Meridional Overturning Circulation of a Snowball Ocean

The Neoproterozoic era might have seen multiple episodes when Earth's surface was entirely frozen. In such a Snowball Earth scenario, the dynamics of the meridional overturning circulation (MOC) could have been drastically different from that of the modern ocean. Lying beneath the thick marine ice cover, the Snowball ocean was expected to be stagnant due to the lack of surface wind stress and air-sea heat fluxes. However, we propose that the Snowball ocean could exchange fresh water with the ice cover, which might have induced strong MOC. Models for the global scale marine ice cover suggest equatorward viscous ice flow was inevitable as a result of the meridional surface temperature gradient. Ice flowed equatorward and melted at low latitudes, thinned the ice at high latitudes, and caused basal freezing there. So being contrary to the modern ocean, the Snowball ocean received net fresh water flux at low latitudes. While in polar regions, brine rejection from freezing sea water led to high salinity water sinking to the abyss and filling the ocean basins. The MOC could be closed by the mixing and upwelling of the abyssal waters at low latitudes. Using an idealized 2-D (latitude-depth) ocean model coupled with a 1-D (latitude) ice flow model, we show that a Snowball ocean could have strong MOC, although the forcing water flux from the ice flow was probably no larger than the discharge of the Amazon River. We discuss the energetics of the overturning circulation, and its characteristics under different parameterization schemes of vertical and horizontal mixing rates. Also being studied are the response of MOC to various forcings: the surface air temperature, the solar radiation input, the geothermal heat flux through the sea floor, etc. The MOC of a Snowball ocean was not merely an odd regime of the global overturning circulations, its coupling with the ice cover and the atmosphere could shed light on our path to resolving many Snowball Earth controversies.