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

Abstract

We investigate suspended particles collected from the upper mixed layer in the inner shelf of the southern East China Sea during autumn 2013 for carbon and nitrogen (POC and PN) contents and their isotope compositions (δ13C and δ15N) along with hydrographic parameters to understand the sources and dynamics of particulate organic matter (POM) in the study area. Results indicated that the extensive hydrological processes affect the biogeochemical composition of suspended POM, as revealed by the horizontally mixing POM and the spatial variation of δ15N and molar C/N ratio. Low C/N (2.4–6.5) and a weak correlation between POC and in situ chlorophyll fluorescence suggested that POM is dominated by the recently formed and well‐preserved planktonic OM. By fitting the linear correlation between δ13C and POC data with a photosynthetic fractionation model, we further disentangled dynamic controls of phytoplankton production and species diversity on δ13C variability (−24.3 to −21.3‰), emphasizing the constant effect of productivity‐derived POC on δ13C (0.02‰ per μg/L). The δ15N variability (2.3–7.4‰) is largely controlled by the mixing of isotopically different nitrogen sources, in which the importance of biological nitrogen fixation is unfolded based on the small δ15N and the negative correlation between δ15N of POM and seawater temperature. This implies that Kuroshio‐induced biological N fixation plays an important role in supporting the marine production in the East China Sea. These hydrologically driven δ13C and δ15N changes of marine productivity‐derived POM suggest that internal biophysical dynamics rather than terrestrial versus marine OM mixing largely control the C and N compositional variability in the shelf seas.

Plankton Community Respiration and Particulate Organic Carbon in the Kuroshio East of Taiwan

“…In this study, the lowest and highest POC concentrations were 1.8 and 77.1 μg C L −1 , respectively, with mean depth-normalized integrated values ranging from 12.7 (±2.3) to 21.6 (±5.2) μg C L −1 ( Figure 4 c). The concentration was in the range of the reported value, 2–99 μg C L −1 , in the KW [ 35 , 36 , 37 , 38 ]. Notably, the POC value is relatively low in the KW compared to that in the East China Sea (ECS) shelf ecosystem; for example, its mean value over the entire ECS shelf was 227.5 (±141.9) μg C L −1 [ 39 ].…”

Simulating the sea-to-air flux of dimethylsulfide in the eastern China marginal seas

“…The atmospheric deposition has significant influence on the phytoplankton bloom dynamics. There are low ratios of C:N (around 2.4-6.5) in the study region (Liu et al, 2019). They found that Kuroshio-induced biological N fixation plays an important role in supporting the marine production in the region.…”

“…Anthropogenic nutrient enrichment in these waters has led to severe eutrophication (Kim et al, 2011), which is exacerbated by atmospheric nutrient (N) deposition threatening the structure and function of regional terrestrial and aquatic ecosystems (Liu et al, 2013). The extremely high N loading has caused Chinese coastal waters to transition from N to P (phosphorus) limited status (Kim et al, 2011;Mackey et al, 2017; T. H. Huang et al, 2019;Liu et al, 2019). The atmospheric deposition has significant influence on the phytoplankton bloom dynamics.…”

“…As marginal seas, the ECMS receive land-based inputs from a vast catchment, and is a key area for the regional biogeochemical cycles of carbon and other nutrients (Hickman et al, 2012). As a transitional zone, marginal seas experience more complex hydrological and biogeochemical processes that distinguish it from the open ocean (Liu et al, 2019).…”

Influence of Hydrodynamics on the Composition and Reactivity of Particulate Organic Matter in a Large River Influenced Ocean Margin

“…Over the past decades, this topic has attracted extensive attention, yet the role of marginal seas as a carbon source or sink remains under debate (Borges et al, 2005;Cai, 2011;Dai et al, 2013Dai et al, , 2022. Marginal seas are characterized by complex hydrodynamic processes that are tightly linked to organic matter cycling (Bao et al, 2018;Chen et al, 2021;Guo et al, 2018;Liu et al, 2019;Pedrosa-Pamies et al, 2013). In particular, on ocean margins influenced by large rivers, the convergence of plumes with ocean currents generates a series of fronts and exerts a pronounced impact on phytoplankton production and the development of hypoxia in bottom waters (Guo et al, 2020;Lv et al, 2022;Wei et al, 2021).…”