Late Season Community-level Production in the Western Arctic as Constrained by High-resolution Observations of Dissolved O2/Ar

Recent changes in sea ice extent, thickness, and open water duration in the Arctic have significant potential to alter biogeochemical cycling and ecosystem dynamics in this climate-sensitive region. Notably, spatial and temporal patterns of primary production and community metabolism might shift in response to sea ice-induced changes in stratification and light availability and subsequent coupling/decoupling (in space and time) with grazers. In recent years early season productivity changes associated with decline in ice thickness and earlier ice retreat have been scrutinized for potential to ‘green’ the Arctic. However, the impact of a longer open water duration to late season productivity is still poorly understood, as there are relatively few observations in this time window. Using high resolution observations of the surface water dissolved O₂/Ar collected on cruises in the U.S. and Canadian Arctic margin in October 2011 and 2012, we calculate net community metabolism and net community production rates for nearly 15,000 locations in the Western Arctic margin. Each cruise sampled a broadly similar swath over 20-25 days, including the Bering Strait, NE Chukchi Sea, and Beaufort Sea as far east as the Canadian archipelago. Recurrent productivity ‘hotspots’, identified by positive O₂/Ar saturation of 5%, and corresponding to a net community productivity rate 50 mmol O₂ m^-2 d^-1 (35 mmol C m^-2 d^-1) were evident in the area near Pt. Barrow and Pt. Hope on both cruises. Outside these locations, significant spatial and temporal variability in community metabolism was evident within and between cruises. In 2012 O₂/Ar saturations were predominantly weakly autotrophic (1-2%) with some areas of weak heterotrophy. In 2011 considerable patchiness in autotrophic and heterotrophic conditions was observed. Results will be discussed in the context of event-scale and seasonal-scale drivers and the potential implications for future warming in the Arctic.