Wisconsin Ice Research Articles

Laurentide Ice Sheet configuration in southern Ontario, Canada during the last glaciation (MIS 4 to 2) from stratigraphic drilling and LIDAR-based surficial mapping

Regional subsurface mapping of glacial depositional systems preserved in buried bedrock paleovalleys, and quantitative analysis of new LiDAR imagery of surface glacial landforms using machine learning techniques, when combined, are powerful tools for assessing the dynamics of the Laurentide Ice Sheet (LIS) during the last (Wisconsinan) glaciation in southern Ontario. While age dating of deposits preserved below Last Glacial Maximum tills (LGM: marine isotope stage (MIS) 2 < c.24 000 years B.P. (ybp)) is still sparse, newly available sedimentological data derived by cored drilling, combined with legacy outcrop data, identify thick (100 m+) successions of glaciolacustrine sediments and a lack of till(s), indicating that the ice sheet margin did not extend beyond the Niagara Escarpment at the western end of Lake Ontario, during the earliest phases of the glaciation (MIS 4) or the ensuing mid-Wisconsinan (MIS 3). Ice was able to extend into New York State blocking the Rome outlet to the Hudson Valley ponding deep proglacial lakes in the glacio-isostatically depressed Huron–Ontario–Erie basins recorded by thick glaciolacustrine sediments in paleovalleys. These were cannibalized by an expanding Late Wisconsinan ice sheet after ∼24 000 ybp recorded by extensive till sheets resting on a marked erosional unconformity, with drumlinized surfaces. Analysis and visualization of LiDAR data identifies discrete statistically validated flow sets of highly elongated streamlined bedforms (mega-scale glacial lineations (MSGLs)). These provide key evidence of a major reorganization of the ice sheet margin during deglaciation into lobate paleo ice streams shortly after 17 400 ybp. MSGLs are cut across earlier LGM drumlinized tills creating widespread “palimpsest” surfaces. At least two principal phases of fast ice flow can be identified, marked by large fluxes of sediment and the rapid building of large gravel and sand-dominated moraine complexes within interlobate depocentres, the largest glacial landforms in southern Ontario. Analysis of LiDAR data further reveals the common presence of DeGeer moraines where ice margins retreated in water, and iceberg scours. Future work using LiDAR mapping has the objective of fully documenting the number, extent, and timing of ice streams to enhance glaciological modelling when the ice sheet rapidly lost mass.

Where ice gave way to fire: deglacial volcanic activity at the edge of the Coast Mountains in Milbanke Sound, BC

Kitasu Hill and MacGregor Cone formed along the Principe Laredo Fault on British Columbia’s central coast as the Wisconsinan ice sheet withdrew from the Coast Mountains. These small-volume Milbanke Sound Volcanoes (MSV) provide remarkable evidence for the intimate relationship between volcanic and glacial facies. The lavas are within-plate, differentiated (low MgO < 7%) Ocean Island Basalts, hawaiites, and mugearites that formed from ∼1% decompression melting of asthenosphere with residual garnet. Kitasu Hill, on glaciated bedrock, formed between 18 and 15 cal ka BP. Dipping, poorly stratified, admixed hyaloclastite, and glacial diamicton with large plutonic clasts and pillow breccia comprise its basal tuya platform (0–43 masl). Subaerial nested cinder cones, with smaller capping lava flows, sit atop the tuya. New marine samples show McGregor Cone formed subaerially but now sits submerged at 43–200 mbsl on an eroded moraine at the mouth of Finlayson Channel. Seismic data and cores reveal glaciomarine sediments draping the cone’s lower slopes and show beach terraces. Cores contain glaciomarine diamictons, ice-rafted debris, delicate glassy air fall tephra, and shallow, sublittoral, and deeper benthic foraminifera. Dates of 14.1–11.2 cal ka BP show volcanism spanned ∼2000 years during floating ice shelf conditions. The MSV have similar proximal positions to the retreating ice sheet, display mixed volcano-glacial facies, and experienced similar unloading stresses during deglaciation. The MSV may represent deglacially triggered volcanism. The dates, geomorphic and geological evidence, constrain a local relative sea level curve for Milbanke Sound and show how ice gave way to fire.

