Large fluxes of continental-shelf-borne dissolved organic carbon in the East China Sea and the Yellow Sea

Fluxes of dissolved organic carbon (DOC) from continental shelves to the ocean may play a critical role in marine carbon cycling and budget. However, these fluxes have been poorly constrained because complicated biogeochemical reactions of riverine, atmospheric, and marine organic carbon occur in continental shelf-waters. We used multiple tracers of DOC such as stable-and radiocarbon isotope ratios of DOC, fluorescent properties of dissolved organic matter (FDOM), and Ra-228 as a water age tracer to investigate the sources and fluxes of DOC in the northwest Pacific continental margin of the East China Sea and the Yellow Sea. Here, we show that there are significant additional (excess) supplies of DOC in the central Yellow Sea relative to the Changjiang (Yangtze River) source, based on these tracers. The marine delta C-13 signature (-21.1 +/- 1.1 parts per thousand) and the radiocarbon age (2000 +/- 400 yr) of DOC suggest that the additional DOC (triangle(DOC)-D-14 =-44 parts per thousand) is supplied from a combination of newly produced DOC and the degradation of particulate as well as sedimentary organic matter. The flux of this additional DOC produced in the continental shelf of the East China Sea to the open ocean is estimated to be similar to 1.9 +/- 0.8 Tg C yr(-1), which is comparable to that from the Changjiang discharge. Our study implies that the fluxes of continental shelf-borne DOC may be important globally and should be considered in estimating global DOC budgets in the marine environment.

Automated summary

The study found significant additional supplies of DOC in the central Yellow Sea, originating from newly produced DOC and the degradation of organic matter. The flux of this additional DOC produced in the East China Sea continental shelf is comparable to that from the Changjiang discharge, indicating its potential global importance in marine DOC budgets.