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29 janvier 2018
Variations de pH de l'océan de surface depuis 1689 et acidification récente de l'océan dans le Pacifique Sud tropical
Variations de pH de l'océan de surface depuis 1689 et acidification récente de l'océan dans le Pacifique Sud tropical

Diploastrea heliopora coral proxy records and δ11B-pH reconstruction. New Caledonia D. heliopora annually-resolved records over the period 1689-2011 CE from precisely dated 230Th/U-age. (a) Coral δ11B signature (left y-axis) with estimated seawater pH (pHSW) on the right y-axis using the δ11BSW=39.61‰ (Foster et al., 2010) and isotopic fractionation factor α[B3-B4] of 1.0272 (Klochko et al., 2006) following the conversion equations of Zeebe et al. (2001) and McCulloch et al. (2012). (b) Coral δ13C (‰ VPDB) and (c) δ18O (‰ VPDB) ratios. To highlight the interannual variability, we applied a 7-year smoothing to the records (bold lines). The long term secular trends of each time series (dashed lines) indicates the long term changes and analysed by Bayesian Change Point Analysis algorithm (Ruggieri, 2013) revealing significant times of emergence.

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

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