Imagine an Earth-like planet with oceans that are comprised roughly 50/50 of heavy water and normal water. My understanding is that while heavy water ice sinks in normal water, it would float on heavy water. But would it float completely below the surface in an ocean that is a mix of heavy and normal water, or would part of it be out of the water like a regular iceberg on Earth?
I want to make sure there isn't any massive flaw in my understanding in whether such a thing (completely underwater icebergs) would be possible.
Thanks everybody. To expand on what I'm thinking about, I'm imagining a planet that has one supercontinent in the north, and the rest of the planet covered in one big super-ocean, with land:water ratio being around 25:75; so an ocean far bigger than any currently on Earth.
I gather from the comments that the big issue is that this ocean would eventually stratify into the different kinds of water. I think what I want to try and do is reverse engineer reasons why the ocean would stay stirred up, such tidal forces from a large orbiting moon, as well as biological processes (part of what I'm imagining for the ecosystem on this planet are lifeforms that photosynthesise with heavy water, so therefore dive down to fill up with D20 and then dive up to be nearer the sun).
I'm less interested in there being super-stable conditions that allow the icebergs to glide at a fixed depth, in fact, the more chaotic the system the better.
Would D2O icebergs be more likely to form if the planet received less energy from it's star? Or if the ocean had significantly less salt than our oceans?
Again, thanks for all your comments!