The sea, characterized by severe climate, is frozen over most of the year. Historically, only a narrow pass up to opened in August–September near its shores, but recently due to climate change in the Arctic the ice-free area in late summer has greatly enlarged. Until recently, the Beaufort Sea was known as an important reservoir for the replenishment of Arctic sea ice. Sea ice would often rotate for several years in the Beaufort Gyre, the dominant ocean current of the Beaufort Sea, growing into sturdy and thick multi-year ice.