Date of Award

Fall 2025

Project Type

Thesis

Program or Major

Oceanography

Degree Name

Master of Science

First Advisor

Rosemarie Came

Second Advisor

Robert Letcher

Third Advisor

Joseph Licciardi

Abstract

For much of the last half century, the primary tool for reconstructing ancient ocean temperatures was the oxygen isotope paleothermometer. However, this method is fundamentally limited by its reliance on assumptions about the δ¹⁸O value of seawater, which introduces uncertainty into paleotemperature estimates. The clumped isotope paleothermometer (Δ47) offers a promising alternative by directly measuring the stochastic "clumping" of heavy isotopes (¹³C and ¹⁸O) within the carbonate lattice—a process governed solely by temperature and independent of seawater isotopic composition (Ghosh et al., 2006; Eiler, 2007). While Δ47 paleothermometry has been applied successfully in diverse contexts, including reconstructing extinct animal body temperatures and constraining diagenetic alteration, questions remain about its sensitivity to mineralogical and biological variability. This study addresses one such question: do different benthic foraminiferal species yield distinct Δ47-temperature relationships? To investigate this, multiple species of calcitic and aragonitic benthic foraminifera were selected from the same sediment cores in the Florida Straits, ensuring that all specimens shared identical environmental growth conditions. Using rigorous cleaning, taxonomic identification, and replication protocols, Δ47 values were measured to determine whether inter-species or inter-mineralogy offsets exist. According to theoretical models (Guo et al., 2009), small but detectable Δ47 differences are expected between calcite and aragonite. However, this study found no statistically significant Δ47 differences either between species or between mineralogies. These results indicate that foraminifera of different carbonate polymorphs may not require separate calibrations when applying Δ47 paleothermometry—a conclusion that lends support to Δ47 as a species- and mineralogy-independent paleotemperature proxy. By contrast, δ¹³C and δ¹⁸O values showed clear species- and mineralogy-specific offsets, consistent with known vital effects and mineralogical influences. The lack of corresponding Δ47 variability underscores the robustness of clumped isotope measurements in eliminating biological and structural offsets. Ultimately, this study reinforces the growing consensus that Δ47 is a powerful tool for reconstructing marine temperatures, and it extends its applicability to a broader array of biogenic carbonate species These findings provide a critical reference point for future paleoclimate studies employing Δ47 in both modern and ancient benthic foraminiferal archives.

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