chronology of late wisconsinan glaciation in middle north america abstract we propose a chronology of late wisconsinan glacial fluctuations in middle north america from alberta to wisconsin based on radiocarbon dates derived solely from wood previous chronologies of the southwestern margin of the north american continental ice sheet have depended to a considerable degree on radiocarbon dates from fine grained organic sediment this material is commonly contaminated with older carbon resulting in chronologic confusion by using only dates from wood much of the confusion disappears however because of the scarcity of wood dates only four of the sixteen identified fluctuations are accurately dated an advance into iowa about 14 000 to 13 500 bp an advance into south dakota and iowa about 12 300 bp an advance into the lake michigan basin about 11 700 bp and an advance into the lake superior basin about 9900 bp in addition the beginning of late wisconsinan glaciation before 20 000 bp is fairly well documented none of the fluctuations in the western part of the region are accurately dated

successions of invertebrate microfossils and the late quaternary deglaciation of the central st lawrence lowland canada and united states abstract foraminiferal and ostracode assemblages in late glacial and early post glacial sediments of the central st lawrence lowland show that a proglacial lake glacial lake st lawrence preceded the champlain sea in some parts of the lowland and that the champlain sea was in contact with the laurentide ice sheet during deglaciation of other parts of the lowland glaciolacustrine and glaciomarine environments were followed by marine environments with salinity as high as 24 34 the higher salinity water in the champlain sea was part of a salt water wedge extending from the gulf of st lawrence into the central st lawrence lowland the beginning of the champlain sea is placed between 11 4 and 11 6 ka bp on the basis of radiocarbon ages for the arrival of the salt water wedge in the central st lawrence lowland the distribution of rhythmites associated with glacial lake st lawrence shows that subaqueous outwash fans in the ottawa area were deposited in glacial lake st lawrence rather than in the champlain sea

accelerator mass spectrometer ages for the younger dryas event in atlantic canada abstract in atlantic canada bulk sediment dates for the onset of a late glacial cooling widely regarded as the younger dryas event are highly variable ranging from 14 300 270 to 10 800 100 yr b p we present the first accelerator mass spectrometer ams 14c dates from atlantic canada at or close to the boundaries of this event from six sites in new brunswick and nova scotia the mean of five dates places the onset of this cooling at ca 10 770 yr b p the inclusion of a sixth perhaps anomalously old date changes the mean to 10 880 yr b p the termination averages three dates ca 10 000 yr b p these dates place the timing of the younger dryas event in atlantic canada closer in line with the traditional chronozone boundaries of 11 000 and 10 000 yr b p in northwest europe

laurentide cordilleran and montane glaciation in the western peace river grande prairie region alberta and british columbia canada abstract geological investigations over the last decade in the western peace river grande prairie district of northwestern alberta and northeastern british columbia have provided important chronostratigraphic information regarding laurentide cordilleran and montane quaternary glacial events numerous 14 c age determinations as well as stratigraphic and sedimentological analyses of numerous exposures indicate that this area was first glaciated by cordilleran ice sometime before the late wisconsinan during the late wisconsinan ca 22 000 14 000 bp laurentide glacier ice covered much of the area between approximately 15 000 and 10 000 bp montane ice affected only the western part of the peace region there is no evidence for synchroneity of the ice advances and therefore no evidence for ice coalescence in this region the resultant ice free corridor was most likely a laterally fluctuating zone which existed during a several thousand year period in the late pleistocene climatic conditions along the corridor during this period were probably unfavorable for human migration but adequate for some plants and small animals numerous isolated areas along the western foothills of the northern rocky mountains west of the laurentide glaciation limit were never glaciated during the late wisconsinan

lake agassiz during the younger dryas abstract lake agassiz was ponded on the northward sloping surface of the hudson bay and arctic ocean basins as the laurentide ice sheet retreated the level of lake agassiz abruptly fell 12 9 cal 11 14 c ka bp exposing the lake floor over a large region for 1000 yr the routing of overflow during this moorhead low water period is uncertain and there is evidence on the continent and in ocean basins for both an easterly route through the great lakes st lawrence to the north atlantic and for a northwesterly route through the clearwater athabasca mackenzie system to the arctic ocean the moorhead low water phase coincides with the younger dryas cooling and a cause effect relationship has been proposed by attributing a change in ocean thermohaline circulation to the re routing of lake agassiz freshwaters from the gulf of mexico to more northern oceans paleoclimatic interpretations from ecosystems in lake sediments in the region and a simple calculation of the paleohydrological budget of lake agassiz indicate that the climate remained wet and cool throughout the yd in this region and was not warm nor dry enough to allow evaporative loss to offset the influx of meltwater and precipitation thus the moorhead phase resulted from changes in the outlet that carried overflow

constraints on lake agassiz discharge through the late glacial champlain sea st lawrence lowlands canada using salinity proxies and an estuarine circulation model during the last deglaciation abrupt freshwater discharge events from proglacial lakes in north america such as glacial lake agassiz are believed to have drained into the north atlantic ocean causing large shifts in climate by weakening the formation of north atlantic deep water and decreasing ocean heat transport to high northern latitudes these discharges were caused by changes in lake drainage outlets but the duration magnitude and routing of discharge events factors which govern the climatic response to freshwater forcing are poorly known abrupt discharges called floods are typically assumed to last months to a year whereas more gradual discharges called routing events occur over centuries here we use estuarine modeling to evaluate freshwater discharge from lake agassiz and other north american proglacial lakes into the north atlantic ocean through the st lawrence estuary around 11 5 ka bp the onset of the preboreal oscillation pbo faunal and isotopic proxy data from the champlain sea a semi isolated marine brackish water body that occupied the st lawrence and champlain valleys from 13 to 9 ka indicate salinity fell about 7 8 range of 4 11 around 11 5 ka model results suggest that minimum 1600 km3 and maximum 9500 km3 estimates of plausible flood volumes determined from lake agassiz paleoshorelines would produce the proxy reconstructed salinity decrease if the floods lasted 1 day to 5 months and 1 month to 2 years respectively in addition champlain sea salinity responds very quickly to the initiation within days and cessation within weeks of flooding events these results support the hypothesis that a glacial lake flood rather than a sustained routing event discharged through the st lawrence estuary during the pbo

evidence for two step deglaciation and its impact on north atlantic deep water circulation oxygen and carbon isotope records from benthic and planktonic foraminifera are presented for the past 35 000 years in the northeastern atlantic the results support the idea that the last deglaci ation took place in two major steps1 4 and conflict with theories calling for a strong reduction in north atlantic deep water formation to explain the abrupt cooling of the younger dryas cold period5 7

salinity history of the northern atlantic during the last deglaciation the claim has been made see broecker et al 1988 that production of north atlantic deep water terminated during younger dryas time and that the onset of this termination occurred about 11 000 years ago when the flow of meltwater from a large segment of the southern margin of the laurentide ice sheet was diverted from the mississippi to the st lawrence drainage fairbanks 1989 points out a serious weakness in this argument based on a sea level curve derived from radiocarbon dates on coral obtained from borings made off the barbados coast he suggests that a lull in the melting of the ice caps during younger dryas time may have more than compensated for the impact of the diversion the purpose of this paper is to reassess the situation regarding the origin of the younger dryas in light of this new evidence currently the salinity of surface waters in the northern atlantic is influenced by three fluxes water vapor transport from the atlantic drainage basin to the pacific indian basin tends to raise the salinity of the entire atlantic the excess over evaporation of precipitation and runoff poleward of 40 n tends to reduce the salinity of waters in this region relative to the atlantic average the conveyor circulation of the atlantic trades more salty waters of the atlantic with less salty waters outside the atlantic tending to drive down the atlantic s salinity the conveyor circulation also flushes the northern atlantic pushing its salinity toward the mean for the atlantic during the period of deglaciation meltwater emanating from the laurentide and scandinavian ice sheets was also important this flux tended to lower not only the salinity of the entire atlantic but also the salinity of surface waters in the northern atlantic relative to the atlantic s mean as deepwater formation in the northern atlantic depends critically on the salinity of surface waters the interactions among these fluxes can change the strength of the conveyor

