Transport of the South China Sea subsurface water outflow and its influence on the carbon chemistry of Kuroshio waters off southeastern Taiwan

Abstract

Depth distributions of pH, dissolved oxygen, dissolved inorganic carbon (DIC), total alkalinity (TA), and δ13CDIC in the water column across the Luzon Strait from the South China Sea to the west Philippine Sea were investigated thoroughly to attest whether the South China Sea subsurface water outflow could act like a “shelf pump” to export the carbon from the interior of the South China Sea into the open Pacific. Results show that the outflow is capable of transporting 17.6 ± 9.0 Tg C a−1 in DIC form out from the South China Sea to the western Pacific, a quantity equivalent to ∼35 ± 18% of the annual export production of the entire South China Sea. Furthermore, owing to the input of this South China Sea outflow, the subsurface waters of the Kuroshio Current become enriched in DIC/TA ratio but depleted in δ13CDIC. Such a change in seawater carbon chemistry might further attenuate the capacity of CO2 sequestration and hamper the use of δ13CDIC data as a tracer to estimate anthropogenic CO2 uptake rate in seawaters around the Kuroshio main path. More importantly, since these modifications can make all their ways northward along with the Kuroshio Current, the effect may reach even as far as to the higher-latitude region in the northwestern Pacific.