Basin-scale changes of total organic carbon profiles in the eastern South Atlantic

Total organic carbon (TOC) samples were collected at 6 stations spaced simi lar to 800 km apart in the eastern South Atlantic, from the Equator to 45 d egreesS along 9 degreesW. Analyses were performed by high temperature catal ytic 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 mu mol C 1(-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) ii observed I n the upper 100 m of the permanently stratified nutrient-depleted Equatoria l. Subequatorial and Subtropical upper ocean. where vertical turbulent diff usion is largely prevented. Conversely, TOC levels in the nutrient-rich upp er 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 t o simple mixing of reactive TOC formed in the surface layer and refractory TOC in deep ocean waters. with a minor contribution (13%) to oxygen consump tion in the prominent subsurface AOU maximum at 200-400 m depth.