geomorphic relations among glacial lake algonquin and the munising and grand marais moraines in eastern upper michigan usa abstract data obtained from ground penetrating radar gpr optically stimulated luminescence osl dating and geostatistical reconstructions of lake algonquin water planes indicate that high standing outwash aprons flanking the munising moraine s southern margin in eastern upper michigan terminate as large coalescing gilbert type ice contact deltas graded to the main level of lake algonquin nearly 30 km of gpr imagery provides clear evidence of topset and foreset beds diagnostic of deltaic deposition landform assemblages suggest that the deltas likely evolved from subaqueous grounding line fans formed along a retreating ice margin characterized by widespread stagnation in time these deltas aggraded to the main lake algonquin level as the ice margin stabilized an osl date of 12 5 1 1 ka on a nearby beach ridge associated with the main algonquin shoreline is consistent with this interpretation these new data coupled with the presence of nested fans at the downstream end of meltwater channels incised into the delta indicate that lake algonquin was falling as delta deposition waned eventually reaching a level concordant with the lower orillia level before final abandonment large regionally extensive heads of outwash marking the crest of the munising moraine are graded to the upper margins of these deltas and by inference must also correlate with main lake algonquin and the associated two rivers deglaciation ca 13 12 5 ka the deltas in turn are conspicuously crosscut by outwash aprons that are graded to levels much lower than any recognized upper group lake algonquin shoreline because these aforementioned heads of outwash part of drexler and others grand marais moraine correlate with the marquette moraine farther west they likely date to the marquette advance ca 11 5 ka thus landforms related to two rivers and to marquette glaciations appear to comingle across the study area in the absence of extensive exposures and datable materials our work highlights the fact that crosscutting relationships and distinct differences in base level can provide an important first step for untangling the complicated landform relationships in this part of michigan

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

ice sheet sources of sea level rise and freshwater discharge during the last deglaciation we review and synthesize the geologic record that constrains the sources of sea level rise and freshwater discharge to the global oceans associated with retreat of ice sheets during the last deglaciation the last glacial maximum 26 19 ka was terminated by a rapid 5 10 m sea level rise at 19 0 19 5 ka sourced largely from northern hemisphere ice sheet retreat in response to high northern latitude insolation forcing sea level rise of 8 20 m from 19 to 14 5 ka can be attributed to continued retreat of the laurentide and eurasian ice sheets with an additional freshwater forcing of uncertain amount delivered by heinrich event 1 the source of the abrupt acceleration in sea level rise at 14 6 ka meltwater pulse 1a 14 15 m includes contributions of 6 5 10 m from northern hemisphere ice sheets of which 2 7 m represents an excess contribution above that derived from ongoing ice sheet retreat widespread retreat of antarctic ice sheets began at 14 0 15 0 ka which together with geophysical modeling of far field sea level records suggests an antarctic contribution to this meltwater pulse as well the cause of the subsequent younger dryas cold event can be attributed to eastward freshwater runoff from the lake agassiz basin to the st lawrence estuary that agrees with existing lake agassiz outlet radiocarbon dates much of the early holocene sea level rise can be explained by laurentide and scandinavian ice sheet retreat with collapse of laurentide ice over hudson bay and drainage of lake agassiz basin runoff at 8 4 8 2 ka to the labrador sea causing the 8 2 ka event

formation of large beaches in an area of rapid differential isostatic rebound the three outlet control of lake agassiz abstract shorelines in basins undergoing differential isostatic rebound do not remain geographically fixed for long periods and are either transgressive or regressive during regression a relatively uniform blanket of shoreface sediment may be deposited but unless regression is slow or punctuated by periods of lake level equilibrium large beaches do not form in contrast along transgressive shorelines which migrate upslope large morphostratigraphic features commonly are maintained along the lake s margin these may subsequently be stranded when lake level declines beaches around isostatically rebounding proglacial lakes are commonly considered to have formed during a period of lake regression punctuated by abrupt drops in lake level however in basins that are differentially rebounding large beaches cannot form this way and only periods of transgressing waters allow enough time for large beaches to form and define a continuous shoreline around the basin with this in mind some of the largest and most extensive beaches in the glacial lake agassiz basin the norcross tintah and upper campbell constructed between 10 4 and 9 4 ka 14 c yr bp are reinterpreted as strandlines that were formed by transgression each of these three transgressions followed lower lake phases and resulted from in sequence differential isostatic rebound of the eastern outlet rebound and ice damming of the northwestern outlet and rebound of the northwestern outlet each of these transgressions ended when lake level reached the southern outlet stranding the norcross tintah and upper campbell beaches about 10 2 9 9 and 9 4 ka 14 c yr bp respectively

synchronization of late glacial vegetation changes at crystal lake illinois usa with the north atlantic event stratigraphy abstract late glacial 17 11 cal ka bp pollen records from midwestern north america show similar vegetation trends however poor dating resolution wide interval pollen counts and variable sedimentation rates have prevented the direct correlation with the north atlantic event stratigraphy as represented in the greenland ice core records thus preventing the understanding of the teleconnections and mechanisms of late quaternary events in the northern hemisphere the widespread occurrence of late glacial vegetation and climates with no modern analogs also hinders late glacial climate reconstructions a high resolution pollen record with a well controlled age model from crystal lake in northeastern illinois reveals vegetation and climate conditions during the late glacial and early holocene intervals late glacial crystal lake pollen assemblages dominated by picea mariana and fraxinus nigra with lesser amounts of abies and larix suggest relatively wet climate despite fluctuations between colder and warmer temperatures vegetation changes at crystal lake are coeval with millennial scale trends in the ngrip ice core record but major shifts in vegetation at crystal lake lag the ngrip record by 300 400 yr this lag may be due to the proximity of the laurentide ice sheet the ice sheet s inherent slowness in response to rapid climate changes and its effect on frontal boundary conditions and lake effect temperatures

