EAPSI: Analyzing lithium and boron isotopes in hot springs and rivers of Taiwan

Washington Kirstin, Los Angeles CA

Investigators

Abstract

Atmospheric carbon dioxide is a direct external driver of Earth's climate. Over geological timescales, carbon dioxide is released through volcanism and is balanced by weathering of silicate minerals. To constrain our understanding of how weathering processes affect Earth's carbon cycle and climate, this project will employ geochemical tools to characterize the chemistry of hot springs and rivers on the island of Taiwan. Taiwan serves as an ideal natural environment for studying hydrothermal inputs to river systems and has been shown to have some of the highest rates of chemical weathering. Lithium and boron isotopes can be used as proxies for chemical weathering intensities through Earth history and today. Interpretations of weathering processes via lithium and boron isotopes are confounded by a lack of data from hot springs; records of chemical weathering should correct for these isotopic inputs through mass balance. Hot spring and river water chemistry will be analyzed in collaboration with Dr. Chen-Feng You's Isotope Geochemistry Laboratory (IGL) at the National Cheng Kung University. Dr. You's expertise in low-temperature geochemistry, and IGL's equipment affords an opportunity to employ unique methods to address the problems presented by this project. In addition to isotopic measurements using a Multi-Collector Inductively-Coupled Plasma Mass Spectrometer (MC-ICP-MS) for lithium and a Thermal Ionization Mass Spectrometer (TIMS) for boron, major elements will be measured for chemical geothermometry. Chemical geothermometry will estimate the subsurface water temperature in hot springs during interaction with rock. This will help to constrain the temperatures lithium and boron isotopes experience during the fractionation. Mixing calculations for hot springs inputs to rivers using lithium and boron isotopes will determine inputs of hot springs, which can inform the global budgets of the isotopes. This NSF EAPSI award is funded in collaboration with the National Science Council of Taiwan.