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

• Published in: Radiocarbon
• Main Authors: Leboucher, Viviane, Orr, James, Jean-Baptiste, Philippe, Arnold, Maurice, Monfray, Patrick, Tisnerat-Laborde, Nadine, Poisson, Alain, Duplessy, Jean-Claude
• Format: Article in Journal/Newspaper
• Language: English
• Published: Cambridge University Press (CUP) 1999
• Subjects: General Earth and Planetary Sciences; Archeology; Antarctic; Southern Ocean; The Antarctic; Pacific; Antarc*; Antarctica
• Online Access: http://dx.doi.org/10.1017/s0033822200019330; https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0033822200019330

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 14 C benchmark used for validating ocean carbon-cycle models, which disagree considerably in this region. Measured 14 C is consistent with the θ-S characteristics of CIVA1. Antarctic Intermediate Water (AAIW) forming north of the Polar Front (PF) is rich in 14 C, whereas surface waters south of the PF are depleted in 14 C. A distinct old 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 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 14 C. Conversely, an increase was found in deeper layers, in the AAIW. Large uncertainties, associated with previous methods for separating natural and bomb 14 C 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 14 C inventories are relatively modest.