This study aims to quantify ground ice content and describe the cryostructures and sediment in 15 ice-bearing permafrost cores collected from nine sand-wedge polygons in University Valley. The objectives were reached through laboratory measurements and computed tomodensitometric (CT) scanned image analysis of the permafrost cores. The soils in the valley were predominantly medium-sand. Four types of cryostructures were present in the cores: structureless, suspended, crustal and porphyritic. Excess ice content ranged from 0 to 93%, gravimetric water content ranged from 13 to 1881% and volumetric ice content varied from 28 to 93%. Median excess ice, volumetric ice and gravimetric water contents significantly increased in the top 20 cm of the cores taken from the polygon shoulders with increasing distance from University Glacier. Ground ice was preferentially stored in the centre of the investigated polygons where the ground surface remains cryotic throughout the year. Conversely, higher ground ice contents were measured in the shoulders of the investigated polygon where the ground surface is seasonally non-cryotic. CT-scanned images were shown to reasonably assess the distribution and presence of excess ice in permafrost cores taken from a cold and hyper-arid environment. The results of this thesis provide the first cryostratigraphic study in the McMurdo Dry Valleys of Antarctica.

>Magister Scientiae - MSc / The extreme conditions of Antarctic desert soils render this environment selective towards a diverse range of psychrotrophic microbial communities. Cracks and fissures in translucent quartz rocks permit an adequate amount of penetrating light, sufficient water and nutrients to support cryptic microbial development. Hypolithons colonizing the ventral surface of these quartz rocks have been classified into three types: cyanobacterial dominated (Type I),moss dominated (Type II) and lichenized (Type III) communities. Eukaryotic microbial communities were reported to represent only a minor fraction of Antarctic communities. In this study, culture independent techniques (DGGE, T-RFLP and clone library construction) were employed to determine the profile of the dominant eukaryotes, fungi and microalgae present in the three different hypolithic communities. The 18S rRNA gene (Euk for eukaryotes), internal transcribed spacer (ITS for fungi) and microalgal specific regions of the 18S rRNA gene, were the phylogenetic markers targeted for PCR amplification from hypolith metagenomic DNA. Results suggest that the three hypolith types are characterized by different eukaryotic, fungal and microalgal communities, as implied by nMDS analysis of the DGGE and T-RFLP profiles. Sequence analysis indicates close affiliation to members of Amoebozoa, Alveolata, Rhizaria (general eukaryote), Ascomycota (fungal) and Streptophyta (microalgal). Many of these clones may represent novel species. This study demonstrates that Dry Valley hypolithons harbour higher eukaryote diversity than previously recognised.Each hypolithon is colonized by specialized microbial communities with possible keystone species. The ecological role of the detected microorganisms in the hypolith environment is also theorized, and a trophic hierarchy postulated.

No description available.

No description available.

No description available.

No description available.

No description available.

Recent work in microbial ecology has focused on elucidating controls over biogeographic patterns and connecting microbial community composition to ecosystem function. My objective was to investigate the relative influences of landscape legacies and contemporary environmental factors on the distribution of soil microbial communities and their contribution to ecosystem processes across a glacial till sequence in Taylor Valley, Antarctica. Within each till unit, I sampled from dry areas and areas with visible evidence of recent surface water movement generated by seasonal melting of ephemeral snow packs and hillslope ground ice. Using T-RFLP 16S rRNA gene profiles of microbial communities, I analyzed the contribution of till and environmental factors to community similarity, and assessed the functional potential of the microbial community using extracellular enzyme activity assays. Microbial communities were influenced by geochemical differences among both tills and local environments, but especially organized by variables associated with water availability as the first axis of an NMDS ordination was strongly related to shifts in soil moisture content. CCA revealed that tills explained only 3.4% of the variability in community similarity among sites, while geochemical variables explained 18.5%. Extracellular enzyme activity was correlated with relevant geochemical variables reflecting the influence of nutrient limitation on microbial activity. In addition, enzyme activity was related to changes in community similarity, particularly in wet environments with a partial Mantel correlation of 0.32. These results demonstrate how landscape history and environmental conditions can shape the functional potential of a microbial community mediated through shifts in microbial community composition. / Master of Science

No description available.

No description available.