Oceanic Radiocarbon Between Antarctica and South Africa Along Woce Section 16 at 30°E

Viviane Leboucher (1) , James C. Orr (1) , Philippe Jean-Baptiste (1) , Maurice Arnold (2) , Patrick Monfray (1) , Nadine Tisnérat-Laborde (3) , Alain Poisson (4) , Jean-Claude Duplessy (1, 5)

1 LSCE - Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette]
2 CEREGE - Centre européen de recherche et d'enseignement des géosciences de l'environnement
3 GEOTRAC - Géochrononologie Traceurs Archéométrie
4 LPCM - Laboratoire de Physique et Chimie Marines
5 PALEOCEAN - Paléocéanographie

Accelerator mass spectrometry (AMS) radiocarbon measurements were made on 120 samples collected between Antarctica and South Africa along 30°E during the WOCE-France CIVA 1 campaign in February 1993. Our principal objective was to complement the Southern Ocean's sparse existing data set in order to improve the 14C benchmark used for validating ocean carbon-cycle models, which disagree considerably in this region. Measured 14C is consistent with the 0-S characteristics of CIVA1. Antarctic Intermediate Water (AAIW) forming north of the Polar Front (PF) is rich in'4C, whereas surface waters south of the PF are depleted in 14C. A distinct old 14C 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 4C 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 14C. Conversely, an increase was found in deeper layers, in the AAIW. Large uncertainties, associated with previous methods for separating natural and bomb 14C when in the Southern Ocean south of 45°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°S, where bomb 14C inventories are relatively modest.

Domaines: Océan, Atmosphère; Interfaces continentales, environnement

Viviane Leboucher, James C. Orr, Philippe Jean-Baptiste, Maurice Arnold, Patrick Monfray, et al.. Oceanic Radiocarbon Between Antarctica and South Africa Along Woce Section 16 at 30°E. Radiocarbon, 1999, 41 (1), pp.51-73. ⟨10.1017/S0033822200019330⟩. ⟨hal-02500995⟩