The importance of terrestrial organic carbon inputs on Kara Sea shelves as revealed by n-alkanes, OC and δ13C values

Organic carbon (OC) and n-alkanes were investigated in the suspended matter (SM) and surficial sediments of the Arctic Ob and Yenisei Rivers and the adjacent Kara Sea. Organic nitrogen and δ13C values were determined as additional parameters in the sediments. OC and n-alkane concentrations were highly variable in space. This variability was interpreted as the result of a complex sedimentation pattern involving the discharges of these two rivers and the seasonal occurrence of a shore-ice front along the coast. Using the constant ratio of high molecular weight odd n-alkanes to OC in both rivers, we estimated that more than 70% of the OC preserved in shelf sediments is terrestrially-derived. This result was substantiated by the overall dominance of land-derived n-alkanes. A second approach using δ13C values and assuming binary dilution of riverine and marine OC led to comparable estimates.