Conservation Genetics of Lake Sturgeon (Acipenser fulvescens): Nuclear Phylogeography Drives Contemporary Patterns of Genetic Structure and Diversity

Sustainable management of exploited and endangered species is facilitated by knowledge of their geographic genetic structure. Lake sturgeon (Acipenser fulvescens) epitomizes both categories, but genetic information has largely been limited to the Laurentian Great Lakes basin. We assessed the hierarchical geographic genetic structure of lake sturgeon across their Canadian range using a variation at 14 microsatellite loci. Observed patterns showed evidence of two ancestral groups which originated from Mississippian and Missourian glacial refugia. Coalescent analysis indicates the two lineages most recently shared common ancestry during the late Pleistocene and were likely isolated by the late Wisconsinan ice advance, with subsequent interpopulation divergences within each lineage reflecting their reciprocal isolation as glacial meltwaters receded. Hierarchical patterns of genetic relationships among contemporary populations largely reflect colonization histories and connections within primary and secondary watersheds. Populations in western Canada showed strong similarities based on their shared Missourian origins and colonization from glacial Lake Agassiz. By contrast, populations in the Great Lakes–St. Lawrence River drainage were largely founded from a Mississippian source. Sturgeon populations in northern parts of Ontario and Quebec showed evidence of mixed ancestry from secondary contact between the two refugial groups through Holocene meltwater lakes. Within major watersheds, the strong similarity among geographically separate populations reflects their shared ancestry during postglacial colonization. The general lack of structure within major river systems highlights historically continuous habitat (connectivity) and gene flow rather than contemporary barriers (dams). These data highlight the importance of Quaternary and prehistoric events on patterns of genetic diversity and divergence within and among contemporary populations, as well as the importance of these populations for conserving the species’ evolutionary legacy.

Post‐Pleistocene dispersal explains the Rapoport effect in North American salamanders

AbstractAimsIn many taxa, the latitudinal span of species' geographic ranges are positively correlated with median latitude (the Rapoport effect). This correlation is frequently explained as adaptation to contemporary climate; however, variability in post‐glacial range expansion among species could also explain this observation. We analyse geographic data for North American salamanders to test the potential causes of Rapoport effects.LocationTemperate North America.TaxonSalamanders (order Caudata).MethodsWe tested for a Rapoport effect by estimating correlations between the latitudinal midpoint and latitudinal range among species. Next, we manipulated species' latitudinal ranges by removing post‐glacial habitat and assessing the impact of species demonstrating post‐glacial range expansion in forming a Rapoport effect. We built ecological niche models for species found south of the Wisconsin Ice Sheet during the Last Glacial Maximum and transferred these models to post‐glacial areas. If dispersal is important in forming a Rapoport effect, then some species may tolerate northern climates but have not expanded northward as a result of variation in geographic access to post‐glacial habitats. We created binary ecological niche models by thresholding using the equal sensitivity and specificity value.ResultsWe recovered a Rapoport effect that was robust to the null models we tested. Analyses that manipulated ranges and species pools supported a role for variation in post‐glacial range expansion among species, especially for eastern North America. Results from transferring ecological niche models indicated that species have suitable habitat north of their range limit.Main conclusionsVariation in post‐glacial range expansion is important in shaping geographic range size clines among species in areas where climates changed rapidly, though we also found support for the climatic variability hypothesis. Post‐glacial colonization and range expansion likely plays an important role in forming latitudinal biodiversity gradients in northern taxa. While ecophysiology and biotic interactions have been emphasized as important contributors to diversity gradients, our study indicates that post‐glacial colonization also plays a key role in forming latitudinal gradients.

Phylogeography of moose in western North America

AbstractSubspecies designations within temperate species’ ranges often reflect populations that were isolated by past continental glaciation, and glacial vicariance is believed to be a primary mechanism behind the diversification of several subspecies of North American cervids. We used genetics and the fossil record to study the phylogeography of three moose subspecies (Alces alces andersoni, A. a. gigas, and A. a. shirasi) in western North America. We sequenced the complete mitochondrial genome (16,341 base pairs; n = 60 moose) and genotyped 13 nuclear microsatellites (n = 253) to evaluate genetic variation among moose samples. We also reviewed the fossil record for detections of all North American cervids to comparatively assess the evidence for the existence of a southern refugial population of moose corresponding to A. a. shirasi during the last glacial maximum of the Pleistocene. Analysis of mtDNA molecular variance did not support distinct clades of moose corresponding to currently recognized subspecies, and mitogenomic haplotype phylogenies did not consistently distinguish individuals according to subspecies groupings. Analysis of population structure using microsatellite loci showed support for two to five clusters of moose, including the consistent distinction of a southern group of moose within the range of A. a. shirasi. We hypothesize that these microsatellite results reflect recent, not deep, divergence and may be confounded by a significant effect of geographic distance on gene flow across the region. Review of the fossil record showed no evidence of moose south of the Wisconsin ice age glaciers ≥ 15,000 years ago. We encourage the integration of our results with complementary analyses of phenotype data, such as morphometrics, originally used to delineate moose subspecies, for further evaluation of subspecies designations for North American moose.

