Annually-resolved coral-based d11B-pH reconstruction for the past 323 years from New Caledonia

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 (ocean acidification; OA) since the late 1800s with pronounced interannual to decadal-interdecadal pH variability in the South Pacific Ocean since 1689 CE. High-amplitude oceanic pH changes, likely related to coherent 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 the late 1881, followed by the prominent role of anthropogenic CO2 in accelerating the process of OA.