Marine Climates of the U.S. Alaskan Coastal Plain During the Late Neogene and Quaternary Interglacials

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Abstract This award supports a project to compare the modern marine climate with that of the last interglacial episode in the Bering Strait region. The two primary goals of the project are to: (1) produce detailed records of seasonal temperature ranges as recorded in the stable isotopic composition of mollusk shells for the modern and the last interglacial, and (2) infer from the stable isotope data the distribution of the major water masses during each time slice. In the first phase of the project, stable isotope methods will be applied to an evaluation of the modern hydrography of the Bering Sea - Chukchi Sea region. Stable oxygen and carbon isotope analyses of ostracodes and mollusks from the shelf will allow quantification of regional differences in water-mass distribution and latitudinal temperature gradients. Isotope profiles of the mollusks will provide a record of the seasonal range of temperature and might be useful in distinguishing seasonally ice- free from ice-covered conditions. This calibration experiment in the modern system will verify the relationship between the isotopic composition of shell carbonate and seawater and identify the geochemical signature of the principal water masses. In the second phase, the results from the modern system will be used to evaluate conditions during the highstand of the last interglacial. Stable isotope analyses will be performed on fossil mollusks and ostracodes collected from the emergent coastal plain deposits of the Pelukian transgression. Collection sites span a relatively broad latitudinal range from St. Lawrence Island to Skull Cliff near Point Barrow; this distribution of sites samples different water masses and points along the north- south temperature gradient. Ostracode specimens collected at discrete intervals from vertical outcrop sections will provide a record of isotopic composition changes within the transgressive units. Temperature ranges and water-mass variations can be interpreted from isotope profiles of mollusks as a complement to the ostracode data to quantify the seasonal components of marine paleoclimate. The underlying scientific goal of the project is to investigate the physical processes which control the advection of heat into the Arctic Ocean through the Bering Strait, and to determine whether these processes have varied significantly between interglacial episodes.