Benthic POC cycling in the Skagerrak basin: The role of lateral POC input

Le résumé fourni par la source

The burial of particulate organic carbon (POC) on continental margins represents a major long-term sink for atmospheric carbon. Hence, accurate descriptions of the benthic marine POC cycle are necessary for understanding the ocean's CO 2 uptake capacity. Here, benthic POC cycling is examined in the Skagerrak basin, the largest depocenter for POC in the North Sea. POC burial fluxes, benthic dissolved inorganic carbon (DIC) fluxes, POC rain rates and burial efficiencies (CBE) are reported at six stations based on porewater, solid phase and in-situ benthic flux measurements. On average, 10.9 mmol m −2 d −1 of POC rains onto the seafloor, of which 6.6 mmol m −2 d −1 is recycled back into the water column as DIC and 4.3 mmol m −2 d −1 is permanently buried in the sediment, resulting in a CBE of 40%. The data indicate that the mass accumulation rate (MAR), faunal activity and the quality of the settling POC are key driving mechanisms for the benthic POC cycle. Three independent approaches are used to distinguish between the contributions of autochthonous and allochthonous POC to the total sedimentary carbon pool. On average, 18 ± 6% of POC originates from local production, while 82 ± 6% is transported laterally into the Skagerrak basin. Considering previously reported MARs, the temporal evolution of POC burial in the Skagerrak basin shows a substantial decline over the last ∼100 years, indicating variability in the lateral POC input. Possible reasons for the POC burial decline are qualitatively discussed, including changes in sediment cycling and primary production in the North Sea.

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