Cw. Boning et Fa. Schott, DEEP CURRENTS AND THE EASTWARD SALINITY TONGUE IN THE EQUATORIAL ATLANTIC - RESULTS FROM AN EDDY-RESOLVING, PRIMITIVE EQUATION MODEL, J GEO RES-O, 98(C4), 1993, pp. 6991-6999
The high-resolution model of the wind-driven and thermohaline circulat
ion in the Atlantic Ocean developed in recent years as a ''community m
odeling effort'' for the World Ocean Circulation Experiment is examine
d for the temporal and spatial structure of the deep equatorial curren
t field and its effect on the spreading of North Atlantic Deep Water (
NADW). Under seasonally varying wind forcing, the model reveals a syst
em of basin-wide zonal currents of O(5 cm s-1), alternating east-west,
and oscillating at an annual period. The current fluctuations are ind
uced by the seasonal cycle of the wind stress in the equatorial Atlant
ic and show characteristics of long equatorial Rossby waves with westw
ard phase propagation of about 15 cm s-1. The mean flow in the deep we
stern tropical Atlantic is governed by a deep western boundary current
(DWBC) with core velocities of more than 10 cm s-1. Only a small frac
tion of the DWBC branches off at the equator, with correspondingly low
mean eastward currents of only about 1 cm s-1. Despite this weak adve
ction along the equator, a well-developed salinity tongue is observed
in the model, which is reminiscent of observed property distributions
at the upper NADW level. The model evaluation indicates the salinity p
attern to be a result of a balance between mean zonal advection and me
ridional diffusion of salt. The presence of the zonal current oscillat
ions appears to have no significance for the existence of the salinity
tongue.