Increasing atmospheric CO2 from man-made climate change is reducing surface ocean pH. Due to limited instrumental measurements and historical pH  records in the world’s oceans, seawater pH variability at the decadal- and centennial scale remain largely unknown and require documentation. Here we present evidence of striking secular trends of decreasing pH since the late 19th century with pronounced interannual to decadal-interdecadal pH variability in the South Pacific Ocean from 1689 to 2011 CE.

High-amplitude oceanic pH changes, likely related to atmospheric CO2 uptake and seawater dissolved inorganic carbon fluctuations, reveal a coupled relationship to sea surface temperature variations and highlight the marked influence of El Niño/Southern Oscillation and Interdecadal Pacific Oscillation. We suggest changing surface winds strength and zonal advection processes as the main drivers responsible for regional pH variability up to 1881 CE, followed by the prominent role of anthropogenic CO2 in accelerating the process of ocean acidification.

Référence : Wu H.C., Dissard D., Douville E., Blamart D., Bordier L., Tribollet A., Le Cornec F., Pons-Branchu E., Dapoigny A., and Lazareth C., 2018. Surface ocean pH variations since 1689 CE and recent ocean acidification in the tropical south Pacific. Nature communications 9, 2543. Doi: 10.1038/s41467-018-04922-1

Projects: AO-IPSL-2014; ANR-Labex L-IPSL (Henry Wu – Post-doc 24 months) & ANR CARBORIC