Yes, but saltwater is very corrosive. Also they were hard to get to. A datacenter in the arctic regions would at least be accessible -- you could build attached housing and heat it with waste heat.

Lake Ontario has 4C water year round not far from shore.

Just need a big enough and deep enough lake in a temperate climate.

Not sure when all that added heat becomes a problem, but it’s gotta get dumped somewhere.

Building things on permafrost always ends badly, that is huge problem in Alaska where they have to constantly re-level buildings and build things on pylons.