Benthic mineralization and exchange in Arctic sediments (Svalbard, Norway)

By means of benthic landers, sediment core incubations and the whole core squeezing (WCS) technique, benthic exchange and mineralization rates were investigated in 4 different fjords of Arctic Norway (Svalbard). These coastal sediments experience constant low temperatures close td 0 degrees C. The sediments were dominated by large densities of bioirrigating macrofauna, which enhanced the benthic in situ Oz uptake by a factor of 1.8 to 2.9 over the diffusive mediated uptake. Recovered sediment cores significantly underestimated the in situ solute exchange rate, presumably due to exclusion of fauna. Faunal activity in situ additionally resulted in a complex sediment structure, which created a smearing of chemical profiles when applying the WCS technique. The benthic exchange rates of dissolved inorganic carbon determined in situ varied between 9 and 20 mmol m(-2) d(-1) at the different stations. Denitrification was of minor importance for benthic mineralization, and the C/N ratio of the effluxing inorganic solutes was close to 10, indicating that relatively fresh organic material was mineralized. The sediment accumulation rate was estimated from Pb-210 profiles to be in the range of 1.3 to 5.9 mm yr(-1). Assuming that our estimated mineralization rates approach the yearly average, it was calculated that 31 to 47 % of the organic carbon reaching the sediment surface was permanently buried. Benthic mineralization rates and carbon burial rates were similar to those obtained in coastal sediments of temperate and tropical regions. This indicates that benthic communities in Arctic sediments rather than being limited by low temperatures are Limited by carbon availability.