The McMurdo Dry Valleys comprise some 4,800km2 of ice-free terrain in east Antarctica and this constitutes the coldest and most arid desert on Earth. The ecosystem of the Dry Valleys is characterized by microbial processes since environmental extremes severely limit higher plant and animal life. A major international collaborative research effort co-ordinated by the International Center for Terrestrial Antarctic Research (ICTAR), identified long-term study sites representative of maritime and inland Dry Valleys environments. The maritime site, Miers Valley, has been the subject of intensive multi-disciplinary study in recent years, of which the work in this thesis is a part. Previous studies have identified soil microbial communities and their putative functional roles, but lithic communities have not been previously appreciated. This thesis reports aspects on the biodiversity and ecology of lithic microbial communities in Miers Valley. A survey of terrain revealed extensive weathered granite, but no porous sandstone or limestone rocks more commonly associated with cryptoendolithic communities (those colonizing pore spaces within rock substrates). Granite was extensively colonized (30-100% of available substrate) by chasmoendolithic microorganisms (colonizing cracks and fissures in weathered rock). Visual examination of colonized rocks revealed a distinct zone of biomass 2-5mm below the rock surface, and this was overlain by a weathered and friable matrix of rock. Microscopy revealed a community dominated by diverse cyanobacterial morphotypes, plus other unidentifiable microbes of varied morphology. A quantitative approach to broad-scale community fingerprinting was adopted, utilizing terminal restriction fragment length polymorphism (TRFLP) and sequence based identifications of restriction fragments. The multi-domain approach encompassed Archaea, Bacteria and Eukarya. The results revealed relatively low species richness (0.6-1.8) for each domain with community richness estimates also relatively low (<3). Nonetheless very clear and statistically supported patterns in the occurrence of phylotypes within chasmolithic communities were related to aspect (which strongly affects temperature and moisture availability in Dry Valleys locations). The bacterial assemblages formed two groups (cold-dry south facing slopes and valley floor moraine). The eukaryal assemblages also formed two groups although here the moraine samples grouped with the warmer wetter north facing slope and the cold-dry south facing slope assemblages formed a separate group. The archaeal assemblages displayed no difference within different valley terrain. Extensive sequence based interrogation of community structure using clone libraries revealed a community dominated by cyanobacteria, Actinobacteria, Deinococci and putative lichens. These phyla are all known for their extreme tolerance to desiccation and occurrence in arid landscapes. Phylogenetic analysis revealed that these abundant taxa shared close affiliation with those from other Antarctic refuge niches such as hypoliths and cryptoendoliths. The cyanobacteria were mainly Oscillatoriales, but other genera such as Chroococcidiopsis and Nostoc commonly recovered in hot desert lithic communities were generally absent. The eukaryal community was dominated by chlorophyte algae, whilst the archaeal phylotypes were a diverse collection spanning both euryachaeal and crenarchaeal lineages. Overall the data revealed the chasmoendolithic community in Miers Valley was widespread and with relatively restricted diversity. The selection pressures related to topology of the valley have resulted in different community structure within the valley. / published_or_final_version / Biological Sciences / Master / Master of Philosophy

Cryoconite holes are vertical columns of meltwater within the shallow subsurface of glaciers. In the McMurdo Dry Valleys (MDV) of Antarctica cryoconite holes are a source of meltwater and harbor microbial communities in an otherwise arid environment with low biologic activity. The holes form as sediments on the ice surface, which are darker than the surrounding ice, are preferentially heated by solar radiation. The warm sediments melt the underlying ice and migrate downwards. An ice lid forms, isolating them from the below-freezing atmosphere enabling them to remain thawed. In this study, field observations, laboratory experiments, and numerical modeling are used to characterize the fundamental variables controlling cryoconite hole development. Field and laboratory results show that solar radiation drives cryoconite hole melting by controlling the energy available to the cryoconite and to warm the surrounding ice. Holes deepen further in warmer ice. Laboratory results show that at temperatures of -10º C at least 405 (W m-2) are needed to warm the cryoconite sufficiently to melt surrounding ice. Numerical modeling shows that increased radiation flux into the subsurface and warmer air temperatures cause cryoconite to descend deeper and the meltwater-filled holes to enlarge, while increased surface ablation decreases their average depth. Cryoconite holes thaw sooner and refreeze later when the optical properties of the ice facilitate greater radiation transmission. Cryoconite warms the ice significantly more than ice without cryoconite. Within the melt-filled hole, the heat capacity of the water keeps the surrounding ice warm for several weeks after the cryoconite-free ice has cooled. The cryoconite itself is last to completely freeze.

