APEX Soil Temperature and Moisture Data from 2018-2020

Geophysical measurements and related field data were collected by the U.S. Geological Survey (USGS) at the Alaska Peatland Experiment (APEX) site in Interior Alaska from 2018 to 2020 to characterize subsurface thermal and hydrologic conditions along a permafrost thaw gradient. The APEX site is managed by the Bonanza Creek LTER (Long Term Ecological Research). In July 2018, soil temperature and moisture sensors were installed at six out of the nine instrument locations (APEX1, APEX2, APEX3, APEX4, APEX7, APEX9). Thermistors (PS103J2, US Sensor, Orange, CA, USA) were placed at depths of 5, 30, 60, 120, and 180 centimeters (cm) with three replicates. Three sites (APEX1, APEX4, APEX9) contained an additional single 240 cm thermistor. Each soil temperature record was processed to remove erroneous values and spikes. Two time-domain reflectometry (TDR) probes (CS-616, Campbell Scientific, Logan UT, USA) were installed at the same six instrument sites to record soil moisture. The first TDR was inserted at a 45-degree angle down from the ground surface (0-20 cm), and the second from 20-40 cm. We applied an organic soils correction to the raw TDR data following the procedure in Bourgeau‐Chavez et al. (2010). Soil temperature and moisture data were recorded continuously from July 2018 through October 2020 on Campbell Scientific data loggers, with some data gaps due to power loss.