Reef Chemistry Question of the Day #16

leptang

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Sea water has been defined as a weak solution of almost everything. Ocean water is indeed a complex solution of mineral salts and of decayed biologic matter that results from the teeming life in the seas. Most of the ocean's salts were derived from gradual processes such the breaking up of the cooled igneous rocks of the Earth's crust by weathering and erosion, the wearing down of mountains, and the dissolving action of rains and streams which transported their mineral washings to the sea. Some of the ocean's salts have been dissolved from rocks and sediments below its floor. Other sources of salts include the solid and gaseous materials that escaped from the Earth's crust through volcanic vents or that originated in the atmosphere.
 
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Randy Holmes-Farley

Randy Holmes-Farley

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Good answers!

Rivers and, to a smaller extent, hydrothermal vents, sweep dissolved elements (salts, typically) into the water. These dissolved salts come from the weathering and hence the slow dissolution of rocks.

Granite, for example, has the following typical composition, so you can see that as it slowly dissolves, lots of different things get added to the oceans.

Granite - Wikipedia, the free encyclopedia

SiO272.04% (silica)
Al2O314.42% (alumina)
K2O4.12%
Na2O3.69%
CaO1.82%
FeO1.68%
Fe2O31.22%
MgO0.71%
TiO20.30%
P2O50.12%
MnO0.05%

The ultimate composition of seawater ends up being a balance between these inputs, and the various sinks, such as precipitation or uptake by organisms followed by deposition into sediments when the organism dies. Scientists study such things as the average residence of a particular chemical in seawater between when it arrives in the water, and when it leaves somehow. Something like sodium has an average life of hundreds of millions of years, while more aggressively taken up (iron) or precipitated (aluminum) elements might last less than a thousand years, on average.

Happy Reefing. :)
 

Simon Garratt

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You forgot one Randy.

The addition of elements via non terrestrial means....space debris, meteorites and such...

Ok Ok, I know its a small addition but it all counts..:)

Long time no speak Randy, Hope you are doing well.

Kind regards

Simon.
 

Simon Garratt

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Lol...I knew my outside the box thinking would come in handy at some point.

Great to see you still helping the masses Randy. Always the voice of reason in the smog that is reefing chemistry...:)

Kind regards
 

Opus

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Off topic some but I saw an article the other day that claims up to half the water on earth is older than our galaxy.
 
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Randy Holmes-Farley

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Off topic some but I saw an article the other day that claims up to half the water on earth is older than our galaxy.

Cool. :)

FWIW, I presume that means the oxygen atoms in the water. Actual water molecules interchange their hydrogen atoms with each other extremely rapidly, so that actual lifetime of an individual water molecule in bulk water is far less than a second. :)
 

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