Stratified oceanic systems are characterized by the presence of a so‐called Deep Chlorophyll a Maximum (DCM) not detectable by ocean color satellites. A DCM can either be a phytoplankton (carbon) biomass maximum (Deep Biomass Maximum, DBM), or the consequence of photoacclimation processes (Deep photoAcclimation Maximum, DAM) resulting in the increase of chlorophyll a per phytoplankton carbon. Even though these DCM (further qualified as either DBMs or DAMs) have long been studied, no global‐scale assessment has yet been undertaken and large knowledge gaps still remain in relation to the environmental drivers responsible for their formation and maintenance. In order to investigate their spatial and temporal variability in the open ocean, we use a global data set acquired by more than 500 Biogeochemical‐Argo floats given that DCMs can be detected from the comparative vertical distribution of chlorophyll a concentrations and particulate backscattering coefficients. Our findings show that the seasonal dynamics of the DCMs are clearly region‐dependent. High‐latitude environments are characterized by a low occurrence of intense DBMs, restricted to summer. Meanwhile, oligotrophic regions host permanent DAMs, occasionally replaced by DBMs in summer, while subequatorial waters are characterized by permanent DBMs benefiting from favorable conditions in terms of both light and nutrients. Overall, the appearance and depth of DCMs are primarily driven by light attenuation in the upper layer. Our present assessment of DCM occurrence and of environmental conditions prevailing in their development lay the basis for a better understanding and quantification of their role in carbon budgets (primary production and export).

中文翻译：

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全球海洋中的深叶绿素最大值：发生、驱动因素和特征

分层海洋系统的特点是存在海洋彩色卫星无法检测到的所谓的深叶绿素 a 最大值 (DCM)。DCM 可以是浮游植物（碳）生物量最大值（Deep Biomass Maximum，DBM），也可以是光适应过程的结果（Deep photoAcclimation Maximum，DAM），导致每个浮游植物碳的叶绿素 a 增加。尽管长期以来对这些 DCM（进一步称为 DBM 或 DAM）进行了研究，但尚未进行全球范围的评估，并且在负责其形成和维护的环境驱动因素方面仍然存在巨大的知识差距。为了研究它们在公海中的时空变化，我们使用由 500 多个 Biogeochemical-Argo 浮标获得的全球数据集，因为可以从叶绿素 a 浓度和颗粒后向散射系数的比较垂直分布中检测到 DCM。我们的研究结果表明，DCM 的季节性动态明显取决于区域。高纬度环境的特点是强烈 DBM 的发生率较低，仅限于夏季。同时，贫营养地区拥有永久性 DAM，在夏季偶尔会被 DBM 所取代，而赤道以下水域的特点是永久性 DBM，受益于光照和营养方面的有利条件。总体而言，DCM 的外观和深度主要由上层的光衰减驱动。