Late Pleistocene mountain glaciation in Alaska: key chronologies

Abstract

Moraine sequences of mountain glaciers can be used to infer spatial and temporal patterns of climate change across the globe. Alaska is an accessible high-latitude location in the Northern Hemisphere and contains a rich record of alpine glaciation. Here, we highlight the key chronologies from three mountain ranges in Alaska that reveal the timing and spatial extent of Late Pleistocene glaciation, and pay particular attention to age of the penultimate glaciation. The most extensive glacier advance of the last glaciation occurred prior to the last global glacial maximum. Cosmogenic exposure ages from moraine boulders in three sites spanning 800 km indicate that this penultimate advance most likely culminated during marine isotope stage (MIS) 4 or early MIS 3. During MIS 2, more limited glacier expansion generated multiple moraines that span from prior to the global Last Glacial Maximum (LGM) through the Lateglacial period. Glaciers retreated from their terminal positions ca. 27-25 ka in arctic Alaska and ca. 22-19 ka in southern Alaska. Moraines in at least two ranges date to 12-11 ka, indicating a glacial advance during the Younger Dryas period. Reconstructed equilibrium-line altitudes of both penultimate and MIS 2 glaciers were lowered only 300-600 mmuch less than elsewhere in the Americas. Alaska is documented to have been more arid during MIS 2, perhaps due in large part to the exposure of the Bering-Chukchi platform during eustatic sea-level lowering. The restricted ice extent is also consistent with the output of climate models that simulate a lack of significant summer cooling.

Ice-age megafauna in Arctic Alaska: extinction, invasion, survival

“…The North Slope has two physiographic units: the Arctic Foothills flanking the northern side of the Brooks Range and the Arctic Coastal Plain lying between the Arctic Foothills and the Arctic Ocean. Much of the North Slope has never been glaciated, and during the Last Glacial Maximum ca 19 cal ka BP glaciers terminated near the northern range front of the Brooks Range (Briner and Kaufman, 2008). North-flowing rivers have deposited extensive gravel deposits on the Arctic Coastal Plain and redistributed older, marine deposits left by Tertiary and Pleistocene sea-level high stands (Dinter et al, 1990).…”

Timing and nature of late Quaternary mountain glaciation

“…Temporal and spatial patterns of glaciation in western North America are described by Briner and Kaufman (2008) and Thackray (2008). Briner and Kaufman (2008) review key glacier chronologies from northern Alaska (Brooks Range), central Alaska (Alaska Range), and south-west Alaska (Ahklun Mountains).…”

“…Briner and Kaufman (2008) review key glacier chronologies from northern Alaska (Brooks Range), central Alaska (Alaska Range), and south-west Alaska (Ahklun Mountains). Cosmogenic exposure ages indicate maximum Late Pleistocene ice extent during MIS 4 or 3.…”

“…Cosmogenic exposure ages indicate maximum Late Pleistocene ice extent during MIS 4 or 3. Briner and Kaufman (2008) attribute limited ice extent during MIS 2, and recession from terminal positions ca. 27-25 ka in northern Alaska and ca.…”

The last deglaciation of Alaska

“…We build from the most recent review of the Pleistocene glacier history of Alaska (Kaufman et al, 2011). There have been some new glacial chronology studies published since that time, and furthermore, unlike past reviews spanning the Late Pleistocene (Briner and Kaufman, 2008;Kaufman et al, 2011) and spanning the Holocene (Barclay et al, 2009;Kaufman et al, 2016), this paper focuses solely on the last deglaciation. This is the first review paper on the glaciation history of Alaska to do so.…”