Primordial He-3 in South Atlantic deep waters from sources on the Mid-Atlantic Ridge

Helium isotope data from three zonal WOCE sections (11 degrees S, 19 degree s S and 30 degrees S) in the South Atlantic are presented. Among other feat ures we find a distinct delta(3)He-maximum above the Mid-Atlantic Ridge (MA R) at all three latitudes. Using a hydrographic multiparameter analysis, we separate He-3 emanating from the MAR from the large-scale He-3 background. To our knowledge, this is the first confirmation of input of primordial He -3 at the MAR in the South Atlantic. The source appears to be weak compared with the Pacific sources, causing He-3 elevations (relative to background values) of only 2-3% directly above the MAR. This exceeds by several times the statistical and systematic data uncertainties, which amount to 0.35% ea ch, so that detailed contouring of the MAR-derived He-3 is possible. At 30 degrees S and 11 degrees S, a significant signal extends westward over at l east 2000 km, whereas at 19 degrees S the signal is more confined to the ri dge area. The westward extensions indicate westward flow at depths near the ridge crest elevation, contradicting flow directions deduced previously by Reid (1989). (C) 2000 Elsevier Science Ltd. All rights reserved.