Examining the drivers of the deoxygenation signal in the northern California Current System

We present an updated analysis of the water mass distributions off Vancouver Island, BC, Canada.

The oxygen signal in the shelf break area off Vancouver Island is dominated by the distributions of the two major contributing water masses, Pacific Subarctic Upper Water (PSUW) and Pacific Equatorial Water (PEW). PEW, transported north through the California Current system, has a distinctly lower oxygen concentration than the more recently ventilated PSUW. It is centred around the 26.5 isopycnal, where O₂ concentrations range from 85 to over 150 mmol/kg. Summer winds regularly cause upwelling of this isopycnal onto the shelf, where it experiences high seasonal O₂ demand due to the increased primary productivity associated with the upwelling regime.

By comparing hydrological and chemical observations from two August cruises (1980 and 2010) to their source water values using an Optimum Multiparameter analysis (OMP), we examine the possibility of changes in the relative water mass contributions between the two years. Considering the recent deoxygenation signal observed in the region, understanding these differences and potentially related changes in the observed oxygen concentration can help us examine whether local processes or larger scale circulation changes are dominating this signal. These results will in future work be used to inform a model analysis of the drivers of deoxygenation on and off the shelf.