The Beaufort Gyre is a core Arctic circulation and its primary freshwater reservoir. Rapid Arctic warming reshapes sea ice and ocean dynamics; two decades of observations show drastic sea level rise and massive freshwater buildup in the gyre. Clarifying its evolution helps decode Arctic circulation and freshwater transport, and reveals its influences on the Atlantic Meridional Overturning Circulation, global thermohaline circulation and global climate.
Using ECMWF ORAS5 reanalysis data, this work investigates multi-scale variations and driving mechanisms of the Beaufort Gyre from 1993 to 2018. Its maximum sea surface height (SSHmax), intensity, area and centroid display distinct interdecadal differences. Gyre parameters stayed stable with mild fluctuations in 1993–1998. During 1999–2010, central SSH surged, the gyre strengthened and expanded, while its core and centroid shifted northwest, occasionally crossing the Northwind Ridge. In 2011–2018, gyre intensity fluctuated interannually, its area slightly contracted, and the core retreated southeastward.
Gyre freshwater storage and sea level changes strongly correlate with gyre evolution, with correlation coefficients above 0.7 between freshwater content and SSHmax, intensity and area. A stronger gyre traps freshwater and lifts sea levels via halosteric effects, with extra freshwater mainly from low-salinity surface water (S<30). The Arctic Oscillation (AO) and Arctic Dipole Anomaly (DA) modulate gyre evolution, where AO dominates. Negative AO and positive DA amplify the gyre and converge freshwater, whereas reverse phases weaken it. Different phase combinations explain staged gyre changes. Positive AO prevailed in 1993–1994 with weak winds, leading to minor variations in gyre, freshwater and sea levels. Negative AO from 1995–2010, coupled with positive DA after 2000, produced strong anticyclonic wind anomalies. Sea ice decline altered surface stress, triggering freshwater accumulation and rapid gyre intensification via Ekman pumping and convergent transport. AO turned positive after 2011, ending gyre strengthening. These stagewise connections prove that the gyre’s stepped intensification and local freshwater enrichment (1993–2018) are closely tied to shifts in atmospheric circulation modes.