Temperature measured in permafrost borehole at ICDP site 5011-3 in El'gygytgyn Crater, 2008-2011

This study focuses on the temperature field observed in boreholes drilled as part of interdisciplinary scientific campaign targeting the El'gygytgyn Crater Lake in NE Russia. Temperature data are available from two sites: the lake borehole 5011-1 located near the center of the lake reaching 400 m depth, and the land borehole 5011-3 at the rim of the lake, with a depth of 140 m. Constraints on permafrost depth and past climate changes are derived from numerical simulation of the thermal regime associated with the lake-related talik structure. The thermal properties of the subsurface needed for these simulations are based on laboratory measurements of representative cores from the quaternary sediments and the underlying impact-affected rock, complemented by further information from geophysical logs and data from published literature. The temperature observations in the lake borehole 5011-1 are dominated by thermal perturbations related to the drilling process, and thus only give reliable values for the lowermost value in the borehole. Undisturbed temperature data recorded over more than two years are available in the 140 m deep land-based borehole 5011-3. The analysis of these observations allows determination of not only the recent mean annual ground surface temperature, but also the ground surface temperature history, though with large uncertainties. Although the depth of this borehole is by far too insufficient for a complete reconstruction of past temperatures back to the Last Glacial Maximum, it still affects the thermal regime, and thus permafrost depth. This effect is constrained by numerical modeling: assuming that the lake borehole observations are hardly influenced by the past changes in surface air temperature, an estimate of steady-state conditions is possible, leading to a meaningful value of 14 ± 5 K for the post-glacial warming. The strong curvature of the temperature data in shallower depths around 60 m can be explained by a comparatively large amplitude of the Little Ice Age (up to 4 K), with low temperatures prevailing far into the 20th century. Other mechanisms, like varying porosity, may also have an influence on the temperature profile, however, our modeling studies imply a major contribution from recent climate changes.本研究聚焦于俄罗斯东北部埃尔吉特金陨石坑湖（El'gygytgyn Crater Lake）跨学科科学考察所钻探钻孔的温度场观测数据。研究获取了两处钻孔的温度数据集：其一为位于湖中心附近、深度达400米的湖基钻孔5011-1；其二为坐落于湖缘、深度140米的陆上钻孔5011-3。通过对与该湖相关的冻土融区（talik）热状态的数值模拟，可约束永久冻土深度与古气候变化。本次数值模拟所需的地下热物性参数，源自对第四纪沉积物及下伏冲击成因岩石的代表性岩芯开展的实验室测量，并辅以地球物理测井数据与已发表文献资料。 湖基钻孔5011-1的温度观测数据受钻探作业引发的热扰动主导，仅钻孔最底端的温度数据具备可靠性。深度140米的陆上钻孔5011-3则拥有超过两年连续记录的无扰动温度观测数据。对该观测数据集的分析，不仅可确定近期多年平均地表温度，还能重建地表温度历史，但该重建过程存在较大不确定性。尽管该钻孔深度远不足以完整重建直至末次盛冰期的古温度序列，但其仍会影响地下热状态，进而对永久冻土深度产生影响。可通过数值建模约束该效应：假设湖基钻孔的观测结果几乎不受地表气温历史变化影响，则可推导出稳态条件下的冰期后升温量为14±5 K，该结果具备明确物理意义。深度约60米的浅层区域温度数据呈现显著曲率特征，这可由小冰期（Little Ice Age）较强的温度波动（振幅可达4 K）解释——彼时低温状态持续至20世纪中后期。其他机制（如孔隙度变化）也可能对温度剖面产生影响，但本研究的模拟结果表明，近期气候变化是塑造该温度剖面的主要驱动因素。