ICELANDIC LAVA FIELDS AS A TERRESTRIAL ANALOG FOR MARS: INVESTIGATION OF HABITABILITY, PRODUCTIVITY AND MICROBIAL DIVERSITY. M. L. Cable1, E. S. Amador2, E. Schwieterman2, M. B. Jacobsen3, C. Yin4, A. M. Stockton1, D. M. Gentry5, A. Stevens6, G. Murukesan7, N. Chaundry8, T. Cullen8, W. Geppert4 and D. Cullen8, 1NASA Jet Propulsion Laboratory, California Institute of Tech-nology, USA (Morgan.L.Cable@jpl.nasa.gov), 2University of Washington, USA, 3University of Copenhagen, Den-mark, 4Stockholm University, Sweden, 5Stanford University, USA, 6The Open University, UK, 7University of Turku, Finland, 8Cranfield University, UK.

Introduction: Our expedition, an international col-laboration inspired by the participation of the 2012 NASA Nordic Astrobiology Summer School [1], fo-cused on the habitability of Icelandic lava fields. These lava fields are excellent analogs for environments of astrobiological interest such as Mars [2, 3]. By study-ing the biodiversity and spatial variations of life in multiple lava fields, we aimed to establish a decision tree type methodology to determine the most promis-ing sites for habitability. We hope this framework can be used to better inform current and future in-situ as-trobiological investigations.

Robotic in-situ sampling presents several challeng-es. Consumables (reagents, solvent, etc.) limit the number of samples that can be investigated. Processing constraints required by extraction techniques are de-pendent on the mission design and cannot be altered in the field. Even if biosignatures are present in a site of astrobiological interest, the spatial and environmental variation may rise and drop below detection thresh-olds. With limited samples and a fixed protocol, it is crucial to choose a representative set of sampling loca-tions to maximize the possibility of detecting evidence of life, if it exists.

One important question that can be explored at ana-log sites on Earth is the relationship between apparent homogeneity of a site and the habitability and biodi-versity of that area. We selected lava field sampling locations such that a remote observer, or surface ex-plorer, would interpret them as visually homogeneous with respect to color, grain size, roughness and tem-perature. We then used various field lab techniques to quantify the differences in gross microbial productivity and diversity over varying spatial scales at each lava field.

Field Sites: Three lava fields, Fimmvörðuháls (63°38’N, 19°26’W), Eldfell (63°25’N, 20°14’W) on the island of Heimaey, and Laugahraun (63°59’N, 19°05’W) (Figure 1), were initially evaluated upon arrival to Iceland during the week of July 22, 2013. The sites were judged for their relevance to our scien-tific and exploration goals, as well as potential for an-thropogenic contamination and future repeatability. Fimmvörðuháls (Figure 2) and Eldfell (Figure 3) were ultimately selected as our primary sampling sites given that: (a) their eruption dates are relatively similar –

2010 and 1973, respectively; (b) they had limited vege-tation; and (c) they had very similar sediment types: basaltic tephra. The Laugahraun lava field, though geologically interesting, proved to be far too vegetated to collect homogeneous samples; futhermore the high tourist traffic decreased our confidence that those sam-ples would not be contaminated by anthropogenic sources.

Figure 1. Context map for Icelandic sampling

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Figure 2. Black box indicates Fimmvörðuháls

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Figure 3. Black box indicates Eldfell sampling loca-

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Field Sampling Methods: Sampling sites were se-lected based on apparent homogeneity with evenly distributed basaltic tephra. A triplicate sample set was collected at each site, with each sample spaced 1 m apart. Subsequent sample sets were collected at dis-tances of 10 m and 100 m. Each sample was taken from ~ 5 cm below the surface using sterile technique.

Field Laboratory Protocols: Soil samples were stored at room temperature prior to analysis. Soil sam-ples with large grain sizes (> 2 mm) were crushed us-ing a sterile hammer or vise grip.

ATP Bioluminescence Assay. Adenosine triphos-phate (ATP) was quantified using the ATP Biolumi-nescence Assay Kit HS II and reader (Merck HyLiTE II) in triplicate for two aliquots of each soil sample.

Figure 4. Variation in ATP content with sampling distance for both lava field sites. Heterogeneity in-creases with distance for Eldfell (older lava field).

Fluorescence Microscopy. Extracted cells were stained with SYBR Gold Nucleic Acid Gel Stain (Invi-trogen) and imaged under 100x magnification using a Partec Cycscope with a 455 nm excitation source and 500 nm dichroic long pass filter. Cell counts were av-eraged from five images for each sample.

Results: ATP was detected in all samples ana-lyzed, indicating actively metabolizing microorgan-isms in every sample site of both locations. At Eldfell, the degree of variation of ATP content increased with distance (Figure 4). At Fimmvörðuháls, however, the difference in ATP content between two samples was similar, regardless of spatial separation. This is con-sistent with lava field age, in that the older lava field (Eldfell, 1973) has had more time to establish a com-plex microbial community, whereas the younger lava field (Fimmvörðuháls, 2010) is most likely still in the initial stages of microbial colonization.

Cell count variation from the fluorescence micros-copy assay did not exhibit the same dependence as ATP variation for either location. This may be due to the fact that the cell counts were low for most samples. This method was also subject to human error and diffi-cult to implement in the field.

Conclusions: Our results are consistent with the interpretation that biological variability in geologically homogeneous sample sites varies with lava field age. Younger lava fields tend to show the same variation in biodiversity and habitability regardless of sampling proximity. Older lava fields are increasingly heteroge-neous at larger spatial scales.

This work has implications for field sampling and analysis of volcanic regions such as those on Mars. Given the ages of lava flows on this and other plane-tary bodies, we anticipate high variation in biodiversity between geologically homogeneous areas, should life exist. We therefore recommend a robotic sampling strategy with as many spatially separated sampling sites as practical, even in areas that appear homogene-ous.

Acknowledgments: Funding for MLC, ESA and ES was provided by the American Philosophical Socie-ty’s Lewis and Clark Fund for Exploration and Field Research in Astrobiology with support from the NASA Astrobiology Institute. AMS was funded by the NASA Postdoctoral Program, administered by Oak Ridge Associated Universities through a contract with NASA. Government sponsorship acknowledged.

References:[1] http://www.nordicastrobiology.net/ Iceland2012. [2] Warner N. H. and Farmer J. D. (2010) Astrobiology, 10, 523-547. [3] Mangold N. et al. (2011) Earth and Planetary Science Letters, 310, 233-243.

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