latest quaternary and holocene paleoceanography of the eastern baffin island continental shelf canada benthic foraminiferal evidence foraminiferal zones radiocarbon ages on shells and corrected ages on pretreated organic sediment from four cores from the eastern baffin island continental shelf suggest a three stage deglacial to postglacial history late wisconsin to holocene the earliest sediments in the cores contain foraminiferal species elphidium excavatum cassidulina reniforme islandiella helenae indicative of distal glaciomarine environments that lasted at least several thousand years an oceanographic change about 8500 years ago is indicated by a melonis zaandamae zone in northern and central shelf cores collected from 200 800 m water depth the presence of m zaandamae in the north and its absence in the south suggest warmer and more saline postglacial water in northern baffin bay whose influence became diluted with cooler coastal meltwater as the current flowed south along the baffin island shelf sediments after 6000 years ago on the northern and central shelf are dominated by agglutinated foraminifera suggesting dis

final stages in the collapse of the laurentide ice sheet hudson strait canada nwt 14c ams dates seismics stratigraphy and magnetic susceptibility logs hudson strait is a key element in the history of ice sheet ocean interactions during the deglaciation of the laurentide ice sheet data from over 30 giant piston cores supplemented by ca 40 14c ams dates on foraminifers and shells from sites within and adjacent to hudson strait are used to describe the timing and sediment processes associated with the final complex phases of deglaciation in hudson strait each core is placed in a regional seismic architectural context through examination of deep tow huntec profiles most cores sample a thin postglacial unit and extend several meters into glacial marine sediment mainly silty clays 14c dates on cores from the adjacent shelf indicate that deglaciation occurred by 13 ka we have not been unable to confirm that hudson strait was ice free by 11 12 ka although this is a probable scenario whole core magnetic susceptibility wcms data are used as the primary signature of changes in the style of sedimentation and provenance and to correlate between cores wcms indicates that there is a regional differentiation in the ms signal associated with bedrock provenance changes in contribution of detrital carbonate and style of sedimentation one low wcms event is present in cores from both the western and eastern basins it dates from 8 0 ka and provides an important regional stratigraphic marker probably associated with the final deglaciation of hudson bay and hudson strait sediment from a southerly source ungava bay continued to be contributed into the 900 m deep eastern basin of hudson strait 8 and 7 ka and thick postglacial sequences were piled within ungava bay between 6 and 7 ka

the quaternary geology of the labrador shelf the regional distribution of glacial and postglacial sediments on the labrador shelf was mapped by medium and high resolution seismics and shows a succession of tills that extend to the continental shelf edge at approximately 600 m the uppermost of these tills is less laterally extensive and does not occur on the labrador shelf bank tops in water depths less than 160 m we infer that the last glacial episode was less extensive than the preceding ones glaciomarine stratified silts and postglacial muds are found overlying the upper till in the deep basins that separate the banks the upper till glaciomarine silts and postglacial muds are interpreted to constitute one complete deglacial cycle radiocarbon age determination suggests this deglacial sequence began at approximately 20 000 years bp on the northernmost labrador shelf and hudson strait seismic evidence indicates a late glacial readvance locally deposited a till that overlies the glaciomarine sediments associated with the last glacial advance

late quaternary sediments and chronology of the northeast labrador shelf karlsefni trough saglek bank links to glacial history core hu87033 015 an 11 m long giant piston core from the western end of karlsefni trough was taken only 25 km from the coast of northernmost labrador the regional acoustic framework was established via a high resolution deep towed huntec dts seismic survey we recognized four acoustic facies that are associated with designated and recovered major lithologic units the ages of these units were determined from 13 accelerator mass spectrometry 14 c dates from marine biogenic carbonates these results suggest that glacial ice was present on the shelf from at least the mid wisconsinan and that the basal sequence contains reworked glacial marine diamicton furthermore our data provide the first evidence that the northern labrador inner shelf was ice free by ca 11 14 c ka the bulk of the postglacial deposition was around 8 2 ka and consists of increased detrital carbonate deposition the deposition of this detrital carbonate is age equivalent with dc 0 on the southeastern baffin shelf and in the north atlantic

