Hindcast (back to 1955) and forecast (up to 2100) of sea-surface pH at BATS and hydrostation S (Bermuda area).

Time-series measurements in the North Atlantic Ocean at the Hydrostation S site (32°10'N, 64°30'W), started in 1954. At that time, temperature and salinity were measured but it was not yet possible to measure the properties of the oceanic carbon cycle. We use these important hydrographic data with the knowledge acquired from more recent measurements (since 1989) of the CO2/carbonate properties at the near-by Bermuda Atlantic Time Series Study (BATS; 31°40'N, 64°10'W), to reconstruct, using two different approaches based upon multi-linear-regressions, the pH at this hydrostation S since its beginning. The results provide good estimates of the ocean acidification in the ocean surface of the area of stations S and BATS since the mid 1950's, an unprecedented near 70-year trend of ocean acidification, as well as a simple way to forecast to 2100 its variations according to the various scenarios of atmospheric CO2 fugacity increase. The simplest approach shown here, further provides an easy way to estimate surface ocean acidification from satellite sea surface temperature measurements.