Knowledge of Southern Ocean carbon cycling is limited by a paucity of phytoplankton primary productivity (PP) and spectral absorption data in this globally-important region. We measured ¹³C-based PP in the Indian sector of Southern Ocean (ISSO) during austral summer 2017, examining its link with spectral absorption coefficients and phytoplankton size structure derived from an absorption-based global model. Phytoplankton productivity was assessed at both coastal (60°S-69°S) and frontal stations (40°S-60°S), characterized by silicate- replete and -deplete water masses, respectively (indicated by measured nutrient ratios) to capture a range of phytoplankton growth conditions. Bio-optical relationships were used as indicators of phytoplankton community size structure and to assess the extent of cellular pigment packaging - a phenomenon reported previously for phytoplankton in this region. Blue-Red (B/R) ratios of phytoplankton absorption (a_ph) spectra indicated that microphytoplankton (more prone to “package effects”) were the dominant size class at most sites sampled. Overall, PP was better explained by a_ph (R² = 0.85) than total chlorophyll-a (R² = 0.64) in surface waters. The a*_ph (675)-chlorophyll-a relationship explained package effects more effectively in frontal regions (R² = 0.63) than stations further south (R² = 0.30). The global absorption-based model captured smaller (pico, nano) phytoplankton size classes but failed to identify larger microphytoplankton, underscoring the need for region-specific algorithm modifications. Our findings improve existing understanding of spatio-temporal trends in PP and bio-optical variability within the Indian Sector of the Southern Ocean (ISSO) – knowledge that is essential to improve capacity to retrieve PP from satellite-based models in this region.

在这个全球重要的地区，由于缺乏浮游植物的初级生产力（PP）和光谱吸收数据，对南大洋碳循环的认识受到限制。我们测量了¹³2017年夏季，印度南部海洋（ISSO）中基于C的PP进行了研究，研究了其与光谱吸收系数和浮游植物大小结构的联系，该光谱吸收系数和浮游植物的大小结构源自基于吸收的全球模型。在沿海地区（60°S-69°S）和额叶站（40°S-60°S）对浮游植物的生产力进行了评估，其特征分别是富含硅酸盐的水质和缺乏硅酸盐的水质（通过测得的养分比表示）以捕获一系列浮游植物的生长条件。生物光学关系被用作浮游植物群落大小结构的指标，并用于评估细胞色素包装的程度-以前曾报道过该地区浮游植物的现象。浮游植物吸收量（_ph值）的蓝红色（B / R）比）光谱表明，在大多数采样点，浮游植物（更容易产生“包裹效应”）是主要的大小类别。总体而言， 地表水中的_ph值（R ²  = 0.85）比总叶绿素a（R ² = 0.64）更好地解释了PP 。a * _ph（675）-叶绿素-a的关系说明，在额叶区域（R ²  = 0.63）比在更南端的站（R ²  = 0.30）。基于全球吸收的模型捕获了较小的（微微，纳米）浮游植物大小类别，但未能识别出较大的浮游植物，这突出说明了需要对特定于区域的算法进行修改。我们的发现增强了对南洋印度洋（ISSO）内PP时空趋势和生物光学变异性的现有理解-这些知识对于提高从该地区基于卫星的模型中检索PP的能力至关重要。