Abstract

The radiogenic Sr isotope system is one of the most commonly used palaeo-weathering proxies. Variations in marine 87Sr/86Sr compositions provide an indication of the relative proportion of silicate material versus carbonate and basaltic material reaching the oceans as a consequence of terrestrial weathering¹. Despite many years of research, however, controversy still exists over exactly what the dominant Sr fluxes are and the timescales over which they may vary². Recently the stable Sr isotope system (δ88Sr) has also become established as a palaeo-proxy, and has an advantage over the radiogenic system in that δ88Sr fractionation also occurs during incorporation into carbonates³. The sensitivity of the stable Sr isotope system to the dominant marine sink means a combination of 87Sr/86Sr and δ88Sr analyses may help resolve the persisting questions over Sr mass balance in the oceans.

In this talk I shall present δ88Sr and 87Sr/86Sr data from various marine inputs, including dissolved and particulate riverine material (which account for >40 % of the global Sr flux to the oceans), hydrothermal fluids, glacial ice and rainwater. This data is compared to δ88Sr values from marine carbonates and the implications for the Sr isotopic evolution of seawater are discussed.

[1] Palmer and Edmond (1989). Earth Planet. Sci. Lett. 92, 11-26. [2] Vance et al. (2009). Nature 458, 293-496. [3] Krabbenhöft et al. (2010). Geochim. Cosmochim. Acta.74, 4097-4109.