a salt oscillator in the glacial atlantic 2 a scale analysis model a proposal has been made by broecker et al 1990 that rapid changes on a time scale of a thousand years or so seen over much of the last major glacial in the greenland ice core record represent significant climate changes and are caused by a salt oscillator in the glacial atlantic this proposal is examined in terms of a rudimentary quantitative model scale analysis asserts that heat transported to the high latitude atmosphere when the thermohaline circulation is turned on is large enough to produce the melting rates found by fairbanks 1989 for the time interval around that of the younger dryas event and that these melting rates are of the same order of magnitude as the mass flux associated with water vapor flux to the pacific ocean estimated by broecker 1989 scale analysis also suggests that the salinity fluxes associated with 1 the water vapor flux mechanism 2 the rapid melting episodes of fairbanks 3 possibly ice sheet growth events 4 net transport by the thermohaline circulation and 5 net transport by turbulent eddy mixing are roughly of the same order of magnitude and therefore may be important mechanisms for producing salinity oscillations on a time scale of a few thousands of years see broecker 1990 by integration of simple salt conservation equations it is found that model oscillations with a period of a few thousand years occur over a significant range of salinity fluxes estimated fluxes fall well within the range for which oscillations exist the model also suggests that there may exist close coupling between the european scandinavian ice sheets and the bimodal response of the oscillator that is significant increases or decreases in continental ice volume may accompany each complete cycle of the oscillator in addition it appears that continental ice may be required for the salt oscillator to function a crucial element which cannot adequately be investigated with the present model concerns the local effect of salinity source sinks associated with melt water production the proximity of these source regions on the neighboring ice sheets to the local regions where production of deep water occurs may play a critical role in the functioning of the proposed salt oscillator in addition further treatment of thermodynamics is needed to investigate the feasibility of a salinity driven oscillator

late pleistocene water bodies in the st lawrence lowland new york and regional correlations in the st lawrence lowland in new york four lake levels and the limit of the champlain sea have been identified each reconstructed level has been traced west southwest from covey hill water levels are correlated with previously identified levels in the lake ontario basin by means of an extended diagram the study area includes the northwestern part of the champlain lowland facilitating correlations of water bodies in the st lawrence and champlain lowlands the highest lake level i in the st lawrence lowland was continuous with lake iroquois in the lake ontario basin and it drained across covey hill at 329 332 m into lake fort ann in the champlain lowland level ii also confluent with lake iroquois drained through covey hill gap at 308 311 m into lake fort ann level iii was continuous with the post iroquois sydney phase in the lake ontario basin and with the highest phase of lake fort ann in the champlain lowland level iv in the st lawrence lowland was continuous with the belleville phase in the lake ontario basin and with a lower phase of lake fort ann in the champlain lowland level v is the limit of the champlain sea in the st lawrence and champlain lowlands projection of the reconstructed marine water surface westward indicates that the champlain sea initially entered the lake ontario basin where it was confluent with the estuarine post iroquois trenton phase subsequent separation of water bodies in the lake ontario basin and st lawrence lowland occurred as a result of isostatic uplift restrictions placed on ice marginal positions by lake levels and the lake outlets indicate that the concept of contemporaneous marine and fresh water events separated by a narrow ice dam at covey hill is implausible marine invasion of the st lawrence lowland along the retreating ice sheet margin occurred subsequent to drainage of glacial lakes through the covey hill channels and the champlain lowland

alternative routing of lake agassiz overflow during the younger dryas new dates paleotopography and a re evaluation abstract overflow from glacial lake agassiz has been implicated in affecting late glacial ocean circulation and climate the timing of the diversion of lake agassiz overflow away from its southern routing to the gulf of mexico correlates closely with the younger dryas ca 11 10 14 c ka new models of paleotopography in the eastern outlet region of lake agassiz adjusted for differential isostatic rebound show that overflow to the superior basin would have occurred when the lake formed its herman norcross and tintah beaches just after 10 9 14 c ka if the laurentide ice sheet lis had retreated from the thunder bay ontario region by that time however the absence of coarse flood deposits normally associated with large overflows plus the morphology of possible overflow channels in the thunder bay region suggest that agassiz overflow may not have been routed into the great lakes during the younger dryas as previously believed in addition non carbonate radiocarbon dates in the thunder bay area are all younger than 10 14 c ka suggesting that this area may not have been deglaciated until after the younger dryas thus preventing lake agassiz overflow through this area an alternative route of overflow from lake agassiz during the younger dryas could have been through the northwestern clearwater outlet to the arctic ocean although all research to date shows that this region was covered by ice until 10 14 c ka on the other hand it is possible that older and coarser overflow sediment may now lie buried beneath finer deposits associated with the 10 14 c ka marquette readvance of the lis which ponded waters in valleys between lake agassiz and lake superior or that eastward overflow in this area was not catastrophic

an 18 000 year palynological record from the southern alberta segment of the classical wisconsinan ice free corridor radiocarbon dates of 18 300 380 years bp gsc 2668 and 18 400 1090 years bp gsc 2670 on moss fragments from the clay near the base of a core from chalmers bog alberta indicate that the classical wisconsinan ice free corridor was in existence in the foothills of southern alberta by this time palynological studies show sparse herbaceous tundra like vegetation probably prevailed at this time in the area surrounding the small lake formed in the abandoned glacial spillway later shrubs became more prominent to form a shrub tundra environment sometime before 8220 years bp gsc 2851 trees began to invade the area and the pinus contorta dominated coniferous forest extant in the area today began to form bog and fen vegetation invaded the shallow lake basin about this time as well to form the bog that occupies the basin to the present day

evidence for a younger dryas like cooling event on the british columbia coast two independent paleoclimatic records from the pacific coast of canada indicate that a late glacial warming trend was interrupted by a return to colder conditions between about 11 000 and 10 200 radiocarbon yr b p correlative with the classical younger dryas chronozone of the north atlantic region fossil benthic foramnifera from three cores from the continental shelf dated by accelerator mass spectrometry show peak abundances of the cold water indicator species cassidulina reniforme at this time fossil pollen spectra from two sites on the queen charlotte islands record a shift from forest to open herb rich vegetation after 11 100 yr b p probably in response to colder and wetter conditions identified by pollen climate transfer functions these preliminary data for a cold oscillation between ca 11000 and 10000 yr ago in the northeast pacific argue that this deglacial phenomenon was not restricted to the north atlantic but was a hemispheric and possibly global event

volume and routing of late glacial runoff from the southern laurentide ice sheet melting of the laurentide ice sheet during the last deglaciation added large volumes of water to many rivers and lakes of north america and to the world s oceans the volume and routing of this meltwater not only helped shape the land s surface but also played a role in the evolution of late glacial climate a computerized model was prepared to quantify meltwater generation from seven drainage areas along the southern side of the laurentide ice sheet at 500 yr time slices between 14 000 and 8000 yr b p nearly all waters reaching the oceans flowed through the st lawrence hudson or mississippi river valleys discharge through the mississippi river to the gulf of mexico during late glacial time varied by more than a factor of 5 ranging between 17 400 m3 sec 1 550 km3 yr 1 and 98 200 m3 sec 1 3200 km3 yr 1 discharge entering the north atlantic ocean through the st lawrence and hudson valleys ranged between 20 300 m3 sec 1 640 km3 yr 1 and 65 300 m3 sec 1 2060 km3 yr 1 with very abrupt twofold changes at about 11 000 10 000 and 9500 yr b p as a result of the rerouting of water from the lake agassiz basin as the areal extent and mass of the laurentide ice sheet diminished the total volume of meltwater plus runoff due to precipitation from its southern side declined from 3800 km3 yr 1 at about 14 000 yr b p to 2100 to 2600 km3 yr 1 between 11 500 and 8000 yr b p no meltwater entered the gulf of mexico after 9500 yr b p after the demise of the ice sheet over hudson bay about 8000 yr b p the modern continental drainage network was established and flows through the st lawrence declined to modern values of about 320 km3 yr 1

