signature of the gold cove event 10 2 ka in the labrador sea abstract one of the least known catastrophic meltwater and sediment release events of the laurentide ice sheet during the early holocene is the so called gold cove proglacial lake outbursts a drainage event through the hudson strait this event may have disturbed circulation in the labrador sea by releasing freshwater here we report data from four sediment cores and re analysis of six published records spatially covering 2000 km from the mouth of hudson strait to the northeastern sohm abyssal plain abundant detrital carbonate dc and less positive 18o values in neogloboquadrina pachyderma sinistral suggest a short lived meltwater event in the hudson strait region this discharge transported detrital carbonate rich sediment and shallow water benthic forams southward along the labrador margin mixing with the north atlantic current near the grand banks sediments associated with this event were guided through the deep labrador sea from the mouth of hudson strait and the northwest atlantic mid ocean channel namoc to the sohm abyssal plain furthermore we report less positive 13c values in the epibenthic foram cibicidoides wuellerstorfi from the southern labrador sea during this event our twenty one 14c ams dates in addition to earlier published radiocarbon dates from the labrador margin suggest that this dc event was coeval with the gold cove proglacial lake outbursts related to re advance of the laurentide ice sheet

detrital carbonate peaks on the labrador shelf a 13 7 ka template for freshwater forcing from the hudson strait outlet of the laurentide ice sheet into the subpolar gyre abstract the laurentide ice sheet lis was a large dynamic ice sheet in the early holocene the glacial events through hudson strait leading to its eventual demise are recorded in the well dated labrador shelf core md99 2236 from the cartwright saddle we develop a detailed history of the timing of ice sheet discharge events from the hudson strait outlet of the lis during the holocene using high resolution detrital carbonate ice rafted detritus ird 18o and sediment color data eight detrital carbonate peaks dcps associated with ird peaks and light oxygen isotope events punctuate the md99 2236 record between 11 5 and 8 0 ka we use the stratigraphy of the dcps developed from md99 2236 to select the appropriate r to calibrate the ages of recorded glacial events in hudson bay and hudson strait such that they match the dcps in md99 2236 we associate the eight dcps with h0 gold cove advance noble inlet advance initial retreat of the hudson strait ice stream hsis from hudson strait opening of the tyrrell sea and drainage of glacial lakes agassiz and ojibway the opening of foxe channel and retreat of glacial ice from foxe basin are represented by a shoulder in the carbonate data r of 350 years applied to the radiocarbon ages constraining glacial events h0 through the opening of the tyrell sea provided the best match with the md99 2236 dcps r values and ages from the literature are used for the younger events a very close age match was achieved between the 8 2 ka cold event in the greenland ice cores dcp7 8 15 ka bp and the drainage of glacial lakes agassiz and ojibway our stratigraphic comparison between the dcps in md99 2236 and the calibrated ages of hudson strait bay deglacial events shows that the retreat of the hsis the opening of the tyrell sea and the catastrophic drainage of glacial lakes agassiz and ojibway at 8 2 ka are separate events that have been combined in previous estimates of the timing of the 8 2 ka event from marine records sw iceland shelf core md99 2256 documents freshwater entrainment into the subpolar gyre from the hudson strait outlet via the labrador north atlantic and irminger currents the timing of freshwater release from the lis hudson strait outlet in md99 2236 matches evidence for freshwater forcing and lis icebergs carrying foreign minerals to the sw iceland shelf between 11 5 and 8 2 ka the congruency of these records supports the conclusion of the entrainment of freshwater from the retreat of the lis through hudson strait into the subpolar gyre and provides specific time periods when pulses of lis freshwater were present to influence climate

origin of unusually thick heinrich layers in ice proximal regions of the northwest labrador sea ten piston cores and a 25 m long giant piston core from the ice proximal region off hudson strait contain heinrich layers 1 and 2 identified by their sedimentary structure and high detrital carbonate content both layers are unusually thick on the upper labrador slope 3 8 2 1 m and on the lower slope and rise 1 5 1 0 m heinrich layers 1 and 2 can be subdivided into three units unit a is restricted to the upper slope and overlies hemipelagic sediment with a gradational boundary it is 6 1 m thick dark black to dark gray in color and made up of coarse ice rafted sand and granules dispersed in hemipelagic mud with a few faint laminations towards the top the overlying unit b is up to 3 35 m thick and consists of two facies i centimeter thick graded carbonate rich mud layers containing dispersed coarser grains in the mud interpreted as nepheloid flow deposits with coarse ice rafted debris and ii carbonate rich finely laminated mud layers which alternate with millimeter thick laminae of ice rafted debris unit c up to 0 90 m thick is devoid of sedimentary structures and consists of hemipelagic sediment with dispersed dropstones that increase in abundance towards the top of the unit data suggest the following sequence of processes could have occurred during the deposition of heinrich layers in ice proximal sites as the laurentide ice sheet grew it extended through the hudson strait ice stream outlet to a floating ice margin near the shelf edge and perhaps beyond to the upper slope and deposited unit a by releasing dropstones from the basal debris rich layer unit b is interpreted to be the deposits of the combined processes of nepheloid layer flow low density turbidity currents and massive ice rafting maximum carbonate content s 50 the lightest n 18 o values in very sparse planktonic foraminifera and low magnetic susceptibility are characteristic of unit b unit c is inferred to represent the time of waning supply of fines as nepheloid flow deposition ceased while the relative concentration of dropstones increased as a result of continuing intense ice rafting due to the reduction of fine grained sediment supply the carbonate concentration decreased to the labrador sea background level this finding was further supported by the appearance of darker colored sediments and heavier n 18 o values in neogloboquadrina pachyderma s which indicates the reduction of meltwater discharge

