The most common habitable planets – II. Salty oceans in low-mass habitable planets and global climate evolution

The available models of global climate evolution in habitable earthlike planets do not consider the effect of salt content in oceans, which affects water evaporation. Two distinct categories of such planets are considered in this work: planets with deep oceans, but with intrinsically high salinities due to the weaker salt removal process by hydrothermal vents; and planets with shallow oceans, where the increase in salt content and decrease in ocean area during the onset of glaciation cause a measurable negative feedback on perturbations, helping delay the onset of ice ages. We developed a toy climate model of a habitable planet on the verge of an ice age, using a range of initial salt concentrations. For planets with deep oceans and high salinity we find a considerable decrease in land ice sheet growth rate, up to ~ 23% considering the maximum salinity range. For planets with shallow oceans, the effect of intrinsic high salinity previously modelled is reinforced by the negative feedback, to the point of effectively terminating the land ice sheet growth rate during the time-scale of the simulations. We also investigate the application of this model to the putative ocean of early Mars, and find that the results lie in between the two categories. We conclude that this new phenomenon, which can be viewed as an abiotic self-regulation process against ice ages, should be taken into account in studies of habitable planets smaller and drier than the Earth, which may well represent the bulk of habitable planets.