Thermokarst lakes are important conduits for organic carbon sequestration, soil organic matter (soil-OM) decomposition and release of atmospheric greenhouse gases in the Arctic. They can be classified as either floating-ice lakes, which sustain a zone of unfrozen sediment (talik) at the lakebed year-round, or as bedfast-ice lakes, which freeze all the way to the lakebed in winter. Another key characteristic of thermokarst lakes are their eroding shorelines, depending on the surrounding landscape, they can play a major role in supplying the lakebeds with sediment and OM. These differences in winter ice regime and eroding shorelines are key factors which determine the quantity and quality of OM in thermokarst lake sediments. We used an array of physical, geochemical, and microbiological tools to identify the differences in the environmental conditions, sedimentary characteristics, carbon stocks and microbial community compositions in the sediments of a bedfast-ice and a floating-ice lake in Far East Siberia with different eroding shorelines. Our data show strong differences across most of the measured parameters between the two lakes. For example, the floating-ice lake contains considerably lower amounts of sediment organic matter and dissolved organic carbon, both of which also appear to be more degraded in comparison to the bedfast-ice lake, based on their stable carbon isotope composition (δ¹³C). We also document clear differences in the microbial community composition, for both archaea and bacteria. We identified the lake water depth (bedfast-ice vs. floating-ice) and shoreline erosion to be the two most likely main drivers of the sedimentary, microbial and biogeochemical diversity in thermokarst lakes. With ongoing climate warming, it is likely that an increasing number of lakes will shift from a bedfast- to a floating-ice state, and that increasing levels of shoreline erosion will supply the lakes with sediments. Yet, still little is known about the physical, biogeochemical and microbial differences in the sediments of these lake types and how different eroding shorelines impact these lake systems.

热岩溶湖是北极地区有机碳固存、土壤有机质（土壤-OM）分解和大气温室气体释放的重要渠道。它们可以分为浮冰湖和固定冰湖，前者在湖床上全年维持着未冻结的沉积物（talik）区域，后者在冬季一直冻结到湖床。热岩溶湖泊的另一个关键特征是它们的海岸线被侵蚀，根据周围的景观，它们在为湖床提供沉积物和有机物质方面发挥着重要作用。冬季冰情和海岸线侵蚀的差异是决定热喀斯特湖沉积物中有机质数量和质量的关键因素。我们使用了一系列物理、地球化学、和微生物工具，用于识别远东西伯利亚具有不同侵蚀海岸线的固冰和浮冰湖沉积物中环境条件、沉积特征、碳储量和微生物群落组成的差异。我们的数据显示两个湖之间的大多数测量参数存在巨大差异。例如，浮冰湖的沉积物有机质和溶解有机碳含量要低得多，根据其稳定碳同位素组成（δ 我们的数据显示两个湖之间的大多数测量参数存在巨大差异。例如，浮冰湖的沉积物有机质和溶解有机碳含量要低得多，根据其稳定碳同位素组成（δ 我们的数据显示两个湖之间的大多数测量参数存在巨大差异。例如，浮冰湖的沉积物有机质和溶解有机碳含量要低得多，根据其稳定碳同位素组成（δ^13C）。我们还记录了古细菌和细菌的微生物群落组成的明显差异。我们确定湖水深度（固定冰与浮冰）和海岸线侵蚀是热喀斯特湖泊沉积、微生物和生物地球化学多样性的两个最可能的主要驱动因素。随着气候持续变暖，越来越多的湖泊可能会从固定状态转变为浮冰状态，而海岸线侵蚀程度的加剧将为湖泊提供沉积物。然而，人们对这些湖泊类型沉积物的物理、生物地球化学和微生物差异以及不同的侵蚀海岸线如何影响这些湖泊系统仍然知之甚少。