Fluxes of particulate organic carbon in the East China Sea in summer

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

Biogeochemical characteristics of suspended particulates at deep chlorophyll maximum layers in the East China Sea

“…However, the POC/Chl a ratio obtained in this study is lower than 30 that estimated (64 g g to Chl a ratio, estimated from phytoplankton cell volumes by the same authors (Table 2). Although the Chl a concentration in our study was measured in sea water in situ by fluorometer attached with the CTD, it is more or less similar to Chl a concentrations obtained in the above-mentioned studies, which were mostly extracted from filtered particles by acetone with (Chang et al, 2003) or without acidification (Hung et al, 2013).…”

Carbonate mineral saturation states in the East China Sea: present conditions and future scenarios

“…4.1, we have clearly shown that the highest surface pH 25 and values in the CDW in summer result mainly from elevated biological production stimulated by the nutrient discharge from the Changjiang runoff. On the other hand, the elevated biological production in the surface layer would export more particles to bottom waters, thereby rapidly transferring organic matter from surface to depth (Iseki et al, 2003;Hung et al, 2010Hung et al, , 2013. In combination with the strong stratification of the water column in summer (Chou et al, 2009b), which can isolate bottom waters from exchanging gas with surface waters, the remineralization of organic matter in the water column and sediment rapidly increased DIC concentrations, thereby depressing pH 25 and to their minimum values in the bottom water in the Changjiang plume area in summer.…”

Impact of Hydrological Conditions on the Biogeochemical Dynamics of Suspended Particulate Organic Matter in the Upper Mixed Layer of the Southern East China Sea

“…A good correlation between the chlorophyll fluorescence and chlorophyll a concentration extracted from suspended particles was often reported in the ECS (Gong et al, ; Liu et al, ; Zhou et al, ). The relationship between POC and chlorophyll a has been used for understanding the role of phytoplankton in POM production (Furuya, ; Hung et al, ). It is expected that in situ phytoplankton productivity is mainly responsible for the variation of POC when the concentrations of POC and chlorophyll fluorescence are positively correlated, which was also observed in the DCM layer of the southern ECS in summer 2013 (Liu et al, ).…”