Date of Award

Winter 2009

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Ocean & Earth Sciences

Committee Director

Gregory A. Cutter

Committee Member

Dennis A. Darby

Committee Member

David J. Burdige

Abstract

Dramatic environmental changes in the Arctic Ocean have been observed for the last two decades including changing the amount of sea ice thickness and extent, and increased river discharge. In order to put these and other current day observations into historical context and perhaps reveal mechanisms controlling them, a suite of paleo-proxies were used to analyze two high resolution cores collected on the 2005 HOTRAX expedition. The goals of this research were: (1) develop an analytical method for determining biogenic calcite, (2) identify the major sources of biogenic matter into the system over the Holocene, and (3) assemble the history of depositional events that have occurred in the Alaskan shelf over the Holocene.

The C/N and δ13C in the very earliest record at Station 5, 12,000 ybp, suggest marine conditions prior to the inundation of glacial outwash and terrestrial organic matter. From 12,000 to 9600 ybp abundant amounts of terrestrially-derived materials were delivered to the Alaskan shelf, confirmed by dolomite, high C/N ratios, heavy δ13C signatures, and low sulfur. Immediately following these terrestrial inputs, a thousand year transition period re-established marine conditions like those found in the late Holocene. In the mid-Holocene, 6000–1000 ybp, increased concentrations of pyrite occurred at this time because enough labile organic matter was deposited for anoxic conditions to occur, and sufficient amounts of sulfate and iron were available. The most recent record, 1000 ybp to present, shows much different biogeochemical conditions than in the mid to early Holocene, organic carbon concentrations are 50% higher, but anoxic conditions do not appear to be present likely due to high amounts of bioturbation, enhancing oxygen penetration into the upper sediments.

In terms of the marine sources of organic matter in the mid and late Holocene, their origin appears to be diatoms or other siliceous organisms. The recent observations of cocolithophores in the Bering Sea suggest that other phytoplankton species could be present in high latitude waters, but they were not found in the Holocene records examined here. With respect to other environmental changes occurring in the Arctic at present, it will interesting to see if increased river discharges shift the Alaskan shelf to a more terrestrially-dominated system as seen in the earliest Holocene.

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DOI

10.25777/015c-rr07

ISBN

9781109705928

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