Seasonal characteristics of new production in the coastal area of Hokkaido, the Okhotsk Sea during the ice-free period

• Published in: Regional studies in marine science 2022-01, Vol.49, p.102110, Article 102110
• Main Authors: Inoue, Kosuke, Shiomoto, Akihiro
• Format: Article
• Language: English
• Subjects: Coastal area of Hokkaido; f-ratio; New production; Nitrate uptake; Okhotsk Sea; Phytoplankton
• ISSN: 2352-4855; 2352-4855
• DOI: 10.1016/j.rsma.2021.102110

Primary production is divided into new or regenerated production based on nitrate or ammonium. New production leads to a net increase in the phytoplankton abundance. Here, we investigated seasonal variations in phytoplankton uptake rates of NO3 and NH4 to estimate the contribution of new production (f-ratio) in the coastal region of Hokkaido, Okhotsk Sea, during ice-free period. High f-ratios (> 0.7) were observed during the spring bloom period (April and May). Relatively high contributions of over 0.4, which have not been previously reported in oligotrophic regions, were frequently observed in the summer and autumn (June to October), despite oligotrophic conditions. In winter (November and December), contributions were below 0.4, despite the relatively high nitrate concentrations. Contributions of new production to that of primary were high during the spring bloom period, summer, and autumn, while being low in the winter. Despite being a relatively eutrophic season, the low contribution in the winter is important because of a significant increase of phytoplankton in the spring bloom and its increase consumption by associated organisms. This seasonal cycle of new production likely plays an important role in the high productivity of fisheries in the study area. •Seasonal variations in new production in Okhotsk Sea coastal area in Japan was investigated.•New production is high during spring and relatively high during summer and autumn than winter.•Proportion of new production (f-ratio) was not linked to nutrient concentrations.•Factors leading to the high production in this sea may be due to the high rate of new production.