Morphological Variability among Spawning Populations of Bering CiscoCoregonus laurettae

Bering Cisco Coregonus laurettae is an anadromous coregonine species known almost exclusively from northwestern North America and with only three documented spawning populations, all in Alaska. Previous studies of Bering Cisco phenotypic variation examined individuals collected primarily in coastal rearing habitats where population affiliation was not known. Here we compare meristic counts and morphometric ratios of pre-spawning adults among the three known populations: one each in the Yukon, Kuskokwim, and Susitna rivers in Alaska. We also compare meristic data with those previously reported for this species. Populations in the Yukon and Kuskokwim rivers were very similar, while the population in the Susitna River was significantly divergent for certain meristic counts and morphometric ratios. Our findings are consistent with recent genetic analyses that found the Susitna River population to be the most divergent of the three populations. While the Yukon and Kuskokwim river populations survived the Wisconsinan Ice Age in the Beringian Refugium, the Susitna River population colonized the drainage following ice retreat sometime in the last few thousand years. The population's divergence from the source population in the Yukon or Kuskokwim river could be due to a founder effect or adaptation to different environmental conditions.

Drumlinized tunnel valleys in south-central Ontario

A network of Late Wisconsin valleys deeply incise thick successions (up to 200 m) of Quaternary sediment and Paleozoic bedrock across south-central Ontario. The valleys have previously been interpreted as an integrated network of tunnel channels recording catastrophic releases of subglacial meltwater across the bed of the Laurentide Ice Sheet (LIS). Recent geologic investigations in the western part of the valley network integrate information gained from surficial sediment and landform mapping, continuously-cored boreholes that penetrate the entire Quaternary sediment succession in valleys as well as intervening uplands, and both water-borne and land-based geophysical surveys. Together, these data provide new insights and a refined interpretation of the genesis, timing and paleoglaciological significance of these valleys.Valleys within the study area are some of the largest observed within the regional network – up to 30 km long, 7 km wide and >175 m deep. They are oriented both north-south and in a radial pattern, varying from NE-SW in the southern part of the study area, to ESE-WNW in the north. An undulating Late Wisconsin till sheet (Newmarket Till) caps the regional uplands and is commonly observed along the flanks and floors of the valleys – all of which show evidence of a drumlinization phase that postdates excavation of most of the valleys. At least two generations of valleys are interpreted from cross-cutting relationships, with abrupt heads and locally perched downflow ends of some valley forms. Radiocarbon age determinations of organic material from both below and above the Newmarket Till constrain the timing of valley excavation to between 28.05 and 12.81 14C kyr BP. Borehole and outcrop data within the valleys reveal four stratigraphic units (SU1-SU4) that form the floor and sediment infill of the valleys. The Newmarket Till (SU1) is commonly underlain by deformed substrates. The till is absent in parts of some valleys and the lowermost parts of the valley fill commonly consist of coarse-grained gravels (SU2) that pass upwards into sands (SU3). The bulk of the sediment infill consists of glaciolacustrine silt-clay rhythmites (SU4) that pass upwards into organic- and mollusk-bearing nearshore and fluviodeltaic deposits that record drainage of proglacial lakes from the study area during deglaciation.It is proposed that these features are a previously unrecognized type of tunnel valley that developed subglacially during Late Wisconsin ice cover. Meltwater surpluses would be generated at the ice-bed interface due to the low-transmissivity substrate in the study area with flow preferentially routed into lows on the bed. Downward incision into confined and pressurized aquifers likely facilitated rapid headward erosion of the valleys enhanced by piping. Waning meltwater flow velocities/discharges allowed ice creep to re-occupy newly-formed valleys permitting renewed till deposition and subsequent drumlinization of the valleys. The valleys also provided efficient routing for meltwater draining the retreating ice marginal zone during deglaciation and allowed localised sand and gravel deposition as eskers and ice-proximal subaquatic fans in the Oak Ridges Moraine and within proglacial lakes that developed during ice retreat. However, there is no evidence for regional-scale catastrophic release of subglacial meltwater in the valley infills. This integrated dataset represents one of the most complete characterizations of subglacial valleys in a terrestrial setting in North America.

Global warming and cooling: friend and foe to mankind.

