Coupled wind-forced controls of the Bering–Chukchi shelf circulation and the Bering Strait throughflow: Ekman transport, continental shelf waves, and variations of the Pacific–Arctic sea surface height gradient

• Published in: Progress in oceanography 2014-06, Vol.125, p.40-61
• Main Authors: Danielson, Seth L., Weingartner, Thomas J., Hedstrom, Katherine S., Aagaard, Knut, Woodgate, Rebecca, Curchitser, Enrique, Stabeno, Phyllis J.
• Format: Article
• Language: English
• Subjects: Anomalies; Basins; Continental shelves; Mathematical models; Shelves; Storms; Straits; Stresses
• ISSN: 0079-6611; 1873-4472
• DOI: 10.1016/j.pocean.2014.04.006

•Bering Strait currents vary with the pressure head, local winds, and shelf waves.•E–W shifts of the Aleutian Low alter the Pacific–Arctic oceanic pressure gradient.•The longitude of N. Pacific storms drives nearshore divergence in western Alaska.•Polar easterlies drive divergence along north-facing arctic coastlines.•Coastal divergence triggers continental shelf waves in the Bering and Chukchi seas. We develop a conceptual model of the closely co-dependent Bering shelf, Bering Strait, and Chukchi shelf circulation fields by evaluating the effects of wind stress over the North Pacific and western Arctic using atmospheric reanalyses, current meter observations, satellite-based sea surface height (SSH) measurements, hydrographic profiles, and numerical model integrations. This conceptual model suggests Bering Strait transport anomalies are primarily set by the longitudinal location of the Aleutian Low, which drives oppositely signed anomalies at synoptic and annual time scales. Synoptic time scale variations in shelf currents result from local wind forcing and remotely generated continental shelf waves, whereas annual variations are driven by basin scale adjustments to wind stress that alter the magnitude of the along-strait (meridional) pressure gradient. In particular, we show that storms centered over the Bering Sea excite continental shelf waves on the eastern Bering shelf that carry northward velocity anomalies northward through Bering Strait and along the Chukchi coast. The integrated effect of these storms tends to decrease the northward Bering Strait transport at annual to decadal time scales by imposing cyclonic wind stress curl over the Aleutian Basin and the Western Subarctic Gyre. Ekman suction then increases the water column density through isopycnal uplift, thereby decreasing the dynamic height, sea surface height, and along-strait pressure gradient. Storms displaced eastward over the Gulf of Alaska generate an opposite set of Bering shelf and Aleutian Basin responses. While Ekman pumping controls Canada Basin dynamic heights (Proshutinsky et al., 2002), we do not find evidence for a strong relation between Beaufort Gyre sea surface height variations and the annually averaged Bering Strait throughflow. Over the western Chukchi and East Siberian seas easterly winds promote coastal divergence, which also increases the along-strait pressure head, as well as generates shelf waves that impinge upon Bering Strait from the northwest.