The paradox of pelagic food webs in the northern Bering Sea—III. Patterns of primary production

Abstract

The advective supply of nutrients to the Bering-Chukchi continental shelf via a north-flowing “river” of oceanic water originating along the continental slope in the Bering Sea maintains a large portion of these shelf waters in eutrophic bloom summer-long. Known as the Anadyr Stream, this nutrient injection sustains conditions of high phytoplankton productivity and biomass in a region of the western Arctic that would otherwise be unproductive, as are adjacent shelf areas unaffected by the current. A production plume dominated by large chain-forming diatoms extends from the Gulf of Anadyr in the south to the southern Chukchi Sea in the north, has daily carbon uptake rates as high as 16 g C m −2 day −1, and has an estimated annual production of about 470 g C m −2 year −1. Maximum production occurs in three pools of especially prolific growth (Gulf of Anadyr, Chirikov Basin and southern Chukchi Sea) where rates could be as great as 720–840 g C m −2 year −1. Outside of the plume, nutrients remain low following the spring bloom and a typical successional flora is dominated by flagellates and small diatoms throughout summer. Post-bloom productivity in this region is generally about 0.5 g C m −2 day −1, and annual production is approximately 80 g C m −2 year −1. The contrasting primary production regimes lead to major differences in food webs and in the energy transferred to higher trophic levels within the western Arctic.