by Roger Bourke White Jr., copyright December 2004
Oceans are salt water. They are so because they accumulate all the soluble minerals that rivers carry into them from eroding the continents. For millennia, man has accomplished minor desalinating projects in his quest to get salt by evaporating sea water. Over geologic time spans, Mother Nature has occasionally accomplished the same thing on a much bigger scale, when inland seas have dried out and left behind the great salt beds which have become the salt domes that underlay some sedimentary rocks.
Seawater is currently too salty for life to thrive in easily. All things that live in seawater have developed methods of getting the salt out of the water before it is used inside cells. These processes are difficult to design and use up significant amounts of chemical energy. If seawater were less salty, life in the seas would be easier to accomplish, and we might see some interesting new life forms develop. It would extend the habitat of those animals that currently live in brackish waters, and many of those animals are valuable to mankind.
What I propose is building low-cost, low-maintenance, long-term evaporation basins that will slowly pull salt out of the seas and pile it up in the huge salt pans that lay nearby many seas and oceans.
I propose setting up giant evaporation basins on the edges of existing seas, letting sea water into them in a controlled fashion, and not letting the brine out. Putting sea water in will be accomplished by the passive process of letting seawater seep into the basins through rock-filled, but porous, channels. Getting the water out of the basin will be the job of the sun -- solar energy evaporating water from the brine.
These evaporation basins should be in desolate locations where they will cause minimal disruption of human and wild life. Good sites would be the sub-sea-level salt pans in Africa and Australia that border oceans and seas. There are several of these: One example is the Qattara Depression in Egypt that figured prominently in the Battle of El Alamein in WWII. Another example is the salt pan that sits at the south end of the Red Sea, northwest of Somalia.
A deep gully can be cut from the ocean to the salt pan and then backfilled with gravel to make a porous channel. The advantage of using a gully-and-porous rock channel over using a conventional surface canal is that it will be much more stable over centuries of use. It's not going to get filled in with blowing sand, or covered over to make a road, or farmed, and the sea level can vary tens of feet up or down before the rock-filled gully stops functioning as a "check valve" -- letting lots of sea water come in, but not letting salt or brine out.
The goal of this project is to reduce salinity in the world's oceans. The total effects of this on the ecosystem are unknown, but here are some of the first-order effects of the process.
Fresh water evaporates more rapidly and freezes more easily than salt water does. It also absorbs carbon dioxide more easily. This means that the atmosphere will become more humid on the average; there will be more of a propensity to accumulate snow; and the waters of the oceans will have a higher propensity to freeze.
These primary effects mean that oceans can freeze farther from the poles in the winter and that the atmosphere can transfer more CO2 into the ocean. It may also mean more clouds because the atmosphere will carry more water. All of the above forces would tend to mitigate the greenhouse effect: Freshening the oceans would have a net cooling effect on the world.
Because fresh water evaporates more easily, more energy would be incorporated into the hydrologic cycle. This would allow energy to move up and off the Earth's surface more easily and provide the world more cooling than it currently has by the "sweating" process of evaporating water at the surface and condensing it at high altitude. There would also be more rain produced around the world.
If more rains produce more ice freezing on the continents, sea levels will drop. If they drop significantly, the evaporation pans will stop working, which will be fine because the pans will have done their job of desalinating by then, and this turning the pans off acts as a negative feedback loop: The pans will stop desalinating when the oceans freshen enough that the ocean level drops.
As the oceans desalinate, their waters will become brackish. This change would be gradual in human terms, sudden in geologic terms, and intermediate in evolutionary terms. It would change the mix of life in the oceans. The change would be something of a regression -- the oceans have been less salty in earlier ages. Thus, this change would probably make it easier for all kinds of life to thrive in the oceans.
But even if life is easier in the oceans, the great extinctions of species and subsequent radiations of improved species would continue. Life will go on; it will just be different, probably a little more plentiful and a little more varied. But a brackish ocean will be more human-friendly than a full salt ocean because humans and human-friendly animals find brackish water easier to use than full salt water.
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