Extreme environments provide a unique source of often highly adapted and tolerant organisms. Research on organisms in these habitats has led to the discovery of novel and useful compounds and may assist in understanding the impact of global change on biodiversity. The Dry Valleys of Eastern Antarctica are vast, ice-free regions believed to be the coldest, driest desert on Earth. Despite these harsh conditions, there is an increasing amount of evidence demonstrating that the soil ecosystems of the Dry Valleys sustain a wide diversity of microorganisms. The research presented is an inter-valley comparison study which aims to scrutinize microbial communities and environmental factors driving their distribution in the Dry Valleys. Automated ribosomal intergenic spacer analysis (ARISA) was used to provide a snapshot of bacterial and cyanobacterial communities living in the mineral sands in Miers Valley, Beacon Valley, Upper Wright Valley and at Battleship Promontory. Rigorous analysis of physico-chemical differences between the soils of these four valleys was undertaken in hope to understand the environmental parameters driving the distribution and biodiversity of microbial communities present. Multivariate statistical analysis and ordination of ARISA and physico-chemical data revealed that bacterial communities from each valley form distinctive clusters. Conversely, cyanobacterial communities showed less diversity and a more even distribution between valleys.

Isotropic ice samples containing measured concentrations of solutes and debris similar to basal material found in several cold-based glaciers in the McMurdo Dry Valleys, Antarctica, were manufactured in a laboratory and tested for peak shear strength at constant strain rates with a direct-shear device. The shear tests show that differences in rheology and shear strength appear to be related to impurity content and concentration. Debris-laden ice becomes more ductile with greater concentrations of solutes, whereas, low solute-concentrations and high debris-concentrations are associated with increases in shear strength and brittle behaviour. Stress exponents from Glen�s flow law calculated for isotropic solute and debris-laden ice ranged between 4 and 5, leading to the conclusion that higher rates of deformation may be expected in dirty basal ice than predicted for glacial ice models that use stress exponents where, n = 3. Observations of both natural and synthetic samples tested over a range of temperatures between -25�C and -5�C showed that natural basal ice samples containing high solute and debris concentrations were highly sensitive to temperature change. These tests showed an approximate 10 % loss in shear strength for every 1�C increase in temperature between -25�C and -10�C. In addition, contrasts in rheology and rates of deformation within basal ice are responsible for the development of debris-laden ice structures in the basal zones of cold-based glaciers that flow over unconsolidated substrates. As layered sedimentary bedding was preserved in frozen blocks within the deforming basal ice of several of these glaciers, the evidence suggests that at some point each glacier has interacted with its bed and entrained portions of the substrate material. Empirical shear strength data and observations of rheological changes attributed to composition together with evidence acquired during fieldwork in Antarctica help to support the argument that cold-based glaciers flowing over unconsolidated sediment are capable of affecting geomorphic change. Hence, isotropic ice models that exclude basal processes may need to be adjusted, especially where small increases in the temperature of the basal zones of cold glaciers may occur. In conclusion, palaeo-climate inferences based purely upon small amounts of geomorphic evidence, which suggest warmer climate conditions, may need to be re-evaluated in order to portray more accurate renditions of formerly glaciated landscapes.

The composition of ice from four case studies based on the facies, solute, stable isotope, and debris content reveals compositional differences reflective of different modes of ice formation. In Southern McMurdo Sound, there is a distinctive geochemical signature that differentiates between meteoric-origin and marine-origin ice. Analysis of the basal ice of three glaciers from the McMurdo Dry Valleys shows that liquid water does contribute to its formation. The basal ice sequences are structurally and compositionally different and are reflective of different modes of formation or entrainment active at the glacier margins. In the cases of the Rhone and Wright Lower glaciers marginal sediments and liquid water are key to understanding the accretion of debris-rich ice and both have basal facies consistent with refreezing in subzero conditions. The liquid water is formed by ephemeral melt during the summer. In the Rhone Glacier, melt water refreezes on the apron and is entrained into the advancing glacier. By contrast, by the Wright Lower Glacier adjacent streams or ponds saturate unconsolidated sediments which are entrained during ice advance. In the Taylor Glacier, the basal ice is comprised of a thick sequence of intercalated layers of clean clear ice and fine-grained debris layers. These laminated facies have a solute composition consistent with evaporites formed from a relict seawater intrusion. The combination of entrained debris, high solutes and laminations is consistent with interaction at the glacier bed and regelation. Interpreting empirically derived co-isotopic slopes is problematic, as highlighted in the case study of the Taylor Glacier where laminated facies have all the hallmarks of refrozen ice, yet plot on a co-isotopic slope that is typically interpreted as meteoric. Similarly, ice from the McMurdo Ice Shelf shows a clear difference in absolute isotope values which is interpreted as being refrozen from seawater, yet its co-isotopic plot is statistically indistinguishable from the meteoric water line. The ice compositional approach has highlighted several shortcomings. Firstly, solutes deposited in inland areas have limited solute pathways and do not distinguish between different types of ice but are useful in distinguishing between marine and continental salts. Secondly, co-isotopic analysis to reconstruct freezing history is dependent on statistically-derived interpretations which do not explain slopes that lie between physically-based models of meteoric and freezing slopes. In empirical studies, slopes between 5 and 8 are common, and are probably cosmopolitan samples. Finally, ice composition is inconsistent between similar ice types in the McMurdo Dry Valleys, as similar facies have different ice compositions, and origins. This underlines the problem with the premise that structurally similar ice facies are formed by the same process.

