Moyer R.P.

Testing coral-based tropical cyclone reconstructions: An example from puerto rico

Kilbourne, K. Halimeda, Ryan P. Moyer, Terrence M. Quinn, and Andrea G. Grottoli. 2011. Testing coral-based tropical cyclone reconstructions: An example from puerto rico. Palaeogeography Palaeoclimatology Palaeoecology 307 (1-4) (JUL 1): 90-7.

Abstract: 
Complimenting modern records of tropical cyclone activity with longer historical and paleoclimatological records would increase our understanding of natural tropical cyclone variability on decadal to centennial time scales. Tropical cyclones produce large amounts of precipitation with significantly lower δ18O values than normal precipitation, and hence may be geochemically identifiable as negative δ18O anomalies in marine carbonate δ18O records. This study investigates the usefulness of coral skeletal δ18O as a means of reconstructing past tropical cyclone events. Isotopic modeling of rainfall mixing with seawater shows that detecting an isotopic signal from a tropical cyclone in a coral requires a salinity of ~33 psu at the time of coral growth, but this threshold is dependent on the isotopic composition of both fresh and saline end-members. A comparison between coral δ18O and historical records of tropical cyclone activity, river discharge, and precipitation from multiple sites in Puerto Rico shows that tropical cyclones are not distinguishable in the coral record from normal rainfall using this approach at these sites.

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.

Abstract: 
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.

CARBON ISOTOPES (δ13C & Δ14C) AND TRACE ELEMENTS (Ba, Mn, Y) IN SMALL MOUNTAINOUS RIVERS AND COASTAL CORAL SKELETONS IN PUERTO RICO

Moyer RP (2008) Carbon Isotopes (δ13C & Δ14C) and Trace Elements (Ba, Mn, Y) in Small Mountainous Rivers and Coastal Coral Skeletons in Puerto Rico. Ph.D. Dissertation, The Ohio State University, School of Earth Sciences, Columbus, OH. 260pp.

Abstract: 
Tropical small mountainous rivers (SMRs) may transport up to 33% of the total carbon (C) delivered to the oceans. However, these fluxes are poorly quantified and historical records of land-ocean carbon delivery are rare. Corals have the potential to provide such records in the tropics because they are long-lived, draw on dissolved inorganic carbon (DIC) for calcification, and isotopic variations within their skeletons are useful proxies of palaeoceanographic variability. The ability to quantify riverine C inputs to the coastal ocean and understand how they have changed through time is critical to understanding global carbon budgets in the context of modern climate change. A seasonal dual isotope (13C & 14C) characterization of the three major C pools in two SMRs and their adjacent coastal waters within Puerto Rico was conducted in order to understand the isotope signature of DIC being delivered to the coastal oceans. Additionally a 56-year record of paired coral skeletal C isotopes (δ13C & Δ14C) and trace elements (Ba/Ca, Mn/Ca, Y/Ca) is presented from a coral growing ~1 km from the mouth of an SMR. Four major findings were observed: 1) Riverine DIC was more depleted in δ13C and Δ14C than seawater DIC, 2) the correlation of δ13C and Δ14C was the same in both coral skeleton and the DIC of the river and coastal waters, 3) Coral δ13C and Ba/Ca were annually coherent with river discharge, and 4) increases in coral Ba/Ca were synchronous with the iii timing of depletions of both δ13C and Δ14C in the coral skeleton and increases in river discharge. This study represents a first-order comprehensive C isotope analysis of major C pools being transported to the coastal ocean via tropical SMRs. The strong coherence between river discharge and coral δ13C and Ba/Ca, and the concurrent timing of increases in Ba/Ca with decreases in δ13C and Δ14C suggest that river discharge is simultaneously recorded by multiple geochemical records. Based on these findings, the development of coral-based proxies for the history of land-ocean carbon flux would be invaluable to understanding the role of tropical land-ocean carbon fluxes in the context of global climate change.
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