Striped Ocean: How Rotation Reshapes Heat on Icy Moons express
In the deep oceans of icy moons, water is not still. Warm plumes rise from the rocky seafloor, but the planet's rotation twists them into long, slanted rolls stretched along the rotation axis. Previously, this process could not be included in global models: it was too complex. The authors devised a simplified recipe (a parameterization scheme) that captures the key effect: this oblique heat transport from the equator to the poles.
The new scheme was tested against detailed calculations in a spherical shell. It turned out that inside an imaginary cylinder touching the seafloor at the poles, the model accurately reproduces heat transport. Collective behavior of these flows alters the heat flux to the surface as strongly as the bottom heating itself. The model does not yet reproduce the exact temperature at the boundaries, but it captures the overall depth contrast. Now global simulations of oceans on icy moons are more honest, and this approach will work for any rapidly rotating ocean with a tiny Rossby number (a measure of rotation's influence).
Original abstract
as written by the authors arXiv:2606.22547
Convection in icy moon oceans is strongly influenced by rotation, organizing into slantwise columnar structures aligned with the planetary rotation axis. They generate significant meridional heat transport, which can affect the ice shell topography, a primary observable of these moons. However, global ocean simulations cannot resolve convection under realistic icy moon conditions, and traditional convection schemes cannot represent slantwise convection. Here, we develop a slantwise convection scheme and implement it in a global ocean model. We perform benchmark tests in a global spherical shell by comparing parameterized fluxes with convection-resolving simulations. The scheme reproduces the meridional heat transport inside the tangent cylinder, where slantwise convection dominates. The resulting meridional heat transport significantly modifies the surface heat flux, producing variations comparable to the imposed bottom heating magnitude. Although the simulations with parameterized convection cannot fully reproduce the temperature structure, likely due to an inability to reproduce the temperature gradients near the boundaries, they capture the bulk interior vertical temperature gradient. The new scheme allows unresolved slantwise convection to be represented in global ocean simulations for icy moons. It is also applicable to other rapidly rotating oceans with small natural Rossby number ($$\mathrm{Ro}^* \ll 1$$), including deep ocean worlds on exoplanets.
The Rossby number is the ratio of inertial forces to the Coriolis force. In the oceans of icy moons, it is so small that rotation completely determines the shape of currents.
In Arthur C. Clarke's '2010: Odyssey Two', Europa's ocean hides life — perhaps such slanted currents distribute nutrients.