Weathering of Ultramafic Rocks

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Peucker-EhrenbrinkEAR-0125873On geologic time scales, atmospheric pCO2 is controlled by the release of Ca and Mg from silicate weathering and subsequent formation of Ca/Mg-carbonates in the ocean. Attempts to deduce the past intensity of silicate weathering have relied mainly on the measured marine 87Sr/86Sr, but lately also on the marine 187Os/188Os record. In order to correlate 87Sr/86Sr and 187Os/188Os in continental runoff with relevant major cations released through silicate weathering, comprehensive data for 87Sr/86Sr, 187Os/188Os, Re, Pt, and major cations (Na, K, Ca, Mg, Si) and anions (Cl, SO4, HCO3) in streams and rivers is needed. Mafic silicates are generally more reactive in the surficial environment than felsic minerals and runoff from ultramafic rocks is characterized by high Ca/Na, Mg/Na and total dissolved loads. Weathering of ultramafic rocks may thus be an important source of riverine Ca and Mg derived from silicate weathering. As a comprehensive data set on ultramafic rock weathering is missing, this project aims to correct that by investigating, in the field and experimentally, how weathering of ultramafic rocks affects riverine, and thus ocean chemistry.