possible effects on deep water formation and on the representativeness of historical section data are discussed

iceberg production debris rafting and the extent and thickness of heinrich layers h 1 h 2 in north atlantic sediments the pattern of heinrich layer distribution for the last two events h 1 14 5 and h 2 21 1 ka mapped from magnetic susceptibility analysis of more than 50 north atlantic ocean cores provides the most detailed information to date on their extent and thickness an integrated spatial average thickness for the layers is 10 15 cm and there is a strong distance decay eastward the pattern of deposition over the north atlantic is similar for events h 1 and h 2 indicating that icebergs followed similar drift tracks rates of iceberg production and sediment flux from the hudson strait drainage basin of the north american laurentide ice sheet the major iceberg source for the events were calculated by using a mass balance approach this provides an envelope of sedimentation rates and the prediction that it would take between 50 and 1250 yr of iceberg sediment delivery to accumulate a heinrich layer averaging 10 cm thick over the north atlantic depending on the model assumptions used the most likely duration of heinrich events is 250 1250 yr

sudden changes in north atlantic circulation during the last deglaciation sudden changes in the flow of warm atlantic surface waters into the norwegian sea occurred frequently during the last deglaciation typically involving shifts in sea surface temperature of 5 c in fewer than 40 years these led to equally large and rapid changes in atmospheric temperatures and to shifts in atlantic deep thermo haline circulation and ice sheet melting rates

origin of the first global meltwater pulse following the last glacial maximum well dated sea level records show that the glacioeustatic rise following the last glacial maximum was characterized by two or possibly three brief intervals of rapid sea level rise separating periods with much lower rates these very high rates of sea level rise indicate periods of exceptionally rapid deglaciation of remaining ice sheets the laurentide ice sheet is commonly targeted as the source of the first and largest of the meltwater pulses mwp ia between 14 200 12 200 14c years b p and 13 700 years ago 11 700 14c years b p in all oceanic records of deglaciation of the former northern hemisphere ice sheets that we review only those from the gulf of mexico and the bermuda rise show evidence of low 18o values at the time of mwp ia identifying the southern laurentide ice sheet as a potential source for mwp ia we question this source for mwp ia however because 1 ice sheet models suggest that this sector of the ice sheet contributed only a fraction 10 of the sea level needed for mwp ia 2 melting this sector of the ice sheet at the necessary rate to explain mwp ia is physically implausible and 3 ocean models predict a much stronger thermohaline response to the inferred freshwater pulse out of the mississippi river into the north atlantic than is recorded this leaves the antarctic ice sheet as the only other ice sheet capable of delivering enough sea level to explain mwp ia but there are currently no well dated high resolution records to document this hypothesis these conclusions suggest that reconstructions of the laurentide ice sheet in the ice 4g model which are constrained to match the sea level record may be too low for time periods younger than 15 000 years ago furthermore 18o records from the gulf of mexico show variable fluxes of meltwater from the southern margin of the laurentide ice sheet which can be traced to the opening and closing of eastward draining glacial lake outlets associated with surging ice sheet behavior these variable fluxes through eastern outlets were apparently sufficient to affect formation of north atlantic deep water thus underscoring the sensitivity of this process to changes in freshwater forcing

laurentide cordilleran ice sheet saddle collapse as a contribution to meltwater pulse 1a the source or sources of meltwater pulse 1a mwp 1a at 14 5 ka recorded at widely distributed sites as a sea level rise of 10 20 m in less than 500 years is uncertain a recent ice modeling study of north america and greenland gregoire et al 2012 has suggested that the collapse of an ice saddle between the laurentide and cordilleran ice sheets with a eustatic sea level equivalent esle of 10 m may have been the dominant contributor to mwp 1a to test this suggestion we predict gravitationally self consistent sea level changes from the last glacial maximum to the present day associated with the gregoire et al 2012 ice model we find that a combination of the saddle collapse scenario and melting outside north america and greenland with an esle of 3 m yields sea level changes across mwp 1a that are consistent with far field sea level records at barbados tahiti and sunda shelf

