Calculated sea surface rise from total Greenland melt


by zankaon
Tags: calculated, greenland, melt, rise, surface
zankaon
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#1
Dec22-07, 03:27 AM
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What might be the calculated sea surface rise from a total Greenland melt? http://en.wikipedia.org/wiki/Sea_level_rise
Volume of ice in km^3 /surface area ocean km^2 = rise in km. S.A. of earth is 510 x 10^6 km^2. ocean is 71% of S.A., or 361 x 10^6 km^2. http://en.wikipedia.org/wiki/Earth Greenland area is 2.166 x 10^6 km^2. 81 % is ice/water or 1.75 x 10^6 km^2. http://en.wikipedia.org/wiki/GreenlandThe key missing ingredient is average ice depth. perhaps 2-3 km at deepest, with central basin of about 1000 ft below sea level. If 1 km av depth, one gets 4.1 meter sea level rise. For .5 km av depth, one gets 2 meter sea level rise. One contained reference mentions 7 meters. http://en.wikipedia.org/wiki/Greenland But wouldn't one also have to consider caveat of part of melt occupying Greenland basin, leaving an archipelago?
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billiards
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Dec22-07, 06:58 AM
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Only the grounded ice that melts will cause sea level change. Floating ice displaces its own weight in water anyway, so if it melts sea level won't change -- basic physics.
binzing
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#3
Dec22-07, 02:28 PM
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Actually the floating ice that melts will lower (albeit it miniscule) the sea level. Remember frozen water expands by 9%.

Andre
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Dec22-07, 02:46 PM
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Calculated sea surface rise from total Greenland melt


it's about grounded ice but without isostacy assumptions, since the loss of ice will cause uplift in Greenland compensated with subsidence in the oceans, which tends to reduce the sea level rise eventually.

But the Greenland ice survived much warmer periods then now, the Hoocene Thermal Optimum for instance from about 9000-6000 years ago, 3000 years of 2-4 degrees higher temperatures. The ice sheet can handle that.
billiards
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#5
Dec22-07, 03:18 PM
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No binzing, the water level would not change if floating ice were to melt, at least i t won't if Archimedes was right. One other minor complication though, the gravitational pull of an ice sheet actually causes the sea to bulge slightly around it, without the ice sheet this bulge wouldn't be present causing local sea level to be slightly lower than it otherwise would have been within the vicinity of the ice sheet. The glacial rebound would also make sea level lower (relative to a fixed marker) in the vicinity - but due to mass balance the sea level would be higher elsewhere around the world to compensate.
Gokul43201
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Dec22-07, 07:02 PM
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Quote Quote by Andre View Post
it's about grounded ice but without isostacy assumptions, since the loss of ice will cause uplift in Greenland compensated with subsidence in the oceans, which tends to reduce the sea level rise eventually.
Andre, can you explain this in layman terms? I'm not sure I follow. Also, what would be the typical timescale for uplift and subsidence?
Andre
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Dec23-07, 07:20 AM
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This effect is what is called isostacy. Perhaps, this explanation will be helpful, which also covers the rate of changes.

But not shown in the animation is that the increased sea level exerts slightly more pressure on the ocean floors and that the total uplifted mass below the former ice sheet should be balanced out by an equal mass subsiding elsewhere. Assuming balancing pressures in the upper mantle or asthenosphere to be about equal everywhere, for this balancing, the now heavier oceans are a logical candidate, this is called Hydro-isostacy.
billiards
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#8
Dec23-07, 09:16 AM
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Caltech seem to be doing some interesting theoretical geophysical assessments of glacial rebound.

http://www.gps.caltech.edu/~jtromp/r...h/glacial.html

A spherical harmonic analysis of the geogravitational field could theoretically be used to monitor the behaviour of ice sheets and tectonic plates.
LURCH
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#9
Dec23-07, 05:10 PM
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Quote Quote by billiards View Post
Only the grounded ice that melts will cause sea level change. Floating ice displaces its own weight in water anyway, so if it melts sea level won't change -- basic physics.
Actually, we had a thread discussing this some time ago, and it turns out that the melting of floating ice would cause some rise in sea levels, albeit very slight. Floating ice is fresh water floating on saltwater. As the ice melts, the seas become slightly less salty. Less salty means less dense, but the mass of the sea remains the same. So, same mass at less density means greater volume. But I have no idea how large this effect would be; probably engligable.

Just threw it in because I think it's interesting!
billiards
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#10
Dec24-07, 06:21 AM
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Quote Quote by LURCH View Post
Actually, we had a thread discussing this some time ago, and it turns out that the melting of floating ice would cause some rise in sea levels, albeit very slight. Floating ice is fresh water floating on saltwater. As the ice melts, the seas become slightly less salty. Less salty means less dense, but the mass of the sea remains the same. So, same mass at less density means greater volume. But I have no idea how large this effect would be; probably engligable.

Just threw it in because I think it's interesting!
Fair point, it is certainly a worthwhile consideration and another complication. Although it turns out that the melted ice shelf water is more dense than the saline water in which it floats - this is because it is much colder - so I have some trouble agreeing with your conclusion.
LURCH
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#11
Dec24-07, 03:47 PM
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More dense than seawater? Does ice-shelf water sink in saltwater?
billiards
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#12
Dec25-07, 08:27 AM
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Yes, well sometimes at least, it is probably how North Atlantic Deep Water is formed. Note that ice under a heavy load has a lower melting point than ice under typical pressures (water having a negative Clapeyron slope - at least under "normal" conditions), meaning that it can melt at temperatures below zero degrees C. So ice that melts under a thick wedge of ice (like at the bottom of an ice shelf) can be very cold and therefore the water will be very dense, ice that melts under less pressurized conditions, for example from an iceberg probably will be a bit warmer so will probably float.


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