I just found a great article that talks about how penguins and seals can survive deep dives. According to Jessica Meir, emperor penguins can dive over to 457 meters (1,500 feet)! She also talks about how they can tolerate extremely low levels of oxygen in their blood.
Penguin Photo from RedOrbit
The article is a bit of an advance read, but has some interesting bits of information about penguins and their diving habits.