K isotopes as a tracer of seafloor hydrothermal alteration

Significance Elemental exchange between seawater and oceanic crust is important both in modulating the ionic composition of seawater over geologic time and in controlling the elemental and isotopic makeup of various solid-earth reservoirs. This study documents large and systematic variations in the K-isotope composition of oceanic crust that has been affected by seafloor hydrothermal alteration. These variations put constraints on the isotopic character of a fundamental flux of the marine K cycle: the hydrothermal flux. We also propose that these variations ought to be exploited in the future as an effective way of tracking oceanic crust as it is subducted into the mantle and sampled by various forms of volcanism.