Origin and distribution of soil organic matter in Taylor Valley, Antarctica

Soil organic matter in the dry valleys of the McMurdo Sound Region sustains a unique terrestrial microbial community in one of the most extreme climat es on earth. The origin of this organic material has long been in question, given the absence of higher plants in this arid ecosystem. We examined the sources and distribution of organic matter from six elevational transects extending along a 30-km section of Taylor Valley (163 degrees E, 77.35 degr ees S), from the head of the valley to the Ross Sea. The delta(13)C and del ta(15)N of soil were determined both to identify potential sources of soil organic matter (i.e., marine, lacustrine, and/or terrestrial) and to map C and N source distribution in the valley. Results suggest that the primary s ource for soil organic matter is not the wind transport of organic material from modern aquatic systems (a long-held hypothesis). Instead, our data in dicate that modern distributional patterns of low-elevation (<150 m above s ea level [a.s.l.]) soil organic matter (SOM) in Taylor Dry Valley are stron gly influenced by the climatic history of the region, with the isotopic sig natures of SOM along the valley door corresponding to the spatial distribut ion of ancient glacial tills and lacustrine systems. At many sites, higher elevation soils (>150 m a.s.l.) have isotopic signatures similar to those o f autotrophs currently inhabiting nearby cryptoendolithic communities, sugg esting that similar autotrophic activity may be occurring in these soils an d that longterm primary productivity in dry valley soils contributes to org anic matter accumulations. Taken together, these findings support a new "le gacy" model for soil organic matter origins and fluxes in the dry valley ec osystem.