Outlook on Bering Sea Oxygen Cycling: Regional Ocean Simulations of Future Change

Estimates suggest that the global ocean oxygen inventory has declined by ~2% since the mid-20th century. Strong signals of decline in dissolved oxygen have been detected in the Gulf of Alaska and subpolar North Pacific. The adjacent Bering Sea region supplies ~60% of U.S. fish catch by weight annually and any environmental changes to the region threaten the U.S. Blue Economy. The region is known to be affected by rapid temperature rise and ocean acidification, but few studies have examined regional oxygen decline. In this study, a regional ocean model (Bering10k) simulated oxygen cycling in the Bering Sea over past (2003-2012) and future (2006- 2100) timeframes. It was expected that oxygen would decline over the 21st century and low oxygen regions would expand spatially. Bering10k hindcast and projection oxygen were validated against observed data (R = 0.75). Future simulations were forced using atmospheric and ocean boundary conditions derived from ensemble members of the CMIP5 archive (CESM, GFDL, MIROC) for two emission scenarios (RCP 4.5, 8.5). Long term trends suggested significant change in bottom oxygen levels on the Bering shelf by the end of the 21st century. These changes were spatially and simulation dependent, with the largest region-wide declines observed in CESM simulations (–6%). Seasonal oxygen minimums increased in frequency in both CESM and MIROC-forced simulations by 2100. Oxygen drivers also changed, with increases in respiration, remineralization and productivity, and decline in apparent oxygen utilization. Future work should quantify simulation-specific drivers in order to determine the importance of solubility, circulation, and biological processes in regional ocean oxygen.