Today’s classic column discusses water’s unusual property of expanding when it freezes (which is the reason ice floats – it is less dense than liquid water). The column implies, however, that if water didn’t expand when it froze, then ice would form from the bottom up in lakes and other bodies of water, and would kill all the fishes and other critters, thus preventing life from evolving.
Now wait just a dang minute!!! I thought it was the very fact that water expands when it freezes that makes freezing fatal. When a fish (or for that matter a human) freezes, the water in the individual cells expands, causing damage, and resulting in death. Seems to me that if water did not expand when it froze, then maybe freezing would only be a temporary setback (since it wouldn’t damage tissue), and then when the warm season comes, the fishes (or the humans) could just thaw out and go about their business.
If I understand it correctly, the advantage most people are referring to (by this I mean, “the one I know about” ;)), is that if ice were more dense than water, lakes etc. would freeze from the bottom up effectively killing all the fish.
Also, I do believe that are some fish that can be frozen and survive. Goldfish are such a species.
I am sure, however, that someone with more knowledge will soon answer this question.
The expansion of water on freezing is responsible for much of the cellular damage caused by freezing a living organism. On the other hand, if water didn’t expand on freezing, bodies of water would freeze from the bottom up instead of the top down, and this would be very bad for the organisms living in that water, as the whole thing would freeze instead of merely a layer of ice over the water.
I would think that the harm freezing water does to the body has more to do with the fact that the body would not be able to utilize the water contained in it for cellular respiration and other bodily functions because the water is frozen.
I don’t know. Maybe it does involve mechanical cellular damage.
“The most merciful thing in the world, I think, is the inability of the human mind to correlate all its contents.”
-H.P. Lovecraft, “The Call of Cthulhu”
The column of discussion; http://www.straightdope.com/classics/a890630b.html Ya don’t want Jil to freeze you out of the board do you?
The thing is a bit more complex than the critters freezing. Remember how up to about 40*C water acts like every thing else? As the water surface cools it becomes denser. The water even lower is still warmer, so you get a turn over of the water, with a resulting mixing of oxygen and nutriants. The warmer water coming up delays the freezing, so light and gas exchanges continues longer. This circulation continues after the surface has frozen furthur mixing things around. Without the mix you wind up with “dead” water lower down. Fishermen know how water stratifies in summer more than in winter.( Warm water on top in summer and it wants to stay there.)
More than that though, if it froze from the bottom up, or ice sank, a body of water of sufficient size would never thaw completly. A layer of ice on the bottom, cold water sinks and it freezes, that continues untill the whole lake is frozen. Summer is a cumen and the surface melts, but water is a great heatsink and the lower ice doesn’t melt. We got all our nutrients trapped down in that ice along with oxygen and plants that should be makin some oxygen.
But on behalf of the American Bar Association I must take issue with Unca’s statement, “…enabling life to go on below. Assuming you call this life.”
“Pardon me while I have a strange interlude.” -Marx
Just wanted to comment about freezing from the bottom up if water was less dense in liquid form. Hooey!
Once the body of water reached a uniform thermal equilibrium that was just below the freezing point, the entire body of water would freeze simultaneously. In other words, the only way to get the water at the bottom to the freezing point would be to get all of the water above it to the freezing point.
BTW, anyone know what happens with an ice rink? I would think that ice crystals would form around the cooling pipes first, but then want to float up. However, this would result in a rough, uneven surface. How do they prevent this?
JoeyBlades, I think you misunderstood John’s comment there.
Down to 4 degrees centigrade, water acts just like everything else in that it gets denser as it cools. It’s the fact that it’s denser that causes the colder liquid to drift to the bottom.
Below 4 degrees centigrade, however, water gets less dense as it gets colder, and the drift reverses - the colder water rises to the top. When it freezes, it gets even less dense and the ice stays at the top.
If water didn’t have that odd density reversal point, colder water would continue to drift to the bottom - and, if ice were denser than liquid water, the ice would form at the bottom and stay there. For deeper bodies of water, that ice would never melt because the intervening layers of cold water and lack of convection currents would act as insulation layers. That’s the process John was referring to.