isotope stratigraphy sedimentation rates deep circulation and carbonate events in the labrador sea during the last 200 ka high resolution stable isotope and accelerator mass spectrometry 14c measurements in 25 box and piston cores from the labrador sea allow the reconstruction of major paleoceanographical changes during the last 200 ka in this basin and also document the links between the interior of the laurentide ice sheet and the north atlantic ocean during this interval two deep circulation regimes are indicated by contrasting sedimentation rates on the slopes i the modern situation is characterized by a gyre of the north atlantic deep water nadw components into the basin which is responsible for the high energy western boundary undercurrent this regime also prevailed during the former true interglacials and possibly during shorter warm intervals e g bolling allerod ii a more frequent nadw free situation during glacial and interstadial intervals is marked by the presence of a vertically homogeneous water mass in the basin sedimentological records also indicate that carbonate events i e pulses of

late quaternary stratigraphy and sedimentology of orphan basin implications for meltwater dispersal in the southern labrador sea abstract orphan basin is a deep water basin on the continental margin off newfoundland which throughout the late quaternary received proglacial sediment from local ice that crossed the continental shelf sediment from more distant sources was transported southward in the labrador current as proglacial plumes and in icebergs five sedimentary facies related to glacial processes are distinguished in cores recovered from orphan basin hemipelagic sediment nepheloid layer deposits layered mud beds rich in ice rafted detritus ird sand and mud turbidites and glaciogenic debris flow deposits ird rich beds correspond to periods of intensified iceberg calving and layered mud turbidites and glaciogenic debris flow deposits with glacial meltwater discharge in the late wisconsinan eight periods of meltwater discharge and iceberg calving from the newfoundland ice sheet are interpreted from the sediment facies in orphan basin these discharges coincide with the terminations of the colder periods of the d o cycles recorded in greenland ice cores the oldest minor meltwater event 27 5 28 5 cal ka corresponds to the first late wisconsinan ice advance across the grand banks and ne newfoundland shelf the following three meltwater discharges 23 23 5 23 8 24 5 and 25 27 cal ka deposited sand turbidites and glaciogenic debris flow deposits seaward of trinity trough which was occupied by an ice stream at this time and mud turbidites in the southern part of the basin derived from a mid shelf ice margin on the grand banks four periods of meltwater discharge occurred during the deglaciation and are centered at 15 18 5 19 75 and 20 75 cal ka the youngest is correlated to heinrich event 1 in the literature the 18 5 and 20 75 cal ka events have been recorded in multiple glacial settings in the north atlantic and therefore are interpreted as large scale events of meltwater discharge and iceberg calving but in orphan basin the 19 75 cal ka event is also of similar scale

late quaternary stratigraphy of laurentian fan a record of events off the eastern canadian continental margin during the last deglacial period abstract examination and correlation of 10 piston cores from laurentian fan off the eastern canadian continental margin revealed a high resolution stratigraphic record of events since the last glacial maximum lgm the five lithofacies identified in the cores are 1 bioturbated olive grey silty mud with varying amounts of biogenic carbonate 2 olive grey and reddish brown silt laminated mud with rare fine to very fine sand beds 3 poorly sorted light grey and brick red gravelly sandy mud 4 colour banded silty mud with colours alternating at a centimetre scale between olive grey and reddish brown and 5 brown silty mud commonly massive but occasionally silt laminated the dominant depositional processes include hemipelagic sedimentation turbidity currents and ice rafting in these sediments colour is diagnostic of the sediment source area with reddish sediment being delivered to the fan from the gulf of st lawrence and laurentian channel whereas greenish sediment arrives on the fan from st pierre bank through grand banks valley turbidites are the most volumetrically significant facies conversely ice rafted beds are volumetrically minor but they are the most chronostratigraphically significant facies and include heinrich layers h0 h1 and h2 the chronological control provided by radiocarbon dating and stable oxygen isotopes suggests that sedimentation rates for the reddish brown turbidites deposited between the lgm and 14 ka exceeded 10 m kyr 1 mapping of the units together with a simple sediment deposition model suggest that these beds resulted from deposition by turbidity currents over 1 km thick that lasted on the order of weeks less information can be ascertained from the olive grey turbidites that interbed with h2 and directly overlie h1 because of a lack of sampling except that they had a lower sedimentation rate and include sediment derived from newfoundland and the grand banks comparison of the stratigraphy on laurentian fan with that of other deep water areas further north southwest grand banks margin flemish pass and the labrador sea shows striking similarities over the late quaternary with the deglacial period characterized by rapid sediment accumulation however only on laurentian fan does sediment gravity flow deposition occur during the lgm reddish brown turbidites deposited on laurentian fan during the deglacial period have no equivalent facies further north these unique features suggest important glaciological differences between the ice stream occupying laurentian channel and ice streams farther north the onset of widespread hemipelagic deposition occurred after ca 12 ka on laurentian fan and in flemish pass but not until ca 8 2 ka in the labrador sea consistent with the earlier retreat of glacial ice out of laurentian channel as compared to hudson strait

the subglacial origin of the lake agassiz ojibway final outburst flood arc shaped scours sandwaves and channels on the hudson bay seafloor suggest that the catastrophic drainage of lake agassiz ojibway occurred as a subglacial flood beneath the laurentide ice sheet which covered northern north america

marine evidence for the last glacial advance across eastern hudson strait eastern canadian arctic data from accelerator mass spectrometer radiocarbon dated sediment cores and huntec high resolution seismic profiles were used to investigate the age and origin of the sediments in the eastern basin of hudson strait the data indicate that the ice contact and glacial marine sediments on the basin flanks and much of the upper sequence in the deep floor of the basin were produced during the noble inlet advance 8 9 to 8 4 ka the last northward expansion of the labrador dome on to southeastern baffin island on the northern flank of eastern basin one sequence of ice contact sediments and glacial marine deposits overlies bedrock the glacial marine sediments are transitional upslope to ice contact sediments and form at least two successive ice sheet grounding zones the earliest abundance peaks of benthic foramininfera in glacial marine sediments date ca 8 6 and 8 4 ka and correlate to sediments near the base of the 58 m thick glacial marine section in the deepest part of eastern basin this correlation suggests that noble inlet ice was grounded throughout eastern basin during the early part of its advance in later stages the thinning ice produced grounding zones on the basin flanks while glacial marine sediments were deposited in the deep basin 1998 john wiley sons ltd

