User blog comment:Mckrongs/Monster Hunter 4 for the Nintendo 3DS/@comment-4639479-20130921211059/@comment-21371438-20130922094957

it's the vortex in Frozen Sea

http://monsterhunter.wikia.com/wiki/Frozen_Sea

"The large vortex in this area is said to be caused by a mysterious sea monster."

also, there is a mysterious skull struck in ice... so, some fans still hope for a giant elder dragon in a higher rank