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

last glacial maximum and deglaciation of devon island arctic canada support for an innuitian ice sheet abstract the extent and origin of quarternary glaciers in the queen elizabeth islands of arctic canada especially during the last glacial maximum lgm has been debated for well over a century no consensus has yet emerged and the spectrum of interpretations within the last decade is the broadest ever the glacial geology of devon island strongly supports the late wisconsinan innuitian ice sheet hypothesis during lgm the southeastern part of the queen elizabeth islands was covered by an ice sheet flowing from a centre or a divide centrally located in the archipelago another ice divide extended from the centre across devon island flow from the innuitian centre and convergent flow from devon island and probably also from cornwallis and bathurst islands sustained an ice stream in wellington channel ice was locally advancing to its lgm limit about 23 ka bp recession in the vicinity of the present coastline was underway by 10 ka bp and final ice remnants west of the present devon ice cap vanished about 8 ka bp the island bears the same two part landscape zonation as do other islands and peninsulas in the region these reflect a cold based core and warm based periphery at lgm

early preboreal cooling in the nordic seas region triggered by meltwater at the younger dryas preboreal transition a high resolution core from the northeastern norwegian sea reveals a two step warming of sea surface temperatures dated at respectively 10 200 10 000 and 9700 9500 14 c yr b p 11 450 11 350 and 11 150 11 000 cal yr b p warming was interrupted by a period having stable temperatures and a reduction in sea surface salinity and we suggest that this pause in warming was triggered by an increase in freshwater supply that may have hampered the north atlantic heat conveyor the freshwater influx correlates to an atmospheric cooling over both the greenland ice sheet and northwest europe and to cooling of surface temperatures in the nordic seas freshwater may have been supplied from the waning fennoscandian ice sheet

dynamics of the laurentide ice sheet in hudson bay canada abstract interpretation of sidescan sonar and high resolution sub bottom seismic data from hudson bay has led to the development of a model for final disintegration of the laurentide ice sheet the well preserved geomorphic features observed from the bay floor are similar to subaerially exposed glaciogenic features observed around the perimeter of hudson bay and can be related to the following three paleoenvironments subglacial erosion deposition ice margin deposition and reworking and post glacial reworking and burial subglacial features observed include fluted terrains with superimposed rogen moraines relief attributed to ice surging eskers subglacial channels and dead ice topography de geer moraines and recessional moraine complexes indicate the mechanism and orientation of ice breakup retreat the orientations of these features are locally consistent with regional trends indicating the overall direction of ice sheet flow and retreat during the last phase of the laurentide ice sheet subglacial channel complexes incised into the till and bedrock and high energy bedforms deposited on the till surface occur in present day water depths down to 160 m due to isostatic depression these could have been as much as 315 m deeper at the time of formation they indicate a wet based glacier with high energy subglacial drainage during the late phases of ice retreat the sidescan sonar data also reveal numerous zones of distinctive morphology attributed to ice breakup and post glacial processes cross cutting relationships allow the determination of the relative ages of these zones from oldest to youngest these zones are interpreted to represent scouring of the bedrock and overburden by the remnants of the ice sheet seafloor scouring by tabular icebergs which moved in a tidally induced arcuate pattern or under the influence of massive glacial lake outflows development of dead ice topography under residual ice masses and random iceberg scouring by smaller icebergs restricted to present day water depths of less than 180 m recently published reconstructions of the collapse of the laurentide ice sheet based on dated quaternary sections on land suggest that the bay was rapidly deglaciated in approximately 400 years the well preserved and distinctive glaciogenic and stratigraphic indicators observed from the bay floor suggest that they were formed by a succession of mechanisms which were too short lived to obliterate the underlying evidence of deglaciation this supports the interpretation of extremely rapid deglaciation of hudson bay and points out that subsequent marine processes have not been sufficient to obliterate the glacial features

