Tropical Climate Variability and the Atlantic Multi-decadal Oscillation from the Geochemistry of Corals and Sclerosponges over the last 500 years

Observational and model data have shown considerable variability to exist in North Atlantic sea surface temperatures and climate. In particular, several climate oscillations have been documented, including the North Atlantic Oscillation (NAO) and the Atlantic Multi-decadal Oscillation (AMO). While the exact forcing of these modes has yet to be defined, they do appear to produce observable climatic variability on multi- decadal time scales. Recent geochemical analyses on climate proxy archives from the western tropical Atlantic have shown variability consistent with that of the AMO. A 300+ year old coral specimen of Montastraea faveolata growing in 6m of water south of Port Everglades, Florida, and a 550+ year old sclerosponge specimen of Ceratoporella nicholsoni collected from 133m of water off of Lee Stocking Island in the Exuma Sound, Bahamas, have been milled at a sub- annual resolution and analyzed for stable C and O isotopes as well as minor element ratios. Salinity calculated from a combination of δ18O and Sr/Ca exhibits similar periodicities to the AMO between ~1700 AD and the present; a rather surprising finding given the significant differences in the local environmental conditions of the two samples. Prior to the 1700s, our sclerosponge record diverges from the AMO record reconstructed from tree rings. Additional analyses from the region will be needed to determine the reasoning for this discrepancy.