Hydrothermal activity is common on rocky bodies in our system now and in the past, providing rich geochemical gradients that are prime targets for astrobiological study. On Mars, these sites in Gusev crater, Nili Patera, and Valles Marineris. We study the lipid biomarkers and associated stable isotope compositions produced by extremophilic microbes in terrestrial hot springs in Yellowstone National Park (USA) and El Tatio geyser field (Chile). We recovered a suite of lipid biosignatures associated with extremophilic archaea, including isoprenoid glycerol dialkyl glycerol tetraethers (iGDGTs) in varying concentrations (200 to >5000 ng g^-1 dry sediment). Spring temperature appears to be the dominant control on iGDGT concentration, whereas spring pH appears to be dominant control on the distribution of cyclic moieties in lipid structures (quantified by the Ring Index). Work to determine lipid δ²H values is ongoing. This research will help with site selection and sample prioritization for future robotic missions to Mars. Harris et al., 2024 AbSciCon Presentation

The stable hydrogen isotope composition (δ²H) of lipid biomarkers can preserve environmental information over geological timescales, aiding studies of past climate, hydrology, and ecology. While much work has focused on eukaryotic lipids (e.g., plant waxes), the potential of archaeal lipid biomarkers remains underexplored. We investigated the H-isotope composition of biphytanes in Sulfolobus acidocaldarius, a thermoacidophile and obligate heterotroph, by varying temperature, pH, shaking rate, electron acceptor availability, or donor flux. Lipid/water H-isotope fractionation (²εL/W) values were consistently negative and largely invariant despite significant changes in doubling times and lipid cyclization. These results align with studies on other heterotrophic archaea and suggest that archaeal lipids reliably record the δ²H of growth water. This highlights their potential as hydrological proxies, especially in extreme or extraterrestrial environments where plant-derived lipids are absent. Harris et al., 2024 AEM Special Issue on Planetary Microbiology

This project aimed to improve biosignature detection on Mars by using Earth’s extreme environments as test beds for refining exploration strategies. We review five terrestrial sites (atacama salars, hydrothermal springs, Antarctic lakes, impact craters, acidic rivers) that serve as analogs to ancient Martian crater lakes, comparing their geology, water chemistry, microbial communities, and preserved biomarkers. We assess how microbial habitability and biosignature preservation vary across extremes in pH, salinity, temperature, and water activity, and we explore how remote sensing and rover-scale measurements can detect these signatures at relevant spatial scales. By linking biomarker preservation potential to mineralogy and environmental settings, the study highlights critical constraints and strategies for selecting landing sites and designing life detection missions on Mars. Harris et al., 2022 Frontiers in Astronomy and Space Sciences

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Arctic lagoons are key coastal habitats that support diverse benthic communities and serve as critical feeding grounds for fish, migratory birds, and marine mammals. With climate change accelerating watershed runoff and coastal erosion, terrestrial carbon (CT) inputs to these systems are expected to rise, potentially altering ecosystem energy pathways. To evaluate the role of CT, we used a Bayesian stable isotope mixing model (simmr) to quantify the contributions of terrestrial inputs, marine shelf organic matter, and benthic microphytobenthos to the diets of 20 genera spanning five trophic guilds. Our results reveal that Arctic lagoon food webs are highly omnivorous and flexible, with terrestrial carbon serving as a significant subsidy and omnivorous fish acting as key conduits transferring CT from lower to higher trophic levels. Harris et al., 2018 Food Webs Harris et al., 2017 Estuaries and Coasts

Antarctica is warming. This causes many changes to lake conditions in the Dry Valleys of Antarctica. Glacial melt and stream flow are increasing, which raises the water level of closed-basin, ice-covered lakes. Warming also thins the permanent ice-cover of these lakes, allowing more light to reach the water column. This increase in light and habitatable space increases phytoplankton carbon fixation, but we don’t know what effects these changes will have on carbon loss rates. We study carbon loss rates in two Dry Valley Lakes: Lake Bonney and Lake Fryxell. Specifically, we will assess decomposition rates by bacterioplankton in the lake water columns and the potential for microbial mat biomass to be advected from lake moats to the surrounding soils. Harris et al., 2018 Post Presentation

Zooarchaeological faunal remains are commonly examined to investigate harvesting behavior. We determined the size, shape, and estimate age of limpet (Patella vulgata) shells from several middens at the Late Norse Sandwick South Site, Unst, Shetland, UK. Midden strata represent distinct occupational phases (Phase 1: AD 1100–1200, Phase 2: AD 1200–1250, Phase 3: AD 1250–1350). Shell length, conicity, and modeled age all declined between Phases 1 and 2, suggesting intensive, size-selective limpet harvesting. The conicity decline between Phases 1 and 2 may also have been caused by increased storminess that accompanied the onset of the Little Ice Age. Harris et al., 2017 Journal of Island and Coastal Archaeolgy