[Farael]

Actually, there is one more argument against tossing the ring into the water (and no, it does not include melting layers of ice.. if anyone wants a dissertation on that, PM me as I did a bit of research on it for University last year, I might still have my papers around)

But going back to the ring and the water.... there are Maiar there.
Even if we assume that Ulmo, a valar, won't be tempted because the Ring is a Maiar thing... I can't recall now the name of the Maiar who helped Ulmo in The Silmarillion but I do recall reading that there were more than one. What if one of THEM was tempted? the Ring could sure do that and.... any Maiar with the Ring is another Sauron... ergo, tossing the ring to the sea will be EXACTLY like giving it to Sauron... might as well try something else!