Age determination, sedimentological, biogeochemical, and plant macrofossils analyses of outcrop PG2038-1@en

Thermokarst lakes are a widespread feature of the Arctic tundra, in which highly dynamic processes are closely connected with current and past climate changes. We investigated late Quaternary sediment dynamics, basin and shoreline evolution, and environmental interrelations of Lake El'gene-Kyuele in the NE Siberian Arctic (latitude 71°17'N, longitude 125°34'E). The water-body displays thaw-lake characteristics cutting into both Pleistocene Ice Complex and Holocene alas sediments. Our methods are based on grain size distribution, mineralogical composition, TOC/N ratio, stable carbon isotopes and the analysis of plant macrofossils from a 3.5-m sediment profile at the modern eastern lake shore. Our results show two main sources for sediments in the lake basin: terrigenous diamicton supplied from thermokarst slopes and the lake shore, and lacustrine detritus that has mainly settled in the deep lake basin. The lake and its adjacent thermokarst basin rapidly expanded during the early Holocene. This climatically warmer than today period was characterized by forest or forest tundra vegetation composed of larches, birch trees and shrubs. Woodlands of both the HTM and the Late Pleistocene were affected by fire, which potentially triggered the initiation of thermokarst processes resulting later in lake formation and expansion. The maximum lake depth at the study site and the lowest limnic bioproductivity occurred during the longest time interval of ~7 ka starting in the Holocene Thermal Maximum and lasting throughout the progressively cooler Neoglacial, whereas partial drainage and an extensive shift of the lake shoreline occurred ~0.9 cal. ka BP. Correspondingly, this study discusses different climatic and environmental drivers for the dynamics of a thermokarst basin.热融湖塘（Thermokarst lake）是北极苔原分布广泛的地貌类型，其高度活跃的过程与当前及过去的气候变化密切相关。本研究针对西伯利亚北极东北部（北纬71°17'，东经125°34'）的埃尔杰恩-库耶勒湖（Lake El'gene-Kyuele），开展了晚第四纪沉积物动力学、盆地与岸线演化以及环境关联的调查。该水体呈现热融湖塘特征，其发育过程侵蚀了更新世冰碛杂岩（Pleistocene Ice Complex）与全新世阿拉斯沉积物（Holocene alas sediments）。本研究的分析方法基于现代湖东岸3.5米沉积物剖面的粒度分布、矿物组成、总有机碳/总氮（TOC/N）比值、稳定碳同位素以及植物大化石（plant macrofossils）分析。研究结果表明，湖盆沉积物主要有两大来源：来自热融斜坡与湖岸的陆源混杂沉积物（terrigenous diamicton），以及主要沉积于深湖盆的湖相碎屑（lacustrine detritus）。该湖及其毗邻的热融湖盆在早全新世时期快速扩张。这一气候较现代更为温暖的时期，植被以落叶松、桦树及灌丛构成的森林或森林苔原为主。全新世暖期（Holocene Thermal Maximum, HTM）与晚更新世的林地均受到野火影响，野火可能触发了热融过程，进而推动后续湖塘的形成与扩张。本研究区域的最大湖深与最低湖生生物生产力，出现在始于全新世暖期、持续至逐步降温的新冰期（Neoglacial）的约7千年时长区间内；而约0.9日历千年距今年份（cal. ka BP）时，湖泊发生了部分排水与岸线的大规模迁移。相应地，本研究探讨了驱动热融湖塘盆地动态变化的不同气候与环境因素。