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

subglacial meltwater discharge in the open marine tidewater glacier environment observations from nordaustlandet svalbard archipelago the ice proximal environment of the nordaustlandet tidewater ice cap svalbard archipelago is one of the best analogues for understanding glacial geologic processes of northern continental shelves during initial pleistocene deglaciation investigations of the proglacial region in 1980 1983 showed that the sedimentary environment is dominated by numerous meltwater outflows which discharge sediment laden water from subglacial meltwater streams during the summer two large stable meltwater outflows were observed in embayments along the southern part of the ice front landsat images show that both outflows have been in approximately the same position since at least 1976 they are located at the intersection of glacial drainage basins and centered over depressions in the underlying bedrock an outflow valley extending away from the ice front was observed in front of the western meltwater outflow sidescan sonar profiling along the glacier front showed a 200 m wide gap in acoustic reflection at the base of the western meltwater outflow probably caused by meltwater effluence enhanced sediment accumulations in this region observed as a 3 ms sediment drape in front of the outflow and large arcuate ridges in the outflow valley testify to the transport efficiency of the subglacial meltwater stream several mounds up to about 25 m high and 200 m wide are observed on sidescan and 3 5 khz profiles directly in front of the outflow although samples from these structures are absent they are most likely composed of sediment and are similar to beaded eskers observed in pleistocene glacimarine sequences indicating locally very high sedimentation rates fine grained components of the subglacial discharge incorporated in the buoyant meltwater plume are usually entrained in a westerly coastal current elevated suspended particulate material concentrations are observed within the coastal waters in a region extending about 15 km perpendicular to the glacier front and at least 60 km along the ice front extending into the northwestern barents sea

ancient selenophysical structure of the grimaldi basin constraints from grail gravity and lola topography abstract the grimaldi impact basin is located near the western limb of the moon and lies to the southwest of the oceanus procellarum a clearly visible positive gravity anomaly exists in its low lying inner wall implying a subsurface mass concentration beneath the crater exploration of this basin could extend our meaningful and fundamental understanding of giant impact processes as well as the structure of mare basins craters limited by the low resolution of previous gravity field models it was once impossible to explore the structure beneath grimaldi the recent high resolution gravity data from the gravity recovery and interior laboratory mission make it possible to break through this barrier prior to our investigation of the selenophysical structure around crater grimaldi we developed a flexure model that includes surface and subsurface loads a localized admittance analysis was performed by combining high resolution gravity data with the high resolution topography data obtained from lunar orbiter laser altimeter within 2 std error constraints we estimated the best fit parameters over grimaldi as well as two other places in its neighborhood all the predicted admittances show a goodness of fit with their corresponding observations the large load ratio 9 2 found at the grimaldi is an indirect mirror of the dominant subsurface load consistent with its large positive gravity anomaly in its low lying floor not only the crustal thickness of 48 km but also the crustal density of 2500 kg m 3 found around grimaldi shows a great accordance with the recent results of grail given the best fit parameters of f bc and c the elastic thickness te is found to be around 28 km over grimaldi taking into account the best fit values in its neighborhood a regional elastic thickness of 30 km could be roughly concluded around grimaldi which is completely in the previous ranges 20

bryozoan rich layers in surficial labrador slope sediments eastern canadian arctic layers rich in remains of a shallow water bryozoan species idmidronea atlantica have been found in quaternary sediments in a piston core taken from 1085 m water depth in the labrador sea 59 700270 n 60 238370 w tens of kilometres from the nearest possible source these layers occur anomalously in pelagic hemipelagic muds with abundant planktic and deep water benthic foraminifera and are thus not in sediments attributable to mud turbidite or debris flows the bryozoan remains appear to be most common in intervals just below heinrich events h1 and h2 14 500 and 20 600 14 c years bp respectively two possible ice related transport mechanisms are suggested to have been involved in the deposition of the bryozoan fragments the first method involved the scouring action of loose pack ice and or bergs dislodging and mobilizing attached bryozoans in shallow water where they could be subsequently entrained in currents and transported to deeper water the second method may have occurred when attached colonies of these animals were frozen in place as winter ice formed in shallow water to be carried out to deeper conditions while still encased in loose floes the subsequent spring summer resume des couches riches en restes d une espece de bryozoaire d eau peu profonde idmidronea atlantica ont ete decouvertes dans un echantillon de sediments datant du quaternaire preleve par un carottier a piston a une profondeur de 1085 m dans la mer du labrador 59 700270 on 60 238370 ow a des dizaines de kilometres de la source possible la plus proche ces couches se retrouvent de facon anormale dans des boues pelagiques hemipelagiques contenant beaucoup de foraminiferes planctoniques et benthiques d eau profonde et ne sont donc pas des sediments attribuables a des turbidites boueuses ou a des ecoulements de debris les restes de bryozoaires semblent etre plus communs dans les intervalles tout juste en dessous des evenements heinrich 1 et 2 respectivement 14 500 et 20 600 14 c bp on suggere deux mecanismes possibles de transport glaciel impliques dans la deposition des fragments de bryozoaires le premier comprend l action d affouillement de glaces a la derive et ou de banquises qui delogent et mobilisent les bryozoaires fixes en eau peu profonde ils pourraient par la suite etre entraines dans des courants et transportes en eau plus profonde le deuxieme mecanisme pourrait survenir lorsque des colonies fixes de ces animaux ont ete geles en place alors que les glaces hivernales se formaient en eau peu profonde les colonies auraient ensuite ete transportees au printemps ete suivant vers des conditions plus profondes alors qu elles etaient encaissees dans des glaces de banc

