What’s the flux? Could off-axis hydrothermal fluids buffer the ocean’s Ni concentration and isotopes

Nickel is a trace metal whose concentration in seawater is crucial to the marine ecosystem. But what controls its concentration, now and in the past? For fifty years, researchers trying to construct a steady-state budget model for marine nickel have struggled to find a solution that fits all observations. While previous efforts considered only the river-ocean-marine sediment system, here we demonstrate that off-axis hydrothermal circulation through oceanic crust is likely a substantial source of Ni that must be included in future budget models. This source may be big enough to explain how the Ni concentration in the oceans remains steady on timescales of tens of millions of years.