Advances in high-precision stable K isotope measurements by MC-ICP-MS

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During my first few years as a Ph.D. student, I worked with Dr. Higgins and collaborators on the development of high-precision stable K isotope measurements using commercially available, state-of-the-art MC-ICP-MS machines.  Our improved precision (ca. 0.17‰) allowed us to identify a range of K isotopic variability in terrestrial materials. An important discovery of this analytical survey was the isotopic offset between the seawater and bulk silicate earth potassium reservoirs. Figure: scans of masses 39 and 41 on the MC-ICP-MS showing significant isobaric interferences on mass 41, a result of argon hydride formation. Source: Morgan, Santiago Ramos et al. (2018) JAAS.

K isotope cycling in deep-sea pore-fluids

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Secondary silicate formation during alteration of marine sediments is one of the main sinks of seawater potassium. Using a combination of high-precision K isotope measurements and geochemical modeling, we can learn about the processes controlling the K concentration and isotopic composition of deep-sea pore fluids. Results from this project shed light on the potential mechanisms responsible for the K isotopic offset between seawater and bulk silicate earth. Figure from Santiago Ramos et al. (2018) GCA.

Low-temperature alteration of oceanic crust and the isotopic budgets of K and Mg in seawater

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Reactions associated with low-temperature alteration of oceanic crust play an important role in the chemistry of seawater. In this study, we use measurements of isotope ratios (7Li/6Li, 26Mg/24Mg, 41K/39K, 87Sr/86Sr) and XRD analyses of secondary minerals in altered crust from Troodos ophiolite and ODP Site 801C to investigate (1) isotopic effects associated with oceanic crust alteration by seawater under low temperatures, and how these might explain modern-day ocean chemistry, and (2) assess possible causes for the observed large range in isotopic compositions of altered basalts. These results will improve future isotope mass balance studies of K and Mg in seawater, and hopefully shed light on the relative importance of the mechanisms responsible for the geochemical cycling of these elements on Earth's surface. This project is in collaboration with Dr. Laurence Coogan, Dr. John Higgins, and Princeton graduate student Jack Murphy. Santiago Ramos et al. (2020) EPSL.