Nickel isotope fractionation during continental weathering

Recent literature has documented systematic variations in the Ni stable isotope compositions of several terrestrial and marine reservoirs of this bioessential trace metal. For example, dissolved Ni in the world's major rivers has been shown to be more enriched in heavy isotopes than the continental rocks from which that Ni was derived (Cameron and Vance, 2014, Geochim. Cosmochim. Acta, 128, 195–211). This observation implies that one or more chemical reactions occurring during weathering of Ni-rich rock drives stable isotope fractionation that results in retention of lighter isotopes of Ni associated with solid phases. We present new Ni isotope analyses of samples from various horizons of the Webster-Addie laterite, near Democrat, North Carolina, USA, as well as results from two sets of experiments designed to constrain the fundamental mechanism(s) driving the isotopic variation observed in that weathering profile.