Water temp columns

[Bubba_Bruiser]

I got to thinking about the post Boss put up, but didn't want to hijack it. What are the differences in the temperature related to the different columns when the water flips for the winter? Say if you have a 55° surface temp, what is it going to be on bottom in 20' of water? I know from walking in a lake in the summer, there feels to be a significant difference in say 6' of water on the bottom. But then again it could just feel that way becuase of my body temperature. Any insight?

[nofearengineer]

Bubba...my opinion is that by the time the surface temps have hit 55 F, the lake will have turned over. The entire lake should be 55 F from top to bottom. In that case, the bass will have no particular reason to be deep, other than to relate to cover, or bright skies and high pressure.

[Bubba_Bruiser]

Then why is it not the same in the summer time?

[nofearengineer]

Water is a very odd molecule, Bubba. Unlike most other molecules, which contract as they get cooler, water contracts as it gets colder, til around 39 F, and at that point, it starts to expand again until it freezes. This fact is actually important for the survival of life on this planet. It is the reason water freezes from the surface down.

Water is also not a particularly good conductor of heat. A copper pot is about 700 times better at conducting heat than the water in it! (As a side note, ice is about 4 times better than water.) Water transfers heat primarily by convection, that is to say, movement of layers due to temperature-dependent density.

During the summer, as surface water is heated by the sun, it gets lighter than the water below it, so it slowly rises. This is somewhat of a "positive feedback" situation; the top of the water gets much, much warmer than the bottom. This can only happen because the water conducts the heat to the cooler layers below at a much, much slower rate than the rate at which it is drawn upwards (convected) by its increased buoyancy. A thermocline results.

The depth of the thermocline depends on a few different things, but is generally determined by water clarity. Muddy water will tend to have a shallower thermocline, because the sunlight heating effect can not penetrate as deep. A thermocline sets up shallower, begins earlier, and remains later in the year in muddy lakes. Deep, clear lakes may develop thermoclines, but they will be deeper, less severe, and much shorter-llived.

Long-winded explantion aside, I think a thermocline is definitely what you are feeling with your feet.

[Bubba_Bruiser]

Thanks for the explanation NFE.