A description of the North Atlantic current system from historical hydrography

A climatological description of the North Atlantic Current (NAC) system has been developed through an analysis of the historical hydrographic bottle data from the NODC archives. The majority of the analysis is conducted upon specific volume anomaly ({dollar}delta{dollar}) surfaces which provide approximations to the neutral surfaces upon which water parcels are free to move and mix laterally. A high resolution regional climatology consisting of the median depth, temperature, salinity, potential density, potential vorticity, and Montgomery potential (an exact stream function on {dollar}delta{dollar} surfaces) is described on a 0.5{dollar}spcirc{dollar} grid on nine {dollar}delta{dollar} surfaces for the Newfoundland Basin. Modal estimates of the same quantities are also calculated by determining the most frequent value within each 0.5{dollar}spcirc{dollar} bin; however, this method is limited to areas with high data densities. This regional climatology allows a more detailed study of the average NAC system than is afforded by other existing climatologies for the North Atlantic. The path of the NAC within the Newfoundland Basin is determined from horizontal probability distributions for the dynamical and property front locations on {dollar}delta{dollar} surfaces; these distributions indicate where the fronts were most likely to have been observed in the past. The fronts are observed to exhibit a pattern of stationary meanders, with troughs located over the Southeast Newfoundland Rise, over the Newfoundland Seamounts, and to the east of the Flemish Cap. The width of the NAC's meander envelope varies from less than 150 km near the Mann Eddy (42{dollar}spcirc{dollar}N, 44{dollar}spcirc{dollar}W) to greater than 300 km over the Southeast Newfoundland Rise. The path and meander patterns appear as consistent features for all seasons and for the four decades spanning 1950-1990. The circulation patterns and transports of the upper ocean within the Newfoundland Basin are also quantified from the historical hydrographic record. Climatologies of these variables are constructed using both the potential energy anomaly (referenced to 1000 and 2000 db) and the Montgomery potential on {dollar}delta{dollar} surfaces. These estimates of the average transports of the NAC range from 45 (20) Sv referenced to 2000 (1000) db near 42{dollar}spcirc{dollar} N, to 25 (15) Sv near 47{dollar}spcirc{dollar} N, to 20 (10) Sv crossing over the Mid-Atlantic Ridge between 49{dollar}spcirc{dollar} and 52.5{dollar}spcirc{dollar} N. Waters are lost to the basin interior from the NAC at the northern edge of two main recirculations of subtropical waters. Seasonal and decadal ensembles of the potential energy anomaly indicate that the circulation pattern and transports in the Newfoundland Basin are remarkably constant with time; a comparison of the transports for tbe 1955-59 and 1970-75 pentads, between which there were reportedly large changes in the upper North Atlantic Ocean (Levitus 1989), is used as an extreme test of this stability. The maximum standard deviation of the transport of the NAC is estimated from hydrographic time series from Ocean Weather Stations C and D, and a collection of stations inshore of the NAC adjacent to the Grand Banks; near 44{dollar}spcirc{dollar} N this deviation is estimated to be less than {dollar}pm{dollar}7.2Sv (ref. to 1000 db). (Abstract shortened by UMI.)...