Fresh Water vs Salt Water

[Ant]

OK I have a question - it's sort of science related so put it in here.

The seas, oceans and some rivers are salt water!

Rain, lakes and some rivers are fresh water.

Rain, on the whole, comes from the sea's and oceans...

As water is evaporated in moisture which then condenses into cloud - where does the salt go? Are there localised fluctuations in the salt concentrations in the seas and oceans.

Will all water become fresh eventually?

[keef_uk]

As I have always understood it Salt is alot heavier then water and cannot evaporate - hence we get the vast salt lakes which are old seas etc..

This is probally totally wrong and there is a better explaination then this

Cheers

[Kaptain Klevtsov]

Rain is basically distilled water when it condenses out of a cloud. Once it hits the ground it begins dissolving minerals etc such as salt. It runs downhill into the sea from where it gets evaporated again. As there is no possibility of the salts evaporating with the water, the salts become concentrated in the sea. If the sea shrinks, the salt concentration gets higher as in the dead sea. Occasionaly (in geological timescales) seas get landlocked forming a big lake sort of thing and evaporate altogether. This gives salt flats like in USA (Utah and Nevada I think).

Kaptain Klevtsov

[themos]

What a coincidence! I was just answering (trying to) the children's questions on that very thing this morning on the school run! i think KK is correct. What keeps lakes and rivers "fresh" is the fact that the water in them doesn't stay there too long and what water there is was recently in a cloud (so not salty). If a lake becomes isolated from the rest of the environment, it will eventually go salty and dry up. Is that right?

Another coincidence is that I was looking at information on very high energy cosmic rays. There was a detector for them in Utah, called the Fly's Eye. It's a skywatcher's paradise there.

[beamish]

KK is correct, the seas not withstanding enormous glacial/icepack melting, will always become saltier.As this is down to the soluble salts in the runoff as described by KK. There are variations in salt conc in the seas hence the markings on the sides of ships(can't recall the name) but certainly changes between polar seas and tropical ones.

The factor, re global warming(whatever the root cause) that is concerning is the melt water from the sources mentioned above, diluting the conc in the northern Atlantic and possibly preventing the continued flow of the Gulf Stream passed the UK and Iceland and onto the Baltic, this is what would effectively plunge the UK in Artic weather similar to that experienced in other northern lattitudes, eg Moscow, New York etc.......

Karlo

[themos]

As this is down to the soluble salts in the runoff as described by KK.

I've just had a visualisation of the effect. The water goes round and round (evaporation->atmosphere->clouds->rain->runoff->river->sea->repeat). But the salt can only go downhill. There's no process that puts dissolved salt back into rock.

[beamish]

My understanding is Yes that is correct ! The seas are all gradually getting saltier (geologic time mind !)

Karlo

[jonifive]

My Saltwater fish tank evaporates about 5litres a day....but that is water not the minerals in the water. I replace that amount with 5litres of pure fresh water. The salinity of the tank water slowly creeps up over about four weeks, so when I do a water change, I dilute the new salt water to about 30ppm, as opposed to 35ppm (Natural seawater level) this keeps things in check.

Not sure if this would happen in the ocean though.

:?

JV

[beamish]

There will of course be absorption of mineral salts by the plants and animals. But over geologic time the earth's sea levels have and will continue to rise and fall,as the polar caps/glaciers have and will continue to freeze, advance then melt and reteat. Certain salts will be encased in deposited rocks and again over time these salts will be leeched back out. Cyclical !!bottom line as i understand it though is there will be a small net gain in the measured salinity of the sea water-with localised variations .

Perhaps this where someone with knowledge of the Gaia (?) theory could jump in ? Ie global balancing a bit like homeostasis for the earth.

Karlo

[Ant]

Very interesting read! Cheers guys.

I'm sure that I'll have more questions...

Ant