The Southern Ocean (SO), in spite of its major contribution to global primary productivity (PP), remains underexplored in this aspect. Light being the most limiting parameter affecting primary production, it is crucial to study the ambient light field to understand PP and associated processes. The current study makes a dual effort to present PP estimates as well as understand the bio-optical variability in the Indian sector of the Southern Ocean (ISSO). Results suggest that PP was highest at Sub-Tropical Front (STF) and lowest at Polar Front-2 (PF2). Most PP profiles were characterized by subsurface maxima, indicating probable photoinhibition or micronutrient limitation at surface layer. Strong correlation between measured and satellite-based integrated PP (R2 = 0.94, RMSE = 77.48, p < 0.01) indicated the efficacy of global models in their original formulation in bio-optically complex SO waters. The maximum photochemical efficiency of phytoplankton (Fv/Fm) measured by fast repetition rate fluorometry varied from 0.1–0.4, implying reduced phytoplankton photosynthetic efficiency in ISSO. The ratio between remote sensing reflectance (Rrs)-derived phytoplankton absorption (aph) at blue-red band (B/R ratio) indicated dominance of smaller phytoplankton in surface and larger phytoplankton at subsurface. Higher Chl-a specific phytoplankton absorption (aph*) than phytoplankton absorption (aph) suggested an adaptation of dominant phytoplankton species to low light, yet a better light harvest efficiency. However, low contribution of aph suggested a strong influence of non-phytoplankton materials to the total absorption budget. We therefore infer that, the surrounding physical environment in terms of nutrients and bio-optical variability modulated phytoplankton size class and thereby productivity more critically in the surface than in the deeper layers of ISSO.

中文翻译：

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南方夏季期间南大洋印度部分初级生产力和生物光学特性的变化

南大洋 (SO) 尽管对全球初级生产力 (PP) 做出了重大贡献，但在这方面仍未得到充分探索。光是影响初级生产的最大限制参数，研究环境光场以了解 PP 和相关过程至关重要。目前的研究做出了双重努力，以提供 PP 估计值以及了解南大洋印度区 (ISSO) 的生物光学变异性。结果表明，PP 在亚热带锋 (STF) 处最高，在极锋 2 (PF2) 处最低。大多数 PP 剖面的特点是地下最大值，表明表面层可能存在光抑制或微量营养素限制。测量和基于卫星的综合 PP 之间有很强的相关性（R2 = 0.94，RMSE = 77.48，p < 0。01) 表明了全局模型在生物光学复杂 SO 水域的原始公式中的功效。通过快速重复率荧光法测量的浮游植物的最大光化学效率 (Fv/Fm) 在 0.1-0.4 之间变化，这意味着 ISSO 中浮游植物的光合效率降低。遥感反射率 (Rrs) 得出的蓝红波段浮游植物吸收 (aph) 之间的比率（B/R 比）表明地表较小的浮游植物和地下较大的浮游植物占优势。比浮游植物吸收 (aph) 更高的 Chl-a 特定浮游植物吸收 (aph*) 表明优势浮游植物物种适应弱光，但光收集效率更好。然而，aph 的低贡献表明非浮游植物材料对总吸收预算有很大影响。