Latitudinal carbon productivity in the Bering and Chukchi Seas during the summer in 2007

• We found that daily carbon uptake rates are lower than those reported previously in the Bering Sea.
• The mean uptake rates in the Chukchi Sea from this study are noticeably lower than those reported previously in decades ago.
• We found that light is an important controlling factor for the phytoplankton productivity rates in the Bering and Chukchi Seas.

The Bering and Chukchi Seas are well known to be one of the most productive regions in the world. However, these regions have many climate induced-environmental changes over the last decades. Whether these changes enhance or reduce the overall primary production is important in major ecosystems of the Bering and Chukchi Seas. During the Oshoro Maru cruise in 2007 as an IPY (International Polar Year) event of Hokkaido University, nitrogen and carbon uptake rates of phytoplankton were measured at 15 productivity stations in the Bering and Chukchi Seas, using a 13C–15N dual isotope tracer technique. The 2007 mean daily carbon uptake rates of phytoplankton were 0.20 and 0.16 g C m−2 d−1, respectively in the southern and northern Bering Sea. These rates are lower than those reported previously in the regions mainly because of the well-known strong seasonal variation of the carbon uptake rate between May (bloom period) and July (post-bloom period; this cruise). In the Chukchi Sea, the mean uptake rates from this study were 1.63 and 0.18 g C m−2 d−1, respectively in the central and northern regions which are noticeably lower than those reported previously in decades ago. Based on the enhancement experiments, light is an important controlling factor for the phytoplankton productivity rates in the Bering and Chukchi Seas during the cruise period as indicated by higher carbon uptake rates with increased light conditions. Accordingly, nutrients might not be the controlling factor, given there were only minimal increases of primary productivity rates with higher nitrate concentrations.