Thermocline

[the_cat_keeper]

What causes thermocline and does it affect the marine life?

 

[archman]

Warmer water mass atop cooler water mass... usually. Warmer water is less dense than cooler water (of the same salinity anyway), so it floats above it's cooler pal. It's basically a difference in densities, which is officially termed a "pycnocline". All thermoclines belong in this category, as do salt wedges, brine seeps, and stuff of that nature.

As for thermoclines affecting marine life, typically it's the plankton that show the most effect. Being "trapped" within their respective mass of water, a layering created by a thermocline can restrict vertical migrations. Sometimes this is good, usually it's not.

 

[the_cat_keeper]

Does it cause certain marine creatures to "disappear", to reproduce, etc?

I noticed we experienced thermoclines in almost all the dives during my last dive trip... and at the same time, there were very few nudibranches compared to previous years. Made me wonder if that was the reason.

 

[drbill]

Archman pretty well covered the topic.

Thermoclines can affect other species as well. For example, our black sea bass seem to hover in the water column just above the thermocline (just like many divers I know). Thermoclines can move up and down (ours has been as shallow as 15' and as deep as 80' the past few weeks), so some species may move with it and be found more frequently at different depths each time one dives.

 

[scowens]

Warmer water mass atop cooler water mass... usually. Warmer water is less dense than cooler water (of the same salinity anyway), so it floats above it's cooler pal. It's basically a difference in densities, which is officially termed a "pycnocline". All thermoclines belong in this category, as do salt wedges, brine seeps, and stuff of that nature.

As for thermoclines affecting marine life, typically it's the plankton that show the most effect. Being "trapped" within their respective mass of water, a layering created by a thermocline can restrict vertical migrations. Sometimes this is good, usually it's not.

Reviving this thread....Obviously there is something I'm missing, but exactly how does a thermocline work? I know that the water seems to "layer" itself, but I also know that water is very thermoly conductive so 'how' can it layer like that? FYI, my experience is in freshwater.

Thanks
Steve

 

[GA Under Water]

http://en.wikipedia.org/wiki/Thermocline

read up on it.

Another way of looking at it. But it isn't Water density. It's more of the same feature that takes color out of your gear as you descend. It doesn't allow heat to the lower layers, + Surface circulation + Dying organizims

http://www.broadwaters.fsnet.co.uk/thermocl.htm

http://www.broadwaters.fsnet.co.uk/epilimni.htm Surface water

http://www.broadwaters.fsnet.co.uk/hypolimnion.htm Below the Thermocline.

 

[archman]

Obviously there is something I'm missing, but exactly how does a thermocline work? I know that the water seems to "layer" itself, but I also know that water is very thermoly conductive so 'how' can it layer like that? FYI, my experience is in freshwater.

I assume you want to know why the different layers of water don't mix? Good question. The *simple* answer is, is that if there aren't any outside environmental influences, they eventually will mix. Or to be more precise, the layers will become so finescale, you can't readily distinguish them. You need to have a highly homeostatic environment to see this level of stratification, however. Like a deep lake.

 

[scowens]

I skimmed through the materials that were posted - thanks alot! I will re-read it this w/e, but I still could not find the answer, although I've learned a great deal. The layer I was refering to above is this: What is going on at the interface when you can be at a thermocline (this hypolimnion) and you can lower your hand and it's cold, but when you raise your hand a few feet, it gets warmer. Water is very thermally conductive, but this physical phenomenom, indicates otherwise. Stated another way, it is, but it isn't. This stuff is just neat! I'm sorry if you've tried to tell me and I'm dense headed, but please refer to my signature. Thanks again for the posts!

Steve

 

[archman]

When you have water masses of different densities, they will not mix readily without an outside energy supplied. Usually this source is wind, at least in shallow waters. Gravity can be the force if lower densites are underneath higher density layers.

A "hypolimnion", which more or less is a deep persistent layer (and generally applied to freshwater systems, not saltwater), typically has a high density. For lower density (=warmer) waters to mix with it (at a rapid rate anyway), an outside energy source needs to be supplied.

Here's a cute kiddie experiment that shows the strength of thermal density gradients.
http://www.exploratorium.edu/science_explorer/watertrick.html

Density is a powerful force.

 

[scowens]

Thanks Archman,

I understand about the denser (colder) water tending to seek the lowest point. So if I have a homeostatic environment or quiet lake, the temperatures will equalize, over time. If I understand correctly, then there are primarily three forces that create/effect thermoclines: Thermal energy source (the sun), kinetic energy source (the wind), and "potential" energy source (gravity). Are there other, outside, sources that I haven't considered?

Also, I guess I was wrong in assuming that the thermocline was a static, level, 'layer' in the water.

Please critique/reply as necessary.

Thanks
Steve