The Xiamen Symposium on Marine Environmental Sciences (XMAS 2025)

Deep-sea carbon export is vital for sustaining deep-sea ecosystems and assessing the ocean’s long-term carbon sequestration. Using biogeochemical profiling floats (BGG-Argo) in the western South China Sea, we quantified high-frequency variations in particulate organic carbon (POC) flux at 1000 meters and explored its link with upper-ocean dynamics. Three years of observations showed a significant increase in carbon flux between September and November, driven by seasonal eddies that enhance nutrient levels, primary productivity, and large particle formation. The average carbon export flux at 1000 meters was 0.25 mol C m⁻² yr⁻¹, about 7.7% of the euphotic zone’s flux. Large particles sank at 90-150 meters/day with a 5-10 day lag, while small particles sank at 10 meters/day with an 80-day lag. Lateral transport events also contributed to deep-sea carbon fluxes, underscoring the importance of shelf-derived inputs. Our findings highlight the dynamic nature of deep-sea carbon export in marginal seas and offer critical insights into deep-sea carbon cycling and ecosystem processes.
 

carbon export, deep ocean, marginal sea, BGC-Argo