These data are in association with a study conducted in the Santa Barbara Basin, California, USA that were used to develop a 20th century record of ocean acidification in the California Current Ecosystem. These data are based on the planktonic foraminifera species G. bulloides' shell characteristics, specifically area-normalized shell weight (ANSW). Carbonate system calculations for the downcore record determined based on the proxy CO32- values using the CO2SYS program are also included in this archive.