Potassium Isotope ratio measurements elucidate physical, chemical, and biological processes.
Leah Morgan, US Geological Survey
Potassium is the last major rock-forming element to be isotopically characterized, due to difficulties with existing analytical techniques. Here we use high-resolution cold plasma mass spectrometry to measure potassium isotopic ratios with precisions improved by a factor of three over previous work. We show that a diverse group of geological and biological samples, including silicate and evaporite minerals, seawater, plant and animal tissues exhibit variability in 41K/39K ratios with a total range of ca. 2.6‰. Seawater and seawater-derived evaporite minerals are systematically enriched in d41K compared to silicate minerals by ca. 0.4 ‰. Igneous, metamorphic, and sedimentary silicates span a range of 2.6‰, and biological samples span a 1.25‰ range. This work suggests that measurements of stable K isotopes will provide unique insights into potassium-based earth and life processes.