evidence for an eolian origin for the silt enriched soil mantles on the glaciated uplands of eastern upper michigan usa abstract we provide textural geochemical and mineralogical data on a thin silty deposit that unconformably mantles glaciated uplands in the eastern upper peninsula of michigan previous research on this deposit which we hypothesize to be loess is nonexistent the uplands were islands or narrow peninsulas within one or more glacial lakes we compare the distribution likely source and nature of the 20 60 cm thick silty mantle by using the loess formation model of mason et al mason j a nater e a zanner c w bell j c 1999 a new model of topographic effects on the distribution of loess geomorphology 28 223 236 which focuses on the generation of eolian silt by saltating sand across upwind barren surfaces parabolic dunes with arms open to the nw are common on former lake floors upwind of the silt mantled uplands attesting to the strength and direction of paleowinds the abrupt termination of the dunes at the footslopes of the uplands associated with silt deposition on upland soil surfaces in downwind locations are both consistent with the model of mason et al mason j a nater e a zanner c w bell j c 1999 a new model of topographic effects on the distribution of loess geomorphology 28 223 236 sediments on former lake floors contain abundant strata of fine medium sand and silt and thus are likely sources for the silt and dune sand the cap dune and lake sediments are similar along many different geochemical axes whereas the substrate sediment i e the drift below the cap is unique cap sediments normally containing roughly 30 silt are enriched in quartz and depleted in ti and zr relative to dune sediment the dune sediment a more residual eolian deposit is enriched in ti and zr relative to the cap probably due to its greater abundance of heavy minerals therefore we conclude that the silty cap is loess that was deflated from abandoned lake floors after nearby glacial lakes drained probably contemporaneously with dune migration across the former lake floors

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

a proposed diachronic revision of late quaternary time stratigraphic classification in the eastern and northern great lakes area abstract a succession of stratigraphic codes 1933 1961 1983 has guided attempts to refine classifications and naming of stratigraphic units for quaternary deposits of the great lakes region the most recent classifications for the late quaternary of the lake michigan lobe 1968 and the eastern great lakes 1972 have been widely used but later work has created the need for revision an attempt has been made to integrate the two previous classifications following the diachronic system of the 1983 code of stratigraphic nomenclature a new nomenclature for the higher more broadly recognized units was presented in 1997 we here present the diachronic nomenclature for finer subdivisions recognized in the eastern and northern great lakes following the interglacial sangamon episode the three parts of the wisconsin episode are further subdivided as follows the ontario subepisode former early wisconsinan comprises the greenwood willowvale and guildwood phases the elgin subepisode former middle wisconsinan comprises the port talbot brimley and farmdale phases and the michigan subepisode former late wisconsinan consists of nissouri erie port bruce mackinaw port huron two creeks onaway gribben marquette abitibi and driftwood phases succeeding interglacial time to the present is the hudson episode

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

the lake superior varve stratigraphy and implications for eastern lake agassiz outflow from 10 700 to 8900 cal ybp 9 5 8 0 14c ka abstract glaciolacustrine rhythmites within sediment cores from lake superior record the regional recession of the laurentide ice sheet lis from 10 700 to 8900 cal ybp ca 9 5 8 0 14 c ka lis retreat from superior opened eastern lake agassiz outlets so that the rhythmites reflect the combined impacts of sediment laden meltwater and lake agassiz discharge multiple rhythmite stratigraphies a time series analysis of the thickness measurements and high resolution inorganic carbonate data demonstrate that this is an annual record varved the varve thickness records primarily document regional ice margin dynamics correlative thick varve sequences at 9100 cal ybp 8 1 14 c ka and 10 400 10 200 cal ybp 9 2 9 0 14 c ka record two periods of enhanced glaciofluvial discharge most likely moraine formation the nakina and nipigon general varve cessation is associated with the circumvention of lake agassiz and glacial meltwater into lake ojibway at 9040 cal ybp 8 1 14 c ka although adjacent to the inlets from lake nipigon rhythmic sedimentation persisted for 200 years positively identifying lake agassiz catastrophic discharge events remains speculative but seems feasible following retreat of marquette ice that had re advanced to fill the basin the initial influx of lake agassiz water is expected at around 10 600 cal ybp 9 4 14 c ka but at this time most of northeastern lake superior was covered by ice three sets of thick thin varves in western lake superior perhaps record influxes of lake agassiz at around 10 630 10 600 and 10 570 cal ybp 9 4 14 c ka varve formation in superior coincides with high lake levels in lake huron suggesting that high lake levels in huron correspond to periods of high agassiz and or meltwater flow into lake superior

