In permafrost regions, the strong spatial and temporal variability in soil temperature cannot be explained by the weather forcing only. Understanding the local heterogeneity of soil thermal dynamics and their controls is essential to understand how permafrost systems respond to climate change and to develop process-based models or remote sensing products for predicting soil temperature. In this study, we analyzed soil temperature dynamics and their controls in a discontinuous permafrost region on the Seward Peninsula, Alaska. We acquired one-year temperature time series at multiple depths (at 5 or 10 cm intervals up to 85 cm depth) at 45 discrete locations across a 2.3 km² watershed. We observed a larger spatial variability in winter temperatures than that in summer temperatures at all depths, with the former controlling most of the spatial variability in mean annual temperatures. We also observed a strong correlation between mean annual ground temperature at a depth of 85 cm and mean annual or winter season ground surface temperature across the 45 locations. We demonstrate that soils classified as cold, intermediate, or warm using hierarchical clustering of full-year temperature data closely match their co-located vegetation (graminoid tundra, dwarf shrub tundra, and tall shrub tundra, respectively). We show that the spatial heterogeneity in soil temperature is primarily driven by spatial heterogeneity in snow cover, which induces variable winter insulation and soil thermal diffusivity. These effects further extend to the subsequent summer by causing variable latent heat exchanges. Finally, we discuss the challenges of predicting soil temperatures from snow depth and vegetation height alone by considering the complexity observed in the field data and reproduced in a model sensitivity analysis.

中文翻译：

---

不连续多年冻土区土壤热动力学局部尺度异质性及控制因素

在永久冻土地区，土壤温度的强烈时空变化不能仅用天气强迫来解释。了解土壤热动力学的局部异质性及其控制对于了解永久冻土系统如何响应气候变化以及开发基于过程的模型或遥感产品来预测土壤温度至关重要。在这项研究中，我们分析了阿拉斯加苏厄德半岛不连续永久冻土地区的土壤温度动态及其控制。我们在 2.3 km ²流域的 45 个离散位置获取了多个深度的一年温度时间序列（间隔为 5 或 10 厘米，深度可达 85 厘米）。我们观察到，在所有深度，冬季温度的空间变异均大于夏季温度的空间变异，其中前者控制了年平均温度的大部分空间变异。我们还观察到 45 个地点 85 厘米深度的年平均地温与年平均或冬季地表温度之间存在很强的相关性。我们证明，使用全年温度数据的层次聚类将土壤分类为寒冷、中等或温暖的土壤与其共处的植被（分别为禾本科苔原、矮灌木苔原和高灌木苔原）密切匹配。我们表明，土壤温度的空间异质性主要是由积雪的空间异质性驱动的，这会导致冬季隔热和土壤热扩散率的变化。通过引起可变的潜热交换，这些影响进一步延伸到随后的夏季。最后，我们考虑到现场数据中观察到的复杂性并在模型敏感性分析中重现，讨论了仅根据雪深和植被高度预测土壤温度的挑战。