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

coupled deep water flow and climate variability in the middle pleistocene north atlantic abrupt changes in the strength of the atlantic meridional overturning circulation comprising northward flow of warm water and a cold southward return flow are implicated in abrupt climate changes in the late pleistocene a sensitive place to assess this circulation is in the cold return flow of deep western boundary currents here in records of flow speed and isotopic composition of surface and bottom waters from a deep western boundary current location near the northern source of north atlantic deep water we show both orbital and millennial scale coupling between deep ocean flow and climate in the middle pleistocene 0 75 0 87 ma when the boundary conditions in terms of the mean state and amplitude of climate change were different from more recent periods the coupling appears as a phased series of events initiated by reduced vertical density gradients and initial ventilation of deep waters the occurrence of these events in interglacials during the middle pleistocene suggests that the millennial scale climate variability in the north atlantic was more pronounced at that time than previously thought this demonstrates that given the right boundary conditions rapid climate shifts can also occur during relatively warm climate conditions

a relative sea level history for arviat nunavut and implications for laurentide ice sheet thickness west of hudson bay abstract thirty six new and previously published radiocarbon dates constrain the relative sea level history of arviat on the west coast of hudson bay as a result of glacial isostatic adjustment gia following deglaciation sea level fell rapidly from a high stand of nearly 170 m elevation just after 8000 cal yr bp to 60 m elevation by the mid holocene 5200 cal yr bp the rate of sea level fall decreased in the mid and late holocene with sea level falling 30 m since 3000 cal yr bp several late holocene sea level measurements are interpreted to originate from the upper end of the tidal range and place tight constraints on sea level a preliminary measurement of present day vertical land motion obtained by repeat global positioning system gps occupations indicates ongoing crustal uplift at arviat of 9 3 1 5 mm yr in close agreement with the crustal uplift rate inferred from the inferred sea level curve predictions of numerical gia models indicate that the new sea level curve is best fit by a laurentide ice sheet reconstruction with a last glacial maximum peak thickness of 3 4 km this is a 30 35 thickness reduction of the ice 5g ice sheet history west of hudson bay

holocene north atlantic overturning in an atmosphere ocean sea ice model compared to proxy based reconstructions climate and ocean circulation in the north atlantic region changed over the course of the holocene partly because of disintegrating ice sheets and partly because of an orbital induced insolation trend in the nordic seas this impact was accompanied by a rather small but significant amount of greenland ice sheet melting we have employed the emic loveclim and compared our model simulations with proxy based reconstructions of 13c sortable silt and magnetic susceptibility used to infer changes in past ocean circulation over the last 9000 years the various reconstructions exhibit different long term evolutions suggesting changes in either the overturning of the atlantic in total or of subcomponents of the ocean circulation such as the overflow waters across the greenland scotland ridge thus the question arises whether these reconstructions are consistent with each other or not a comparison with model results indicates that 13c employed as an indicator of overturning agrees well with the long term evolution of the modeled atlantic meridional overturning circulation amoc the model results suggest that different long term trends in subcomponents of the amoc such as iceland scotland overflow water are consistent with proxy based reconstructions and allow some of the reconstructions to be reconciled with the modeled and reconstructed from 13c amoc evolution we find a weak early holocene amoc which recovers by 7 kyr b p and shows a weak increasing trend of 88 1 msv kyr toward present with relatively low variability on centennial to millennial timescales