ams radiocarbon dating and varve chronology of lake soppensee 6000 to 12000 14c years bp for the extension of the radiocarbon calibration curve beyond 10000 14c y bp laminated sediment from lake soppensee central switzerland was dated the radiocarbon time scale was obtained using accelerator mass spectrometry ams dating of terrestrial macrofossils selected from the soppensee sediment because of an unlaminated sediment section during the younger dryas 10000 11000 14c y bp the absolute time scale based on counting annual layers varves had to be corrected for missing varves the soppensee radiocarbon verve chronology covers the time period from 6000 to 12000 14c y bp on the radiocarbon time scale and 7000 to 13000 calendar y bp on the absolute time scale the good agreement with the tree ring curve in the interval from 7000 to 11450 cal y bp cal y indicates calendar year proves the annual character of the laminations the ash layer of the vasset killian tephra massif central france is dated at 8230 140 14c y bp and 9407 44 cal y bp the boundaries of the younger dryas biozone are placed at 10986 69 cal y bp younger dryas preboreal and 1212 86 cal y bp allerod younger dryas on the absolute time scale the absolute age of the laacher see tephra layer dated with the radiocarbon method at 10 800 to 11200 14c y bp is estimated at 12350 135 cal y bp the oldest radiocarbon age of 14190 120 14c y bp was obtained on macrofossils of pioneer vegetation which were found in the lowermost part of the sediment profile for the late glacial the offset between the radiocarbon 10000 12000 14c y bp and the absolute time scale 11400 13000 cal y bp in the soppensee chronology is not greater than 1000 years which differs from the trend of the u th radiocarbon curve derived from corals

a holocene history of dune mediated landscape change along the southeastern shore of lake superior abstract causal links that connect holocene high stands of lake superior with dune building stream damming and diversion and reservoir impoundment and infilling are inferred from a multidisciplinary investigation of a small watershed along the se shore of lake superior radiocarbon ages of wood fragments from in place stumps and soil o horizons recovered from the bottom of 300 ha grand sable lake suggest that the near shore inland lake was formed during multiple episodes of late holocene dune damming of ancestral sable creek forest drownings at 3000 1530 and 300 cal years bp are highly correlated with local soil burial events that occurred during high stands of lake superior during these and earlier events sable creek was diverted onto eastward graded late pleistocene meltwater terraces ground penetrating radar gpr reveals the early holocene valley of sable creek now filled and its constituent sedimentary structures near planar paleosols identified with gpr suggest two repeating modes of landscape evolution mediated by levels of lake superior high lake stands drove stream damming reservoir impoundment and eolian infilling of impoundments falling lake superior levels brought decreased sand supply to dune dams and lowered stream base level these latter factors promoted stream piracy breaching of dune dams and aerial exposure and forestation of infilled lakebeds the bathymetry of grand sable lake suggests that its shoreline configuration and depth varied in response to events of dune damming and subsequent dam breaching the interrelated late holocene events apparent in this study area suggest that variations in lake level have imposed complex hydrologic and geomorphic signatures on upper great lakes coasts

the application of radiocarbon age estimates to the dating of glacial sequences an example from the miami sublobe ohio u s a abstract despite the importance of dating glacial sequences little evidence has been available to highlight the stratigraphic issues associated with the interpretation of age analysis a compilation of radiocarbon data from the miami sublobe of the laurentide ice sheet provides a large enough data set more than 133 dates to identify at least two sources of error sample and unit variability and transportation problems analysis of different samples from the same stratigraphic level commonly differ by more than the reported one sigma error and 2 000 year differences do occur glacial entrainment and transportation emplace older organic material over younger in situ materials and this effect may also give age errors in the data set of up to 2 000 years at a minimum multiple radiocarbon ages from a sequence of units are necessary to assign a reliable age to events within a glacial sequence however representing multiple ages poses its own problems a graphical representation that combines the probability of each sample appears to be one solution

sediment sequences and palynology of outer south bay manitoulin island ontario connections to lake huron paleohydrologic phases and upstream lake agassiz events abstract south bay on the southern coast of manitoulin island is a fjord like embayment connected to lake huron by a natural narrow gap in the bay s outer sill 6 5 14 m above the lake a seismic profile pollen plant macrofossil grain size analyses and other sediment properties of two piston cores from a shallow outer basin of the bay document a 9 m thick sediment section comprising rhythmically laminated clay under silty clay containing zones with small molluscan shells and marsh detritus a sandy pebbly layer under soft silty clay mud overlies these sediments this stratigraphy represents inundation by deep glacial lake algonquin followed by the shallowing post algonquin series of lakes and exposure in the early holocene by 5 lake stanley lowstands in the lake huron basin separated by 4 lake mattawa highstands overflow from south bay in the first lowstand is thought to have eroded the outer sill gap marsh environments are inferred to have formed in the bay during subsequent lowstands the lake mattawa highstands are attributed to outburst floods mainly from glacial lake agassiz palynological evidence of increased spruce occurrence an apparent regional climate reversal during the dry pine period is attributed to cold northwest winds from the lake superior basin and a lake effect from the mattawa highstands in the lake huron basin lake waters transgressed south bay following the pine period to form the nipissing shore on manitoulin island transfer of lake huron basin drainage to southern outlets and continued glacioisostatic uplift of the region led to the present configuration of south bay and lake huron

