No abstract

Studies of C cycle alterations are extremely important to identify changes due to climate change, especially in the polar ecosystem. The objectives of this study were to (i) examine patterns of soil CO2-C and N2O-N emissions, and (ii) evaluate the quantity and quality of soil organic matter across a glacier retreat chronosequence in the Maritime Antarctica. Field measurements were carried out during January and February 2010 (summer season) along a retreating zone of the White Eagle Glacier, at King George Island, Maritime Antarctica. Soil samples (0-10cm) were collected along a 500-m transect at regular intervals to determine changes in soil organic matter. Field CO2-C emission measurements and soil temperature were carried out at regular intervals. In addition, greenhouse gas production potentials were assessed through 100days laboratory incubations. Soils exposed for a longer time tended to have greater concentrations of soluble salts and possess sandier textures. Total organic C (3.59gkg(-1)), total N (2.31gkg(-1)) and labile C (1.83gkg(-1)) tended to be lower near the glacier front compared with sites away from it, which is correlated with decreasing degree of humification of the soil organic matter with exposure time. Soil CO2-C emissions tended to increase with distance from the glacier front. On average, the presence of vegetation increased CO2-C emissions by 440%, or the equivalent of 0.633g of CO2-C m(-2)h(-1). Results suggest that newly exposed landsurfaces undergo soil formation with increasing labile C input from vegetation, accompanied by increasing soil CO2-C emissions. Despite the importance of exposure time on CO2-C production and emissions, there was no similar trend in soil N2O-N production potentials as a function of glacial retreat. For N2O, instead, the maximum production occurred in sites with the first stages of vegetation growth.

Thawed soils in Antarctica represent organic carbon (C) reservoirs with great potential to increase the net losses of CO 2 to the atmosphere under climate change scenarios. This study spatially zones CO 2 emissions from soil and vegetation along a transect in front of the retreating margin of Ecology Glacier in Admiralty Bay, King George Island, South Shetlands, near the Polish Antarctic station Henryk Arctowski. Two experiments were carried out to determine soil respiration: (1) a transect of 150 measuring points spaced 1 m apart, statistically analysed with split moving windows, identified three regions with different patterns of CO 2 emissions; (2) a survey with three grids containing 60 sampling points, with a minimum distance between points of 0.30 m, totalling 2.7 × 1.5 m, in each of the identified locations. The survey showed that CO 2 emission rates decreased (from 2.38 to 0.00 μmol m -2 s -1 ) and soil temperature at 5 cm depth increased (from 1.9 to 7°C) near the glacier. The site farthest from the glacier provided an emission 3.5 times higher than the closest site. The spatial variability of CO 2 emissions decreased with distance from the glacier. Soil development and vegetation are identified as key drivers of CO 2 emissions. Soil formation and vegetation growth increased with longer exposure since deglaciation, leading to enhanced homogeneity of CO 2 emissions, independent of permafrost occurrence and stability.

No abstract

O Complexo Campos Gerais é um fragmento da crosta siálica Arqueana, situado no extremo sudoestedo Cráton do São Francisco. Com base em critérios de campo e petrografia, foi possível subdividirseus componentes ortognaissicos em dois grupos. O Ortognaisse Campos Gerais possui como principalcaracterística sua estrutura migmatítica e composição tonalítica a monzogranítica. O Ortognaisse Serrado Quilombo caracteriza-se pelo seu bandamento composicional irregular herdado da deformação deuma suíte de rochas tonalíticas e graníticas. As paragêneses metamórficas observadas, com presença deortopiroxênio metamórfico reliquiar, indicam que o primeiro evento metamórfico da região atingiu a fáciesgranulito, durante o Arqueano, sendo responsável pela sua migmatização. Os ortognaisses são intrudidospor corpos circunscritos de metatonalitos e pelos leucogranitos Córrego do Sapateiro e Itapixé. Todas asunidades litodêmicas sofreram metamorfismo em fácies xisto-verde durante o Neoproterozóico. Os elementosmetamórficos e estruturais presentes no conjunto sugerem que a região funcionou como antepaís durante aorogenia paleoproterozóica, e foi afetada por zonas de cisalhamento sinistrógiras durante o Neoproterozóico,relacionadas ao evento Brasiliano.Palavras-chave: Arqueano; TTG; Cráton do São Francisco. ABSTRACT: The Campos Gerais Complex is a fragment of typical Archean continental crust, located in the southwestborder of the São Francisco Craton. Based on field and petrographic criteria, the ortogneiss unit was separatedin two: the Campos Gerais Orthogneiss has migmatitic structure and compositional range from tonalite tomonzo-granite, with presence of relict orthopyroxene; and the Serra do Quilombo Orthogneiss, caracterizedby compositional banding, developed from the deformation of cross-cutting tonalitic to granitic rocks. Thepresence of orthopyroxene indicates that the first metamorphic event ocurred in granulite facies during theNeoarchean, and was responsible for the migmatization of the Campos Gerais orthogneisses. The migmatiticorthogneisses were intruded by homogeneous metatonalitic bodies and by the Córrego do Sapateiro adItapixé leucogranites. All rock units suffered Neoproterozoic upper greenschist facies metamorphism. Themetamorphic and structural features suggest that the region worked as the foreland zone to the Paleoproterozoicorogeny, and was transected by sinistral Neoproterozoic mylonite zones related to the Brasiliano event.