Chlorofluoromethane distributions in the deep equatorial Atlantic during January-March 1993

Chlorofluoromethanes were sampled along two zonal sections, at 4 degrees 30 S and 7 degrees 30 N between the African and American continents (A7 and A6 WOCE sections) and two meridional sections, at 35 degrees W and 3 degrees 50W, during the CITHER 1 cruise (part of the French program CITHER (CIrculation THERmohaline) during January-March 1993. The results reported here deal primarily with the North Atlantic Deep Water, just ten years after the first CFM snapshot of the tropical Atlantic ocean obtained during the Transient Tracers in the Ocean Program (TTO) (Weiss et al., 1985. Nature 314, 608-610). The data provide evidence for the eastward bifurcation of the deep flow near the equator, on both UNADW and LNADW levels. The distributions clearly show the CFM signal corresponding to the UNADW penetrating into the eastern basin: at 3 degrees 50W the CFM core extends from 4 degrees S to 3 degrees N with a maximum around 2 degrees S. On both UNADW and LNADW levels, the bifurcation does not occur exactly on the equator but a few degrees south and seems to be partly induced by topographic effects. Previously published circulation schemes for UNADW and LNADW levels are compared to the CITHER 1 CFM data. Great variability is revealed and new patterns from the data are highlighted. The "young" deep component of the AABW flow seems to be stopped by the topography just north of the equatorial channel. TTO and CITHER 1 data set comparison and "apparent" ages lead to minimal values of the propagation rate of the CFC signal at low latitudes. (C) 1998 Elsevier Science Ltd. All rights reserved.