749 / 2024-09-19 11:08:06

Seasonal dynamics of particle size distribution and carbon export in the marginal sea of the western Pacific Ocean

Particulate Organic Carbon Export,Particle size distribution,In situ opticle observation,Machine learning,Subtropical marginal sea

The gravitational sinking of organic particles transfers organic carbon from the surface to the deep ocean, a fundamental mechanism of the biological carbon pump, crucial for regulating climate change and supplying energy to deep-sea biota. However, in subtropical marginal seas, monsoons and plumes significantly influence particle organic carbon (POC) production, while sinking processes are impacted by complex physical-biological interactions, complicating the resolution of POC fate through limited sampling. In this study, we utilized the Underwater Vision Profiler 5 along with high-resolution remote sensing and reanalysis products to reconstruct the monthly climatology of particle size distribution (PSD) parameters and POC flux. Basin-scale reconstructions reveal that in oligotrophic basin regions, biovolume and PSD slope exhibit inverse trends, with slope decreasing and biovolume increasing in spring, indicating the production of larger particles and a higher potential for POC export. Conversely, nutrient supply from high-productivity plumes stimulates pico-phytoplankton blooms in summer, leading to a concurrent increase in biovolume and PSD slope, thereby enhancing carbon export. The reconstructed POC export from the euphotic zone in the South China Sea is approximately 116.4 Tg C y^-1, comparable to estimates from food web models, accounting for about 18% of net primary production. Our study elucidates the complex seasonal dynamics of particle properties and carbon export in various ecosystems of low-latitude marginal seas, providing new insights into the production and transformation of marine particles.