Detection of Ocean Acidification in Coastal Waters

The addition of fossil fuel carbon dioxide to the atmosphere is rapidly changing seawater chemistry and the calcium carbonate saturation state of the world’s oceans as a result of the acidifying effects of CO₂ on seawater. This acidification makes it more difficult for marine organisms (e.g., corals, plankton, calcareous algae, and mollusks) to build skeletons, tests, and shells of calcium carbonate. Impacts on these calcifying organisms will lead to cascading effects throughout marine ecosystems. Hydrographic cruises in the coastal waters of the northeastern Pacific along Washington and Oregon indicate that the ocean uptake of anthropogenic CO₂ has shoaled the aragonite saturation horizon so that seasonal upwelling exposes significant portions of the shelf to waters that are undersaturated with respect to aragonite. The corrosive waters reached mid-shelf depths of ~ 40-120 m. In the region of the strongest upwelling, the isolines of Ωarag = 1.0, DIC = 2190 and pH = 7.75 closely followed the 26.2 potential density surface. This density surface shoaled from a depth of ~175 m in the offshore waters and breached the surface over the shelf near the 100 m bottom contour, ~ 40 km from the coast. These results indicate that the upwelling process caused the entire water column shoreward of the 50 m bottom contour to be become undersaturated with respect to aragonite, a condition that was not predicted to occur in surface waters until 2050. While little is known about how these seasonal processes might impact the development of calcifying organisms or the finfish that populate this region, results from laboratory studies show that many species are highly sensitive to changes of this magnitude.