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Global cycles of Ca and Mg using Ca and Mg isotope ratios during continental weathering

Final Activity Report Summary - BUDGETS OF Ca AND Mg (Global cycles of Ca and Mg using Ca and Mg isotope ratios during continental weathering)

The solid earth, hydrosphere and atmosphere interact over geological timescales to shape the surface of the Earth, climate, life, and erosion as well as the development of soils. Earth scientists have a general understanding and conceptual models of the critical processes that may have acted over geological history, but finding quantitative tracers of these processes remains difficult.

Geochemistry is the study of chemical reactions and processes that act on Earth, and the aim of my work was to trace and quantify the chemical reactions that link the solid Earth, i.e. tectonics, the hydrosphere, i.e. oceans and rivers, and the atmosphere, i.e. climate. More specifically, my work involved the measurement of the isotope ratios of magnesium (Mg), calcium (Ca) and strontium (Sr). These isotope ratios show very small variations, lower than the part per thousand level, which could be detected by modern high precision mass spectrometers. The variations in these isotope ratios were linked to the chemical reactions affecting these elements and differences in the initial source material. The isotope ratios could therefore be used to trace the chemical reactions at the surface of the Earth and the origin of the materials involved in these reactions.

The objectives of my research were to improve quantification of the global cycles of Mg, Ca and Sr. These elements are released from rocks during weathering and transferred to the oceans by rivers. Once in the oceans in solute form Ca, Mg and Sr are returned to the solid phase by forming Ca carbonate, and as such have a strong influence on the carbon budget of Earth, and hence climate. By better quantifying the elements’ global cycles it was hoped to better understand the links between the solid earth and the atmosphere.

The work conducted during the Marie Curie fellowship was twofold and included:

1. collection of a substantial new data set of Mg isotope ratios on Swiss samples that were exceptionally well characterised with a view to better understand the mechanisms that released Mg to the solute phase during weathering. The interpretation of this data set was ongoing by the time of the project completion.
2. modelling and interpreting Mg isotope data from a Californian soil profile and
3. interpretation and modelling of previously collected Ca isotope data form the largest rivers in the world, which were used to better quantify the global Ca budget.

Although the Marie-Curie intra-European fellowship was now terminated, much of the work that was initiated during this period would continue to be pursued by the lead researcher.