New constraints on the last deglaciation of the Cordilleran Ice Sheet in coastal Southeast Alaska

Abstract

Understanding marine-terminating ice sheet response to past climate transitions provides valuable long-term context for observations of modern ice sheet change. Here, we reconstruct the last deglaciation of marine-terminating Cordilleran Ice Sheet (CIS) margins in Southeast Alaska and explore potential forcings of western CIS retreat. We combine 27 new cosmogenic 10Be exposure ages, 13 recently published 10Be ages, and 25 new 14C ages from raised marine sediments to constrain CIS recession. Retreat from the outer coast was underway by 17 ka, and the inner fjords and sounds were ice-free by 15 ka. After 15 ka, the western margin of the CIS became primarily land-terminating and alpine glaciers disappeared from the outer coast. Isolated alpine glaciers may have persisted in high inland peaks until the early Holocene. Our results suggest that the most rapid phase of CIS retreat along the Pacific coast occurred between ~17 and 15 ka. This retreat was likely driven by processes operating at the ice-ocean interface, including sea level rise and ocean warming. CIS recession after ~15 ka occurred during a time of climatic amelioration in this region, when both ocean and air temperatures increased. These data highlight the sensitivity of marine-terminating CIS regions to deglacial climate change.

An early dog from southeast Alaska supports a coastal route for the first dog migration into the Americas

“…This date is approximately a thousand years older than current estimates [ 11 , 61 ]. While the continental, interior route between the two North American ice sheets only became biologically viable after approximately 13 000 years BP [ 17 , 18 ], the Cordilleran Ice Sheet likely rapidly retreated along the NPC, creating an ecologically viable corridor around southeast Alaska beginning at least 17 000 years ago [ 20 , 62 ], with the inner fjords and sounds ice-free by 15 000 years ago [ 22 ]. Archaeological [ 7 ] and genetic [ 3 , 4 ] evidence supports the hypothesis that the first humans migrating into the Americas used a coastal route instead of the continental route [ 5 , 18 , 63 ].…”

“…Another hypothesis is that the retreat of the Cordilleran Ice Sheet along the Northwest Pacific coast (NPC), combined with ocean levels lower than today, provided an earlier, ice-free coastal corridor for early humans and other biota [ 20 , 21 ]. Islands along the NPC, including the Alexander Archipelago in southeast Alaska, held a unique biotic diversity and were resource-viable by approximately 17 000 ago, when the Cordilleran Ice Sheet started to retreat at its westernmost edge [ 20 , 22 ]. This timing is roughly contemporaneous with the genetic evidence for the first human migration wave into the New World [ 5 , 15 , 18 , 20 ], and consistent with genetic data that suggest dogs had already been domesticated.…”

Whole‐genome resequencing reveals persistence of forest‐associated mammals in Late Pleistocene refugia along North America’s North Pacific Coast

“…Bathymetry (Carrara et al, 2003(Carrara et al, , 2007 and palynology (Ager, 2019;Barrie et al, 1993;Mann & Hamilton, 1995) support the persistence of refugia of varying complexities. Cosmogenic exposure dating has shed recent doubt on hypothesized refugial locations (Lesnek et al, 2018(Lesnek et al, , 2020, although many small refugia may remain unsampled, potentially located further west on the continental shelf only exposed during lower sea levels. Consistent signatures of refugial persistence across taxa (Colella, Lan, et al, 2018;Foster, 1965;Heaton et al, 1996;Hewitt, 2000Hewitt, , 2003Sawyer et al, 2019;Slager et al, 2020;Weckworth et al, 2005), now including martens, and the rapid colonization of previously glaciated regions following glacial recession support the persistence of complex and taxonomically diverse refugial communities along the coast during the LGM and perhaps earlier glacial advances.…”

Late Quaternary sea level, isostatic response, and sediment dispersal along the Queen Charlotte fault

“…A minimum ice thickness of 400 m is suggested for some shelf areas (Josenhans et al, 1995;Barrie and Conway, 1999), and an ~690 m thickness is suggested in the northern Hecate Strait and Dixon Entrance . Off southeastern Alaska, ice is considered to have reached the shelf break, particularly down the sea valleys such as Chatham Strait, though many areas off the Alexander Archipelago (Prince of Wales and Baranof Islands) are considered to never been Research Paper glaciated, similar to Haida Gwaii (Kaufman and Manley, 2004;Carrara et al, 2007;Lesnek et al, 2018Lesnek et al, , 2020Brothers et al, 2020). Glaciation reached its maximum extent sometime after 23.0 ka (Blaise et al, 1990).…”

“…Ice had largely left the lowlands and offshore region by 14.5-13.0 ka (Barrie and Conway, 1999;. Off southeast Alaska, the initial retreat of marine-terminating ice margins from their maximum extent was driven by factors acting on the ice-ocean interface, including sea-level rise and ocean warming, leading to intense ice loss via calving in the early stages of deglaciation (Lesnek et al, 2018(Lesnek et al, , 2020.…”