younger dryas sea level and meltwater pulse 1b recorded in barbados reef crest coral acropora palmata the younger dryas climate event occurred during the middle of the last deglacial cycle and is marked by an abrupt shift in the north atlantic polar front almost to its former glacial position trending east to west using high precision and high accuracy u th dated barbados reef crest coral acropora palmata we generate a detailed sea level record from 13 9 to 9000 years before present kyr b p and reconstruct the ice volume response to the younger dryas cooling from the mid allerod 13 9 kyr b p to the end of the younger dryas 11 65 kyr b p rates of sea level rise decreased smoothly from 20 mm yr 1 to 4 mm yr 1 culminating in a 400 year slow stand before accelerating into meltwater pulse 1b mwp 1b the mwp 1b event at barbados is better constrained as beginning by 11 45 kyr b p and ending at 11 1 kyr b p during which time sea level rose 14 2 m and rates of sea level rise reached 40 mm yr 1 we propose that mwp 1b is the direct albeit lagged response of the northern hemisphere ice sheets to the rapid warming marking the end of the younger dryas coinciding with rapid warming in the circum north atlantic region and the polar front shift from its zonal to meridional position 11 65 kyr b p as predicted by glaciological models the ice sheet response to rapid north atlantic warming was lagged by 400 years due to the thermal inertia of large ice sheets the regional circum north atlantic younger dryas climate event is elevated to a global response through sea level changes starting with the global slowdown in sea level rise during the younger dryas and culminating with mwp 1b no meltwater pulses are evident at the initiation of the younger dryas climate event as is often speculated

chronology of glacial lake agassiz meltwater routed to the gulf of mexico abstract sediment cores with new radiocarbon dates from the southern outlet of glacial lake agassiz indicate that meltwater delivery to the mississippi valley was disrupted at 10 800 14 c yr b p and the outlet was abandoned by 9400 14 c yr b p these findings confirm the timing of generally accepted terminations of the lockhart and emerson phases of lake agassiz additionally the radiocarbon chronology indicates that the spillway was fully formed by 10 800 14 c yr b p and that the occupancy in late emerson time was likely short lived with minimal spillway erosion

coarse textured basal zones in thin loess deposits products of sediment mixing and or paleoenvironmental change abstract the purpose of this research was to characterize and interpret the coarse basal zones that are common in thin loess deposits that overlie coarser textured sediment to that end we sampled nine pedons in northeastern wisconsin and the upper peninsula of michigan each of which had formed in thin 55 cm loess over sandy glacial sediment at most of these sites the loess became noticeably coarser near the lithologic discontinuity the loess has a primary particle size mode in the coarse silt or fine very fine sand fraction 30 65 m and a secondary mode in the fine or medium sand fraction 200 400 m we attribute the secondary mode to mixing of underlying sands into the loess either during loess deposition or by post depositional pedoturbation in thin loess pedoturbation processes can penetrate into the underlying sediment facilitating mixing upward as far as 50 cm into the loess silt from the loess has also been mixed into the underlying sandy sediment alternatively in some pedons the loess itself coarsens with depth the particle size mode for the loess becomes increasingly coarser with depth this coarsening suggests that during loess deposition one or more of the following was occurring 1 wind velocities were decreasing over time 2 the textural character of the loess source area s were changing decreasing or 3 additional source areas with finer textured sediment became more dominant over time our research demonstrates the utility of detailed particle size data for detecting and interpreting the paleoenvironmental history of loess we also document the extent to which pedoturbation can impact the original textural characteristics of loess or any sediment that occurs as a thin surficial mantle

stabilization of glaciers terminating in closed water bodies evidence and broader implications 1 the behavior of glaciers terminating in deep water is determined by the interaction of buoyancy iceberg production and the sensitivity of ice flow to subtle changes in resistance at the glacier bed modeling efforts assume rapid evacuation of icebergs but some glaciers terminate in closed basins where icebergs may accumulate multibeam bathymetric survey of a glacial lake in iceland that received outlet glaciers during the little ice age document near parallel flow of narrow ice fingers that extended up to 1 km beyond the grounding line these previously unseen features apparently occurred when iceberg production exceeded iceberg melt resulting in iceberg buttressing of the ice margin similar stabilization of ice flow may resolve long standing debates about past continental ice sheet behavior including the rapid readvance of the laurentide ice sheet into lake superior ca 11 ka and the genesis of glacial flutes observed in the central arctic ocean basin

late glacial allerod younger dryas buried organic deposits nova scotia canada a contribution to the north atlantic seaboard programme of igcp 253 termination of the pleistocene abstract numerous deposits of organic shallow pond sediments and wetland peat accumulations buried by minerogenic sediments have been discovered throughout nova scotia they are interpreted as representing a late glacial climatic oscillation correlative with the allerod younger dryas event of europe and the north atlantic ocean the organic deposits began forming during the warm or warming interval following deglaciation and often record a transition to colder conditions the climatic reversion recorded in many deposits began about 10 8 ka bp and continued or sustained cooling culminated in the burial of the organic deposits by minerogenic sediments indicative of solifluction and mass wasting processes some deposits provide strong evidence for regeneration or rejuvenation of local glaciers as the organic deposits are not as susceptible as lake sediments to contamination by old carbon they provide a more reliable chronological framework for deglaciation and late glacial vegetational history palynological evidence shows that pioneer herb tundra communities colonized some areas shortly after 13 ka bp willow and birch shrubs followed soon after spruce woodlands had migrated into the region prior to 10 8 ka bp but had not yet reached the northeast mainland and cape breton island cooling after 10 8 ka bp decimated tree populations and favoured a return to shrub and herb communities the record in the buried deposits was then truncated by deposition of minerogenic sediments and lake sediment sequences from deeper basins with continuous sedimentation are required to complete the record

