The temperatures of the water in an open pond like this can fluctuate 15 to 20 degrees in a day/night cycle.
There is an aeration point in each pond to provide the necessary oxygen exchange for the ecosystem to overwinter. The snow and ice are left undisturbed to provide quiet, stable environment for the fish.
Checking to make sure that the fish are healthy under the ice is important. Hopefully, you can do this a few times during the winter without removing the snow and ice. An underwater camera to look things over can work well.
Aeration this heavy will ensure that dead zones are less prevalent. Normally, I recommend slower aeration during the winter with more aeration points to eliminate the dead zones.
Heavy snow and ice will provide the quiet, stable environment for the fish that is important for their survival in extreme weather conditions. The aeration and hole associated with it are also essential for overwintering success.