abrupt holocene climate transitions in the northern north atlantic region recorded by synchronized lacustrine records in iceland abstract two high sediment accumulation rate icelandic lakes the glacial lake hvitarvatn and the non glacial lake haukadalsvatn contain numerous tephra layers of known age which together with high resolution paleomagnetic secular variations allow synchronization with a well dated marine core from the shelf north of iceland a composite standardized climate record from the two lakes provides a single time series that efficiently integrates multi proxy data that reflect the evolution of summer temperatures through the holocene the first order trends in biogenic silica bsi 13c and c n rise relatively abruptly following deglaciation reaching maximum values shortly after 8 ka following a complex minimum between 8 7 and 8 0 ka the holocene thermal maximum htm in the lakes is marked by all proxies with a sharp transition out of the 8 ka cold event into peak summer warmth by 7 9 ka and continuing warm with some fluctuations until 5 5 ka decreasing summer insolation after the htm is reflected by incremental cooling initially 5 5 ka with subsequent cold perturbations recorded by all proxies 4 3 to 4 0 ka and 3 1 to 2 8 ka the strongest disturbance occurred after 2 ka with initial summer cooling occurring between 1 4 and 1 0 ka followed by a more severe drop in summer temperatures after 0 7 ka culminating between 0 5 and 0 2 ka following each late holocene cold departure bsi re equilibrated at a lower value independent of the sediment accumulation rate some of the abrupt shifts may be related to icelandic volcanism influencing catchment stability but the lack of a full recovery to pre existing values after the perturbation suggests increased periglacial activity decreased vegetation cover and glacier growth in the highlands of iceland the similarity in timing direction and magnitude of our multi proxy records from glacial and non glacial lakes and from the adjacent marine shelf suggests that our composite record reflects large scale shifts in ocean atmosphere circulation throughout the northern north atlantic

north atlantic nordic seas exchanges abstract the northeastern part of the north atlantic is unique in the sense that it is much warmer in the surface than other ocean areas at similar latitudes the main reason for this is the large northward transport of heat that extends to high latitudes and crosses the greenland scotland ridge to enter the nordic seas and the arctic there the warm atlantic water is converted to colder water masses that return southwards over the ridge partly as surface outflows and partly as overflows through the deep passages across the ridge in this paper the state of knowledge on the exchanges especially across the eastern part of the greenland scotland ridge is reviewed based on results from the ices nansen north atlantic norwegian sea exchanges project from the nordic woce project and from other sources the accumulated evidence allows us to describe the exchanges in fair detail the origins of the waters the patterns of their flow towards and over the ridge and their ultimate fate there is also increasing information on temporal variations of the exchanges although dynamical changes are still not well understood quantitative estimates for the volume transport of most of the overflow branches seem reasonably well established and transport measurements of the atlantic inflows to the nordic seas are approaching acceptable levels of confidence which allows preliminary budgets to be presented the deep overflows are driven by pressure gradients set up by the formation of deep and intermediate water the dominance of deep overflows over surface outflows in the water budget argues that this thermohaline forcing also dominates over direct wind stress and estuarine forcing in driving the atlantic water inflow across the greenland scotland ridge while wind stress seems to influence the characteristics and distribution of the atlantic water north of the ridge

anthracitization of coals in the south wales coalfield abstract investigations by the institute of geological sciences on potential geothermal water sites in the coalfield of south wales have been reported they are of considerable interest and revive the controversy about the nature of the heat source responsible for the anthracitization of some coals in this classic area in the absence of exposed post carboniferous igneous rocks in the coalfield general opinion has favoured heat generation by friction along faults or disturbances we re examine the evidence in the light of more recent geophysical and geochemical investigations which suggest the possibility of igneous intrusions at a depth of about 3 5 km or shallower the likely age of such intrusions is also considered high seismic velocity basement rocks rise to only 2 5 km beneath the surface of the carboniferous in the northwestern anthracitized zone of the coalfield and we suggest that anthracitization in south wales is not the result of depth of burial nor of frictional heat but of proximity to a magmatic heat source associated with crystalline rocks of the basement