major end moraines of younger dryas age on wollaston peninsula victoria island canadian arctic implications for paleoclimate and for formation of hummocky moraine some of the most extensive and massive end moraines of younger dryas age 11 10 14c ka bp yet recognized in north america occur on wollaston peninsula of victoria island on the western part of the peninsula numerous closely spaced end moraines formed in the interval starting 11 100 100 radiocarbon years ago and ending about 10 500 10 200 years ago net recession was generally slow throughout and was punctuated by moraine building and at least two readvances recession is mapped with a resolution that is approximately decadal the moraines form an orderly nested succession and are consistently associated with westward shedding of meltwater which formed a sequence of marine limit deltas we lack firm independent proxy climate evidence needed to assess whether these moraines formed because of cold younger dryas climate rather than because of controls such as topographic setting and water depth but climatic control seems probable the moraines evidently retain glacier ice cores as do most similarly

age verification of the lake gribben forest bed and the younger dryas advance of the laurentide ice sheet analysis of nine wood samples from the lake gribben forest bed near lake gribben michigan yielded a combined age of 10 025 100 14c years bp which confirms and refines prior age estimates for the bed the stratigraphic position of these samples below a prograding ice contact fan indicates the time that a glacial margin reached the southern edge of the lake superior basin geomorphic tracing and correlation of associated deposits indicate that a contemporaneous margin extended almost 1000 km from duluth minnesota across the lake superior basin to north bay ontario along the southern shore of lake superior ice margin expansion began during and ended at the close of the younger dryas a surging glacier system would not produce a nearly linear moraine system across both a major basin lake superior and a major upland abitibi upland therefore we attribute this advance of the laurentide ice sheet to climatic forcing of the younger dryas event

evidence for the two creeks interstade in the lake huron basin new radiocarbon age dates for the cheboygan bryophyte bed in northern lower michigan indicate that the bed was not deposited during the mackinaw interstade as was previously proposed but is correlative to the two creeks forest bed deposited during the two creeks interstade approximately 11 850 bp furthermore the till overlying the bryophyte bed does not represent continuous deposition by ice throughout the two creeks interstade as proposed by others but represents deposition during the greatlakean stade a major implication resulting from the reassignment of the age of the cheboygan bryophyte bed is that the straits of mackinac could have been ice free during the two creeks interstade and that during that time the kirkfield phase of glacial lake algonquin may have extended into the lake michigan basin

holocene climatic change and the development of the lake effect snowbelt in michigan usa lake effect snow is an important constraint on ecological and socio economic systems near the north american great lakes little is known about the holocene history of lake effect snowbelts and it is difficult to decipher how lake effect snowfall abundance affected ecosystem development we conducted oxygen isotope analysis of calcite in lake sediment cores from northern lower michigan to infer holocene climatic variation and assess snowbelt development the two lakes experience the same synoptic scale climatic systems but only one of them huffman lake receives a significant amount of lake effect snow a 177 cm difference in annual snowfall causes groundwater inflow at huffman lake to be 18o depleted by 2 3 relative to o brien lake to assess when the lake effect snowbelt became established we compared calcite 18o profiles of the last 11 500 years from these two sites the chronologies are based on accelerator mass spectrometry 14c ages of 11 and 17 terrestrial plant samples from huffman and o brien lakes respectively the values of 18o are low at both sites from 11 500 to 9500 cal yr bp when the laurentide ice sheet lis exerted a dominant control over the regional climate and provided periodic pulses of meltwater to the great lakes basin carbonate 18o increases by 2 6 at o brien lake and by 1 4 at huffman lake between 9500 and 7000 cal yr bp suggesting a regional decline in the proportion of runoff derived from winter precipitation the great lakes snowbelt probably developed between 9500 and 5500 cal yr bp as inferred from the progressive 18o depletion at huffman lake relative to o brien lake with the largest increase of lake effect snow around 7000 cal yr bp lake effect snow became possible at this time because of increasing contact between the great lakes and frigid arctic air these changes resulted from enhanced westerly flow over the great lakes as the lis collapsed and from rapidly rising great lakes levels during the nipissing transgression the 18o difference between huffman and o brien lakes declines after 5500 cal yr bp probably because of a northward shift of the polar vortex that brought increasing winter precipitation to the entire region however 18o remains depleted at huffman lake relative to o brien lake because of the continued production of lake effect snow

the continental tree ring record absolute chronology 14c calibration and climatic change at 11 ka abstract tree ring chronologies are unique archives for various parameters indicating climatic change the wood structure of trees deposited in river gravel below the water table is well preserved even after several millennia and it provides information on a time scale of solar years during the past 25 years in the hohenheim tree ring laboratory long tree ring chronologies have been constructed now reaching back to 11 400 yr dendro b p in this contribution we demonstrate the evidence for climatic change in the early holocene which can be obtained both from botanical properties e g parameters of ring growth and from the isotopic information recorded in tree rings

