Abstract

Water parcels close to their freezing point contract and become heavy on warming if they are sufficiently fresh, but expand and become buoyant when salty. We explore the resulting divergent behavior of hydrothermal plumes in fresh verses salty icy ocean worlds, with particular emphasis on Enceladus and Europa. Salty oceans develop buoyant plumes which rise upwards in the water column when energized by localised hydrothermal vents. Fresh oceans, instead, develop bottom-hugging gravity currents when heated near the freezing point, because of the anomalous contraction of fluid parcels on warming. The contrasting dynamics are highlighted and the implications discussed.