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 climates 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° E, 77.35° S), from the head of the valley to the Ross Sea. The δ13C and δ15N 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 source for soil organic matter is not the wind transport of organic material from modern aquatic systems (a long-held hypothesis). Instead, our data indicate that modern distributional patterns of low-elevation (<150 m above sea level [a.s.l.]) soil organic matter (SOM) in Taylor Dry Valley are strongly influenced by the climatic history of the region, with the isotopic signatures of SOM along the valley floor corresponding to the spatial distribution of ancient glacial tills and lacustrine systems. At many sites, higher elevation soils (>150 m a.s.l.) have isotopic signatures similar to those of autotrophs currently inhabiting nearby cryptoendolithic communities, suggesting that similar autotrophic activity may be occurring in these soils and that long-term primary productivity in dry valley soils contributes to organic matter accumulations. Taken together, these findings support a new “legacy” model for soil organic matter origins and fluxes in the dry valley ecosystem.