lake agassiz outburst age and routing by labrador current and the 8 2 cal ka cold event abstract catastrophic drainage of glacial lake agassiz impounded by the laurentide ice sheet lis into hudson bay and strait is widely thought to have caused the 8 2 cal ka cold event though the path of its drainage in the north atlantic is poorly known analysis and compilation of 10 sediment cores from 8 sites distributed on the eastern canadian continental shelf and upper slope south of hudson strait revealed distinct beds with elevated detrital carbonate dc concentrations known by their distinct composition to originate from erosion of carbonate bedrock and carbonate rich glacial sediments in the hudson bay hudson strait region at all but one site radiocarbon ages bracketing and within the thickest and most widespread of these beds are coeval with the age constraints for the agassiz floods in hudson strait and southeastern hudson bay the dc distribution and concentration of this bed are consistent with southward transport in the labrador current transfer function analysis of dinoflagellate assemblage data from cores on the central labrador shelf in hudson bay and on the northeast newfoundland shelf reveal that early holocene seasonal ice cover was 5 6 months longer than at present requiring the application of a 200 year reduction to the radiocarbon age constraints on the lake agassiz outburst floods the age of the floods is reduced to about 8 33 cal ka 7 5 14 c ka from the previous determination of 8 47 cal ka 7 7 14 c ka with a similar reduction in their error ranges to 8 04 8 49 cal ka from 8 16 8 74 cal ka based on present current routing the agassiz floodwaters and icebergs are inferred to have travelled south in the labrador current and to have possibly become incorporated into the north atlantic current and transported to the nordic seas there the freshwater additions would have lessened deepwater production with a concomitant reduction in northward heat transport in the upper limb of the atlantic meridional overturning circulation thereby contributing to the 8 2 cal ka cold event variation in the calcite and dolomite content of the agassiz dc bed two salinity reductions during agassiz bed deposition and low level shorelines of lakes agassiz and ojibway suggest that more than one outburst was delivered during the final agassiz drainage the 8 2 cal ka cold event registered in greenland was coeval with a second or later flood which possibly accompanied the final collapse of the lis in hudson bay

freshwater outburst from lake superior as a trigger for the cold event 9300 years ago paleoclimate proxy records reveal a pervasive cooling event with a northern hemispheric extent approximately 9300 years ago coeval changes in the oceanic circulation of the north atlantic imply freshwater forcing however the source magnitude and routing of meltwater have remained unknown located in central north america lake superior is a key site for regulating the outflow of glacial meltwater to the oceans here we show evidence for an approximately 45 meter rapid lake level fall in this basin centered on 9300 calibrated years before the present due to the failure of a glacial drift dam on the southeast corner of the lake we ascribe the widespread climate anomaly approximately 9300 years ago to this freshwater outburst delivered to the north atlantic ocean through the lake huron north bay ottawa river st lawrence river valleys

a subtropical fate awaited freshwater discharged from glacial lake agassiz 1 the 8 2 kyr event is the largest abrupt climatic change recorded in the last 10 000 years and is widely hypothesized to have been triggered by the release of thousands of kilometers cubed of freshwater into the north atlantic ocean using a high resolution 1 6 global ocean ice circulation model we present an alternative view that freshwater discharged from glacial lake agassiz would have remained on the continental shelf as a narrow buoyant coastal current and would have been transported south into the subtropical north atlantic the pathway we describe is in contrast to the conceptual idea that freshwater from this lake outburst spread over most of the sub polar north atlantic and covered the deep open ocean convection regions this coastally confined freshwater pathway is consistent with the present day routing of freshwater from hudson bay as well as paleoceanographic evidence of this event using a coarse resolution 2 6 version of the same model we demonstrate that the previously reported spreading of freshwater across the sub polar north atlantic results from the inability of numerical models of this resolution to accurately resolve narrow coastal flows producing instead a diffuse circulation that advects freshwater away from the boundaries to understand the climatic impact of freshwater released in the past or future e g greenland and antarctica the ocean needs to be modeled at a resolution sufficient to resolve the dynamics of narrow coastal buoyant flows

holocene thinning of the greenland ice sheet the nature of the response of the greenland ice sheet gis to climate change is a fundamental question in climate science but the details remain unclear during the holocene climate optimum 6 000 to 9 000 years ago for example many locations in the northern hemisphere showed unusual warmth yet changes in greenland appeared inconsistent vinther et al now standardize the previously disparate seeming ice core records of climate history on the gis during the holocene and find consistent evidence for a stronger climate optimum than was previously recognized together with elevation reduction and marginal ice sheet thinning the response of the greenland ice sheet gis to changes in climate remains uncertain during the holocene climatic optimum an unusually warm period from about 9 000 to 6 000 years ago changes in greenland appear inconsistent with the rest of the northern hemisphere here the greenland holocene temperature history and the evolution of gis surface elevation are extracted from four gis locations the results may resolve this disparity on entering an era of global warming the stability of the greenland ice sheet gis is an important concern1 especially in the light of new evidence of rapidly changing flow and melt conditions at the gis margins2 studying the response of the gis to past climatic change may help to advance our understanding of gis dynamics the previous interpretation of evidence from stable isotopes 18o in water from gis ice cores was that holocene climate variability on the gis differed spatially3 and that a consistent holocene climate optimum the unusually warm period from about 9 000 to 6 000 years ago found in many northern latitude palaeoclimate records4 did not exist here we extract both the greenland holocene temperature history and the evolution of gis surface elevation at four gis locations we achieve this by comparing 18o from gis ice cores3 5 with 18o from ice cores from small marginal icecaps contrary to the earlier interpretation of 18o evidence from ice cores3 6 our new temperature history reveals a pronounced holocene climatic optimum in greenland coinciding with maximum thinning near the gis margins our 18o based results are corroborated by the air content of ice cores a proxy for surface elevation7 state of the art ice sheet models are generally found to be underestimating the extent and changes in gis elevation and area our findings may help to improve the ability of models to reproduce the gis response to holocene climate

