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.

No description available.

No description available.

Historical climate disturbances such as glacial cycling and fluctuating stream, lake, and sea levels strongly influence the distribution and evolutionary trajectories of Antarctic terrestrial species. Antarctic invertebrates, with limited long-range mobility, including the ubiquitous sentinel nematode species Scottnema lindsayae, are especially sensitive to climate disturbances. We tested hypotheses associated with the historical geographic and population genetic structure of this species as it occurs across the McMurdo Dry Valleys (MDVs) of Antarctica. In order to reconstruct the influence of climate disturbance and ecological conditions on this species, partial mitochondrial COI gene sequences were sequenced and analyzed from individual S. lindsayae collected from sites across the MDVs reflecting a opposing gradients of climate disturbance during the Last Glacial Maximum (LGM). We found that populations were strongly geomorphic barriers with distinct haplotypes associated with valleys except among valleys that experienced glacial advance and retreat during the LGM. One monophyletic clade corresponds with valley systems that were undisturbed during the LGM indicating putative refugia areas. A second monophyletic clade corresponds to recent dispersal and expansion of evolutionarily younger populations into valleys that were strongly reworked by glacial activity during the LGM. Our work shows that contemporary populations of these animals are strongly structured by prior climate history. Such findings can be useful for interpreting long-term monitoring of demographic shifts of soil organisms in response to changing climate trends in the McMurdo Dry Valleys.

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

Satellite investigations have documented Antarctic sea ice area, but are restricted in their ability to provide volume, as the procedure to derive thickness is still under development. This procedure requires the measurement of sea ice freeboard, the segment of ice held above the ocean surface by buoyancy. This measurement can be made by satellite altimeters and in conjunction with density and snow depth information; sea ice thickness can be estimated via the hydrostatic equilibrium assumption. The ability to monitor the spatial and temporal characteristics of the thickness distribution must be improved as we strive to understand the linkages between the glaciological, atmospheric and oceanic components of the Antarctic climate system. A key sector in which these components interact is the Antarctic coast. There, offshore winds drive coastal polynyas creating vast amounts of sea ice, and ice shelf interaction modifies ocean properties. Together they condition the ocean for downwelling, driving the global oceanic circulation. In light of this, the coastal Antarctic is a fundamental region in regard to Antarctic sea ice processes and the Earth climate system. McMurdo Sound occupies a coastal area in proximity to an ice shelf in the south-western corner of the Ross Sea. The sound has witnessed scientific investigation for over a century with a fully established research programme since the 1960s. However, the sea ice research in this region is spatially restricted. This thesis aims to expand the knowledge of sea ice in McMurdo Sound to a larger area using space-borne remote sensing instrumentation and design of in situ measurement campaigns. In doing so, this work evaluates the capabilities of satellite platforms to record sea ice freeboard in the coastal Antarctic, whilst developing knowledge of ice shelf-sea ice interaction. This work provides the first satellite altimeter based investigation of sea ice freeboard in McMurdo Sound using ICESat over the period 2003-2009. No observable trend was observed for first-year sea ice freeboard in the region in line with larger scale assessments in the Ross Sea. However, there was significant increase in the freeboard of a temporary multiyear sea ice regime, the segment of the largest increase linked to the outflow of supercooled Ice Shelf Water (ISW) from the McMurdo and Ross Ice Shelf cavities. This remote sensing assessment supports the in situ and modelling work of many others who have identified the influence of ISW on sea ice processes in this region, in particular, that it is thicker than it would otherwise be. The influence of ISW on altimetric sea ice thickness retrievals was also quantified using a Global Navigation Satellite System (GNSS) evaluation of freeboard to thickness conversion. This revealed that a sub-ice platelet layer, created by supercooled ISW and with an estimated solid fraction of 0.16, accumulates beneath the sea ice cover and influences the thickness estimates from the GNSS-derived surface elevation. A cautionary conclusion is reached that within 100 km of ice shelves this buoyant influence should be considered, and in close proximity (< 50 km) can result in overestimations of sea ice thickness of ~ 12 %. It is also suggested that the sea ice freeboard anomalies that result from enhanced growth, driven by supercooled water advection could be used to map the presence of ISW in the coastal Antarctic. Looking to future ability to monitor Southern Ocean sea ice thickness from space, the first comprehensive evaluation of CryoSat-2 (CS-2) over Antarctic sea ice is provided. Using three separate retracking procedures, CS-2 is shown to be capable of detecting the development of a fast ice cover in McMurdo Sound. The role played by a snow cover with layering typical of the Antarctic appears to cause a positive bias in the ice freeboard for a waveform fitting procedure currently used over Arctic sea ice. The identification of open water and the establishment of accurate sea surface heights are also indicated as causing errors (in the order of cms) in the study region. CS-2 is shown to be capable of recording sea ice growth over two growth cycles in McMurdo Sound. This work has advanced the application of satellite investigative techniques to Antarctic sea ice, providing hope that such techniques may be capable of revealing larger scale connections between sea ice and ice shelves.

