>I will have to assume they are using the sea because its the least likely assailable location by anyone who might seek to take the weapons?
Largely political. They couldn't find any nations willing to host the weapons for destruction, so doing it in international waters was the best available option.
Well, honestly the part that confuses me is that the article tells us that half of Syria's weapons have already been disposed of in other European countries.
It's been a while since I've read up on it, but as I recall, Syria was also turning over stockpiles of potentially weaponizable industrial chemicals. That may be where the discrepancy is here.
EDIT:
Some more reading suggests that they're actually being shipped to Italy for storage to get them out of Syria ASAP, and then the actual processing/destruction is occurring in international waters.
Largely political. They couldn't find any nations willing to host the weapons for destruction, so doing it in international waters was the best available option.