Nutrient and phytoplankton dynamics driven by the Beaufort Gyre in the western Arctic Ocean during the period 2008-2014

Nutrient and phytoplankton pigment data were collected during summer cruises in 2008-2014 to examine how the Beaufort Gyre (BG) affected regional differences in nutrient stocks and the phytoplankton community. The results showed a gradual decrease in nutrient concentrations and increasing depth of the chlorophyll maxima toward the center of the gyre. A horizontal map of nitrate at a depth of 50 m indicated nitrogen deficiency in the gyre compared with that in the surroundings. Biogeochemical model simulations suggested that an increased freshwater convergence, driven by the strengthened BG and sea ice retreat, was primarily responsible for the decrease in nutrient stocks. In the BG zone, the contribution of diatoms to the phytoplankton community decreased, accompanied by the increased contribution of small flagellates. The current state of the BG under anticyclonic winds negatively affected the diatom biomass and biological carbon pump. The possible rotation of wind regimes from anticyclonic to cyclonic might relieve the nitrogen deficiency for phytoplankton growth in the western Arctic Ocean.