I hope I am not too late! I did not see this post last week, whatever you do, do not use thermite to loosen the hatch to attempt to peer inside it.
But even more importantly, if you find something in the ice, let it be, don't take it back with you, and do not thaw it out.
I just hope you listen to my advice. In the event that you do not or did not, or I am too damned late, I will be in my basement with a rifle and a lot of canned food.
UncleRhino