Figure 1.

Procedure for tracer quantification: (A) Curved outer sides of the permafrost core was covered with tracers. (B) The outer layers (dashed lines) were removed one by one using sterile tools and extreme caution to avoid cross contamination between layers. (C) Resulting inner core, smaller in diameter and free of tracers and potential microbial contamination. (D) The inner core was transversely split in two using sterile chisel. (E) From the newly exposed surface, soil was collected from the center of the inner core for quantification of tracer elements. (F) Quantification of tracers in all the collected layers and from the center of the permafrost core.