I tried looking for environmental impact studies for Microsoft's data center project, but all I could find were object tracking models that their team built for tracking marine life.

If a published study on this exists, I'd love to take a look.

Not likely, water is a good heat conductor so there will just be a area of slightly warmer water near the outlet. You might get a micro ecology with some tropical fish far from their normal grounds but nothing dramatic will happen.

It'll certainly not be worse for the environment than any normal data centre, unless it springs a leak and something toxic escapes.

Maybe, but it could also reduce fossil fuels used to operate less efficient cooling systems in traditional data centers. I’d love to see a breakdown on the impact of each approach.