Ocean-ice momentum flux reversal and the associated stabilization of the Beaufort Gyre and freshwater accumulation

Driven by the Beaufort High and associated wind-stress curl, the anticyclonic ocean gyre over the Canada Basin, as known as the Beaufort Gyre, is a dominant feature of the Arctic Ocean circulation. The Beaufort Gyre is the largest freshwater reservoir in the Arctic Ocean  (Proshutinsky et al., 2009) and also is a region of the largest summer sea ice area decline during the past decades (Comiso et al., 2008). Observational studies have found that due to the large decreases in the extent and thickness of sea ice in the region, the volume of freshwater retained in the gyre has overall increased by about 25 % since the 1970s. Proshutinsky et al (2015) hypothesized that if the Beaufort Gyre weakens in the future, the massive volume of trapped freshwater will leak out, through the Transpolar Current, to the Greenland Iceland and Norwegian (GIN) Seas to potentially disrupt deep water formation, and thus the Atlantic Meridional Overturning Circulation (AMOC).

Satellite altimetry measurements showed that the Beaufort Gyre intensified and accumulated freshwater in the mid-2000s due to the persistent negative stress curl of the Beaufort High. However, since about 2009 the Beaufort Gyre has stabilized, and no longer accumulates freshwater. A paper published in Geophysical Research Letters showed that geostrophic ocean currents in the Canada Basin have increased to rival and sometimes exceed ice drift speeds, and thus the resultant momentum stress exerted on the ocean by the ice drift and the resultant Ekman pumping have reversed. Therefore, the study concluded that the recent stabilization of the Beaufort Gyre and freshwater accumulation is due to the reversed ocean-ice momentum flux.

Figure 1 from Proshutinsky et al. (2009): Climatology of freshwater content in the Arctic Basin (shown in colors). Solid lines depict mean 1950 – 1980 salinity at 50 m. Freshwater content is calculated relative to salinity 34.8 on the basis of 1950 –1980 data from Timokhov and Tanis [1998] averaged for all decades. The Beaufort Gyre Region (BGR) is bounded by thick dashed blue lines.

Dewey, S., Morison, J., Kwok, R., Dickinson, S., Morison, D., & Andersen, R. (2018). Arctic ice‐ocean coupling and gyre equilibration observed with remote sensing. Geophysical Research Letters45(3), 1499 – 1508.  https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017GL076229

Proshutinsky, A., Krishfield, R., Timmermans, M. L., Toole, J., Carmack, E., McLaughlin, F., … & Shimada, K. (2009): Beaufort Gyre freshwater reservoir: State and variability from observations. Journal of Geophysical Research: Oceans114, C00A10, doi:10.1029/2008JC005104.

Comiso, J. C., Parkinson, C. L., Gersten, R., & Stock, L. (2008): Accelerated decline in the Arctic sea ice cover. Geophysical Research Letters, 35,
L01703. https://doi.org/10.1029/2007GL031972

Proshutinsky A, Dukhovskoy D, Timmermans M.-L., Krishfield R, Bamber J. L. (2015): Arctic circulation regimes.Phil. Trans. R. Soc. A 373: 20140160. http://dx.doi.org/10.1098/rsta.2014.0160













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