Spatial characteristics and removal of dissolved black carbon in the western Arctic Ocean and Bering Sea

Abstract

In the Arctic, large amounts of black carbon (BC) are released into river water and transported to the oceans as dissolved BC (DBC). However, the cycling and fate of DBC in the ocean is poorly understood. Here, DBC, dissolved organic carbon (DOC), absorbance, and δ18O were analyzed to examine the spatial characteristics and removal of DBC in the western Arctic Ocean and the Bering Sea during the boreal summer. DBC concentrations ranged from 0.67 to 4.18 μmol-C L−1. In the sea-ice free regions, high DBC and DOC concentrations and a254 values corresponded to high δ18O-derived meteoric water contents, indicating that river discharge dominated their spatial patterns. By contrast, sea-ice meltwater (SIM) appeared to dilute DBC and DOC in SIM impacted waters (SIM > 3.5%). The departure of DBC from conservative mixing lines suggested that 47–84% of riverine DBC was removed over the shelves with 7–23% transported to the upper Canada Basin. These results suggest that shelf regions are crucial sites for riverine DBC removal that modulate the delivery of DBC to the open Arctic Ocean.