Tides and Currents

Both diurnal and semidiurnal tides occur in the Bering Sea. Tidal amplitude at the Bering Sea coast varies from <0.5 m along the eastern Chukotka Coast to 1-2 m along the Alaskan Coast, to >2 m along Koryak and Kamchatka coasts, to >5 m in Kuskokwim Bay and up to 8.5 m in Bristol Bay. On the Aleutian Islands the tidal magnitude is between 1.5 and 2.3 m. Owing to interaction with topography, tidal currents may amplify to significantly exceed the mean flow. For example, the mean flow over Bristol Bay's middle shelf is only 2cms-1, whereas the tidal currents attain 20cms-1. Tidal currents play an especially important role in nutrients and sediment transport between the shelf edge and deep ocean.

The two major factors that largely determine the Bering Sea circulation are (a) winds and (b) inflows and outflows through straits that connect the sea with the North Pacific and Arctic Ocean. Pacific waters carried by the Alaskan Stream, a jet current with a speed up to 100 cm s-1, enter the Bering Sea via several straits between the Aleutian Islands. The most important straits are Unimak Pass (165° W), Amukta Pass (172° W), Amchitka Pass (180° W), Buldir Pass (175° E), and Near Strait (169° E). The northward inflows to the Bering Sea are concentrated along the eastern side of these passes, whereas the outflows are shifted to their western side. The net northward flow through Near Strait, Buldir, Amchitka, and Amukta passes are, respectively, 9, 1, 2, and 0.5 Sv (1 Sv=106 m3 s-1), while the net southward flow through Kamchatka Strait is 12 Sv. Upon entering the Bering Sea, the Pacific waters turn east and continue along the Aleutian Islands as the Aleutian North Slope Current. After reaching the Eastern Bering Sea Shelf, this current turns northwest and flows off the shelf break as the Bering Sea Slope Current (with an average speed up to 15 cm s-1) until Cape Navarin (62.5° N 179° E), where it splits. The southward branch, the swift (up to 100 cm s-1) Kamchatka Current, follows the continental slope off Koryak Coast and Kamchatka Peninsula and exits the Bering Sea via Kamchatka Strait. The northern branch (Anadyr Current) flows over the northern Bering Sea shelf via Anadyr Strait toward Bering Strait. The dominant flow over the Eastern Bering Sea Shelf is rather diffuse and sluggish and generally directed northwest. The only coherent shelf current is the northward Alaskan Coastal Current with an average speed of 3-5 cm s-1.

0 0

Post a comment