Observation of the Circulation in the Newfoundland Basin in Winter 1997

Abstract

A hydrographic survey was performed in January?February 1997 to document the winter circulation of the North Atlantic Current system in the Newfoundland Basin, as part of the Fronts and Atlantic Storm Tracks Ex-periment (FASTEX). Eighty-seven conductivity?temperature?depth (CTD) stations were occupied along a four-section trapezoid, which spanned the ?Northwest Corner? and the branching of the North Atlantic Current along 35°W. Realistic sea surface temperature analyses were produced every 15 days, using all available data collected in this area during the two months of the FASTEX experiment. These maps were combined with sea level anomaly fields from the TOPEX/Poseidon and ERS-2 satellites at the same time intervals to analyze the features of the main currents in the area and their evolution. These combined analyses, providing a coherent overview of the fronts and jets identified along the ship track, and the CTD stations are further used to estimate their transports. The general pattern is a 15 Sv (Sv ≡ 106 m3 s?1) transport by the North Atlantic Current at 47°N, 43°W, the existence of a recirculating gyre inside the Northwest Corner, and a complex branching of the circulation associated with significant surface fronts. The recirculating gyre forms a closed circulation, in which a very deep warm eddy, 100 km wide, was sampled at the end of February: its mixed layer was 800 m deep and its transport was 27 Sv. Along 35°W, three fronts were identified between 45° and 52°N: the Northern Subarctic Front, the Southern Subarctic Front, and the Mid-Atlantic Front, whose origins are precisely located. The currents associated with these fronts transport 26 Sv toward the east before crossing the Mid-Atlantic Ridge and supplying the eastern part of the North Atlantic basin. An important transport (14 Sv) was calculated near 46°N, 37°W, which mostly fed the current associated with the Mid-Atlantic Front.