Sulfate reduction and total benthic metabolism in Shelf and Slope sediments off Nova Scotia

Studies of sediment oxygen consumption, carbon dioxide efflux, and sulfate reduction were carried out in muddy sediments on the Nova Scotia continenta l margin to examine seasonal and spatial variation in carbon mineralization . Differences in sediment texture were predominantly caused by variation in the size and abundance of faunal fecal pellets, and carbon and nitrogen co ntent were lower on the Slope than on the Shelf. Fluxes derived from shipbo ard incubations of subcores obtained from boxcores were compared to publish ed values from the same cruises obtained from microelectrode and porewater profiles, and multicorer incubations. Carbon mineralization measured by eit her oxygen consumption or CO2 release was generally not significantly diffe rent within stations. Oxygen consumption was highest at the shallowest stat ion (Emerald Basin, 230 m) and least on the Slope (800 m), with intermediat e values in the Laurentian Trough (500 m), but temporal differences in flux es were not consistent between stations. Shipboard oxygen consumption rates obtained with subcore incubations from boxcores were usually similar to ra tes from incubations of multicorer samples. Rates of oxygen uptake determin ed from microelectrodes and carbon dioxide flux from porewater samples were lower than rates from core incubations, likely due to exclusion of bioturb ation from profile calculations. Total benthic metabolism was dominated by sulfate reduction at all stations to at least 35 cm sediment depth, with ag ain higher rates on the Shelf than on the Slope. Despite the greater depth of the Slope compared to Emerald Basin, the relative decline in carbon mine ralization is slight, suggesting the significance of lateral input to the S lope from the Scotian Shelf Compared to sandy banks that comprise most of t he shelf, the relative importance of fine shelf sediments is accentuated, b ecause mineralization processes in these sediments (particularly sulfate re duction) involve a greater length of sediment column than in organic-poor s ands. Moreover, the relatively high mineralization that occurs on the Slope must be included in carbon budgets of the continental margin, especially i n the event of significant offshelf transport.