deep circulation change linked to heinrich event 1 and younger dryas in a middepth north atlantic core a core from the mid atlantic ridge at 43 5 n and 3 km water depth shows distinct evidence of the deglacial events known as heinrich event 1 probably the marine equivalent of oldest dryas cooling in europe and the younger dryas the heinrich event dated at three levels to between 14 3 and 15 0 ka is marked by a minimum in foraminifera per gram by maxima in rates of sedimentation ice rafted debris per gram and relative abundance of n pachyderma s and by a 18o minimum in planktonic foraminifera the younger dryas event is marked by peak abundance of n pachyderma s and a planktonic 18o maximum benthic foraminiferal 13c reaches minimum values during both the heinrich event and the younger dryas our data indicate pronounced changes in surface water properties were coupled with reduced production of north atlantic deep water at each of these times

holocene climatic instability a prominent widespread event 8200 yr ago the most prominent holocene climatic event in greenland ice core proxies with approximately half the amplitude of the younger dryas occurred 8000 to 8400 yr ago this holocene event affected regions well beyond the north atlantic basin as shown by synchronous increases in windblown chemical indicators together with a significant decrease in methane widespread proxy records from the tropics to the north polar regions show a short lived cool dry or windy event of similar age the spatial pattern of terrestrial and marine changes is similar to that of the younger dryas event suggesting a role for north atlantic thermohaline circulation possible forcings identified thus far for this holocene event are small consistent with recent model results indicating high sensitivity and strong linkages in the climatic system

geochemistry and genesis of geothermal well water from a carbonate evaporite aquifer in chongqing sw china thermal water is an important natural resource the hydrogeochemistry and geothermometry of thermal water from the qianyi well twqw which is associated with the tongjing warm springs located in the eastern sichuan fold belts in chongqing sw china was investigated the reservoir of this region consists of upper and middle triassic carbonate and evaporite rocks the twqw was of ca mg so4 type with water temperature of 47 3 c plotting on the giggenbach na k mg diagram indicates that the twqw was immature due to a mixing of shallow karst groundwater and thermal water the mixing model indicates that the twqw was composed of 49 deep thermal water and 51 shallow karst groundwater geothermometers suggest a reservoir temperature of about 79 c locating this aquifer at a depth of 2 5 km the d and 18o values plot near the local meteoric water line suggesting that the twqw originates from local meteoric water at recharge elevations of 780 1160 m a s l a conceptual model of the genesis for tongjing warm springs was developed rainfall infiltrates via karst outcrops in the elevated areas of the northern tongluoxia anticline extracts heat from reservoir rocks at depth dissolves minerals and becomes thermal water the thermal water is driven by gravity flows through the carbonate evaporite aquifer and follows the tongluoxia anticline of the eastern sichuan fold belts to the southwest the thermal water ascends to the surface along the incision created by the wentang river and mixes with shallow karst groundwater to create warm springs this study may be relevant to other karst geothermal reservoirs in china

postglacial sequence stratigraphy of lake melville labrador abstract in lake melville labrador the quaternary glacimarine sediments reflect a single retreat phase of the laurentide ice sheet during the early holocene based on extensive airgun and high resolution seismic surveys sediment deposits are subdivided into thirteen units that are associated with glacial paraglacial and postglacial styles of deposition their distribution patterns reflect paleo positions of a retreating ice margin during the period between 10 000 and 9000 years before present formation of paraglacial deltas during the early to mid holocene 6 9 ka and postglacial tidal influenced deposition during the late holocene

evidence from driftwood records for century to millennial scale variations of the high latitude atmospheric circulation during the holocene different holocene sea ice drift patterns in the arctic ocean have been hypothesized by dyke et al from radiometric analyses of driftwood collected in the canadian arctic archipelago a dynamic thermodynamic sea ice model is used to simulate the modes of arctic ocean ice circulation for different atmospheric forcings and hence determine the atmospheric circulations which may have accounted for the inferred ice drift patterns the model is forced with the monthly mean wind stresses from 1968 a year with very large ice export and 1984 very low ice export two years with drastically different winter sea level pressure patterns and with different phases of the nao index the simulations show that for the 1968 wind stresses a weak beaufort gyre with a broad transpolar drift stream tds shifted to the east are produced leading to a large ice export from the arctic similarly the 1984 wind stresses lead to an expanded beaufort gyre with a weak tds shifted to the west and a low ice export these results correspond to the patterns inferred by dyke et al based on the simulations the driftwood record suggests that for centuries to millennia during the holocene the high latitude average atmospheric circulation may have resembled that of 1968 1984 and today s climatology with abrupt changes from one state to the other