early holocene dune activity linked with final destruction of glacial lake minong eastern upper michigan usa abstract the early holocene final drainage of glacial lake minong is documented by 21 osl ages on quartz sand from parabolic dunes and littoral terraces and one radiocarbon age from a lake sediment core adjacent to mapped paleoshorelines in interior eastern upper michigan we employ a simple model wherein lake level decline exposes unvegetated littoral sediment to deflation resulting in dune building dunes formed subsequent to lake level decline prior to stabilization by vegetation and provide minimum ages for lake level decline optical ages range from 10 3 to 7 7 ka 15 ages on dunes adjacent to the lowest lake minong shoreline suggest final water level decline 9 1 ka the clustering of optical ages from vertically separated dunes on both sides of the nadoway gros cap barrier around 8 8 ka and a basal radiocarbon date behind the barrier 8120 40 14 c yr bp 9 1 cal ka bp support the hypothesis that the barrier was breached and the final lake level drop to the houghton low occurred coincident with 1 high meltwater flux into the superior basin and 2 an abrupt negative shift in oxygen isotope values in lake huron

kame deltas provide evidence for a new glacial lake and suggest early glacial retreat from central lower michigan usa abstract in association with an undergraduate honors seminar at michigan state university we studied two small kame deltas in north central lower michigan these recently identified deltas provide clear evidence for a previously unknown proglacial lake glacial lake roscommon in this large basin located in an interlobate upland our first goal was to document and characterize the geomorphology of these deltas because both deltas are tied to ice contact ridges that mark the former position of the retreating ice margin within the lake our second goal was to establish the age of one of the deltas thereby constraining the timing of ice retreat in this part of michigan for which little information currently exists both deltas are composed of well sorted fine and medium sands with little gravel and have broad nearly flat surfaces and comparatively steep fronts samples taken from the upper 1 5 m of the deltas show little spatial variation in texture aside from a general fining toward their outer margins gullies on the outer margins of both deltas probably postdate the formation of the deltas proper we suggest that they formed by runoff during a permafrost period subsequent to lake drawdown we named the ice lobe that once covered this area the mackinac lobe because it had likely advanced into the region across the mackinac straits area five of six optically stimulated luminescence osl ages from one of the deltas had minimal scatter and were within 1000 years of one another with a mean age of 23 1 0 4 ka these ages suggest that the mackinac lobe had started to retreat from the region considerably earlier than previously thought even while ice was near its maximum extent in illinois and indiana and the remainder of michigan was ice covered this early retreat which appears to coincide with a short lived warm period indicated from the greenland ice core formed an opening that was at least occasionally flooded thick and deep fine textured deposits which underlie much of the region probably date to this time our work provides the first evidence of this extremely early ice retreat from central lower michigan occurring almost 4000 years before the southern margin of the ice saginaw lobe had started its retreat from the state

intensity gradients and reversals in late glacial environmental change in east central north america abstract radiocarbon dated pollen sites from the allegheny plateau east and the till plains west document significant vegetational and climatic change between 15 000 and 9000 14 c bp south of the great lakes although limited by the problems of no analog vegetation pollen transfer functions tf and response surfaces rs quantify the climatic changes including a cold oscillation chronologically equivalent to the european younger dryas phase i before ca 13 000 14 c bp conditions across the region were similar january 20 to 16 c july 12 c rs or 19 c tf mean annual precipitation 80 to 90 cm year 1 phase iia between ca 13 000 and 11 000 14 c bp n s and e w climate gradients were initiated till plains temperatures increased by ca 8 c in january and by 8 c rs or 2 3 c tf in july plateau increases for january were 3 6 c and for july were 8 c rs or 1 2 c tf precipitation generally increased somewhat phase iib ca 11 000 to 10 000 14 c bp gradients became less pronounced the western sites show a climate reversal january drop of ca 5 to 2 c july drop to ca 1 2 c becoming more like the plateau sites which show a brief small fluctuation this is followed by an abrupt 10 to 20 cm year 1 reduction in precipitation january warming of ca 3 c and continued cooler julys phase iii after 10 000 14 c bp gradients similar to those of today developed the changes in phases iib and iii are probably linked to the drainage history of the great lakes and via that history to the changes on the european continent

reconciling records of ice streaming and ice margin retreat to produce a palaeogeographic reconstruction of the deglaciation of the laurentide ice sheet abstract this paper reconstructs the deglaciation of the laurentide ice sheet lis including the innuitian ice sheet from the last glacial maximum lgm with a particular focus on the spatial and temporal variations in ice streaming and the associated changes in flow patterns and ice divides we build on a recent inventory of laurentide ice streams and use an existing ice margin chronology to produce the first detailed transient reconstruction of the ice stream drainage network in the lis which we depict in a series of palaeogeographic maps results show that the drainage network at the lgm was similar to modern day antarctica the majority of the ice streams were marine terminating and topographically controlled and many of these continued to function late into the deglaciation until the ice sheet lost its marine margin ice streams with a terrestrial ice margin in the west and south were more transient and ice flow directions changed with the build up peak phase and collapse of the cordilleran laurentide ice saddle the south eastern marine margin in atlantic canada started to retreat relatively early and some of the ice streams in this region switched off at or shortly after the lgm in contrast the ice streams draining towards the north western and north eastern marine margins in the beaufort sea and in baffin bay appear to have remained stable throughout most of the late glacial and some of them continued to function until after the younger dryas yd the yd influenced the dynamics of the deglaciation but there remains uncertainty about the response of the ice sheet in several sectors we tentatively ascribe the switching on of some major ice streams during this period e g m clintock channel ice stream at the north west margin but for other large ice streams whose timing partially overlaps with the yd the drivers are less clear and ice dynamical processes rather than effects of climate and surface mass balance are viewed as more likely drivers retreat rates markedly increased after the yd and the ice sheet became limited to the canadian shield this hard bed substrate brought a change in the character of ice streaming which became less frequent but generated much broader terrestrial ice streams the final collapse of the ice sheet saw a series of small ephemeral ice streams that resulted from the rapidly changing ice sheet geometry in and around hudson bay our reconstruction indicates that the lis underwent a transition from a topographically controlled ice drainage network at the lgm to an ice drainage network characterised by less frequent broad ice streams during the later stages of deglaciation these deglacial ice streams are mostly interpreted as a reaction to localised ice dynamical forcing flotation and calving of the ice front in glacial lakes and transgressing sea basal de coupling due to large amount of meltwater reaching the bed debuttressing due to rapid changes in ice sheet geometry rather than as conveyors of excess mass from the accumulation area of the ice sheet at an ice sheet scale the ice stream drainage network became less widespread and less efficient with the decreasing size of the deglaciating ice sheet the final elimination of which was mostly driven by surface melt

