``What comes up … must come down'': Peat carbon and mineral-interactions in Arctic Coastal tundra

Coastal arctic tundra is a significant landscape unit above 65o N, and in the absence of significant nitrate, sulfate or manganese, these wet, permafrost-influenced soils have few electron acceptors readily available to support microbial anaerobiosis. Based on morphological criteria and satellite photos, we selected 4 drained, thaw-lake basins (DTLBs) of vastly differing ages - 50 to 5500 years, based on 14C-dating efforts near Barrow AK. Replicate 100m transects for each thawed-lake basin were collected using a towable 500 MHz ground-penetrating radar system. Inspection of the raw profiles in the field further suggested points along which 20m-length common-midpoint gathers were also obtained to discriminate contrasting propagation speeds within the top 0.5 m of the surface. At later visits, several SIPRE cores were taken to 0.5 m-depth, and the cores stored frozen until analysis. The cores were measured, and physical/color and mineral data collected to correlate with the CMP velocity-profiles. The point of these measurements was to ascertain the minimum-depth to mineral material below the surficial peats, and to build-up a profile of basin age versus mineral-depth. Availability of inorganic reducing agents may provide a significant constraint on soil microbial C-processing. Minimum-tension microlysimeters (PTFE and iron-free) were deployed along replicate transects in each of 5 basins, and filtered soil-pore water was collected from 0-10 cm, as was filtered, acidified standing water from early June-Sept of both 2009 and 2010. Results of inorganic analyses are presented in a separate poster. Fluorescence spectroscopy was used to monitor seasonal patterns in DOC composition, and fluorescence emission intensity of soil pore-water was inversely proportional to basin age - humic signature emission spectra peaked sharply at 445 nm, and a broader secondary maximum occurred at 500 nm. Fluorescence emission varied 5-fold among basins, and decreased at all sites as soil temperatures warmed. Thermal analysis (TG-DTA) showed clear patterns within soil cores, as the ΔH of combustion decreased with increasing depth. When we compared soil horizons of comparable depth from different-aged basins, we observed significantly higher energy density in the surface peats in the order: Ancient ~ Old > Medium > Young. To achieve a higher degree of molecular detail from humics of different-aged basins, we have employed room temperature electron spin resonance spectroscopy to quantify spins arising from semiquinone radicals. We have not established a simple relationship between ESR spin-density and the combustion-derived measures, and are exploring the possibility that high Fe levels at the site may be robbing intensity from the quinone radicals, with cryoturbation becoming increasingly dominant after 1000+ yrs of basin-evolution.