Tritium and primordial 3He in the North Atlantic: a study in the region of Charlie-Gibbs fracture zone

Abstract

The plume of primodial 3He seen at a depth of about 3 km in the North Atlantic during the GEOSECS program in 1972 was observed again in the vicinity of the Charlie-Gibbs Fracture Zone. Most evidence suggests that the Fracture Zone is not source of this helium, but no feasible alternative can be identified. A series of stations on a transect from 25° to 45°W at an average latitude of about 52°N shows three distinct cores of high tritium water (Labrador Sea, Denmark Straits and Iceland-Faroes waters) as well as evidence of recirculated Antarctic Bottom Water-Denmark Straits Water near the floor of the western extremity of the Fracture Zone. Tritium concentrations across this section are everywhere in excess of pre-nuclear era levels, indicating some degree of deep-water communication with the surface ocean on decade timescales. The eastward and lower limits of the southward components of the southeasterly transport of the Labrador Sea water are estimated to be 0.7 cm s −1.