Thermocline?

It is my understanding that the thermocline ceases to exist in winter. After the lake turns over, it is no longer stratified. On the other hand, I’m wrong about half the time.

If it even exists in the winter, my guess is that it would likely be right below the ice. Even if there was a thermocline it would be reversed from the summer thermocline.

Water is most dense at 39f, so it’ll be colder on top than the bottom.

The water turns over (flips) at some point in the fall. This causes the cold water below the thermocline to mix with the warm water above the thermocline. This essentially equalizes the lakes water temperature from top to bottom.
No major temperature differences will exist in the lake again until the beginning of the next summer. In ~ late June to July of the following year when the surface (top layer) in the water column warms up enough the lake will form a thermocline once again, causing the cycle to repeat. As the summer progresses the thermocline will gradually get deeper as the lake heats up.
As mentioned the water right below the ice may be slightly colder since it is more dense, but the difference is generally negligible.
I don’t own one now but probes can be purchased that you lower into the water and read back depth vs. temperature. I don’t see the need for one for ice fishing personally. Perch can be caught thru the ice between 5 feet to 45 feet in the lake I fish.

Hope that clear it up

OK, question here, what is back depth vs. temperature?

I believe he meant “and read-back depth vs. temp”

munchy wrote:

I believe he meant “and read-back depth vs. temp”

Thank you Munchy for providing the clarity. I used to have such a probe when I used my downriggers for lake trout. Got sick of fishing like that, boring. When trolling for lake trout in the summer locating the thermocline was critical.

By definition, thermocline is zone in the water column where greatest change in water temperature occurs. You will need a temperature probe to read that. Slowly lower probe, As you do, you will notice slow decline in temp. When you reach a layer where greatest change occurs, that is the thermocline. Below this layer, temperature will change much slower, once again. And as has been written, thermocline will not exist in winter. As surface temperatures decrease in the fall, the water will increase in density. As it sinks, it mixes with water below untill the entire column is uniform. This is th efall turnover. In winter, the temperature will be warmer towards bottom, but only by a few degrees. This is why ice floats. Water has its’ least density at 32 degrees. A bit long winded, but I hope, helpful.

This may help as well

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No need for temp probes, if you adjust your depth finder properly you may also be able to see the thermocline. It should be a steady line at its depth. Sometimes clutter forms above or below the line.

Above the thermocline it may be say 70 F and in the epilimnion below the thermocline it may be 50 degrees. The termocline may be (10 to greater than 15)’ in length in the water column. This can sometimes make it hard to pin point on the fish-finder. Also with the probe you can target specific species easier. big pike, rainbow and brown trout will reside between (>60 to 55)F. Lake trout will often be in the epilimnion below the thermocline at 50 degrees F.

I use my Marcum 825 to find theroclines every outing.Temp gauge is very accurate and a 2-3 deg. change from surface temp just below ice to the bottom is common, does not sound like much but it makes a differance some days.Fish seek warmer water in winter. Does not change some times hardly at all at say 20 feet of depth, drill 20 yds away and in 25 feet of water and at 22 ft. it is suddenly 3 deg. warmer. I always do better in the warmest water can find. I believe there is a therocline on most lakes I fish in winter u just have to look and find it. Fish safe.

Reason # XXXXX284929 I love this website… So much information

A thermocline is usually defined as a significant temp change in a relatively small depth change. As a scuba diver I have seen a surface temp of 70 with a gradual decrease to 65 degrees at 18-20 feet, then a rapid drop of 10 to 12 degrees in the next 2 or 3 feet. At 22 feet it might be 54-55 degrees and gradually decrease to 51 or 52 degrees at 35 to 40 feet. In a deeper lake it is not uncommon to have a second thermocline at about 40 feet and a temp in the low 40s below the second thermocline. Sometimes a diver will even see the thermocline as a distortion similar to a cooking oil mixed with water in a pan on the stove. You definitely feel the temp change on your face below the second thermocline. I have to imagine it is like “Bobbing for Budweisers in the beer cooler” toward the end of the party.

In the winter there is not a significant enough temperature variation to have a true thermocline, but even a small temp change may be enough to attract fish. Keep in mind that water under ice will run low on oxygen later in the winter and some species of fish have a tendency to be shallower. Use your electronics and lake maps to develop a game plan. Hope this helps.

Denny O wrote:

OK, question here, what is back depth vs. temperature?

munchy wrote:

I believe he meant “and read-back depth vs. temp”

I understand thermocline, I just never heard the other reference.
So the simple answer to my question would be that
Thermocline = (back depth vs. temperature) or read-back depth vs. temperature)?

Forget he said “back”, he was referencing using a probe to find the thermocline. By dropping a probe down you can get a readout on the probes display that says the temperature at a given depth.

There is no such thing as “back depth”

munchy wrote:

Forget he said “back”, he was referencing using a probe to find the thermocline. By dropping a probe down you can get a readout on the probes display that says the temperature at a given depth.

There is no such thing as “back depth”

Thanks for the clarity Munchy. Sorry for any confusion that is exactly what I intended to say: read back the depth vs. the waters temperature, typically at 5′ intervals