millennial scale changes of surface and deep water flow in the western tropical atlantic linked to northern hemisphere high latitude climate during the holocene there is increasing evidence that the preceding holocene climate was as unstable as the last glacial period although variations occurred at much lower amplitudes however low latitude climate records that confirm this variability are sparse here we present a radiocarbon dated holocene marine record from the tropical western atlantic aragonite dissolution derived from the degree of preservation of the pteropod limacina inflata records changes in the corrosiveness of the bottom water at the core site due to the changing influence of northern versus southern water masses the 18 o difference between the shallow living planktonic foraminifera globigerinoides sacculifer and the deep living globorotalia tumida is used as proxy for changes in the vertical stratification of the surface water hence the trade wind strength at this latitude we compared our data to high latitude records of the north atlantic region a good agreement is found between the aragonite dissolution and the strength in the island scotland overflow water which contributes significantly to the north atlantic deep water this suggests that large scale variations in the atlantic thermohaline circulation occurred throughout the holocene concurrently the comparison of our 18 o with the gisp2 glaciochemical records points to global holocene atmospheric reorganizations seen in both the tropics and high northern latitudes

deep water renewal by turbidity currents in the sulu sea the ventilation of the intermediate and deep layers of the ocean is governed by convection dense water formed at the sea surface through air sea interaction processes mainly at high latitudes sinks to great depths convection determines the heat salt and dissolved gas budgets of the ocean s interior and therefore exerts a significant influence on the earth s climate convective processes can also be initiated by the flow of dense water over submarine sills separating ocean basins with water masses of different buoyancy here we report the observation of relatively light deep water in the overflow region near the sill in the northern part of the 5 000 m deep sulu sea because of its buoyancy this water could not have reached the sea floor of its own accord turbidity currents induced by changes in water density that result from sediment influx occur in this region at intervals of several decades as indicated by the frequent deposition of graded sequences of silty mud on the abyssal plain we suggest that such turbidity currents combined with the effects of classical hydrological plume convection are capable of bringing light water to large depths in tropical regions where normal oceanic convection is relatively weak this mechanism may contribute significantly to the ventilation of deep basins

some seismic signatures in the romanian crust abstract some new seismic reflection data in the w of the moesian platform focsani depression and transylvania depression show seismic patterns which reflect the local structure and evolution of the each area these local areas were affected by subsidence which over printed the changes on the old pattern the old and more or less reflective lower crust was fractured and some rigid blocks have preserved the reflectivity up to the present the ba ilesti section illustrates a transparent or diffractive upper crust and a well marked lower crust by an alternation of reflective and non reflective zones the crystalline crust of the r mnicu sa rat section has two patterns one relatively reflective near the bottom of the depression the w side whilst the other on the e flank of depression is transparent the e flank seems to be more fractured due to some tensile fractures originating in the bending stress during subsidence the t rgu muressection has a specific crustal pattern a near transparent crystalline crust overlies a very large crust mantle transition zone which is fragmented in alternated reflective and transparent blocks

mechanisms of abrupt climate change of the last glacial period 1 more than a decade ago ice core records from greenland revealed that the last glacial period was characterized by abrupt climate changes that recurred on millennial time scales since their discovery there has been a large effort to determine whether these climate events were a global phenomenon or were just confined to the north atlantic region and also to reveal the mechanisms that were responsible for them in this paper we review the available paleoclimate observations of abrupt change during the last glacial period in order to place constraints on possible mechanisms three different mechanisms are then reviewed ocean thermohaline circulation sea ice feedbacks and tropical processes each mechanism is tested for its ability to explain the key features of the observations particularly with regard to the abruptness millennial recurrence and geographical extent of the observed changes it is found that each of these mechanisms has explanatory strengths and weaknesses and key areas in which progress could be made in improving the understanding of their long term behavior both from observational and modeling approaches are suggested finally it is proposed that a complete understanding of the mechanisms of abrupt change requires inclusion of processes at both low and high latitudes as well as the potential for feedbacks between them some suggestions for experimental approaches to test for such feedbacks with coupled climate models are given

could meltwater pulses have been sneaked unnoticed into the deep ocean during the last glacial the lack of climatic imprint l eft by t he meltwa t er pulse 1a 14 5 ka bp equivalent to a sea level rise of 14 to 20 meters is puzzling recent studies sugge st the event might have occurre d as a hyperpycnal flow i n t he gulf of me xico preve nting its detection in oc eanic records throughout the north atlantic we present a suite of simula tions with the loveclim climate model which mimic th e e ffect of h yperp ycnal f low u nder lgm conditions in a first attempt to constrain its climatic effects analysing the ocean dynamics associated with the anomalous freshwater input we show that the proposed mechanism is capable of sneaking a signif i cant propo rtion of the mwp into the ocean 6 meters equivalent sea level rise using our model under lgm boundary cond itions we also de monstrate t hat in our model the meridional circulati on i s more sensitive t o such inputs i n t he arctic ocean than in the gulf of mexico

