5 ms·

hmmm, the ocean's pretty heavy. i wonder what extracting an incompressible fluid from the seafloor's support structure will do to weaken it. will they fill it w

hmmm, the ocean's pretty heavy. i wonder what extracting an incompressible fluid from the seafloor's support structure will do to weaken it. will they fill it with saltwater instead? i guess it shouldnt be much different than oil drilling :\

Danieru 13y ago
This might be off-topic but water is in-fact compressible: http://en.wikipedia.org/wiki/Properties_of_water#Compressibility http://en.wikipedia.org/wiki/Properties_of_water#Compressibi...
- leeoniya 13y ago
  not off-topic, maybe just a bit too pedantic. "The low compressibility of water means that even in the deep oceans at 4 km depth, where pressures are 40 MPa, there is only a 1.8% decrease in volume." also: http://en.wikipedia.org/wiki/Oil_platform#Deepest_oil_platforms http://en.wikipedia.org/wiki/Oil_platform#Deepest_oil_platfo...
  - sp332 13y ago
    1.8% of 4 km is 72m, which is very significant when talking about sea level changes.
    - leeoniya 13y ago
      it looks like most "deep" platforms listed in the wiki link are ~400m, so this would be 7.2m (assuming the compressibility factor is linear). either way it doesn't matter for this argument. we're talking about the difference between water and whatever it's replaced with such as "nothing" or something cheap and abundant with similar properties. also, the water we're talking about is not itself 4 km deep. it may be under 4km of sea water, but the fresh water under the seafloor may be only 500m deep with an equivalent pressure of 4 - 4.5 km.
    - Jtsummers 13y ago
      Volume, not height. At 4km, 100 L of water would be compressed to 98.2 L. Also, that's at 4km depth, not the compression of everything above that point, but rather the compression of things at that point.
- jbattle 13y ago
  Getting further afield, water's density actually changes considerably with a change in temperature. http://en.wikipedia.org/wiki/Properties_of_water#Density_of_water_and_ice http://en.wikipedia.org/wiki/Properties_of_water#Density_of_... I'm not sure how common this is but I know Lake Michigan goes through an annual cycle where the water alternately mixes and segregates (by temperature). In the summer, the warm, less dense water rises to the top and stays there. In the winter, very cold water is actually lighter than slightly warmer water and a similar stratification happens. In spring and autumn the water temperatures near the surface equalize with water deeper in the lake and much if not all of the lake water circulates ("turns over"). http://www.lakeaccess.org/ecology/lakeecologyprim4.html http://www.lakeaccess.org/ecology/lakeecologyprim4.html
  - b_emery 13y ago
    Very common - this is one of the basic mechanisms that mix lakes. To clarify, the summer surface waters are heated by the sun, causing stratification. This is usually broken down in the fall by the combination of wind mixing and heat extraction (leading to denser surface waters which sink). This is an important component of ocean surface dynamics as well. The mechanism just described can mix the top few hundred meters of the North Atlantic in winter.
teh_klev 13y ago
Water is compressible, which is why we don't use it for brake fluid and safety critical hydraulic applications.
- lostlogin 13y ago
  Is it that or its conversion to steam at a relatively low temperature or its ability to rust out the brakes?
  - Jtsummers 13y ago
    As you said, density change over the temperature range where hydraulic systems are used, and corrosive properties of water. Also its freezing point. Oils just have better properties for the desired application.
    - lostlogin 13y ago
      Great point - it's never below freezing where I am. It's amazing to experience water in a brake line if its not too dangerous. You get most the normal functionality if you stamp on the pedal.
mankypro 13y ago
From a purely practical point of view, isn't the "community at large" worried about the "rising" sea levels? If we took the fresh water from the aquifers, then refilled them with sea water, presumably that would put a dent in the rising sea levels? I know, I know...just trying to be pragmatic.
- mnw21cam 13y ago
  http://what-if.xkcd.com/33/ http://what-if.xkcd.com/33/ shows just how much the sea level would drop if all ships disappeared. That's probably more volume than you're likely to drink from an aquifer. There's a reason for the saying "a drop in the ocean". Besides, once we had used that water, it would run back into the sea.
  - eru 13y ago
    We wouldn't use the aquifers' water for drinking. (Or at least, drinking doesn't make a dent.) Agriculture and industry are the big users.
  - kamjam 13y ago
    Sometime in the last few years, we reached a point where there are, by weight, more ships in the ocean than fish Nice link. This made me sad :'(
nocoment 13y ago
> will they fill it with saltwater instead? Push CO2, get back carbonated water? Then it is $1/liter + carbon credits for what doesn't come back up. :)
- HCIdivision17 13y ago
  Bizarrely, that could be immensely dangerous. There have been a few lakes with large quantities of dissolved co2 that have critically released that gas when jostled, either by vibration or temperature shock (of a couple degrees leading to mixing). There's no telling if it would happen in the ocean, but if currents are slow, a cascade of gas rushing to the surface could be pretty bad. [0] https://en.m.wikipedia.org/wiki/Lake_nyos https://en.m.wikipedia.org/wiki/Lake_nyos
ds9 13y ago
Upon reading the headline I too immediately wondered, if the fresh water is sucked out, wouldn't the ocean collapse the roof of the space? Other posters here are saying, replace it with salt water or CO2. The CO2 idea was answered. As for the "swap seawater for fresh" idea, as soon as you put a significant amount of sea water in there, you no longer have fresh water coming out! The only way to get a freshwater supply from this would be to take all it out before replacing, but then you have the "supporting the ocean bottom" problem in the interim.
- mkingston 13y ago
  Actually, the mixing properties are incredibly important. Even under the ocean much oil isn't in big cavities, it's in porous rock. If this is the case with fresh water, the structure containing the fresh water might actually sufficiently support the salt water on top of it as we reduce the internal pressure when extracting fresh water. Even if not, we can drill and extract fresh water at one end and pump in salt water at the other, until the water we get out becomes too saline. In porous rock the mix rate would be quite low; kind of like pumping salt water into a sponge at one end and extracting the fresh water at the other end (for a while). This is quite a common practice in the oil industry. Finally, salt water is more dense than fresh water. If these reservoirs underwater actually are big cavities; we can just pump salt water in the bottom and pump fresh water out the top. NB: When I say "we can just", I mean, take a wild best guess about where the bottom and top of the well is based on crazy amounts of uncertain data extracted on a well-by-well basis.

