Potassium isotope fractionation during low-temperature biogeochemical processes

Although a recent development of mass spectrometers, such as multi-collector inductively coupled mass spectrometer (MC-ICP-MS), has led to non-traditional stable isotopes in earth and environmental sciences, potassium (K) isotopes are still in the incipient stage yet. Potassium is a major element in continental crust (2.3 wt.%), oceanic crust (0.16 wt.%), and seawater (400 ppm), and is one of major nutrients in the plants. Potassium in the crust mostly exists in silicate minerals and therefore, over 90% of riverine K is derived from silicate weathering. Although the fractionation of K isotopes with mass 39 and 41 is little during high-temperature magmatic differentiation (alpha= +/- 0.07%o, 2sd), it is significant during low-temperature processes, up to +/- 1.3%o (2sd). Therefore K isotopes can be used as a tracer for understanding silicate weathering, paleo-climate and paleo-environment. This review introduces the characteristics of K isotopes, the analytical methods, and the major factors causing K isotope fractionation in the surface environments, such as primary mineral dissolution, secondary mineral formation and plant uptake.