glacial water mass geometry and the distribution of δ13c of σco2 in the western atlantic ocean 1 oxygen and carbon isotopic data were produced on the benthic foraminiferal taxa cibicidoides and planulina from 25 new piston cores gravity cores and multicores from the brazil margin the cores span water depths from about 400 to 3000 m and intersect the major water masses in this region these new data fill a critical gap in the south atlantic ocean and provide the motivation for updating the classic glacial western atlantic 13c transect of duplessy et al 1988 the distribution of 13c of co2 requires the presence of three distinct water masses in the glacial atlantic ocean a shallow 1000 m southern source water mass with an end member 13c value of about 0 3 0 5 vpdb a middepth 1500 m northern source water mass with an end member value of about 1 5 and a deep 2000 m southern source water with an end member value of less than 0 2 and perhaps as low as the 0 9 values observed in the south atlantic sector of the southern ocean ninnemann and charles 2002 the origins of the water masses are supported by the meridional gradients in benthic foraminiferal 18o a revised glacial section of deep water 13c documents the positions and gradients among these end member intermediate and deep water masses the large property gradients in the presence of strong vertical mixing can only be maintained by a vigorous overturning circulation

sediment dynamics during heinrich event h1 inferred from grain size abstract throughout the last glacial period massive volumes of icebergs were discharged periodically through hudson strait during so called heinrich h events these icebergs transported sediments that were subsequently deposited in distinct layers across the north atlantic as they melted the objective of this research was to measure and describe sedimentation associated with a meltwater plume discharged during the h1 ice rafting event at about 17 ka by examining sediment texture the h1 layer was sampled in 11 piston cores that cover about 4000 km of the slope between hudson strait and the gulf of maine disaggregated inorganic grain size digs distributions were determined using a coulter counter additionally the caco 3 content and the 63 m fraction were measured and digs distributions were sorted using entropy analysis entropy analysis proved to be a useful tool for distinguishing between sediment delivery mechanisms textural interpretation of sediment dynamics during the h1 event was broadly consistent with facies interpretations h1 layer sediments were mainly delivered by plume and ice rafting with some samples showing higher energy sorting in general plume deposition was dominant within 1000 km of hudson strait and distal sediments were mainly delivered by ice rafting entropy analysis of digs distributions provides a robust means of understanding fine fraction

reply to the comment on the timing of the gold cove glacial event a comment on signature of the gold cove event 10 20 ka in the labrador sea by pearce c abstract pearce 2015 commented about the paper titled signature of the gold cove event 10 2 ka in the labrador sea by rashid et al 2014 suggesting that due to an oversight error in re calibration of four 14c dates of kaufman and williams 1992 and kaufman et al 1993 rashid et al 2014 misidentified the gold cove event furthermore as a result of this error findings and conclusions in rashid et al 2014 are difficult to justify the correlations of several dc layers in the labrador sea here we reply to pearce 2015 comments we further elaborate our reasoning behind the identification of 10 2 ka event

freshwater outbursts to the oceans from glacial lake agassiz and their role in climate change during the last deglaciation abstract lake agassiz was the largest lake in north america during the last deglaciation as the laurentide ice sheet lis retreated large volumes of water stored in this proglacial lake were episodically released into the oceans these waters were variably routed to the gulf of mexico arctic ocean north atlantic ocean and hudson bay during this period the three largest cooling events in the northern hemisphere closely followed 4 of the 5 largest outbursts from lake agassiz 1 the younger dryas which was preceded by a release of 9500 km 3 2 the preboreal oscillation preceded by releases of 9300 km 3 and 5900 km 3 and 3 the 8 2 ka cold event preceded by a 163 000 km 3 outburst these are respectively fluxes of 0 30 sv 0 29 sv 0 19 sv and 5 2 sv if released in 1 year because the influx of freshwater reaching the north atlantic ocean can inhibit thermohaline circulation partly depending on whether the ocean was in a glacial interglacial or transitional mode of circulation we believe that at least these large outbursts from lake agassiz may have provided the triggers for changes in ocean circulation and in turn for widespread climate change

cosmogenic 10be and 26al ages of holocene moraines in southern norway i testing the method and confirmation of the date of the erdalen event c 10 ka at its type site abstract cosmogenic nuclide dating 10be and 26al is applied to boulders on two moraine ridges at the type site of the early holocene erdalen event southern norway dated previously using radiocarbon quartz rich rock samples yielded 10be age estimates between 9 8 1 2 and 10 1 1 1 ka external uncertainties 1 with an average of 9 95 ka these age estimates are statistically indistinguishable from the independent radiocarbon age estimate 26al age estimates which ranged from 9 4 1 1 to 11 2 1 3 ka and averaged 10 1 ka provided useful corroboration of the 10be results although current levels of precision and accuracy are insufficient to distinguish between the ages of younger inner and older outer moraines the results demonstrate the potential of the method at suitable sites where radiocarbon dating is not possible several environmental factors including effective glacial erosion stability of moraine slopes snow cover of sufficiently shallow depth and short duration and the absence

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

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

abrupt early holocene 9 9 9 6 ka ice stream advance at the mouth of hudson strait arctic canada radiocarbon dated glacial geologic evidence documents an abrupt advance of the northern margin of the labrador sector of the laurentide ice sheet during the last deglaciation ice flow directional indicators together with ice marginal features found onshore and offshore delimit an ice stream that advanced north northeast 300 km crossed the mouth of hudson strait and outer frobisher bay and overran summits 400 m above sea level on outer hall peninsula southeast baffin island fifty eight 14 c ages including 27 accelerator mass spectrometry ages on single shells indicate that the advance was extremely rapid the entire advance retreat cycle took place in an 300 yr 14 c interval 9 9 9 6 ka at its maximum extent the ice stream supported a calving margin 200 km long terminating in open water 500 m deep implying a massive iceberg release marine evidence for the outflow is preserved along the labrador sea shelf as thick carbonate rich glacial marine drift but has not been recognized farther east in the north atlantic either the discharge of icebergs was insufficient to produce a trans north atlantic carbonate rich heinrich layer or the icebergs tracked southward where they encountered warming sea surface temperatures although the advance seems to have been coincident with a brief interval of minor regional cooling it failed to trigger a significant climate perturbation suggesting that the ocean atmosphere system had attained its stable interglacial condition by that time