late pleistocene chronology and environment of the ice free corridor of northwestern alberta abstract pollen and macrofossil analyses of two radiocarbon dated lake sediment cores in the upper peace river district were used to investigate the controversial late glacial geochronology of the ice free corridor the basal mineral rich sediments contain reworked radiogenically dead palynomorphs as well as intrusive modern carbon analyses of the basal sediments from boone lake show that two 14c ages greater than 12 000 yr b p are spuriously old due to contamination by organic matter of cretaceous age the data support occlusion or near occlusion of laurentide and cordilleran ice in the peace river area during the late wisconsinan period the sediment record began around 12 000 yr b p in the ice dammed and enlarged boone lake an initially open sedge dominated cover was invaded by sage willow grass and poplar by 11 700 yr b p suggesting that a habitable landscape has existed in the area for at least 12 millennia the data however do not support the ice free corridor arguments of b o k reeves 1973 arctic and alpine research 5 1 16 1983 in quaternary coastlines and marine archaeology towards the prehistory of land bridges and continental shelves p m masters and n c fleming eds pp 389 411 academic press new york who suggests that ice occlusion did not occur in the peace river valley during the last 55 000 yr

late quaternary paleohydrology of the gulf of st lawrence quebec canada based on diatom analysis abstract postglacial sediments from three cores raised from the gulf of st lawrence along the path of the laurentian channel were analyzed for diatoms a sequence of four distinct zones was defined from oldest to youngest 1 characterized by low diatom concentrations this zone is mainly represented by heavily silicified species delphineis surirella stephanopyxis turris coscinodiscus radiatus and paralia ornata that were probably deposited by glacial drift in a glaciomarine environment from about 18 000 to 14 000 years bp 2 this postglacial sedimentation zone deposited around 13 000 years bp is marked by high diatom concentrations with cold water marine species thalassiosira antarctica resting spores and porosira glacialis the upper part of the zone suggests a gradual warming with the appearance of temperate water species bacterosira bathyomphala and chaetoceros spp both resting spores and vegetative cells 3 an important cooling of surface temperatures is noticed by the resurgence of cold species porosira glacialis thalassiosira antarctica resting spores and thalassiosira hyalina this zone is associated with the younger dryas chronozone dated from 10 800 to 10 300 years bp this interval is also characterized by two marked freshwater pulses coming from the outflow of laurentide ice sheet meltwater on the surface layer of the goldthwait sea although well defined in the northwestern gulf area core 90 031 015 the influence of this meltwater decreases considerably or even disappears in cabot strait core 89 007 111 and offshore core 90 031 044 evidence of reduced postglacial glacial runoff on surface water supports the conclusion that it could not have generated the younger dryas cooling episode 4 the diatom assemblages from 10 000 years bp through recent correspond to the progressive establishment of modern like surface water conditions

glacial lake outburst erosion of the grand valley michigan and impacts on glacial lakes in the lake michigan basin abstract geomorphic and sedimentologic evidence in the grand valley which drained the retreating saginaw lobe of the laurentide ice sheet and later acted as a spillway between lakes in the huron and erie basins and in the michigan basin suggests that at least one drainage event from glacial lake saginaw to glacial lake chicago was a catastrophic outburst that deeply incised the valley analysis of shoreline and outlet geomorphology at the chicago outlet supports j h bretz s hypothesis of episodic incision and lake level change shoreline features of each lake level converge to separate outlet sills that decrease in elevation from the oldest to youngest lake phases this evidence coupled with the presence of boulder lags and other features consistent with outburst origin suggests that the outlets were deepened by catastrophic outbursts at least twice the first incision event is correlated with a linked series of floods that progressed from huron and erie basin lakes to glacial lake saginaw to glacial lake chicago and then to the mississippi the second downcutting event occurred after the two rivers advance of the lake michigan lobe outbursts from the eastern outlets of glacial lake agassiz to glacial lake algonquin are a possible cause for this period of downcutting at the chicago outlets

paleo oceanographie isotopique des mers post glaciaires du quebec abstract the main hydrological characteristics of the post glacial seas of quebec the gold thwait champlain iberville tyrrell seas and the gulf of laflamme have been investigated by a determination of the isotopic composition 14 c 13 c 18 o of the fauna and sediments of their basins the carbonates are generally depleted in 18 o specially shallow water mollusks which show isotopic compositions as low as pdb 18 o 15 the depletion in heavy isotopes is mainly related to the influx of continental waters particularly glacial meltwater in such basins the isotope geochemistry differs from what is observed in open environments and therefore the standard isotopic paleotemperature technique may not be used directly new data on the isotopic composition of glacial lakes and melting water of the laurentide ice sheet compared with data from present arctic environments have enabled us to calibrate a linear 18 o salinity relationship and to evaluate salinity changes in time and space it is concluded that the present marginal basins of quebec do not show any large differences in either salinity or temperature from the post glacial basins more brackish water has characterized the surficial layers since deglaciation shoaling of the basins due to glacio isostatic rebound later induced local variations in the temperature and salinity the water becoming progressively warmer and more brackish in these basins the geochemistry of carbon is more complex the in situ biological production of co 2 caused large variations in the 13 c content of the carbonates independently of any direct continental influence the observed anomalies in 14 c activity of fossil mollusks are believed to be related to the old water effect and to local influx of dead carbon originating from dissolution by ice meltwater of surrounding carbonate bearing bedrock

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

water mass exchange between the north atlantic and the norwegian sea during the past 28 000 years the greenland iceland and norwegian gin seas are important regulators of heat transport in the northern hemisphere and of ocean atmosphere co2exchange1 5 rapid changes in the circulation of surface and deep waters in this region may induce nonlinear climatic effects and climate instabilities2 3 here we present carbon and oxygen isotope data that provide a record of circulation changes in the gin seas during and at the termination of the last glacial maximum lgm inflow of nutrient depleted waters from the gin seas to form intermediate waters of the north atlantic resulted in nutrient enrichment of north atlantic deep water and consequent enhanced drawdown of atmospheric co2 contributing to the lower atmospheric during the lgm the onset of deglaciation occurred at a time of low salinity in the gin seas and thus of reduced thermohaline circulation although strong thermohaline circulation was later reinitiated in the north atlantic as deglaciation proceeded it cannot therefore have caused the onset of warming similarly we find that rapid changes in thermohaline circulation cannot account for the transient return to a cooler climate during the younger dryas episode

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

a reevaluation of the timing and causes of high lake phases in the lake michigan basin abstract radiocarbon age control on the type glenwood calumet and toleston shoreline features and on the abandoned chicago outlet at the south end of the lake michigan basin provides a basis for reevaluating the timing and causes of high lake phases in the basin radiocarbon dates suggest that glenwood level 195 m shoreline features formed between 14 100 and 12 700 yr b p glenwood i and ii phases calumet level 189 m between 12 700 and 11 000 yr b p calumet i and ii phases and toleston level 184 5 m between 5000 and 4000 yr b p nipissing phase and that the chicago outlet was cut to its present level 180 m on bedrock while the lake was at the glenwood level this new chronology is inconsistent with j h bretz hypothesis 1951 american journal of science249 401 429 that the progressive lowering of lake level resulted from episodic down cutting of the outlet instead the changes in lake level appear to relate to changes in the amount of glacial meltwater and precipitation entering the basin we hypothesize that the glenwood phases correspond with times when discharge from the huron and erie basins also entered the lake michigan basin lake border and early port huron glacial phases the calumet phases with times when drainage was from the lake michigan basin alone late port huron and two rivers glacial phases and the nipissing phase with the postglacial middle holocene transgression caused by differential uplift in the basin estimates of relative net inputs to the basin during the glenwood calumet and nipissing lake phases are consistent with estimates of relative outputs i e discharge through the chicago outlet the magnitude of relative differences in inputs and outputs between phases is sufficient to explain lake level changes of 4 5 to 6 m

