Thanks guys. We've had some of that wind. Rarely is it more than slightly breezy here. 10 mph is something to really comment on. Rod, without measuring the temp profile of the whole column, do we safely assume the pond is not turning over twice per day, but that the surface water is going from 32 degrees up into the 50s and is more or less sitting on top of the major mass of pond water that's not fluctuating much at all? That would provide for a nearly constant refuge for the fishes.
IMO, your fish are probably in a pretty safe refuge.
Of course, water is a very strange substance. The solid phase (ice) is less dense than the liquid phase. Very few other materials are like that.
As a consequence, the maximum density of water occurs at 39F. So there will be a period in the spring where the water that cools and freezes at the surface does NOT sink, due to the warmer water (35-43F) in the deeper basin actually being denser. The same thing holds true with the water heated in the shallows, once it warms past 39F, it also tend to stay in place and "float" on the colder water.
Very strange indeed! Of course, that means there will always be the possibility that strange weather conditions will cause some harmful results in your pond as an exception to the usual process.
In your location it is very likely that you have a spring turnover as the water warms. If your pond had an average temperature of 34F, as the top warms due to solar heating and contact with a warmer atmosphere, when the water at the surface approaches 39F, it will sink to the bottom and displace colder water. I suspect this process is NOT sudden, and does NOT occur simultaneously across the entire pond, so the fish can easily handle that annual event.
I believe the most common dangerous turnover in the spring occurs when a pond has warmed up a fair bit for its climate zone, and then experiences a significant "cold rain" event. That cold, dense surface (or creek) water running in very suddenly can cause the pond to turnover. This can bring the low-oxygen bottom water into the column where the fish live, and can even bring up organic debris from the bottom which starts to oxidize, further stealing the remaining oxygen from the fish.
