To explore the global warming effects on the central Arctic, our investigation was conducted between the Chukchi Sea Borderland and the western Canada Basin in July 2021. Although ice was melting, coverage remained above 70% in this region. The distribution of phytoplankton exhibited the vertical peak at the subsurface (50-80m) under the controls of the summer Bering Sea Water (sBSW) and Alaskan Coastal Water (ACW) transported by the Beaufort Gyre (BG). Within the CML, the average of picoplankton (< 2 μm) contributed about 65% of the total Chl a, with the maximum located in the warmer ACW influenced by the BG. Net picoplankton (> 20 μm) were dominant along the sBSW. As ice concentration decreased, alleviated light limitation often enhanced the maximum potential photosynthetic efficiency, even though phytoplankton biomass did not increase immediately. Net community production (NCP), derived from O2/Ar ratios, indicated an autotrophic ecosystem with a rapid increase from the ice edge to open water. NCP was strongly associated with removal of dissolved inorganic nitrogen (DIN), a result of phytoplankton uptake of bioavailable nitrogen that is well-mixed after winter. Compared with historical observations and hydrological changes over time, phytoplankton and NCP in the study area are likely to increase due to global warming, intrusion of summer Bering Sea Water and the intensification of the Beaufort Gyre.

net community production, phytoplankton photosynthesis, nutrient removal