Contribution of Small Phytoplankton to Primary Production in the Northern Bering and Chukchi Seas

The northern Bering and Chukchi seas are biologically productive regions but, recently, unprecedented environmental changes have been reported. For investigating the dominant phytoplankton communities and relative contribution of small phytoplankton (<2 mu m) to the total primary production in the regions, field measurements mainly for high-performance liquid chromatography (HPLC) and size-specific primary productivity were conducted in the northern Bering and Chukchi seas during summer 2016 (ARA07B) and 2017 (OS040). Diatoms and phaeocystis were dominant phytoplankton communities in 2016 whereas diatoms and Prasinophytes (Type 2) were dominant in 2017 and diatoms were found as major contributors for the small phytoplankton groups. For size-specific primary production, small phytoplankton contributed 38.0% (SD = +/- 19.9%) in 2016 whereas 25.0% (SD = +/- 12.8%) in 2017 to the total primary productivity. The small phytoplankton contribution observed in 2016 is comparable to those reported previously in the Chukchi Sea whereas the contribution in 2017 mainly in the northern Bering Sea is considerably lower than those in other arctic regions. Different biochemical compositions were distinct between small and large phytoplankton in this study, which is consistent with previous results. Significantly higher carbon (C) and nitrogen (N) contents per unit of chlorophyll-a, whereas lower C:N ratios were characteristics in small phytoplankton in comparison to large phytoplankton. Given these results, we could conclude that small phytoplankton synthesize nitrogen-rich particulate organic carbon which could be easily regenerated.

Automated summary

The northern Bering and Chukchi seas are biologically productive regions, but recent environmental changes have had unprecedented effects. This study investigated the dominant phytoplankton communities and their contributions to primary production in these regions. The results showed that diatoms and phaeocystis were dominant phytoplankton communities in 2016, while diatoms and Prasinophytes were dominant in 2017. Small phytoplankton contributed differently to total primary production in the two years. Furthermore, there were distinct biochemical differences between small and large phytoplankton.