Semester of Graduation

Summer 2018

Degree

Master of Science (MS)

Department

Geography and Anthropology

Document Type

Thesis

Abstract

Coral Sr/Ca is a widely-used proxy for sea surface temperature (SST); however, discrepancies in the coral Sr/Ca-SST relationship among colonies of the same species makes uncertainty in absolute temperature reconstructions larger than the climate signal yet climate variability studies are possible. Furthermore, the riverine input of terrestrial carbonate weathering products to the coastal waters can disrupt the coral Sr/Ca-SST signal by changing local seawater chemistry. This study evaluates the fidelity and reproducibly of coral SST proxies (Sr/Ca, Li/Ca, Mg/Li, Sr-U, Mg/Ca, and U/Ca) and a riverine-upwelling proxy (Ba/Ca) in four Orbicella faveolata colonies in two reefs offshore from Veracruz, Mexico (19.06°N, 96.93°W) at various water depths (3–6 m). Previous studies found micro-sampling the skeleton of O. faveolata challenging for recovery of full geochemical seasonal cycles and they suggest using weekly resolution. This study uses laser ablation inductively coupled plasma mass spectrometry to micro-sample O. faveolata at ~weekly resolution for an interval of nine years. A finer micro-sampling resolution (< weekly) resulted in a loss of the seasonal cycle possibly due to micro-scale heterogeneities in the distribution of elements in the coral skeleton. Coral Ba/Ca has anomalous values that coincide with increasing coral Sr/Ca values suggesting terrestrial waters enriched in Sr and Ba are altering seawater chemistry at sites near the Jamapa River. Coral Li/Ca is the best performing coral SST proxy evaluated by this study (Li/Ca, Mg/Ca, Mg/Li, Sr/Ca, U/Ca, and Sr-U in increasing order determined by the error of reconstruction (ºC) of the three-colony average). Coral Li/Ca has the highest correlation with SST and the means and variance are the same among colonies resulting in statistically similar calibration equations suggesting coral Li/Ca captures regional SST without influence from upwelling, terrestrial runoff, or intercolony differences making it suitable for reconstructing absolute SST. Coral Li/Ca calibration equations are similar to those determined for Pacific Porites corals suggesting little species effect or site dependence for this proxy. The coral Li/Ca result is exciting for future work with modern and fossil O. faveolata corals for developing SST reconstructions particularly for nearshore reefs yet further tests are needed to assess the spatial robustness of this proxy.

Date

5-29-2018

Committee Chair

DeLong, Kristine

Available for download on Tuesday, May 27, 2025

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