Siberian fire regime shifts during interglacials of the last 3.6 Myrs inferred from sedimentary records of Lake El’gygytgyn (NE Asia)

预测和适应当前和未来气候变化对社会的影响需要深入了解地球表面的内部自然反馈，而不是人类对自然生态系统的影响。北部高地和冻土带生物群对气候变化特别敏感，并在全球生物物理和生物地球化学循环中发挥基本作用，例如通过它们的火灾机制。然而，火、植被和气候之间的长期反馈在很大程度上是未知的，特别是在东西伯利亚，尽管长期的自然变化强烈地影响着短期变化。高度不确定的是，目前北极地区气温上升和火灾活动增加是否以及如何已经预示着火灾制度的变化，以及这些变化是否会伴随着生物群的变化。该项目研究了西伯利亚东北部在多个上更新世间冰期期间的火情变化，使用了过去3.6百万年来唯一的连续沉积记录，即来自El‘gytgyn湖(ICDP站点5011-1)的记录。聚焦于不同强度(最高温度)的间冰期、生物群配置(冻土带、北部夏绿或北部常绿森林)和全球陆地-海洋-大气边界条件，我的目标是回答是什么驱动了高纬度地区火灾制度的长期变化-气候或植被，以及哪些内部火灾-永久冻土侵蚀反馈稳定或破坏了植被类型。将使用(I)沉积木炭组成和流入作为现代常绿北方落叶松森林中常见的高强度、林分替代火灾和相关燃料的替代品，以及(Ii)从相同样本中新的低温火灾沉积替代品--分子标志物左旋葡聚糖及其异构体，代表现代北方落叶松森林的地表火灾状况，重建区域火灾状况。项目更新的目的是将重建火灾历史的重点转移到比现在更温暖的间冰期，并确定与晚更新世相比，早更新世的火情变化。为了评估火灾制度转变的驱动因素，将从统计上将火灾记录与来自花粉记录的定量土地覆盖重建以及来自同一地点的独立气候重建和全球汇编进行比较。为了评估频繁发生的火灾是否影响了永冻层退化和沉积物侵蚀，将把火灾记录与使用端元模拟分析对现有粒度数据集进行重新评估后得出的区域和地方侵蚀指标进行统计比较。这将允许在比全新世更温暖的气候下概念化依赖于时间尺度的火-气候-植被-永久冻土关系--适用于未来预测北部高地环境变化所需的火-植被模型的参数化。

Predicting and adapting to the impacts of ongoing and future climate change for society requires a deep understanding of internal natural feedbacks at the Earth surface beyond the influence that humans exert on natural ecosystems. The high-northern boreal and tundra biomes are especially sensitive to climate change and play a fundamental role in global biophysical and biogeochemical cycles, for example via their fire regime. However, the long-term feedbacks between fire, vegetation and climate are largely unknown, especially from Eastern Siberia, although long-term natural variability strongly influences short-term variability. Highly uncertain is, if and how currently increasing temperatures over the Arctic and increasing fire activity are already an indication for shifts in fire regimes and if they will be accompanied by biome shifts. The project studies northeastern Siberian fire regime shifts during multiple Plio-Pleistocene interglacials using the only continuous sedimentary record covering the last 3.6 Myrs, i.e., from Lake El’gygytgyn (ICDP Site 5011-1). Focusing on interglacials of different strengths (maximum temperature), biome configurations (tundra, summergreen boreal or evergreen boreal forest) and global land-ocean-atmosphere boundary conditions, I aim to answer the timely questions on what drove long-term shifts in fire regimes in higher latitudes – climate or vegetation, and which internal fire-permafrost erosion feedbacks stabilized or destabilized vegetation types. Regional fire regimes will be reconstructed using (i) sedimentary charcoal composition and influxes as proxies for high-intensity, stand-replacing fires and associated fuels, common in modern evergreen boreal forest, and, from the same samples, (ii) new sedimentary proxies for low-temperature fires – the molecular markers levoglucosan and its isomers, representing the surface fire regime in modern summergreen boreal larch forests.The project renewal aims to shift the focus in the reconstruction of fire histories to warmer-than-present interglacials and determine source-area specific fire regime shifts for the Early Pleistocene in comparison to the Late Pleistocene. To assess the drivers of fire regime shifts, fire records will be statistically compared with quantitative land cover reconstructions from pollen records and independent climate reconstructions from the same site and global compilations. To assess if frequent fires affected permafrost degradation and sediment erosion, the fire records will be statistically compared with regional and local erosional proxies derived from a re-evaluation of existing grain size data sets using end-member modelling analysis. This will allow to conceptualize time-scale dependent fire-climate-vegetation-permafrost relationships under warmer-than-Holocene climates – suitable for the parametrization of fire-vegetation models required for future predictions of high-northern environmental change.