The impact of Freshening on phytoplankton production in the 1 Pacific Arctic Ocean 2 3

22 Since the 1990’s, drastic melting of sea ice and continental ice in the Arctic region, 23 triggered by global warming, has caused substantial freshening of the Arctic Ocean. While 24 several studies attempted to quantify the magnitude of this freshening, its consequences on 25 primary producers remain poorly documented. In this study, we evaluate the impact of the 26 freshwater content (FWC) of the upper Arctic Ocean on phytoplankton across the Pacific 27 sector, from the Bering Strait (65°N) to the North Pole (86°N), during summer 2008. We 28 performed statistical analyses on the physical, biogeochemical and biological data acquired 29 during the CHINARE 2008 cruise to investigate the effect of sea-ice melting on the Arctic 30 phytoplankton. We found that the strong freshening observed in the Canada Basin had a 31 negative impact on primary producers as a result of the deepening of the nitracline and the 32 establishment of a subsurface chlorophyll maximum (SCM). In contrast, regions with lower 33 freshening, such as the Chukchi shelf and the marginal ice zone (MIZ) over the Chukchi 34 Borderland, exhibited a shallower nitracline sustaining relatively high primary production and 35 biomass. Our results imply that the predicted increase freshening in future years will likely 36