The Supernova and Nova Impact Theory, SNIT, proposes correlation between the right ascension locations of supernova remnants at the time of impact with respect to locations of red sand deposits and major oil fields indicating that the sand and oil fields are scars of the impact of the debris stream on our planet. The supernovas aiding the melt of the Wisconsin Glaciations ice caps also produce deep hydrocarbon deposits in the mantle forming many of the world’s oil producing areas. A Specific mega event forms the Fertile Crescent and is correlated with an exit crater of an interstellar meteor that penetrates and exits the earth’s mantle while forming the mud volcanic basin of the Black Sea. The Monogem Ring Supernova causes the beginning of the Wisconsin Ice Age by placing iron deposits in the eastern Pacific Ocean via its western terminus locations and the eastern terminus locations are suggested by high quality iron ore and manganese deposits on land in Eurasia, Africa, and the Cook Islands. SN 1006’s deflected north western termini begins in the Greenland region and moves to the southeast to cause death via hotspots during 2014-2016 in Kazakhstan, India, and Pakistan. Grouped lower Alaskan average temperatures in the winter of 2016 are an indicator of the end of the drought in California. The impacts of supernovas 1054 and 1006 are marked by an out of season tornado outbreak in November 2005 and the record tornado outbreak in April 2011, respectively.

Seafloor features delineate Late Wisconsinan ice stream configurations in eastern Parry Channel, Canadian Arctic Archipelago

Multibeam imagery and 3.5 kHz sub-bottom profiles acquired from CCGS Amundsen between 2003 and 2013 by ArcticNet and the Ocean Mapping Group at the University of New Brunswick provide information on seafloor features, geology, bathymetry and morphology in eastern Parry Channel and the adjoining large channels in the Canadian Arctic Archipelago. Together these include Peel Sound, Barrow Strait, Lancaster Sound, Wellington Channel, Prince Regent Inlet, Admiralty Inlet and Navy Board Inlet. Those data are in part complemented by high resolution single channel seismic reflection profiles acquired by the Geological Survey of Canada in the 1970s and 1980s and by sediment cores that provide chronological and depositional information.The occurrence and pattern of streamlined mega-scale ridge and groove lineations (MSGLs) indicate that these waterways were occupied by glacial ice streams in the past. Chronological information from marine and adjoining terrestrial areas suggests a long history of glacial events ranging in time from Early Pleistocene to Late Wisconsinan. Seafloor morphology and MSGL trends together with terrestrial ice flow patterns indicate that ice streams flowed into Barrow Strait from Peel Sound and Wellington Channel, and ice streams in Prince Regent, Admiralty and Navy Board inlets flowed northward into and eastward along Lancaster Sound. Recession of the ice stream westward along Parry Channel occurred ∼16 cal ka BP to 10.8 cal ka BP. Thick ice-contact sediments deposited by a late ice advance from Prince Regent Inlet constitute the seabed across a large area of western Lancaster Sound. Timing for that late ice advance appears to be bracketed between the 11.5 cal ka BP lift-off of the eastern Parry ice stream north of Prince Leopold Island and the ∼10.0 cal ka BP deglaciation of Prince Regent Inlet. Seafloor morphology and lineation trends suggest that ice delivered by the ice stream in Peel Sound was the westernmost tributary to the ice stream occupying Lancaster Sound during the late Wisconsinan glaciation. Bathymetric data and MSGLs indicate that the ice stream emanating from M'Clintock Channel flowed westward.

The North American Late Wisconsin ice sheet and mantle viscosity from glacial rebound analyses

