Transport of Aged Dissolved Organic Carbon via the Surface Current Revealed by Radiocarbon

Abstract

The East Sea (also known as the Japan Sea) is connected to the Northwest Pacific via shallow straits and has independent deep water circulation, as a model miniature ocean. The radiocarbon age of dissolved organic carbon (DOC) in the East Sea ranged from 2,000 to 3,700 years, exceeding the water turnover time (∼100 years). The oldest DOC was found in the subsurface layer characterized by the Tsushima Warm Water. Comparison of the radiocarbon content and concentration of DOC in the East Sea to those in the ocean suggests that aged DOC was transported conservatively from the Northwest Pacific to the East Sea via the shallow Tsushima Warm Current. The fractions of DOC released by serial-oxidation of the oldest DOC sample had identical radiocarbon ages, implying that refractory DOC was produced in situ and added to the DOC pool in the East Sea.