Metal isotopes as chemical weathering tracers

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The rising global temperature is leading to increasing glacial melting and permafrost thawing, resulting in enhanced silicate, sulfide, and carbonate weathering. Elevated sulfide weathering in glaciated regions dominated by high physical erosion generates acidity that can dissolve carbonate, partially counteracting CO2 consumption by silicate weathering. Understanding the balance of the weathering fluxes, which affect the release or drawdown of CO2, is critical for understanding future global warming. Thus, there is a pressing need to develop reliable chemical weathering tracers which will require a comprehensive understanding of isotope fractionation processes. The long-term goal is to use metal isotopes to advance the understanding of metal cycles, which have important implications on the exploration of natural resources, fate and transport of contaminants, impacts of resource development such as mining, shale gas extraction, and geological carbon storage on the quantity and quality of surface water and groundwater. The specific goal for a five-year period (2020-2025) is to develop the applications of 7Li/6Li and 71Ga/69Ga as chemical weathering proxies, particularly in distinguishing silicate, sulfide, and carbonate weathering processes with the support of 87Sr/86Sr. This goal can be achieved through three highly innovative objectives: 1) Assess the role of secondary mineral formation and organic accumulation in controlling Li concentration and isotope composition in arid environments; 2) Determine the magnitudes and mechanisms of Ga isotope fractionation during continental weathering processes, through laboratory experiments and geochemical modelling; then experimental results will be used to interpret Ga isotope behavior in the Zackenberg River Catchment of Greenland; 3) Evaluate the Ga isotope geochemistry in sulfate rich and acidic environments by characterizing Ga isotopes in precipitates and hot spring waters in equilibrium with a variety of bedrock terrains; then the role of adsorption by iron colloids on Ga isotope fractionation during transport in rivers fed by Tamagawa hot springs (Japan) will be tested. Radiogenic Sr isotopes are mainly used as a tool to support the understanding of geochemical processes controlling Li and Ga isotope geochemistry. This research program will advance understanding of Ga isotope fractionation processes, thus, providing a foundation to use Ga isotopes as a geochemical tracer, particularly in tracing silicate vs. sulfide weathering processes, which is necessary for understanding future global warming. Understanding of Li cycles in arid environments will advance knowledge of economically significant sources of Li. Moreover, there is a shortage of highly qualified personnel (HQP) in Canada. HQP trained under this program will gain strong knowledge and technical skills in geochemistry to tackle scientific challenges regarding environmental issues related to natural resource development and climate change.