Dissolved Inorganic Carbon ([DIC], δ 13 С(DIC)) in Waters of the Eastern East Siberian Sea

Concentrations and carbon isotope composition of dissolved inorganic carbon (DIC) and isotope composition (δD, δ18O) of waters were studied in the eastern East Siberian Sea, along two submeridional sections extending from the Indigirka and Kolyma mouths to the edge of perennial ice. Estimated contents of river waters, sea ice meltwater, and modified waters showed that the eastern part of the shelf of the East Siberian Sea in summer, 2017 was globally freshened by riverine waters (6–57%). A slight contribution of sea ice meltwater (2–3%) was found only in the surface waters of the Kolyma section. The waters of the Indigirka section experienced intense modification, which is related to the ice formation and reaches 20% ice extraction from water. The concentration and δ 13 C values of DIC are controlled by mixing between sea water and river runoff. Their shift relative to the values determined by conservative mixing suggests that shelf waters contain an excess of DIC with an isotopically light carbon. Main processes leading to these shifts are the decomposition of organic matter and water modification. The rate of the latter is 3–4 times higher than that of organic matter oxidation. The isotope composition and concentrations of DIC could partially reflect the influence of Pacific seawaters coming through the Bering Strait and the Chukchi Sea.