The REEFCORES-3 ocean research cruise (aboard the Antsiva schooner) carries on from the CNRS-INEE REEFCORES (REEFs and CORals from the EparseS) programme conducted between 2010 and 2014, coordinated by IFREMER (Stéphan Jorry) and CEREGE (Gilbert Camoin). The programme proposes to reconstruct sea level variations and environmental and climate changes from the terminal Quaternary to present, based on studying modern carbonate platforms (Eparses Islands and Western Madagascar). This is a collaborative research programme between IFREMER, IUEM, CEREGE and TOTAL. Two cruises performed in 2011 (REEFCORES-1, RV Marion Dufresne) and 2013 (REEFCORES-2, Antsiva schooner) made it possible to acquire an initial series of sedimentology data (sediment samples taken in lagoons) and seismic data in shallow water (0 to 200 metres), with the aim of mapping the morphology of former reef rims which are now drowned, quantify the accumulation of sediments in lagoons when the islands were drowned during the last rise in sea level (over the past 20,000 years), and above all to assess the potential of some sites in the Eparses Islands to set up drilling in the near future. The results of the first two exploratory cruises in the REEFCORES programme were complemented by bathymetric and seismic data obtained on the slopes and ocean basins adjacent to the Eparses Islands during the PTOLEMEE research cruise (CNFH cruise performed in 2014 on RV L'Atalante, PAMELA project). In this context, the REEFCORES-3 mission's objective was to acquire additional bathymetric and seismic data in shallow water, in order to map all of the drowned reef terraces, to complement acquisitions in lagoons in order to refine the distribution and quantification of sediment volumes trapped in the lagoons, as well as to finalise the site survey for the positions of future drilling (REEFCORES-4 currently being planned). These objectives were supplemented by acquiring geophysical data on the continental shelf next to Madagascar, to attempt to characterize the way a mixed system responds to changes in sea level.