the 22nd Pacific−Asian Marginal Seas meeting (PAMS)

The southern Sea of Okhotsk is characterized by high primary productivity and a distinctive geomorphology, with a deep basin adjacent to the continental shelf. Elevated springtime surface chlorophyll-a concentrations suggest the presence of an efficient biological shelf pump; however, its quantitative contribution to particle export remains poorly constrained. Here, we quantify seasonal variability in particle fluxes and their sources using sediment trap observations and shelf sediment data. Time-series sediment trap samples were collected at 550 m depth on the slope of the Kuril Basin from Dec. 2022 to June 2023 and analyzed for biogenic silica (BSi), particulate organic carbon (POC), calcium carbonate (CaCO₃), and lithogenic material. Temperature at 50 m depth was obtained from a moored sensor, and sea-ice concentration was derived from satellite observations. Particle fluxes were partitioned into autochthonous fluxes from freshly produced phytoplankton and ice algae, and allochthonous fluxes from advected or resuspended particles, based on shelf sediment composition. The allochthonous fluxes increased during sea-ice formation and the early influence of the East Sakhalin Current (ESC), whereas the autochthonous fluxes increased markedly in April following sea-ice retreat and again in June under warmer conditions those are relevant to biological production. Over the seven-month period, autochthonous POC and CaCO₃ accounted for ~60% of integrated fluxes, while autochthonous BSi was comparable to allochthonous BSi. The autochthonous fluxes exhibited strong seasonality, with spring maxima. Enhanced April POC export coincided with elevated BSi and CaCO₃, indicating mineral ballasting. These results demonstrate that the southern Sea of Okhotsk functions as an efficient biological carbon pump driven by shelf–basin interactions.