Concretionary horizons, unusual pedogenetic processes and features of sulfate affected soils from Antarctica
Introduction
Overall, Antarctica characterized by a weak soil development, closely related to parent material composition, has been due to a general low chemical weathering (Campbell and Claridge, 1987). The broad variety of climates across the continent directly influences soil properties and their distribution (Bockheim, 2015; Zawar-Reza and Katurji, 2014). Maritime Antarctica, compared to the mainland, has a comparatively mild climate, due to higher temperatures and higher precipitation in liquid form. These milder conditions, when combined with sulfide minerals oxidation and/or greater microbial decomposition of guano, allow a much greater soil development, attaining significant chemical weathering and deep soils for Antarctic standards (Campbell and Claridge, 1987; Michel et al., 2014; Poelking et al., 2015; Schaefer et al., 2015; Simas et al., 2007b, Simas et al., 2007a).
Chemical weathering significantly influences global climate change, earth surface processes, nutrient cycling, oceanic chemical composition and phytoplankton production in ice-free Antarctica coastline (Dold et al., 2013; Souza et al., 2012; van de Flierdt, 2011; Zachos et al., 1999). Also, with increasing human pressure on Maritime Antarctica, better understanding of its terrestrial environment is crucial for developing conservation strategies.
Oxidation of soils formed in sulfidic parent material leads to the reduction of pH below 3.5 and in increase in soluble sulfates which induces formation of iron and aluminum (hydroxi) sulfates, such as jarosite, natrojarosite, schwertmannite, sideronatrite and tamarugite (IUSS Working Group WRB, 2014; Soil Survey Staff, 2014). Acid sulfate soils are detrimental to most plants and, if sufficiently acid at the soil surface, may prevent plant growth. Although acid sulfate soils have been previously reported in Maritime Antarctica (Simas et al., 2007a; Souza et al., 2014), no detailed study about the nature of the sulfide oxidation process in Antarctica and its effect on pedogenesis has been carried out to this day. The objective of the present study is to evaluate the soil genesis from Barton Peninsula along two toposequences developed under sulfides influence, emphasizing active chemical processes in a typical periglacial environment of Maritime Antarctica, and the unusual formation of petroplintite.
Section snippets
Study area
King George Island is part of the South Shetlands Archipelago, western Antarctic Peninsula. The study area is Barton Peninsula, the second largest ice-free area of King George Island, covering about 12 km2 (Fig. 1). The region has a sub-Antarctic maritime climate, with mean air temperature of −1.8 °C, mean summer temperature of 1.6 °C (December through February), and the mean annual rainfall is 437 mm (Shin et al., 2014).
The geology of Barton Peninsula is dominated by volcanoclastic sediments
Material and methods
Seven pedons were selected (Fig. 2), described, sampled and classified according to Soil Taxonomy (Soil Survey Staff, 2014) and WRB (IUSS Working Group WRB, 2014) during the 2014 austral summer. Soil samples were collected from the surface down to the lithic contact or permafrost table, at each soil pedon.
Samples were air dried and sieved through a 2 mm sieve prior to texture and chemical analyzes (EMBRAPA, 1997). Sand, silt and clay were determined by the pipette method after dispersion with
Physical and chemical properties of soils
Four of the seven soils studied were classified as Leptic Cambisol or Petroplinthic Cambisol (IUSS Working Group WRB, 2014), which corresponds to the order of Petraquepts the US Soil Taxonomy (Soil Survey Staff, 2014) (Table 1). An Ornithic–Lithic Leptosol with a strong influence of nesting birds was described, whereas two soils with permafrost were classified as Turbic Cryosols and Psammoturbel (IUSS Working Group WRB, 2014; Soil Survey Staff, 2014), respectively. Further information is
Soil formation processes
Soils from Barton Peninsula showed chemical and mineralogical properties closely related to the sulfidic parent material, to ornithogenesis, or both. Soils were grouped into: a) acid sulfate soils (P2, P3, P4 and P5) derived from pyrite-rich andesite (acid, dystrophic, high P adsorption, goethite in the clay fraction and CIA values above 70); b) alkaline soils (P1 and P6) developed from basalt (eutrophic, neutral pH, low P adsorption, clay fraction dominated by 2:1 minerals and CIA values close
Conclusions
- 1.
Unlike previous studies that considered chemical weathering as insignificant in Barton Peninsula, this study demonstrates that even under typical periglacial conditions in Antarctica, some areas present active chemical weathering processes, such as sulfurization and phosphatization, which cannot be underestimated.
- 2.
The sulfurization and phosphatization (combined or not) are chemical processes that promote strong soil acidification, release exchangeable bases and accelerate mineralogical changes
Acknowledgements
The authors thank CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico), CAPES (Coordenação de Aperfeiçoamento de Pessoal de Nível Superior) and FAPEMIG (Fundação de Amparo à Pesquisa do Estado de Minas Gerais) for financial support. We are grateful to INCT da Criosfera, TERRANTAR and MARINHA DO BRASIL (PROANTAR PROGRAM) for financial support and field assistance.
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2022, CatenaCitation Excerpt :However, the role of lithological diversity in the evolution of periglacial environments are poorly studied. Recent pedological studies in Antarctica have highlighted the importance of substrates in soil-landscape interactions (Francelino et al., 2011; Moura et al., 2012; Michel et al., 2014; Souza et al., 2014; Rodrigues et al., 2019; Lopes et al., 2019, 2021). Snow Island, located in the South Shetlands Archipelago (Fig. 1), is an area with great potential for interpreting landform-soil relationships in a periglacial setting of Maritime Antarctica, because of a great lithological diversity, particularly at President Head Peninsula, the most important ice-free area of the Island.