rapid early holocene deglaciation of the laurentide ice sheet the demise of the laurentide ice sheet during the early holocene epoch is the most recent and best constrained disappearance of a large ice sheet in the northern hemisphere and thus allows an assessment of rates of ice sheet decay as well as attendant contributions to sea level rise here we use terrestrial and marine records of the deglaciation to identify two periods of rapid melting during the final demise of the laurentide ice sheet when melting ice contributed about 1 3 and 0 7cm of sea level rise per year respectively our simulations with a fully coupled ocean atmosphere model suggest that increased ablation due to enhanced early holocene boreal summer insolation was the predominant cause of laurentide ice sheet retreat although the surface radiative forcing in boreal summer during the early holocene is twice as large as the greenhouse gas forcing expected by the year 2100 the associated increase in summer surface air temperatures is very similar we conclude that our geologic evidence for a rapid retreat of the laurentide ice sheet may therefore describe a prehistoric precedent for mass balance changes of the greenland ice sheet over the coming century

numerical modeling of late glacial laurentide advance of ice across hudson strait insights into terrestrial and marine geology mass balance and calving flux a time dependent finite element model was used to reconstruct the advance of ice from a late glacial dome on northern quebec labrador across hudson strait to meta incognita peninsula baffin island and subsequently to the 9 9 9 6 ka 14c gold cove position on hall peninsula terrestrial geological and geophysical information from quebec and labrador was used to constrain initial and boundary conditions and the model results are compared with terrestrial geological information from baffin island and considered in the context of the marine event dc 0 and the younger dryas cooling we conclude that advance across hudson strait from ungava bay to baffin island is possible using realistic glacier physics under a variety of reasonable boundary conditions production of ice flux from a dome centered on northeastern quebec and labrador sufficient to deliver geologically inferred ice thickness at gold cove hall peninsula appears to require extensive penetration of sliding south from ungava bay the discharge of ice into the ocean associated with advance and retreat across hudson strait does not peak at a time coincident with the start of the younger dryas and is less than minimum values proposed to influence north atlantic thermohaline circulation nevertheless a significant fraction of freshwater input to the north atlantic may have been provided abruptly and at a critical time by this event

abrupt deglaciation events and holocene palaeoceanography from high resolution cores cartwright saddle labrador shelf canada the uppermost quaternary sediments in cartwright saddle labrador shelf are acoustically laminated with reflectors that can be traced over long distances two piston cores from the saddle record changes in sediment and meltwater delivery from the northeast margin of the laurentide ice sheet lis during deglaciation variations in sediment properties indicate a similar history of sediment accumulation over the last 12 kyr the temporal sampling interval reaches decadal resolution in the last deglacial period 7 9 ka analyses of total carbonate content sediment magnetic variables foraminiferal species and stable isotope measurements on planktic foraminifers show that abrupt changes occurred ca 10 9 9 2 8 8 7 9 and 7 ka with 450 yr correction there was no distinct change in sediment character during much of the younger dryas chronozone in the 18o record the 8 8 ka event is a dramatic 1 shift toward lower values which we associate with the noble inlet glacial event within hudson strait we do not see the pronounced low 18o event at 7 1 ka reported off nova scotia but surprisingly neither the nova scotia records nor other records in the labrador sea capture the impressive 8 8 ka change serious consideration must be given to the final collapse of the lis as the cause of the 8 2 cal ka cold event recorded in greenland and northwest europe copyright 1999 john wiley sons ltd

high resolution holocene palynological record from the scotian shelf abstract because of their location at the confluence of polar and subtropical airmasses and near a transition zone between the cold labrador current and the gulf stream the atlantic provinces experience some of the most dynamic climate conditions in canada major climate changes occurred during the holocene as shown by pollen records from lakes but previous paleoceanographic studies based on low resolution proxy data records do not show major changes during the past 8000 years therefore the holocene history of canada s atlantic region was examined using a high resolution palynological record from the scotian shelf la have basin sea surface conditions were reconstructed using proxy data from dinoflagellate cysts and paleobioclimatic transfer functions ocean atmosphere interactions are determined by onshore offshore correlation of marine and pollen records from nova scotia results show a succession of major paleoceanographic events sea surface temperatures sst february and august up to 5 c higher than today s average and slightly higher salinity are reconstructed between 10 5 and 8 5 ka the last pulse of meltwater from the residual ice sheet affected the shelf waters between 8 5 and 6 5 ka by lowering the sst in february and the salinity most previous studies failed to record this event since 6 5 ka august temperature generally remained around today s value while february temperature was generally 2 c above it except for recurring colder and lower salinity intervals these cold intervals have a recurrence of about 1000 years a slight cooling of summer sst is recorded in the last 500 years comparison with climatic reconstructions from nova scotia pollen records shows a difference in timing between ocean and atmosphere the onset of the climatic optimum hypsithermal in nova scotia lags by about 2000 years until 8 ka relative to the ocean but it lasted longer the neoglacial cooling in atlantic canada however started earlier 2 ka than the late holocene ocean cooling la have basin s holocene paleoceanography presents some differences from most other studies from the region 1 the hypsithermal started earlier 2 the last pulse of meltwater is recorded 3 the last 6500 years are punctuated by colder intervals increased productivity and blooms of toxic algae in the early holocene are probably due to a combination of factors increased nutrients and a greater stability of the water column because of meltwaters higher sst and increased upwelling or storm activity

