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The North Atlantic Current and surrounding waters: At the crossroads

Authors

  • T. Rossby


Abstract

The North Atlantic Current is a well-defined western boundary current that flows north along the east side of the Grand Banks from 40° to 51°N, where it turns sharply to the east and begins its journey across the ocean. The current is unique in transporting warm tropical waters to much higher latitudes than any other western boundary current and thus plays a crucial role in ameliorating the climate of the European subcontinent. The North Atlantic Current originates in the Gulf Stream when the latter curves north around the Southeast Newfoundland Rise, a major submarine ridge that stretches SE from the Grand Banks. A well-defined front delineates the path of the current as long as it flows north as a western boundary current. After the current turns east in the north, it broadens into a widening band of eastward drift without a sharp or permanent front in the sense of the eastward flowing Gulf Stream after it separates from Cape Hatteras. The North Atlantic Current transports more than 40 Sv (1 Sv = 106 m³ s−1) in the south and about 20 Sv by the time it flows east across the Mid-Atlantic Ridge. The currents along the northward flowing front are quite swift, with typical maximum average speeds in the upper 300 m near 1 m s−1 (= 2 knots). The current meanders almost as wildly as a “snaking” river, but unlike steep meanders in the Gulf Stream these meanders appear to be stable, and with one exception have not been observed to break off to form pools of warm and/or cold waters as frequently occurs in the Gulf Stream. The meanders appear to be induced by major topographic features along the path of the current, namely, the Southeast Newfoundland Rise, the Newfoundland Seamounts, and Flemish Cap. Strong recirculations develop on the concave side of the meanders. One of these, the “Mann eddy” at the first meander crest of the North Atlantic Current, should be regarded as a permanent feature of the North Atlantic circulation. Other meanders also contain recirculations that can persist for months. Under certain conditions these can merge together to form an extended SW flow (recirculation) just east of the North Atlantic Current.

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Ancillary