The West Coast Ocean Acidification cruise (WCOA) was conducted on the R/V Wecoma from August 11 to September 3, 2011. The first Cruise in 2007 was conducted near the beginning of the upwelling season. The 2nd cruise was timed to correspond to the end of the upwelling season, when hypoxic conditions are expected to attain maximal development. The primary objective of the 2nd cruise was to characterize the chemical relationship between hypoxia and ocean acidification, with the goal of creating predictive relationships to hindcast pH and carbonate saturation states using oxygen, temperature, salinity, and nutrient data. Parameters measured at 93 stations along the Washington/Oregon/California coast included dissolved inorganic carbon (DIC), total alkalinity, oxygen, spectrophotometric pH, and nutrients. Chlorophyll and zooplankton samples were also collected at select stations and depths. Underway measurements included pCO₂ (air and water), DIC, pH, salinity, and temperature. Wave gliders and profiling floats were deployed prior to the cruise to provide additional information on surface and subsurface properties along the cruise track.

This cruise was conducted in collaboration with Dr. Burke Hales of Oregon State University, who conducted high-resolution surveys of the same chemical parameters on the Oregon continental shelf in late April-early May 2011 and one week after the 2011 WCOA cruise. The cruise also included the participation of an NSF-funded piggyback project led by Dr. Miguel Goni (also of OSU) to study the organic carbon cycle on both the 2011 WCOA cruise and the high-resolution Oregon surveys. Members of Dr. Bill Peterson's group from the Northwest Fisheries Science Center also participated on the cruise to study impacts of ocean acidification on marine zooplankton. The cruise was funded by the NOAA Global Carbon Cycle and NOAA Ocean Acidification Programs.