Physicochemical and Biological Controls on Carbon and Nitrogen in Permafrost from an Ultraxerous Environment, McMurdo Dry Valleys of Antarctica

Abstract

Little is known about the abundance and source of soil organic carbon and biogeochemical cycling in permafrost soils from the ultraxerous environment of the Dry Valleys of Antarctica. Here we investigate the distribution, source and cycling of organic carbon, total nitrogen and carbonates in the icy permafrost soils of University Valley, Quartermain Mountains. Results indicate that organic carbon content is lowest in icy soils from the perennially cryotic zone (<40 μg g−1 dry soils) and higher in the icy soils from the seasonally noncryotic zone, where the highest concentrations were found in the warmer‐wetter section of the valley and near a frozen pond (up to 313 μg g−1 dry soils). The δ13Corg of organic carbon in the icy soils showed that it is derived from the weathering of Beacon Supergroup sandstone that hosts active endolithic communities. The C:N ratios in icy soils formed two populations: one with ratios <5 and the other with ratios near the Redfield ratios. The low C:N ratios suggest that physicochemical processes dominates these soils, as supported by the absence of microbial activity and atmospherically deposited NO3 with minimal postdeposition modification. The near Redfield C:N ratios can be explained by physical processes (translocation of SOC in the soils from snow meltwater) or balanced microbial activity. The latter is supported by the δ13CCaCO3 values of carbonates that suggest a contribution from microbially respired endolith‐derived organic matter, providing indirect evidence of heterotrophic activity in permafrost soils from an ultraxerous environment.

Low Energy Subsurface Environments as Extraterrestrial Analogs

“…Temperatures in these environments rarely reach above freezing, resulting in a soil profile almost exclusively of permafrosts. These are oligotrophic systems, with potential electron acceptors such as nitrates, sulfates, and perchlorates as well as electron donors such as formate, acetate, and other small organic acids are present in these primarily mineral soils ( Kounaves et al, 2010b ; Parro et al, 2011 ; Jackson et al, 2016 ; Faucher et al, 2017 ).…”

Reconstructing 15 Myr of environmental change in the McMurdo Dry Valleys through permafrost geochemistry

“…0.11 ± 0.09 mg g -1 dry soil). These values are much higher than those found in other ultraxerous surfaces like University Valley (Faucher et al, 2017) and sites in the Mackay Glacier region (Van Goethem et al, 2020). While the biochemical signature of lower units of the core are compatible with their paleoenvironments, the upper samples (<1 m) show a clear shift attributable to post-depositional conditions.…”

“…Barrett et al, 2007a, Van Goethem et al, 2020. For instance, C:N ratios in the perennially cryotic zone of University Valley were well below ratios associated with biological processes (<1.5; Faucher et al, 2017).…”

“…Head III, 2007). These ambient conditions make the stable uplands inhospitable, supporting exclusively endolithic microbial communities and heterotrophic microbial communities in the sediment (Faucher et al, 2017).…”

“…Autochthonous primary production by mosses, lichens, terrestrial cyanobacteria and algae is limited to the low elevations (Friedmann and Ocampo, 1976, Friedmann, 1982, Schwarz et al, 1992, Friedmann et al, 1993, Seppelt and Green, 1998, Pannewitz et al, 2005, Novis et al, 2007. The high elevations lack all types of vascular and cryptogamic vegetation and support exclusively endolithic microbial communities, which grow in the interstitial spaces in fissures rocks, and heterotrophic microbial communities in the sediment (Faucher et al, 2017). The presence of terrestrial heterotrophs can be explained by potential external sources of C org and N such as modern lacustrine cyanobacteria detritus (e.g.…”