a paleomagnetic approach toward refining holocene radiocarbon based chronologies paleoceanographic records from the north iceland md99 2269 and east greenland md99 2322 margins 1 we report the intercalibration of paleomagnetic secular variation psv and radiocarbon dates of two expanded postglacial sediment cores from geographically proximal but oceanographically and sedimentologically contrasting settings the objective is to improve relative correlation and chronology over what can be achieved with either method alone core md99 2269 was taken from the hunafloaall trough on the north iceland shelf core md99 2322 was collected from the kangerlussuaq trough on the east greenland margin both cores are well dated with 27 and 20 accelerator mass spectrometry 14c dates for cores 2269 and 2322 respectively paleomagnetic measurements made on u channel samples document a strong stable single component magnetization the temporal similarities of paleomagnetic inclination and declination records are shown using each core s independent calibrated radiocarbon age model comparison of the psv records reveals that the relative correlation between the two cores could be further improved starting in the depth domain tie points initially based on calibrated 14c dates are either adjusted or added to maximize psv correlations radiocarbon dates from both cores are then combined on a common depth scale resulting from the psv correlation support for the correlation comes from the consistent interweaving of dates correct alignment of the saksunarvatn tephra and the improved correlation of paleoceanographic proxy data percent carbonate these results demonstrate that psv correlation used in conjunction with 14c dates can improve relative correlation and also regional chronologies by allowing dates from various stratigraphic sequences to be combined into a single higher dating density age to depth model

a new glacial isostatic adjustment model of the innuitian ice sheet arctic canada abstract a reconstruction of the innuitian ice sheet iis is developed that incorporates first order constraints on its spatial extent and history as suggested by regional glacial geology studies glacial isostatic adjustment modelling of this ice sheet provides relative sea level predictions that are in good agreement with measurements of post glacial sea level change at 18 locations the results indicate peak thicknesses of the innuitian ice sheet of approximately 1600 m up to 400 m thicker than the minimum peak thicknesses estimated from glacial geology studies but between approximately 1000 to 1500 m thinner than the peak thicknesses present in previous gia models the thickness history of the best fit innuitian ice sheet model developed here termed sjd15 differs from the ice 5g reconstruction and provides an improved fit to sea level measurements from the lowland sector of the ice sheet both models provide a similar fit to relative sea level measurements from the alpine sector the vertical crustal motion predictions of the best fit iis model are in general agreement with limited gps observations after correction for a significant elastic crustal response to present day ice mass change the new model provides approximately 2 7 m equivalent contribution to global sea level rise an increase of 0 6 m compared to the innuitian portion of ice 5g sjd15 is qualitatively more similar to the recent ice 6g ice sheet reconstruction which appears to also include more spatially extensive ice cover in the innuitian region than ice 5g

contrasting trends in north atlantic deep water formation in the labrador sea and nordic seas during the holocene the holocene north atlantic deep water formation is studied in a 9 000 year long simulation with a coupled climate model of intermediate complexity forced by changes in orbital forcing and atmospheric trace gas concentrations during the experiment deep water formation in the nordic seas is reduced due to an enhanced influx of sea ice from the central arctic decreasing both surface salinity and density whereas deep water formation in the labrador sea increases due to surface cooling this leads to changes in the distribution of oceanic heat transported northwards by the atlantic ocean with less heat released 120 wm 2 in february in the nordic seas amplifying the surface cooling and increasing the sea ice cover in the labrador sea the oceanic heat release increases slightly 14 wm 2 thus dampening locally the cooling trend the overall atlantic overturning strength remains constant throughout the experiment over the nordic seas reduced evaporation contributes to the surface freshening

observed increases in bering strait oceanic fluxes from the pacific to the arctic from 2001 to 2011 and their impacts on the arctic ocean water column 1 mooring data indicate the bering strait throughflow increases 50 from 2001 0 7 sv to 2011 1 1 sv driving heat and freshwater flux increases increase in the pacific arctic pressure head explains two thirds of the change the rest being attributable to weaker local winds the 2011 heat flux 5 1020j approaches the previous record high 2007 due to transport increases and warmer lower layer ll temperatures despite surface temperature sst cooling in the last decade warmer ll waters arrive earlier 1 6 1 1 days yr though winds and sst are typical for recent decades maximum summer salinities likely set in the bering sea remain remarkably constant 33 1 psu over the decade elucidating the stable salinity of the western arctic cold halocline despite this freshwater flux variability strongly driven by transport exceeds variability in other arctic freshwater sources remote data winds sst prove insufficient for quantifying variability indicating interannual change can still only be assessed by in situ year round measurements

