Within the framework of EPOCA (European Project on OCean Acidification ) and the French INSU project PHARE, we are adapting the boron isotope technique to ancient corals with the scope to reconstruct “past” ocean pH changes. In this study, we applied the technique to surface seawater pH reconstructions based on tropical 20th century corals from Fiji. Models estimated a pH drop close to 0.07 pH units in the South Western Equatorial Pacific since the onset of the industrial era (Sabine et al., 2004). To reconstruct such a change in pH, the isotopic composition of boron (δ11B) in coral material has to be determined with a precision better than ±0.2‰. This analytical criteria was meet on a Multi-Collector ICPMS Neptune. We selected a Porites coral for the reconstruction of the time dependent evolution of pH. Our results show a progressive decrease of seawater pH between 1900 and 2000 of 0.08 +/- 0.02 pH units. This decrease in pH agrees with projections of surface ocean pH for the Fiji area obtained with the biogeochemical ocean circulation model NEMO-PISCES. Our results further reveal that seawater pH changes in the Fiji area are strongly affected by regional processes such as the South Pacific Convergence Zone (SPCZ) tightly linked the Pacific Decadal Oscillation (PDO). This last observation highlights the potential of the δ11B-pH technique for studying past changes of ocean dynamics. Hönisch, B., Hemming, N. G., Grottoli, A. G., Amat, A., Hanson, G. N. & Bijma, J. (2004). Assessing scleractinian corals as recoders for paleo-pH: Empirical calibration and vital effects. Geochimica et Cosmochimica Acta, 68(18), 3675-3685. Sabine, C. L., Feely, R. A., Gruber, N., Key, R. M., Lee, K., Bullister, J. L., Wanninkhof, R., Wong, C. S., Wallace, D. W. R., Tilbrook, B., Millero, F. J., Peng, T. H., Kozyr, A., Ono, T. & Rios, A. F. (2004). The Oceanic Sink for Anthropogenic CO2. Science, 305, 367-371.