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Global Biogeochemical Cycles

Arctic carbon sinks: Present and future

Authors

  • John J. Walsh


Abstract

Surface air temperatures of the Arctic rose 1.2° −1.5°C from 1880 to 1980, in contrast to a global warming of only 0.4° −0.5°C; since 1980, six of the warmest years in the past century have been observed. Polar enhancement of a temperature rise, induced possibly by anthropogenic release of “greenhouse” gases, CO2, N2O, CH4, and freons, to the atmosphere, is attributed to altered ice/snow albedo at sea level, i.e., melting of sea ice. A 5% decline of sea ice extent in the Arctic and Antarctic from 1979 to 1987 may have resulted in increased light availability within previously ice-covered polar regions. If such a short-term trend were to continue, it might lead to a negative biogeochemical feedback, i.e., enhanced extraction of atmospheric CO2 during marine photosynthesis. As a consequence of deep vertical mixing in the Antarctic Ocean, however, primary production during the austral summer may have actually declined in response to a reduction in extent of meltwater regions, where stratified water columns allow carbon fixation tenfold that of open water. In contrast, within shallow adjacent seas of the Arctic Ocean, where shelf regions are tenfold larger than those of the Antarctic, the positive global consequences of greenhouse warming at polar latitudes will probably be felt first. Specifically, the Pacific-influenced regions of the Chukchi and East Siberian Seas, where sufficient nutrients and shallow depths prevail, now have annual primary productions of >200 g C m−2 yr−1, tenfold that of other high Arctic shelves, and may supply 50% of the carbon respiration demands within the halocline of the deep Canadian and Eurasian basins via brine-mediated runoff. Continued melting of ice in the Arctic could increase by an order of magnitude the present CO2 sink of ∼0.1 × 109 t C yr−1.

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