Distributed Temperature Profiling System Provides Spatially Dense Measurements and Insights about Permafrost Distribution in an Arctic Watershed

Abstract. Soil temperature has been recognized as a property that strongly influences a myriad of hydro-biogeochemical processes, as well as containing important information on the properties modulating the soil thermal flux. In spite of its importance, our ability to acquire soil temperature data with high spatial and temporal resolution and coverage is limited, because of the high cost of equipment, the difficulties of deployment, and the complexities of data management. Here we propose a new strategy that we call Distributed Temperature Profiling (DTP), which consists of cheap, low-impact, low-power, vertically resolved temperature probes that independently and autonomously record soil temperature. We developed a prototype DTP system for characterizing and monitoring near-surface thermal properties, using an unprecedented number of laterally and vertically distributed temperature measurements. The DTP system was tested in an Arctic ecosystem near Nome, AK, to identify near-surface permafrost distribution and various thermal regimes in a discontinuous permafrost environment during the summer time. Results show that the DTP system enabled successful acquisition of vertically resolved profiles of summer soil temperature over the top 0.8 m at numerous locations. DTP also enabled high resolution identification and lateral delineation of near-surface permafrost locations from surrounding zones with no permafrost or deep permafrost table locations overlain by a perennially thawed layer. The DTP strategy overcomes some of the limitations associated with – and complements the strengths of – borehole-based soil temperature sensing as well as Fiber-Optic Distributed Temperature Sensing (FO-DTS) approaches. Combining DTP data with co-located topographic and vegetation maps obtained using Unmanned Aerial Vehicle (UAV) and Electrical Resistivity Tomography (ERT) data allowed us to identify correspondences between surface and subsurface property distribution, and in particular between topography, vegetation, shallow soil properties, and near-surface permafrost. Finally, the results highlight the considerable value of the newly developed DTP strategy for investigating the significant variability and complexity of subsurface thermal and hydrological regimes in discontinuous permafrost regions.