The origin of sediment organic carbon influences hydrophobic organic pollutant dynamics in Arctic shelf sediments

The fate of hydrophobic organic pollutants in the marine environment is largely controlled by organic carbon (OC) cycling processes. The Arctic is warming three times as fast as the global average, resulting in a profound alteration in OC fluxes to the Arctic Ocean. Consequently, remote Arctic shelf sediments serve as an ideal receptor for assessments of the impact of OC quantity and quality on pollutant fate.

Here, we compiled a database of congener-specific polychlorinated biphenyl (PCB) concentrations (510 entries, 84 sites) in surface sediment of four Eurasian Arctic shelves via integration of new measurements and literature data. Total organic carbon content and isotopic data were retrevied from CASCADE (The Circum-Arctic Sediment CArbon DatabasE) to examine the PCB storage in sediment as a function of OC source (marine versus terrestrial). In order to reduce the impact of variability in water-phase concentrations caused by region, latitude and depositional year, we controlled for these factors. The adjusted concentrations (in ng-PCB/g-OC) in sediment with high fractions of marine OC are 0.82-1.22 log units higher in Barents and Kara Seas and 0.092-1.49 log units higher in Laptev and East Siberian Seas, compared to those with high fractions of terrestrial OC. Albeit uncertainties in current estimations due to wide geographical coverage and correction assumptions, these values are comparable to previously reported differences of partition coefficients between marine and terrestrial OC in other regions (e.g., 0.2-1 log units higher in marine OC sites in Baltic Sea, compared to terrestral OC sites).

Based on these results, PCB accumulation in Arctic shelf sediment was predicted for future climate change scenarios using an observational dataset of terrestrial inputs and marine OC fluxes derived from the global state-of-the-art ocean- and sea ice biogeochemistry model FESOM2.1-REcoM3. The accumulated amount of PCBs in  marine OC in Arctic shelf sediments from 2000-2100 is estimated to be about 26 tonnes, which is more than 8 times higher than the accumulated amount in terrestral OC from both coastal erosion and riverine inputs. These results demonstrate that shifts in OC fluxes as a consequence of climate change can impact storage capacity of hydrophobic organic pollutants in aquatic systems.