A pole-to-equator ocean overturning circulation on Enceladus

Lobo, Ana H.; Thompson, Andrew F.; Vance, Steven; Tharimena, S.

doi:10.1038/s41561-021-00706-3

Cited by 41 publications

(49 citation statements)

References 36 publications

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“…This is rather different from the physical picture presented by Lobo et al (42), who describe an ocean that is strongly stratified and whose circulation is confined near the ice shell. These differences likely stem from the values adopted for the eddy diffusivity representing baroclinic instability,  GM , and diapycnal diffusivity associated with convective mixing,  conv : Lobo et al (42) assume a very large value of  GM = 1000 m 2 /s based on observations of Earth's ocean, and a rather small  conv = 0.01 m 2 /s for the convective regions over the poles. This dominance of lateral baroclinic instability over vertical convection gives rise to very strong stratification that, in turn, confines the vertical extent of the circulation.…”

Section: Patterns Of Ocean Circulation Temperature and Salinitycontrasting

confidence: 83%

How does salinity shape ocean circulation and ice geometry on Enceladus and other icy satellites?

et al. 2022

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Of profound astrobiological interest, Enceladus appears to have a global saline subsurface ocean, indicating water-rock reaction at present or in the past, an important mechanism in the moon’s potential habitability. Here, we investigate how salinity and the partition of heat production between the silicate core and the ice shell affect ocean dynamics and the associated heat transport—a key factor determining equilibrium ice shell geometry. Assuming steady-state conditions, we show that the meridional overturning circulation of the ocean, driven by heat and salt exchange with the poleward-thinning ice shell, has opposing signs at very low and very high salinities. Regardless of these differing circulations, heat and fresh water converge toward the equator, where the ice is thick, acting to homogenize thickness variations. Among scenarios explored here, the pronounced ice thickness variations observed on Enceladus are most consistent with heating that is predominantly in the ice shell and a salinity of intermediate range.

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Section: Patterns Of Ocean Circulation Temperature and Salinitycontrasting

confidence: 83%

How does salinity shape ocean circulation and ice geometry on Enceladus and other icy satellites?

et al. 2022

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“…We also find it significant that the composition of the ocean column is depth‐dependent, such that anion and cation concentrations, pH, and redox conditions close to the seafloor are not apparently reflective of the composition nearer to the surface or at the base of the ice shell. A caveat is that the results presented here do not account for homogenizing or mixing of the ocean column's composition by advection or convection, or latitudinal changes; a comprehensive ocean circulation model (e.g., Lobo et al., 2021 ) would be required to place such constraints.…”

Section: Resultsmentioning

confidence: 99%

“…Adjusted Mass of Europa's Hydrosphere After Accounting for Sediments Predicted to Precipitate on the Seafloor and Mass of Gases Exsolved at low Pressure in the Ocean Column the surface or at the base of the ice shell. A caveat is that the results presented here do not account for homogenizing or mixing of the ocean column's composition by advection or convection, or latitudinal changes; a comprehensive ocean circulation model (e.g.,Lobo et al, 2021) would be required to place such constraints.…”

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confidence: 99%

A Metamorphic Origin for Europa's Ocean

Daswani

Vance

Mayne

et al. 2021

Geophysical Research Letters

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Key to understanding the past and present habitability of Jupiter's moon Europa is its composition and evolution. Europa hosts a E 100 km deep liquid water ocean beneath its 3-30 km ice shell (e.g., Schubert et al., 2009). Water, solutes and possible oxidants needed to carry out metabolic processes (Gaidos et al., 1999;Hand et al., 2007) in Europa's ocean were delivered through some combination of Europa's accreted materials, release by subsurface geochemical reactions, and subsequently by meteoritic or Io-genic influx.Surface spectra were initially interpreted as hydrated surface salts from a sulfate-rich ocean (McCord et al., 1998), consistent with models of brine evolution in CI chondrite bodies (Kargel, 1991;Kargel et al., 2000;Zolotov & Shock, 2001). These models propose that Europa's ocean evolved from a reduced Na-Cl-dominated composition to a more oxidized Mg-sulfate ocean as a result of: (a) thermodynamic equilibrium (including by hydrothermal activity) between the ocean and silicate interior, while reduced volatiles 2 H E and 4 CH E produced by water-rock interaction escaped (Zolotov & Kargel, 2009;Zolotov & Shock, 2001, 2004; and/or (b) large fluxes of surface-derived oxidants delivered into the ocean through overturning of the icy lithosphere (Hand et al., 2007;Pasek & Greenberg, 2012). Recently, however, a sulfate-rich ocean has been challenged because the interpretation of hydrated sulfate salts on the surface as an oceanic signature is not apparently consistent with more recent spectroscopic observations. These observations favor instead

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“…The four major drivers of ocean circulation on icy moons are bottom heating (Amit et al., 2020; Soderlund, 2019; Soderlund et al., 2013), the salinity flux induced by freezing and melting of ice (Ashkenazy & Tziperman, 2021; Lobo et al., 2021), the temperature variation just beneath the ice‐shell due to the dependence of the freezing point of water on pressure (Kang et al., 2021), and tidal heating (Matsuyama et al., 2018; Tyler, 2014). In this work, we focus on the first and do not address the others.…”

Section: Introductionmentioning

confidence: 99%

Exploring Ocean Circulation on Icy Moons Heated From Below

et al. 2022

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We numerically explore convection and general circulation of an ocean, encased in a spherical shell of uniform thickness, heated from below by a spatially uniform heat flux, and whose temperature at the upper surface is relaxed to the freezing point of water. The role of salt is not considered. We describe the phenomenology and equilibrium solutions across a broad range of two key non‐dimensional numbers: the natural Rossby number, a measure of the influence of rotation, and the ratio of inner to outer radius of the moon's ocean, a measure of the geometry of the moon's tangent cylinder. Two distinct regimes of circulation are identified, both dominated by Taylor columns aligned with the rotation axis—“plumes” and “rolls” which predominate inside and outside the tangent cylinder, respectively. Inside the tangent cylinder, convective plumes align with Taylor columns that extend from the bottom to the ice shell. The plumes energize geostrophic turbulence which in turn generates a general circulation consisting counter‐rotating zonal jets. Moreover, the plumes are efficient at transferring heat from the bottom to the surface, resulting in loss of heat from the ocean to the polar ice. If the plumes are suppressed rolls outside the tangent cylinder become the dominant mode of heat transfer resulting in equatorial cooling. We conclude that if moons such as Enceladus and Europa were to be predominantly heated from below, they will likely have a “Jovian‐like” circulation: an unstratified, turbulent, geostrophically controlled ocean with strong “Taylor column” behavior and a circulation dominated by counter‐rotating zonal jets.

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A pole-to-equator ocean overturning circulation on Enceladus

Cited by 41 publications

References 36 publications

How does salinity shape ocean circulation and ice geometry on Enceladus and other icy satellites?

How does salinity shape ocean circulation and ice geometry on Enceladus and other icy satellites?

A Metamorphic Origin for Europa's Ocean

Exploring Ocean Circulation on Icy Moons Heated From Below

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