The Beaufort Gyre: Mean State and Response to Decadal Forcing
The Beaufort Gyre (BG) is a circulation feature in the Arctic Ocean that has accumulated an unprecedented amount of relatively fresh ocean water in the past decades. Here we investigate the processes through which the Beaufort Gyre exchanges this relatively fresh water with its environment, using the E3SM-HiLAT ocean-sea ice model. We find that over decadal timescales, changes in BG volume are controlled by Ekman pumping/suction resulting from combined wind and ice-ocean stresses.
The Beaufort Gyre has accumulated an unprecedented amount of relatively fresh water in the past decades. If released and transported downstream to the subpolar North Atlantic Ocean, the excess water might affect the global ocean circulation via suppression of deep-water formation, with potentially significant impacts on climate. Understanding the processes for freshwater accumulation and release is important for assessing if, when, and how the current excess of freshwater may be released.
The Beaufort Gyre (BG) has increased its liquid freshwater content (FWC) by 40% in the past two decades. If released and transported downstream to the subpolar North Atlantic Ocean, the excess water might affect ocean circulation via suppression of deep-water formation. However, which layer is responsible for BG freshwater accumulations and releases over decadal timescales and the corresponding physical processes remain unclear, hampering our attempts to make future predictions. Here we use an ocean-sea ice model to explore such changes in its three characteristic layers (upper mixed-layer water, Pacific Water in the middle layer, and Atlantic Water in the lower layer). We find that the asymmetry of the BG, which has been simplified as a symmetric bowl shape in most previous studies, is important in determining the BG's layered mean state. Over decadal timescales, changes in BG volume are controlled by annual-mean Ekman pumping/suction resulting from combined wind and ice-ocean stresses. This study emphasizes the role of asymmetric geometry in determining the BG mean volume balance. It also explores the role of mean flow across the gyre's lateral boundaries in regulating BG's volume and FWC over decadal timescales.