a heinrich like event h 0 dc 0 source s for detrital carbonate in the north atlantic during the younger dryas chronozone in the north atlantic we define h 0 as a heinrich like event which occurred during the younger dryas chron on the se baffin shelf prior to 11 ka surface water productivity was reasonably high as measured by the numbers of diatom and planktic foraminifera per gram but an abrupt increase in detrital carbonate dc 0 event from approximately 15 up to 50 carbonate by weight occurred at 11 14c ka and continued to circa 10 ka these deposits 2 6 m thick are dominated by detrital calcite and silt and clay sized sediments during this event dc 0 h 0 ice extended onto the inner shelf but did not reach the shelf break and probably originated from a center over labrador ungava as a consequence the pattern of ice rafted debris and sediment provenance shown by h o in the north atlantic is different from that during h 1 14 5 ka or h 2 20 ka when the ice sheet extended along the axis of hudson strait and may have reached the shelf break for example there is no concrete evidence for dc o is cores on the floor of the labrador sea due east of hudson strait hu75 55 56 but h o has been noted in cores off newfoundland and west of ireland a coeval carbonate event to dc 0 but this one dominated by dolomite occurs in hu82 su5 on the west side of davis strait with a source either from northern baffin bay or cumberland sound although other sources for north atlantic detrital carbonate cannot be totally excluded our evidence suggests that h 0 represents the expression of glaciological instability of the laurentide ice sheet within the general region of hudson strait and probably to the north cumberland sound and northernmost baffin bay there is one younger dc event dated circa 8 4 ka present in sediments along the labrador margin and in hudson strait which represents the final collapse of the ice sheet within hudson strait and hudson bay

complexity of holocene climate as reconstructed from a greenland ice core glaciochemical time series developed from summit greenland indicate that the chemical composition of the atmosphere was dynamic during the holocene epoch concentrations of sea salt and terrestrial dusts increased in summit snow during the periods 0 to 600 2400 to 3100 5000 to 6100 7800 to 8800 and more than 11 300 years ago the most recent increase and also the most abrupt coincides with the little ice age these changes imply that either the north polar vortex expanded or the meridional air flow intensified during these periods and that temperatures in the mid to high northern latitudes were potentially the coldest since the younger dryas event

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

oxygen isotope fractionation between apatite and aqueous phase phosphate 20 45 c abstract replacement of biogenic caco3 by apatite is an important mode of authigenic apatite formation in marine sediments active along the peru margin today synthesis experiments mimicking this process were undertaken in abiotic inorganic systems in order to determine the oxygen o isotope fractionation between apatite and aqueous phase inorganic phosphate po4 aq caco3 solids were added to po43 solutions made with 18o labeled waters and o isotope fractionations between solid and aqueous phase po43 were determined in a series of experiments at 20 45 c results of 18o analyses of apatite synthesis systems indicate that o isotope fractionation between solid and aqueous phase po43 is 1 not affected by variations in water 18o values 2 initially non equilibrium and 3 relatively small 1 fractionations determined from long term up to 6 years room temperature experiments were 1 due to initial rapid precipitation short experimental run periods 1 week to 4 months resulted in fractionations between apatite and po4 aq that were initially reversed from those of long term experiments over time and with progressive recrystallization these fractionations evolved to reach values consistent with long term experiments

lake agassiz final drainage event in the northwest north atlantic 1 the 8 2 ka climate event recorded in greenland ice cores is subject of debates with respect to causal linkage with a collapse of the atlantic meridional overturning due to the drainage of the late glacial lake agassiz here we present records from the nw north atlantic down current the flood discharge route showing that the 9 5 8 ka interval was marked by a succession of events the drainage itself corresponds to a twin layer of carbonate rich turbidites deposited within the calibrated 8 35 8 5 ka interval proxies of sea surface and deep current conditions do not indicate significant concomitant changes in the nw north atlantic the dataset however supports the concept that the 8 2 ka climate event may represent one of the manifestations of climate instability during an interval with major changes of land drainage in ne america due to the collapse of the laurentide ice sheet subsequent fast sea level rise and large scale reorganization of the north atlantic thermohaline circulation pattern

cooling of northwest atlantic slope waters during the holocene 2 greenland ice cores depict a holocene climate that was warm and stable compared to the preceding 100 kyr yet most elements of the climate system were undergoing large secular changes during the last 11 kyr summer insolation in the northern hemisphere declined to last glacial maximum lgm levels atmospheric co2 increased 20 ppmv and the carbonate ion concentration of the deep sea decreased 5 10 mmol kg broecker et al 1999 signaling a large shift in the global carbon cycle the oxygen isotope composition of atmospheric o2 an indicator of global productivity and hydrology increased 0 5 retracing roughly 50 of the non ice volume deglacial decrease bender et al 1999 the monsoons of asia and

fine scale sediment structure and geochemical signature between eastern and western north atlantic during heinrich events 1 and 2 abstract heinrich iceberg rafting events 1 and 2 h1 and h2 in the labrador sea are identified by their typical nepheloid flow deposit sedimentary structure high bulk carbonate increase in iceberg rafted detritus ird and depletion of 18o in the surface dwelling foraminifer neogloboquadrina pachyderma s h layers in this region have sedimentological characteristics different than those in the north atlantic and consist of ird interspersed in pelagic sediments high resolution 14c ams dates allowed us to delineate the leads and lags in instability between different ice streams of the former laurentide ice sheet lis our data suggest that the discharge from the hudson strait ice stream was followed by cumberland sound ice sheet during h1 and h2 new radiogenic isotopes from the ice proximal and surficial sediments of the greater hudson strait region and labrador sea h0 h1 and h2 layers suggest that carbonate rich layers were only derived from hudson strait not baffin bay fine scale structure of h1 and h2 intervals in labrador sea slope cores is characterized by two lithic peaks dominated by detrital carbonate grains and a single peak in cores from the central labrador sea a similar pattern in the structure of h1 and h2 is observed along the western european margin these findings contrast with north atlantic h1 and h2 intervals which are characterized by a peak of carbonate rich grains followed by a peak of quartz and volcanic grains this comparison with north atlantic and western european margin cores leads us to suggest that the coupling or lack thereof between the lis and european ice sheet is related to the depositional processes occurring along the margins as well as the distance from the sources and the ability of the oceanic currents to disperse icebergs any significant change in ice sheet dynamics would be recorded close to the ice sheet margin while distal locations would only record extreme events we hypothesize that the discordance between the findings reported in the literature is most likely similar to the difference between the upper slope deep labrador sites and the flemish pass site described in this contribution but requires vigorous testing

