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The Paleoceanography of the Bering Sea During the Last Glacial Cycle
MASSACHUSETTS INST OF TECH CAMBRIDGE JOINT PROGRAM IN APPLIED OCEAN SCIENCE AND ENGINEERING
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In this thesis, I present high-resolution stable-isotope and planktonic-fauna records from Bering Sea sediment cores, spanning the time period from 50,000 years ago to the present. During Marine Isotope Stage 3 MIS3 at 30-20 ky BP kiloyears before present in a core from 1467 m water depth near Umnak Plateau, there were episodic occurrences of diagenetic carbonate minerals with very low deltaC13 -22.40, high deltaO18 6.50, and high MgCa, which seem associated with sulfate reduction of organic matter and possibly anaerobic oxidation of methane. The episodes lasted less than 1000 years and were spaced about 1000 years apart. During MIS3 at 55-20 ky BP in a core from 2209 m water depth on Bowers Ridge, N. pachyderma s. and Uvigerina deltaO18 and deltaC13 show no coherent variability on millennial time scales. Bering Sea sediments are dysoxic or laminated during the deglaciation. A high sedimentation rate core 200cmky from 1132 m on the Bering Slope is laminated during the Boelling warm phase, Alleroed warm phase, and early Holocene, where the ages of lithological transitions agree with the ages of those climate events in Greenland GISP2 to well within the uncertainty of the age models. The subsurface distribution of radiocarbon was estimated from a compilation of published and unpublished North Pacific benthic-planktonic C14 measurements 475-2700 m water depth. There was no consistent change in C14 profiles between the present and the Last Glacial Maximum, Boelling-Alleroed, or the Younger Dryas cold phase. N. pachyderma s. deltaO18 in the Bering Slope core decreases rapidly in less than 220 y by 0.7-0.80 at the onset of the Boelling and the end of the Younger Dryas. These isotopic shifts are accompanied by transient decreases in the relative abundance of N. pachyderma s., suggesting that the isotopic events are transient warmings and sustained freshenings.
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