Latest Pleistocene and Holocene local glacial history of Baranof Island, southeast Alaska

Abstract New cosmogenic 10 Be exposure ages and a proglacial lake sediment archive provide the first record of local ice cover following the deglaciation of the Cordilleran Ice Sheet (CIS) in southeast Alaska. Exposure ages from Necker Bay corroborate existing evidence for a CIS deglaciation age of ∼15–14 ka from the outer coast of Baranof Island. We date retreat farther inland on the western and eastern flanks of the island to the Early Holocene, providing evidence for an ice cap persisting on Baranof Island ∼3 ka after CIS retreat. Baranof Lake sediment cores document continued local ice cover until ∼10.4 ka, after which glaciers receded to their Holocene minima until ∼8 ka. Glaciers grew through the remainder of the Holocene, reaching their maxima during the last millennium before retreating rapidly during the last century. Remote sensing analysis of glacial change around Baranof Lake from 1948 to 2023 CE shows that the rate of glacier area loss increased by an order of magnitude after 1986 CE, from −0.03 km 2 /yr to −0.29 km 2 /yr. This trend in glacier area loss is reflected across Alaska and western Canada, highlighting the sensitivity of Beringian glaciers to climate changes and the significant contribution they will make to sea-level rise this century.