"dead zones": Excess fertilizer runoff causes excess growth which then leads to oxygen depletion as it dies and decays. Basically 'eutrophication' but of the oceasn instead of lakes.

And yes, the North Pacific gyre, aka the Great Pacific Garbage Patch collects old plastic. That does NOT mean bottles per gallon, it means small pieces distributed over a large mass of water,but adding up to a large collection.

http://en.wikipedia.org/wiki/Great_Pacific_Ga...