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To better estimate annual primary production in the Amundsen Sea, which is one of the highest productivity regions in the Southern Ocean, the seasonal variations in carbon and nitrogen uptake rates of phytoplankton were investigated in this study. Based on 13 C-15 N dual isotope tracer techniques, the average daily productivities for the Amundsen polynya (AP), Pine Island polynya (PIP) and nonpolynya regions were 0.25, 0.16 and 0.12 g C m -2 day -1 , respectively. The average daily uptake rates of total nitrogen were 60.2, 53.5 and 34.8 mg N m -2 day -1 for the AP, PIP and non-polynya stations, respectively. In spite of the high concentration of nitrate in the Amundsen Sea, daily nitrate uptake rates (mean ± SD = 0.02 ± 0.01 g N m -2 day -1 ) were lower than ammonium uptakes for all productivity stations in this study, which resulted in a significantly lower f-ratio (mean ± SD = 0.44 ± 0.24) than that (mean ± SD = 0.71 ± 0.15) of the previous year. The substantially lower uptake rates of carbon and nitrogen and the f-ratio, especially in the AP, are due to a large seasonal variation in the uptake rates mainly caused by the shorter daytime duration and partly due to lower light availability induced by deeper mixed conditions in the present study compared with the previous study in 2010/2011. The large seasonal variation in daily phytoplankton production should be considered to better estimate annual production as a basic food source for higher trophic levels in the Amundsen Sea.

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Although the Ulleung Basin is an important biological ''hot spot'' in East/Japan Sea (hereafter the East Sea), very limited knowledge for seasonal and annual variations in the primary productivity exists. In this study, a recent decadal trend of primary production in the Ulleung Basin was analyzed based on MODIS-derived monthly primary production for a better annual production budget. Based on the MODISderived primary production, the mean daily primary productivity was 766. the Ulleung Basin during the study period. The monthly contributions of primary production were not largely variable among different months, and a relatively small interannual production variability was also observed in the Ulleung Basin, which indicates that the Ulleung Basin is a sustaining biologically productive region called as ''hot spot'' in the East Sea. However, a significant recent decline in the annual primary production was observed in the Ulleung Basin after 2006. Although no strong possibilities were found in this study, the current warming sea surface temperature and a negative phase PDO index were suggested for the recent declining primary production. For a better understanding of subsequent effects on marine ecosystems, more intensive interdisciplinary field studies will be required in the Ulleung Basin.