circulation and transport in the western boundary currents at cape farewell greenland the circulation and volume transports in the western boundary currents around cape farewell greenland are derived from full depth hydrographic and velocity measurements from august september 2005 the western boundary currents from surface to seafloor transport 40 5 8 1 sv southwards in the irminger sea and 53 8 10 8 sv northwards in the labrador sea the deep western boundary current dwbc defined as water with potential density greater than 27 80 kg m 3 transports 12 3 2 5 sv southwards in the irminger sea the deep water transport is reduced south of cape farewell where it changes flow direction from southwards to northwards the south corner at a section over the eirik ridge a bathymetric feature extending southwest of cape farewell the dwbc transports 8 7 1 7 sv westwards the reduction in transport at the south corner is associated with decreased velocities within the deepest layers and the volumetric loss of the most saline deep water types the observations suggest that the part of the shallow and deep western boundary currents diverge at the south corner downstream in the eastern labrador sea the deep water transport is increased to 19 7 3 9 sv northwards with the addition of recirculating denser deep waters the representativeness of the results from the semi synoptic survey are discussed with reference to companion current meter measurements of the dwbc

seasonal variability of the labrador current and shelf circulation off newfoundland 1 three dimensional finite element models were established for the newfoundland and labrador shelf to investigate climatological monthly mean wind and density driven circulation the model was forced using wind stresses from the national center for environmental prediction national center for atmospheric research reanalysis data prescribed at the sea surface large scale remote forcing determined from a north atlantic model monthly mean temperature and salinity climatology and m2 tide on the open boundary the model results were examined against various in situ observations moored current meter tide gauge and vessel mounted acoustic doppler current profiler data and satellite drift measurements and discussed together with literature information the seasonal mean circulation solutions were investigated in terms of relative importance of wind to density forcing for the labrador current the model results indicate significant seasonal and spatial variations consistent generally with previous study results and in approximate agreement with observations for the major currents the region is dominated by the equatorward flowing labrador current along the shelf edge and along the labrador and newfoundland coasts the labrador current is strong in the fall winter and weak in the spring summer the mean transport of the shelf edge labrador current is 7 5 sv at the seal island transect and 5 5 sv through the flemish pass the seasonal ranges are 4 5 and 5 2 sv at the two sections respectively density and wind driven components are both important in the inshore labrador current the density driven component dominates the mean component of the shelf edge labrador current while the large scale wind forcing contributes significantly to its seasonal variability

structure and origin of holocene cold events abstract the present interglacial the holocene spans the period of the last 11 700 years it has sustained the growth and development of modern society the millennial scale decreasing solar insolation in the northern hemisphere summer lead to northern hemisphere cooling a southern shift of the intertropical convergence zone itcz and a weakening of the northern hemisphere summer monsoon systems on the multidecadal to multicentury scale periods of more stable and warmer climate were interrupted by several cold relapses at least in the northern hemisphere extra tropical area based on carefully selected 10 000 year long time series of temperature and humidity precipitation as well as reconstructions of glacier advances the spatiotemporal pattern of six cold relapses during the last 10 000 years was analysed and presented in form of a holocene climate atlas hoclat see http www oeschger unibe ch research projects holocene atlas a clear cyclicity was not found and the spatiotemporal variability of temperature and humidity precipitation during the six specific cold events 8200 6300 4700 2700 1550 and 550 years bp was very high different dynamical processes such as meltwater flux into the north atlantic low solar activity explosive volcanic eruptions and fluctuations of the thermohaline circulation likely played a major role in addition internal dynamics in the north atlantic and pacific area including their complex interaction were likely involved

