Arctic carbon sinks: Present and future

Abstract

92-30570I 17With past ONR support from Grant N00014-87-J-1218, we had successfully coupled simple biological models of phytoplankton production (light and nutrient regulation of one size fraction) to time-dependent, 3-dimensional physical models of basin circulation at 25-30 km resolution in the Gulf of Mexico . While these coupled models mimicked seasonal cycles of phytoplankton abundance in basin waters, as estimated by changes in chlorophyll stocks, they failed to replicate fluctuations of biological populations within more complex slope and shelf regions.Accordingly, a more diverse biological model of particle decay within the aphotic zone (3 size classes of phytoplankton, macroaggregates, and zooplankton fecal pellets) was coupled to a static, 2-dimensional model of slope circulation at 0.5 km resolution in the Middle Atlantic Bight (Walsh et al., 1991). By specifying the influx of these particles, both at the shelf-break and from the overlying slope euphotic zone, with variable sinking velocities, the second set of coupled models reproduced seasonal time series of organic carbon caught by moored sediment traps on the slope and rise.A total of 8 publications were derived from this ONR grant: yr-1 , gases, C0 2 , N 2 0, CH4, and freons, to the tenfold that of other high Arctic shelves, atmosphere, is attributed to altered ice/ and may supply 50% of the carbon snow albedo at sea level, i.e., melting of respiration demands within the halocline sea ice.A 5% decline of sea ice extent of the deep Canadian and Eurasian basins in the Arctic and Antarctic from 1979 to via brine-mediated runoff. Continued 1987 may have resulted in increased light melting of ice in the Arctic could availability within previously ice-covered increase by an order of magnitude the polar regions.If such a short-term trend present CO 2 sink of 1-0.i x 109 t C yr'. were to continue, it might lead to a negative biogeochemical feedback, i.e., enhanced extraction of atmospheric CO 2 INTRODUCTION during marine photosynthesis.As a consequence of deep vertical mixing in the The global temperature of surface air Antarctic Ocean, however, primary producincreaseu by 0.4*-0.5*C from 1880 to 1980, tion during the austral summer may have while temperatures of Arctic regions actually declined in response to a reduc-(%64*-90N) instead rose by as much as tion in extent of meltwater regions, where 1.2*-1.5 0 C over this period [Hansen et stratified water columns allow carbon al., 1983]. After 1980, six of the fixation tenfold that of open water.In warmest years in the past century have contrast, within shallow adjacent seas of subsequently been observed , 1981, the Arctic Ocean, where shelf regions are 1983, reflecting tenfold larger than those of the possible early signs of a "greenhouse" warming of the Earth [Hansen and Lebedeff, Copyright 1989Copyright 1988. Initial one-dimensional [Hansen et by the American Geophysical Union. al., 19811 and then three-dimensional climate models of varying sophisticationPaper number 90GB00583. [Mitchell,...

Phytoplankton productivity on the Canadian Shelf of the Beaufort Sea

“…This suggests, perhaps, that much of the organic matter sinks to the bottom of the shelf during the growing season, a situation that is often characteristic of systems with mismatching phytoplankton and zooplankton cycles (Wassmann 1998). This value is close to the value of 0.4 to 0.6 typically used to model the carbon cycle in the Arctic Ocean (Walsh 1989).…”

Abundance and production of bacteria and viruses in the Bering and Chukchi Seas

“…Nagel 1992, McRoy 1993. The results suggest the region to have far-reaching biogeochemical importance as a sink for atmospheric CO2 (Walsh 1989) and a source of fixed carbon to the Arctic Ocean basins (Walsh et al 1989).…”

“…The high BCD/PP ratio suggests the possibility that there are times and/or regions of net hetei-otrophy within the Chukchi Sea which, along with organic matter sedimentation onto the shelf and export to the Arctic basin (Walsh et al 1989), would serve to balance the exceptionally hlgh autotrophic production In the northern Bering and southern Chukchi Seas.…”

Phytoplankton production in the North Water Polynya: size-fractions and carbon fluxes, April to July 1998

“…The role of the Arctic Ocean as a carbon source or sink is not certain as yet, due to insufficient knowledge of its primary production regime (Walsh 1989). Even though data on primary production in the Arctic Basin are accumulating (Kristiansen et al 1994, Cota et al 1996, Pomeroy 1997, especially since satellite images for chlorophyll have become available, data on the partitioning of production into different size fractions of biogeochemical significance, i.e.…”