No description available.

Reactive halogen species (RHS) are responsible for ozone depletion and oxidation of gaseous elemental mercury and dimethyl sulphide in the polar boundary layer, but the sources and mechanisms controlling their catalytic reaction cycles are still not completely understood. To further investigate these processes, ground– based Multi–Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) observations of boundary layer BrO and IO were made from a portable instrument platform in McMurdo Sound during the Antarctic spring of 2006 and 2007. Measurements of surface ozone, temperature, pressure, humidity, and wind speed and direction were also made, along with fourteen tethersonde soundings and the collection of snow samples for mercury analysis. A spherical multiple scattering Monte Carlo radiative transfer model (RTM) was developed for the simulation of box-air-mass-factors (box-AMFs), which are used to determine the weighting functions and forward model differential slant column densities (DSCDs) required for optimal estimation. The RTM employed the backward adjoint simulation technique for the fast calculation of box-AMFs for specific solar zenith angles (SZA) and MAX-DOAS measurement geometries. Rayleigh and Henyey-Greenstein scattering, ground topography and reflection, refraction, and molecular absorption by multiple species were included. Radiance and box-AMF simulations for MAX-DOAS measurements were compared with nine other RTMs and showed good agreement. A maximum a posteriori (MAP) optimal estimation algorithm was developed to retrieve trace gas concentration profiles from the DSCDs derived from the DOAS analysis of the measured absorption spectra. The retrieval algorithm was validated by performing an inversion of artificial DSCDs, simulated from known NO2 profiles. Profiles with a maximum concentration near the ground were generally well reproduced, but the retrieval of elevated layers was less accurate. Retrieved partial vertical column densities (VCDs) were similar to the known values, and investigation of the averaging kernels indicated that these were the most reliable retrieval product. NO₂ profiles were also retrieved from measurements made at an NO₂ measurement and profiling intercomparison campaign in Cabauw, Netherlands in July 2009. Boundary layer BrO was observed on several days throughout both measurement periods in McMurdo Sound, with a maximum retrieved surface mixing ratio of 14.4±0.3 ppt. The median partial VCDs up to 3km were 9.7±0.07 x 10¹² molec cm ⁻ in 2007, with a maximum of 2.3±0.07 x 10¹³ molec cm⁻², and 7.4±0.06 x 10¹² molec cm⁻² in 2006, with a maximum of 1.05 ± 0.07 x 1013 molec cm⁻². The median mixing ratio of 7.5±0.5 ppt for 2007 was significantly higher than the median of 5.2±0.5 ppt observed in 2006, which may be related to the more extensive first year sea ice in 2007. These values are consistent with, though lower than estimated boundary layer BrO concentrations at other polar coastal sites. Four out of five observed partial ozone depletion events (ODEs) occurred during strong winds and blowing snow, while BrO was present in the boundary layer in both stormy and calm conditions, consistent with the activation of RHS in these two weather extremes. Air mass back trajectories, modelled using the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model, indicated that the events were locally produced rather than transported from other sea ice zones. Boundary layer IO mixing ratios of 0.5–2.5±0.2 ppt were observed on several days. These values are low compared to measurements at Halley and Neumayer Stations, as well as mid-latitudes. Significantly higher total mercury concentrations observed in 2007 may be related to the higher boundary layer BrO concentrations, but further measurements are required to verify this.