Anomalies of the natural convection of water near 3.98$^\circ$C

Natural convection of water in a cylindrical cavity with an open surface at a temperature of about 3.98$^\circ$C (temperature of the maximum water density) is accompanied by typical anomalies on time dependences of temperatures of water layers. In particular, stabilization of temperature $T_{st}$ is observed in the bottom region of the cavity and duration of such stabilization $t_{st}$ may reach several hours depending on the experimental conditions. The results for solutions of sodium chloride and ethanol at a relatively low rate of water cooling show that temperature $T_{st}$ coincides with temperature $T_{\operatorname{max}}$ corresponding to the maximum density of solutions.