My 8-year-old son asked this question and i couldn’t give him a definite answer. So he’s wondering if it would do the same thing as a balloon pushed underwater in the bathtub (which kind of makes sense to me, due to the density differences, not just gravity alone).
But I told him I’d ask those more knowledgeable than me.
There is a YouTube channel called Action Lab that asks and tests all kinds of questions like that. I don’t know if this specific one was answered, but you and your son would probably enjoy a lot of the videos on there.