Spatial Distributions of Riverine and Marine Dissolved Organic Carbon in the Western Arctic Ocean: Results From the 2018 Korean Expedition

Abstract Seasonal primary production and river discharge increases in the Arctic Ocean exert a significant influence on the dissolved organic carbon (DOC) cycle. To improve our knowledge of the spatial heterogeneity of DOC source and concentration in the rapidly changing Arctic Ocean, we investigated the distributions of riverine and marine DOC in the western Arctic Ocean during the summer of 2018. Although the surface bulk DOC concentration indicated no clear distinction in its distribution between the Chukchi Borderland (CBL)/northern Chukchi Sea (NCS) and East Siberian Sea (ESS)/Mendeleyev Ridge (MR) regions, the estimated riverine DOC concentration (28 ± 4.2 μM C) and its contribution (40 ± 5.7%) in the surface layer of the CBL/NCS region were higher than those (19 ± 5.6 μM C and 26 ± 8.5%) in the ESS/MR region, which was attributed to the accumulation of freshwater, strong stratification, and a longer residence time in the CBL/NCS region. In contrast, although marine DOC was the dominant DOC component in both the CBL/NCS and ESS/MR regions, the higher marine DOC concentration (54 ± 8.1 μM C) and its contribution (73 ± 8.2%) in the East Siberian shelf/slope region were consistent with high bacterial abundance, which was associated with extremely high surface phytoplankton blooms sustained by nutrient supply from the deep layer, suggesting that the supply of bioavailable DOC resulted in active bacterial activities. Overall, the spatial differences in water properties between the two regions had large influences on the regional distributions of riverine and marine DOC.