Coral Skeletal Records of Water Quality Change in Mesoamerica

Corals are thought to incorporate metals into their aragonitic skeletons in direct proportion to those found in the surrounding seawater. As they can live for hundreds of years, they are unique recorders of water quality over anthropogenic time scales. We utilized cores from the massive coral Montastrea faveolata from four locations across the Mesoamerican Barrier Reef, the second largest barrier reef on the planet. The sites were chosen to span an inferred gradient of runoff, from the high runoff Sapodilla Cayes and Cayos Cochinos to Utila and Turneffe Atoll, the farthest from major runoff effects. Surface samples of corals at all sites confirm that Turneffe is the least runoff-affected site. Annual samples of coral skeletal material were separated and cleaned using a multi-step leaching procedure to remove surface and interstitial contamination. 18 metals were then measured using an inductively coupled plasma mass spectrometer and normalized to calcium. Ba/Ca, a proxy for sedimentation, shows similar patterns for annual samples from the Sapodilla Cayes and Cayos Cochinos. At both sites, background Ba/Ca increases between ~1950-1970, indicating an overall increase in the amount of sediment reaching the reefs. Also, large spikes in the record may record massive runoff events from storms tracking overland, such as Hurricane Fifi in 1974. 100-150 year long records of Ba/Ca and other metals from these four sites will be compared to investigate changes in water quality over time and location on the reef.