The crust, which is Earths outer solid layer of rock, is around 20km thick if I remembered correctly, and the ocean is nowhere near that, so there would be rock under the ocean.
If you find a better answer, then use it, because I'm not completely sure, but that's my best guess based on the possible answers
Free oxygen atoms can replace the chlorine in chlorine monoxide, releasing a free atom of chlorine which can then recombine with an oxygen atom in ozone, destroying more ozone.
