Why does the ocean elevate?

umm actually your totally wrong

ice EXPANDS when it frezes, so the sea would push away to compensate. As it melts the water contracts so it takes up a smaller area thefore it would be smaller. The difference with polar ice would be the ice FLOTING ontop of the water and as it equalises with it melts the total area would rise acordingly, once you take out the shrinking which occures because its now a liquid

oh and B\W antatica IS land so if it all melted it WOULD be in the sea not on land
 
I don't know what that was about, but just for clarification:

If ice on land melts, the sea level increases.

If ice floating on water melts, the sea level does not increase because the ice has already displaced its own weight of water (Archimedes Principle).

The lower density of ice is shown by the non-submerged portion. As it melts its volume reduces - eventually to nothing.
 
are you saying that because its floting the extra room is above the water level?
 
Catastrophe said:
I don't know what that was about, but just for clarification:

If ice on land melts, the sea level increases.
Click to expand...

If the ice layer was thick and heavy enough, also the land formerly carrying it will rise.
 
Asguard

Do yourself a favour. Try this:

Fill a glass just short of the top and add an ice cube. Mark the level. Watch the ice melt and the level stay the same. The ice displaces its own weight of water. Because ice is less dense than water ice floats. As the ice melts there is less water to displace until there is no ice left. Try it.

mercurio

This does happen but the land is rising from being compressed. The land expands into air. It does not affect the sea level.
 
Catastrophe said:
mercurio

This does happen but the land is rising from being compressed. The land expands into air. It does not affect the sea level.
Click to expand...

I think most tectonic plates do not stop at the exact border between sea and land, so that would seem to be a bit over-idealised.

In practice I think you'll find that the rising land mass has quite an effect on the shallower parts coming up with the rest.

So they might fall dry, and at least that amount of water would largely flow back to the greater basin. All in all it would not make such a huge difference, but more than you'd care to mop up by hand, at least. ;)
 
mercurio

"I think most tectonic plates do not stop at the exact border between sea and land, so that would seem to be a bit over-idealised."

You are quite correct. Most plate boundaries are way out in the oceans.

"In practice I think you'll find that the rising land mass has quite an effect on the shallower parts coming up with the rest."

Surely if the land is rising (dry land - not under oceans) the average sea levels will be falling?

OK, I just found this: emphasis mine

"Changes in sea-level are of two different types, regional and global. The most important cause of a global change in sea level is an increase or decrease in the extent of the world's ice sheets and glaciers. When these grow larger sea-level drops because water becomes locked up in ice; and when they melt, sea-level rises. ... Regional sea-level change occurs when a specific area of land rises or falls relative to the general sea level. Two of the main causes are tectonic lifting of land, which is common in regions where oceanic crust is being forced benrath continental crust, and glacial rebound, which is a slow rise of an area of land after an ice sheet which once weighed it down has melted."

"Earth" DK.

As I see it, rising of sea bed will increase sea level, but rising of dry land, without rise of sea bed will decrease sea level. Do you agree?
 
So the main effects are degree of glaciation, but the regional effects work in both ways. When the water is tied up as ice the underlying land is compressed but when the ice melts the land rises but the sea bed is compressed.
 
Didn't mean to be hard to understand, sorry: what I meant that when the land rises, say Antarctica, the bays around would come up with it. These are quite large, and would empty into the sea behind, mostly. So locally the sealevel would drop dramatically, and the ocean as a whole would be that tiny bit higher (by the ouflowing water from the bays). So to make it clear without any doubt: locally the levels would drop, but globally not, they would rise by a few millimeters or centimer, maybe. Didn't do the math.

Similar things happened in Europe too, several thousands of years BC, when the British Channel and part of the North Sea were dry land. I also remember several features in Dutch geography are attributed to the weight of ice masses weighing on mountain ranges as far away as the Alps, which is nearly a thousand km's distant. Kind of plate leverage effect.
 
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mercurio

You have not taken account the water in the ocean compressing the crust, have you. Crust is crust and can be compressed by glaciation or deeper water.

I don't see what your core idea is. Please explain.
 
