Coral Temperature Proxies for Orbicella faveolata in Southwestern Gulf of Mexico

Authors: Marissa Anne Vara*, Louisiana State University, Kristine L. DeLong, Louisiana State University , Achim Herrmann, Louisiana State University, Gilman Ouellette, Louisiana State University, Julie N. Richey, United States Geological Survey
Topics: Paleoenvironmental Change
Keywords: sea surface temperature, corals, seasonal variations, Gulf of Mexico, elemental ratios
Session Type: Paper
Day: 4/10/2018
Start / End Time: 10:00 AM / 11:40 AM
Room: Napoleon B2, Sheraton 3rd Floor
Presentation File: No File Uploaded

Coral Sr/Ca is a widely-used proxy for sea surface temperature (SST); however, discrepancies in Sr/Ca-SST relationship among colonies of the same species may reduce confidence in absolute temperature reconstructions. Additionally, terrestrial carbonate weathering can disrupt temperature-based coral Sr/Ca signals by changing local Sr/Ca of seawater in nearshore reef environments. We evaluate the relationship between SST and alternative elemental ratios (Li/Ca, Li/Mg, Sr-U, and Ba/Ca) in three Orbicella faveolata colonies recovered in 1991 by the U.S. Geological Survey from offshore of Veracruz, Mexico (19.06°N, 96.93°W). Previous studies found micromilling skeletal structure of O. faveolata challenging and suggested weekly resolution to recover full seasonal SST cycles. We use laser ablation inductively coupled plasma mass spectrometry to sample at ~weekly intervals spanning four years. Coral Li/Ca co-varies inversely with SST and means and seasonal variance are reproducible among colonies. The Li/Ca-SST relationships for these O. faveolata colonies are similar to each other and those reported for Porites. Coral Ba/Ca analyses reveal elevated values in winters that coincide with increases in coral Sr/Ca in the deeper colony suggesting upwelling of waters enriched in Sr and Ba. In shallower corals, increased Ba/Ca does not coincide with increased coral Sr/Ca indicating no direct influence from runoff. Coral Li/Mg and Sr-U do not show substantial seasonal variations thus are unlikely SST proxies. The lack of mean shifts in coral Li/Ca shows promise for absolute SST for these corals in Veracruz.

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