Seafloor hydrothermal control over ocean dynamics in Enceladus

Abstract

Cassini observations imply that there is a global ocean underneath Enceladus’s ice shell with hydrothermal seafloor activity. Previous numerical simulations showed that convection in Enceladus’s unconsolidated core may produce a heterogeneous seafloor heat flux and hydrothermal activity, potentially explaining the South Polar ice thinning and plume activity. How the ocean transports heat and hydrothermal products is the missing piece of the Enceladus puzzle. Here we perform three-dimensional numerical simulations of the ocean dynamics using a very heterogeneous bottom boundary condition from three-dimensional hydrothermal core simulations. We gradually increase the heterogeneity amplitude of the bottom heat flux until its peak-to-peak value reaches 60 times its mean. We show that a strong zonal flow diminishes low-latitude heat transfer, whereas the heat flux remains efficient in polar regions, which explains the ice shell variations derived from gravity and topography observations. Using passive tracers, we predict rising times of hours to weeks, which are compatible with previous predictions. Our simulations confirm that a strong heterogeneous seafloor heat flux concentrates upwellings at the South Pole, thus efficiently transporting organic matter from hydrothermal vents to erupting plumes.