Late Pleistocene and early Holocene sea-level history and glacial retreat interpreted from shell-bearing marine deposits of southeastern Alaska, USA

We leverage a data set of >720 shell-bearing marine deposits throughout southeastern Alaska (USA) to develop updated relative sea-level curves that span the past similar to 14,000 yr. This data set includes site location, elevation, description when available, and 436 C-14 ages, 45 of which are published here for the first time. Our sea-level curves suggest a peripheral forebulge developed west of the retreating Cordilleran Ice Sheet (CIS) margin between ca. 17,000 and 10,800 calibrated yr B.P. By 14,870 +/- 630 to 12,820 +/- 340 cal. yr BP., CIS margins had retreated from all of southeastern Alaska's fjords, channels, and passages. At this time, isolated or stranded ice caps existed on the islands, with alpine or tidewater glaciers in many valleys. Paleoshorelines up to 25 m above sea level mark the maximum elevation of transgression in the southern portion of the study region, which was achieved by 11,000 +/- 390 to 10,500 +/- 420 cal. yr B.P. The presence of Pacific sardine (Sardinops sagax) and the abundance of charcoal in sediments that date between 11,000 +/- 390 and 7630 +/- 90 cal. yr B.P. suggest that both ocean and air temperatures in southeastern Alaska were relatively warm in the early Holocene. The sea-level and paleoenvironmental reconstruction presented here can inform future investigations into the glacial, volcanic, and archaeological history of southeastern Alaska.

Automated summary

The study reveals a peripheral forebulge developed west of the retreating Cordilleran Ice Sheet in southeastern Alaska between ca. 17,000 and 10,800 calibrated yr B.P. By 14,870 +/- 630 to 12,820 +/- 340 cal. yr BP., CIS margins had retreated, with isolated or stranded ice caps existing on islands, indicating warm temperatures in the early Holocene.