Aquatic Sciences Meeting, Albuquerque 2001

PC11 Human Activities and Aquatic Ecosystems

Date: Thursday, February 15, 2001

Location: Southwest Hall

Schell, D, M, Inst. of Marine Science, University of Alaska Fairbanks, Fairbanks, AK 99775, USA, schell@ims.uaf.edu

DECLINING PRODUCTIVITY IN THE BERING SEA INDICATED BY ISOTOPE RATIOS

The keratinous baleen plates of bowhead whales provide a continuous record of the isotope ratios in the zooplankton and by proxy, of the phytoplankton of the regions through which the whales migrate. Over the past five decades, average del C13 values in the biota of the Bering and Chukchi seas have decreased by 2.7 ppt and del N15 by 1.2 ppt. During the same period, the top consumers (sea lions, seals, some sea birds) have also undergone declines in population and have shown evidence of nutritional stress. In this environment of short intense summers, these changes are interpreted as a result of decreased seasonal primary production. Although phytoplankton cell growth rates and del C13 have been shown to be directly related, the decrease in nitrogen isotope ratios is more problematic. Nitrogen fixation may be becoming more important in this environment as onshelf advection of nitrate decreases in response to climatic warming and decreased winter mixing and nutrient supply.

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Aquatic Sciences Meeting, Albuquerque 2001

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