13 - The element barn

Summary

This chapter is intended to provide a geochemical overview of a number of important elements. The elements will be grouped according to mixed criteria, in particular their position in the periodic table and their geochemical properties. We will describe the major mineral phases that host these elements in the mantle and the crust, their properties in solution, and the processes by which they are transferred from any major reservoir (mantle, crust, ocean) to its neighbors. We will not reproduce here the terrestrial abundances, which can be found in Appendix A. We will nevertheless provide the reader with some important data. Condensation temperatures in the solar nebula (Wasson, 1985; Lodders, 2003) define the volatile versus refractory character of the element. The solubility and complexation data in surface waters (Morel and Hering, 1993) and the residence times in seawater (Broecker and Peng, 1982) constrain the concentration level and speciation in natural waters at low temperature. Different parts of geochemical cycles may receive uneven attention. This inhomogeneous treatment reflects the power of geochemistry: different elements are used to trace different processes. The atmophile elements, which essentially fractionate in to the atmosphere and the ocean are not considered in this chapter (N, O, H), while only the long-term aspects of the carbon cycle have been addressed.