Distribution of 210Pb and 210Po and Particulate Organic Carbon (POC) Fluxes in the Northwestern Pacific Ocean in Summer 2024

During the 71st cruise of the R/V Akademik Oparin in the summer of 2024, we assessed the distributions of dissolved and particulate forms of 210Pb and 210Po in the Sea of Japan, the Sea of Okhotsk, and the northwestern Pacific Ocean. Quantitative estimates of vertical fluxes were derived based on measured concentrations of suspended particulate matter (SPM) and particulate organic carbon (POC). This study provides the first in situ measurements of these radionuclides and the first estimates of derived fluxes for the Sea of Okhotsk. The study confirmed the existence of two contrasting biogeochemical regimes: a sedimentation regime in the productive waters of the Sea of Okhotsk and a recycling regime in the oligotrophic waters of the open ocean, separated by the dynamic transition zone of the Kuril Islands. The calculated POC fluxes confirmed the high efficiency of the biological pump in the coastal seas. The identified anomalies in the distribution of radionuclides indicate a significant role of lateral transport and the sorption of organic carbon onto mineral particles in shaping vertical fluxes matter.