Paper No. 9
Presentation Time: 9:00 AM-6:00 PM
DATING THE FIRST MILLENNIUM AD GLACIAL HISTORY OF ADAMS INLET, GLACIER BAY NATIONAL PARK AND PRESERVE, SOUTHEAST ALASKA
Glacier Bay National Park and Preserve located in southeastern, Alaska has a long and complex Holocene glacial history. Adams Inlet is a small inlet located within the East Arm of the Park where previous glacial stratigraphic and radiocarbon dating identified two major ice advances about 2500 and 1500 yr BP in the region. Ice from the West Arm flowed into the mouth of Muir Inlet from the lower bay area, while ice in upper Muir Inlet flowed eastward into the upper reaches of Adams Inlet, with lakes created during both events. Following these periods of ice advance and lake creation, ice advanced out of Adams and Muir Inlets into the lower bay during the Little Ice Age. Recession of the ice in Muir Inlet began about 1872 and continues today, with sediment infilling the bay concurrent with isostatic uplift. This study presents new tree ring data and calibrated radiocarbon dates that together with stratigraphic work details the First Millennium AD (FMA) advance for Adams Inlet including the Casement Glacier.Calendar dating of 87 tree cores and cross sections from detrital logs at five locations in Adams Inlet and a tree-ring-width series from Casement Glacier Valley from an overrun forest, show that trees were likely killed during three stages within approximately 200 years by a series of ice-related events centered on AD 600 years. Previous radiocarbon dates on in situ stumps that were rooted in lake sediments or on gravel above lake sediments suggest that Muir Inlet was filled with ice, entering initially into the mouth of Muir Inlet from the lower bay and by ice flowing out of both Muir and Wachusett Inlets, turning the area into a large lake that killed the local forest. This glacial lake was later overrun by ice from the Casement Glacier advance and other terrestrial glaciers flowing from adjacent valleys, as well as ice penetrating east from Muir Inlet. The FMA is an important period for studying climate variability because of the geologic and climatic evidence that suggest cooling in the Gulf of Alaska resulted in many land-terminating glaciers expanding at this time.