Danieru 13y ago

This might be off-topic but water is in-fact compressible: http://en.wikipedia.org/wiki/Properties_of_water#Compressibility http://en.wikipedia.org/wiki/Properties_of_water#Compressibi...

leeoniya 13y ago
not off-topic, maybe just a bit too pedantic. "The low compressibility of water means that even in the deep oceans at 4 km depth, where pressures are 40 MPa, there is only a 1.8% decrease in volume." also: http://en.wikipedia.org/wiki/Oil_platform#Deepest_oil_platforms http://en.wikipedia.org/wiki/Oil_platform#Deepest_oil_platfo...
- sp332 13y ago
  1.8% of 4 km is 72m, which is very significant when talking about sea level changes.
  - leeoniya 13y ago
    it looks like most "deep" platforms listed in the wiki link are ~400m, so this would be 7.2m (assuming the compressibility factor is linear). either way it doesn't matter for this argument. we're talking about the difference between water and whatever it's replaced with such as "nothing" or something cheap and abundant with similar properties. also, the water we're talking about is not itself 4 km deep. it may be under 4km of sea water, but the fresh water under the seafloor may be only 500m deep with an equivalent pressure of 4 - 4.5 km.
  - Jtsummers 13y ago
    Volume, not height. At 4km, 100 L of water would be compressed to 98.2 L. Also, that's at 4km depth, not the compression of everything above that point, but rather the compression of things at that point.
jbattle 13y ago
Getting further afield, water's density actually changes considerably with a change in temperature. http://en.wikipedia.org/wiki/Properties_of_water#Density_of_water_and_ice http://en.wikipedia.org/wiki/Properties_of_water#Density_of_... I'm not sure how common this is but I know Lake Michigan goes through an annual cycle where the water alternately mixes and segregates (by temperature). In the summer, the warm, less dense water rises to the top and stays there. In the winter, very cold water is actually lighter than slightly warmer water and a similar stratification happens. In spring and autumn the water temperatures near the surface equalize with water deeper in the lake and much if not all of the lake water circulates ("turns over"). http://www.lakeaccess.org/ecology/lakeecologyprim4.html http://www.lakeaccess.org/ecology/lakeecologyprim4.html
- b_emery 13y ago
  Very common - this is one of the basic mechanisms that mix lakes. To clarify, the summer surface waters are heated by the sun, causing stratification. This is usually broken down in the fall by the combination of wind mixing and heat extraction (leading to denser surface waters which sink). This is an important component of ocean surface dynamics as well. The mechanism just described can mix the top few hundred meters of the North Atlantic in winter.

