Permafrost soil samples from Svalbard 2010 (150 cm depth).

Drilling, handling and dividing permafrost cores without microbial contamination is of great concern because contamination e.g. from the active layer above may lead to incorrect interpretation of results in experiments investigating potential and actual microbial activity in these low microbial biomass environments. Here, we present an example of how microbial contamination from active layer soil disrupted analysis of the potentially active microbial community in permafrost soil. We also present the development and use of two tracers: 1) fluorescent plastic microspheres and 2) Pseudomonas putida genetically tagged with Green Fluorescent Protein production to mimic potential microbial contamination of two permafrost cores. A protocol with special emphasis on avoiding microbial contamination was developed and employed to examine how far microbial contamination can penetrate into permafrost cores. The quantity of tracer elements decreased with depth into the permafrost cores, but the tracers were detected as far as 17 mm from the surface of the cores. The results emphasize that caution should be taken to limit microbial contamination during permafrost coring and subsequent sampling handling.