The ice content of palsas and peat plateaus, estimated with high-frequency induced polarisation

帕尔萨斯和泥炭沼泽是在永久冻土中形成的特殊地貌。它们覆盖了加拿大、俄罗斯欧洲、西伯利亚和北芬诺斯坎迪亚的亚北极地区的大片地区。这些地貌储存了大量的碳和氮素，它们可能会因全球变暖而释放到地球大气层中。因此，它们可能有助于反馈机制，加速气候变化。冻土中的含冰量是控制冻土对温度升高的敏感度的一个重要指标。冰含量也是任何数值模拟的关键参数，这些数值模拟试图预测气候变化条件下棕榈滩和泥炭高原的退化。同时，冰层含量及其空间变化很难测量，这是了解退化过程细节所必需的。在这个项目中，我们将应用一种创新的地球物理方法，高频诱导极化，来确定芬诺斯坎迪亚特定棕榈树和泥炭高原下的冰含量。该方法在1赫兹到250千赫的频率范围内确定与频率相关的电学性质(电导率和介电常数)。由于冻结水的电介电常数在该频率范围内表现出特征行为，因此该方法适用于冰含量的估计。最近的研究表明，在实际条件下，在野外尺度上估算冰量是可能的。我们将在挪威北部选定的四个地点进行测量，确定冰含量及其空间变化。在一个地点，我们将进行重复测量，以捕捉地下条件随时间的变化，这是已知的相当快的。我们的结果将为在全球变暖的背景下推进对棕榈滩和泥炭高原命运的预测提供基础。这些数据将构成缩小数值模拟要求与缺乏实际地面信息之间的差距的一步。芬诺斯坎迪亚的研究地点代表了大片的亚北极地区，因此对理解永久冻土退化的贡献将具有全球意义。

Palsas and peat Pleateaus are specific landforms that are shaped by processes in permanently frozen ground. They cover extensive areas in subarctic regions in Canada, European Russia, Siberia and Northern Fennoscandia. The landforms store a significant amount of Carbon and Nitrogene, which might be released into Earth’s atmosphere by global warming. Therefore, they may contribute to feedback mechanisms and accelerate climate change. Ice content in frozen ground is an essential quantitiy that controls how sensitive frozen ground is to a temperature increase. Ice content is also a key parameter for any numerical simulation trying to predict the degradation of palsas and peat plateaus under climate change conditions. At the same time, ice content and its spatial variation is difficult to measure at a reolution required to understand the details of degradation processes. In this project, we will apply an innovative geophysical method, high-frequency induced polarisation, to determine ice content under specific palsas and peat plateaus in Fennoscandia. The method determines the frequency-dependent electrical properties (electrical conductivity and permittivity) in a frequency range between 1Hz and 250kHz. Since the electric permittivity of frozen water exhibits a characteristic behavior in that frequency range, the method is suitable to estimate ice content. Recently, it was demonstrated that ice content estimation is possible und real conditions at the field scale. We will carry out measurements at four selected in Northern Norway and determine ice content and its spatial variation. At one site, we will carry out repetitive surveys in order to capture the variation of subsurface conditions with time, which is known to be quite rapid. Our results will provide a basis to advance the prediction of the fate of palsas and peat plateaus in the context of global warming. The data will constitute a step towards closing the gap between the requirements of numerical simulation, and the lack of actual ground information. The studied sites in Fennoscandia are representative of large subarctic regions, and therefore the contributions to the understanding of permafrost degradation will be of global relevance.