August 27 - Trista Vick-Majors
There is a large liquid water reservoir beneath the Antarctic ice sheet (~107 km3), and to date, ~400 subglacial lakes have been identified in West and East Antarctica. It has been hypothesized that dark chemosynthetic microbial ecosystems exist at subzero temperatures at the ice sheet bed, but direct observations have been lacking. Subglacial Lake Whillans (SLW) lies beneath ~800 m of ice on the lower portion of the Whillans Ice Stream in West Antarctica and is part of an extensive and active hydrological system. The subglacial drainage network regulates water transport to a subglacial estuary at the edge of the Antarctic continent, linking the hydrological system to the sub-ice-ocean cavity beneath the Ross Ice Shelf. The drilling location to access SLW was selected using reflection seismology and ice-penetrating radar data, and corresponded to the region of maximum predicted water column thickness, lowest hydropotential, and largest satellite-measured surface elevation changes.
During January 2013, a hot water drilling system was used to create a ~0.6 m diameter borehole through the overlying ice sheet into SLW, allowing for physical measurements and the direct collection of water column and sediment samples. The water column of SLW contained metabolically active microorganisms and was derived primarily from glacial ice melt with solute sources from lithogenic weathering and a minor seawater component. The water showed oxygen under-saturation and N:P molar ratios implied a biologically nitrogen deficient environment, relative to phosphorus. Rate experiments revealed that chemoautotrophic primary production in SLW was adequate to support heterotrophic metabolism in the subglacial ecosystem. The most abundant microorganisms in the SLW water column were most closely related to chemolithoautotrophic species that use reduced nitrogen, iron, or sulfur compounds as energy sources. These new data indicate that environments beneath the world’s major ice sheets support viable ecosystems and corroborate previous reports suggesting that subglacial microbial communities can mobilize elements from the lithosphere, influence marine geochemical and biological systems, and significantly affect climate during deglaciation. Given the prevalence of subglacial water in Antarctica, our data from SLW lead us to contend that aquatic microbial ecosystems are common features of the subsurface environment that exists beneath the Antarctic ice sheet.
Antarctic subglacial lakes have been repeatedly identified as some of the most promising terrestrial analogs for potential life habitats on icy bodies and moons in the solar system. Further, the scientific exploration of subglacial lakes presents similar technological and scientific challenges and requires analogous concern about forward contamination as astrobiological studies of other planetary bodies. The sampling and analysis of a sub-ice aquatic environment experiencing long-term isolation from solar energy and atmospheric input has broadened our understanding on the extent of Earth’s biosphere, providing information that will aid in defining the limits and survivability of life in the sub-ice oceans of Europa, Enceledus, Ganymede, and Titan.
