Liquid-liquid critical point in heavy water

According to the liquid-liquid critical-point hypothesis about water, two l iquid waters exist at low temperatures and are supposed to be merged at a c ritical point. The low-temperature metastable melting curves of D2O ices ha ve been measured. It is found that the melting curve of D2O ice III is smoo thly curved around 25 MPa and 238 K, whereas the melting curve of D2O ice I V undergoes an abrupt change of slope at 100 MPa and 220 K. This is consist ent with the existence of a liquid-liquid critical point in the region betw een the melting curve of D2O ice III and the melting curve of D2O ice IV.