Soil chronosequences and bacterial communities of the Central Transantarctic Mountains, Antarctica

The Beardmore Glacier region of the Central Transantarctic Mountains (CTAM), approximately 600 km south of the McMurdo Dry Valleys (MDV), has been studied to a much lesser extent than the accessible MDV and other regions of the continent. The CTAM were visited in the 2010/2011 austral summer, and two concurrent studies undertaken; these are presented in the form of manuscripts for publication in peer-reviewed journals, as a thesis by publication. Soil chronosequences in three of the largest ice-free areas (Ong Valley, Mount Achernar, and the Dominion Range), at altitudes above 1600 m along the polar plateau margin, were examined. Transects perpendicular to the current ice edge reveal a gradual increase in soil depth (from 2 cm to > 80 cm to underlying ice), weathering, horizonation, salt content, and a decrease in pH; all of these factors are consistent with increased soil development since time of deglaciation. Such fine scale variation in soil properties, previously overlooked in the CTAM region, cannot be mapped by Soil Taxonomy subgroups, as commonly utilised in Antarctic soil mapping. Patterns of soil thickness, clast abundance and soil chemistry all indicate a bi-modal form of soil development. It is proposed that the soil profile deepens by addition of englacial debris to the subsoil via the sublimation of underlying ice, and the weathering of supraglacial clasts at the soil surface. The molecular characterization of bacterial communities in CTAM soils is the southernmost culture-independent soil survey to date. Community fingerprinting (ARISA) and 16S rRNA gene pyrosequencing demonstrated significantly different bacterial communities between eight discrete CTAM locations (5 at low altitude near the Ross Ice Shelf coast, 3 near the polar plateau > 1600 m). Abiotic environmental variables, especially those related to long-term exposure of soils to the atmosphere, correlate well with inter-site community variation. Mount Howe, the southernmost soil on the planet (87° S), harbours an extremely low biomass bacterial community, of a fundamentally different composition to all other sites. It appears that observed DNA sequences at Mount Howe are the result of atmospherically deposited bacteria, the soil being unable to support edaphic life due to extreme local climatic conditions. These two studies extend previous knowledge of soil development and distribution, and microbial ecology, to the southernmost extent possible. These observations may serve as important baseline data for monitoring of this fragile system in the face of future and ongoing environmental changes