Midorikawa et al. (2010), from the Geochemical Research Department, evaluated long-term trends of ocean acidification across latitudes in the North Pacific Ocean. Focused on evaluating latitudinal variations, they took samples from the 3°N to the 33°N, all on the 137°E. At these points, they measured partial pressure of CO2 in the sea (pCO2 sea), sea surface salinity, sea surface temperature and amount of dissolved inorganic carbon (DIC). They found in the time series data that there were decreasing trends in pH in the Pacific Ocean. This pH decrease each year came with seasonal changes ranging from 0.0015 to 0.0021 in the winter and 0.0008 to 0.0019 in the summer. Variability in pH was greatly affected by seasonal and temperature change and latitudinal differences. In fact, rising sea surface temperature accounted for up to 44% of the pH decrease in the southern subtropical region while sea surface temperature actually slowed the pH decrease in the northern subtropical region.
Midorikawai T, Masao I, Saitoi S, Sasanoi D, Kosugii N, Motoi T, Kamiya H, Nakadate A, Nemoto K, and Inoue HY. Decreasing pH trend estimated from 25-year time series of carbonate parameters in the western North Pacific. Tellus. 10 June 2010. [cited 2011 Nov 14]; 62B: 649-659.