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.
Export of dissolved inorganic carbon (DIC) to adjoining oceans enhances the potential of CO2 sequestration in marginal seas. By using a series of measured DIC depth profiles and reported flow transports, we estimated that the intermediate outflow (100–600 m) from the South China Sea is capable of transporting 6.5 ± 4.1 Tg (1 Tg = 1012g) of biologically mediated carbon (DICbio) annually to the East China Sea (ECS) via the northwardly flowing Kuroshio current. The mixing and transport of these DIC‐rich waters would raise 3% and 16% of DIC/TA ratio and the Revelle factor of the adjoining seawaters, respectively. Upon upwelling onto the ECS shelf, these DIC‐rich waters would counteract the potential of CO2 uptake of shelf waters that might have been enhanced by the accompanying increase in nutrient inputs, thus complicating assessment of the ECS as a net CO2 source or sink.
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