meltwater and precipitation runoff to the north atlantic arctic and gulf of mexico from the laurentide ice sheet and adjacent regions during the younger dryas runoff from north america may have played a significant role in ocean circulation and climate change during the last deglaciation because the driving force behind such changes may have been related to salinity of the north flowing atlantic ocean conveyor circulation it is critical to know the volume timing and location of fresh water entering the north atlantic from the melting laurentide ice sheet during the younger dryas cold episode 11 000 10 000 years b p there was a two fold increase in the volume of meltwater plus precipitation runoff to more than 1700 km yr 1 flowing through the st lawrence valley to the north atlantic mainly because retreating ice allowed the glacial lake agassiz basin to drain eastward into the great lakes at this time there was a corresponding decline in discharge from lake agassiz through the mississippi river to the gulf of mexico runoff to the arctic ocean also increased at about the beginning of the younger dryas from 740 to 900 km yr 1 because of the capture of what is now the headwater region of the mackenzie river watershed this in combination with rising sea level and warming climate may have increased the amount of pack ice reaching the north atlantic through the norwegian sea from the arctic ocean at 10 000 years b p eastward overflow from the western interior of north america was blocked by advancing ice again forcing overflow to the gulf of mexico and possibly to the northwest into the arctic ocean although total runoff to the oceans from all regions draining from the laurentide ice sheet did not vary substantially between 12 000 and 9000 years b p if discharge to the gulf of mexico is excluded fresh water reaching the north atlantic averaged 4000 km yr 1 during the younger dryas in contrast to 2870 km yr 1 just before this cold episode and 3440 km yr 1 just after it

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

the preboreal oscillation around the nordic seas terrestrial and lacustrine responses the occurrence of an early preboreal climatic cooling oscillation pbo in lacustrine and glacial records from northwest europe iceland and greenland is reviewed and documented the often subtle response of the proxy records to this oscillation in combination with its short duration make it difficult to detect owing to its chronostratigraphic position between the 10 000 9900 and 9600 9500 14 c plateaux c 11 300 11 150 calendar yr bp it is also difficult to 14 c date with precision we find that the vegetation response to the pbo varies between sites and regions in contrast to the pioneer vegetation in iceland and southern sweden the expanding birch pine forest in germany denmark was more susceptible to deteriorating growing conditions the combined lacustrine tree ring and glacial records imply that the pbo was characterised by cool and humid conditions throughout northwestern and central europe this is documented by vegetation changes decreased aquatic production increased soil erosion increased 2 h and 13 c content in tree rings readvances or stillstands of the ice sheet in norway and finland and ingression of brackish water into the baltic icelandic proxy records from lake sediments and glacial moraines imply cooler conditions than during the previous preboreal period but not as extreme as during the younger dryas greenland records suggest that the early preboreal was characterised by ice readvances as an effect of cool climate and increased precipitation in relation to the younger dryas it was not until the end of the pbo that climate was warm enough to melt the land based ice sheet this preboreal oscillation found on both sides of the nordic seas is interpreted as an effect of increased freshwater forcing on the thermohaline circulation in the nordic seas which is implied by a simultaneous and distinct rise in the atmospheric 14 c 12 c ratio a slow down of the thermohaline circulation may tempor arily have pushed the polar front further south 1997 by john wiley sons ltd preboreal oscillation thermohaline circulation lacustrine records glacial records chronology

