Organic matter remineralization in marine sediments: A Pan-Arctic synthesis

Climate change in the Arctic is ongoing and causes drastic modification on the ecosystem functioning. In soft-bottom environments, organic matter remineralization is considered an important ecosystem function. Here we provide a large scale assessment of the current knowledge on the benthic organic matter remineralization and its potential response to climate change. Sediment oxygen demand (SOD) values (n = 1154), measured throughout the Arctic, were gathered from 30 publications and 16 databases and nutrient flux values, available in a far lesser extent (n < 80), were also compiled. Generalized additive models were used to estimate the influence of explanatory variables on benthic oxygen fluxes and for interpolating SOD to the whole Arctic region. This first pan-Arctic review of the distributions of SOD showed that oxygen fluxes strongly depended on water depth, i.e. followed the general trend observed for other regions, and also on the availability of labile organic matter. The continental shelves (representing ~50% of Arctic Ocean's total area) were characterized by the highest SOD values (10.5 ± 7.9 mmolO2 m-2 d-1) and differences among shelves were observed; SOD values in inflow, interior and outflow shelves were 11.8 ± 8.0, 6.2 ± 5.6 and 3.9 ± 3.5 mmolO2 m-2 d-1, respectively. Moreover, seasonal variation in SOD changed significantly among areas. The interpolation based on the best-fitted model showed high respiration in the inflow and interior shelves. In the inflow shelves, characterized by productive waters, benthic activities replenish bottom water with nutrients which may augment primary productivity, whereas sediments from the interior shelves, e.g. under the direct influence of the Mackenzie River, consume nutrients.