Europa's Ocean Translates Interior Tidal Heating Patterns to the Ice‐Ocean Boundary

• Published in: AGU advances Vol. 4; no. 6
• Main Authors: Lemasquerier, D. G., Bierson, C. J., Soderlund, K. M.
• Format: Journal Article
• Language: English
• Published: Hoboken John Wiley & Sons, Inc 01-12-2023; Wiley
• Subjects: Equilibrium; Europa; Heat; Heating; Ice; Jupiter; numerical modeling; Ocean circulation; ocean dynamics; Ocean floor; Oceanic convection; Polar environments; rotating thermal convection; tidal heating
• ISSN: 2576-604X; 2576-604X
• DOI: 10.1029/2023AV000994

The circulation in Europa's ocean determines the degree of thermal, mechanical and chemical coupling between the ice shell and the silicate mantle. Using global direct numerical simulations, we investigate the effect of heterogeneous tidal heating in the silicate mantle on rotating thermal convection in the ocean and its consequences on ice shell thickness. Under the assumption of no salinity or ocean‐ice shell feedbacks, we show that convection largely transposes the latitudinal variations of tidal heating from the seafloor to the ice, leading to a higher oceanic heat flux in polar regions. Longitudinal variations are efficiently transferred when boundary‐driven thermal winds develop, but are reduced in the presence of strong zonal flows and may vanish in planetary regimes. If spatially homogeneous radiogenic heating is dominant in the silicate mantle, the ocean's contribution to ice shell thickness variations is negligible compared to tidal heating within the ice. If tidal heating is instead dominant in the mantle, the situation is reversed and the ocean controls the pole‐to‐equator thickness contrast, as well as possible longitudinal variations.
Plain Language Summary
Europa, an icy moon of Jupiter, is believed to have a deep salty ocean beneath its ice crust. One of the drivers of ocean circulation is heating from the rocky mantle located under the ocean. This heating is due to (a) the decay of radioactive elements in the mantle (“radiogenic heating”), and (b) the periodic deformation of the mantle as Europa revolves around Jupiter, due to the gravitational force exerted by the gas giant (“tidal heating”). Tidal heating is strongly heterogeneous: higher at the poles, and lower at the points facing and opposite to Jupiter. We investigate the effect of large‐scale heating variations using simulations of the ocean dynamics, although at less extreme parameters than the real Europa ocean, and neglecting the effects of salinity and phase change. We show that if tidal heating is dominant, the ocean circulation does not erase the variations of bottom heating and transposes them particularly well in latitude up to the ice‐ocean boundary. This has consequences on the ice shell equilibrium: if mantle heating is heterogeneous, thickness variations could be controlled by the oceanic heat flux, resulting in thinner ice at the poles. These results now await comparison with measurements from Europa Clipper.
Key Points
We use an idealized model of thermally driven flows in Europa's ocean, neglecting salinity and feedback effects of the ice
Heterogeneous tidal heating in the mantle modifies the mean circulation in Europa's ocean and could drive large‐scale thermal winds
The tidal heating anomaly in latitude is efficiently translated upwards, leading to a higher heat flux into the ice shell at the poles