The Jewel Ice Sheet is a treasure cache frozen beneath very hard ice.
The ice sheet is very large with dozens of huge icicles jutting out from it. The ice itself is almost impossible to break and seems to be able to reform quickly, shown when even the use of flamethrowers could not melt the ice long enough. Beneath the ice is a cave full of treasure, amassed over centuries.
Thirty years ago, Chinjao broke through the ice with his head, gaining access to the vast riches that lay beneath. He vowed to never let anyone near this treasure, which had been collected by the people in his family.
Sometime later, after losing his drill-shaped head in a battle against Vice Admiral Garp, Chinjao returned to the island and tried to break the ice again, but could not. He then cursed Garp and his family for costing him his access to the treasure, swearing to not even forgive his grandchildren.