4800 YEAR CLIMATE RECORD FROM OSTRACODS, CATALINA ISLAND, SOUTHEASTERN DOMINICAN REPUBLIC

A 31-cm sediment core from a back-barrier wetland on Catalina Island, southeastern Dominican Republic provides a 4800-year record of changing storm frequency and water balance. The core was analyzed for particle size distribution and faunal remains, principally fish scales, foraminifera, and ostracod tests. Stable oxygen-isotope ratios were measured on Cyprideis sp. and Perissocytheridea sp. ostracods. Chronology is provided by AMS radiocarbon dates. The sediment record implies three distinct depositional periods, with wetter conditions (interval-1, 4800-4400 y BP) followed by transitional period (interval-2, 4400-2100 y BP) to dry climatic conditions (interval-3, 2100 y BP to present). Prior to 4400 y BP, sediments are coarser and contain higher relative abundance of nearshore marine foraminifera and fish scales. The coarser sediments and faunal compositions of this interval are interpreted here as the result of frequent storm overwash events, and the more dominant mineralogy of high-Mg calcite indicates a wetter climate.

The shift from wetter to drier climate during interval-2 is observed in the change in grain size distribution toward finer grain sizes, disappearance of fish scales, and a shift in dominance from nearshore marine to brackish water forams. During interval-3, the prevalence of finer grain sizes and the absence of fish scales suggest decreasing seawater overwash from storm events. Ostracod δ¹⁸O values trend from lower (older sediments) to higher (younger sediments), interpreted as evidence of increasing evaporation to precipitation ratios. This strongly supports the hypothesis of the wet to dry climate shift observed in the mineralogy and grain-size distributions.

Our interpretation of decreasing storm frequency and increasing aridity is supported by regional paleoclimate records and SSTs from Haiti and Puerto Rico. Because of the brackish nature of the wetland, it is necessary to take into account salinity, species used in the analysis, and Sr/Ca ratios of the carbonate tests. We can estimate the oxygen isotopic composition of the wetland water in which the ostracods lived and can incorporate this climate record in to a regional context.