Pigment evidence of phytoplankton community shifts driven by rapid changes in the western Arctic Ocean, 2008–2018

Abstract Rapid warming in the Arctic have influenced the ecological and biogeochemical systems in the Arctic Ocean, particularly the phytoplankton community that plays a fundamental role in food webs and carbon cycle. Our 10‐yr study found an abrupt change in the phytoplankton community in the western Arctic Ocean basin between 2008 and 2018. This shift involved the replacement of nanoplanktonic prymnesiophytes with picoplanktonic prasinophytes. This change was closely associated with a sudden deepening of both the nitracline (from an average depth of 37 ± 15 to 45 ± 8 m) and the chlorophyll maximum layer (from an average depth of 47 ± 16 to 57 ± 10 m) after 2012, driven by thickening of the relatively fresh surface layer ( S < 31) in the western Arctic Ocean basin. The northwestward movement and intensification of the Beaufort Gyre may have exacerbated this surface freshening of the western Arctic Ocean by regulating freshwater redistribution, thereby driving changes in the phytoplankton community.