the marine record of deglaciation from the continental margin off nova scotia continental margin sediments off nova scotia accumulate at high rates up to 360 cm kyr 1 and contain a history of millennial scale environmental changes which are dominated by the proximity of the laurentide ice sheet during the latest quaternary using stable isotope ratios of oxygen accelerator mass spectrometer radiocarbon dating micropaleontology and sedimentology we document these changes in six piston cores ranging in water depth from 450 to 4300 m we find that maximum 18o in n pachyderma occurred about 15 ka and preceded the maximum abundance of this species in these cores by 1000 years between 13 and 14 ka we find a second peak in abundance of n pachyderma minimum 18o and two pulses of ice rafting the sediment lithology supports terrestrial studies which indicate that there was a general withdrawal of ice beyond the upper paleozoic and mesozoic red beds by 14 ka in southeastern canada so the ice rafting events between 13 and 14 ka probably reflect ice stream activity in the st lawrence valley the younger dry as event is recognized as a peak in abundance of n pachyderma and ice rafting dated as 11 3 ka but meltwater discharge to the gulf of st lawrence was either too small or occurred over too long a time to leave a distinct 18o minimum off nova scotia at 7 1 ka in the middle of holocene warming we find a third peak in abundance of n pachyderma and another 18o minimum but no ice rafting we interpret these data as evidence of a late occurring meltwater event which if correct could have originated in the great lakes in the labrador ungava region or in both the final millennial scale phenomenon off nova scotia is the onset of neoglaciation marked by increased ice rafting and increased n pachyderma beginning about 5 kyr ago

reduced meltwater outflow from the laurentide ice margin during the younger dryas the cause of the younger dryas cold event which interrupted the last deglaciation is still a matter of debate1 a prevalent hypothesis proposed by broecker et al 2 is that the abrupt climate change was driven by a decrease in the rate of north atlantic deep water production triggered by a sudden dilution of north atlantic surface water in response to the diversion of laurentide icesheet melt water from the mississippi drainage system to that of the st lawrence river here we investigate the feasibility of this triggering mechanism by reconstructing sea surface temperature salinity and sea ice cover records for the outlet of the gulf of st lawrence into the north atlantic ocean these reconstructions based on dinoflagellate cyst assemblages3 4 in sediment cores from the region show reduced meltwater runoff low temperatures and extensive sea ice cover during the younger dryas dated here between 10 800 and 10 300 bp meltwater pulses did occur before and after the younger dryas event as early as 11 700 bp during the development of the champlain sea in the st lawrence lowland and afterwards until 10 100 bp at the resolution of our salinity proxy 0 7 the meltwater pulses preceding the younger dryas did not affect sea surface salinity off the shelf break these constraint on the meltwater outflow through the st lawrence drainage system do not support the triggering mechanism of the broecker et al hypothesis2 unless the north atlantic thermohaline circulation is more sensitive to small salinity changes than most models suggest23

sediments sedimentation rates and environments southeast baffin shelf and northwest labrador sea 8 26 ka ten 14c dated cores are described from the labrador sea continental slope and hatton and resolution basins on the southeast baffin shelf based on sharply defined detrital carbonate layers in the labrador sea cores we propose that the laurentide ice sheet reached the shelf break at both 20 and 15 14c ka 24 3 and 18 2 sidereal ka and contributed significant sediment to the northwest labrador sea both times the flux was 720 kg m2 ka during these periods of maximum ice extent the laurentide ice sheet retreated from its 15 ka position at the shelf break to the inner shelf between 14 and 12 14c ka ice proximal conditions recognized by relatively light 18o on near surface planktonic foraminifera high detrital carbonate and benthic foraminiferal faunas dominated by elphidium excavatum forma clavata cassidulina reniforme prevailed until at least 10 14c ka the ice readvanced toward resolution basin and across part of hatton basin at 11 14c ka accelerator mass spectrometry dates on core tops i

role of the thermohaline circulation in the abrupt warming after heinrich events evidence of rapid climate oscillations during the last glacial period has been identified in climate records from greenland ice cores1 2 and ocean sediments in the north atlantic3 4 these records show that periods of gradual cooling are terminated by abrupt warming events5 with the coldest periods coinciding with the deposition of ice rafted debris so called heinrich events throughout the north atlantic heinrich events are thought to be a signature of massive iceberg discharges owing to collapse of the laurentide ice sheet bond et al 5 have proposed that the decrease in meltwater flux following collapse and retreat of the ice sheet enhanced the ocean s thermohaline circulation6 thereby increasing advection of heat from the tropics and giving rise to abrupt climate warming here we test this idea using a simple ocean model coupled to a model of a periodically surging ice sheet we find that massive discharges of icebergs first stop the thermohaline circulation because of the consequent freshwater influx cooling the north atlantic region this is followed by a rapid restart of the circulation leading to abrupt warming thus our model can reproduce the qualitative features of the climate oscillations seen in the ice core and ocean records