I believe that they keep ice rinks smooth by first freezing everything and then periodically melting a thin layer at the top (using Zamboni machines), letting that thin layer re-freeze to a (relatively) smooth surface.
There is also a species of North American turtle (red-eared slider, perhaps?) that freezes solid in its first year, then thaws out in spring. If it freezes again as an adult, however, it dies. Apparently it has some kind of natural anti-freeze.
“The dawn of a new era is felt and not measured.” Walter Lord
No, I didn’t miss the point. I was just extending the point. If water didn’t have “that odd density reversal point”, the colder water would tend to descend and stay on the bottom, as you say, but it would only be able to freeze once the entire body of water fell just below the freezing point and therefore all of the water would freeze simultaneously.
??? I’m afraid that makes no sense at all. The colder water at the bottom of a lake would freeze first for the same reason that the colder water at the top of a lake freezes first under current conditions - because it’s colder than the rest of the water. The entire body of water wouldn’t freeze simultaneously under either condition.
We’re talking about a theoretical scenario where water behaves differently than real life.
WillGolfForFood writes:
It makes perfect sense. How do you suppose the water at the bottom gets below the freezing point? This could only occur if the cold from the surface is conducted through the entire body of water which would mean that the entire body of water would reach the freezing point simultaneously.
You know, it seems like we could solve this riddle of how water would freeze if it behaved like other materials by simply looking at how other materials solidify.
For example, how do molten metals harden? Has anyone personally observed this process? My guess is that they would begin to harden on the bottom, but that a crust also forms on the surface (which is exposed to the relatively frigid air), and that the whole mass would thus harden from the outside in. So with water, you should have ice on the bottom, a crust of ice on the top, and bubble of liquid in the middle, gradually shrinking.
Can we look at this a little differently? If ice was denser than water, any ice that formed at the surface, sides or any other place in a large body of water would sink. Once this chunk of ice was sitting on the bottom, it would have a hard time thawing, because the pressure of the overlying water would resist its expansion. This is the same effect seen in fog at below freezing temps. The surface tension of the droplet resists the expansion needed for freezing.
Along the same line of reasoning, the temp of deep sea water, absent any thermal outlet, is 4 deg. C. Coincidence?
Ahh, I think I see the problem here. If a cold source were at the top of the lake, ice crystals would of course form there first - at which point they’d promptly sink (because, in this alternate world, water acts like most other materials and frozen water is denser than liquid water). The frozen water would stay at the bottom of the lake, forming a permanent layer of permafrost wherever the body of water was deep enough.
Note, though, that the above scenario ignores the fact that the top of bodies of water on our planet are affected by a heat source (the sun’s rays) rather than a cold source, so water that got denser as it cooled and turned into ice would still initially form at the bottom.
What we think of as bitterly cold weather in the winter is caused by our local heat source (the sun) not being quite as effective in the winter as it is in the summer. If we didn’t have a constant heat source pounding on the surface of our planet every day we’d all get a lot colder than we do currently.
Ahh… but in bizarro world, the liquid water would migrate towards the bottom long before it turned to ice. Warmer, unfrozen water molecules closer to the bottom would continuously exchange places with the colder water nearer the top. It would be like a bubble sort with the warmer water slowly making it’s way to the surface to be cooled.
Right. Thus far I have been ignoring the fact that the surface of the water will behave as a solar collector and that the Earth beneath the water will behave as a giant heat sink. These effects complicate things slightly.
TNTruth asks:
Actually, that probably is a bit of a coincidence and a bit of a myth. The freezing point of sea water is lower than the freezing point of fresh water and therefore the point where colder sea water begins to descend is slightly lower than 4C. The temperatures that we find in the deep seas are a result of a phenomenon called arctic bottom water drift, where dense, near freezing water from the melting ice at the polar caps has spread across the ocean floor. This bottom water has spread fairly evenly and is held fairly constant by the pressure from water above, except in exceptionally deep trenches where temperatures have been recorded as low as 0C. Further confirmation comes from the fact that bottom waters that are separated by aseismic ridges can have significantly higher temperatures (around 20C) at the same depths where 4C bottom waters would be found elsewhere.