Water Temperature Physics

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windapp

Contributor
Messages
614
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Location
Windsor Ontario
# of dives
50 - 99
I have seen many posts on this website with people claiming they dove in 33-38 degree fahrenheight (0.5-3.3 degrees celcius) water in a lake or quarry in the middle of the summer. I would like to point out that this is impossible. Water reaches its maximum density at 4 degrees celcius (39.2 degrees fahrenheight), and if there was something at depth to make it colder (which there isn't), it would simply rise to the surface, and warm up. In the winter time, water below 4 degrees celcius rises and freezes, and water at 4 degrees celcius sinks to the bottom. This is why the water very deep in a freshwater quarry or lake is exactly 4 degrees year round, and can never be any colder.
 
I am a big fan of physics myself. In fact, I took PHYSICS 101 three times in college.

However, I have been diving in Summersville Lake, West Virginia, in early June. I spent a lot of time at 25 feet doing drills. The temperature at 25 feet was 37 degrees F.

It must have been God that made the water so cold in the summer. Because if physics can't explain it, then it must be God.
 
Your computer thermometer has an accuracy swing of + or - 3 degrees? Or the lake is not all fresh water due to the surrounding earth and minerals?
 
Edit: oh, you're talking about the summer. Yup, you're right for most latitudes. Never mind.

I'm a big fan of physics too! In fact I have a degree in it! :D
 
g2:
Indeed! But that is its maximum density, not its coldest temperature. For fresh water to freeze it must reach 32F (0C), which means the water near the surface must have become that cold, otherwise it would never freeze. And because it's less dense when it's colder than 39.2F, it will rise. Ice divers (in fresh water) will often find the coldest water near the surface. Kind of a reverse thermocline.

If you look very closely at my post, I was referring to fresh water at depth in the summer. Of course, water near the surface will reach 0 C, and transition through the temperatures going down to 0 C in order to freeze. However, if the water at the surface is 4 degrees celcius or higher, by virtue of the fact that any water below it must be at least as dense as the surface water (or it would rise), none of the water below the surface in this condition can be colder than 4 degrees celcius.

As for sea-water ice, I have no idea where you got your facts, but there is salt water under the ice in the arctic. The freezing process is more complex as the ice is almost completely fresh water, and the salt concentrates in the water below.
 
Both my Suunto D3 and Cressi-Sub Archimedes II read a minimum of 37 degrees F after a 40 minute dive at 25 feet.

The dive manuals for both instruments indicate temperature accuracy +/- 2 degrees C (3.6 degrees F) within 20 minutes of temperature change.

So if we are to believe windapp, both instruments, made by two different companies, were off by exactly the same number of degrees, and the error was in the same direction.

Can someone here with a degree in statistics give us a p value for the likelihood of such an event?
 
Can someone here with a degree in statistics give us a p value for the likelihood of such an event?

You can install the p value yourself. It isn't that hard, you just have to punch a hole in your drysuit.:snicker:

Seriously (still lightheartedly), assuming that your temperature gauge is correct, that may indicate that the water wasn't very fresh. Higher salinity would cause colder, saltier water to collect at the bottom. That might drop the maximum density temp to 37F.
 
Probably due to an inaccurate thermometer. It could also be due to colder water rising but getting stopped by a thermocline or current.
 

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