If oceans were fresh...

[ifm2181]

Theoretically, what would the effects of an all-fresh-water world be, besides the obvious effects on aquatic life forms? How would the atmosphere be affected, and various other systems, be changed?

 

As far as I can tell, the oceans:

- Will be colder because salt water holds heat better

- Will be harder to float in because of a lower TDS

- Will be able to support larger creatures because of a higher DO content, since cold water holds oxygen better

[YT2095]

I`m no expert but if I rem correctly the salinity of the oceans is essential for the gulf stream (or something like that).

in effect it follows a global patern yearly and when it gets further north towards the ice the salinity drops, creating currents underneath for the return path.

if all the water were salt free the density would remain the same only being affected by the temp changes alone, and that wouldn`t be sufficient for the maintainance of our current system, basicly the weather as we know it would be radicaly altered!

 

I dare not even Try and predict the effects it would have, but it would certainly be nothing that we`re familiar with.

[ifm2181]

Yeah, I figured it would affect the global air currents.

Also, I bet it would affect the amount of precipitation. Since salt water's warmer, it would likely evaporate easier, as well. If it were all fresh water, it would likely rain a lot less because not as much is evaporating.

[coquina]

Theoretically' date=' what would the effects of an all-fresh-water world be, besides the obvious effects on aquatic life forms? How would the atmosphere be affected, and various other systems, be changed?

 

As far as I can tell, the oceans:

- Will be colder because salt water holds heat better

- Will be harder to float in because of a lower TDS

- Will be able to support larger creatures because of a higher DO content, since cold water holds oxygen better[/quote']

 

Well - if the oceans were fresh, it is hard to imagine what the land would be like. I guess the continents would have to consist of a diamond hard, non-erodable material, since the saltiness of the oceans is derived from the material that is eroded into them by way of rivers and streams.

[Blackfin]

If all the oceans were fresh, well, you could essentially say life would not exist - because obviously water-soluble salts could not exist on the planet or they would dissolve into the ocean and make it salty again - and about 75% of a human's body mass is a saline solution. o.O Tears, blood, anyone? Sodium/potassium pumps?

 

...When I first saw this question, my first impulse was to write, "They'd get salty again." XD

[Ophiolite]

...When I first saw this question, my first impulse was to write, "They'd get salty again." XD

And again, and again, and again. Salt is continually being extracted from the seas by evaporation in closed or semi-closed basins. The salt deposits are then recycled into the mantle by subduction, some of which is then incorporated in the lavas that emerge from the descending plate. If this process was not continuoulsy extracting salt from the ocean's they would be substantially saltier than they are.

[ifm2181]

Well - if the oceans were fresh, it is hard to imagine what the land would be like. I guess the continents would have to consist of a diamond hard, non-erodable material, since the saltiness of the oceans is derived from the material that is eroded into them by way of rivers and streams.

Yes, very true.

If all the oceans were fresh' date=' well, you could essentially say life would not exist - because obviously water-soluble salts could not exist on the planet or they would dissolve into the ocean and make it salty again - and about 75% of a human's body mass is a saline solution. o.O Tears, blood, anyone? Sodium/potassium pumps?

 

...When I first saw this question, my first impulse was to write, "They'd get salty again." XD[/quote']

Or at least, the life would be greatly different.

And yes, they would get salty again. XD

 

And again, and again, and again. Salt is continually being extracted from the seas by evaporation in closed or semi-closed basins. The salt deposits are then recycled into the mantle by subduction, some of which is then incorporated in the lavas that emerge from the descending plate. If this process was not continuoulsy extracting salt from the ocean's they would be substantially saltier than they are.

I thought salt didn't evaporate because it doesn't actually dissolve in water? I was under the impression that only the water did the evaporating, leaving the rest to just sit there and be whatever it is.

[Bettina]

And again, and again, and again. Salt is continually being extracted from the seas by evaporation in closed or semi-closed basins. The salt deposits are then recycled into the mantle by subduction, some of which is then incorporated in the lavas that emerge from the descending plate. If this process was not continuoulsy extracting salt from the ocean's they would be substantially saltier than they are.

 

 

Could you clarify this? I know the oceans contain about 3.5% salt, and was told it will get saltier as time passes because salt constantly enters the oceans and it does not "evaporate". I know you didn't mean it the way you stated, so what did you mean.

 

Bettina

[ecoli]

If all the oceans were fresh, well, you could essentially say life would not exist -

 

Not as we know it, anyway. Life could've evolved differently.

[coquina]

Could you clarify this? I know the oceans contain about 3.5% salt' date=' and was told it will get saltier as time passes because salt constantly enters the oceans and it does not "evaporate". I know you didn't mean it the way you stated, so what did you mean.

 

Bettina[/quote']

 

http://pubs.usgs.gov/publications/text/understanding.html

 

Until Ophie gets around to a more detailed reply - look at the section on Oceanic - Continental Convergence.