deglaciation lake levels and meltwater discharge in the lake michigan basin abstract the deglacial history of the lake michigan basin including discharge and routing of meltwater is complex because of the interaction among 1 glacial retreats and re advances in the basin 2 the timing of occupation and the isostatic adjustment of lake outlets and 3 the depositional and erosional processes that left evidence of past lake levels in the southern part of the basin a restricted area little affected by differential isostasy new studies of onshore and offshore areas allow refinement of a lake level history that has evolved over 100 years important new data include the recognition of two periods of influx of meltwater from lake agassiz into the basin and details of the highstands gleaned from sedimentological evidence major disagreements still persist concerning the exact timing and lake level changes associated with the algonquin phase approximately 11 000 bp a wide variety of independent data suggests that the lake michigan lobe was thin unstable and subject to rapid advances and retreats consequently lake level changes were commonly abrupt and stable shorelines were short lived the long held beliefs that the southern part of the basin was stable and separated from deformed northern areas by a hinge line discontinuity are becoming difficult to maintain numerical modeling of the ice earth system and empirical modeling of shoreline deformation are both consistent with observed shoreline tilting in the north and with the amount and pattern of modern deformation shown by lake level gauges new studies of subaerial lacustrine features suggest the presence of deformed shorelines higher than those originally ascribed to the supposed horizontal glenwood level finally the lake michigan region as a whole appears to behave in a similar manner to other areas both local other great lakes and regional u s east coast that have experienced major isostatic changes detailed sedimentological and dating studies of field sites and additional development of geophysical models offer hope for reconciling the field data with our understanding of earth rheology

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

geology of the small tharsis volcanoes jovis tholus ulysses patera bibils patera mars abstract jovis tholus ulysses patera and biblis patera three small volcanoes in the tharsis area of mars provide important insight into the evolution of volcanism on mars all three are interpreted to be shield volcanoes indicating that shield volcanism was present from the outset in tharsis jovis tholus is the least complex with simple repeated outpouring of lavas and caldera forming events ulysses patera is dominated by a giant caldera within which is a line of cinder cones or domes suggesting terminal stages of volcanism in which the magma had either significant volatiles or increased viscosity biblis patera is characterized by nested calderas which have expanded by block faulting of the flank it also exhibits lava flows erupted onto the flanks from events along concentric fractures these shields are different from the younger tharsis montes shields only in terms of the volume of erupted material the limited shield volume suggests that the magma source which fed the shields was rapidly depleted the relatively large size of the calderas probably results from relatively large shallow magma bodies rather than significant burial of the flanks by younger lavas eruption rates consistent with typical terrestrial basaltic eruption rates suggest that these volcanoes were probably built over time spans of 10 4 to 10 5 years stratigraphic ages range from early to upper hesperian absolute ages range from 1 9 to 3 4 ga

reply to comments by carlson et al 2009 on radiocarbon deglaciation chronology of the thunder bay ontario area and implications for ice sheet retreat patterns

testing northwest drainage from lake agassiz using extant ice margin and strandline data extant data on shorelines and ice margins in the glacial lake agassiz basin defines the limits of lake agassiz through deglacial time the ice sheet margin had not retreated far enough northwards by the beginning or end of the younger dryas chronozone for the lake to drain northwest however once lake agassiz reached the campbell beach stage at 10 800 10 300 cal bp then projections of lake agassiz strandlines were higher than the topography allowing for the first possible pathway to the northwest this relationship is used to reject the recent assertion that there was northwest drainage from lake agassiz at the beginning and end of the younger dryas chronozone

radiocarbon vs calendar ages of major lateglacial hydrological events in north america abstract the age of late quaternary events has largely been established by radiocarbon dating which does not directly measure calendar sidereal years because the production of 14 c in the atmosphere has varied through time recent research allows the radiocarbon time scale to be converted to sidereal years back as far as the last deglacial period the calibration curve of stuiver and reimer 1993 radiocarbon 35 215 230 is presented and used to determine the true calendar age of several major lateglacial hydrological events in north america and to illustrate how the actual length of these events may substantially deviate from those calculated in radiocarbon years

