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Total organic carbon (TOC) samples were collected at 6 stations spaced ~800 km apart in the eastern South Atlantic, from the Equator to 45°S along 9°W. Analyses were performed by high temperature catalytic oxidation (HTCO) in the base laboratory. Despite the complex advection and mixing patterns of North Atlantic and Antarctic waters with extremely different degrees of ventilation, TOC levels below 500 m are quasi-constant at 55±3 µmol C l-1, pointing to the refractory nature of deep-water TOC. On the other hand, a TOC excess from 25 to 38 g C m-2 is observed in the upper 100 m of the permanently stratified nutrient-depleted Equatorial, Subequatorial and Subtropical upper ocean, where vertical turbulent diffusion is largely prevented. Conversely, TOC levels in the nutrient-rich upper layer of the Subantarctic Front only exceeds 9 g C m-2 the deep-water baseline. As much as 70% of the TOC variability in the upper 500 m is due to simple mixing of reactive TOC formed in the surface layer and refractory TOC in deep ocean waters, with a minor contribution (13%) to oxygen consumption in the prominent subsurface AOU maximum at 200-400 m depth.
Financial
support for this work came from the Spanish
‘Comisión Interministerial de Ciencia y Tecnología
(CICYT)’, contract No. ANT94-1168-E, and from
the ‘Institut Français de Recherche pour l’exploitation
de la Mer (IFREMER)’, contract No 94 1430
087. A fellowship from the EC MAS2 project
CT93-0065 allowed M.D. Doval to carry out this
work. X.A.A.-S. was partially funded by a ‘Contrato
de Incorporación’ of the Spanish ‘Ministerio de
Educación y Ciencia’.
Peer reviewed