This is adding the ocean as a new layer in the overall heat dissipation stack for datacenter computing; it's impacting a whole new ecosystem that it wasn't before. Thus, we need to be asking these kinds of questions about how this will impact oceanic ecosystems.
Then a study (ideally multiple studies) should be commissioned to find this out. We shouldn't just do it because we can, and because armchair physicists are pretty sure that it's insignificant.
Because, that's what Microsoft (and their partner) did. They did it because they could.
Remember when we, as a global society, believed that CFCs would have an insignificant impact on the environment? I do. Perhaps we should tread a bit more lightly when we're already running into species extinction and global climate change issues.
In which case, we'll just end up talking past each other, so I'll wish you a good day.