Paleoclimate investiations on sediment core PG1984 from Lake Sysy-Kyuele, northern Siberia

In northeastern Siberia, Russia, a 1.2 m sediment core was retrieved and radiocarbon dated from a small and shallow lake located at the western side of the lower Lena River (N 69°24', E 123°50', 81 m a.s.l.). The objective of this paper is to reconstruct the palaeoenvironmental variability and to infer major palaeoclimate trends that have occurred since ~ 13.3 cal. kyrs BP. We analysed the diatom assemblages, sedimentology (grain size, total organic carbon (TOC), total nitrogen (TN)), and the elemental and mineralogical composition using X-ray fluorescence (XRF) and X-ray diffractometry (XRD) of the sediment core. Our results show parallel changes in the diatom species composition and sediment characteristics. Enhanced minerogenic sediment input and the occurrence of pyrite is indicative of a cold period between ~ 12.7-11.6 cal. kyrs BP. The diatom data enable a qualitative inference about the local ecological conditions to be made, and reveal an oligotrophic lake system with alkaline and cold conditions during the earliest Holocene. Moderately warmer climates are inferred for the period from ~ 9.1 to 5.7 cal. kyrs BP. The major shift in the diatom assemblage, from dominance of small benthic fragilarioid taxa to a more complex diatom flora with an influx of several achnanthoid and naviculoid diatom species, occurred after a transitional period of about 1400 years (7.1 to 5.7 cal. kyrs BP) at ~ 5.7 cal. kyrs BP, indicating a circumneutral and warmer hydrological regime during the Holocene thermal maximum (HTM). Diatom valve concentrations declined starting ~ 2.8 cal. kyrs BP, but have been rising again since less than or equalt to 600 cal. years BP. This has occurred in parallel to the increased presence of acidophilous diatom taxa (e.g. Eunotia spp.) and decreased presence of small benthic fragilarioid species in the most recent sediments, which is interpreted as the result of neoglacial cooling and subsequent recent climate warming. Our findings are compared to other lake-inferred climate reconstructions along the Lena River. We conclude that the timing and spatial variability of the HTM in the lower Lena River area reveal a temporal delay from north to south.

在俄罗斯西伯利亚东北部，研究人员从勒拿河下游西侧的一个小型浅湖（北纬69°24'，东经123°50'，海拔81米）中获取了一根1.2米长的沉积岩芯，并对其进行了放射性碳定年。本文旨在重建约13.3校正千年以来的古环境变化，并推断该时期发生的主要古气候趋势。我们分析了该沉积岩芯的硅藻组合、沉积学特征（粒度、总有机碳（TOC）、总氮（TN）），并利用X射线荧光光谱（XRF）和X射线衍射（XRD）技术分析了其元素与矿物组成。结果显示，硅藻物种组成与沉积特征呈现同步变化。矿质沉积物输入增加及黄铁矿的出现，表明约12.7-11.6校正千年期间存在一个寒冷期。硅藻数据可用于定性推断当地生态条件，结果显示全新世早期该湖泊为贫营养系统，且处于碱性寒冷环境。约9.1至5.7校正千年期间，气候被推断为中度温暖。硅藻组合在约5.7校正千年发生了重大转变：此前约1400年（7.1至5.7校正千年）为过渡期，之后小型底栖脆杆藻属类群的主导地位被取代，多种曲壳藻属和舟形藻属物种涌入，形成更为复杂的硅藻群落；这表明全新世大暖期（HTM）期间存在近中性且更温暖的水文状况。硅藻壳浓度自约2.8校正千年起下降，但自≤600校正年以来再次上升。与此同时，近期沉积物中嗜酸硅藻类群（如Eunotia属）的占比增加，小型底栖脆杆藻属物种占比减少；这一现象被解释为新冰期冷却及随后近期气候变暖的结果。我们将研究结果与勒拿河沿岸其他基于湖泊的气候重建结果进行了对比。结论表明，勒拿河下游地区全新世大暖期（HTM）的发生时间及空间变化呈现出从北向南的时间延迟特征。