Quantifying basalt denudation rates and their contribution to the global carbon dioxide budget using cosmogenic Mn-53

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Chemical weathering of silicate rocks at the Earth's surface consumes atmospheric carbon dioxide and thus has the potential to influence global climate. In particular, the weathering of basalt rocks could be an important sink for carbon dioxide. Our understanding of what controls the chemical weathering rates of rocks has been limited by our inability to measure rates over the timescales that are relevant to land-forming processes. During the last two decades this situation has improved due to the development of terrestrial cosmogenic nuclide techniques, able to quantify denudation and thus extract rates of chemical weathering over millennial timescales and longer. Basaltic terrains have received little attention in this work, due in part to a lack of suitable target elements for cosmogenic nuclide measurements. However, recent progress has shown cosmogenic Mn-53 is able to quantify denudation rates in iron oxides, which means that it can be measured in basalt. Our overall aim is to take advantage of this new ability and to quantify the importance of basalt weathering as a global atmospheric carbon dioxide sink. To achieve this we will collect samples from two climatically diverse environments: the Paraná flood basalts in humid southern Brazil and the Etendeka flood basalts in arid Namibia. These rocks were originally extruded as one body but were split in two and separated due to the opening of the Atlantic Ocean. While they are lithologically the same, they experience very different amounts of precipitation and both are affected by dramatic temperature gradients. Cosmogenic Mn-53 concentrations in the rock samples will reveal rates of denudation and subsequently the influence that climatic factors have on rates of weathering. Additional investigations into the relationships between chemical and physical weathering, coupled with rates of denudation from nearby non-basaltic lithologies, will allow us to develop a broad understanding of the rates at which basalt weathers and the factors that control theserates.