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

• Published in: Journal of geophysical research. Oceans Vol. 127; no. 7
• Main Authors: Jung, Jinyoung, Lee, Youngju, Cho, Kyoung‐Ho, Yang, Eun Jin, Kang, Sung‐Ho
• Format: Journal Article
• Language: English
• Published: 01.07.2022
• ISSN: 2169-9275; 2169-9291
• DOI: 10.1029/2021JC017718

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. Plain Language Summary The Arctic Ocean is experiencing rapid environmental changes due to accelerated warming, a decline in sea ice coverage, and an increase in river discharge from Arctic rivers. However, it is not clear how these environmental changes affect the Arctic carbon cycle, particularly the quality and quantity of dissolved organic carbon (DOC). In this study, we used physical, chemical, and biological hydrographic datasets obtained from the western Arctic Ocean during the summer of 2018 and distinguished riverine and marine DOC from bulk DOC to clearly understand their distributions and utilization. The spatial distributions of riverine and marine DOC showed clear distinctions in their distributions between the Chukchi Borderland (CBL)/northern Chukchi Sea (NCS) and East Siberian Sea (ESS)/Mendeleyev Ridge (MR) regions. The high riverine DOC concentration in the CBL/NCS region was associated with the regional characteristics, including the accumulation of freshwater, strong stratification, and a longer residence time. On the other hand, anomalously high primary production was observed in the ESS/MR region, resulting in the large contribution of marine DOC. Our results highlight that the regional characteristics of water properties in the study region exerted significant influences on the spatial distributions of riverine and marine DOC. Key Points Riverine and marine dissolved organic carbon (DOC) were distinguished using hydrographic datasets obtained from the western Arctic Ocean Spatial distribution of riverine DOC showed higher abundance in the Chukchi Borderland and the northern Chukchi Sea Anomalously high primary production by the upwelling event enhanced marine DOC production in the East Siberian shelf/slope region