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

Published online by Cambridge University Press:  18 July 2016

Viviane Leboucher
Affiliation:
Laboratoire des Sciences du Climat et de l'Environnement (LSCE), Avenue de la Terrasse, F-91198 Gif-sur-Yvette Cedex, France
James Orr
Affiliation:
Laboratoire des Sciences du Climat et de l'Environnement (LSCE), DSM/CEN Saclay/CEA, L'Orme, Bât. 709, F-91191 Gif-sur-Yvette Cedex, France
Philippe Jean-Baptiste
Affiliation:
Laboratoire des Sciences du Climat et de l'Environnement (LSCE), DSM/CEN Saclay/CEA, L'Orme, Bât. 709, F-91191 Gif-sur-Yvette Cedex, France
Maurice Arnold
Affiliation:
Laboratoire des Sciences du Climat et de l'Environnement (LSCE), Avenue de la Terrasse, F-91198 Gif-sur-Yvette Cedex, France
Patrick Monfray
Affiliation:
Laboratoire des Sciences du Climat et de l'Environnement (LSCE), Avenue de la Terrasse, F-91198 Gif-sur-Yvette Cedex, France
Nadine Tisnerat-Laborde
Affiliation:
Laboratoire des Sciences du Climat et de l'Environnement (LSCE), Avenue de la Terrasse, F-91198 Gif-sur-Yvette Cedex, France
Alain Poisson
Affiliation:
Laboratoire de Physique et Chimie Marines (LPCM), Université Pierre et Marie Curie, 4, place Jussieu, F-75252 Paris Cedex 05, France
Jean-Claude Duplessy
Affiliation:
Laboratoire des Sciences du Climat et de l'Environnement (LSCE), Avenue de la Terrasse, F-91198 Gif-sur-Yvette Cedex, France
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Abstract

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Accelerator mass spectrometry (AMS) radiocarbon measurements were made on 120 samples collected between Antarctica and South Africa along 30°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 14C benchmark used for validating ocean carbon-cycle models, which disagree considerably in this region. Measured 14C is consistent with the θ-S characteristics of CIVA1. Antarctic Intermediate Water (AAIW) forming north of the Polar Front (PF) is rich in 14C, 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 14C 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.

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Articles
Copyright
Copyright © The American Journal of Science 

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