Enhancing Our Understanding of Ancient Oceans Through the Investigation of Molybdenum Behavior Under Sulfidic Conditions

Rachel Faye Phillips, University of Texas at El Paso


The most abundant trace metal in the ocean today, molybdenum (Mo), exhibits distinct behavior in oxygenated water, where it remains predominantly dissolved, compared to euxinic (i.e., oxygen-free and sulfidic) water, in which it is sequestered into the sediment. This dissimilar behavior allows us to use Mo concentrations and isotopic compositions in sediment to reconstruct marine oxygenation conditions throughout geologic history. However, Mo sequestration mechanisms under euxinic conditions remain unresolved, which limits the accuracy and precision of reconstructions made using Mo signatures in the rock record. For my doctoral research, I experimentally investigated abiotic and biotic Mo sequestration mechanisms under various euxinic conditions with the goal of defining the major controlling factors and the dominant pathways of Mo removal in relevant natural systems. Results indicate that Mo sequestration under euxinic conditions is strongly dependent on pH and iron concentrations, and thus, these parameters should be considered when interpreting Mo signatures in sediment. Moreover, abiotic and biotic experiments result in very similar dissolved Mo behavior and precipitated Mo species, suggesting that Mo reduction and sequestration in nature involves predominantly abiotic processes. Because accurate ancient reconstructions are critical for climate change models, it is more important than ever to assess and improve the reliability of such proxies. Additionally, Mo is a key component of enzymes that catalyze fundamental metabolic processes, and thus, the study of ancient Mo bioavailability may illuminate early evolutionary trends on Earth. This research also has significant industrial applications, specifically for renewable energy technologies. The synthesis of molecular hydrogen (H2) has been a major focus in the field of renewable energy due to its potential as a fuel, and H2 synthesis is catalyzed by Mo-sulfides, emphasizing the importance of studying formation mechanisms and chemical characteristics of various Mo-sulfide species.

Subject Area

Biogeochemistry|Geochemistry|Paleoclimate Science

Recommended Citation

Phillips, Rachel Faye, "Enhancing Our Understanding of Ancient Oceans Through the Investigation of Molybdenum Behavior Under Sulfidic Conditions" (2023). ETD Collection for University of Texas, El Paso. AAI30817494.