Core/mantle Partitioning of Chlorine and a New Estimate for the Hydrogen Abundance

Introduction: Chondrites have been used to ascertain the Earth abundances of all but the most volatile elements. Of these, H abundance has dramatic ramifications for the properties of the planet, including rheology and melting relations of the mantle and density and phase relations in the core, yet is poorly known. The very mechanisms of formation of Earth and degassing history depend on the amount of water originally accreted and ultimately lost. If the Earth’s chlorine abundance were well known, it could be used to constrain its H content, because 1) Cl has a strong affinity for water – it is a hydrophilic element; 2) the H/Cl mass ratio of chondrites is relatively constant (Table 1), and 3) the ratios of volatile elements in Earth closely resemble chondritic abundances [1]. We have constrained the Cl abundance on Earth and are able to refine the H (water) estimate of Earth using a completely new method.