Date of Award

Spring 2018

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

H. Rodger Harvey

Abstract

Changes in the global climate may have a pronounced effect on the biogeochemical cycling of trace elements like selenium (Se) in the Arctic Ocean. This study described the first quantitative examination of the biogeochemical cycle of selenium in the Amerasian Basin, providing the baseline from which future changes can be identified. Aerosol, dissolved and particulate water samples were collected for Se determinations during the U.S. GEOTRACES GN01 Arctic expedition that sampled the two parts of the Amerasian Basin in 2015: The Makarov Basin on the way to the North Pole and the Canada Basin on the return trip to Dutch Harbor, Alaska.

Particulate Se concentrations were low throughout the cruise with the highest concentrations occurring at the bottom depths of the shallow shelf stations (0.06 nM). Particulate Se to particulate organic carbon atomic ratios were around phytoplankton ratios (~10-6) on the shelf, but were elevated (10-5) in the basin. Aerosol Se concentrations were low (0.01 – 0.11 nmol m-3, n=13), but enrichment factors were elevated and ranged from 1540 to 66698, suggesting distant fossil fuel combustion or local gaseous sources such as marine biogenic release of dimethyl selenide as a dominant source of aerosol Se. Generally, the depth profiles of the dissolved Se species did not resemble those of nutrient-like profiles seen in other ocean basins. Prediction of selenite and selenate concentrations using silicate and phosphate concentrations, shown to be accurate in other oceans, tended to overestimate selenate and underestimate selenite concentration throughout the Amerasian Basin. This lack of agreement suggests a slower than normal oxidation rate from selenite to selenate.

Estimated fluxes of total dissolved Se indicate that 1.0 ± 0.5 x 108 mol Se enter and 1.0 ± 0.1 x 108 mol Se leave the Amerasian Basin each year. The Atlantic Ocean is the dominant factor in both input and removal of water to and from the Arctic. Therefore, it likely plays a major role in the Se budget of the Arctic and future efforts should be made to directly measure the input and removal of Se via the Atlantic Ocean. The overlap in total input and removal fluxes suggest that the Se cycling in the Amerasian Basin is at steady state.

Due to the cycle being in steady state, residence times of Se were calculated throughout the basin. Selenium was calculated to have a total Amerasian Basin residence time of 149 ± 112 years and 151 ± 27 years by dividing the Se inventory by the total input rate and total removal rate respectively. Se in the intermediate basin layer, the basin water above the Lomonosov Ridge sill depth, had a residence time of 71 ± 22 years. These residence times are roughly 5 and 2 times longer than the residence time of the water highlighting the high rate of dissolved Se regeneration.

The Arctic Ocean will continue to change in response to a warming climate. Increased river discharge, smaller ice extent, and ice-free summers are likely to modify the biogeochemical behavior of trace elements in the Arctic and this study provides information on how the Se cycle might be affected.

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DOI

10.25777/54wh-fz94

ISBN

9781392058237

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