laurentide and montane glaciation along the rocky mountain foothills of northeastern british columbia mapping the surficial geology of the trutch map area nts 94g provides new data on the timing of continental and montane glaciations along the foothills of northeastern british columbia striated surfaces on mountain crests were dated to the late wisconsinan substage by cosmogenic dating the striations were produced by eastward flowing ice emanating from the region of the continental divide this ice was thick enough to cross the main ranges and overtop the rocky mountain foothill summits at 2000 m above sea level asl it is argued here that such a flow unhindered by topography could only have been produced by the cordilleran ice sheet and not by local cirque glaciation during this time the cordilleran ice sheet dispersed limestone and schist erratics of western provenance onto the plains beyond the mountain front conversely the laurentide ice sheet did not reach its western limit in the foothills until after cordilleran ice retreated from the area during its maximum the laurentide ice penetra

megaflooding associated with glacial lake agassiz abstract significant baseline and episodic megaflooding from glacial lake agassiz was routed to the south east and north coasts of north america over the lake s nearly 6000 year history the five phases of lake level change were controlled by which outlet was active which in turn was controlled by ice margin position and glacioisostatic adjustment the southern outlet is the oldest and best understood outlet while successively younger outlets are progressively less understood eastern drainage synchronous with the younger dryas chronozone had been assumed by most studies but a spillway to accommodate the 90 m drop in lake level is yet to be described with the south and east outlets unable to accommodate the necessary lake level drawdown the northwest outlet has become the default outlet with arctic ocean core data supporting it however extant terrestrial data from the continent only provides data for a large flood from the fort mcmurray area closer to the end of the younger dryas coinciding with the timing of the preboreal oscillation the challenge remains to find agreement between the marine and terrestrial records uncontroversial is the geomorphic and sedimentologic evidence for flooding into and out of the lake consisting of large spillways large boulders and in places giant current ripples composed of boulders flood discharge estimates into and out of the lake range from 0 04 to 1 sv with final subglacial drainage into the tyrell sea estimated at 5 sv sufficient to raise global sea level by 0 18 m and initiate the 8 2 ka stadial

northwest outlet channels of lake agassiz isostatic tilting and a migrating continental drainage divide saskatchewan canada lake cores obtained from the northwest outlet of glacial lake agassiz in northwest saskatchewan canada provide a minimum date for the cessation of the flood from the northwest outlet and a chronology for abandonment of mid holocene channels that presently straddle the mackenzie and churchill drainage divide the stratigraphy of a vibracore taken from long lake consists of a lower pebble gravel fining to massive sand silty clay and then fibrous peat wood fragments from the base of the clay yielded an accelerator mass spectrometry ams date of 9120 bp because the lake is scour in origin and is in the head of the spillway the date is considered to be a minimum estimate for cessation of the flood from the northwest outlet at the beginning of the emerson phase a vibracore taken at haas lake in an abandoned channel surrounded by muskeg with no influent streams consists of 0 8 m of stratified pebble gravel containing abundant shell and wood fragments overlain by 1 62 m of gyttja with a sharp conformable lower contact ams dates range from 5590 bp from the topmost gravel to 3080 bp within the gyttja the gravel is interpreted as fluvial recording a river draining wasekamio lake north into the clearwater river across the present day drainage divide today a drop of 2 m occurs from wasekamio lake southeast to lac ile a la crosse along 150 km of lake basins parallel to the cree lake moraine the dates from haas lake suggest that before 5200 bp the drainage divide was about 100 km further southeast implying that during the emerson phase lake level was controlled by a sill near flatstone lake at about 430 m instead of between wasekamio lake and the clearwater river as was previously proposed holocene differential isostatic uplift caused the flow reversal in the upper churchill basin anastomosed channels at the mouth of rivers flowing north into lakes indicate that uplift is still active in the area today

late quaternary paleoceanography of deep and intermediate water masses off gaspe peninsula gulf of st lawrence foraminiferal evidence radiocarbon dated benthonic foraminiferal zones in three cores provide new information on the evolution of the deep and intermediate water masses off gaspe peninsula the deglacial phase in the deep laurentian channel began before 14 000 bp and was characterized by low salinity 20 or alternating low salinity and saline 35 water this was followed by a cold saline phase which ended ca 13 500 bp and a salinity minimum 30 33 5 which began ca 12 100 bp between 8700 and 7900 bp the temperature and salinity of the deep water mass increased resulting in the modern deep water mass temperature 4 6 c salinity 34 5 34 9 at the end of the goldthwait sea episode the salinity of the deep water was apparently controlled by the meltwater flux from the ice front during the deglacial phase after the deglacial phase the characteristics of the deep water mass were determined by the composition of offshore water entering the laurentian channel runoff from the lake agassiz great lakes system does n

evidence from the lake champlain valley for a later onset of the champlain sea and implications for late glacial meltwater routing to the north atlantic abstract ocean circulation models indicate that freshwater runoff from the north american continent during the last deglaciation may have had an effect on north atlantic ocean circulation and thereby have altered regional climate one such example is a flood from lake agassiz which has been proposed by previous workers to have caused the onset of the younger dryas at around 12 850 calibrated years b p by entering the north atlantic through the gulf of st lawrence we present two radiocarbon ages from terrestrial organic sources in the champlain valley that we associate with the pre champlain sea proglacial lake phases a musk ox bone with an ams age of 11 362 115 14 c years b p 13 438 13 020 calibrated years b p and a wood fragment with an ams age of 10 901 76 14 c years b p 12 995 12 793 calibrated years b p these ages together with a glacial lacustrine varve estimate suggest that the initiation of the champlain sea may not have occurred until after the onset of the younger dryas if the lake agassiz flood event occurred before the opening of the champlain sea then the floodwaters would have been diverted down the champlain and hudson valleys to the north atlantic another possibility is that the agassiz flood may have been contemporaneous with the opening of the gulf of st lawrence it is also possible that there may have been a large enough flood produced by meltwater originating in the champlain valley and st lawrence lowlands at the inception of the champlain sea to have affected ocean circulation without the influence of lake agassiz

routing of meltwater from the laurentide ice sheet during the younger dryas cold episode rooth1 proposed that the younger dryas cold episode which chilled the north atlantic region from 11 000 to 10 000 yr bp was initiated by a diversion of meltwater from the mississippi drainage to the st lawrence drainage system the link between these events is postulated to be a turnoff during the younger dryas cold episode of the north atlantic s conveyor belt circulation system which currently supplies an enormous amount of heat to the atmosphere over the north atlantic region2 this turnoff is attributed to a reduction in surface water salinity and hence also in density of the waters in the region where north atlantic deep water nadw now forms here we present oxygen isotope and accelerator radiocarbon measurements on planktonic foraminifera from orca basin core en32 pc4 which reveal a significant reduction in meltwater flow through the mississippi river to the gulf of mexico from about 11 200 to 10 000 radiocarbon years ago this finding is consistent with the record for lake agassiz which indicates that the meltwater from the southwestern margin of the laurentide ice sheet was diverted to the northern atlantic ocean through the st lawrence valley during the interval from 11 000 to 10 000 years before present yr bp

high resolution seismic reflection profiling of neotectonic faults in lake timiskaming timiskaming graben ontario quebec canada the timiskaming graben is a 400 km long 50 km wide north west trending morphotectonic depression within the canadian shield of eastern north america and experiences frequent intraplate earthquakes the graben extends along the border of ontario and quebec connecting southward with the nipissing and ottawa bonnechere grabens and the st lawrence rift system which includes a similar structure underlying the hudson valley of the eastern usa together they form a complex failed rift system related to regional extension of north american crust during the breakup of rodinia and later pangea the timiskaming graben lies within a belt of heightened seismic activity western quebec seismic zone with frequent moderate magnitude greater than magnitude 5 earthquakes including a magnitude 6 2 in 1935 these events threaten aging urban infrastructure built on soft glacial sediments post glacial landslides along the ottawa valley suggest earthquakes as large as magnitude 7 the inner part of the timiskaming graben is filled by lake timiskaming a large 110 km long post glacial successor to glacial lake barlow that was ponded by the laurentide ice sheet 9500 years ago the effects of frequent ground shaking on lake floor sediments was assessed by collecting more than 1000 line kilometres of high resolution chirp seismic profiles late glacial lake barlow glaciolacustrine and overlying post glacial sediments are extensively deformed by extensional faults that define prominent horsts and grabens multibeam bathymetry data suggest that faults influence the morphology of the modern lake floor despite high sedimentation rates and indicate recent neotectonic deformation the lake timiskaming area provides evidence of post glacial intracratonic faulting related to recurring earthquake activity along a weak spot within the north american plate

