Water Temperature Physics

[DivemasterDennis]

or your thermometer was less than physics lab precise.

 

[DivemasterDennis]

Brrrrr! As a warm water diver who has dove in water as cold as 49 degrees F, I find this discussion interesting to a point, but end up wondering whether the 2 degrees difference at issue is of any real significance to a very very very cold diver. My body can feel temperature changes of about four degrees, but all water over 82 degrees feels about the same - nice and warm, and all water under 60 degrees feels to me the same-- really cold. Ok, not so cold as 39 degrees- I guess I don't really want to know what the feels like.
DivemasterDennis

 

[-hh]

... and if there was something at depth to make it colder (which there isn't)...

What if there were a cold spring in the deepest water of the quarry? You could have cold water entering creating a localized cold spot. The deepest part of some quarries is relatively small compared to the overall surface area, while the water would rise and warm as it approached the surface, it might be possible to get an area colder then what the physics you using would normally allow.

True, and the physic side of this discussion that says that water is most dense at 39F, so you would have to rely on just such an "other" factor. So while a 'colder' current could cause the effect, a simple groundwater spring it isn't cold enough: it would have to be runoff from very recently melted ice (glacial or seasonal) that hasn't yet had the chance to warm up to groundwater temperature.

There are other factors at work here. True, the "maximum density" info is correct....for water and not water solutions Solution chemistry (and physical properties, such as freezing points and boiling points as well as density) is different for pure substances. Quarry and lake water, while fresh, is not PURE. When substances dissolve in water, the freezing point usually drops. Therefore, it is entirely possible...indeed, likely...that the low temperatures mentioned are completely correct.

Possible, sure, but not with a solution that we would nominally still consider to be "Fresh" water. IIRC, seawater is typically a 3.5% salt concentration and that only depresses the freezing point by around 4 degrees (to 28F)...you could argue that one could have a cold+dense layer of saltwater below a freshwater quarry, although if we're being that pedantic, it would have to resist convection based mixing as well, so there would have to be a distinct halocline present (as evidence of non-mixing).

Insofar as divers claiming freshwater bottom temperatures significantly below 39F...this is a thermometer gage calibration error...yes, the statistical odds of this are 99.99% While electronics have certainly gotten better, we're simply not going to get a Laboratory Quality measurement system as a secondary feature in a dive computer...and even if we were to do so, it would then have to be sent in for calibration every 6-12 months.

Brrrrr! As a warm water diver who has dove in water as cold as 49 degrees F, I find this discussion interesting to a point, but end up wondering whether the 2 degrees difference at issue is of any real significance to a very very very cold diver. My body can feel temperature changes of about four degrees, but all water over 82 degrees feels about the same - nice and warm, and all water under 60 degrees feels to me the same-- really cold. Ok, not so cold as 39 degrees- I guess I don't really want to know what the feels like.
DivemasterDennis

There's probably not really all that much significance at a few degrees when it is this far down. I've done sub-45F and sub-39F dives ... both wet ... and they really aren't a ton of fun as far as I'm concerned. To reminisce, water below 40F hitting your exposed face and climbing up inside your wetsuit is literally painful and it is easy to get hypothermic.


-hh