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), its central part (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 and/or ice), the lower zone likely represents the most favorable ecological habitats. Given the strong dependence of geochemistry on geographic parameters, we developed 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 random forest model predictions was moderately high with R2 values for total water-soluble salts, water-soluble N:P, ClO4-, and ClO3- of 0.81, 0.88, 0.78, and 0.74, 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.

Elevational Constraints on the Composition and Genomic Attributes of Microbial Communities in Antarctic Soils

“…For example, the sampling locations ranged in elevation from ∼100 m to over 2,000 m above sea level (ASL), and these soils contained a wide range of concentrations of soluble salts (average, 5.7 × 10 3 mg/kg; range, 12.6 to 6.7 × 10 4 mg/kg). Due to the ambient temperatures being well below freezing for most of the year, water availability in these soils is low, and most soils have had prolonged periods of time since the last wetting (mean age since the last wetting, ∼20,000 years) ( 2 ). In general, higher-elevation soils were farther from the Ross Ice Shelf, drier (based on the age of the last wetting as estimated by Diaz et al [ 2 ]), and saltier and contained less organic carbon ( 2 , 29 ).…”

“…Ice-free surfaces in Antarctica represent >54,000 km 2 (∼0.5%) of the total land area of the continent, and most of these ice-free areas are located >5 km from the coast ( 1 ). These inland soils can vary in age, from incipient soils that were recently covered in ice to soils that have been ice-free and developing in place for thousands of years or even longer ( 2 ). The environmental conditions and geochemical characteristics of Antarctic soils can be highly variable ( 3 – 5 ).…”

“…However, nearly all of these soils developed under extremely cold and dry conditions—some of the coldest and driest conditions on Earth ( 6 ). Most Antarctic soils have extremely low organic carbon concentrations ( 7 , 8 ), and the nearly complete absence of liquid water can lead many Antarctic soils (particularly those at higher elevations) to accumulate high concentrations of salts over time ( 2 ). These salts include nitrate (NO 3 − ), sulfate (SO 4 2− ), perchlorate (ClO 4 − ), and chlorate (ClO 3 − ) salts derived from atmospheric deposition and chemical weathering ( 2 , 3 , 9 ).…”

“…Most Antarctic soils have extremely low organic carbon concentrations ( 7 , 8 ), and the nearly complete absence of liquid water can lead many Antarctic soils (particularly those at higher elevations) to accumulate high concentrations of salts over time ( 2 ). These salts include nitrate (NO 3 − ), sulfate (SO 4 2− ), perchlorate (ClO 4 − ), and chlorate (ClO 3 − ) salts derived from atmospheric deposition and chemical weathering ( 2 , 3 , 9 ). Despite extremely challenging conditions, Antarctic soils can harbor diverse and active microbial communities ( 4 , 10 ).…”

“…This region (∼84.5°S to 86.4°S, ∼174.1°W to 177.4°W) includes many ice-free features adjacent to an ∼130-km-long and ∼10-km-wide south-north outlet glacier of the East Antarctic Ice Sheet (EAIS). These soils are highly variable with respect to their ages (amount of time ice-free), geochemistries, and other site conditions (including elevation, temperature, and moisture availability [ 2 ]). We analyzed the prokaryotic communities in these soils by coupling a variety of cultivation-independent analyses, including quantitative PCR (qPCR), marker gene amplicon sequencing, and shotgun metagenomic sequencing.…”