Geochemical zones and environmental gradients for soils from the Central Transantarctic Mountains, Antarctica

Abstract

Abstract. Previous studies have established links between biodiversity and soil geochemistry in the McMurdo Dry Valleys, Antarctica, where environmental gradients are important determinants of soil biodiversity. However, these gradients are not well established in the Central Transantarctic Mountains, which are thought to represent some of the least hospitable Antarctic soils. We analyzed 220 samples from 11 ice-free areas along the Shackleton Glacier (~ 85 °S), a major outlet glacier of the East Antarctic Ice Sheet. We established three zones of distinct geochemical gradients near the head of the glacier (upper), central (middle), and at the mouth (lower). The upper zone had the highest water-soluble salt concentrations with total salt concentrations exceeding 80,000 µg g-1, while the lower zone had the lowest water-soluble N : P ratios, suggesting that, in addition to other parameters (such as proximity to water/ice), the lower zone likely represents the most favorable ecological habitats. Given the strong dependence of geochemistry with geographic parameters, we established multiple linear regression and random forest models to predict soil geochemical trends given latitude, longitude, elevation, distance from the coast, distance from the glacier, and soil moisture (variables which can be inferred from remote measurements). Confidence in our model predictions was moderately high, with R2 values for total water-soluble salts, water-soluble N : P, ClO4-, and ClO3- of 0.51, 0.42, 0.40, and 0.28, respectively. These modeling results can be used to predict geochemical gradients and estimate salt concentrations for other Transantarctic Mountain soils, information that can ultimately be used to better predict distributions of soil biota in this remote region.

Exploring the Boundaries of Microbial Habitability in Soil

“…Sites ranged in elevation from ∼150 to 2,221 m above sea level (m.a.s.l) and most soils are likely to have been exposed for prolonged periods of time, with the approximate time since last wetting (estimated from ClO 4 − concentrations, Jackson et al., 2015, 2016) ranging from <10 years to >2 million years (mean: ∼20,000 years). Not surprisingly given the absence of plants in this region, the measured soil organic carbon concentrations were low, from ∼3 to 60 mg × g soil −1 (mean = 13 mg × g soil −1 ), and most of the collected soils have high soluble salt concentrations (Diaz et al., 2021). As expected, the soils contained almost no water at the time of collection (0.001–0.11 g H 2 O × g dry soil −1 , mean of 0.02 g H 2 O × g dry soil −1 ).…”

“…As expected, the soils contained almost no water at the time of collection (0.001–0.11 g H 2 O × g dry soil −1 , mean of 0.02 g H 2 O × g dry soil −1 ). In general, soils located further inland at higher elevations were drier, saltier, and contained less organic carbon (Diaz et al., 2021). These soil characteristics are not unique to the Shackleton Glacier region as ice‐free soils found in other regions of Antarctica have comparable edaphic characteristics (Bockheim, 1997; Magalhães et al., 2012).…”

“…A more parsimonious explanation is that these variables are indicative of a suite of environmental properties that together restrict microbial life. Elevation likely correlates with a number of variables that increase in magnitude further inland and higher in elevation in the Shackleton Glacier region that may reduce microbial habitability: higher UV radiation, lower temperatures, lower water availability, and increased soluble salt concentrations (Diaz et al., 2021). The accumulation of high concentrations of chlorate salts, on the other hand, may influence habitability due to its toxic properties but this seems unlikely due to the fact that we observed soils with detectable and undetectable microbial communities in close proximity across this region (Figure 1).…”

“…Soils (0–5‐cm depth) were collected in sterile polyethylene bags using hand trowels that were sterilized with ethanol before each collection. Approximately 2–5 kg of soil was collected from each location and, after thorough homogenization, a 50–100 g subsample was used for downstream microbial analyses (Diaz et al., 2021). GPS coordinates, photographs of the soil surface, elevation, and other metadata were collected at the time of soil sample collection.…”

“…Anions were analyzed using a Dionex ICS‐2100 ion chromatograph and an AS‐DV automated sampler. Cations were analyzed by optical emission spectrum on a PerkinElmer Optima 8300 inductively coupled plasma mass spectrometer (ICP‐OES) (Diaz et al., 2021). Relative soil exposure ages were estimated using perchlorate concentrations in 1:5 soil to water leaches and annual fluxes from the McMurdo Dry Valleys, Antarctica.…”