Similarities and differences between chlorine and bromine (isotope) geochemistry

Chlorine and bromine are often still considered very comparable elements because of their similar geochemical behaviour, most prominently because on Earth they concentrate in seawater and are most commonly present as the halide ions (Cl-; Br-). There are however small differences in their chemical characteristics that cause significant variations in their concentration ratios (reported as the Br/Cl ratio) and in their isotope characteristics (reported as ?37Cl and ?81Br). In this talk I will discuss how relatively small differences between these similar elements (think of ionic radii, masses, oxidation-reduction potentials) can cause significant variability on the Br/Cl ratios and also in their isotope variations. The isotope variations of Cl are by now relatively well understood, but variation in Br isotopes, detailed research of which only started about 10 years ago, are not at all well understood. I will point to this fact in the talk and will give a few examples of the research that is planned at IPGP to get a better understanding of the Br isotope variations.