A multiproxy record of terrestrial inputs to the coastal ocean using minor and trace elements (Ba/Ca, Mn/Ca, Y/Ca) and carbon isotopes (δ13C, Δ14C) in a nearshore coral from Puerto Rico

Small mountainous rivers (SMRs), despite their disproportionate size relative to larger rivers, may contribute as much as one third of the total terrigenous material exported to the coastal ocean. Corals growing near the mouths of tropical SMRs have the potential to provide records of terrigenous material fluxes because they are long lived and elemental and isotope signatures within their skeletons are useful proxies of palaeoceanographic variability. Here, a 56 year record of coral skeletal Ba/Ca, Mn/Ca, Y/Ca, delta C-13, and Delta C-14 measurements is presented from a Montastraea faveolata colony growing similar to 1 km from the mouth of an SMR in eastern Puerto Rico. Coral Ba/Ca was coherent with river discharge and coral skeletal delta C-13 at annual periodicity corresponding to synchronous depletions of both delta C-13 and Delta C-14 in the coral skeleton, and Mn/Ca and Y/Ca were not coherent with river discharge at annual periodicity. Coherence between river discharge and Ba/Ca and the concurrent timing of increases in Ba/Ca with decreases in delta C-13 and Delta C-14 indicate that river discharge is simultaneously recorded by all three geochemical tracers. A reconstruction of Rio Fajardo discharge is presented for a period in which no instrumental discharge records exists shows good fidelity with the timing of increased discharge during the wet season. Thus, coral-based multiple-proxy records can be valuable tools for reconstructing the timing and variability of SMR discharge to the coastal ocean. Such records are critical to understanding changes in material fluxes and biogeochemical cycles in coastal environments due to land use and climate change.