simulated influences of lake agassiz on the climate of central north america 11 000 years ago eleven thousand years ago large lakes existed in central and eastern north america along the margin of the laurentide ice sheet the large scale north american climate at this time has been simulated with atmospheric general circulation models1 2 but these relatively coarse global models do not resolve potentially important features of the mesoscale circulation that arise from interactions among the atmosphere ice sheet and proglacial lakes here we present simulations of the climate of central and eastern north america 11 000 years ago with a high resolution regional climate model nested within a general circulation model the simulated climate is in general agreement with that inferred from palaeoecological evidence our experiments indicate that through mesoscale atmospheric feedbacks the annual delivery of moisture to the laurentide ice sheet was diminished at times of a large cold lake agassiz relative to periods of lower lake stands the resulting changes in the mass balance of the ice sheet may have contributed to fluctuations of the ice margin thus affecting the routing of fresh water to the north atlantic ocean a retreating ice margin during periods of high lake level may have opened an outlet for discharge of lake agassiz into the north atlantic a subsequent advance of the ice margin due to greater moisture delivery associated with a low lake level could have dammed the outlet thereby reducing discharge to the north atlantic these variations may have been decisive in causing the younger dryas cold event3 4

abrupt drainage cycles of the fennoscandian ice sheet continental ice sheets are a key component of the earth s climate system but their internal dynamics need to be further studied since the last deglaciation the northern eurasian fennoscandian ice sheet fis has been connected to the black sea bs watershed making this basin a suitable location to investigate former ice sheet dynamics here from a core retrieved in the bs we combine the use of neodymium isotopes high resolution elemental analysis and biomarkers to trace changes in sediment provenance and river runoff we reveal cyclic releases of meltwater originating from lake disna a proglacial lake linked to the fis during heinrich stadial 1 regional interactions within the climate lake fis system linked to changes in the availability of subglacial water led to abrupt drainage cycles of the fis into the bs watershed this phenomenon raised the bs water level by 100 m until the sill of the bosphorus strait was reached flooding the vast northwestern bs shelf and deeply affecting the hydrology and circulation of the bs and probably of the marmara and aegean seas

sedimentation and stratigraphy at eyjabakkajokull an icelandic surging glacier a model for sedimentation by surging glaciers is developed from analysis of the debris load sedimentary processes and proglacial stratigraphy observed at the icelandic surging glacier eyjabakkajokull three aspects of the behavior of surging glaciers explain the distinctive landformsediment associations which they may produce a sudden loading of proglacial sediments during rapid glacier advances results in the buildup of excess pore pressures failure and glacitectonic deformation of the overridden sediments b reactivation of stagnant marginal ice by the downglacier propagation of surges is associated with large longitudinal compressive stresses these induce intense folding and thrusting during which basal debris rich ice is elevated into an englacial position in a narrow marginal zone as the terminal area of the glacier stagnates between surges debris from this ice is released supraglacially and deposited by meltout and sediment flows c local variations in overburden pressure beneath stagnant crevassed ice cause subglacial lodgement tills which are sheared during surges to flow into open crevasses and form crevasse fill ridges

middle holocene mobilization of aeolian sand in western upper michigan and the potential relationship with climate and fire a forested dunefield covers the baraga plains in western upper michigan the ages of five dunes from across the dunefield were determined by optically stimulated luminescence osl employing the single aliquot regenerative dose sar method on quartz grains the results indicate that sand mobilization was restricted to the middle holocene at around 7 ka four environmental variables rapid climatic oscillations fire strong winds and a dry climate are invoked as a combined cause of dune formation this study provides further evidence for the wide extent of aeolian activity in the upper midwest of north america during the middle holocene

osl ages on glaciofluvial sediment in northern lower michigan constrain expansion of the laurentide ice sheet abstract we report new ages on glaciofluvial outwash sediment from a large upland in northern lower michigan the grayling fingers the fingers are cored with 150 m of outwash which is often overlain by the informal blue lake till of marine isotope stage mis 2 they are part of an even larger interlobate upland comprised of sandy drift known locally as the high plains the ages determined using optically stimulated luminescence osl methods indicate that subaerial deposition of this outwash occurred between 25 7 and 29 0 ka probably associated with a stable mis 2 ice margin with mean ages of ca 27 ka these dates establish a maximum limiting age of ca 27 ka for the mis 2 late wisconsin advance into central northern lower michigan we suggest that widespread ice sheet stabilization at the margins of the northern lower peninsula during this advance and later during its episodic retreat partly explains the thick assemblages of coarse textured drift there our work also supports the general assumption of a highly lobate ice margin during the mis 2 advance in the great lakes region with the fingers an interlobate upland remaining ice free until ca 27 ka

thunder bay ontario was not a pathway for catastrophic floods from glacial lake agassiz a series of airgun single channel seismic reflection profiles from thunder bay and the adjacent isle royal trough of lake superior suggest that water from glacial lake agassiz did not catastrophically drain into lake superior at this locality as has been previously suggested thunder bay is underlain by a relatively smooth bedrock surface the double bedrock sill at its mouth is not significantly incised and no subaqueous fans occur at the base of the escarpment into the superior basin the thunder bay area contains none of the features observed further north in lake superior which have been interpreted as flood related from earlier seismic surveys these previously reported northern features are interpreted as resulting from a younger post marquette catastrophic release of lake agassiz water the absence of such features in the thunder bay area suggests that lake agassiz did not drain catastrophically through the bay at the beginning of the younger dryas cold interval