Whitey Bay is a New World pirate captain known as the Ice Witch. She is one of the many pirates allied with Whitebeard who journeyed to Marineford to rescue Ace.
She commands an icebreaker ship, capable of navigating through ice-covered waters. When she learned about Ace's impending execution, Whitey Bay and her crew joined forces with other pirates and Whitebeard's crew to save him.
Upon arriving at Marineford as the war with the Marines commenced, the pirate alliance found their ships frozen in place by Aokiji. However, this obstacle did not deter Whitey Bay and her crew. Thanks to their icebreaker ship, they broke through the ice and continued sailing. As they moved forward, they created another opening in the Marines' formations, providing an additional path for Whitebeard and his allies to advance, alongside the opening created earlier by Oars Jr.
Source: http://onepiece.wikia.com/wiki/Whitey_Bay
