Soils were collected from the frozen permafrost layer (> 60 cm below the surface) at five sites underlying moist acidic tussock or wet sedge vegetation, and on three glacial surfaces on the North Slope of Alaska during summer 2018.  Soil cores were collected at Imnavait wet sedge tundra using a SIPRE corer, and the permafrost layer (1.0 – 1.3 m below the surface) was separated from the soil core using a knife.  At the other four sites, 1 m x 1 m x 1 m soil pits were excavated using a jack hammer, shovels, and pickaxe.  Soil sampling at each site took place over the course of one day.  From each site, an equal mass of soil (~2.5 kg) was placed in four Ziploc bags (1 gallon) and then each soil sample was quintuple-bagged.  Following collection, soil samples were immediately transferred to coolers in the field and then stored in freezers at the Toolik Field Station for ≤ 4 weeks until overnight shipment on dry ice to the Woods Hole Oceanographic Institution (WHOI).  All soil samples were frozen upon arrival at WHOI and immediately placed into freezers until leachate preparation.

Two permafrost leachates were prepared from permafrost soils collected at each site, except for Sagwon moist acidic tundra, which did not have an experimental replicate.  Dissolved organic carbon (DOC) was leached from each permafrost soil at WHOI as described in the following five steps.  First, frozen soil in one or two Ziploc bags was broken into smaller pieces inside the bag using a clean chisel.  Second, 0.8 to 3.3 kg of frozen soil was transferred to a new Ziploc bag (1 gallon) and then thawed in a chest cooler at 4 °C for up to 20 hours.  Third, the thawed permafrost soil was added to five liters of MilliQ water (Millipore Simplicity ultraviolet, UV, system) in a MilliQ-rinsed high density polyethylene (HDPE) bucket (5 gallon).  Each bucket was covered with a HDPE lid and allowed to leach at 4 °C for 24 hours.  Fourth, the permafrost leachate was filtered through a sieve with 60 mm nylon mesh screening (Component Supply) into a new, MilliQ-rinsed 5 gallon HDPE bucket and then placed in the chest cooler at 4 °C for ≤ 1 day to allow suspended particles to settle before additional filtration.  Fifth, the 60-mm filtered leachate was filtered through 10 mm (Geotech Environmental Equipment, Inc.) and then finally through 0.2 mm (Whatman), MilliQ-rinsed high-capacity cartridge filters.  Four liters of the final 0.2-mm filtered permafrost leachate (now referred to as permafrost leachate) were then transferred to a precombusted (450 °C; 4 h) 4 L glass amber bottle and kept at 4 °C prior to further analysis. 

References: 

Bowen, J. C.,  C. P. Ward, G. W. Kling, R. M. Cory..  Arctic amplification of global warming strengthened by sunlight oxidation of permafrost carbon to CO2.    In review.