Low benthic respiration and nutrient flux at the highly productive Amundsen Sea Polynya, Antarctica

Abstract

We investigated rates of total oxygen uptake (TOU) sulfate reduction (SRR), and benthic nutrient flux (BNF) in sediments of polynya (730-825 m water depth), ice shelf (1064 m water depth), and marginal sea-ice zone (530 m water depth) to evaluate the role of benthic mineralization in degrading organic material produced by primary production in the Amundsen Sea polynya (ASP), Antarctica. Despite high primary production (110 mmol C m^-2 d^-1) in the water column, benthic carbon mineralization in the ASP (average, 2.1±0.3 mmol C m^-2 d^-1) was strikingly lower than in other less productive polar regions, accounting for only 1.9% of primary production. Low sediment accumulation rates (0.18-0.20 cm yr^-1) and sinking fluxes of organic matter likely caused the low oxygen consumption rates (2.44-3.11 mmol m^-2d</sup>1^{) and low effluxes of dissolved inorganic nitrogen (0.12-0.13 mmol m^-2 d^-1) and phosphate (0.017-0.018 mmol m^-2 d-1) in the ASP. Carbon oxidation by sulfate reduction (0.11-0.19 mmol Cm^-2 d}-1<sup>) comprised only 10% of total benthic mineralization, indicating that anaerobic C oxidation plays a minor role in total C oxidation. Our results, including low sediment accumulation rates and benthic metabolic rates, suggest that most organic carbon produced by <em>Phaeocystis</em> blooms would be respired to CO₂ in the water column, and thus the organic carbon reaching the sediment is not adequate to stimulate benthic metabolism in the ASP.