Mining the ocean

[Jed Rothwell]

In the US, 45% of the annual production of magnesium (143,000 tons) is 
extracted from approximately 0.05 cubic kilometers of seawater; 0.2 cubic 
kilometers of seawater would supply the entire world.

The most abundant useful elements in seawater appear to be Na, Cl, Mg. S, 
K, Ca, Br and Sr.

Unfortunately, there is very little Pd or Au in seawater. Some sources 
claim there may be tons of Au per cubic kilometer, but most indicate much 
less than that.

See:
http://gill.tamug.tamu.edu/mars615/extraction_of_useful_substances.htm
http://165.95.49.52/MARS615/Extraction%20of%20Useful%20Substances%20from%20the%20Sea%20(2003).pdf
http://www.agu.org/eos_elec/97025e-table.html
http://www.seafriends.org.nz/oceano/seawater.htm
- Jed