" So locally the sealevel would drop dramatically, and the ocean as a whole would be that tiny bit higher (by the ouflowing water from the bays). "

Do you mean the sea level would drop or, because the land rises, the sea level now does not reach so high up the land? If the land rises and water tips down from the land (other things being equal) the level increases slightly even though it is lower in relation to the land. It is the land rising that causes this. The sea-level is almost exactly the same. It does not drop dramatically.
 
Without wanting to get into semantics here, and I don't want to side-track the discussion, it's just that it's one of those seemingly simple 'would-it-rise-or-fall' type of questions that I think is easy to get wrong.

You are right, I didn't include the weight of the water. Now that I do, it only makes my case stronger, since the pressure of the water that was in the bays encircling the hypothetical rising Antarctica is *no longer there* to weigh upon it, and makes the land come up even more....

That water has to go somewhere, together with the melted ice: into the ocean. So the ocean leve rises. It does not remain the same or get lower.

As I said, it's just one of those book-keeping thingies: want to get the balance right in the end.
 
mercurio

I think we are discussing at cross purposes. I said the water level would rise if ice on land melted. I said it would not rise if ice on water melted and that cannot be argued with. The ice block in a glass of water experiment will prove that to anyone in about 15 minutes.
 
mercurio

There is a point you should consider in your rising Antarctica argument. The effect of the melting ice is immediate - as the ice melts and reaches the ocean, the level rises. The 'rising land after the ice melts' effect will take a long, long time - as will the compression of the crust under the ocean.
 
Ad 1:

I wasn't arguing with that, mind you.

Ad 2:

time is not really important. We're talking principles here. The ice could theoretically be melting so slow that it would not make a difference either, but we're not interested in that either. It would come up, sooner or later, with the predicted effect.

Anyway: did you know that most of that whole tectonic movement is being suspected as having been *caused* by Life in the first place? We've all been brought up with the idea it's something that 'just happens', but that does not appear to be the case. It's highly cyclical, and could even be seen as a very slow part of our 'weather'.
 
"Anyway: did you know that most of that whole tectonic movement is being suspected as having been *caused* by Life in the first place?"

No. Please elaborate.
 
Well, to begin with life speeds up sedimentation. Those sediments add up to a stupendous weight, all bearing down on the right places, the subduction zones ('sedimentation wedges').

This keeps the process going, which might have stopped otherwise. See Mars and other 'dead' planets, tectonically.

But some results in anomalies in hotspots and deep layers that crystallized in the 'wrong' form leads to suspicion that bacteria at enormous depths have something to do with it too, leading to underground collapses, and sudden subterranean convolutions that should not otherwise have happened.

So which started which is maybe lost in the mists of time, but there seems to be a collusion between life and tectonic movement that goes much deeper than you would think at first.

All this does not mean there are no other forces involved, more geophysical in nature or having to do with tidal pressures (moon) or others, but we tend to forget we're actors in this game, not pure spectators.
 
"Well, to begin with life speeds up sedimentation. "

Can you please explain the connection between life and sedimentation.
 
Roots crack rocks, acids of biological origins dissolve rocks. What we call topsoil is a living thing, and although most erosion specialist focus on erosion OF topsoil, in fact topsoil IS a process of erosion. Rivers, rain and wind generally make it reach the lowest points, as sludge. Also think all those carcasses of krill sinking year after year, nicely collected and compacted materials. Mudstreams doing 70 miles per hour or so over the ocean bottom. All redistribution of fine sediment, on its way to the lowest points.

The subduction zones mentioned earlier.

Strangely, a lot of deserts are created by life too, like us humans and goats. Lots more fine particles to blow into the oceans, too. This is a side-effect, not my main point, but it adds up.

"Life as a form of planetary crust rot" ;)

added:

some numbers:

It is estimated that the rivers and streams flowing from the United States alone discharge 225 million tons of dissolved solids and 513 million tons of suspended sediment annually to the sea. Recent calculations show yields of dissolved solids from other land masses that range from about 6 tons per square mile for Australia to about 120 tons per square mile for Europe.

http://oceanography.palomar.edu/salty_ocean.htm
 
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