dynamics of meltwater discharge from northern hemisphere ice sheets during the last deglaciation during the last ice age ice sheets covered large portions of north america europe asia and the arctic ocean the ice sheets were composed of meteoric water enriched in the light isotope of oxygen 16o leaving oceanic seawater correspondingly enriched1 2 in 18o the volume of past continental ice sheets during the last glacial maximum 18 000 yr ago has been estimated from terrestrial evidence of ice limits3 glaciological modelling4 the 18o of foraminifera from deep sea cores5 6 and sea level evidence from raised coral terraces7 8 oxygen isotope studies of planktonic foraminifera reveal that 18o shifts during deglaciations in areas near sources of ice meltwater like the gulf of mexico and labrador sea baffin bay are often larger than the corresponding average global oceanic shift9 11 and that these variations reflect the timing of ice decay without the ocean mixing lag contained in both distal and benthic 10o variations12 we show here that geographically distinct planktonic 18o gradients can be related to the volume of meltwater discharged through specific meltwater outlets and thus to the initial volume of the ice sheets at the commencement of deglaciation and to the subsequent dynamics of ice sheet decay

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

evidence from fram strait 78 n for early deglaciation recent syntheses of the history of the last northern hemisphere glaciation and deglaciation illustrate that understanding of the mechanisms and timing of deglaciation before approximately 12 000 years bp1 5 is limited after 12 000 yr bp however there is sufficient evidence from radiocarbon dated moraines raised beaches varved lake sediments and pollen records to provide a reasonable temporal and geographic picture of the decay of the ice sheets here we report on the first oxygen isotope record from the norwegian greenland sea that is radiocarbon dated directly by accelerator mass spectrometry a significant light oxygen isotope event is recorded at approximately 15 000 years bp which suggests that the marine based barents shelf ice sheet disintegrated rapidly at this time recent studies6 7 have estimated that the decay of this ice sheet could have contributed as much as 15 metres to eustatic sea level rise the decay of the barents shelf ice sheet is the earliest major deglacial event yet dated and may have triggered subsequent deglacial events through eustatic sea level effects

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

petrographic evidence from the eastern canadian margin of shelf crossing glaciations abstract it is difficult to evaluate when and where glaciers extended across the outer continental shelf off eastern canada the outer shelf and upper slope are commonly hard bottomed or have a great thickness of post glacial sediment in either case making direct sampling and dating of ice margin sediment impossible the timing and extent of glacier ice is important for understanding continental slope sedimentation and ice sheet dynamics we have therefore determined the lithologic components of the 1 4 mm granule fraction of over 100 well dated samples from 40 cores from the more distal parts of the deep water margin off nova scotia and newfoundland this fraction is demonstrably ice rafted in these cores and geographic variation in component results from input of icebergs at different calving margins the samples show that heinrich layers have a distinctive granule fraction that shows some areal variation as a result of dilution by sources other than hudson strait heinrich event 2 ca 21 ka is widespread as far southwest as the west scotian slope but by the last glacial maximum lgm numerous discrete sources of ice rafted granules are recognised implying that calving ice margins were present in several places off newfoundland and nova scotia including off banquereau a distinctive purplish lgm gravelly mud is recognised on the eastern newfoundland margin derived from a calving margin on the ne newfoundland shelf at the time of heinrich event 1 ca 14 ka there was a calving ice outlet somewhere on the grand banks and another in halibut channel retreat of ice from the gulf of st lawrence can be tracked by changing granule petrology from the lgm to 13 ka these data suggest that final ice retreat from many parts of the outer shelf was later than is shown in many recent ice margin reconstructions