I've seen tons of posts referencing thermoclines, and while I know what they are, and how they affect my fishing, I'd like to see any information - including myths or misconceptions about them, or even turnover - included in the conversation. Even a simple FAQ link or wiki page will do!
It's winter, so let's try and get a thread going that combines some science with experience.
I'll make a small point to get started. A common misconception I hear is that there is no oxygen in the water below the thermocline. Not true. The proper statement would be there is very little oxygenation below the thermocline. If there is abundant O2 use below the thermocline, then it can become oxygen poor. However, in some lakes there is plenty of O2 to support fish. Think about lakes with trout and/or salmon. They stay below the thermocline in summer. The warm water will kill them, being cold water species.
How does this relate to bass fishing? I catch smallmouth from very deep, as many northerners will also report. Below the thermocline? Maybe. I don't think the thermocline is the impassable barrier some make it out to be. In some lakes, maybe, but certainly not all. I think the main limiting factor may temperature, not O2.
Another tidbit: The thermocline is not a simple line between the two layers - the warmer epilimnium on top, the colder hypolimnium below - but a thin band of transition water that can be as thin as a few feet, or as thick as 15 feet. So, it isn't always just a thin line on your graph.
Last bit on turnover: Storms or current change can cause localized turnover, where the three layers mix. It doesn't mean the whole lake has turned over, but it can affect fishing.
What do you have on the topic, or can add to what I posted?