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Geological Sciences Seminar: Danielle Santiago Ramos, Woods Hole Oceanographic Institution

Tuesday, Apr 13, 2021 12:00 PM
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Faculty/Staff, Students, Alumni/Friends
Department of Geological Science

Potassium cycling in seawater: Insights from stable potassium isotopes (41K/39K)

Although potassium is a major cation in the oceans, the behavior of stable potassium isotopes (41K/39K) in seawater has been largely unexplored. Here we use high-resolution, inductively coupled (cold) plasma multi collector mass spectrometry to measure 41K/39K ratios in a wide range of geological samples. Measurements of potassium isotopes in rivers, high-temperature hydrothermal fluids, siliciclastic sediments, deep-sea pore-fluids, and altered oceanic crust permit a preliminary characterization of the potassium isotope mass-balance in seawater. Our results suggest that K isotope fractionation during (1) continental silicate weathering, (2) marine sedimentary diagenesis, and (3) low-temperature oceanic crust alteration all likely contribute to the high 41K/39K ratio of seawater (δ41K = 0‰) compared to bulk silicate Earth (δ41K = -0.54‰). We propose that this seawater isotopic enrichment results from both secondary silicate formation (when 39K is preferentially removed) and chemical diffusion (since 39K has a higher diffusion rate than 41K in liquid water) in marine and terrestrial environments. Overall, our results demonstrate that high-precision measurements of 41K/39K ratios can provide new constraints on the relative importance of different sources and sinks within the global potassium cycle in seawater.

Danielle Santiago Ramos is an isotope geochemist interested in understanding the links between seawater chemistry and long-term climate stability on Earth. In addition to that, she also uses isotopes to investigate a variety of other processes, from the anthropogenic contamination of rivers and tap water to the mechanisms controlling osmotic regulation in animal cells. Danielle received her Ph.D. from Princeton University and is currently a Postdoc Scholar at the Woods Hole Oceanographic Institution, where she uses potassium isotopes to track the deep cycling of incompatible elements and volatiles in subduction zone settings. In addition to research, Danielle is involved in diversity and inclusion efforts around undergraduate recruitment/retention and is a Professional Development Facilitator with the Latinas in Earth and Planetary Sciences.

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Email Kelly Wells,, for Zoom link and password.

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