....wait, here it is.
Picture yourself deep underwater. You're in your own pond and you're 14 feet down. It's summer time and there's a big ol' high pressure system that's been delivering 99 degrees temperatures, but the water is cool and heavy. Look around. You don't see any rooted plants. It's too dark for plants to grow. You don't see any live algae even. The light is too thin for even single-celled plants to grow. What you do see is crud. Lots of it. Dead algae from above is drifting down, dead leaves, chunks of dead fish. It's all falling down in a slow gentle rain around you. There is one organism that likes it where you are. It's bacteria. Nasty little critters too small for the eye to see. These bacteria feed on all the debris but they don't produce a speck of oxygen. The water is cold, heavy..dense and dark. Up on the surface it's windy out today. The wind is ramping off your south road at about 30 knots, but you can't feel it. Just the dark and the cold. And absolutely NO oxygen.
Now picture yourself about four feet under the surface. The water is really warm, like a bathtub. Maybe 18 degrees warmer than down on the bottom! But plants are all around. Algae everwhere. Rooted plants, too. All producing oxygen. That wind is creating whitecaps above you. Oxygen is king. The water isn't as heavy either. It's lighter and less dense. It dances on top of the deeper, colder layer like a hot air balloons drift above the land.
Now, as fall arrives and the nights start to cool, the surface temperature starts to creep down. The differential that was once 18 degrees is 16, then it's 13, and ten and eight. Suddenly the warm water isn't dancing anymore. It's nearly as heavy as the water below. It's like your eleven-year-old son who wants a piggy back ride. He might just collapse on top of you!
Then something happens. It's cool and windy out, or there's a cool rain falling and that differential drops to about nothing and WHOOSH!!! the pony ride is over. Top and bottom mix, maybe in just a couple of hours. All of the crud and anoxic water is suddenly everywhere. Oxygen plummets, clarity plummets, and shoreline plants sometimes even starve for light and die.
Anywayssssss........What I'm saying is that it's not so much the differential that makes it turn over, it's the reduction and elimination of the differential. Your three degree difference, if following a couple of months of larger differentials could make you about to "flip". Once it does there will be a period of time where the temperature differential will virtually cease to exist. Now if you've been aerating all summer, then you've likely never had this big differential and you may not turn over at all.
