The temporal evolution of fluid flow through the Tahiti barrier reef traced by Sr isotopes and pore water chemistry

The internal fluid circulation of the Tahiti barrier reef has been studied with Sr isotopes and pore water chemistry. The study is based on 15 sample series recovered over 2 years from a 150-m deep core drilled through the entire barrier reef down to the volcanic basement. ature data suggest that the interstitial fluids originate from seawater that penetrated the volcanic basement to at least 200 m depth on the ocean-sided slope below the barrier reef. Subsequently, the fluids migrated upward driven by buoyancy through the entire reef. al evolution of the interstitial fluids is mainly controlled by basalt–seawater interaction and by admixture of seawater from the open ocean during upward migration. These processes are monitored with 87Sr/86Sr isotope ratios, H4SiO4 concentrations and alkalinity to give a picture of the evolution of interstitial fluid flow over 2 years. The results indicate that the internal circulation patterns change through time. The modifications concern mainly the residence time of the fluids within the volcanics and the intensity and localization of lateral seawater admixture within the karstified Pleistocene reef.