British Geological Survey, United Kingdom

The coral reef framework off Tahiti was drilled during Integrated Ocean Drilling Program (IODP) Expedition 310 in order to study environmental change (including sea level rise) following the Last Glacial Maximum (LGM). Cores from sites located in the three drilling areas (Tiarei to the north, Faaa to the west, and Maraa to the southwest of the island of Tahiti) were studied in order to characterize the microbioerosion patterns in the post-LGM deglacial reef framework. A total of 19 samples were examined for information on environmental conditions directly after the demise of the shallow-water corals and during subsequent encrustation by coralline algae and microbialites. Microbioerosion patterns imply that conditions during reef growth were deeper euphotic to dysphotic. The reasons for the largely absent shallow euphotic indications lay in the proposed rapid sea level rise leaving a drowned reef in a "cryptophotic" position of most samples, in enhanced turbidity condensing the photic zonation, or in a combination of these factors. The sea level rise scenario combined with increased nutrient levels are considered the primary factors because entirely cryptophotic conditions of the sediment cores are less probable.