Beaufort Gyre freshwater reservoir: State and variability from observations

TLDR

The Beaufort Gyre’s large freshwater content is primarily driven by Ekman pumping from the Arctic High, with a seasonal cycle shaped by mechanical and thermal processes that produce peaks in June–July and November–January. We investigate basin‑scale mechanisms regulating anomalies in freshwater content in the Beaufort Gyre, exploring its mean annual cycle and interannual and decadal variability. Using historical observations and data from 2003–2007, the study examines how Ekman pumping and ice transformations influence freshwater content across the gyre. Between 2003–2007, FWC increased strongly, peaking at ~170 cm a⁻¹ in the EP‑influenced center, while from 1950–2000 the 1990s saw a shift southeast and contraction of the maximum, yet total FWC rose by over 1000 km³ relative to climatology.

Abstract

We investigate basin‐scale mechanisms regulating anomalies in freshwater content (FWC) in the Beaufort Gyre (BG) of the Arctic Ocean using historical observations and data collected in 2003–2007. Specifically, the mean annual cycle and interannual and decadal FWC variability are explored. The major cause of the large FWC in the BG is the process of Ekman pumping (EP) due to the Arctic High anticyclonic circulation centered in the BG. The mean seasonal cycle of liquid FWC is a result of interplay between the mechanical (EP) and thermal (ice transformations) factors and has two peaks. One peak occurs around June–July when the sea ice thickness reaches its minimum (maximum ice melt). The second maximum is observed in November–January when wind curl is strongest (maximum EP) and the salt input from the growing ice has not yet reached its maximum. Interannual changes in FWC during 2003–2007 are characterized by a strong positive trend in the region varying by location with a maximum of approximately 170 cm a −1 in the center of EP influenced region. Decadal FWC variability in the period 1950–2000 is dominated by a significant change in the 1990s forced by an atmospheric circulation regime change. The center of maximum FWC shifted to the southeast and appeared to contract in area relative to the pre‐1990s climatology. In spite of the areal reduction, the spatially integrated FWC increased by over 1000 km 3 relative to climatology.