Profiles of diatoms, pollen, XRD, XRF and organic composition of two sediment cores (PG2022 and PG2023) from Lake Kyutyunda in Yakutia, NE Siberia, Russia

Although the climate development over the Holocene in the Northern Hemisphere is well known, palaeolimnological climate reconstructions reveal spatiotemporal variability in northern Eurasia. Here we present a multi-proxy study from north-eastern Siberia combining sediment geochemistry, and diatom and pollen data from lake-sediment cores covering the last 38,000 cal. years. Our results show major changes in pyrite content and fragilarioid diatom species distributions, indicating prolonged seasonal lake-ice cover between ~13,500 and ~8,900 cal. years BP and possibly during the 8,200 cal. years BP cold event. A pollen-based climate reconstruction generated a mean July temperature of 17.8°C during the Holocene Thermal Maximum (HTM) between ~8,900 and ~4,500 cal. years BP. Naviculoid diatoms appear in the late Holocene indicating a shortening of the seasonal ice cover that continues today. Our results reveal a strong correlation between the applied terrestrial and aquatic indicators and natural seasonal climate dynamics in the Holocene. Planktonic diatoms show a strong response to changes in the lake ecosystem due to recent climate warming in the Anthropocene.
We assess other palaeolimnological studies to infer the spatiotemporal pattern of the HTM and affirm that the timing of its onset, a difference of up to 3,000 years from north to south, can be well explained by climatic teleconnections. The westerlies brought cold air to this part of Siberia until the Laurentide ice-sheet vanished 7,000 years ago. The apparent delayed ending of the HTM in the central Siberian record can be ascribed to the exceedance of ecological thresholds trailing behind increases in winter temperatures and decreases in contrast in insolation between seasons during the mid to late Holocene as well as lacking differentiation between summer and winter trends in paleolimnological reconstructions.

尽管北半球全新世（Holocene）的气候演化进程已得到广泛认知，但古湖沼学（palaeolimnology）气候重建结果显示，北欧亚大陆存在显著的时空气候变异性。本研究针对东北西伯利亚开展多代用指标分析，整合了覆盖过去38000个校准年（cal. years）的湖沉积岩芯的沉积物地球化学、硅藻及孢粉数据。研究结果揭示了黄铁矿含量与脆杆藻属硅藻类群分布的显著变化，表明在约13500~8900校准年前（cal. years BP）存在长期季节性湖冰覆盖，且在8200校准年前的冷事件期间可能也存在类似情况。基于孢粉的气候重建结果显示，在约8900~4500校准年前的全新世暖期（Holocene Thermal Maximum, HTM），七月平均气温达17.8℃。晚全新世出现的舟形硅藻类群指示季节性湖冰覆盖时长缩短，这一趋势延续至今。本研究结果表明，所采用的陆地与水生代用指标与全新世自然季节性气候动力过程具有强相关性；浮游硅藻则对人类世（Anthropocene）近期气候变暖引发的湖泊生态系统变化表现出显著响应。
本研究还评估了其他古湖沼学研究，以推演全新世暖期的时空分布格局，并证实其起始时间存在北南方向最大达3000年的差异，这一现象可通过气候遥相关（climatic teleconnections）得到合理解释。在7000年前劳伦冰盖（Laurentide ice-sheet）消融前，西风带持续为西伯利亚该区域输送冷空气。西伯利亚中部记录中全新世暖期结束时间明显滞后，这一现象可归因于：中晚全新世期间冬季气温升高、季节日射差减小引发的生态阈值突破，以及古湖沼重建中未区分夏季与冬季气候趋势变化。