The microbial plankton community is an integral part of the pelagic ecosystem. It hosts essential functional groups that play a vital role in organic carbon production, release, uptake, and degradation within open-ocean ecosystems. Given its significance, carbon biomass estimates are urgently needed, especially in oligotrophic regions, to provide and enhance our knowledge of biogenic carbon pools. They also aid in validating biogeochemical models that characterize the functioning of these extensive marine ecosystems within the global carbon cycle. This study addresses the temporal variability of microbial community biomass in two oceanic zones: the west-central (Perdido) and southern (Coatzacoalcos) areas of the Gulf of Mexico. During three seasonally contrasting periods (nortes, rainy, and dry seasons), seawater samples were collected from the euphotic zone in both regions to estimate the carbon biomass of different pico- (<2–3 µm), nano-, and microplankton groups (>3–200 µm). Carbon biomass assessments for the microbial groups were based on their abundance and carbon conversion factors. Overall, we found a significant contribution of pico-prokaryotic components (heterotrophic bacteria, Prochloroccocus, and Synechoccocus) to the total microbial carbon stock of the euphotic zone (84–89 % global estimates). The finding suggests these microorganisms are key functional groups that drive carbon production and fate in the Gulf of Mexico ecosystem. Pico-cyanobacteria, especially Prochloroccocus, were the dominant primary producers (68–82 % total autotrophic carbon), mainly in the upper layer of the oligotrophic euphotic zone. This vertical pattern implies that the deep chlorophyll-a maximum (DCM) depth level was unrelated to a net increase in phytoplankton biomass in the three study periods. The distribution of microbial carbon biomass exhibited striking differences associated with winter mixing (the nortes season), high river discharge accompanied by cross-shelf transport (the rainy season), and the dynamics of mesoscale structures. Ecological aspects, such as the habitat preference of the organisms and the seasonal complementary development of mixotrophic and heterotrophic grazers and their prey, were also essential drivers in regulating the microbial carbon pool of both oceanic regions. The microbial carbon assessments conducted in this study contribute to identifying and quantifying key planktonic functional groups involved in the biogeochemical carbon cycle in the Gulf of Mexico open-ocean ecosystem.

中文翻译：

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墨西哥湾两个海洋区域微生物碳生物量变异的驱动因素


浮游微生物群落是远洋生态系统的组成部分。它拥有重要的功能群，在开放海洋生态系统中的有机碳生产、释放、吸收和降解中发挥着至关重要的作用。鉴于其重要性，迫切需要碳生物量估算，特别是在贫营养地区，以提供和增强我们对生物碳库的了解。它们还有助于验证生物地球化学模型，这些模型描述了全球碳循环中这些广泛的海洋生态系统的功能。本研究解决了两个海洋区域微生物群落生物量的时间变化：墨西哥湾中西部（佩尔迪多）和南部（夸察夸尔科斯）区域。在三个季节对比时期（北方、雨季和旱季），从两个地区的富光带采集海水样本，以估计不同皮浮游生物（<2–3 µm）、纳米浮游生物和微型浮游生物群的碳生物量（ >3–200 µm）。微生物群的碳生物量评估基于其丰度和碳转化因子。总体而言，我们发现微微原核成分（异养细菌、原绿球菌属和聚球藻属）对真光带微生物碳储量的显着贡献（全球估计为 84-89%）。研究结果表明，这些微生物是驱动墨西哥湾生态系统碳生产和命运的关键功能群。微微蓝藻，特别是原绿球菌，是主要的初级生产者（68-82% 的自养碳总量），主要分布在贫营养性真光带的上层。 这种垂直模式意味着深层叶绿素最大（DCM）深度水平与三个研究期间浮游植物生物量的净增加无关。微生物碳生物量的分布表现出与冬季混合（北方季节）、伴随跨陆架运输的高河流流量（雨季）以及中尺度结构的动态相关的显着差异。生态方面，例如生物体的栖息地偏好以及混合营养和异养食草动物及其猎物的季节性互补发展，也是调节两个海洋区域微生物碳库的重要驱动因素。本研究中进行的微生物碳评估有助于识别和量化墨西哥湾开放海洋生态系统生物地球化学碳循环中涉及的关键浮游功能群。