This is pure speculation on my part but I actually think Antarctica is where The Garden of Eden is and THAT is what they're really trying to hide there. Of course they can't get in due to the angel guarding it bit maybe they're trying to find a way. I also think it could just be them doing experiments/magic to summon the demonic or things like that.
There's certainly SOMEthing they're hiding down there. What exactly that is, well, that's a matter for speculation.
But to think that in the 1950s and 1960s, all these countries that were otherwise at war and who never agreed on anything else would suddenly get together to protect Penguins. Environmentalism just wasn't a thing back then. Admiral Byrd indicated that there were vast reserves of natural resources down there, and you know full well that the US and the Soviets would have been vying like nobody's business to get there first to exploit them.