North Atlantic Oscillation–induced changes of the upper layer circulation in the northern North Atlantic Ocean

Abstract

Hydrographic data of the 1990s along World Ocean Circulation Experiment sections A1E (Greenland‐Ireland) and A2 (Newfoundland‐France) indicate a redistribution of cold, low‐saline subarctic waters and warm, saline subtropical waters in the upper layer of the northern North Atlantic within about 2 years after the North Atlantic Oscillation had turned from a period with strong westerlies until 1995 to a period with weak westerlies in 1996 and 1997. In the latter period, subarctic waters spread preferably southward along the continental slope east of Newfoundland rather than eastward with the North Atlantic Current (NAC) into the Irminger, Iceland, and West European Basins. As a consequence, the Subarctic Front and the associated NAC shifted eastward in the Newfoundland Basin, where subarctic waters accumulate, and westward in the Iceland Basin, where a large, warm, and saline anomaly was found in 1996 and 1997, indicating a contraction of the subpolar gyre. In the Irminger Basin the anomaly occurred in 1998 and 1999. Whereas the cyclonic circulation in the Irminger and Iceland Basins weakened, it intensified in the Newfoundland Basin, where a strengthened Labrador Current retroflection joined the NAC. This and the increased anticyclonic recirculation of subtropical waters in the Newfoundland and West European Basins caused a considerable reduction of the northward heat transport across 47°N in the upper layer in 1997. The anticyclonic circulation occurring in the West European Basin suggested a northward expansion of the subtropical gyre.