Micromorphological and microchemical indicators of pedogenesis in Ornithogenic Cryosols (Gelisols) of Hope Bay, Antarctic Peninsula

Abstract

Micromorphological investigations of Antarctic soils are comparatively scarce, however, they could help understand the genesis of cryogenic soils under extreme polar conditions and different biotic factors. In most areas of Maritime Antarctica, the soil structure is apparently influenced by the local lithology, cryoturbation, guano deposition and reaction of guano solutions. The present study was carried out in Hope Bay, in the northern part of the Antarctic Peninsula, possibly one of the oldest sites of penguin occupation in the region. We describe and analyze the most important micro and sub-microscopic features of selected Ornithogenic Cryosols (Gelisols) from this part of Antarctic Peninsula, representing a transitional climatic zone between the wetter South Shetlands and the much drier Weddell Sea sector. Nine pedons representing the main ornithogenic soils found in ice-free areas of Hope Bay were selected for the micromorphological study. Undisturbed soil blocks were sampled at different depths, ranging between 0 and 30 cm. The microstructure and sub-microstructure were further investigated using a JEOL 8200 and a Zeiss scanning electron microscopes, both coupled with an microprobe (SEM/WDS). These pedons have a very limited surface accumulation of organic matter formed by mosses and lichens, changing abruptly to a mineral phosphatic horizon of bleached colours, and usually hardcemented by ice. A small to medium-sized granular structure is generally observed, with ovoidal, subrounded forms, including several well-defined ornithogenic materials, such as P-rich organic remains, nodular phosphates forms and minute fragments of bone apatite. The chemical composition of ornithogenic materials and phosphatic coatings indicates the presence of discrete forms of taranakite, minyulite, leucophosphite, struvite and fluorapatite, typical of phosphatization process in these soils. Phosphatization and enhanced chemical alteration of the substrate and is one of the main soil-forming process in ornithogenic soils, resulting in P-rich ovoidal aggregates formation. P-rich solutions penetrate desiccation fractures and cleavage planes in large clasts and react preferably with plagioclases. P reacts with Al and Fe to form various amorphous and crystalline P phases. Present day permafrost cementation of deeper phosphate layers indicate that warmer/wetter conditions occurred in the past, during which P was leached downwards and reacted with the rock substrates, developing stable ovoidal aggregates, now incorporated in ice-cemented subsurface horizon.

Interpreting environmental changes from radionuclides and soil characteristics in different landform contexts of Elephant Island (maritime Antarctica)

“…Another main factor of soil formation is the biological activity, both by fauna and flora effects. Among the best developed soils in maritime Antarctica are those derived from bird colonies; the Ornithogenic soils have large amounts of nutrients (e.g., Moura, Francelino, Schaefer, Simas, & Mendonça, ; Pereira, Schaefer, Ker, Almeida, & Almeida, ; Tatur & Myrcha, ) that further influence soil processes involving the mobilization of chemical elements (Otero, Fernández, de Pablo, Nizoli, & Quesada, ; Quayle, Peck, Peat, Ellis‐Evans, & Harrigan, ). In Cryosols of King George Island, Simas et al () found that noncrystalline phases reach as much as 75% of the clay fraction for some Ornithogenic soils and crystalline Al and Fe phosphates occur in the clay at sites directly affected by penguin activity.…”

Characterization of products of the early stages of pedogenesis in ornithogenic soil from Maritime Antarctica

“…We studied the short-range order inorganic phases and organo-mineral complexes in the clay fraction of selected Antarctic soils because the crystalline minerals have been discussed widely by other authors (Tatur, 1989;Simas et al, 2007;Pereira et al, 2013). In addition, we proposed an extended sequential extraction procedure, adapted from Simas et al (2006) and Mendonça et al (2013a), to characterize the short-range order phases of the clay fraction of Antarctic soil better.…”

Paisagens Polares Não Glaciais (Proglacial, Paraglacial E Periglacial): Revisão De Conceitos E Constribuições Da Pesquisa Pedogeomorfológica Brasileira

“…Os resultados encontrados por essas pesquisas têm comprovado que a região da Península Antártica e o Arquipélago das Shetlands do Sul apresentam maiores temperaturas e precipitação em comparação com outras partes da Antártica (Vieira et al, 2010;Chaves et al, 2017), propiciando estabelecimento mais efi ciente de processos pedogenéticos e a consequente consolidação de sistemas periglaciais (Francelino et al, 2011;Moura et al, 2012). Os principais processos de formação de solo atuantes na região incluem a translocação de argilas, o tiomorfi smo, podzolização e a fosfatização (Simas et al, 2007;Simas et al, 2008;Pereira et al, 2013;Michel et al, 2014;Lopes et al, 2017;Daher et al, 2019). A diversidade pedológica está relacionada principalmente à diversidade do material de origem, colonização biológica atual e pretérita, e ocorrência e distribuição do permafrost (Simas et al 2008;Moura et al 2012).…”