teh_klev 13y ago

Water is compressible, which is why we don't use it for brake fluid and safety critical hydraulic applications.

lostlogin 13y ago
Is it that or its conversion to steam at a relatively low temperature or its ability to rust out the brakes?
- Jtsummers 13y ago
  As you said, density change over the temperature range where hydraulic systems are used, and corrosive properties of water. Also its freezing point. Oils just have better properties for the desired application.
  - lostlogin 13y ago
    Great point - it's never below freezing where I am. It's amazing to experience water in a brake line if its not too dangerous. You get most the normal functionality if you stamp on the pedal.

mankypro 13y ago

From a purely practical point of view, isn't the "community at large" worried about the "rising" sea levels? If we took the fresh water from the aquifers, then refilled them with sea water, presumably that would put a dent in the rising sea levels? I know, I know...just trying to be pragmatic.

mnw21cam 13y ago
http://what-if.xkcd.com/33/ http://what-if.xkcd.com/33/ shows just how much the sea level would drop if all ships disappeared. That's probably more volume than you're likely to drink from an aquifer. There's a reason for the saying "a drop in the ocean". Besides, once we had used that water, it would run back into the sea.
- eru 13y ago
  We wouldn't use the aquifers' water for drinking. (Or at least, drinking doesn't make a dent.) Agriculture and industry are the big users.
- kamjam 13y ago
  Sometime in the last few years, we reached a point where there are, by weight, more ships in the ocean than fish Nice link. This made me sad :'(

nocoment 13y ago

> will they fill it with saltwater instead? Push CO2, get back carbonated water? Then it is $1/liter + carbon credits for what doesn't come back up. :)

HCIdivision17 13y ago
Bizarrely, that could be immensely dangerous. There have been a few lakes with large quantities of dissolved co2 that have critically released that gas when jostled, either by vibration or temperature shock (of a couple degrees leading to mixing). There's no telling if it would happen in the ocean, but if currents are slow, a cascade of gas rushing to the surface could be pretty bad. [0] https://en.m.wikipedia.org/wiki/Lake_nyos https://en.m.wikipedia.org/wiki/Lake_nyos

ds9 13y ago

Upon reading the headline I too immediately wondered, if the fresh water is sucked out, wouldn't the ocean collapse the roof of the space? Other posters here are saying, replace it with salt water or CO2. The CO2 idea was answered. As for the "swap seawater for fresh" idea, as soon as you put a significant amount of sea water in there, you no longer have fresh water coming out! The only way to get a freshwater supply from this would be to take all it out before replacing, but then you have the "supporting the ocean bottom" problem in the interim.

mkingston 13y ago
Actually, the mixing properties are incredibly important. Even under the ocean much oil isn't in big cavities, it's in porous rock. If this is the case with fresh water, the structure containing the fresh water might actually sufficiently support the salt water on top of it as we reduce the internal pressure when extracting fresh water. Even if not, we can drill and extract fresh water at one end and pump in salt water at the other, until the water we get out becomes too saline. In porous rock the mix rate would be quite low; kind of like pumping salt water into a sponge at one end and extracting the fresh water at the other end (for a while). This is quite a common practice in the oil industry. Finally, salt water is more dense than fresh water. If these reservoirs underwater actually are big cavities; we can just pump salt water in the bottom and pump fresh water out the top. NB: When I say "we can just", I mean, take a wild best guess about where the bottom and top of the well is based on crazy amounts of uncertain data extracted on a well-by-well basis.