an extensive and dynamic ice sheet on the west greenland shelf during the last glacial cycle considerable uncertainty surrounds the extent and timing of the advance and retreat of the greenland ice sheet gis on the continental shelf bordering baffin bay during the last glacial cycle here we use marine geophysical and geological data to show that fast flowing ice sheet outlets including the ancestral jakobshavn isbrae expanded several hundred kilometers to the shelf edge during the last glaciation ca 20 ka retreat of these outlets was asynchronous initial retreat from the shelf edge was underway by 14 880 calibrated cal yr b p in uummannaq trough radiocarbon dates from the adjacent disko trough and adjoining trough mouth fan imply later deglaciation of jakobshavn isbrae and significantly an extensive readvance and rapid retreat of this outlet during the younger dryas stadial yd this is notable because it is the first evidence of a major advance of the gis during the yd on the west greenland shelf although the short duration suggests that it may have been out of phase with yd temperatures

thermal maturity of lower paleozoic sedimentary successions in arctic canada mean maximum graptolite reflectance values from numerous sections in arctic canada range from 0 6 in cornwallis island and northwestern devon island to 4 7 in ellesmere island we attribute this great lateral reflectance variation to differing burial depths of the graptolite bearing strata beneath thick synorogenic siliciclastic covers we attribute the low maturity of rocks in northern cornwallis and eastern bathurst islands to a maximum burial of about 2 km elsewhere we used the paleogeographic location and proximity to the ellesmerian overthrust wedge to interpret the measured reflectance values in northern ellesmere island where the highest graptolite reflectance values 4 7 occur as much as 9 6 km of synorogenic siliciclastics accumulated on a tectonically loaded carbonate shelf initial synorogenic siliciclastics encountered substantial submarine to basin relief and thus about 2 km of sediment were deposited prior to the initiation of deposition on the adjacent drowned shelf also the deep water sequence probably was underlain by attenuated continental crust adjacent to the southeastward advancing ellesmerian overthrust wedge together these factors caused deposition of as much as 7 6 km of sediment in western melville island and as much as 9 6 km in northeastern ellesmere island on the drowned shelf synorogenic stratal thicknesses were less a feature we attribu e to a thicker more rigid crustal sequence and greater distance from the ellesmerian tectonic loading we expect liquid hydrocarbons to be generated from the organic matter in the shales in areas with a graptolite r0 maximum gr0 max of less than 1 7 the presence of two types of solid bitumens having different reflectances morphologies and optical textures suggests that hydrocarbons were generated and migrated through the graptolite bearing strata we expect only gaseous hydrocarbons in areas where gr0 max exceeds 2 0 r0

baffin island and west greenland current systems in northern baffin bay abstract temperature salinity and direct velocity observations from northern baffin bay are presented from a summer 2003 survey the data reveal interactions between fresh and cold arctic waters advected southward along baffin island and salty and warm atlantic waters advected northward along western greenland geostrophic currents estimated from hydrography are compared to measured ocean currents above 600 m depth the baffin island current is well constrained by the geostrophic thermal wind relation but the west greenland current is not furthermore both currents are better described as current systems that contain multiple velocity cores and eddies we describe a surface intensified baffin island current seaward of the continental slope off canada and a bottom intensified west greenland current over the continental slope off greenland acoustic doppler current profiler observations suggest that the west greenland current system advected about 3 8 0 27 sv sv 10 6 m 3 s 1 towards the north west at this time the most prominent features were a surface intensified coastal current advecting 0 5 sv and a bottom intensified slope current advecting about 2 5 sv in the same direction most of this north westward circulation turned southward in the baffin island current system the baffin island system was transporting 5 1 0 24 sv to the south east at the time that includes additional contributions from nares strait to the north 1 0 0 2 sv and lancaster sound to the east 1 0 0 2 sv net freshwater fluxes were 72 and 187 msv for the west greenland and baffin island currents respectively empirical uncertainty arises from unknown temporal variations at weekly time scales and pertubations introduced by unresolved eddies eddies with 10 km horizontal and 400 m vertical scales were common and recirculated up to 1 sv our 2003 observations represent conditions when the north atlantic oscillation index nao was close to zero analysis of historical hydrographic data averaged along isobaths during nao positive years reveals a baroclinic circulation in baffin bay more intense than 2003 with stronger southward flow of fresher arctic waters along baffin island and stronger northward inflow of saltier atlantic waters along greenland during negative nao years this cyclonic circulation weakens as evidenced by a 1979 synoptic survey of the hydrography along baffin island

