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In a future world, where there is almost no fresh water resources left, a radical scientist comes up with an idea to turn all the oceans into fresh water.

The general idea is to be able to precipitate the salt, so that it sinks to the ocean bed. Whatever sediment and salt get added through rivers (of which, there are very few) and drains, immediately precipitate to the bed, leaving the sea water fresh.

Now, with fresh water in the seas, what things should be considered to maintain the ecological balance as much as possible? We've already lost a lot of animals and ecosystems, we wouldn't want to lose more. Whether or not there are solutions, what are the problems to be considered? (Solutions are welcome!)

One thing I can think of, is the salt water fish. As a solution, the scientist could probably genetically alter them to adapt to fresh water. What else?

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  • $\begingroup$ Land animals in the north would be effected. Salt water is heavier and with fresh water the Gulf Stream would not be bringing warm equatorial water as far north as it currently does. This would cause starvation for countless millions of people, at least until fresh water fish started breeding in the oceans. $\endgroup$ – the_OTHER_DJMethaneMan Apr 22 '15 at 13:45
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    $\begingroup$ I'd like to point out that at that drastic a level, the Earth would have lost Antarctica, the glaciers in Yellowstone National Park, Lake Titicaca, every iceberg in the north Atlantic, and even the groundwater needed by flora for basic survival. There are much bigger consequences from this than human survivability you'll need to address. See this $\endgroup$ – Frostfyre Apr 22 '15 at 14:40
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    $\begingroup$ If we can genetically alter fish to live in freshwater, why not just genetically alter humans to drink salt water instead? $\endgroup$ – DA. Apr 22 '15 at 18:53
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    $\begingroup$ Finally, why desalinate the entire global oceanic ecosystem with this magic sinking salt? Just create a bay or ponds/inlet and just desalinate those on an on-needed basis. That's be a much more practical solution. $\endgroup$ – DA. Apr 22 '15 at 18:57
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    $\begingroup$ Forgive me if this is an obvious question, but... If this scientist has some magic way of causing all the salt to precipitate out of seawater, would it not make sense to do that after the water has been taken out of the sea? So, let it flow into large reservoirs, and do it there? That avoids the ecological impact, solves the drinking water issue, and hey, free salt. $\endgroup$ – anaximander Apr 23 '15 at 14:47
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Most of the life forms, plant and animal, are dependent on salt water for their biology. Precipitating all the salt out would cause an ecological disaster.

Much of the life in the oceans would die very shortly after. On top of that our weather will be affected. salt water has a much lower freezing temperature and without salt more of the oceans would freeze during winter, the couple degrees difference can change the 'coastline' by miles and miles. I'm also sure it would mess with the ocean currents, possibly stopping them. and alter the evaporation rate, making it easier which would allow for more and greater storms.

Since most of the water would still need to be transported to people (unless everyone moved to the coast), there would be no reason to treat the whole ocean only what is going to be removed and transported to those in need.

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    $\begingroup$ i'd probably be better off just treating a part of the ocean than the whole of it, like i noted in my reply to @DJMethaneMan's comment. If there are no more answers posted, i'll accept this one. Sorry for the lack of up votes, i do not have enough reps. $\endgroup$ – insanity Apr 22 '15 at 14:21
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    $\begingroup$ How Stuff Works and the USGS have some good information on desalinization. And here's a bit about the impact of salt on evaporation. $\endgroup$ – Frostfyre Apr 22 '15 at 14:25
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    $\begingroup$ @Samuel I didn't say the Oceans would freeze, I said more of it would freeze, those few degrees could be miles different in what freezes and how long it stays frozen $\endgroup$ – bowlturner Apr 22 '15 at 18:37
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    $\begingroup$ @Twelfth I'd love to see your source for that. Seawater freezes at about −2 °C. Further, from Wikipedia "The coldest seawater ever recorded (in a liquid state) was in 2010, in a stream under an Antarctic glacier, and measured −2.6 °C". $\endgroup$ – Samuel Apr 22 '15 at 20:43
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    $\begingroup$ @Twelfth Completely saturated salt water? Ha, are we no longer talking about any ocean on Earth? I don't disagree that there is a negative feedback effect for freezing salt water, but you're talking about ridiculous changes in salinity to get to complete saturation. As I linked before, the lowest recorded temperature for liquid seawater was -2.6°C, clearly that's because anything colder was frozen. $\endgroup$ – Samuel Apr 22 '15 at 22:09
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Climate on your globe will be forever altered, though it's difficult to fully describe how as we really aren't sure what currently drives the process. You risk messing around with thermohaline circulation (also known as the great oceanic heat conveyor belt). One part we do know is this system is dependant on salt water concentrations to run. Water warms in the tropics and moves along the surface of the ocean towards land. In the atlantic, this current keeps England relatively warm and in the pacific it brings wet and warmer weather to the pacific northwest. The water then cools, sinks into the ocean, and returns towards the tropics in a giant loop.

