2014 GSA Annual Meeting in Vancouver, British Columbia (19–22 October 2014)

Paper No. 43-9
Presentation Time: 11:00 AM


GRANIERO, Lauren E.1, GROSSMAN, Ethan L.1, O'DEA, Aaron2, ROBBINS, John A.1, MORALES, Jorge3 and THOMPSON, Ricardo4, (1)Dept. of Geology & Geophysics, Texas A&M University, College Station, TX 77843, (2)Smithsonian Tropical Research Institute, Balboa Ancon, Panama, 2072, Panama, (3)Smithsonian Tropical Research Institute, Galeta Marine Laboratory, Colón, Panama, (4)Smithsonian Tropical Research Institute, Naos Island Marine Laboratory, Panama City, 20521-9100, Panama

Mollusk shell O-, C-, and N-isotope values are useful indicators of nutrient conditions in nearshore environments. Using measurements of seawater temperature, δ18O (δw), dissolved inorganic carbon δ13C (δ13CDIC), and salinity values collected biweekly over a year, we tested the fidelity of shell δ18O and δ13C profiles to record δw, δ13CDIC, and nutrient variations in tropical waters. Preliminary results from five Pacific cone snail (Conus) specimens suggest measured shell δ18O correlates with predicted shell δ18O calculated using δw and water temperature. Seasonal upwelling in the Pacific drove higher amplitudes in shell δ18O (~1.5‰) compared with the Caribbean (<0.5‰). However, both Pacific and Caribbean shell δ13C profiles are relatively invarient, likely reflecting reduced seasonality in the Caribbean and overall lack of variability in DIC source in shallow environments on both sides of the Isthmus of Panama. Predicted shell δ13C curves approximated using measured δ13CDIC are ~1-2‰ higher than actual shell δ13C profiles, suggesting the incorporation of light metabolic C in Conus shells. In addition, we tested N-isotope ratios (15N/14N) in tissues and shell organic matrix of modern bivalves (Isognomon alatus, Pinctada imbricata, and Brachidontes exustus) as a proxy for natural and anthropogenic nutrient fluxes in coastal environments in the Bocas del Toro Archipelago (Caribbean), Panama. For all species, there is no consistent Δ15Ntissue-shell offset between stomach, gill, mantle, and muscle tissues and shell δ15N values. Two species, P. imbricata and I. alatus show significant δ15N tissue-shell correlation. Heavily populated and river influenced sites show higher δ15N values on average (4.4‰) compared with open-ocean sites (3.2‰) in the Bocas del Toro Archipelago. Shell δ18O values corroborate δ15N interpretations of marine versus terrestrial influence with lower values (-1.5‰) in sites influenced by freshwater influx compared with open-ocean sites (-1.0‰). Our results show that O-, C-, and N-isotopes in mollusk shell carbonate and organic matrix are useful indicators of nutrient sources in the southwest Caribbean and eastern tropical Pacific.