Part of the global DOC versus AOU (dissolved organic carbon/apparent oxygen utilization) data compilation, WOCE14

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, 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.

本数据集的总有机碳（Total Organic Carbon, TOC）样品采集于南大西洋东部沿西经9度、从赤道至南纬45°的海域，共布设6个站位，站位间距约800公里。样品分析采用高温催化氧化法（High Temperature Catalytic Oxidation, HTCO），于基础实验室完成。尽管北大西洋与南极水域的平流混合模式复杂，且二者水体换气程度差异悬殊，但500米以深的总有机碳浓度准恒定于55±3微摩尔碳每升，这表明深水总有机碳具有难降解的特性。另一方面，在永久层化、营养盐匮乏的赤道、亚赤道及亚热带上层海洋中，垂直湍流扩散被大幅抑制，该海域上层100米水体的总有机碳储量存在25至38克碳每平方米的超额量。与之相反，亚南极锋带营养盐富集上层的总有机碳浓度仅比深水基线高出9克碳每平方米。上层500米范围内约70%的总有机碳浓度变异，可归因于表层生成的活性总有机碳与深水难降解总有机碳的简单混合；该混合过程对200-400米深度处显著的表观氧消耗量（Apparent Oxygen Utilization, AOU）峰值层的耗氧量贡献仅为13%。