Introduction to the Special Collection on the Arctic Ocean's Changing Beaufort Gyre

The Beaufort Gyre circulation system is a central part of the Arctic climate undergoing significant change in all environmental parameters. This paper presents two decades of intensive observations in the Beaufort Gyre and then introduces the publications that comprise this special collection on the changing Beaufort Gyre. Observations spanning 2003–2024 are analyzed to characterize the Beaufort Gyre's evolving freshwater and heat content, which are related to wind forcing modulated by the presence of sea ice. Following a period of sustained freshwater and heat accumulation in the first half of the record, freshwater and heat content have been declining in recent years. Trends indicate that prevailing winds are changing such that they are becoming less effective at spinning up the gyre and accumulating freshwater. This forcing is dominating over a trend to a weakening sea-ice pack that is less effective at spinning down the gyre. Details on the changing Beaufort Gyre are examined in the publications in this special collection, including studies on its sea ice, upper-ocean properties, freshwater sources and content, the fundamental dynamical balances of the Beaufort Gyre, water-mass circulation, and biogeochemistry. These studies bring new understanding of the Beaufort Gyre that is essential for accurately characterizing the Arctic climate system and informing future projections.