Why is the sea salty?


Pygmy Octopus
Apr 19, 2003
Slightly off topic, but cephs live in it...

A friend asked me this one out of the blue at lunchtime. I trotted off the old explanation about rivers washing dissolved minerals into the sea and millions of years of evaporation doing the rest. Then I went digging around on the web...

Seems this old chestnut was originally proposed by Sir Edmund Halley ( of comet fame ) and he also proposed calculating the age of the ocean from salinity - which works out at about 800 million years. Hmmm... :bugout:

Other sources indicate that we must add hydrothermal vents and ocean floor volcanism as sources of dissolved minerals.

Then, of course, there must be some kind of equilibrium mechanism to prevent salinity increasing forever - unless the Earth really is 800 million years old!

Another source indicated that the sodium for salt came mostly from weathering of the land, while the chlorine came from deep ocean volcanic outgassing.

Ask a simple question! :?

It seems like quite a debate. Anyone care to stick an oar in? :biggrin2:
There are many salt deposits that were formed in the distant past, most of them formed when parts of the ocean were cut off from free flowing currents. I know of a Devonian? age salt deposit in the northeast US, and here in the great western desert we have a Jurassic age salt deposit, I would guess there are millions of tons of salt in it (they want to make nuclear waste storage facilities out of some old salt mines). Yearly there are millions of tons of salt extracted from evaporation ponds around the great salt lake also. Seems to me that if all the salt that came out of the ocean eroded back into the ocean it would be a whole lot saltier.
Perhaps this is the sort of question that could be approached less directly? I'm wondering if perhaps it's better to meditate on the nature of the ocean itself--what it is, why it exists, why it exists WHERE it exists... I'm thinking you can maybe think of the ocean merely as the world's "sump" or "sink." Anything that drains, drains there. The ocean is not so much SALTY as it is "full of materials that are readily water-soluble." In other words, it's less "why is the ocean salty" than it is "why WOULDN'T it be salty?" Take a planet like ours and dump water on it regularly over eons, you get oceans with stuff dissolved in them.

As a non-geologist/oceanographer, perhaps I'm missing some pretty crucial stuff...but in general, I'm kinda thinking that if Earth lacked mineral salts in its crust but instead had Kool-Aid, we'd be asking "why is the ocean Kool-Aid-ey?" :heee: Ideas?

I'm with you on the "sump" theory. It makes as much sense now as it did when Sir Edmund thought it.

My curiosity was prompted by the differences in the theories. Firstly, what systems could be involved in "removing" salt (and other minerals) from the sea? Does the high pressure of the deep sea abyss allow reactions which would not be possible in shallower waters? Does salt actually crystallize out in some parts of the deep ocean? Secondly, the idea of sodium from the land and chlorine from the sea is all very well with respect to the ocean networks, but as far as I am aware the Dead Sea has no volcanic outgassing to provide chlorine. All of that thick brine must have come from the surrounding flood basin.

At what concentration does Kool-aid crystallize anyway? I expect it's similar to Tizer.
More questions come from this thread. There are different kinds of evaporite deposits that come from ocean water, such as, Potassium Phosphate, mined for fertilizer, Calcium Sulphate (Gypsum?), mined for wall board. Just how much of the salt in the ocean is actually Sodium based? And what circumstances deside which mineral is formed when sea water evaporates?
:?: :?: :?:
This is all rather heavy, interesting discussion!! Why is my blood salty? Is there a finite amount of salt on this planet? If the human population continues to expand, and we eat more fish, will there be less salt in the sea and more salt on land (bound in our bodies). Is the earth around a cemetery more salty than that of a daisy-filled green pasture?
Steve O'Shea said:
Why is my blood salty?
Interesting you should ask! Some years ago I read a fascinating little article. It was focusing on a couple of biologists specializing in "pie in the sky" science. If I recall, they admitted their ideas were far-fetched...they were simply trying to push the boundaries of theory. One idea they were pondering was, I think, an old one about floating, self-sufficient vegetative microecosystems. Mangroves or some other similar plant would have a symbiotic relationship with sponges or some other creatures in their roots which would enable them to float stably. Rafts of them would drift out into the ocean, inhabited by any number of terrestrial and marine critters above and below. Sort of an advanced version of what you find in the sargasso sea.

This related indirectly to the other part of their theorizing, which I found fascinating. They were toying with a sort of "perspective shift" in biology. They noted that, much like their mangrove rafts ideas, what one may perceive as an "individual" is almost always a functional amalgamation of dozens or hundreds of more or less independent organisms, working together in symbiosis (and antagonistically as parasites) to form a whole. They suggested that we view terrestrial life as an extension of the ocean--in fact, as miniature pockets of ocean opportunistically inhabited by many forms of life, that still manage to function as though they were oceans, occasionally meeting and exchanging various elements of themselves, and striving to maintain a controlled oceanlike environment--thus, salty blood. Technically (by this theory) we never left the ocean at all--we took it with us.

I know a lot of this isn't NEW, but I liked the concept of terrestrial animals not just using oceanlike conditions internally but rather literally as a very odd, highly subdivided extension of the ocean itself. Even if it's totally silly, it's a cool way to think of things.

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