Changes in Acidification of the Water Column Across the California Coastal Upwelling Front

Abstract

The waters off the coast of California experience upwelling that brings cold, nutrientrich, relatively acidic waters onto the continental shelf. During the wintertime, this upwelling system creates a front, and the pH of the coastal water demonstrates chemical changes. In December of 2021, the University of Washington’s Oceanography senior class went on board the R.V. Thomas G. Thompson that sailed from Hawaii to San Diego. During this transect, the rosette was deployed 24 times. The sensors on the rosette measured the pH of the water column. This data was analyzed and compared to bottle samples taken from the Niskin bottles at the last five stations. The results of the pH analysis show the transition between Station 14, within the subtropical gyre, and 20, on the continental shelf. The pH values between these two stations decreased by 0.27. At 200 m, the pH values were 8.05 and 7.78 for Station 14 and 20, respectively. Along isopycnals, the coastal waters were found to be more acidic than those offshore - reflecting either respiration or upwelling. The pH values at this location have not noticeably decreased in the last couple of years, but the data does not go back far enough.