Energy balance, discharge and travel times of hydrothermal outcrop-to-outcrop flow in 18–22 Ma oceanic crust of the equatorial Pacific Ocean: insights from numerical modelling

Abstract Interactions between thermally driven seawater circulation and sub-seafloor basalt play an important role in global geochemical cycles, influencing the nutrient supply to deep-sea ecosystems and the formation of mineral deposits. In the off-axis area of ridge flank hydrothermal systems, low-permeability sediments may overlie the permeable basalt. However, seamounts protruding from the seafloor and faults provide hydraulic connections, giving rise to so-called hydrothermal siphons, in which one outcrop acts as a recharge and the other as a discharge site. Temperature measurements in bottom sediments have confirmed the occurrence of such circulation systems in the study area. Previous numerical models either used coarse numerical grids or were only able to show the general principles of such systems, e.g. by using pre-conditioned pressure fields. A numerical model with high grid resolution showed that flow is dominated by convection cells, which move horizontally at around 0.21 m/a, although the internal velocity distribution is large. Local recirculation cells form at both the recharge and the discharge sites.