glacial lake agassiz the northwestern outlet and paleoflood valley morphology and sediment in the fort mcmurray region of alberta indicate that a catastrophic flood discharged down the lower clearwater and athabasca river valleys 9900 yr b p geomorphic and chronologic evidence suggests that glacial lake agassiz emerson phase was the probable water source as the flood incised a drainage divide located near the alberta saskatchewan border the level of glacial lake agassiz decreased by 46 m discharged 2 4 x 106 m3 s for at least 78 days and stabilized at 438 m above sea level in the lake wasekamio area at that time water entered the arctic ocean via glacial lake mcconnell and the mackenzie river rather than the gulf of mexico via the mississippi river as previously thought such a large influx of fresh water 8 6 km3 h into the arctic at the close of the last glaciation may have had an abrupt major influence on northern climate

quaternary stratigraphy of the prophet river northeastern british columbiathis article is one of a selection of papers published in this special issue on the theme geology of northeastern british columbia and northwestern alberta diamonds shallow gas gravel and glaciers exposures in the prophet river valley in northeast british columbia provide a unique glimpse into the quaternary history of the northwest canadian boreal plains the region shows evidence of late wisconsinan laurentide glaciation in the form of widespread till containing abundant erratic clasts derived from the canadian shield vertical sections along the prophet river expose non glacial and advance glacial sediments below this till pre late wisconsinan non glacial or interglacial floodplain sediments are interbedded with fluvial gravels at many sites macrofossils within horizontally laminated organic rich black clay and silt indicate deposition on the floodplain of the paleo prophet river within an oxbow lake the climate during deposition is interpreted to be similar to present supporting a dominantly spruce forest wood obtained from eight sites provided non finite radiocarbon ages and one sample provided an age of 49 300 2000 bp which is also considered non finite glaciolacustrine clays and s

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

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

younger dryas climatic reversal in northeastern usa ams ages for an old problem abstract late glacial macrofossils from a 10 m core from alpine swamp new jersey were radiocarbon dated using accelerator mass spectrometry ams the arrival of the first trees to the area following deglaciation is indicated by maximum percentages of spruce pollen and a date of 12 290 440 yr b p on a single spruce needle subsequent spread of deciduous hardwoods was followed by the expansion of boreal taxa including spruce picea fir abies larch larix laricina paper birch betula papyrifera and alder alnus three ams dates on paper birch seeds and a spruce needle during this boreal expansion indicate that it took place between 11 000 and 10 000 yr b p the timing of this vegetational shift and its correlation with late glacial pollen stratigraphy from many sites in southern new england indicate that a climatic reversal correlative with the younger dryas characterized the north atlantic seaboard of the united states

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

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

lakes of the huron basin their record of runoff from the laurentide ice sheet the 189 000 km2 hur n basin is central in the catchment area f the present q s r lanrentian great lakes that now drain via the st lawrence river to the north atlantic ocean during deglaciation from 21 7 5 ka bp and owing to the interactions of ice margin positions crustal rebound and regional topography this basin was much more widely connected hydrologi cally draining by various routes to the gulf of mexico and atlantic ocean and receiving over flows from lakes impounded north and west of the great lakes hudson bay drainage divide early ice marginal lakes formed by impoundment between the laurentide ice sheet and the southern margin of the basin during recessions to interstadial positions at 15 5 and 13 2 ka be in i each of these recessions lake drainage was initially southward to the mississippi river and gulf of mexico in the first recession drainage subsequently switched eastward along the ice margin to the north atlantic ocean in the second recession drainage continued southward through the michigan basin and later eastward via the ontario basin and mohawk river valley to the north atlantic ocean during the final retreat of ice in the huron basin from 13 to 10 ka be proglacial lake drainage switched twice from the michigan basin and the mississippi river system to the i north atlantic via the ontario basin and mohawk river valley finally diverting to the champlain sea in the st lawrence river valley at about 11 6 ka be new seismo and litbo stratigraphic information with ostracode data from the offshore lacustrine sediments were integrated with the traditional data of shorelines uplift histories of outlets and radio carbon dated shallow water evidence of transgressions and regressions to reconstruct the water level history and paleolimnological record for the northern huron basin for the 11 7 ka bp period negative excursions in the 8 80 isotopic composition of ostracodes and bivalves in southern lake michigan southwestern lake huron and eastern lake erie indicate an influx of water from ice marginal lake agassiz in central north america about 11 ka be a major decline in water levels of the huron basin after 10 5 ka bp followed the high level main lake algonquin phase as ice receded and drainage was established through the north bay area to ottawa river valley during the subsequent mattawa stanley phase the lake level history was dominated by fluctuations of tens of meters highstands of the earliest oscillations whose origin is not clear might be related to some of the well known post algonquin shorelines after 9 6 ka be it is suggested that large inflows from lake agassiz and hydraulic damming in downstream outlets were the likely cause of the lake mattawa highstands a lowstand at 9 3 9 1 ka bp occurred when these inflows were diverted or impeded by an ice advance in the nipigon basin area while undiluted meltwater continued to enter the huron basin assemblages and isotopic composition of the ostracode fauna indicate very dilute meltwater during the lowstands as late as 7 5 ka be and precipitation runoff with comparatively higher dissolved solids dur ing the highstands we speculate that the water composition of the lake mattawa highstands was dom inated by the agassiz inflows by that time much of lake agassiz was remote from ice marginal envi ronments and the inflows were drawn from surface water of the southern sector of the lake which was largely supplied by runoff and dissolved solids from the exposed land area of western canada major inflows apparently ended about 8 ka be but northern proglacial lakes apparently continued as melt water persisted in the huron basin until about 7 5 ka bp the cessation of major inflows initiated the final lowstand in the huron basin and the present hydrological regime of local runoff

stable isotope evidence for glacial lake drainage through the st lawrence estuary eastern canada 13 1 12 9 ka abstract postglacial varved and rhythmically laminated clays deposited during the transition from glacial lake vermont lv to the champlain sea cs record hydrological changes in the champlain st lawrence valley cslv at the onset of the younger dryas 13 1 12 9 ka linked to glacial lake drainage events oxygen isotope 18o records of three species of benthic foraminifera cassidulina reniforme haynesina orbiculare islandiella helenae from six sediment cores and the freshwater ostracode candona from one core were studied results show six large isotope excursions 0 5 to 2 in c reniforme 18o values five excursions in h orbiculare

evolution and paleohydrology of glacial lakes barlow and ojibway abstract the evolution of lakes barlow and ojibway two large ice contact glacial lakes that covered parts of northern ontario and western quebec from about 10 1 8 0 ka bp during the retreat of the laurentide ice sheet was reconstructed using deglaciation landforms ice flow indicators inscribed on bedrock 14 c dates of early postglacial vegetation accumulated in lake basins the distribution of mysis relicta a biological indicator of lacustrine submergence varve chronology and a detailed photogrammetric survey of the lake limit although the rate of ice retreat varied greatly throughout the basin the average rate in lake barlow ojibway was 450 m year rates of ice retreat deduced from varve chronology were assessed using predictable relationships between the lake limit the shoreline gradient and the rate of relative uplift over a 590 km long profile the gradient on the maximum elevation of the lake defines a parabola that is attributed to restrained rebound although in part it could be due to the position of the profile with respect to the overall uplift pattern generated by the ice sheet the life span of the lake determined from varve chronology 2110 years shows excellent agreement with the age difference obtained between that of marine shells overlying lake ojibway sediments at its northern end in hudson bay and the oldest radiocarbon ages on basal organics in lakes in the southern part of the barlow ojibway basin both lakes drained eastward through the ottawa river between 10 1 and 8 0 ka bp and the average yearly discharge to the north atlantic ocean during the last 1000 1500 years is estimated at about 946 km 3 at break up of the ice sheet in southern hudson bay at about 8 0 ka bp lake ojibway drained abruptly releasing an estimated 114 396 km 3 of freshwater into the tyrrell sea and raising sea level by about 30 cm

