LA-ICP-MS analyses of Caribbean coral Diploria strigosa reveals deviations in geochemical trends following explosive eruption of La Soufrière in April 2021.

Volcanic tephra produced from explosive volcanism modifies chemical cycles in local and regional environments. In tropical volcanic island settings, pristine tephra produced from explosive volcanism is deposited directly into the surrounding seawater and impacts the physicochemical conditions of the marine ecosystem. Additionly, intense weathering of terrestrial deposits prolongs the input of tephra into the coastal environments for extended periods. Coral reefs growing around the coasts of volcanic islands react to changes in surrounding seawater conditions which is the basis of many tropical palaeoclimate studies. We use a common massive Caribbean coral Diploria strigosa to investigate volcanic distrubances in the physicochemical conditions of the marine ecoystem following the April 2021 explosive eruption of La Sourfrière (St. Vincent). A coral core was sampled from the north-west coast of Barbados in July 2022 and from St. Vincent in March 2024. These locations were chosen to compare how tephra quantities and grainsizes differences influence the physicochemical conditions and consequenlty the geochemical imprint of the eruption in coral skeletons. Element/Ca ratios were measured along the theca of each sample using LA-ICP-MS analyses. Our preliminary results from the proximal sample show clear disturbances in the seasonality of common geochemical proxies used for sea surface temperature calibrations (i.e. Li/Mg, Sr/Ca, U/Ca). Additionally, we show that Pb/Ca, Y/Ca, La/Ca and Nd/Ca are elevated following the eruption and exhibit seasonality which was absent prior to the eruption. The seasonal signal decreased progressively each year following the eruption and it interpreted to represent seasonal runoff during the rainy season.