A review of the oceanographic structure and biological productivity in the southern Okhotsk Sea

•The scientific knowledge on the southern Okhotsk Sea biogeochemistry and its relationship with its rich primary productivity was actualized.•The formation mechanisms of different water masses are starting to be revealed using chemical tracers, especially radionuclides.•The high seeding potential of Thalassiosira by ice–melting has been repeatedly featured, and it was placed as reason for its highest abundance in spring.•The total carbon mass flux is highest in April – June. Its maximum (up to 1165 mg C m−2 day−1) occurs several days after the sea ice retreatment•Further research is needed on the formation of the Intermediate Cold Water, the Cold Water Belt and the solubilization process of particulate Fe. The southern Okhotsk Sea is one of the best fishing grounds in Japan, and the biogeochemistry, primary productivity, and physical aspects of this region have been heavily researched. However, a comprehensive review of the literature has not been written since that by doctor Takatoshi Takizawa more than 40 years ago (1982). This review actualizes the share–ground knowledge of the influence of oceanographic conditions on the primary productivity of the area. This review includes topics from physical/chemical oceanography and hydrobiology, focusing on the complex oceanological structures that support the high primary productivity of the southern Okhotsk Sea. It is known that the formation of all water masses is ultimately a consequence of the seasonal interchange of the Soya Warm Current and the East Sakhalin Current. However, it was revealed that there may be over- or under-estimations in different material and heat fluxes among water masses, especially regarding the dense Soya Warm Current. Recent studies have investigated the formation mechanisms of different water masses using chemical tracers, particularly radionuclides. Although promising if properly combined with traditional techniques, more isotopes or compounds are required to derive further conclusions. In terms of biological aspects, the high seeding potential of Thalassiosira after sea ice melting has been featured by many authors, and it was considered as the reason for its highest abundance in spring. The total carbon mass flux, which is essential for scallop farming, is highest in April–June, normally 120–160 mg C m−2day−1. The total carbon mass flux is maximum (up to 1165 mg C m−2day−1) after the spring bloom peak, and the spring bloom is strongly linked to sea ice retreatment. It was identi