What is Sealed Beneath the Ice?

According to a recent article from The Independent, scientists have discovered that over one hundred plumes of methane gas are now being released from the ocean that was once concealed by the Arctic ice shelf.  It would appear that these huge levels of gas will perpetuate climate change at an even more accelerated rate than our own feeble efforts have thus far produced.  But what of your campaign world?  Are there more monstrous things hidden below the depths and held at bay by the frozen waters of the icy north?  Read more about the actual occurence here.