Observations of sea level and crustal response to glacial loading cycles provide constraints on the mantle rheology function, E, and as well as on the ice load, I, with the latter being largely free from a-priori glaciological or climate assumptions and appropriate, therefore, for testing any such hypotheses. This paper presents new results for both continental-mantle E and I for the Late Wisconsin ice sheet, using geological evidence for relative sea-level change (rsl) and tilting of palaeo-lake shorelines, complemented with loose constraints from observations of present-day radial crustal displacement across North America. The focus is on evidence from near or within the former maximum ice margins and the resulting earth response is representative of sub-continental mantle conditions. The inversion of the sea-level information has limited resolution for earth rheology and simple three-layer models, characterized by depth-averaged effective lithospheric thickness (H) and upper- and lower-mantle viscosities (ηum and ηum respectively) adequately describe the response function, yielding parameters (earth model E-6) of H = 102 (85–120) km, ηum = 5.1 × 1020 (3.5–7.5)x1020, ηlm = 1.3 × 1022 (0.8–2.8)x1022 where the numbers in parenthesis are 95% confidence limits. The details of the ice sheet, with one exception, are not strongly dependent on the rheological assumptions within this range. The exception is the lower mantle viscosity that remains correlated with the magnitude scaling of the ice sheet: a link that is largely broken by introducing constraints from glacial loading effects on the Earth's rotation and dynamic flattening. The difference between the continental ηum and the comparable estimate of (1–2.5)x1020 for ocean mantle is statistically significant. Shoreline gradient information from Glacial Lakes McConnell, Agassiz, Algonquin and Ojibway provide strong constraints on the response within the interior of the ice sheet and the resulting ice sheet model (LW-6) is characterized by multiple ice domes from at least ∼17–18 ka onwards. The resolution for earlier periods is largely constrained by global ice volume considerations. The two principal domes are over southern Nunavut (the Keewatin Dome) and over Québec-Labrador, both of ≥3500 m thickness, separated by an ice ridge some 1500 m lower than the domes, the latter a requirement imposed by the gradient information. Over western Canada ice thickness gradients east of the Cordilleras are partly constrained by the shoreline data for former Lake McConnell (as is the lateglacial ice thickness of the Keewatin dome) and indicate that any ice-free corridor between the Laurentian and Cordilleran components is unlikely to have existed before ∼13ka. Reconstructions of the glacial lakes are consistent with the locations and timing of the observational evidence for the four major lake systems with the likely drainage routes identified. The evolution of the LW-6 ice-volume function, expressed as equivalent sea level, is characterized by a rapid decrease in ice volume from ∼15 to 14.5 ka, corresponding to the Bølling-Allerød period, in the main from rapid ice retreat along the southern margin, with further contributions from drainage through the St Lawrence River valley and from ice retreat from the major northern straits and gulfs, but not Hudson Strait where the rsl data point to late removal of ice (after 10 ka). The contribution of the drainage of the lakes to global sea level rise is small, < 1 m at the end of 9 ka, with final drainage of the Agassiz, Algonquin and Ojibway lakes occurring through Hudson Strait. The comparison of model predictions based on the above model parameters are, with one exception, consistent with observed GPS rates but do indicate a differential offset between the origins of the geodetic and geophysical reference frames, with the geodetic frame moving relative to the geophysical frame in direction approximately parallel to the earth's rotation axis.

Uncovering the hidden part of a large ice stream of the Laurentide Ice Sheet, northern Ontario, Canada

Abstract This investigation was prompted by an enigmatic ice-flow anomaly (Area A) on the Glacial Map of Canada which covers about 10 000 km 2 in the Hearst/Kapuskasing area of northeastern Ontario. It consists of streamlined landforms and striations indicative of a major ice flow toward 130° oriented at right angle to another toward 220°. Both are late glacial flows but long-lasting disagreement exists regarding their relative age. The analysis of aerial photographs and satellite images in conjunction with a detailed survey of bedrock cross-striated surfaces over an area of about 30 000 km 2 within and around Area A clearly indicate that the 130° flow preceded the 220° flow. The earlier conflicting interpretations within Area A are attributed mainly to the sporadic occurrence of relict striated surfaces formed by older southwestward (220°–240°) Wisconsinan ice flows that have locally escaped destruction by late glacial flows, with the result that the southwestward flows are older (Wisconsinan) at some sites and younger (late glacial 220°) at others relative to the 130° flow. When considered with other factors such as the maximum elevation reached by the youngest late glacial flow, these ice-flow relationships indicate that Area A is the outcropping southern part of a much larger ESE ice-flow system, which is probably related to a large fluted belt located to the north and that was identified as the Winisk Ice Stream. The distal part of the ice stream, except for Area A, escaped detection by remote sensing mapping methods because depositional and erosional features associated with it are masked by deposits laid down by the younger (220°, Cochrane) ice flow and/or by postglacial marine and organic deposits (or were destroyed by the younger ice flow). The only reliable indicators of the passage of the ice stream in this “buried” section are ESE relict striations crossed by SW striations. The advancing ice stream toward the ESE not only preceded the late Cochrane 220° flow but probably outlasted it, as suggested by the mapping of several thousand iceberg furrows in Quebec and Ontario, also directed toward the ESE and overprinted on flutes formed by the last glacial flow. If this interpretation is correct, this makes the Winisk Ice stream the largest terrestrial ice stream in the Hudson Bay basin. An alternative interpretation associates this fluted belt to the exposed western fringe of streamlined bedforms from a late Hudson lobe buried by younger sediments.

