Reconstructing Caribbean Salinity Changes Over Time Utilizing Coral Skeleton Geochemistry

In 2002, a large number of coral cores (Montastraea faveolata and Siderastrea sidereal) were collected from the Lesser Antilles (Barbuda to Union Island) with the primary objective being the examination of the interaction between salinity, water, and temperature in the Atlantic and the Caribbean. Here, we discuss the use of stable isotopes and the trace element composition of coral skeletons as a multi- proxy approach to reconstructing regional climate, water mass flow, and riverine (Amazon and Orinoco) inputs. As instrumental records from all of the collection locations demonstrate similar variations in water temperature, changes between the oxygen isotopic signatures of the corals at the individual localities should principally reflect salinity conditions. To this extent, early findings from specimens collected at Bequia, Union Island, Guadaloupe, and St. Croix exhibit differences in oxygen isotope composition, with the specimens originating from the more southerly islands possessing oxygen isotopic values which are more negative than their northern counterparts. These differences will allow for the quantification of salinity changes experienced in this region. On a local scale, some corals demonstrate less pronounced cyclicity in oxygen isotopes, while maintaining a clear annual carbon cycle. This seems to suggest that runoff from land may be both amplifying the carbon isotopic signature and masking that of the oxygen. Preliminary investigations suggest that fine-tuning both age control and sampling techniques can eliminate some of the observed ambiguity and highlights the need for more refined practices for the analysis of coral geochemical records.