IN SITU CONTAMINATION OF MELT PROBES: IMPLICATIONS FOR FUTURE SUBGLACIAL MICROBIOLOGICAL SAMPLING AND ICY WORLDS LIFE DETECTION MISSIONS

Subglacial environments contain thriving ecosystems that are of significant scientific interest. Retrieving pristine samples for microbiological study beneath thick glacial ice presents a significant barrier. For planetary protection and to maintain sample integrity, retrieval of subglacial materials must not introduce microbial and chemical contamination. Melt probes, such as the Ice Diver, offer an efficient means of penetrating thick ice; these tools can also be thoroughly cleaned prior to deployment for the collection microbial samples from subglacial zones. While surface cleaning is an important step, we currently do not understand if these probes drag native microbes immured in the ice as they melt to subglacial targets at depth. Here we present results from a novel ice block experiment designed to determine the potential for englacial materials to be dragged by the Ice Diver during melt operations. A 2.0m x 0.4m x 0.38m ice block was inoculated with a model laboratory microbe (E. coli) and fluorescent (fitC) beads (1 µm diameter). Melt samples were collected through a port in the Ice Diver nose over the length of the ice block: before, during and after passing through the microbial layer then total E. coli cell and fluorescent bead concentrations were determined at depth.

Our results show that concentrations of E. coli and beads spike as the probe entered the microbial layer, followed by a ~91% reduction as the nose of the probe exited the layer. A second spike was observed when the Ice Diver tail (the widest portion of the probe) entered the microbial layer. Finally, a return to background cell concentrations was observed as the tail exited the dope layer. We conclude that microbial cells are indeed dragged deeper into the ice by melt probes, however this occurs in a predictable manner. While cells are dragged they can be recovered if melt water is collected. Though largely recovered the fluorescent beads (1 µm) are distinct from microbial cells and require further testing to understand their transport in ice. Our work highlights the importance of characterizing microbial assemblages at the ice surface and throughout glacier melting studies to ensure deeper samples are free of surface contaminants. On vehicle cleaning, e.g. germicidal UV, should be explored to help decimate dragged microorganisms during the melt process.