Saturday, 15 July 2006

Phosphate minerals in ornithogenic Cryosols of Maritime Antarctica.

Felipe N.B. Simas1, Carlos E.G.R. Schaefer1, MArtin Saunders2, Vander Freitas de Melo3, Marcelo B. Guerra4, and Robert Gilkes5. (1) Departamento do Solos-Universidade Federal de Viçosa, Campus da Universidade, Viçosa, Brazil, (2) University of Western Australia, Center for Microscopy and Microanalysis – The University of Western Australia, Nedlands, WA, 6009. Australia, Perth, Australia, (3) Universidade Federtal do Parana, Rua dos Funcionários, 1540 - Juvevê 80035-070 - Curitiba - Paraná. Brasil, Curitiba, Brazil, (4) Universidadde Federal de Viçosa, Departamento de Solos – Universidade Federal de Viçosa. Av. PH Rolfs s/n, Viçosa, 36570-000, Minas Gerais. Brasil., Viçosa, Brunei, (5) School of Earth and Geographical Sciences The University of Western Australia, 35 Stirling Highway, Crawley 6009, Perth, Australia

Intense bird activity on coastal ice-free areas of Admiralty Bay, Maritime Antarctica, leads to the formation of the so-called ornithogenic soils. The interaction of P-rich guano with the mineral substrate results in diverse secondary P phases. In the present work XRD, SEM/EDS, TEM/EDS and selective chemical dissolution were used to characterize P-rich phases in ornithogenic cryosols from Admiralty Bay, King George Island. Crystalline Al and Fe phosphates (leucophosophite, minyulite and variscite) occur only at sites directly affected by penguin activity where they constitute up to 30 % of the clay fraction. Highly reactive non-crystalline Al, Si, Fe and P phases are dominant in the clay fraction sometimes accounting for over 50 % of the clay fraction. On abandoned rookery sites on basaltic substrates the interaction between penguin guano and inherited clay-sized minerals has lead to the formation of crystalline Al and Fe phosphates which constitute the large P reserves of these soils. Leaching of P-rich solutions from upslope rookeries affects soils in downslope areas where the phosphate reacts with soil organic matter complexes and allophane-like phases. The extremely high proportions of non-crystalline phases in soils at this locality results in the chemical characteristics of ornithogenic sites and in particular the speciation of phosphate being determined by these highly reactive phases. Knowledge of the chemistry of such phases may be useful in assessing anthropogenic impacts and environmental health in this fragile environment.

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