A subglacial landform assemblage on the outer shelf of M'Clure Strait, Canadian Arctic, ploughed by iceberg keels

M'Clure Strait in the Canadian Beaufort Sea (Fig. 1) is one of the largest cross-shelf troughs in the High Arctic, with a length of over 1000 km and a maximum cross-trough width of about 250 km (Batchelor & Dowdeswell 2014). It is thought to be the former location of a fast-flowing ice stream which drained the northwestern Laurentide Ice Sheet during the Late Wisconsinan, and probably a number of earlier Quaternary full-glacial periods (Stokes et al. 2006, 2009; Niessen et al. 2010; Batchelor et al. 2013). The Late Wisconsinan ice stream in M'Clure Strait is interpreted to have extended to the shelf break between 21–16 ka before undergoing rapid retreat (Stokes et al. 2009). Low rates of postglacial sedimentation have led to the preservation of an unusual assemblage of cross-cutting glacigenic landforms on the seafloor of outermost M'Clure Strait (Fig. 1). Fig. 1. ( a ) Swath bathymetry of the outer shelf of M'Clure Strait, Arctic Canada, superimposed on IBCAO v. 3.0 bathymetry (5 m contours). Multibeam acquisition system Kongsberg EM302. Frequency 30 kHz. Grid-cell size 10 m. Dashed line D indicates that the linear ridge-and-groove structures are probably continuous either side of the data gap. ( b ) Location of the study area (red box; map from IBCAO v. 3.0). MS, M'Clure Strait. ( c ) Schematic diagram showing the interpreted distribution of submarine landforms on the seafloor of M'Clure Strait which is described in the text. The probable direction of former ice flow is shown by a black arrow. The outer-shelf of M'Clure Strait contains several sets of landforms: linear ridge-and-groove structures, sinuous ridges, a wide trough-parallel ridge and three types of linear to curvilinear depressions. Multibeam imagery of the landforms is shown in Figure 1, together with a map of their distribution. Linear ridge-and-groove structures have an east–west orientation, parallel …

Late Wisconsinan ice sheet flow across northern and central Vermont, USA

A compilation of over 2000 glacial striation azimuths across northern and central Vermont, northeastern USA, provides the basis for interpreting a sequence of ice flow directions across this area. The oldest striations indicate widespread ice flow to the southeast, obliquely across the mountains. Similarly oriented striations between northern Vermont and the ice sheet's terminus in the Gulf of Maine suggest that a broad area of southeast ice flow existed at the Last Glacial Maximum. Younger striations with more southerly azimuths on both the mountain ridgelines and within adjacent valleys indicate that ice sheet flow trajectories in most areas rotated from southeast to south, parallel to the North–South alignment of the mountains, as the ice sheet thinned. This transition in ice flow direction was time transgressive from south to north with the Green Mountains eventually separating a thick south-flowing lobe of ice in the Champlain Valley from a much thinner lobe of south-flowing ice east of the mountains. While this transition was taking place yet ice was still thick enough to flow across the mountains, ice flow along a narrow ∼65 km long section of the Green Mountains shifted to the southwest such that ice was flowing into the Champlain Valley. The most likely process driving this change was a limited period of fast ice flow in the Champlain Valley, a short-lived ice streaming event, that drew down the ice surface in the valley. The advancing ice front during this period of fast ice flow may be responsible for the Luzerne Readvance south of Glens Falls, New York. Valley-parallel striations across the area indicate strong topographic control on ice flow as the ice sheet thinned.

New marine evidence for a Late Wisconsinan ice stream in Amundsen Gulf, Arctic Canada

Amundsen Gulf and adjoining Dolphin and Union Strait and Coronation Gulf form the southwestern end of the Northwest Passage adjacent to the Beaufort Sea. Extensive high resolution multibeam sonar imagery and sub-bottom profiles of the seabed have been acquired, primarily in Amundsen Gulf, by ArcticNet and the Ocean Mapping Group at the University of New Brunswick. These data reveal a variety of seabed landforms including mega-scale glacial ridge and groove lineations, drumlins, moraines, iceberg scours, bedrock outcrops, and discontinuous sediment deposits of variable thickness. The lineations are widespread, especially in southeastern Amundsen Gulf. They resemble modern and paleo bedforms reported from Antarctica, Svalbard, Greenland and other Canadian Arctic channels, where they have been ascribed to ice streams.The glacial sole marks on the seabed in Amundsen Gulf and regional data from the adjacent mainland and islands outline the configuration of a glacial ice stream from the Laurentide Ice Sheet that occupied Amundsen Gulf and adjoining waterways during the Late Wisconsinan. Part of the northwestward flowing ice stream was deflected around the Colville Mountains on Victoria Island and rejoined the main ice stream in Amundsen Gulf by way of Prince Albert Sound. The grounded Amundsen Gulf ice stream extended northwestward to the outer slope in the Beaufort Sea where it was buttressed by Arctic Shelf Ice. Maximum ice stream extent is inferred to have been coincident with the Late Glacial Maximum. Multi-sequence ice-contact sediments and stratigraphic relations with glaciomarine sediments indicate that several ice advances and retreats occurred in the northwestern part of the gulf. Final retreat from the maximum position began prior to 13,000 cal yr BP and terrestrial dates indicate that the retreating ice front had reached Dolphin and Union Strait by about 12.5 cal ka BP.

