A coral record of seawater barium concentration recording variations in continental freshwater input to the Gulf of Panama

Andrea Guerra, Rutgers University, Dept. of Marine and Coastal Sciences, New Brunswick, NJ, United States, Andrea G Grottoli, Ohio State University, School of Earth Sciences, Columbus, United States, Reinhard Kozdon, Rutgers University New Brunswick, New Brunswick, NJ, United States and Robert M Sherrell, Rutgers University, Marine and Coastal Sciences and Earth and Planetary Sciences, New Brunswick, NJ, United States
Abstract:
The Gulf of Panama (GP) experiences strong wind-driven cool upwelling conditions in early spring, and non-upwelling, warm, rainy conditions in summer-fall. The coral proxy Ba/Ca has been used previously as an upwelling tracer, since [Ba] increases with depth in the upper ocean. Recent work by LaVigne et al. (GCA, in review) presents an absolute calibration of Ba/Ca against seawater [Ba] for three GP coral species; their single-year record shows that continental runoff in summer-fall is the main driver of seasonal [Ba] variations, despite the strong seasonal upwelling. We investigated temporal variations in freshwater-driven surface water [Ba] by determining Ba/Ca and Sr/Ca by ICP-OES in a Pavona clavus coral core from Contadora Island, GP covering the period 1999-2004. Sampling at 1mm intervals over a ~10cm section of the core yielded ~20 samples per year, allowing a high-resolution reconstruction of the period 1999-2004. Variations in Sr/Ca show seasonal and interannual variations that compare well to independent GP sea surface temperature (SST) records for this period, indicating that Sr/Ca records variations in upwelling intensity, and providing the age model for the core. Using the recent Ba/Ca calibration, we find that surface water [Ba] varies from 40-90nM, with lowest concentrations during maximum upwelling and highest concentration peaks corresponding to high SST in the rainy late summer-fall before the onset of the following upwelling season. Preliminary comparisons of derived surface water [Ba] to regional rainfall records suggest that Ba/Ca holds promise as a rainfall (runoff) proxy, with potential to track longer term variations in regional eastern equatorial climate. Minima in [Ba] show interannual variations from 40-52nM, correlated to upwelling intensity (SST minima), indicating that upwelling strength, related to winds, is after all recorded in this coral, even though runoff has the larger effect on seasonal [Ba] variations.
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