Ground-truthing lithium paleo-proxies: Experimental study on the Li incorporation and isotope fractionation during inorganic calcite and aragonite precipitation

University Of Hawaii, Honolulu

Investigators

Abstract

Chemical break down of continental silicate rocks (referred to as “weathering”) consumes atmospheric CO2. During this process, lithium (Li) contained in silicate rocks is released and eventually delivered into the ocean by rivers. Intensity of weathering is known to influence the amount and isotopic composition (δ7Li) of Li delivered into the ocean. Thus, changes in the concentration of Li in seawater and its δ7Li can provide valuable information on the history and evolution of silicate weathering and its roles in regulating global carbon cycle and the Earth’s climate. Calcium carbonate (CaCO3) minerals produced by certain groups of marine organisms are known to incorporate trace amounts of Li from seawater, and thus they can be used as a recorder for those changes. However, our current understanding on how Li is incorporated into CaCO3 and what controls the process is extremely limited. In this study, researchers from the University of Hawaii (UH) will perform a series of laboratory experiments to better understand the mechanism of Li incorporation into CaCO3. This work will pave the road for further development in the use of marine CaCO3 minerals as the tracer for past changes in seawater Li and hence continental silicate weathering. The project will enhance education and career development in the geosciences for graduate and undergraduate students at the University of Hawaii. This team will also talk about their findings in the annual open house events such as “Mad About Science” and “Science Alive” at the Bishop Museum Weathering of continental silicate rocks while releasing and eventually delivering Li into the ocean by rivers. Changes in seawater Li concentration and δ7Li can provide valuable information on the history and evolution of silicate weathering and its roles in regulating global carbon cycle and the Earth’s climate. CaCO3 minerals that incorporate Li can be used as a recorder for those changes. This study will be based on well-established inorganic CaCO3 precipitation experiments, where an array of solution physicochemical parameters will be systematically varied from the same control condition for straightforward comparisons of their impacts on δ7Li and Li concentrations in CaCO3. Furthermore, with the use of seeds, both calcite and aragonite samples will be synthesized under identical experimental conditions to examine the polymorphic controls on Li incorporation. This project is expected to provide by far the most complete experimental datasets, which will be combined with the use of surface kinetic modelling to establish a firm inorganic (kinetic and equilibrium) baseline for the elemental and isotopic partitioning of Li between solution and CaCO3 minerals. The project enhances education and career development in the geosciences for graduate and undergraduate students at the University of Hawaii, where the student population has diverse and often underrepresented ethnic background. This team will also talk about their findings in the annual open house events such as “Mad About Science” and “Science Alive” at the Bishop Museum This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.