Pelagic nitrogen flux in the northern Bering Sea

Abstract

Nitrogen uptake rates are reported for the water masses found in the northern Bering and southern Chukchi Seas. Four water masses are identified in the study area: Anadyr, modified Bering Shelf, Alaskan Coastal and Siberian Coastal. Nitrate-rich Anadyr water drives the very productive “west bloom”, where uptake rates for total nitrogen (nitrate, ammonium and urea combined) are >6.0 mg-at. N m −2 h −1 and nitrate contributes up to 50% of the total. Nitrate contributes <35% to total nitrogen uptake rates of 1.80 mg-at. N m −2 h −1 in the modified Bering Shelf water mass. Nitrogen uptake in Alaskan Coastal water is lowest (1.0 mg-at. N m −2 h −1) with new production (i.e. nitrate uptake) only 15% of the total. A simple nitrogen budget suggests that 29 and 62% of the annual nitrogen productivity in the modified Bering Shelf and Anadyr waters, respectively, can be exported through Bering Strait into the southern Chukchi Sea for deposition. This large allochthonous source of phytodetritus, and a similarly large autochthonous source, can lead to the high organic carbon content found in the sediments of the southern Chukchi Sea.