all age depth models are wrong but how badly the uncertainty and error associated with fitted age depth models were investigated by fitting a range of models to sets of simulated radiocarbon dates based on varved sediments and comparing the modelled relationship with the varve timescale with large numbers of dates cubic smooth splines out perform other models with few dates no model reliably provides a good fit to reality and calculated confidence intervals are over optimistic c 2003 elsevier ltd all rights reserved

the influence of meltwater on the labrador current in heinrich event 1 and the younger dryas abstract the labrador current transports freshwater from the arctic regions to the northern atlantic and the freshwater flux can influence the meridional overturning circulation the response of the labrador current to meltwater processes is unclear during the deglaciation of the ice sheets around the northwest atlantic this study utilized cores from flemish pass to monitor variations in the strength of the labrador current by using the sortable silt proxy the carbonate content the amount of ice rafted detritus and xrf chemical data were measured to identify the main meltwater events during the last deglaciation this study observed a clear enhancement of the flow strength of the labrador current in heinrich event 1 and the younger dryas with the greatest flow strength during the younger dryas event the onset of the current enhancement was dated at ca 13 cal ka bp which preceded the enhanced ice rafted deposition in hudson strait by about one thousand years the current enhancement in flemish pass during the younger dryas event corresponds to the freshening of the surface water thus meltwater preceding significant iceberg supply has an important effect on the labrador current in heinrich events on the laurentide ice sheet margin

rapid changes in the mechanism of ocean convection during the last glacial period high amplitude rapid climate fluctuations are common features of glacial times the prominent changes in air temperature recorded in the greenland ice cores1 2 are coherent with shifts in the magnitude of the northward heat flux carried by the north atlantic surface ocean3 4 changes in the ocean s thermohaline circulation are a key component in many explanations of this climate flickering5 here we use stable isotope and other sedimentological data to reveal specific oceanic reorganizations during these rapid climate change events deep water was generated more or less continuously in the nordic seas during the latter part of the last glacial period 60 to 10 thousand years ago but by two different mechanisms the deep water formation occurred by convection in the open ocean during warmer periods interstadials but during colder phases stadials a freshening of the surface ocean reduced or stopped open ocean convection and deep water formation was instead driven by brine release during sea ice freezing these shifting magnitudes and modes nested within the overall continuity of deep water formation were probably important for the structuring and rapidity of the prevailing climate changes

late quaternary detrital carbonate dc layers in baffin bay marine sediments 67 74 n correlation with heinrich events in the north atlantic abstract episodes of glaciation in the region north of baffin bay resulted in the erosion of paleozoic carbonate outcrops in nw greenland and the canadian high arctic these events are recognized in the marine sediments of baffin bay bb as a series of detrital carbonate rich dc layers bbdc layers thin southward within baffin bay thus the contribution of baffin bay ice rafted carbonate rich sediments to the north atlantic is probably slight especially compared with sediment output from hudson strait during heinrich events we reexamine cf aksu 1981 a series of nine piston cores from the axis of baffin bay and across the davis strait sill and provide a suite of 21 ams 14 c dates on foramininfera which bracket the ages of several dc layers the onset of the last dc event is dated in six cores and has an age of ca 12 4 ka in northern and central baffin bay a thick dc layer occurs at around 4 m in the cores and is dated 40 ka there were three to six dc intervening events the youngest bbdc event possibly a double event lags heinrich event 1 h 1 off hudson strait dated at 14 5 ka but it is coeval with the pronounced warming seen in gisp2 records from the greenland ice sheet during interstadial 1 we hypothesize that bbdc episodes are coeval with major interstadial 18 o peaks from gisp2 and other greenland ice core records and are caused by or associated with the advection of atlantic water into baffin bay cf hiscott et al 1989 and the subsequent rapid retreat of ice streams in the northern approaches to baffin bay

