Verification of tropical cyclone deposits with oxygen isotope analyses of coeval ostracod valves

Abstract

Reconstruction of prehistoric tropical cyclone (TC) activity often relies on the identification of distinctive overwash deposits (tempestites) in coastal lagoon sediments. Similar sediment deposits, however, can result from high-energy events other than TCs. In this study we assessed the utility of using the geochemistry of ostracod valves, specifically their stable oxygen isotope composition (δ18O), as a potential validation variable that could reduce the chances of misidentifying an overwash deposit as having been generated by a TC, when in fact it formed from another high-energy depositional process (type 1 error). We applied this technique to a sediment core recovered from Laguna Alejandro, Dominican Republic, which had already been analyzed for other sedimentary TC proxies. Negative δ18O anomalies identified in the ostracod valve stable isotope record are associated with TC deposits and are most easily explained by large influxes of 18O-depleted meteoric waters typical of intense tropical storms. There is potential for this technique to be used to identify TC landfalls that are not represented by overwash deposits. We, however, propose a more conservative approach and suggest this technique be used to validate the origin of a storm deposit and reduce the odds of a type 1 error.