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A pole-to-equator ocean overturning circulation on Enceladus

Abstract

Enceladus is believed to have a saltwater global ocean, heated at the ocean–core interface and losing heat to the floating ice shell above. This configuration suggests an important role for vertical convection. The ice shell has dramatic meridional thickness variations that, in steady state, must be sustained by the ocean circulation against processes acting to remove these anomalies. This could be achieved through spatially separated regions of freezing and melting at the ocean–ice interface. Here, we use an idealized, dynamical ocean model forced by an observationally guided density flux at the ocean–ice interface to argue that Enceladus’s interior ocean should support a meridional overturning circulation. This circulation establishes an interior density structure that is more complex than in studies that have focused only on vertical convection, including a shallow freshwater lens in the polar regions. Spatially separated sites of ice formation and melt enable Enceladus to sustain significant vertical and horizontal stratification, which influences interior heat transport and is critical for understanding the relationship between a global ocean and the planetary energy budget. On the basis of our model, the presence of low salinity layers near the polar ocean–ice interface implies the ocean’s bulk salinity could substantially exceed values inferred from Cassini plume samples.

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Fig. 1: Diagram of Enceladus-like ocean and circulation.
Fig. 2: Steady-state distribution of density layers in the control run.
Fig. 3: Characteristics of the control simulation.
Fig. 4: Phase diagram depicting isopycnal slope.

Data availability

The data used in this article are available in the Caltech Data Repository: https://doi.org/10.22002/D1.1874.

Code availability

A copy of code is stored in the Caltech Data Repository: https://doi.org/10.22002/D1.1873.

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Acknowledgements

A portion of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (80NM0018D0004). This work was partially supported by JPL’s Strategic Research and Technology Development programme, and by the Icy Worlds node of NASA’s Astrobiology Institute (13-13NAI7 2-0024). ©2020. All rights reserved. A.F.T. was supported by the David and Lucile Packard Foundation.

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A.H.L., A.F.T. and S.D.V. conceived and designed the study. A.H.L. and A.F.T. wrote the code, ran the experiments and analysed results. A.H.L., A.F.T., S.T. and S.D.V. co-wrote the paper.

Corresponding author

Correspondence to Ana H. Lobo.

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The authors declare no competing interests.

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Peer review information Primary Handling Editors: Tamara Goldin; Stefan Lachowycz. Nature Geoscience thanks Louis-Alexandre Couston and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary information

Supplementary Information

Supplementary Discussions 1 and 2, Figs. 1–3 and Table 1.

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Lobo, A.H., Thompson, A.F., Vance, S.D. et al. A pole-to-equator ocean overturning circulation on Enceladus. Nat. Geosci. 14, 185–189 (2021). https://doi.org/10.1038/s41561-021-00706-3

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