laser vs settling velocity differences in silt grainsize measurements estimation of palaeocurrent vigour the use of grain size distribution of muds for the reconstruction of past deep ocean currents is becoming established and applied in the palaeoceanographic community the methods are also applicable to shallow marine and tidal flat muds with similar inferences concerning the energy of wave and current sorting being drawn fine sediment grain size distributions can be obtained using a variety of instruments based on fundamentally different theoretical principles these machines may give varying sometimes misleading results giving divergent interpretations of flow speed history the new evidence presented here combined with earlier work suggests that of the three most commonly used analytical methods for fine silts with clays settling velocity sedigraph should be the method and instrument of choice with electrical resistance pulse counters e g coulter counter as a suitable alternative the data also show that laser particle sizers should be avoided for palaeocurrent reconstructions because the measured size of platey minerals can be dominated by their large projected area this causes them to be recorded as the same size as larger equant grains although they have much smaller settling velocity and were deposited in aggregates this produces results with a weaker relationship to the dynamics of deposition the central problem is thus that some coarse clay fine silt is recorded as medium to coarse silt the key size in the sortable silt mean size method of inferring changes in flow speed for coarse silts e g loess the laser gives more satisfactory results

recirculating components to the deep boundary current of the northern north atlantic abstract the meridional overturning system of the north atlantic is conventionally thought of as transporting warm water 4 c to high latitudes and covd water to low latitudes the northern cold water sources for this system are dense overflow from the nordic seas and less dense water from the labrador sea lsw the overflow components are carried westward by a deep northern boundary current dnbc that is shown here actually to begin southeast of the overflow regions the dnbc lies along the southern side of a system of islands and submarine ridges that divides the nordic seas from the subpolar basins the overflows act to increase the transport of the dnbc and this transport is further increased through the entrainment of warm waters once inside the labrador sea the dnbc is joined by lsw before continuing south to low latitudes as a cold deep western boundary current dwbc however published transport estimates are larger than can be explained by warm water entrainment alone thus indicating entrainment also of recirculating cold components the subject of this paper their sources are shown to be the lsw and cold abyssal waters originating from the southern hemisphere the lsw is entrained downward into the denser part of the dnbc and laterally into the upper part of the dwbc whereas the cold abyssal waters are supplied by an eastern intensified northward flow in the eastern atlantic that serves as the initial source of the dnbc and by a similar northward flow in the western atlantic the meridional overturning system described includes recirculations and poleward transport of cold water in addition tothe components described by the conventional system the cold abyssal waters in both the eastern and western basins have relatively low levels of oxygen and high concentrations of silicate reflecting their southern origin but their influence in the northwestern atlantic is somewhat obscurred by strong recirculating cyclonic gyres in the newfoundland and labrador basins this influence is detected by a deep silicate maximum extending poleward from the mid latitude western atlantic through the two gyres with eastern concentration and recirculating back diluted toward the south in the dwbc within the respective basins such a maximum also extends northward through the irminger basin into the dnbc but there is an ambiguity as to whether this is a direct extension of the signal from the south in the western basin or if it comes from the mid latitude eastern basin by way of westward flow through the charlie gibbs fracture zone it is perhaps consequence of both estimates of the volume transports of the various recirculating cold components indicate that they supply about as much water to the deep boundary currents as do the combined cold water sources in the north

