LATE HOLOCENE CLIMATE VARIABILITY FROM ST. CROIX, USVI REEF CORALS

We present a multi-century climate record using the skeletal geochemistry of Siderastrea siderea and Orbicella faveolata corals collected near Salt River Bay, St. Croix, USVI. Samples ranging in age from modern to approximately 2100 years old were collected, slabbed, and milled with each coral representing approximately 25 to 40 years of growth. Skeletal δ¹⁸O values correlate strongly with sea surface temperature (SST) and sea surface salinity (SSS). Seasonal variations in skeletal δ¹⁸O values are controlled primarily by changes in SST and secondarily by inferred changes in water δ¹⁸O due to precipitation and runoff. Analysis of these variations in the St. Croix corals indicates either a gradual rise in SST or a decline in SSS over the last several centuries. The remaining coral slabs were analyzed with Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) for trace element geochemistry. Unusually high ratios of Ba/Ca correspond with an influx of sediment typically associated with increased runoff from storm events. The presence of spikes in Ba/Ca may indicate that seasonal variations in skeletal δ¹⁸O values result from a decline in SSS instead of a gradual rise in SST.