Expanded Late Wisconsinan ice cap and ice sheet margins in the western Queen Elizabeth Islands, Arctic Canada

Recent mapping of surficial geology and geomorphology in the western Canadian High Arctic (Melville and Eglinton islands), together with new radiocarbon dates acquired from ice-contact raised marine sediments, document expanded late Wisconsinan ice limits for the northwest Laurentide Ice Sheet and the western Innuitian Ice Sheet. An extension of the northwestern margin of the Laurentide Ice Sheet onto Eglinton Island is proposed based on evidence from till containing erratics derived from the Canadian Shield and a pattern of meltwater channels indicating ice retreat offshore into M'Clure Strait. Expansion of the western Melville Island Ice Cap (part of the western, lowland sector of the Innuitian Ice Sheet) to its offshore late Wisconsinan limit was facilitated by coalescence with the Laurentide Ice Sheet, whose buttressing allowed thickening to occur. Estimates of ice extent and thickness (>500 m) of the western Melville Island Ice Cap are in agreement with high marine limits (≤70 m asl). Lateral and proglacial meltwater channels, moraines and glaciomarine, glaciolacustrine and glaciofluvial deposits indicate radial retreat of the western Melville Island Ice Cap onto central highlands after ∼13.0 cal ka BP. Older marine limit shorelines on southern Eglinton Island (∼13.6 cal ka BP) are broadly synchronous with the early and rapid deglaciation of other areas formerly glaciated by the northwestern Laurentide Ice Sheet to the southeast and southwest (∼14.2–13.6 cal ka BP). The collapse of the northwest Laurentide Ice Sheet in M'Clure Strait beginning at ∼14.2 cal ka BP, in addition to prior inferred thinning, opens the possibility that it made a significant contribution to meltwater pulse 1A.

Measurements and numerical simulation of fabric evolution along the Talos Dome ice core, Antarctica

We present measurements of fabrics and microstructures made along the Talos Dome ice core, a core drilled in East Antarctica in the framework of the TALDICE project. Fabric and average grain size data are analyzed regarding changes in climatic conditions. In particular, the fabric strength increases sharply going downward from Holocene to Wisconsin ice. Following (Durand et al., 2007), this change is associated with a positive feedback between variations in ice viscosity, due to variations in dust content, and the impact of a shear stress component, increasing with depth. A ViscoPlastic Self-Consistent modeling approach is used to simulate the fabric evolution for a “perfect dome” configuration. The discrepancies between the measured and the simulated fabrics highlight the depth ranges where shear strongly affects the fabric strengthening. Finally, the grain size and fabric analyses show the occurrence of dynamic recrystallization mechanisms (continuous and discontinuous) along the core.

Homotherium serum and Cervalces from the Great Lakes Region, USA: geochronology, morphology and ancient DNA

A scimitar‐toothed cat (Homotherium serum) and stag moose (Cervalces sp.) are described from Tyson Spring Cave, Fillmore County, Minnesota. These specimens represent the first records of both species in the state, and the first record for H. serum in the Great Lakes region. Although the Cervalces specimen remains undated, it shares features with pre‐Wisconsin specimens from the eastern Great Plains. The H. serum individual dates to c. 26.9 ka, when the Wisconsin ice margin was less than 60 km away. Genetic analyses support the identity of the Homotherium specimen as conspecific with Homotherium serum found in older Beringian deposits, as well as both the early divergence of tribes Homotherini and Smilodontini within Machairodontinae and the early divergence of this Machairodontinae from the lineage that produced extant cats.