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

a regional 8200 cal yr bp cooling event in northwest europe induced by final stages of the laurentide ice sheet deglaciation the most notable change in 18o in greenland ice cores during the holocene occurs at 8200 cal yr bp here we present a new high resolution marine record from the northern north sea along with tree ring data from germany which contain evidence of a pronounced temperature drop 2 c contemporaneous with that of the greenland ice core records the synchronous timing of the cooling event in the greenland ice cores marine record and tree ring data from northwest europe reflects a regional influence on the north atlantic ocean atmospheric system suggesting a prominent role of the north atlantic thermohaline circulation the operation of the north atlantic ocean circulation is sensitive to variation in the freshwater budget implying that any change in freshwater flux is capable of altering the north atlantic circulation system we hypothesise minor but long term freshwater fluxes in the final stages of the deglaciation of the laurentide ice sheet as a forcing mechanism 1998 john wiley sons ltd

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

a 200 year mid european air temperature record preserved in lake sediments an extension of the δ18op air temperature relation into the past abstract a detailed history of the water oxygen isotope ratios of lake ammersee southern germany was established for the last two centuries by analyzing oxygen isotope ratios of ostracod shells from a sediment core in a three to five year resolution empirical analysis and modelling of the isotope hydrology of the lake show that the oxygen isotopic composition of the lake water is mainly controlled by the isotopic composition of local precipitation for the last 200 years the lake isotope record is strongly correlated to the air temperature record from hohenpeisenberg situated within the lake s catchment area thus the mid european relation between 18 o in precipitation and air temperature documented for the last 20 years can be extended over a longer time and a larger temperature range the results provide further support for the validity of ostracod 18 o from ammersee sediments as a quantitative proxy for mean annual air temperature probably extending back to the last glaciation

great lakes paleohydrology complex interplay of glacial meltwater lake levels and sill depths the oxygen isotope record of ostracode and clam shells recovered from great lakes cores of known age allows definition of times when meltwaters from the laurentide ice sheet were important components of lake water in the several lake basins since 12 ka we find that the lowstands in lake huron and georgian bay are characterized by isotopically light waters 18 o values of 20 to 22 relative to smow standard mean ocean water and the highstands by isotopically heavy waters of more local origin these data can be used to determine the degree of hydraulic separation among the early holocene lakes southern lake michigan for instance may mix with northern source waters only during times of rising and high water levels generally it is characterized by waters of local origin

glacial geology of western hudson strait canada with reference to laurentide ice sheet dynamics hudson strait is a large marine trough that connected the marine based interior of the laurentide ice sheet with the ocean field investigations of the glacial geology of western hudson strait have helped to define the role of the strait in laurentide ice sheet dynamics in general ice converged on western hudson strait from the north west and south upon reaching the strait ice flowing from foxe and ungava peninsulas turned eastward within less than 10 km of the coast to parallel eastwardly flowing ice in the strait glacial erosion of western hudson strait is identified as slight the texture carbonate content ph and the presence of several types of erratics distinguish till on nottingham salisbury and mill islands in western hudson strait from till on southern foxe peninsula and northern ungava peninsula till on the islands is characterized by higher ph and higher proportions of silt clay and carbonate than till on either adjacent peninsula in addition the presence of red sandstones porphyritic intrusives stromatolites omarolluks and iron formation are restricted to the islands with few exceptions that can be explained by ice rafting carbonate is present in the pebble and boulder fractions of till on foxe peninsula and in all fractions of till on the islands but is absent from till on ungava peninsula these data suggest that ice from distant and widely distributed source regions affected western hudson strait and along with evidence for a rapid change in ice flow direction along the margins of hudson strait suggest that the strait was occupied by a relatively fast moving ice stream that had a substantial impact on the interior of the ice sheet through downdraw

