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Consequences of large-scale mass redistribution on Earth's surface

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jay.yoon314
#1
Apr2-12, 09:02 PM
P: 22
Consider the following scenario: We isolate the Caribbean Sea and the Gulf of Mexico from the Atlantic Ocean by constructing dams that extend to the bottom of all channels and waterways that presently connect these bodies of water to the Atlantic Ocean. There are 17 listed in Wikipedia: http://en.wikipedia.org/wiki/Categor..._the_Caribbean.

Many of these waterways are very deep, and damming even one of them would be extremely difficult, let alone all of them, of course. If this was done, and in addition all rivers that flowed into the Gulf of Mexico and Caribbean Sea were also dammed to cut off one of the sources of water inflow (the other being precipitation directly over the gulf/sea), there would be a large net loss of water from these bodies of water.

If only the rivers had been blocked off, and the waterways connecting these bodies of water to the Atlantic Ocean were not, the decrease in water inflow due to the elimination of river flow into the Gulf and the Caribbean would simply be compensated for by ocean water from the Atlantic flowing into the Gulf and the Caribbean, with the net result being that the sea level in the Gulf and the Sea would remain for all practical purposes constant.

Since we've blocked off both the rivers and the waterways/channels, the result is that within several decades or so, all the water from the Gulf and the Caribbean will have evaporated, leaving a dry seabed. I'm not sure exactly how long this would take, but I'm quite positive it would eventually occur.

Some more details follow: If one of the dams that blocked the Gulf and the Caribbean from the Atlantic Ocean was broken so that over the course of, say, a year, the water from the Atlantic Ocean would flow back into the dry basin that was previously the Gulf and the Caribbean Sea, what would be the effect of this large-scale redistribution of water on the surface of the Earth?

Since the present-day volume of the Gulf and the Caribbean combined is roughly 9.0 million cubic kilometers, with a mass of 9.0 * 1018 kg, let's assume that this amount of water would flow back into the basin; essentially, the former state of the geography prior to the "experiment" is restored to its initial state.

Let us further assume that the water, when flowing back into the dry seabed, would move precisely from east to west, since the Caribbean and Gulf is presently situated in such a way that it is a westernmost extremity of the Atlantic Ocean; if it was evaporated away and replenished, water would obviously be relocated from east to west. Incidentally, this is in the opposite direction that the Earth rotates, which is west to east.

Here's the actual question: does this massive and fairly rapid redistribution of mass in the form of water, with the rough quantities/magnitudes mentioned above and the directionality opposite to the Earth's rotation, have any effect on the Earth's rotational velocity?

If so, why, and would this amount of water, which being close to 1/140 of the total ocean mass/volume on Earth, is very large compared to most quantities, but still quite small compared to the total mass of the Earth (around 1/500,000 of the Earth's total mass)? I am thinking that even though the mass might not be very large compared to the total mass of the Earth, because it is located as far as can possibly be to the Earth's center of mass, its moment of inertia will be large and thus a change in the Earth's surface mass distribution (namely water) can have a disproportionately large effect; perhaps large enough to cause a large disruption.

Further, if so, would the rotation of the Earth be slowed down or sped up? Would this effect, if it occurred, be temporary or permanent? (I'm guessing that the water + Earth's solid components together make up a closed system, for a start).

Is it theoretically possible for the solid Earth beneath the oceans to suddenly rotate more slowly than the oceans, the effect being that the inertia of the Earth's oceans makes the oceans as a whole rotate faster than the solid Earth beneath it, with the result possibly being that the coastlines creep eastward until a new equilibrium is reached? Could this lead to oceans being pushed upward and inland?

Finally, in the spirit of 2012, could this scenario as a whole, excluding the previous paragraph which was just far-out speculation, lead to an instance of "true polar wander," or a "pole shift?" From what I know of these two phenomena, they are triggered by formation of ice sheets; when a continental ice sheet develops far from the equator, this excess mass causes the Earth's axis of highest moment of inertia to reorient itself to account for the new mass. Would the chances of such a "pole shift" be heightened if the Caribbean/Gulf were located farther from the equator and nearer the poles?

Thanks a lot. Rough order of magnitude estimates and more detailed quantitative answers are both equally appreciated.
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K^2
#2
Apr2-12, 09:33 PM
Sci Advisor
P: 2,470
a) That would mess up Gulfstream. I think Europeans might be a bit upset about the impact that will have on their agriculture.

b) It won't dry out completely. The area would collect significant rainfall. Rate of evaporation is likely to exceed it while the entire area is covered with water, but once the gulf shrinks a bit, rainfall rates will catch up, and it will stabilize. It's hard to tell how significant the water level drop would be by that point.

c) The impact on Earth's rotation will be negligible either way.
jay.yoon314
#3
Apr2-12, 09:58 PM
P: 22
Quote Quote by K^2 View Post
a) That would mess up Gulfstream. I think Europeans might be a bit upset about the impact that will have on their agriculture.

b) It won't dry out completely. The area would collect significant rainfall. Rate of evaporation is likely to exceed it while the entire area is covered with water, but once the gulf shrinks a bit, rainfall rates will catch up, and it will stabilize. It's hard to tell how significant the water level drop would be by that point.

c) The impact on Earth's rotation will be negligible either way.
The Mediterranean Sea is believed to have completely dried out in less than 1,000 years after the Strait of Gibraltar was blocked, and in that situation, rivers were (obviously) not blocked.

mfb
#4
Apr3-12, 02:54 PM
Mentor
P: 11,815
Consequences of large-scale mass redistribution on Earth's surface

With an average depth of ~1km, you would increase the height of ~1*10^19kg by ~500m, which modifies the moment of inertia of the earth by ~6*10^(-10) or 50Ás/day. Each day would be 50Ás longer than now, which would increase the number of required leap seconds a bit.
This is an effect you would get even without opening/breaking a dam.

I would expect that this event would fill the gulf+caribbean sea much quicker than 1 year. But a controlled opening of the dams could give you 1 year. In that case, the water in the sea has enough time to stay roughly in an equilibrium, and the whole process just gets reversed, without any significant east->west movement.

And yeah, this plan would probably make a lot of people very angry, as it would modify the global ocean currents a lot.


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