lithofacies types and vertical profile models an alternative approach to the description and environmental interpretation of glacial diamict and diamictite sequences abstract increased knowledge of modern glacial depositional environments has resulted in rapidly evolving classifications of glacial tills these are based to a large degree on theoretical considerations of likely depositional processes the classifications are sophisticated and more advanced than the establishment of simple field criteria whereby individual till facies can be identified in quaternary and pre quaternary successions this situation is compounded in many quaternary terrains by the continued description of tills in terms of laboratory derived analytical data only reflecting a traditional interest in stratigraphic correlation rather than reconstruction of depositional environment detailed sedimentological logging of lithofacies is rarely undertaken there is thus considerable confusion as to what is being described or sampled when analytical data are presented for many pleistocene tills the same remarks apply to pre pleistocene tillites a lithofacies code is presented here for the rapid description and visual appraisal of field sequences or drill cores containing unconsolidated diamicts or lithified diamictites the term till is not used as it has a strict genetic definition referring to direct aggregation and deposition by glacier ice use of a four part code in conjunction with codes already published for fluvial sediments allows fundamental field properties to be depicted independent of genetic terminology and provides a firm basis for subsequent environmental interpretation and analytical work the value of this approach is illustrated by comparing a representative suite of vertical profiles of diamict assemblages deposited by modern grounded glaciers with a classic late pleistocene glacigenic sequence at scarborough bluffs ontario

vertebrate paleontology and the alleged ice free corridor the meat of the matter abstract the existence of a full glacial ice free corridor through western alberta has been argued for many years it has been assumed to have existed notwithstanding a near total lack of evidence by many in the north american archeological community as a means of explaining the occurrence of early man south of the ice in early postglacial time in the last 15 years much has been done to fill the knowledge gap including theories on alternate routes but there is still no consensus quaternary vertebrate fossils from alberta accompanied by numerous radiocarbon dates with a clear gap between 21 ka bp and at least 11 6 ka bp now suggest that alberta was overridden by ice during an extensive late wisconsinan glaciation therefore a full glacial ice free corridor could not have existed however much of the province could have served as a migration route northward and southward both before and after late wisconsinan glaciation the preglacial passage could not have been a corridor because numerous megafaunal remains and conifer wood from numerous localities with finite dates from ca 43 ka to 21 ka bp indicate extensive ice free conditions similarly a late pleistocene corridor critically appraised from the standpoints of vertebrate paleontology and archeology is irrelevant because by the time human migrants arrived in southern alberta less than 11 ka bp the ice had been in retreat for well over 1000 years relative to human influx the continuing use of the term corridor with its connotation of a narrow or restricted passage seems inappropriate

evidence of cordilleran late wisconsinan glaciers in the ice free corridor abstract glaciers flowing down the athabasca river valley during the last glacial period were fed both by local montane glaciers and by cordilleran ice moving easterly across the continental divide from british columbia resulting in a major eastward surge into the ice free corridor the timing of this event has been disputed for many years and has important implications for the study of paleoenvironmental conditions and the north south migration of biota in the corridor chronologic and lithostratigraphic data from the jasper region suggest that this event took place in the late wisconsinan subtill radiocarbon dates on wood in the athabasca river valley indicate that non glacial alluvial sediments began accumulating there sometime before 48 ka a finite date of 29 100 560 bp gsc 3792 on wood under till near jasper provides a maximum age for the onset of the last glaciation in the region although ice from west of the rocky mountain trench probably did not cross the continental divide until after 21 5 ka the occurrence of supraglacial metamorphic erratics as well as the distribution and nature of mapped glacial deposits and the trend of subglacial paleoflow indicators in the region east of the rockies suggests that late wisconsinan glaciers flowing from the mountains coalesced with laurentide glaciers and were deflected southeasterly along the mountain front an even more extensive glacial event may have effected the region in pre late wisconsinan times the model of late wisconsinan glaciation presented here is in agreement with all known radiocarbon data from the area and is especially attractive when supratill dates on non woody lacustrine organics are viewed in light of possible contamination by old carbon

geochemical proxies of north american freshwater routing during the younger dryas cold event the younger dryas cold interval represents a time when much of the northern hemisphere cooled from 12 9 to 11 5 kiloyears b p the cause of this event which has long been viewed as the canonical example of abrupt climate change was initially attributed to the routing of freshwater to the st lawrence river with an attendant reduction in atlantic meridional overturning circulation however this mechanism has recently been questioned because current proxies and dating techniques have been unable to confirm that eastward routing with an increase in freshwater flux occurred during the younger dryas here we use new geochemical proxies mg ca u ca and 87sr 86sr measured in planktonic foraminifera at the mouth of the st lawrence estuary as tracers of freshwater sources to further evaluate this question our proxies combined with planktonic 18oseawater and 13c confirm that routing of runoff from western canada to the st lawrence river occurred at the start of the younger dryas with an attendant increase in freshwater flux of 0 06 0 02 sverdrup 1 sverdrup 106 m3 s 1 this base discharge increase is sufficient to have reduced atlantic meridional overturning circulation and caused the younger dryas cold interval in addition our data indicate subsequent fluctuations in the freshwater flux to the st lawrence river of 0 06 0 12 sverdrup thus explaining the variability in the overturning circulation and climate during the younger dryas

the chronology climate and confusion of the moorhead phase of glacial lake agassiz new results from the ojata beach north dakota usa rapid drainage of glacial lake agassiz to the north atlantic ocean has been implicated as a triggering mechanism for the younger dryas yd cold event 13 11 6 ka cal a key component to this hypothesis is the interpretation that the ojata beach of lake agassiz in north dakota usa formed during a regression of the lake at the beginning of the yd this paper reviews the chronological data for the lowwater moorhead phase presents new radiocarbon and optically stimulated luminescence osl ages for the ojata beach and utilizes plant and insect macrofossils to reconstruct the paleoenvironmental conditions during the moorhead phase in eastern north dakota the integrated analysis of the geochronologic data emphasizes the need to distinguish between in situ and reworked plant macrofossils new ages obtained stratigraphically below the ojata beach sediments and reinterpreted chronologic data for the moorhead phase suggest that contrary to previous interpretations the ojata beach is a record of transgression of the lake in the later part of the yd and the oldest in situ minimum age for the moorhead phase is 10 47775 ka 14 c bp paleoenvironmental analysis indicates that a

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

benthonic foraminiferal faunal and isotopic data for the postglacial evolution of the champlain sea benthonic foraminiferal faunal and isotopic data from champlain sea sediments approximately 12 500 to 10 000 yr b p in age in two piston cores from lake champlain provide a detailed apparently continuous record of the evolution of the champlain sea cassidulina reniforme and islandiella helenae are the dominant benthonic foraminifera during the initial phase of the champlain sea and are replaced by elphidium excavatum forma clavatum and protelphidium orbiculare as the dominant species during the remainder of the sea s history the oxygen isotopic data show a gradual decrease in 18o between approximately 12 500 and 10 900 yr b p followed by a more rapid decrease during the interval 10 900 to 10 000 yr b p the 13c data have a similar trend as 18o with generally decreasing values up the section the isotopic and faunal data suggest that nearly marine conditions were present in the initial plase of the champlain sea followed by gradually decreasing salinities and increasing temperatures as the sea evolved the beginning of the rapid isotopic decrease at approximately 10 900 yr b p marks the onset of the largest environmental change in the history of the champlain sea probably reflecting a major pulse of meltwater from the laurentide ice sheet

laurentide glaciation in west central alberta a single late wisconsinan event the grande prairie region in west central alberta shows evidence of late wisconsinan laurentide glaciation in the form of a widespread till containing abundant erratic clasts derived from the canadian shield two sections located on the smoky river at watino and on the simonette river 80 km to the southwest expose sediment lying stratigraphically below the till a similar sequence is exposed in both localities 5 10 m of coarse quartzite gravel overlain by a thick sequence of sand and silt the gravel contains no laurentide erratics and is thus preglacial the contact between the basal gravel and the overlying sand and silt is sharp and conformable 14c dates from the base of the simonette section and throughout the watino section suggest a middle wisconsinan age thus the sediment exposed is interpreted as a conformable middle wisconsinan sequence the sedimentary sequences were deposited in a moderate to low energy braided stream system flowing towards the north the general fining up trend in the