timing equilibrium line altitudes and climatic implications of two early holocene glacier readvances during the erdalen event at jostedalsbreen western norway following the younger dryas the e rst evidence of glacial activity in southern norway in response to climatic change occurred during the early holocene when terminal moraines from the erdalen event formed beyond the position of later little ice age moraines in front of present outlet glaciers on both sides of the jostedalsbreen ice cap sets of pre little ice age marginal moraines have been morphostratigraphicallycorre lated with the erdalen event the lithostratigraphyin a peat bog at hellemyrane in jostedalen western norway provides e rm evidence for a two phase erdalen event associated with two glacier readvances of nigardsbreen at the preboreal boreal transition radiocarbon dates from the peat bog give age estimates for the two phases the e rst erdalen event readvance took place between 10 100 and 10 050 cal bp while the second occurred close to 9700 cal bp the lowering of the equilibrium linealtitude ela during these readvances is estimated using the little ice age ratio lr approach to be about 230 m and 215 m respectively the e rst readvance is attributed to an increase in winter precipitation while the second readvance may have been primarily caused by a marked drop in summer temperature which reactivated already existing ice masses

upper cenozoic history of the labrador sea baffin bay and the arctic ocean a paleoclimatic and paleoceanographic summary foraminifera palynomorphs and stable isotopes in planktonic foraminifera have been studied in piston cores from the northern labrador sea southern baffin bay and the alpha ridge region of the central arctic ocean foraminifera in cores from the labrador sea and southern baffin bay show glacial interglacial 18o values similar to those reported from the norwegian and greenland seas in contrast to the eastern north atlantic ocean however peaks of subarctic foraminifera and dinoflagellates in the western north atlantic cores show that relatively warm atlantic surface water continued to flow into the northern labrador sea during the early glaciation growth phases of isotopic stages 2 4 6 and 8 boreal and subarctic pollen suggest that warm atlantic air flowed into the northern labrador sea and baffin bay during the ice sheet growth phases the advection of warm air masses and the presence of open waters during the summer probably provided moisture for the growth of the laurentide innuitian and greenland ice sheets isotopic and microfossil records in arctic cores can also be tentatively correlated with major high latitude north atlantic glacial interglacial events magnetostratigraphic palynological and amino acid dating however shows that sedimentation on the alpha ridge has been very slow during the past 0 73 m y therefore events of less than 20 000 years duration cannot be clearly discerned interpretation of pre pleistocene paleoenvironments is further limited by the sparseness of calcareous and siliceous microfossils

changes in atmospheric circulation and ocean ice cover over the north atlantic during the last 41 000 years high resolution continuous multivariate chemical records from a central greenland ice core provide a sensitive measure of climate change and chemical composition of the atmosphere over the last 41 000 years these chemical series reveal a record of change in the relative size and intensity of the circulation system that transported air masses to greenland defined here as the polar circulation index pci and in the extent of ocean ice cover massive iceberg discharge events previously defined from the marine record are correlated with notable expansions of ocean ice cover and increases in pci during stadials without discharge events ocean ice cover appears to reach some common maximum level the massive aerosol loadings and dramatic variations in ocean ice cover documented in ice cores should be included in climate modeling

postglacial changes of terrestrial and marine environments along the labrador coast palynological evidence from cores 91 045 005 and 91 045 006 cartwright saddle the palynology of cores from cartwright saddle led to reconstruction of sea surface conditions on the basis of transfer functions using dinoflagellate cyst assemblages and to correlations with vegetational history on adjacent land as derived from pollen assemblages from deglaciation to about 8000 bp dinoflagellate cyst assemblages dominated by algidasphaeridium minutum indicate arctic type sea surface conditions and pollen assemblages reveal tundra vegetation in southeastern labrador codominance of a minutum and brigantedinium spp indicate persistence of cold sea surface conditions august temperature 3 c and extensive sea ice cover up to 11 months year until ca 6000 bp however the occurrence of abies which reached a maximum abundance at ca 7000 6000 bp and increasing percentages of alnus indicate northward tree migration and development of shrub tundra as a result of warmer terrestrial conditions around 6000 bp the significant occurrence of peridinium faeroense and nematosphaeropsi

the 8200 year b p event in the slope water system western subpolar north atlantic 1 stable isotope trace metal alkenone paleothermometry and radiocarbon methods have been applied to sediment cores in the western subpolar north atlantic between hudson strait and cape hatteras to reveal the history of climate in that region over the past 11 kyr we focus on cores from the laurentian fan which is known to have rapid and continuous accumulation of hemipelagic sediment although results among our various proxy data are not always in agreement the weight of the evidence alkenone sea surface temperature sst 18o and abundance of globigerinoides ruber indicates a continual cooling of surface waters over laurentian fan from about 18 c in the early holocene to about 8 c today alternatively mg ca data on planktonic foraminifera indicate no systematic change in holocene sst the inferred long term decrease in sst was probably driven by decreasing seasonality of northern hemisphere insolation two series of proxy data show the gradual cooling was interrupted by a two step cold pulse that began 8500 years ago and lasted about 700 years although this event is associated with the final deglaciation of hudson bay there is no 18o minimum anywhere in the labrador sea yet there is some evidence for it as far south as cape hatteras finally although the 8200 year b p event has been implicated in decreasing north atlantic ventilation and hence widespread temperature depression on land and at sea we find inconsistent evidence for a change at that time in deep ocean nutrient content at 4 km water depth