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Seabird distribution and oceanic features of the Amundsen and southern Bellingshausen seas

Published online by Cambridge University Press:  07 May 2004

David G. Ainley
Affiliation:
H. T. Harvey and Associates, PO Box 1180, Alviso, CA 95002, USA Email: harveyecology@worldnet.att.net
Stanley S. Jacobs
Affiliation:
Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964, USA
Christine A. Ribic
Affiliation:
USGS, Wisconsin Cooperative Wildlife Research Unit, Department of Wildlife Ecology, University of Wisconsin, Madison, WI 53706, USA
Ian Gaffney
Affiliation:
1021 Greenwich St, San Francisco, CA 94013, USA

Abstract

We describe the distribution and estimate the abundance of seabirds in the Amundsen and southern Bellingshausen seas, and attempt to identify the mesoscale and larger ocean and ice features that explain the birds' discontinuous occurrence patterns. Our general objective was to assess if ocean fronts, especially near the continental shelf break, enhance feeding opportunities for top trophic-level predators. A variety of subsurface thermohaline fronts occurred on both sides of the shelf break, at shallower depths from west to east, and with warmer and saltier water on their northern sides. Pack ice overlaid some of these fronts, especially in the Amundsen Sea. Seabirds comprised either an ice group in pack ice or in polynyas, or an open-water group in waters north of the pack. In the Amundsen Sea, bird densities were near 0 birds km−2 in waters overlying the continental shelf, an unexplained pattern found previously in the Ross Sea but not repeated in the Bellingshausen Sea (5 birds km−2 over the shelf). Both groups were more abundant (densities 3–9 birds km−2) near the frontal zones, the ice edge and the shelf break. In the Amundsen Sea, the distribution of ice-group species was related statistically to proximity of fronts and the pack-ice edge, thermocline slope, and depth of the chlorophyll maximum; water-group distribution was related to distance to the fronts and sea-surface temperature. In the Bellingshausen Sea, distribution of both groups was related to distance to the fronts. Many thousands of petrels, found roosting during daylight on icebergs situated near the shelf break, escaped standard census techniques and, thus, are likely to have diluted positive correlations of avian occurrence patterns with physical features of the environment. While the emperor penguin was seen in high numbers and can dive deep enough to forage within the subsurface fronts, those ocean and food-web processes that apparently affect increased food availability for surface and shallow-diving foragers in the frontal regions remain unclear.

Type
Papers—Life Sciences and Oceanography
Copyright
© Antarctic Science Ltd 1998

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