Modelling Enceladus’ ocean stratification, circulation, and impacts upon potential observables

Ames, F. (2026) Modelling Enceladus’ ocean stratification, circulation, and impacts upon potential observables. PhD thesis, University of Reading. doi: 10.48683/1926.00128543

Abstract/Summary

Enceladus - an ice-covered moon of Saturn - harbours a global subsurface ocean, a prime target in the search for life. Material lofted into space via plumes erupting from fissures in its south polar ice shell is believed sourced from the ocean, and has been used to infer the ocean composition. This thesis highlights the role of ocean stratification and circulation in modulating the representability of plume material of the bulk ocean, and the sensitivity of these to ocean salinity effects. A general circulation model (GCM) is adapted from terrestrial applications for the study of Enceladus. Leveraging this, it is shown that the ocean beneath Enceladus’ south polar ocean should be stratified if steady state is assumed for its overlying ice shell. Stratification arises owing to ocean salinity effects via two mechanisms: the reversal in the thermal expansion coefficient (αT ) at low salinity, and ice melting. Stratification extent is modulated by mean salinity, ice melting rate, as well as uncertain mixing induced by eddies (κGM ) and tidal- and librational- energy dissipation (κz). Stratification is shown to delay transit of hydrothermally- derived particulates to the plumes by 1000s to 100,000s of years. It is therefore argued that robust modelling of ocean bottom-to-top transport within Enceladus should account for ice shell freshwater fluxes, and a non-linear equation of state that permits αT to vary within the ocean. Assuming a steady state ice shell, constraints are then obtained upon the relative freshening of Enceladus’ south polar ocean. Relative freshening is found stronger for larger melting rate, weaker κz and larger bulk ocean salinity. The work suggests that salt concentrations within plume material may represent an underestimate of the salinity of the bulk ocean. Enceladus’ 3D time-mean ocean circulation is demonstrated to produce a motionally induced magnetic field. This magnetic signature is found to differ at differing ocean salinity, but is likely too weak to detect using modern fluxgate magnetometers. Results obtained here inform future efforts to obtain alternative constraints upon Enceladus’ ocean salinity via its magnetic signature.

Item Type	Thesis (PhD)
URI	https://centaur.reading.ac.uk/id/eprint/128543
Identification Number/DOI	10.48683/1926.00128543
Divisions	Science > School of Mathematical, Physical and Computational Sciences > Department of Meteorology
Date on Title Page	September 2025
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