Of course radioactive elements have a habit of turning themselves into other elements without your asking them to. Sadly none of them seems to favour gold as a final destination, lead seems to be more common.
Unfortunately I fear Jake may have to put his get-rich-quick from seawater scheme on the back burner. I calculate that to end up with 1cc of gold you'd have to process 10,000 litres of seawater. Gold is so inert. however ,that you're in real danger of not finding an extraction process. Meanwhile the seawater, far from being pure H2O, is contaminated with so many other things that your filtration process is going to be continually blocked by bits of crud. I think if it was possible it would be being done.
Now a small submarine dredging for diamonds on the continental shelf of Namibia - that might work!