Phosphate breakdown in ocean?

[jordsyke]

So this may be a stupid question but I've just been reading the whole nitrate / phosphate breakdown on different forums and supposedly it ias taken out at around 16:1. But for most people this leaves them with no nitrates and some phosphates left over. So I am wondering if anyone knows how this residual phosphate is broken down in nature, is it an organism, or a chemical breakdown, or just the fact that the ocean is just so goddam huuuuuuge.