Knowledge Bank

Elemental proxies are used to reconstruct oceanic conditions that pre-date modern records. Such proxies have been established in corals, but few attempts have been made in sclerosponges. Acanthocheatetes wellsi (high Mg-calcite, collected from Palau and Saipan) and Astrosclera willeyana (aragonite, collected in Saipan) were stained in situ and left to grow on the reef for two years. We measured P, Pb, Sr and Ba (standardized to Ca) in two-year bulk samples from all specimens and 0.5mm high-resolution samples from two A. wellsi from Palau, one A. wellsi and one A. willeyana from Saipan. Interspecific differences in bulk P/Ca, Pb/Ca Sr/Ca, and Ba/Ca are likely due to mineralogical effects. Bulk sclerosponge P/Ca was higher, and Pb/Ca was lower, in Palau than in Saipan suggesting that these elements are sensitive to regional oceanographic conditions. At high-resolution, only P/Ca signatures were highly reproducible within and among species indicating that sclerosponges reliably record these elemental ratios in their skeletons. Furthermore, the apparent relationship between P/Ca, temperature, rainfall, and nutrient concentrations in Saipan indicates that sclerosponge P/Ca could be a paleonutrient recorder.