The Jewel Ice Sheet is a treasure cache frozen beneath extremely 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. However, when Luffy defeated him with Gum Gum no Thor Elephant Gun, he inadvertently restored Chinjao's drill-shaped head and as a result, Chinjao let go of his vendetta against Garp and his family, even allying himself with Straw Hat Pirates against Donquixote Doflamingo.
During the battle, he lost his drill-shaped head once again when Chinjao's grandson Sai defended Baby 5 from his grandfather after he became infuriated by Sai aiding the enemy when Sai attempted to stop Baby 5 from committing suicide. Sai managed to surpass his grandfather by imbuing his leg with the Hasshoken secret technique Hasshoken Ogi: Kiryu Kirikugi, causing his grandfather to lose his drill-shaped head once more. However, Chinjao was overcome with joy and acknowledged Sai's strength by bestowing him with the title of Don and making him the 13th commander of the Happo Navy. Chinjao also noted that with his strength, Sai should be capable of breaking apart the Jewel Ice Sheet, indicating that the Chinjao Family may once again have access to the treasure that lay beneath it.