Buried remnants of the Laurentide Ice Sheet and connections to its surface elevation

Abstract

The Laurentide Ice Sheet (LIS) occupied a large part of North-America during the late Pleistocene. Determining the proper surface geometry and elevation of the LIS is of central importance to estimate global changes in sea-level and atmospheric circulation patterns during the late Pleistocene and Holocene. Despite largely disappearing from the landscape during the late Holocene, LIS remnants are found in the Penny and Barnes ice caps on Baffin Island (Canada) and ongoing permafrost degradation has been exposing relics of the LIS buried along its northern margin since the late Pleistocene. Here, we use the δ18O records of six LIS remnants and the late Pleistocene δ18O-elevation relation to establish ice elevation in their source area during the last glacial maximum (LGM). Contrary to some modeled reconstructions, our findings indicate an asymmetric LIS topography with higher ice on Keewatin Dome (~3200 m) and thinner ice in the prairies along the Plains divide (1700–2100 m) during LGM. The resiliency of icy permafrost to past warm intervals preserved relics of the LIS; these ice-marginal landscapes, now poised for thaw, should uncover more valuable clues about the conditions of the last major ice sheet on Earth.

Global Isotope Hydrogeology―Review

“…Smith, Chu, et al, ). Applying methods designed to estimate groundwater recharge elevations may also help better quantify the structure and size of late‐Pleistocene ice sheets (e.g., Lacelle et al, ).…”

Thermokarst lake development in syngenetic ice-wedge polygon terrain in the Eastern Canadian Arctic (Bylot Island, Nunavut)

“…14 C-dated at 9860 yr BP, and found within ice-contact deposits (sands, gravels and pebbles) with lithological properties corresponding to the surrounding Precambrian and Cretaceous-Tertiary rocks. Lacelle et al (2018) and Coulombe et al (2019) later proposed that Laurentide ice and Bylot ice were converging in the valley. Glacial retreat was then accompanied by a marine transgression phase, associated with the deposition of silts and clays, and which lasted until about 6000 yr BP ( 14 C ages in shells at different altitudes ranging from 9860 to 6100 yr BP).…”

Thermokarst lake inception and development in syngenetic ice-wedge polygon terrain during a cooling climatic trend, Bylot Island (Nunavut), eastern Canadian Arctic

“…This interpretation is based on the presence of marine shells (Mya truncata species), 14 C dated at 9860 BP, and found within ice-contact deposits (sands, gravels and pebbles) with lithological properties corresponding to the surrounding Precambrian and Cretaceous-Tertiary rocks. Lacelle et al (2018) and Coulombe et al (2019) later proposed that Laurentide ice and Bylot ice were converging in the valley. Glacial retreat was then accompanied by a marine transgression phase, associated with the deposition of silts and clays, which lasted until about 6000 BP ( 14 C ages ranging from 9860 to 6100 BP in shells at different altitudes).…”

“…Once initiated, thermokarst lakes in continuous permafrost tend to develop laterally: first by the coalescence of polygonal and/or ice-wedge trough pools overlying melting icewedge networks (Czudek and Demek, 1970;Mackay, 2000;French, 2017) and then by thermal and mechanical shoreline erosional processes, such as wave-induced erosional niche development or mass wasting through thaw slumping and block failures (Kokelj and Jorgenson, 2013). Ultimately, and depending on local landscape conditions (e.g., soil type, vegetation cover, topography), thermokarst lake development generally ends with one or more of the following: rapid drainage resulting from shoreline breaching, either during higher-than-average lake-level episodes (e.g., Jones and Arp, 2015;Lantz and Turner, 2015;Mackay and Burn, 2002;Turner et al, 2010) or due to ice-wedge melting and thermal erosion gullying (e.g., Fortier et al, 2007;Godin and Fortier, 2012); lake-level drawdown due to factors that lead to increased evaporation (Bouchard et al, 2013a;Riordan et al, 2006); subsurface drainage (groundwater infiltration) through an open talik (Yoshikawa and Hinzman, 2003); or terrestrialization via rapid peat accumulation and lake infilling (Payette et al, 2004;Roach et al, 2011).…”