Tree ring-dated glacial history for the first millennium CE, Casement Glacier and Adams Inlet, Glacier Bay, Alaska, USA

摘要

Calendar dating of tree-ring series from 16 logs sampled near the margin of Casement Glacier combined with tree-ring dates on 36 detrital logs from Adams Inlet, Glacier Bay National Park and Preserve, Alaska, show killing of trees by ice and lake sediments from the mid-sixth through mid-seventh centuries C.E. The dates from the land-terminating Casement Glacier show ice advance into a forest between 560 and 570 C.E. within a few kilometers of the 2011 retreating margin.Advance of the tidewater glacier in Muir Inlet blocked offAdams Inlet forming Lake Adams between 540 and 640 C.E. This glacier and lake history for Glacier Bay is consistent with other land-terminating ice expansions across the Gulf of Alaska that similarly show advance centered on 600 C.E., as well as other proxy records from lakes all suggesting cooling during this interval. The cooling closely follows a series of eruptions in the mid to late sixth century, which may have contributed to the cooling. Radiocarbon ages in Adams Inlet suggest that Lake Adams persisted through 880 cal. yr C.E. and drained by 1170 cal. yr C.E. Ice retreat and this lake drainage are broadly coincident with Medieval warming recognized along the Gulf of Alaska in dendroclimatic reconstructions. Shortly after this retreat, Little Ice Age readvance occurred with Casement Glacier coalescing with glaciers in Adams Inlet and the West Arm, subsequently filling all of Glacier Bay to its Holocene maximum by 1750 C.E.