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Vast Freshwater Reserves Found Beneath the Oceans

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Re: Vast Freshwater Reserves Found Beneath the Oceans

#31

Post by b_emery »

jbattle wrote: post #15
Danieru wrote: post #5

Earlier quoted context omitted.

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

Getting further afield, water's density actually changes considerably with a change in temperature. 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 wa…

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.

Re: Vast Freshwater Reserves Found Beneath the Oceans

#33

Post by Jtsummers »

sp332 wrote: post #14
leeoniya wrote: post #6

Earlier quoted context omitted.

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_platfo...

1.8% of 4 km is 72m, which is very significant when talking about sea level changes.

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.

Re: Vast Freshwater Reserves Found Beneath the Oceans

#34

Post by Jtsummers »

lostlogin wrote: post #8
teh_klev wrote: post #7

Earlier quoted context omitted.

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

Is it that or its conversion to steam at a relatively low temperature or its ability to rust out the brakes?

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.

Re: Vast Freshwater Reserves Found Beneath the Oceans

#35

Post by schiffern »

ryan_j_naughton wrote: post #30
schiffern wrote: post #28

Earlier quoted context omitted.

>until the energy costs of desalination are low enough. Really? You think desalination is the ultimate goal? I much prefer free, ecosystem-provided desalination (aka rooftop rain-water harvesting). As for agricultural water use, I highly suggest picking up a copy of P.A. Yeoman's classic Water For Every Farm . It details how proper runoff management, evaporation control, and correctly-scaled earthworks can provide re…

I agree that not all dams are bad. The real issue with dams is the scale. We are on track to dam the majority of the world's rivers over the next 50 years, and this will have significant effects on river and coastal ecosystems. >> I much prefer free, ecosystem-provided desalination (aka rooftop rain-water harvesting). I agree; however, this is not an infinite supply. Taking water from rivers is effectively a form of…

>The real issue with dams is the scale.

I couldn't agree more.

>I agree; however, this is not an infinite supply.

Well no system can provide an infinite supply, but rainwater harvesting could support the current human population at a first-world standard of living (something our present system does not provide). Many areas famous for recent crippling droughts suffered from flooding only months before. This is a spectacular failure in water management.

As to cost, I haven't seen any comparisons of the lifetime cost of rooftop rainwater harvesting vs centralized pumped underground pipe distribution. I know rainwater harvesting is much more common in Australia, so they might have more data. I suspect it's strongly dependent on the cost of energy.

One thing I forgot to mention about desalination: current technology (specifically the Affordable Desalination Collaboration’s pilot plant) is at 30% of the thermodynamic limit. So we can expect a 3x improvement in performance, but no more. http://www.usbr.gov/research/AWT/energy_use.html

Re: Vast Freshwater Reserves Found Beneath the Oceans

#36

Post by mkingston »

devindotcom wrote: post #3

Good, now we can put off thinking about conservation yet again! Our great-grandchildren will have plenty of time to think of something.

Possibly good indeed. Spending that money now against our great-grandchildren's future earnings might not be in their best interest.

Besides, don't we have enough on our plate with CO2? Sure, theoretically we could focus on both, but we seem to be doing a pretty bad job with the CO2.

Also, I'd probably rather drain these non-renewable fresh-water sources and spend the saved money on improving the quality of life of those who need it most (developing world), all the while with a long-term focus on better energy for desalination/reuse. To be fair, though, this entire paragraph is a pipe-dream.

Re: Vast Freshwater Reserves Found Beneath the Oceans

#37

Post by mkingston »

ds9 wrote: post #26
leeoniya wrote: post #2

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 :\

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…

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.

Re: Vast Freshwater Reserves Found Beneath the Oceans

#38

Post by InclinedPlane »

schiffern wrote: post #28
ryan_j_naughton wrote: post #17

Regarding criticism that this isn't renewable and delays the move to renewable resources: At the rate we are damming rivers, we will destroy many river ecosystems. This new potable water source seems less harmful than dams and could be a bridge until the energy costs of desalination are low enough. If this discovery spurs investment in desalination (since this is simply cheaper desalination due to the lower salinity)…

>until the energy costs of desalination are low enough. Really? You think desalination is the ultimate goal? I much prefer free, ecosystem-provided desalination (aka rooftop rain-water harvesting). As for agricultural water use, I highly suggest picking up a copy of P.A. Yeoman's classic Water For Every Farm . It details how proper runoff management, evaporation control, and correctly-scaled earthworks can provide re…

Whether you're desalinating or just doing runoff management you're mucking about with the Earth's water cycle either way.

The bigger issue is actually just using waste water recycling, which is today a feasible proposition but for public perception.

Re: Vast Freshwater Reserves Found Beneath the Oceans

#40

Post by mkingston »

clord wrote: post #4

We're contemplating going after harder-to-get fossil water because the easy stuff is depleted and can no longer keep up. Sounds like the situation we're in with oil. In the case of water, which replenishes, the 'production cycle' is actually the global fresh-water cycle. If we dirty all of the fresh water faster than the earth can clean it, we're going to have to start drilling for the fossil stuff in hard-to-reach p…

Danger pay is not nearly as true as it used to be[1]. Though I guess perception-of-danger pay might still be in play.

1. http://www.forbes.com/sites/robertbradley/2013/03/25/oil-gas... (honestly, I can't really be bothered tracking down the BLS reports.. this is the first article I found with any numbers and it reinforces what I've been told by a friend in the industry)

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