Séminaire ISTeP - Ed Tipper

(St Andrews, UK)

Ca isotope constraints on the global biogeochemical cycle of Ca

At the Earth's surface, calcium (Ca) is a critical element at a variety of scales: it is soluble in natural waters, a biological nutrient, and a major constituent of the dominant mineral sink for carbon in the ocean (CaCO₃). There is a 5 per mil variation in Ca isotopic composition (⁴⁴Ca/⁴⁰Ca expressed as δ⁴⁴Ca) in the various Ca reservoirs on Earth, suggesting Ca isotopes as promising tracers of Ca cycling in both the present and the past.  This talk will discuss Ca cycling both in the terrestrial and the marine realm.  One of the major goals with Ca isotopes has been to reconstruct seawater Ca isotope variations over time.  To be able to do this nambiguously, it is necessary to understand the controls of Ca isotopes on the continents, because the continents provide the main input of Ca to the oceans via rivers.  Modern rivers show a much smaller range in δ⁴⁴Ca than marine carbonates, indicating that in the past, either rivers showed much more variation than the present day, or that other factors control the isotopic composition of marine carbonates.  This talk will discuss mechanisms for changing the riverine Ca isotope composition, as well as suggesting reasons for the variations in marine carbonates.

11/10/2013 à 12h30, Salle Fourcade