Summer mean circulation of the northwestern Atlantic Ocean

Abstract

The Mellor et al. (1982) method is applied to a new high‐resolution analysis of the temperature and salinity fields in order to determine the summer transport and circulation of the northwestern Atlantic Ocean. This high‐resolution analysis is carried out using an objective analysis scheme which is a modification of that used by Levitus (1982). In view of the strong topographic control exhibited by the circulation features in the area (i.e., the shelf break Labrador and Greenland currents), the scheme preferentially searches for data along, rather than across, isobaths. The horizontal resolution is 1/3° by 1/3°, with 37 vertical levels. The data were obtained from the Marine Environment Data Service archived data and was supplemented by a subset of the National Oceanographic Data Center data from J. Reid and by additional data for the 1980s from Fukumori and Wunsch (1991). Summer mean transports of 49 and 46 Sv are found in the Labrador Sea and the Irminger Sea, respectively. Most of the transport through the region is determined by the transport through the eastern boundary, emphasizing the importance of the eastern Atlantic for determining the circulation in the west. The local wind stress forcing plays a relatively unimportant role in driving the transport in the northwestern Atlantic Ocean. The current structure is obtained by combining the results from the Mellor et al. (1982) method together with a level of no motion (at the bottom) calculation. Using these two methods, the bottom currents are evaluated, and hence the current structure for the whole domain is determined. The results show that the bottom currents follow the planetary potential vorticity (ƒ/H) lines closely. The strongest currents are found along the shelf breaks, offshore from the coasts of Greenland and Labrador. The results also indicate the presence of cross‐shelf flow on the western side of the Labrador Sea. The cross‐shelf transport (∼5 Sv) of fresh shelf waters may well be important in modifying the salinity characteristics, and hence convective properties, of the central Labrador Sea.