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

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

the northwest atlantic mid ocean channel of the labrador sea iv petrography and provenance of the sediments the northwest atlantic mid ocean channel namoc of the labrador sea is associated with a 500 m thick sequence of well bedded turbidites along the axis of the labrador and newfoundland basins and extends onto the western sohm abyssal plain the specific source areas of these terrigenous turbidites on the shelves and landmasses surrounding the labrador sea were not known hitherto because the morphological connections in the head region of the namoc with canyons on the slope are masked by young ice rafted and bottom current transported sediments petrographic analysis of channel sands and gravels suggests a dominant canadian source for the channel segment north of the confluence with the imarssuak mid ocean channel imoc based on the predominance of lower paleozoic detrital carbonates the imoc provides sediment from sources around the west reykjanes basin i e the east coast of greenland and iceland however source specific minerals or rock fragments from the tertiary alkali basalts of southwest greenla

late deglaciation of the central labrador coast and its implications for the age of glacial lakes naskaupi and mclean and for prehistory the age of the marine limit and associated deglaciation has been estimated from relative sea level curves for the hopedale and nain areas of the central labrador coast as approximately 7600 200 and 8500 200 yr ago respectively these ages indicate that the ice margin remained on the coast for up to 3000 yr longer than previously estimated because the central coast is due east of glacial lakes naskaupi and mclean the earliest the lakes could have formed was 8500 200 yr ago with their largest phases being fully established only after 7600 200 yr ago this suggests that the age of the lakes and associated deglaciation of the central labrador ungava region is younger by at least 1500 yr than previously estimated a late glacial marine based ice mass in ungava bay that dammed the lakes collapsed ca 7000 yr ago within this time frame therefore the glacial lakes only existed for 500 yr the persistence of the laurentide ice sheet margin on the central labrador coast until 7600 yr ago probably restricted the northward movement of early prehistoric people into northern labrador

glaciomarine environments in canada an overview the present understanding of canada s glaciomarine environments owes much to the remarkable role played by the scientists of the geological survey of canada their efforts have led to the review and partial revision of three scientific paradigms 1 there is a mechanical rather than a climatic control of the collapse of a tidewater ice sheet 2 ice sheets were mostly grounded on canada s continental shelves rather than with floating ice shelves 3 ice loaded glaciomarine sediments are sometimes indistinguishable from deposits of till a proposed stratigraphic framework for canadian glaciogenic sequences can be quantified allowing insights into ice sheet dynamics for instance the arctic margin of the wisconsinan ice complex appears to have generated comparatively little meltwater ice margin retreat being principally by iceberg calving surprisingly the atlantic margin of the wisconsinan ice complex appears to have transported larger quantities than its pacific counterpart this is contrary to t

a regional stratigraphic isochron ca 800014c yr b p from final deglaciation of hudson strait sedimentologic rock magnetic and x ray fluorescence data from two marine sediment cores in hudson strait suggest that a red hematite rich clay layer was deposited throughout the strait during the final collapse of the laurentide ice sheet in the vicinity of northern hudson bay and western hudson strait this layer which can be recognized by its reddish pink color 10yr6 2 to 5yr4 2 and relatively high hematite proportions low magnetic susceptibility and magnetite to hematite ratio is dated from 8000 to 790014c yr b p at both ends of the strait the dubawnt group a proterozoic bedrock unit in northern hudson bay is the most likely source of this stratigraphic isochron in eastern hudson strait the recognition of this red unit and other distal glaciomarine sediments from 8400 to 790014c yr b p indicates that little sediment from the nearby labrador dome reached eastern hudson strait during this 500 yr interval this time interval immediately postdates the noble inlet advance a northward flow of labrador ice across eastern hudson strait onto southern baffin island from ca 8900 to 840014c yr b p one explanation for the lack of labrador sediments is that the northern margin of the labrador dome was cold based for up to 500 yr following the noble inlet advance

