[A-OS13] Exploring Variability and Changes in Ocean Biogeochemical Cycles

[AOS13-P03] Seasonal variation in organic carbon consumption in the East China Sea: A comparison between summer and winter

*Chung-Chi Chen¹ (1.National Taiwan Normal University)

Keywords:The East China Sea, The Changjiang (Yangtze) River, Planktonic community respiration, Organic carbon consumption, Inorganic nutrient, Continental shelf

The East China Sea (ECS), one of the world's largest continental shelves, plays a crucial role in regulating coastal carbon fluxes through organic carbon production and consumption. While summer conditions have been extensively studied, winter periods remain less understood, hindering accurate assessments of annual organic carbon consumption. To address this gap, two research cruises covering most of the ECS shelf were conducted in July 2007 and January 2008 to explore seasonal variations and underlying mechanisms governing organic carbon consumption. Results indicated substantial discharge of dissolved inorganic carbon from the Changjiang (Yangtze) River into the ECS during summer, promoting phytoplankton growth through allochthonous nutrient inputs. In winter, despite lower riverine discharge, significant fluvial nutrient input persisted; however, phytoplankton growth was not stimulated, likely due to temperature constraints. Planktonic community respiration (CR) exhibited strong seasonal differences, with summer rates doubling those in winter. Elevated summer plankton CR rates were linked to higher planktonic biomass, supported by fluvial dissolved inorganic nutrients and organic carbon from the Changjiang River. These findings highlight that organic carbon consumption in the ECS is regulated by distinct factors in summer and winter. Beyond planktonic biomass, environmental variables such as temperature must be considered when estimating plankton CR, particularly in cold winter months.