then are sea levels also rapidly rising?
If the polar ice cap is at a record low size then is sea level at a record high?
Since most of the ice is in the sea already, how much does whether or not it’s liquid or solid make a difference to sea level?
Most of the ice is *not * in the sea already. Most of it is on land in Antarctica.
The North polar ice cap *is * in the sea, and in theory could melt without changing the sea level much (there’d be a slight rise due to thermal expansion of the water). But if the South polar ice cap melted and drained into the sea it would raise sea levels considerably.
And Greenland.
And there is more to the melting than just raising sea levels. The addition of so much light weight, fresh water in the area of the North Atlantic might disrupt the oceanic converyor (the Gulf Stream is part of it) which is a current that does a lot to equalize global temperatures by transpoting heat from from warm areas to the poles…
I remember reading that if ice didn’t float, life couldn’t exist on Earth. Is that true?
Sea levels are rising, and some of this is due to melting of polar and glacial ice. As others have mentioned, the Greenland and Antarctic Ice Caps are on land, as are montane glaciers. As these melt, they will contribute to sea level rise. Only the Antarctic Ice shelves, and polar sea ice in the Arctic and Antarctic, are over water.
Besides melting ice, thermal expansion of the oceans is also contributing to sea level rise. As the oceans warm, the water expands and takes up more space, and sea level rises. Although the temperature rise so far has been small, the oceans are so enormous that the effect can be significant, and may be the most important factor over the next century.
And if the Antarctic icecap were to melt, then the land itself would rebound, much as parts of northern Europe are currently doing, raising sea levels even more in the longer term. Indeed, in several million years, sea levels will rise dramatically anyway as Antarctica clears the south polar area and the ice swaps from being land-borne to sea-borne.
A bit of an overstatement, but not by much. If ice were more dense than liquid water, as is the case for most substances, then any time you had ice in the ocean, it’d sink to the bottom. Since little to no sunlight can reach the bottom, that ice would stay frozen down there, and any new ice that formed would also sink down to join it. In fairly short order, you’d end up with most of the water on the planet trapped in ice at the bottom of the ocean basins, with a thick, sludgy brine at the top, which would not be a very good thing for most life on the planet. There would still be life around the thermal vents in the middle of the ocean, where you’d get pockets of melted water at the bottom, but that wouldn’t do much good for us.
Not that this is particularly relevant, since ice does, indeed, float. We’re just worried about it melting, not about it sinking.
Actually, would it? Wouldn’t it melt by the time it got there?
What would melt it? It would displace the warmer and less dense liquid water below it.
The surrounding warmer water that it’s displacing on its way down. It takes a long time to reach the ocean floor. That itty little snowflake or hailstone isn’t going to survive to reach the depths.
Why wouldn’t it melt? If it would remain at the bottom of the ocean frozen, then the water already down there should be under the right conditions to freeze. Just from the fact that the bottom of the ocean isn’t already frozen, it seems reasonable to conclude that if it was, it wouldn’t stay that way. It may be cold down there, but salt water under a few hundred atmospheres of pressure (that’s what I’m guessing it is) doesn’t freeze or stay frozen easily.
It isn’t just the ocean. Lakes are pretty uniform in temperature. When it gets cold the surace gets cold first. That wter sinks to the bottom and the warmer water rises to be cooled in its turn. If the ice sinks to the bottom, sure some of it might melt but in doing so it will cool the water there even more until eventually the whole lake will be frozen from top to bottom. Lakes and streams, which should also freeze solid, are the source of our fresh water.
Life is amazingly persistant and I’m reasonably sure some form of life would exist. After all, there is a toxic fungus, or something, that grows in snow and creates “pink snow.” Without a plentiful supply of water, though, it would be difficult to evolve large critters.
We’re not talking about snowflakes or hailstones. The main problem is, as David Simmons says, ice that forms on the surface of the water during winter. If ice were heavier than water, blocks of ice would form on the cold water surface and then sink to the bottom. The water on the sea floor is only slightly above freezing anyway. Not only would the ice blocks withstand melting as they sank, if they were large enough, they would serve to transport cold temperatures (actually lack of heat*) from the cold air to the sea bottom, perhaps causing more water to freeze aroung them when they reached it.
*Technically, the sinking of ice would cause heat transport upwards in the water column as it displaced warmer water below it.
The reason it doesn’t is because frozen water (and in fact, water that’s just slightly above freezing) is less dense, so any water that got that cold would rise to higher levels where it could be heated by the Sun. Water’s maximum density comes at about 4 Celsius (at least, at atmospheric pressures: the temperature might be a bit different at sea-bottom pressures), so I’d expect the water on the ocean floor to be at about that temperature.
But if ice were heavier than water (OK if solid H[sub]2[/sub]O were heavier than liquid H[sub]2[/sub]O) then blocks of ice would not form in the first place because the solid H[sub]2[/sub]O would precipitate and melt on the way down. If the water were shallow enough and still enough (remember that there is energy and thus heat in motion), then this would lead to a solid ice sheet, but I’d suggest that the open ocean is a different matter.
You have a point. The first crystals of ice to form might tend to sink towad the bottom and melt. However, in melting it cools the water around it and sooner or later the body of water would be solid ice. I don’t think it would need to be still either. If the air is cold energy is being continually abstracted from the water. Heavy ice, even small crystals, sinkes and so liquid water is continually exposed to the cold air and loses energy to the air as long as there is any water. The fact that ice floats means a layer of surface ice is formed and this insulates the rest of the water from the cold air.
Not so. There is energy in motion and there is energy in heat but not both at the same time in the same body. A moving body doesn’t warm up just because it is moving. If it heats up it is because of friction with the medium in which it is moving and some of the energy of motion is converted to energy of heat.
As **David ** says, although the ice might melt on the way down, you are still going to have a continuous precipitation of cold dense water downwards and accumulating on the bottom. If the air above the water body is very cold - well below zero - eventually the water column will be so cold throughout so that the ice won’t melt on its way down. There will be no way to transmit heat downwards, so that the ice will not melt once it reaches the bottom.
This process of course will work better in shallow seas like the Arctic Ocean. However, even under present conditions the deep seas, even in the tropics, are only a few degrees above freezing. This situation is only maintained because when water gets colder than 4 C it becomes less dense and rises. If very cold water did not rise, the deep seas could get colder than 0 C. You would end up with glaciers flowing from polar areas across the sea floor until most of it was covered. There would still be liquid water near the surface in tropical and maybe temperate areas,but much of the oceans would be ice.
It should also be remembered that an ice sheet on the top of the water acts as an insulator and prevents a body of water from cooling further. If ice did not stay on the surface, heat could be removed from the water more readily by the cold air above it.
Ahyes, Quark, I think I get your drift on the motion and heat business. If the water is turbulent there is interal friction within it and heat is developed there from the friction. Then it becomes a question of how much heat is generated from friction compared to how much is taken out of the water by the cold air.
The is a question of fact and I suppose you would need to run experiments to find the answer. My feeling is that the turbulence is fighting a gradually losing battle. During every calm period the water would cool down faster and wouldn’t warm up enough in turbulent periods to recover. But that’s just a guess.
erm, very interesting, guys, but totally irrelevent. The fact is that water DOES float. Speculating about what would happen if it didn’t is a futile excercise, with no right answers. Besides, it’s not what the OP was asking about.
Thanks. However the OP was well answered in the first responses. The OP poster then followed up with a question about what would happen if ice didn’t float.
And we don’t mind wasting time in idle speculation, it’s fun, and our time isn’t all that valuable or we wouldn’t be here. If your time is, don’t read the stuff.