Aragonite saturation state dynamics in a coastal upwelling zone

Coastal upwelling zones may be at enhanced risk from ocean acidification as upwelling brings low aragonite saturation state ((Ar)) waters to the surface that are further suppressed by anthropogenic CO2. (Ar) was calculated with pH, pCO(2), and salinity-derived alkalinity time series data from autonomous pH and pCO(2) instruments moored on the Oregon shelf and shelf break during different seasons from 2007 to 2011. Surface (Ar) values ranged between 0.66 +/- 0.04 and 3.9 +/- 0.04 compared to an estimated pre-industrial range of 1.0 +/- 0.1 to 4.7 +/- 0.1. Upwelling of high-CO2 water and subsequent removal of CO2 by phytoplankton imparts a dynamic range to (Ar) from similar to 1.0 to similar to 4.0 between spring and autumn. Freshwater input also suppresses saturation states during the spring. Winter (Ar) is less variable than during other seasons and is controlled primarily by mixing of the water column.