It would be a real challenge to actually photograph the entire underwater part of an iceberg. It's probably never been done. If you could find one in clear water, and set off some enormous set of flashes underwater, it just might be possible. That would be a good project for National Geographic.
I'm not sure the local whale population would be too happy with setting off something underwater to generate that much light. Would be interesting, though.
And the bottom of such a huge iceberg can't possible be as well lit as if the sun was hitting it from below. (And of course it looks like that because it's an above water shot, flipped.)
Now the interesting thing to do would be to take one of these iceberg pictures for real. Since we can't see through this much see water the thing to do is make a huge grid of cameras and put it directly up against the iceberg.
Alternatively, once could lower a line of cameras to scan the iceberg.
icebergs turn over quite often, as the seawater eats away at the bottom until they become top-heavy. When they do you get that really strange brilliant blue color which comes from dense glacial ice which has had all the air bubbles forced out.
"Fake" is a little strong. As he says at the end of the article, you couldn't capture an image like that with a single photograph. He strove for accuracy, but who knows how close he got - the article doesn't go into that. His clients thought it was realistic enough and evocative enough to give him $1m.
The image purports to show a mass of hidden iceberg underneath the water. What it show instead is two above-water icebergs, one of which was flipped upside-down. That is totally fake in my book. If it happens to be accurate (and like you say, we have no information about that), it might correctly illustrate the idea, but the photograph is still fake.
http://www.telegraph.co.uk/news/earth/earthpicturegalleries/...
http://www.divephotoguide.com/underwater-photography-special...