Role of sediment denitrification in water column oxygen dynamics: comparison of the North American East and West Coasts

[摘要] Low oxygen concentrations, either natural or anthropogenically driven, canseverely affect coastal marine ecosystems. A deeper understanding of oxygendynamics is required in order to improve numerical models, eventually topredict the timing and severity of hypoxia. In this study we investigate theeffect of sediment denitrification on oxygen concentrations in bottom watersover the continental shelf. We used two coupled physical-biological modelsbased on the Regional Ocean Modelling System (ROMS) to compare summersimulations with and without denitrification within the sediments for twoNorth American shelves: the Middle Atlantic Bight (MAB) and the VancouverIsland Shelf (VIS). These regions belong to western and eastern boundarycurrent systems, respectively, and are characterized by different physicaland biological dynamics. Both models assume couplednitrification-denitrification within the sediments. Denitrificationrepresents a loss of bioavailable nitrogen through the production ofdinitrogen gas, with the potential to affect biogeochemical cycles. In ourMAB model, this loss of regenerated nutrients through denitrification withinthe sediments significantly affects primary production, since recyclednitrogen supports most of the primary production in that region. Thediminished primary production and consequent decrease of organic matter fluxto the seafloor leads to less sediment oxygen consumption and higher oxygenconcentrations in bottom waters. However, changes in regenerated nitrogen onthe VIS barely affect primary production due to the efficient supply of newnutrients through wind-driven upwelling during summer and the nutrient-richcoastal current. We recommend that modelling experiments focusing onoxygen dynamics (as well as oxygen budget calculations) should includesediment denitrification in coastal regions where regenerated primaryproduction dominates productivity.

[学科分类] 地球化学与岩石