Freshwater distributions and water mass structure in the Amundsen Sea Polynya region, Antarctica

Randall-Goodwin, E., Meredith, M. P., Jenkins, Adrian, Yager, P. L., Sherrell, R. M., Abrahamsen, E. Povl, Guerrero, R., Yuan, X., Mortlock, R. A., Gavahan, K., Alderkamp, A.-C., Ducklow, H., Robertson, R. and Stammerjohn, S. E. (2015) Freshwater distributions and water mass structure in the Amundsen Sea Polynya region, Antarctica. Elementa: Science of the Anthropocene, 3. 000065. ISSN 2325-1026

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Official URL: https://doi.org/10.12952/journal.elementa.000065

Abstract

We present the first densely-sampled hydrographic survey of the Amundsen Sea Polynya (ASP) region, including a detailed characterization of its freshwater distributions. Multiple components contribute to the freshwater budget, including precipitation, sea ice melt, basal ice shelf melt, and iceberg melt, from local and non-local sources. We used stable oxygen isotope ratios in seawater (d18O) to distinguish quantitatively the contributions from sea ice and meteoric-derived sources. Meteoric fractions were high throughout the winter mixed layer (WML), with maximum values of 2-3% (±0.5%). Because the ASP region is characterized by deep WMLs, column inventories of total meteoric water were also high, ranging from 10-13 m (±2 m) adjacent to the Dotson Ice Shelf (DIS) and in the deep trough to 7-9 m (±2 m) in shallower areas. These inventories are at least twice those reported for continental shelf waters near the western Antarctic Peninsula. Sea ice melt fractions were mostly negative, indicating net (annual) sea ice formation, consistent with this area being an active polynya. Independently determined fractions of subsurface glacial meltwater (as one component of the total meteoric inventory) had maximum values of 1-2% (±0.5%), with highest and shallowest maximum values at the DIS outflow (80-90 m) and in iceberg-stirred waters (150-200 m). In addition to these upwelling sites, contributions of subsurface glacial meltwater could be traced at depth along the ∼ 27.6 isopycnal, from which it mixes into the WML through various processes. Our results suggest a quasi-continuous supply of melt-laden iron-enriched seawater to the euphotic zone of the ASP and help to explain why the ASP is Antarctica's most biologically productive polynya per unit area.

Item Type: Article
Subjects: F600 Geology
F700 Ocean Sciences
F800 Physical and Terrestrial Geographical and Environmental Sciences
F900 Others in Physical Sciences
Department: Faculties > Engineering and Environment > Geography and Environmental Sciences
Depositing User: Rachel Branson
Date Deposited: 31 Mar 2020 15:01
Last Modified: 08 Sep 2020 14:30
URI: http://nrl.northumbria.ac.uk/id/eprint/42636

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