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In August 1993, we measured photosynthesis, chlorophyll a, bacterial secondary production, microb~al community respiratory rate, bacterial abundance, dissolved free armno acids, nitrate, phosphate, silicate, and dissolved oxygen in the eastern Chukchi Sea. Our crulse track was mostly in loose pack ice e x c e e d~n g 50% ice cover, with heavier ice cover near 7 5" N. We sclmpled over the continental shelf and slope, in deep water in the Canadian Basin, and over the Chukchi Cap. Primary production was highest over the upper continental slope, averaging 748 mg C m-' d -' In deep water and heavier ice cover in the Canadian Basin, primary productivity averaged 123 mg C m-' d-l. However. microbial community respiratory rates averaged 840 mg C m ' d-l over the upper slope and 860 mg C m-2 d.' in the Canadian Basin. Nitrate was virtually depleted In the .upper m~x e d layer, suggesting some nutrient limitation and dependence on regenerated ammonium in late summer. This is supported by f-ratios ranging from 0.05 to 0.38. Estimates of annual prlmary production of organlc carbon, both from our 'v and 13<1 assimilation measurements and from the supersaturation of dissolved oxygen in the upper mixed layer at all stations, suggest that significant primary production occurs well beyond the continental shelves out into the so-called perennial pack ice. Respiratory activity in the upper mixed layer exceeded primary productivity at the deep-water stations, a s it often does in summer oligotrophic conditions at lower latitudes. These observations suggest that rates of both autotrophic and heterotrophic biological activity in the upper mixed layer of the deep waters of the Arctic Ocean may be considerably higher than suspected and should b e incorporated lnto models of polar proccsscs.

Estimates of nutrient demand by dense mats of ice algae in the high Arctic indicate that substantial nutrient fluxes are necessary to satisfy the observed growth over the 2-month bloom. In our study area, Barrow Strait, the quantity of nutrients in the surface-mixed layer is about 3-10 times greater than estimates of total demand during the bloom, and nutrient fluxes in the water column are estimated to be of the same order of magnitude as algal demand. The fluxes in the water column are predicted to vary by more than an order of magnitude over the fortnightly tidal cycle, assuming that fluxes depend upon the strength of tidal currents and the vertical nutrient gradients. In the latter half of the bloom, when biomass levels are high, it appears that established populations of ice algae may experience cyclic conditions of nutrient limitation during neap tides when nutrient fluxes are minimal. Contributions from regeneration and brine exclusion from the ice sheet appear to satisfy only a portion of the bloom's total requirement for nutrients. INTRODUCTIONDense growths of ice algae are a ubiquitous feature beneath annual sea ice in polar regions during the springtime. In the high Arctic these microalgae are largely concentrated at the ice-water interface on or within the skeletal layer of the congelation ice. MacroScopically, they resemble a mottled goldenbrown carpet about 1-2 cm thick. We have found that these algae grow for at least 2 months (April-May) in the central portion of the Northwest Passage. Moreover, the ice alga. e often achieve high levels of biomass (80-100 mg chlorophyll m -e) that are similar to water column values integrated over the depth of the euphotic zone in many planktonic systems.

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