the impact of cold north atlantic sea surface temperatures on climate implications for the younger dryas cooling 11 10 k the sensitivity of global climate to colder north atlantic sea surface temperatures is in vestigated with the use of the giss general circulation model north atlantic ocean temperatures 18 000 b p resembling those prevalent during the younger dryas were incorporated into the model of the present climate and also into an experiment using orbital parameters and land ice characteristic of 11 000 b p the results show that with both 11 000 b p and present conditions the colder ocean temperatures produce cooling over western and central europe in good agreement with younger dryas paleoclimatic evidence cooling also occurs over extreme eastern north america although the precise magnitude and location depends upon the specification of ocean temperature change in the western atlantic despite the presence of increased land ice and colder ocean temperatures the younger dryas summer air temperatures at northern hemisphere midlatitudes in the model are warmer than those of today due to changes in the orbital parameters chiefly precession and atmospheric subsidence at the perimeter of the ice sheets

a large drop in atmospheric 14c 12c and reduced melting in the younger dryas documented with 230th ages of corals paired carbon 14 14 c and thorium 230 230 th ages were determined on fossil corals from the huon peninsula papua new guinea the ages were used to calibrate part of the 14 c time scale and to estimate rates of sea level rise during the last deglaciation an abrupt offset between the 14 c and 230 th ages suggests that the atmospheric 14 c 12 c ratio dropped by 15 percent during the latter part of and after the younger dryas yd this prominent drop coincides with greatly reduced rates of sea level rise reduction of melting because of cooler conditions during the yd may have caused an increase in the rate of ocean ventilation which caused the atmospheric 14 c 12 c ratio to fall the record of sea level rise also shows that globally averaged rates of melting were relatively high at the beginning of the yd thus these measurements satisfy one of the conditions required by the hypothesis that the diversion of meltwater from the mississippi to the st lawrence river triggered the yd event

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

north atlantic thermohaline circulation during the past 20 000 years linked to high latitude surface temperature during a surface cooling event 10 000 to 12 000 years ago higher cd ca and lower 13c 12c ratios are observed in benthic foraminifera shells from rapidly accumulating western north atlantic sediments data from sediment cores show that marked nutrient depletion of intermediate waters occurs in association with reduced glacial north atlantic deep water flux it is proposed that cold high latitude sea surface temperatures enhance intermediate water formation at the expense of deep water formation

desalination of a sedimentary rock aquifer system invaded by pleistocene champlain sea water and processes controlling groundwater geochemistry the objective of this study was to identify geochemical processes and quaternary geological events responsible for the variations in groundwater geochemistry observed in a sedimentary rock aquifer system including brackish to saline groundwater inorganic constituents and environmental isotopes were analyzed for 146 groundwater samples dissolution of carbonates dominates in recharge areas resulting in ca mg hco3 groundwater further along flow paths under confined conditions ca2 na ion exchange causes groundwater evolution to na hco3 type na cl groundwater is also found and it falls on a seawater mixing line using conservative tracers cl and br the original champlain sea water is shown to have been in the region a mixture of about 34 seawater and 66 freshwater a composition still retained by some groundwater na cl groundwater thus results from mixing with former champlain sea water and also from solute diffusion from overlying marine clay the system is thus found to be at different stages of desalinization from the original champlain sea water still present in hydraulically stagnant areas of the aquifer to fully flushed conditions in parts where more flow occurs especially in recharge zones the geochemical processes are integrated within the hydrogeological context to produce a conceptual geochemical evolution model for groundwater of the aquifer system

global nature of the younger dryas cooling event inferred from oxygen isotope data from sulu sea cores the younger dryas an approximately 1 000 year long return to near glacial conditions interrupted the glacial holocene climate transition during which most of the northern hemisphere ice sheets melted evidence for the younger dryas event has been found mainly in sediments from the north atlantic ocean and northwest europe and this has led to the idea that the event was caused by an injection of meltwater into the north atlantic ocean1 3 this model however has been recently questioned in the light of coral reef data on the rate of sea level changes during this transition4 here we present high resolution oxygen isotope records from benthic and planktonic foraminifera from two radiocarbon dated cores in the sulu sea showing that the younger dry as occurred synchronously in the surface and deep waters of the sulu sea and the northern atlantic ocean by combining our results with other palaeoclimate data we suggest that the younger dry as event was a global phenomenon and we believe it to have been caused by low atmospheric co2concentrations

late quaternary paleoenvironments of northwestern north america implications for inland versus coastal migration routes abstract although the long held normative view of new world colonization relies on entrance through an interior ice free corridor by terrestrially adapted big game hunters a recently demonstrated human presence in southern chile dating prior to the existence of the corridor route implies different colonization scenarios which must be seriously considered a renewed focus of archaeological and paleoecological research on early post glacial landscapes in northwestern north america has revitalized the ice free vs coastal corridor controversy geological findings from glacial geology and paleo sea levels support the possibility of coastal migration from beringia to the pacific northwest between about 14 000 and 10 000 bp and preliminary paleoecological data suggest that the coastal landscape was in part vegetated and probably able to support a terrestrial fauna including humans the same cannot be said about the ice free corridor

a series of large late wisconsinan meltwater floods through the champlain and hudson valleys new york state usa abstract the champlain valley in northeastern new york lies at the junction of two important late wisconsinan proglacial outflow routes the hudson valley to the south and the st lawrence valley to the northeast freshwater outflow from proglacial lakes in the hudson champlain valleys glacial lake albany vermont and the combined ontario and st lawrence valleys glacial lake iroquois may have affected ocean circulation and thereby altered climate during the last deglaciation we have estimated steady state and three flood pulse discharges from these large meltwater reservoirs into the north atlantic using channel geometry and a high resolution digital elevation model of the late wisconsinan paleogeography of the region we estimate the steady state meltwater discharge into the north atlantic to be 0 3 0 6 sv the first flood event was a combined iroquois vermont outflow at around 10 900 14 c yr bp that released 700 km 3 of meltwater into the north atlantic through the hudson valley with an estimated discharge of 1 1 sv a second outflow event released 2500 km 3 through the hudson valley shortly after the first event finally approximately 1500 km 3 was released to the north atlantic through the gulf of st lawrence at the incursion of the champlain sea about 150 300 years later

geology of northeast british columbia and northwest alberta diamonds shallow gas gravel and glaciersthis article introduces a selection of papers published in this special issue on the theme geology of northeastern british columbia and northwestern alberta diamonds shallow gas gravel and glaciers this special issue reports on some of the results of a multi disciplinary research program conducted in the boreal plains of northwest alberta and northeast british columbia several innovative approaches to conducting geoscientific research in this remote drift covered region are presented including geochemical analysis of bentonites for evaluating kimberlite potential the use of electromagnetic surveys for mapping buried aggregate deposits and paleo topographic mapping techniques to define buried channels results of the program include the discovery of several large aggregate deposits the first kimberlite indicator minerals in northeast british columbia a significant sphalerite dispersal train in northwest alberta the first documented report of kimberlite sourced bentonites and numerous previously unknown interglacial sites together these papers provide a greatly enhanced understanding of the glacial history quaternary stratigraphy and kimberlite geology of northwest alberta and northeast bri

