Abstract
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 µm) 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.
Highlights
The biologically productive northern Bering Sea and the Chukchi Sea are important conduit of water masses and organic matters from the North Pacific Ocean transported into the Arctic Ocean and biologically productive regions [1,2,3,4,5]
The ARA07B cruise was conducted in the northern Bering Sea and the Chukchi Sea during 5–19 August, 2016 onboard the Icebreaker R/V Araon (Figure 1; Table 1)
For determining the dominant phytoplankton communities and the relative contribution of small phytoplankton (
Summary
The biologically productive northern Bering Sea and the Chukchi Sea are important conduit of water masses and organic matters from the North Pacific Ocean transported into the Arctic Ocean and biologically productive regions [1,2,3,4,5]. Seasonal sea ice cover has been retreating earlier and forming later in the Pacific Arctic region over the last decade [10]. These current and ongoing changes in environmental conditions could subsequently cause changes in biogeochemical processes and alter marine ecosystem structure in the northern Bering and Chukchi seas [11,12].
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