Optical Dating Tests of Quaternary Sediments from the Central Arctic Ocean

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AbstractBergerOPP-98-18070The Arctic region has been predicted to be very sensitive to global climatic changes. Sediments deposited in the Arctic Ocean may record signals of past Arctic environmental changes such as growth and decay of circum-Arctic grounded ice sheets, meltwater discharges, and changes in extent and composition of central Arctic Ocean sea-ice cover. However, since recent glaciations/interglaciations (the last several hundred thousand (ka) years), these sediments have been difficult or impossible to date. Absolute dating of Arctic Ocean sediments has remained largely an enigma, and therefore the paleoceanographic and paleoclimatic Pleistocene record of the central Arctic Ocean is poorly known.Radiocarbon (14C) dating is restricted to the last 30-40 ka and only recently has high precision dating been developed. Oxygen-isotope and paleomagnetic stratigraphy depend on uniform and continuous sedimentation. Oxygen-isotope stratigraphy is problematic because foraminiferal abundances are discontinuous in the Arctic. Nevertheless, for accurate correlation of the depositional history of the Arctic Ocean with other oceans and circum-Arctic lands, numeric dating is essential. For example, isolated foraminifera abundance peaks probably represent an absence of extensive sea-ice cover, and so it is critical to determine the forams' ages for paleoclimatological studies in the Northern Hemisphere.The Principal Investigator will test and develop an alternate, absolute dating technology, thermoluminescence (TL)-dating which has a time range of 0-400 ka for terrestrial sediments. He will further develop his TL-dating technique at three sites in the western Arctic Ocean by broadly testing the signal-zeroing and dosimetry assumptions of the feldspar-specific infrared-optically-stimulated-luminated (IR-OSL) version of optical dating. The IR-OSL technique has greater inherent sensitivity and precision than TL. He will perform zeroing tests with sediments from upper parts of cores distributed across the Arctic Ocean and sediments having associated 14C dates. Also, dosimetry tests will be conducted on representative cores. Finally, three optical-dating tests will be conducted on sediments from well-dated cores from the North Atlantic to provide a baseline comparison from a simpler environment.This project will provide a foundation for: 1) extending absolute-dating chronologies for the central Arctic Ocean beyond the range of AMS(accelerated mass spectrometry) 14C dating; 2) direct dating of the preserved record of the last Arctic glacial/interglacial periods manifested by foram abundance peaks; and 3) providing a high-quality chronology for regional correlations for Arctic land-ocean correlations. Direct dating of foraminifera abundance peaks on will answer important questions about the history of Arctic Ocean sea-ice cover.