Experimental phase diagram of water in the investigated P - T region, melting lines are reproduced from refs. 31 , 43 . The region of stability of plastic ice VII from numerical simulations 8 is shown with white dashed lines, pressures and temperatures are shifted to match the experimental melting line. The measured thermodynamic points are represented as circles with colours corresponding to the phase attribution (a selection of thermodynamic points from previous experiments 34 are represented as squares). Error bars on the pressure determination are of 0.5 GPa for the high-pressure isobars, whereas they are of 0.1 GPa for the thermodynamic points close to the melting as the melting was used to calibrate the pressure.