heinrich event 0 dc 0 in sediment cores from the northwest labrador sea recording events in cumberland sound layers of ice rafted limestone debris rich sediment were deposited in the northwest labrador sea and the north atlantic during the last glacial period 10 80 ka these sediments were deposited by heinrich events h events which record catastrophic collapses of the laurentide ice sheet in the region of the hudson strait these intervals of detrital carbonate rich sediments are referred to as detrital carbonate layers dc in the northwest labrador sea accelerator mass spectrometry ams 14c dates provide a strong constraint on the timing for these events h 1 dc 1 and h 2 dc 2 dc 0 also known as h 0 correlative to the younger dryas cooling event is not as distinct a sediment unit in the northwest labrador sea as dc 1 and dc 2 an analysis of sediments from two cores hu75009 iv 055 and hu75009 iv 056 off the mouth of the hudson strait in the northwest labrador sea basin sheds new light on the missing dc 0 sediment unit timing for the dc 0 event in cores 055 and 056 is bracketed between 11

preferential dissolution of 234u and radiogenic pb from α recoil damaged lattice sites in zircon implications for thermal histories and pb isotopic fractionation in the near surface environment abstract zircons from two archean samples a 2732 ma trondhjemite and a 2728 ma dacite both from the western superior province were washed in hydrofluoric acid hf at moderate temperatures zircon residues and hf wash solutions were analyzed for u pb isotope systematics and 234u 238u ratios in an attempt to study the effect of hf washing on selective dissolution of radiogenic isotopes in areas damaged by recoil on a conventional concordia diagram the datum from one analyzed wash solution plots below concordia near the array of discordant data from magnetic unabraded zircon fractions which record a lower concordia intersection of about 230 ma data points from hf wash residues of two different zircon fractions from the trondhjemite are also discordant and collinear with near concordant data from abraded unleached fractions which record the true age of crystallization however this array has a negative lower concordia intercept of 749 ma the residue and wash from hf treatment of a single zircon fraction from the dacite are collinear with the crystallization age of the sample as defined by near concordant data from unleached fractions this line has a lower concordia intersection of 1388 ma also negative but distinct from the trondhjemite residue line the discordance of strongly washed residues is proportional to the calculated recoil dosage of the grains leach residues show negative 234u 238u anomalies while the leaches themselves show 234u excess on the order of 10 these results can be explained by the bulk dissolution of altered and metamict crystal domains during the hf wash accompanied by leaching of 234u and radiogenic pb from recoil damaged lattice sites in alteration free zircon residues studies were also carried out on zircons washed in nitric acid these show small ca 0 5 negative 234u anomalies this suggests that small amounts of radiogenic pb can be leached from damaged lattice sites by nitric acid the negative age lower concordia intercepts of pb loss lines defined by hf leach residues can be explained if early radiation damage has been annealed so that only more recently formed radiogenic pb atoms are in damaged crystal lattice sites and are susceptible to leaching since this pb fraction is relatively young the residue pb is biased toward anomalously old values a model is proposed for early burial and heating of the rocks above the annealing temperature for recoil damage followed by uplift and cooling several hundred million years after crystallization this model predicts a cooling time of 2500 20 ma for the trondhjemite and 2295 35 ma for the rhyolite comparison with metamorphic and cooling histories from ar ar studies suggest that the long term annealing temperature for low levels of recoil damage in zircon is in the range 250 300 c approximately the same as for fission tracks these results demonstrate that hf and possibly to a small extent hno3 can preferentially leach radioactive daughter elements from damaged zircon lattice sites in addition to dissolving metamict domains the threshold recoil dosage for dissolution of damaged zircon appears to be slightly in excess of 1 5 1015 decay events mg the isotopic composition of the leached pb is sensitive to the annealing history of the zircon thus in addition to supplying the magmatic crystallization age of the sample the hf leaching of zircon might be useful for constraining its later low temperature thermal history leaching from recoil damaged sites also occurs in the natural environment and this may lead to significant enhancement of 206pb 204pb in groundwater

subseabed disposal a geosciences perspective billions of dollars are spent every year in the search for natural resources utilizing the most sophisticated technology available to assess the geological geochemical and geophysical characteristics of a particular region this technology can also be used however to search for the most desolate isolated useless terrain available to be used as a repository for high level nuclear waste this terrain is not limited to the 30 of the planet s surface upon which we live it includes the 70 lying beneath the ocean waters as well

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