Natural and Anthropogenic Carbon Cycling

Abstract

The East Sea (Japan Sea) is experiencing changes in water temperature, oxygen content, and deep water circulation pattern. These changes, in turn, have affected and will continue to affect carbon cycling in the East Sea, directly and indirectly. As the physical dynamics of the East Sea resembles that of the open ocean, studying inorganic and organic carbon cycling in the East Sea may improve our understanding of global carbon cycling, and consequently enable us to predict more accurately the response of the carbon cycle to global climate change. In our review of inorganic carbon cycling, we focus on the uptake of anthropogenic carbon by the East Sea and the shoaling of the saturation depths of the aragonite and calcite caused by acidification. The saturation depths for aragonite and calcite in the East Sea have shoaled by about 80–220 and 500–700 m, respectively, compared to pre-industrial values. Anthropogenic CO2 in the bottom water of the Japan Basin ranged from 15 to 20 μmol kg−1. The largest water-column inventory of anthropogenic CO2, about 80 mol C m−2, was found in the Japan Basin. The uptake rate of anthropogenic CO2 decreased from 0.6 ± 0.4 mol C m−2 year−1 during the 1992–1999 period to 0.3 ± 0.2 mol C m−2 year−1 during the 1999–2007 period, potentially reflecting the slowing of deep water ventilation in the East Sea. In our review of organic carbon cycling, we focus on sinking particulate organic carbon (POC) and dissolved organic carbon (DOC). Sinking POC flux in the East Sea generally reflected conspicuous events in biological production at the surface. Sinking POC flux in the East Sea was higher than in the nearby Kuroshio region. DOC concentration in the Ulleung Basin of the East Sea was higher than in the open oceans. The high content of the lithogenic component and low radiocarbon content in sinking particles in deep waters suggests that the contribution of resuspended sediment, and potentially other allochthonous sources of organic carbon, is considerable in the East Sea.