NASA Exobiology Grant NNX08AO19G

NSF/OPP Project G-441-M

Dale Andersen - Carl Sagan Center for the Study of Life in the Universe

Dawn Sumner - UC Davis

Ian Hawes - Aquatic Research Solutions

Rebekah Shepard - UC Davis

Alfonos Davila - Carl Sagan Center for the Study of Life in the Universe

Wayne H. Pollard - McGill University

Christopher P. McKay - NASA Ames Research Center

Darlene Lim - Carl Sagan Center for the Study of LIfe in the Universe

Bernard Laval - University of British Columbia

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Our research in Antarctica will support a robust interdisciplinary scientific effort that will investigate the benthic microbial ecosystem found in Lake Joyce, a perennially ice-covered lake in the McMurdo Dry Valleys. The most abundant record of the first ~3 billion years of life on Earth consists of fossilized microbial communities, e.g. stromatolites and microbialites. Modern microbial communities make analogous structures that vary depending on biological and environmental factors. Understanding the early evolution of life depends on inferring biological properties from the remnants of fossilized microbial communities. Most of our understanding of microbialite formation comes from tropical or subtropical locations. We propose to add to our understanding of microbialite formation by investigating modern calcifying microbial communities in Lake Joyce, Antarctica. Previous work on uncalcified mats in Lake Hoare, Antarctica, demonstrates that microscale gradients in water chemistry are directly related to both mat morphology and metabolic activity. Because cyanobacteria are the major primary mat producers in both lakes and cyanobacteria create intricate, calcifying mats in diverse other settings, we hypothesize that the patterns of carbonate precipitation in Lake Joyce record cyanobacterial activity, both morphologically and geochemically, and that microbial influences will be identifiable and applicable to interpreting the origins of ancient microbialites.This study will develop a predictive understanding of what underlies both the development of the ridged and peaked morphology in microbial mats at extreme low temperature and irradiance and how organisms forming these structures interact with water chemistry to form intricate microbialites. While of interest in its own right, when combined with existing research on microbialite formation, this new data from an extreme environment will help set limits for the types of community and environmental conditions that are prerequisites to their formation. Our results will add significantly to the understanding of carbon cycling within the dry valleys and will broaden our understanding of the complex physical-biogeochemical interactions occurring in the water column, in mats, and at the sediment-water interface in MCM lakes. They will contribute to the McMurdo Long Term Ecological Research project whose focus is the physical, chemical and biological linkages of the lakes, streams, soils and glaciers located primarily in nearby Taylor Valley. We will fully characterize carbonate precipitation in the lake, specifically evaluating the roles of lake chemistry and microbial processes. We will conduct in situ measurements to determine rates of primary productivity within the photosynthetic benthic mats of L. Joyce. This will be the second set of such measurements within the MCM lakes (the only other being in Lake Hoare) with a new focus on mats with significant morphological complexity. We will use these data to constrain the origins of mats with intricate topography, specifically evaluating the role microbial properties on the development of topography. We will place results into the context of other modern and ancient microbialites with a strong emphasis on identifying key structures that reflect microbial behaviors. Thus, results from this highly collaborative research effort will provide innovative and novel insights into MCM lacustrine processes and microbial ecology as well as the controls on morphology in microbialites of any age.  Studies of these unique ecosystems, and particularly the adaptive strategies of organisms living in an environment with very low levels of light and low temperature, will also help provide constraints on the ability of life to adapt to episodes of global glaciation, such as the postulated “Snowball Earth” periods that may have taken place several times during the Neoproterozoic (about 550 to 830 Myr ago).