4 ms·

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/Proper

by 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.

by 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.