Thickness of tropical ice and photosynthesis on a snowball Earth

On a completely ice-covered "snowball" Earth the thickness of ice in the tr opical regions would be limited by the sunlight penetrating into the ice co ver and by the latent heat flux generated by freezing at the ice bottom - t he freezing rate would balance the sublimation rate from the top of the ice cover. Heat transfer models of the perennially ice-covered Antarctic dry v alley lakes applied to the snowball Earth indicate that the tropical ice co ver would have a thickness of 10 m or less with a corresponding transmissiv ity of > 0.1%. This light level is adequate for photosynthesis and could ex plain the survival of the eukaryotic algae.