The temporal evolution of the tracer signal in the Deep Western Boundary Current, Tropical Atlantic

Four World Ocean Circulation Experiment (WOCE) repeat cruises (October 1990 to March 1994) in the tropical Atlantic off Brazil are used to study the spatial and temporal evolution of the chlorofluorocarbon (CFC) (components CFC-11 and CFC-12) and tritium signal in the upper North Atlantic Deep Water (NADW). Its shallowest part, located in the tropical Atlantic around 1600-m depth, is the shallow upper North Atlantic Deep Water (SUNADW). It is characterized by a distinct tracer maximum, which is presumably received through winter time convection in the subpolar North Atlantic. Here we discuss the tracer fields and the temporal evolution of the tracer signal of the SUNADW in the tropical Atlantic along two meridional sections at 44 degrees and 35 degrees W and two zonal sections at 5 degrees and 10 degrees S off Brazil. The spatial and temporal development of the tracer field in the tropical Atlantic as well as the correlation with hydrographic parameters show that the temporal tracer change being due to the arrival of "younger" water is disturbed by other processes. In particular, the impact of variable mixing and spreading pathways on the observed tracer variability in the SUNADW is evident in the observations