Runaway cooling on ocean planets

Nakayama et al. "Runaway climate cooling of ocean planets in the habitable zone: a consequence of seafloor weathering enhanced by melting of high-pressure ice"
https://arxiv.org/abs/1907.00827

Prediction that planets with high pressure ice at the base of the ocean will experience runaway cooling due to the temperature of the ocean floor being kept at melting point by heating from below. The rocky core is assumed to be undergoing plate tectonics, not sure if a stagnant lid would change things. This probably does not apply to synchronously-rotating planets.