This study uses data along the West Coast of North America to analyze the spatial and temporal evolution of water properties to around 500 m depth. The analysis uses potential density as the vertical coordinate and bottom depth and latitude as the horizontal coordinates. The study uses historical data from the World Ocean Database 2009 from 25°N to 50°N and 1950–2012 for a large-scale analysis of water-property spatial structure and temporal trends in the California Current System (CCS), finding significant trends from 1980 to 2012 along density surfaces near the core of the California Undercurrent (CUC), including decreasing dissolved oxygen (DO) concentration, increasing warmth and salinity, and decreasing potential vorticity. All these changes are consistent with an increasing influence of Pacific equatorial waters with time. Mixing characteristics along the core of the CUC reveal that the 1980–2012 trends in the water-mass properties in the CUC are mostly consistent with a northward shift of these properties, with additional decreases in DO concentration. These modifications are associated with the shoaling and strengthening of the CUC. The changes also imply increased ocean total (natural and anthropogenic) acidification, as the trend in the DO concentration is consistent with a natural decrease in pH all along the CUC, suggesting that significantly more acidic waters are feeding upwelling onto the shelf around 2012 than around 1980.

Meinvielle M. & Johnson G. C., in press. Decadal water-property trends in the California Undercurrent, with implications for ocean acidification. Journal of Geophysical Research: Oceans. Article (subscription required).