 

This is a subduction zone. When seawater becomes saturated with salt, the excess is precipitated into sediment. Where there are leading edge convergent boundaries - ie the northwestern coast of the United States and South America, the ocean bottom is subducted beneath the continental mass.

 

When it descends to a certain depth, the water from the sediment changes to steam, which builds pressure and causes volcanoes to form a few miles inland. The Cascade Range and the Andes were formed as a result of this. A unique form of lava called "Andesite" erupts from these volcanoes.

 

http://www.geology.sdsu.edu/how_volcanoes_work/subducvolc_page.html

[ifm2181]

Hm, interesting.

(Hey, this topic actually went somewhere. Cool. )

[Ophiolite]

Could you clarify this? I know the oceans contain about 3.5% salt, and was told it will get saltier as time passes because salt constantly enters the oceans and it does not "evaporate". I know you didn't mean it the way you stated, so what did you mean.

The interesting thing is that broadly speaking sea water does not get saltier with the passage of time.

Now, sea water is around 200 times saltier than fresh water. [There is very little fresh water that does not contain some dissolved salts.] But although it is comparatively fresh that small quantity of dissolved salt is still there. So, the water disgorged into the ocean every day adds salt. But every day a larger volume of water evaporates from the oceans and seas, leaving the dissolved salts behind. Some of this water falls as rain directly on the oceans, and so has no effect, but some falls on the land, flows to the sea, and along the way dissolves some more salts.

You know this already. And it seems, as you say, that the concentration of salt should increase over time. [in the 19th century scientists tried estimating the age of the Earth from the salinity of the oceans.] But it does not increase. Something must be removing the salt, and keeping the concentration in approximately the same concentration over millions of years.

There are a couple of mechanisms:

1) Water can become trapped in isolated basins, where it evaporates, perhaps eventually drying up entirely. During this process various salts are deposited in turn. (My memory may be faulty, but I think the sequence of the major items is calcium carbonate, gypsum, halite (common salt).

The basin may periodically be exposed to the ocean again, receiving a fresh influx of water, so that a series of sequences are built up. These evaporite deposits are common in the Middle East, but we also find them in the remains of the old Tethys Ocean, which is represented today by the Mediterranean, Black, Caspian and Aral Seas. During the Permian and Triassic periods much of Northern Europe from Poland through to the UK was the site of a shallow sea in which thick evaporite deposits were laid down. These deposits can total 1,000s of feet thick, so that a substantial volume of salt can be removed in this way. (If all the salt in the oceans were extracted and psread out over the land surface it would be about 500' thick.)

2) Clay minerals may absorb some dissolved materials into their structure.

3) During diagenesis (the process of change in sediments that occurs as they are buried and subject to increasing temperature and pressure) water is squeezed out of the sediments, but the dissolved salts tend to be retained.

 

Together these mechanisms remove salt from sea water at approximately the same rate at which it is added by rivers, so a balance is achieved. Some of this salt eventually finds its way back into the oceans, when the sediments are caught up in descending plates in subduction zones, and eventually get erupted as constituents of lavas, as noted by Coquina. [And I'll blame Coquina for my overly long, rambling reply, as she said "Until Ophie gets around to a more detailed reply", so I felt honour bound to make it lengthy. ]

[des]

Since the ice caps are certainly melting, oceanic salinity is definitely falling. We don't know exactly where the shut off valve is, in terms of deep ocean currents, but at some point it's assumed... the gulf stream conveyor, as mentioned, for example, will simply stop delivering warm water from the Carribean to England, which will in turn translate to overall ambient temperature, in effect freezing western Europe over solid. Imagine the same thing happening worldwide, follow the map of deep sea currents. Merry old England isn't the only one in trouble. Did your own home town once host an ice field? Because it's highly speculated that salt, or the lack thereof, is an ice age trigger. Cold toward the poles, with drastically increased snowfall, while the equatorial regions parch under cloudless skies. But no worries. After several thousand years, with enough water again safely locked in ice caps, oceanic salinity will once again return to normal, those blessed currents will return, driving warmth to extreme latitudes, restoring rainfall at the equator, and we can go back to business as usual.

[Aardvark]

These evaporite deposits are common in the Middle East, but we also find them in the remains of the old Tethys Ocean, which is represented today by the Mediterranean, Black, Caspian and Aral Seas.

 

 

Unfortunately your information is now out of date.

 

The Aral Sea no longer exists.

[ed84c]

I thought there is still a small lake in the middle?

[Aardvark]

Yes, a small, hyper-saline lake with no life.

 

Where once was a sea with large numbers of unique species, rich fisheries and moderating effect on the local climate.

 

The sea was killed by diverting water to agriculture. Without the sea the climate is more extreme. So the agriculture has been wrecked.

 

A rather bitter irony.