Overview
Geomicrobiology is an interdisciplinary study of the interaction between microorganisms and the abiotic (physical) environment. Local geology and chemistry determine the variety and density of microbe populations in a system. The organisms, in turn, can alter and control abiotic factors around them, which influences the greater ecosystem. Many organisms on Earth obtain energy from light through photosynthesis, but in the permanent darkness of a subglacial environment microbes are only supported by organic matter deposits or matter generated by chemolithoautotrophy (utilizing inorganic compounds in the bedrock).
Much is still unknown about sediments and waters in subglacial Antarctica, but preliminary results from the WISSARD project suggest that these dark ecosystems are relatively rich in organic matter. Direct measurements and DNA sequencing revealed chemolithoautotrophy as well as heterotrophy (the metabolism of organic substances).
Lake Whillans remains the only Antarctic subglacial ecosystem sampled to date, so our knowledge of life beneath the ice and its role in global processes is still limited. The SALSA project will advance our understanding of organism survival in extreme environments and the interaction between life and climate. The potential historical record stored in subglacial systems, combined with the relative simplicity of this ecosystem, provide powerful tools for understanding the past and future impacts of biogeochemical cycling on the local and global climates. The potentially unique adaptations these organisms use for survival under extreme conditions could also harbor new applications in the biotechnology industry and inform our search for lifeforms on icy worlds throughout the solar system.
Environmental Stewardship
Preventing contamination during subglacial sampling is a top priority for the SALSA project. Introducing surface organisms into the ancient lake environment would not only compromise our samples but also introduce foreign contamination into an ecosystem that has been relatively isolated for tens of thousands of years. A clean drilling approach previously tested in the lab and the field will ensure that we maintain the pristine nature of this habitat. Click this link to learn more: Scientific Stewardship
Sample Collection
The SALSA team will access Lake Mercer via a small hole drilled through 1,000 m (~3,200 ft) of ice covering the liquid water basin below. Equipment will be lowered into the hole to collect samples, take readings, and photograph a subglacial world never before seen by human eyes.
The Niskin sampler, a special container that can be triggered to close at a specific depth, will retrieve water samples for tests in the lab. A CTD instrument containing a cluster of sensors will measure temperature, conductivity, and pressure at various depths in the water column. A remote operated vehicle (ROV) will take more comprehensive water measurements away from the drill hole and record hi-resolution video as operators maneuver it throughout the subsurface lake.
Retrieving sediments from the lake bottom will be essential to helping us understand the effect of historical and contemporary geochemical factors on lifeforms in the lake. A hot water corer will carve out basal ice cores (from the base of the glacier) and a special corer, designed to preserve core-top sediment while capturing a deep core, will collect samples from the bottom of Mercer.
Physiological Characteristics
Any organisms present in the lake must rely on local ions, gases, and solid phase minerals to survive. As on land, different types of organisms obtain their energy/food from different sources, either directly from inorganic compounds or by consuming material produced by another organism. As we study the compounds present in Lake Mercer we can begin to build a kind of “food web” that links the initial sources of energy to final products via all the intermediate organisms that capture, utilize, and transform these compounds to survive.
Measuring the form and amount of various chemicals in the water will allow us to predict the type of metabolism local lifeforms may use to obtain energy. By integrating this information with genomic sequences gathered from ice, water, and sediment samples, we can draw strong inferences on the ability of microbes to grow and convert carbon in Mercer.
The relative importance of chemoautotrophic versus heterotrophic carbon pathways can be determined by measuring carbon isotopes, dissolved organic carbon, methane, and other compounds. Through various sample tests we can determine the quantity, type, and quality of inorganic and organic matter available to organisms as well as the rates of production/consumption for compounds like methane and carbonate. With this knowledge we can begin to trace the path of carbon through the ecosystem and build a model of the metabolic web that supports Lake Mercer’s microbial community.