CONCENTRATION AND ISOTOPIC COMPOSITION OF ND IN THE SOUTH-ATLANTIC OCEAN

Profiles of the concentration and isotopic composition of Nd are presented for the South Atlantic Ocean. Concentrations range from 8 pmol/l at the surface to 28-38 pmol/l in deep waters. The Nd isotopic composition is more radiogenic in the South Atlantic (average epsilon(Nd)(0) = -9.2 +/- 1.5 based on the 27 measurements presented here) than in the North Atlantic (epsilon(Nd)(0) = -12.6 +/- 2 based on 56 published data). The evolution of Nd concentration and isotopic composition within a given water mass appears to be largely dominated by mixing on the scale of the entire Atlantic Ocean. Epsilon(Nd)(0) values as high as -6.2 observed at intermediate depths (800-1000 m) in the southeast Atlantic and in Upper Circumpolar Water (150-1500 m) probably trace waters returning from the Pacific Ocean. This could argue in favour of the recent hypothesis that cold water return in the Drake Passage plays a significant role in closing the global thermohaline circulation.