It's actually thought that metling ice could adjust the oceans salt concentrations enough to disrupt this cycle, let alone all salt being removed from it...and the end result is a bit of a 'day after tomorrow' style story, without the silly storms. England, Scotland, and Ireland all enter a freezing cycle where they take on the climate closer to what a land that far north should see (average around -10C colder as a minimum). We would also see the tropics water warm further and surface temperatures would start to reach record highs relatively quickly. Hurricanes use the surface heat of the ocean to fuel itself (a large hurrican actually drags cold water up from the depths and kills its own fuel source)...with a larger fuel source it stands to reason these systems could become significantly stronger and we could see some monster storms.

We would get frozen icecaps pretty quickly as well...saltwater affects the temperature at which water freezes, lowering it significantly and allowing for cold ocean water not to freeze right away. Funny enough, this would actually have quite the warming effect on the globe as water mass transitions to ice and releases the energy involved with it's freezing. Speculative, but you might see a 2-5 degree temperature increase on world wide averages pretty quickly too. This would be temporary as I suspect the ice formed would begin reflecting large amounts of sunlight reaching earth and start a cooling trend.

The tropical areas of your globe will become much more humid (especially near these oceans) and I suspect you'll see a significantly larger amount of rain. If nothing makes up for the thermohaline circulation, you'll also see the equator gain a tremendous amount of heat and keep it. So warm wet tropics with tons of rain and potentially the most fierce hurricanes we've witnessed.

There's no possible way of resolving the impact to the ecosystem either...very few species are capable of crossing salt water into fresh water and this salt precipitation event would likely become a mass extinction event that would rival the meteor impact that ended the dinosaurs as far as number extinct species is concerned. We're not talking a few salt water fish either, we're talking every last living creature in the ocean, including many that we're not even aware of yet. I'm not sure if there is a single fresh water Cephalopod for example. Good chance you'd cause a massive plankton die off with this as well.

I'm actually thinking you could post an answer to the question 'how to I end life on earth' with 'remove salt from the oceans' and be somewhat correct.

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    $\begingroup$ wow, you make me feel guilty for proposing such a thing, even if its fictitious! $\endgroup$ – insanity Apr 22 '15 at 18:08
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    $\begingroup$ lol sorry, guilt is not my intent. The Earth is a pretty impressive balancing act and salt is at the core of it though. $\endgroup$ – Twelfth Apr 22 '15 at 18:11
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The consequences would be drastic and gobal.

Sea life is adapted to salt water, there's a reason that most fish and plant life is adapted to either the sea or fresh waters and not to both.

Most marine life at the bottom of the ocean will be killed by the massive amounts of salt. Most marine life in the top will be killed by the lack of it.

Freshwater species would start to move out to colonize the ocean but most of them are adapted to smaller rivers and lakes, it would take them considerable time to evolve into the new niches - we're talking thousands or hundreds of thousands of years.

In the meantime weather patterns are going to be disrupted in unpredictable ways. Ocean currents will shut down or change, arctic ice may well recover for a while as the water becomes easier to freeze but that's going to be a small consolation compared to the amount of devastation caused everywhere else!

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I don't know if having freshwater oceans is important to your world, but if he has a way to easily desalinate the water, why not just pump and treat what you're actually going to use?

For instance, if California goes through another drought, they'd just have to run some high capacity pipes out into the ocean, run the water through the process to remove the salt, and then place it into aquifers and other places it can be used.
Treating the entire ocean is overkill, and would cause more problems than it would solve.

The process could also be mobile. Put the equipment onto trucks and drive it to the places that need it, but where treatment plants haven't been built yet.
The trucks could pump the water, treat it, and then put it into tanker trucks to transport inland to help people that need it. Thinking central Africa, etc.

There are ways to desalinate water, but they are difficult and expensive. A fast/cheap way would solve a lot of water problems without having to destroy marine ecology.

Where this could be useful on a large scale is when there is no existing ecosystem, like say Mars. Mars has a lot of salts in it's soil. If we someday teraform Mars and give it oceans, they will be very salty. By starting out with a clean slate, you could maybe begin the process from the ground up with freshwater animals instead. It would be mostly ice unless we figured out a way to warm the place up...

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