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International audience; In the Caribbean archipelago, the rare pre-Columbian underwater remains identified to date are generally located at shallow depths on coastal margins such as the Los Buchillones site in Cuba, the Îlet Colas or the Îlet Chasse site in Guadeloupe. The new discoveries in the Grand Cul-de-Sac Marin are of a completely different nature. Following reports in 2012, surveys were organized: a sample of 160 lithic pieces scattered on the seabed between 2.50 m and 4 m deep was taken more than 1 km offshore. It is macrolithic tools in andesite. The most spectacular are axes blades and abrasive tools such as grinding stones, grinders, mortars and circular polishers. There are also elongated pebbles bearing percussion marks attesting to their use as hammers. The status of this vast deposit is still undetermined. It could result from the repetition over the centuries of marine accidents leading to cargo losses. Another hypothesis supposes that these artefacts come from camps or pre-Columbian villages installed on a paleo-littoral and whose vestiges were submerged by the sea following the post-glacial rise of the sea level, or because of great storms causing the erosion of the substrate. The hypothesis of submergence of pre-ceramic sites by rising sea level is reinforced by the discovery of a layer of peat around 5 m deep dated around 4000-5000 BC and containing remains of freshwater trees reflecting a terrestrial environment.

A multiproxy analysis of lacustrine sediments cored in Grand-Case Pond at Saint-Martin, north of the Lesser Antilles archipelago, reveals three distinct climatic periods for the last 3700 years. From 3700 to ~2500 yr cal. BP and from 1150 yr cal. BP to the present, carbonate mud deposition occurred in connection with pond lowstands. These periods were also punctuated by severe drought events, marked by gypsum laminae, and hurricane landfalls, leading to marine sand inputs into the pond. The intermediate time interval, from 2500 to 1150 yr cal. BP, is typified by black organic mud deposition, suggesting that hypoxic to anoxic conditions prevailed at the pond bottom. These were probably linked with a perennial pond highstand and reflect more uniform and wetter climatic conditions than today. The carbon isotopic composition of the ostracod Perissocytheridea bisulcata shows that the lowest δ13C values are recorded during the hypoxic periods, as a consequence of bacterial recycling of isotopically depleted organic matter. Such a climatic history agrees closely with that documented from other records in the Caribbean area, such as the Cariaco Basin, central coast of Belize or Barbados. By constrast, discrepancies seem to emerge from the comparison between hurricane activity recorded at Saint-Martin on the one hand and Vieques (Puerto Rico) on the other hand. We explain this apparent contradiction by a balance between two distinct storm paths in response to latitudinal shifts of the Intertropical Convergence Zone (ITCZ). Stronger storm activity over the Gulf coast and the inner Caribbean Sea is favoured by a southern position of the ITCZ in connection with dry climatic conditions. Plausible links with the North Atlantic Oscillation (NAO) are also suggested.

International audience