Abstract
Abstract. To understand carbon cycling in marginal seas better, particulate organic carbon (POC) concentrations, POC fluxes and primary production (PP) were measured in the East China Sea (ECS) in summer 2007. Higher concentrations of POC were observed in the inner shelf, and lower POC values were found in the outer shelf. Similar to POC concentrations, elevated uncorrected POC fluxes (720–7300 mg C m−2 d−1) were found in the inner shelf, and lower POC fluxes (80–150 mg C m−2 d−1) were in the outer shelf, respectively. PP values (~ 340–3380 mg C m−2 d−1) had analogous distribution patterns to POC fluxes, while some of PP values were significantly lower than POC fluxes, suggesting that contributions of resuspended particles to POC fluxes need to be appropriately corrected. A vertical mixing model was used to correct effects of bottom sediment resuspension, and the lowest and highest corrected POC fluxes were in the outer shelf (58 ± 33 mg C m−2 d−1) and the inner shelf (785 ± 438 mg C m−2 d−1), respectively. The corrected POC fluxes (486 to 785 mg C m−2 d−1) in the inner shelf could be the minimum value because we could not exactly distinguish the effect of POC flux from Changjiang influence with turbid waters. The results suggest that 27–93% of the POC flux in the ECS might be from the contribution of resuspension of bottom sediments rather than from the actual biogenic carbon sinking flux. While the vertical mixing model is not a perfect model to solve sediment resuspension because it ignores biological degradation of sinking particles, Changjiang plume (or terrestrial) inputs and lateral transport, it makes significant progress in both correcting the resuspension problem and in assessing a reasonable quantitative estimate of POC flux in a marginal sea.
Highlights
Continental margins only account for 8 % of the surface area of the ocean, but they contribute approximately 30 % of global primary production (Liu et al, 2000). Walsh (1989) proposed that continental shelf regimes were an important organic carbon source to the open ocean because marginal seas have elevated phytoplankton primary production and higher particulate organic carbon (POC) inventories as compared to those in the open ocean
KW primarily occurred in the southeast corner; TCWW was present mainly in the middle shelf of the East China Sea (ECS); Changjiang diluted water (CDW) was confined mainly to the northwest corner; YSW occurred in the northeast; CUW was present along the coast of mainland China beyond the influence of CDW, and south of the YSW area the surface waters of the middle shelf were TCWW + YSW
High concentrations (200–450 μg L−1) of POC were observed in coastal surface waters (e.g., CDW, S19, S19A, S29 and S18), followed by the middle shelf (80–160 μg L−1), and generally decreased towards the shelf, with the lowest values (40–70 μg L−1) found in the outer shelf (Fig. 2d) with the exception high POC values (72–140 μg L−1) in the southern ECS
Summary
Continental margins only account for 8 % of the surface area of the ocean, but they contribute approximately 30 % of global primary production (Liu et al, 2000). Walsh (1989) proposed that continental shelf regimes were an important organic carbon source to the open ocean because marginal seas have elevated phytoplankton primary production and higher particulate organic carbon (POC) inventories as compared to those in the open ocean. Continental margins only account for 8 % of the surface area of the ocean, but they contribute approximately 30 % of global primary production (Liu et al, 2000). Marginal seas are believed to influence marine carbon biogeochemical cycling and fishery crucially (Liu et al, 2010, and references therein; Chou et al, 2009a, b, 2011; Gong et al, 2011). One of the major objectives of the international research project Land-Ocean Interaction in the Coastal Zone (LOICZ) is to quantify the exchange of carbon between continental shelves, marginal seas, and the open ocean. The East China Sea (ECS) is among the largest marginal seas on the earth and has a high primary production (0.3 to 1.5 g C m−2 d−1) in coastal areas, during the summer months (Gong et al, 2003).
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