Novel about a magnetic reversal. U.S. flash freezes and Antarctica rapidly thaws and reveals ancient Cyclops and other giants. Main character is a young lady. She meets up with other people and eventually escapes to military ship in the ocean.
Antarktos Rising by Jeremy Robinson (2011) This book has almost all the things you have listed: Frozen USA though from crustal displacement instead of magnetic reversal, thawing Antarctica with return of Biblical giants, main character is a young lady (Mirabelle Whitney), the other people teams from various nations on a race to claim the continent, and lastly escape from the continent via ship. It was pretty good as I recall, much better than I expected, and supposedly to be made into a movie per the cover.