Development and use of a Distributed Temperature Profiling (DTP) System to Estimate Arctic Soil Thermohydrology and Depth to Permafrost, and their Relationships with Geomorphological and Vegetation Properties

A substantial improvement in our ability to quantify and monitor soil and permafrost thermohydrology is important for improving our prediction of Arctic ecosystem feedbacks to climate under warming temperatures. In particular, understanding the relationships between soil thermal and hydrological behaviors, soil physical properties (incl. fraction of soil constituents, bedrock depth, permafrost characteristics), and landscape properties could greatly improve our predictive understanding of the subsurface storage and fluxes of water, carbon and nutrients in permafrost environments. However, obtaining such information is extremely challenging using conventional measurement approaches.

We developed a novel approach called Distributed Temperature Profiling (DTP) to address this measurement challenge. This system involves a network of vertically-resolved thermistor probes (>10 thermistors/probe) with an accompanying data acquisition system to autonomously sense the temperature regime at numerous depths and locations. The DTP system has been developed with an extraordinarily low production and assembly cost; uses automated data acquisition, management and transfer; and leverages open source software and hardware to encourage community-based development and deployment. Here, we describe the new DTP system and its joint use with electrical resistivity tomography (ERT) datasets, soil sample analysis, soil moisture data, and UAV-inferred vegetation indexes, digital surface elevation models and snow thickness to investigate the characteristics of and controls on permafrost processes in a watershed on the Alaskan Seward Peninsula. Together, the various datasets allowed us to distinguish shallow permafrost from deep permafrost with an overlying perennially thawed layer (i.e., suprapermafrost talik) implying year-round subsurface fluid flow and transport. In addition, relationships between the subsurface permafrost/soil characteristics, the topography, the snow thickness and vegetation distribution were identified. Finally, spatial and temporal variations in DTP and ERT, both showing strong lateral variations over a few meters, indicate the presence of preferential flow paths to depths of 20m.