Southern Ocean phytoplankton growth is limited by low iron (Fe) supply and irradiance, impacting the strength of the biological carbon pump. Unfavorable upper ocean conditions, such as low nutrient concentrations, can lead to the formation of deep chlorophyll or biomass maxima (DCM/DBM). While common in the Southern Ocean, these features remain understudied due to their subsurface location. To increase our understanding of their occurrence, we studied the responses of phytoplankton communities from a Southern Ocean DCM to increasing light, Fe, and manganese (Mn) levels. The DCM communities were light- and Fe-limited, but light limitation did not increase phytoplankton Fe requirements. The greatest physiological responses were observed under combined Fe/light additions, which stimulated macronutrient drawdown, biomass production and the growth of large diatoms. Combined Mn/light additions induced subtle changes in Fe uptake rates and community composition, suggesting species-specific Mn requirements. These results provide valuable information on Southern Ocean DCM phytoplankton physiology.

中文翻译：

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南大洋深层叶绿素最大值的表征：浮游植物对光、铁和锰富集的响应

南大洋浮游植物的生长受到低铁 (Fe) 供应和辐照度的限制，影响了生物碳泵的强度。不利的上层海洋条件，例如低营养浓度，可能导致深层叶绿素或生物量最大值（DCM/DBM）的形成。虽然这些特征在南大洋很常见，但由于其位于地表以下，因此仍未得到充分研究。为了加深对它们发生的了解，我们研究了南大洋 DCM 浮游植物群落对光照、铁和锰 (Mn) 水平增加的反应。DCM群落受到光和铁的限制，但光限制并没有增加浮游植物对铁的需求。在铁/光混合添加下观察到最大的生理反应，这刺激了常量营养素的减少、生物量的产生和大型硅藻的生长。锰/光的组合添加引起铁吸收率和群落组成的微妙变化，表明物种特定的锰需求。这些结果为南大洋 DCM 浮游植物生理学提供了有价值的信息。