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Oceanic radiocarbon between Antarctica and South Africa along WOCE Section 16 at 30 degrees .

Viviane Leboucher, James Orr, Baptiste Philippe Jean, Maurice Arnold, Patrick Monfray, Laborde Nadine Tisnerat, Alain Poisson, Jean Claude Duplessy

Abstract


Accelerator mass spectrometry (AMS) radiocarbon measurements were made on 120 samples collected between Antarctica and South Africa along 30 degrees E during the WOCE-France CIVA1 campaign in February 1993. Our principal objective was to complement the Southern Ocean's sparse existing data set in order to improve the (super 14) C benchmark used for validating ocean carbon-cycle models, which disagree considerably in this region. Measured (super 14) C is consistent with the theta -S characteristics of CIVA1. Antarctic Intermediate Water (AAIW) forming north of the Polar Front (PF) is rich in (super 14) C, whereas surface waters south of the PF are depleted in (super 14) C. A distinct old (super 14) C signal was found for the contribution of the Pacific Deep Water (PDW) to the return flow of Circumpolar Deep Waters (CDW). Comparison to previous measurements shows a (super 14) C decrease in surface waters, consistent with northward displacement of surface waters, replacement by old deep waters upwelled at the Antarctic Divergence, and atmospheric decline in (super 14) C. Conversely, an increase was found in deeper layers, in the AAIW. Large uncertainties, associated with previous methods for separating natural and bomb (super 14) C when in the Southern Ocean south of 45 degrees S, motivated us to develop a new approach that relies on a simple mixing model and on chlorofluorocarbon (CFC) measurements also taken during CIVA1. This approach leads to inventories for CIVA1 that are equal to or higher than those calculated with previous methods. Differences between old and new methods are especially high south of approximately 55 degrees S, where bomb (super 14) C inventories are relatively modest.

Keywords


salinity;Antarctic Ocean;South Africa;Indian Ocean;Antarctica;Southern Africa;hydrochemistry;carbon cycle;geochemical cycle;Atlantic Ocean;sea water;C 14 C 12;sampling;mass spectra;spectra;Africa;carbon;isotopes;radioactive isotopes;carbon dioxide;stable isotopes;geochemistry

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