Abstract Few sedimentary archives of lake meromixis are available in palaeolimnological records, because long-term observations are limited in time and indisputable sediment proxies of hypolimnetic anoxia are still scarce. Here we use visible and near infrared (VNIR), and short-wave infra-red (SWIR) hyperspectral imaging combined with geochemical analyses to reconstruct lake stratification history, redox status and mixing conditions in the water column of Lake Son Kol (Kyrgyzstan) in Central Tian Shan during the last 8500 years. In particular, the detection of Bacteriopheophytin a (Bphe a), a pigment produced by anoxygenic phototrophic bacteria at the chemocline of meromictic lakes, emphasizes episodes of multi-decadal to centennial hypolimnetic anoxia in Lake Son Kol. Phases of hypolimnetic anoxia are inferred from the deposition of dark organic sediments within a stratified lake system, which occurred during periods of increased snowmelt (and solid winter precipitation) and warmer spring/summer temperatures that promoted floods and the export of terrestrial material from the catchment. Prolonged euxinic conditions in bottom waters (involving the development of a stable chemocline) are reported around 8500, 8400, 8200–7800, 7700–7500, 7300–7000, 6500–6100, 6000–5700 and 5500–5250 cal yr BP. At ca. 5250 cal yr BP, the chemocline abruptly vanished as Lake Son Kol tipped into a regime with predominantly cooler and well-mixed conditions (predominance of oxygenic phototrophs), coeval with higher lake levels. The disappearance of hypolimnetic anoxia in Lake Son Kol coincides with strengthened wind conditions that imply enhanced lake overturning and upward mixing of nutrients in the water column. This study reveals the strong potential of hyperspectral imaging, in combination with more classical palaeolimnological approaches, to reconstruct the lake trophic and mixing history and explore the controlling mechanisms at work on decadal to centennial timescales. Our results outline how abrupt ecosystem changes may occur even in the absence of anthropogenic climate change.

中文翻译：

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天山中部（吉尔吉斯斯坦）高海拔湖泊系统百年尺度中全新世中全新世缺氧事件的证据

摘要 由于长期观测时间有限，且对下湖水缺氧的无可争议的沉积物代用物仍然缺乏，古湖泊学记录中很少有关于湖泊分枝杆菌的沉积档案。在这里，我们使用可见光和近红外 (VNIR) 以及短波红外 (SWIR) 高光谱成像结合地球化学分析来重建 2017 年 10 月 19 日的 Son Kol 湖（吉尔吉斯斯坦）水体中湖泊分层历史、氧化还原状态和混合条件。近8500年的中天山。特别是，细菌脱镁叶绿素 a (Bphe a) 的检测强调了 Son Kol 湖中数十年至百年的低水位缺氧事件，它是一种由分生湖趋化层处的缺氧光养细菌产生的色素。从分层湖泊系统中深色有机沉积物的沉积推断出水下缺氧的阶段，这种沉积发生在融雪增加（和冬季固体降水）和春季/夏季温度升高的时期，促进了洪水和陆地物质从集水区的输出. 据报道，底部水域中长期的euxinic 条件（涉及稳定趋化层的发展）大约为 8500、8400、8200-7800、7700-7500、7300-7000、6500-6100、6000-5500-2 年和 5500 年卡。在大约 在 5250 cal yr BP，随着 Son Kol 湖进入一个主要是凉爽和混合良好的条件（含氧光养生物的优势），与更高的湖泊水位同时期，趋化层突然消失了。Son Kol 湖低水位缺氧的消失与风力条件增强相吻合，这意味着湖泊倾覆和水体中营养物质的向上混合。这项研究揭示了高光谱成像与更经典的古湖泊学方法相结合的强大潜力，可以重建湖泊的营养和混合历史，并探索在十年到百年时间尺度上起作用的控制机制。我们的结果概述了即使在没有人为气候变化的情况下，生态系统的突然变化也可能发生。重建湖泊的营养和混合历史，并探索在十年到百年时间尺度上起作用的控制机制。我们的结果概述了即使在没有人为气候变化的情况下，生态系统的突然变化也可能发生。重建湖泊的营养和混合历史，并探索在十年到百年时间尺度上起作用的控制机制。我们的结果概述了即使在没有人为气候变化的情况下，生态系统的突然变化也可能发生。