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

distinguishing current effects in sediments delivered to the ocean by ice ii glacial to holocene changes in high latitude north atlantic upper ocean flows abstract shallow ocean flows in the northern north atlantic are of key importance in the regulation of earth s climate in the northern north atlantic nutrient rich cold arctic ocean outflow of modified atlantic water plus pacific and ice melt waters flow in the east greenland current egc and in the baffin island current which feeds into the labrador current the outflows east of greenland carry a substantial amount of warm salty north atlantic water that flows into the nordic seas mixes recirculates much of it via the arctic ocean and contributes to both shallow and deep overflows a key to understanding oceanic control of earth s climate therefore resides in establishing the changes in these high latitude currents we have analysed 28 cores comprising 2900 measured samples in the high latitude n atlantic and arctic oceans of which 80 pass the reliability test of a correlation coefficient between sortable silt mean and percentage r 0 5 mccave and andrews 2019 quat sci rev 212 92 107 there is a close similarity between the pattern of holocene decrease in the strength of the irminger current inflow to the nordic seas and outflow recorded in the egc and in deep overflow east of reykjanes ridge this suggests that the flow of the egc is strongly influenced by the influx of north atlantic water rather than supply of fresher water from ice sheet melt or pacific origin in contrast to the flows east of greenland those west of greenland show a slow holocene increase in flow the freshest coldest deep denmark strait overflow recorded at orphan knoll as well as labrador sea water flow on the slope north of the grand banks also show this gradual increase this points to control on deep water overflows by the flux of cold fresh water from greenland and the arctic some of which may have come from the pacific via the bering strait models also show a holocene east west difference in deep water formation with increase in the labrador sea and decrease in the nordic seas in almost all cases holocene flow speed maxima lag the local holocene thermal maxima by between 0 and 1000 years it is therefore highly unlikely that the local holocene thermal maxima are responses to increased flow of shallow currents in the adjacent ocean areas decelerations in flow speed accompany holocene coolings while accelerations accompany warmings the lgm was a period of slow flow and meltwater events usually show slowdowns as well however heinrich events show slowdowns in some regions and faster flow in others

sortable silt and fine sediment size composition slicing parameters for palaeocurrent speed and palaeoceanography fine sediment size 63 ixm is best measured by a sedimentation technique which records the whole size distribution repeated size measurement with intermediate steps of removal of components by dissolution allows inference of the size distribution of the removed component as well as the residue in this way the size of the biogenic and lithogenic noncarbonate fractions can be determined observations of many size distributions suggest a minimum in grain size frequency curves at 8 to 10 ixm the dynamics of sediment erosion deposition and aggregate breakup suggest that fine sediment behavior is dominantly cohesive below 10 1xm grain size and noncohesive above that size thus silt coarser than 10 ixm displays size sorting in response to hydrodynamlc processes and its properties may be used to infer current speed silt that is f mer than 10 ixm behaves in the same way as clay 2 xm useful parameters of the distribution are the 10 63 ixm mean size and the percentage 10 63 ixm in the fine fraction we cannot use size distributions to distinguish the nature of the currents therefore to infer water mass advection speeds i e the mean kinetic energy of the flow ku regions of high eddy kinetic energy ke must be avoided at the present such abyssal regions lie under the high surface k e of major current systems gulf stream kuroshio agulhas antarctic circmpolar current and brazil falldand currents in the argenthe basin this is probably a satisfactory guide for the pleistocene with regard to the carbonate subfraction of the size spectrum size modes due to both cocco iths and foramlnlferal fragments can be recognized and analyzed with the boundary between them again at about 10 lm the flux of less than 10 lm carbonate at pelagic sites above the lysocline is another candidate for a productivity indicator

changes in the deep western boundary current at 53 n abstractsouthward transports in the deep western boundary current across 53 n over 1949 99 are determined from a historical reconstruction long term mean transports for given water masses for net southward transport the southward component of the transport not including recirculation given in parentheses are 4 7 2 3 sv 5 1 2 4 sv sv 106 m3 s 1 for the denmark strait overflow water 6 1 2 7 sv 6 8 1 7 sv for the iceland scotland overflow water 6 5 2 6 sv 7 1 1 8 sv for classical labrador sea water and 2 3 1 9 sv 2 7 3 4 sv for upper labrador sea water the estimates take into account seasonal and interannual variability of the isopycnal positions and suggest the importance of including this factor a strong correlation 0 91 is found between variability of the total and baroclinic transports with the barotropic velocity removed at the annual time scale this correlation drops to 0 32 if the baroclinic transports are instead computed based upon the use of a fixed le