Eastern Beringia and beyond: Late Wisconsinan and Holocene landscape dynamics along the Yukon Coastal Plain, Canada

Terrestrial permafrost archives along the Yukon Coastal Plain (northwest Canada) have recorded landscape development and environmental change since the Late Wisconsinan at the interface of unglaciated Beringia (i.e. Komakuk Beach) and the northwestern limit of the Laurentide Ice Sheet (i.e. Herschel Island). The objective of this paper is to compare the late glacial and Holocene landscape development on both sides of the former ice margin based on permafrost sequences and ground ice. Analyses at these sites involved a multi-proxy approach including: sedimentology, cryostratigraphy, palaeoecology of ostracods, stable water isotopes in ground ice, hydrochemistry, and AMS radiocarbon and infrared stimulated luminescence (IRSL) dating. AMS and IRSL age determinations yielded full glacial ages at Komakuk Beach that is the northeastern limit of ice-free Beringia. Herschel Island to the east marks the Late Wisconsinan limit of the northwest Laurentide Ice Sheet and is composed of ice-thrust sediments containing plant detritus as young as 16.2calkaBP that might provide a maximum age on ice arrival. Late Wisconsinan ice wedges with sediment-rich fillings on Herschel Island are depleted in heavy oxygen isotopes (mean δ18O of −29.1‰); this, together with low d-excess values, indicates colder-than-modern winter temperatures and probably reduced snow depths. Grain-size distribution and fossil ostracod assemblages indicate that deglaciation of the Herschel Island ice-thrust moraine was accompanied by alluvial, proluvial, and eolian sedimentation on the adjacent unglaciated Yukon Coastal Plain until ~11calkaBP during a period of low glacio-eustatic sea level. The late glacial–Holocene transition was marked by higher-than-modern summer temperatures leading to permafrost degradation that began no later than 11.2calkaBP and caused a regional thaw unconformity. Cryostructures and ice wedges were truncated while organic matter was incorporated and soluble ions were leached in the thaw zone. Thermokarst activity led to the formation of ice-wedge casts and deposition of thermokarst lake sediments. These were subsequently covered by rapidly accumulating peat during the early Holocene Thermal Maximum. A rising permafrost table, reduced peat accumulation, and extensive ice-wedge growth resulted from climate cooling starting in the middle Holocene until the late 20th century. The reconstruction of palaeolandscape dynamics on the Yukon Coastal Plain and the eastern Beringian edge contributes to unraveling the linkages between ice sheet, ocean, and permafrost that have existed since the Late Wisconsinan.

End of the Pleistocene: elk-moose (Cervalces) and caribou (Rangifer) in Wisconsin

Fossils of caribou (Rangifer tarandus) and elk-moose (Cervalces scotti) were found in a Wisconsinan–Holocene outwash bog on Kluck Farm, near Bevent, Marathon County, Wisconsin. These caribou fossils are the northernmost records for the state, and the extinct Cervalces the 1st known from the state and northernmost record for the species. The site is located at the mapped ice front of the Green Bay Lobe of the late Wisconsinan Valder's Readvance, which was present between 12,500 and 11,500 years before present. Examination of accelerator mass spectrometry 14C data indicated that the elk-moose was older than the caribou by 1,6000–1,700 years. Matching the radiocarbon dates with those of nearby sites and to their pollen records helps to clarify the nature of climatic conditions and corresponding plant communities at the upper Pleistocene boundary. The pattern of replacement of taiga forest southward and westward of the Green Bay Lobe to warmer, open-range conditions, with invading prairie, pine (Pinus), and deciduous trees, resembles changes that took place earlier, when glaciers and cool climate occurred south of the late Wisconsinan ice fields. Perhaps cursorial carnivores preyed on the large cervids, which were made more visible in openings of the taiga and grassland and by the typical succession expected of boreal wetlands to dry prairie or park-like savanna copses of spruce (Picea), oak (Quercus), and pine.

Floodplain width adjustments in response to rapid base level fall and knickpoint migration

Geomorphology has long been engaged in characterizing the form and understanding the evolution of floodplains. This study primarily examines floodplain width in four tributaries to the Minnesota River in southern Minnesota, namely the Maple, Le Sueur, and Blue Earth Rivers and Seven Mile Creek. The tributary systems are relatively young, having formed after retreat of the Wisconsinan ice sheet, and are rapidly evolving in response to a base level fall of nearly 70 m–13,400 YBP. As a result, the lower reaches of all four river channels are aggressively incising. This study applies a new, freely available, open-code plug-in for ArcGIS to measure floodplain width as a function of elevation above the geomorphic top of bank. Systematic changes are observed in all four systems. Above the steep, incising knickzone reaches of each of the tributaries, relatively wide, and mostly unconfined, floodplains are observed. Within the knickzone, floodplains progressively narrow to between 25–60% of their width above the knickzone, despite the fact that sediment loads increase significantly in the downstream direction. A power law relationship is consistently observed between floodplain width and the ratio of local channel slope to contributing drainage area to about the negative one-third power in all four rivers. This same power law relationship is observed for two other rivers that differ significantly from our study systems in climatic and tectonic environment as well as base level history.