late quaternary deglaciation of the southwestern st lawrence lowland new york and ontario the style of deglaciation and maximum extent of earliest proglacial lakes have been reconstructed for the southwestern st lawrence lowland of new york and ontario using ice marginal sediments and landforms strandline features and the areal distribution of candona subtriangulata bearing rhythmites an important recessional position the carthage harrisville ice border fronted proglacial lake iroquois in the eastern lake ontario basin subsequent ice retreat probably earlier than 12 500 yr b p allowed lake iroquois to expand along the northwestern flank of the adirondack mountains and into the st lawrence lowland contrasting styles of deglaciation controlled primarily by water depth resulted in a land based ice margin which withdrew gradually off the northern slope of the adirondack mountains while the ice margin in the western st lawrence lowland retreated rapidly in the deep waters of lake iroquois the maximum extent of ice retreat during the early phases of lake iroquois has been estimated on the basis of the distribution of the ostracode condona subtriangulata in lake iroquois and younger sediments in new york and by northward projections of iroquois shoreline elevations to the region bounded by the madawaska highlands ontario results indicate that the southwestern st lawrence lowland was rapidly deglaciated during the highest phases of lake iroquois the distribution and radiocarbon chronology of fossiliferous sediments relating to lower post iroquois levels also confirm that these extensive proglacial lakes occupied the lowland well before the champlain sea incursion

the chronology of the last deglaciation implications to the cause of the younger dryas event it has long been recognized that the transition from the last glacial to the present interglacial was punctuated by a brief and intense return to cold conditions this extraordinary event referred to by european palynologists as the younger dryas was centered in the northern atlantic basin evidence is accumulating that it may have been initiated and terminated by changes in the mode of operation of the northern atlantic ocean further it appears that these mode changes may have been triggered by diversions of glacial meltwater between the mississippi river and the st lawrence river drainage systems we report here accelerator mass spectrometry ams radiocarbon results on two strategically located deep sea cores one provides a chronology for surface water temperatures in the northern atlantic and the other for the meltwater discharge from the mississippi river our objective in obtaining these results was to strengthen our ability to correlate the air temperature history for the northern atlantic basin with the meltwater history for the laurentian ice sheet

stable isotope o and c and pollen trends in eastern lake erie evidence for a locally induced climatic reversal of younger dryas age in the great lakes basin a cool period from about 11000 to 10 500 bp 11 to 10 5 ka is recognized in pollen records from the southern great lakes area by the return of picea and abies dominance and by the persistence of herbs the area of cooling appears centred on the upper great lakes a high resolution record ca 9 mm y from a borehole in eastern lake erie reveals in the same time interval this pollen anomaly isotope evidence of meltwater presence a 3 per mil shift in 18o and a 1 1 per mil shift in 13c increased sand and reduced detrital calcite content all suggesting concurrent cooling of lake erie the onset of cooling is mainly attributed to the effect of enhanced meltwater inflow on the relatively large upstream main lake algonquin during the first eastward discharge of glacial lake agassiz termination of the cooling coincides with drainage of lake algonquin and is attributed to loss of its cooling effectiveness associated with a substantial reduction in its surface area it is hypothesized that the cold extra inflow effectively prolonged the seasonal presence of lake ice and the period of spring overturn in lake algonquin the deep mixing would have greatly increased the thermal conductive capacity of this extensive lake causing suppression of summer surface lakewater temperatures and reduction of onshore growing degree days alternatively a rapid flow of meltwater buoyed on sediment charged denser lakewater may have kept the lake surface cold in summer other factors such as wind shifted pollen deposition and possible effects from the younger dryas north atlantic cooling could have contributed to the great lakes climatic reversal but further studies are needed to resolve their relative significance

late weichselian environmental history in southeastern sweden during the deglaciation of the scandinavian ice sheet abstract late weichselian litho bio and chronostratigraphy 14 c and varves in southeastern sweden provide a detailed picture of the deglaciation pattern and dynamics shore displacement late glacial sedimentation and history of the landscape vegetation and climate two plausible glacial models were tested against lithologic chronologic and climatic data permafrost at and outside the ice margin and topographic conditions beneath the ice apparently caused inward spread of frozen glacier bed conditions this led to a buildup of a large zone of debris rich basal ice a climatic amelioration about 12 700 yr b p changed the temperature profile in the ice sheet deposition of basal melt out till began at the previously frozen glacier bed and a rapid recession of the clean ice set in thin exposed debris rich basal ice which was separated from the active ice margin about 150 yr later in this zone of stagnant ice there followed a 200 300 yr period marked by subglacial and supraglacial melt out and resedimentation forming a large hummocky transverse moraine the mild climate favored rapid plant immigration and a park tundra was established the gradual closing of the landscape was interrupted by a 100 to 150 yr period of tundra vegetation and a cool dry climate with local vegetational differences caused by differences in soil moisture about 12 000 yr b p a second climatic amelioration set in and during the next 1000 yr a birch and pine woodland gradually developed soils stabilized and empetrum heaths became abundant as the climate gradually deteriorated at the end of this period by 11 000 yr b p the area had become a tundra again with scattered birch stands dominated by herbs such as artemisia chenopodiaceae grasses and sedges some 500 yr later a birch pine woodland again succeeded and within about 500 yr the vegetation changed to a rather closed woodland as the climate ameliorated further however the time lag between climatic and vegetation change was considerable

late quaternary vertebrates and the opening of the ice free corridor with special reference to the genusbison abstract the ice free iorridor opened physically in early deglaciation after 14 ka bp but at first was not necessarily passable in an ecological sense one way to gauge the timing of its ecological opening is to establish a chronology for the arrival of immigrant animal species the bison have excellent potential because of the abundance of their remains late pleistocene and early holocene bison finds from western canada north to the peace river area extend the known database and provide new insights bison of southern appearance referable tob bison antiquus were present as far north as the peace river region until about 10 ka bp bison populations in western canada apparently underwent a rapid change at that time such that barely 500 years later bison of northern appearance referable tob bison occidentalis were established the rapidity and pervasiveness of this change seem to defy an evolutionary explanation rooted in punctuated equilibrium or phenotypic change and could indicate a sudden population influx through the newly opened corridor thus far no late glacial bison in western canada have been dated in excess of 11 5 ka bp with the possible exception of material from empress alberta if a steppe tundra was established before that time the absence of bison with either southern or northern affinities seems inexplicable outburst floods have undoubtedly removed part of the record by scouring gravel fills from valleys but it is doubtful that they completely obliterated the fossil record of a gregarious herbivore such as the bison

impacts of post glacial lake drainage events and revised chronology of the champlain sea episode 13 9 ka abstract lithologic chirp compressed high intensity radar pulse sonar paleomagnetic stable isotopic and micropaleontological analyses of sediment cores from lake champlain new york vermont were used to determine the age of the post glacial champlain sea marine episode the timing of salinity changes and their relationship to freshwater discharge from mid continent glacial lakes calibrated radiocarbon ages on plant material provide an improved post glacial chronology overcoming problems from shell ages caused by carbon reservoir effects up to 1500 yr the final drainage of glacial lake vermont and the inception of marine conditions occurred 13 1 12 8 ka kiloannum calendar years and a sharp decrease in champlain sea salinity from 25 to 7 8 psu practical salinity units occurred approximately 11 4 11 2 ka reduced salinity was most likely caused by rapid freshwater inflow eastward from glacial lake algonquin into the champlain basin the timing of inferred freshwater event coincides with the widespread climatic cooling called the preboreal oscillation

the impact of glacial lake runoff on the goldthwait and champlain seas the relationship between glacial lake agassiz runoff and the younger dryas abstract the freshwater flux to the north atlantic ocean during the last deglaciation included runoff meltwater plus precipitation from glacial lake st lawrence ca 11 6 ka bp from glacial lake agassiz 10 9 9 9 and 9 5 8 0 ka bp and from glacial lake barlow ojibway 9 5 8 0 ka bp runoff from the glacial lakes does not appear to have mixed with the deep water of the goldthwait sea in the gulf of st lawrence and was part of the surface outflow to the north atlantic ocean radiocarbon dated invertebrate faunal assemblages show that the major impact of lake agassiz runoff to the north atlantic ocean during the 10 9 to 9 9 ka bp interval occurred after 10 5 ka bp resulting in the freshening of the champlain sea the younger dryas cold episode on the other hand began about 11 0 ka bp the discordance between the major impact of lake agassiz runoff on the champlain sea and the beginning of the cold episode indicates that lake agassiz runoff did not trigger the younger dryas cooling however the runoff from glacial lake agassiz may have sustained the cold climate during the latter part of the younger dryas cold episode