Date

Spring 2016

Document Type

Master's Thesis

Degree Name

Master of Science (M.S.)

Department

Moss Landing Marine Laboratories

Abstract

Ice sheets are losing volume and regions of sea ice cover are shifting; these changes in Arctic and sub-Arctic regions amplify climate change through positive feedback mechanisms. A history of sea ice cover and iceberg activity in high latitude seas would help to predict climate change. Sea ice and icebergs entrain and dump sediment into the oceans; both transport sand, but glacial ice is much more likely to entrain gravel (>2 mm) than sea ice. This study uses siliciclastics >63 μm from Bering Sea Site U1343 to track icebergs and sea ice during the Mid-Pleistocene, a period of change in global climate cycles. Fine sand (63<<250 μm) averages 10% of the bulk sediment at U1343 from 910 to 860 ka. A new method uses a ratio (fine sand/gravel count) to indicate the more likely presence of sea ice. Icebergs are likely present during Marine Isotope Stage (MIS) 23 and in the latter part of MIS 22 when four pulses of gravel-size ice rafted debris come before the deglaciation. A period of low ice rafted debris in MIS 22 when the sea level is decreasing rapidly is interpreted as a time of more open water. Sea ice is suggested at the coldest time in MIS 22 and at the start of the deglaciation, consistent with the Sea Ice Switch (Gildor and Tziperman 2000) hypothesis for the Mid-Pleistocene climate transition. Abundant fine sand in MIS 21 suggests the presence of sea ice in the early interglacial.

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