Coral skeletal carbon isotopes (d13C and D14C) record the delivery of terrestrial carbon to the coastal waters of Puerto Rico

Moyer, R. P., and A. G. Grottoli. 2011. Coral skeletal carbon isotopes (delta(13)C and delta(14)C) record the delivery of terrestrial carbon to the coastal waters of puerto rico. Coral Reefs 30 (3) (SEP): 791-802.

Tropical small mountainous rivers deliver a poorly quantified, but potentially significant, amount of carbon to the world’s oceans. However, few historical records of land–ocean carbon transfer exist for any region on Earth. Corals have the potential to provide such records, because they draw on dissolved inorganic carbon (DIC) for calcification. In temperate systems, the stable- (d13C) and radiocarbon (D14C) isotopes of coastal DIC are influenced by the d13C and D14C of the DIC transported from adjacent rivers. A similar pattern should exist in tropical coastal DIC and hence coral skeletons. Here, d13C and D14C measurements were made in a 56-year-old Montastraea faveolata coral growing *1 km from the mouth of the Rio Fajardo in eastern Puerto Rico. Additionally, the d13C and D14C values of the DIC of the Rio Fajardo and its adjacent coastal waters were measured during two wet and dry seasons. Three major findings were observed: (1) synchronous depletions of both d13C and D14C in the coral skeleton are annually coherent with the timing of peak river discharge, (2) riverine DIC was always more depleted in d13C and D14C than seawater DIC, and (3) the correlation of d13C and D14C was the same in both coral skeleton and the DIC of the river and coastal waters. These results indicate that coral skeletal d13C and D14C are recording the delivery of riverine DIC to the coastal ocean. Thus, coral records could be used to develop proxies of historical land– ocean carbon flux for many tropical regions. Such information could be invaluable for understanding the role of tropical land–ocean carbon flux in the context of land-use change and global climate change.