Isotropic ice samples containing measured concentrations of solutes and debris similar to basal material found in several cold-based glaciers in the McMurdo Dry Valleys, Antarctica, were manufactured in a laboratory and tested for peak shear strength at constant strain rates with a direct-shear device. The shear tests show that differences in rheology and shear strength appear to be related to impurity content and concentration. Debris-laden ice becomes more ductile with greater concentrations of solutes, whereas, low solute-concentrations and high debris-concentrations are associated with increases in shear strength and brittle behaviour. Stress exponents from Glen�s flow law calculated for isotropic solute and debris-laden ice ranged between 4 and 5, leading to the conclusion that higher rates of deformation may be expected in dirty basal ice than predicted for glacial ice models that use stress exponents where, n = 3. Observations of both natural and synthetic samples tested over a range of temperatures between -25�C and -5�C showed that natural basal ice samples containing high solute and debris concentrations were highly sensitive to temperature change. These tests showed an approximate 10 % loss in shear strength for every 1�C increase in temperature between -25�C and -10�C. In addition, contrasts in rheology and rates of deformation within basal ice are responsible for the development of debris-laden ice structures in the basal zones of cold-based glaciers that flow over unconsolidated substrates. As layered sedimentary bedding was preserved in frozen blocks within the deforming basal ice of several of these glaciers, the evidence suggests that at some point each glacier has interacted with its bed and entrained portions of the substrate material. Empirical shear strength data and observations of rheological changes attributed to composition together with evidence acquired during fieldwork in Antarctica help to support the argument that cold-based glaciers flowing over unconsolidated sediment are capable of affecting geomorphic change. Hence, isotropic ice models that exclude basal processes may need to be adjusted, especially where small increases in the temperature of the basal zones of cold glaciers may occur. In conclusion, palaeo-climate inferences based purely upon small amounts of geomorphic evidence, which suggest warmer climate conditions, may need to be re-evaluated in order to portray more accurate renditions of formerly glaciated landscapes.

Thesis (Ph. D.)--Montana State University--Bozeman, 2005. / Typescript. Chairperson, Graduate Committee: John C. Priscu. Includes bibliographical references (leaves 181-201).

No description available.

In the McMurdo Dry Valleys, Victoria Land, East Antarctica, melting of glacial ice is the primary source of water to streams, lakes, and associated ecosystems. To better understand meltwater production, three hypotheses are tested: 1) that small changes in the surface energy balance on these glaciers will result in large changes in melt, 2) that subsurface melt does not contribute significantly to runoff, and 3) that melt from 25-m high terminal cliffs is the dominant source of baseflow during cold periods. These hypotheses were investigated using a surface energy balance model applied to the glaciers of Taylor Valley using 14 years of meteorological data and calibrated to ablation measurements. Inclusion of transmission of solar radiation into the ice through a source term in a one-dimensional heat transfer equation was necessary to accurately model summer ablation and ice temperatures. Results showed good correspondence between calculated and measured ablation and ice temperatures over the 14 years using both daily and hourly time steps, but an hourly time step allowed resolution of short duration melt events and melt within the upper 15 cm of the ice. Resolution of short duration melt events was not important for properly resolving seasonal ablation totals. Across the smooth surfaces of the glaciers, ablation was dominated by sublimation and melting was rare. Above freezing air temperatures did not necessarily result in melt, and low wind speed was important for melt initiation. According to the model, subsurface melt between 5 and 15 cm depth was extensive and lasted for up to six weeks in some summers. The model was better able to predict ablation if some subsurface melt was assumed to drain, lowering ice density, consistent with observations of a low density weathering crust that forms over the course of the summer on Dry Valley glaciers. In extreme summers, drainage of subsurface melt may have contributed up to half of the observed surface lowering through reduction of ice density and possibly through collapse of highly weathered ice. When applied spatially, the model successfully predicted proglacial streamflow at seasonal and daily time scales. This was despite omitting a routing scheme, and instead assuming that all melt generated exits the glacier on the same day, suggesting refreezing is not substantial. Including subsurface melt as runoff improved predictions of runoff volume and timing, particularly for the recession of large flood peaks. Because overland flow was rarely observed over much of these glaciers, these model results suggest that runoff may be predominantly transported beneath the surface in a partially melted permeable layer of weathered ice. According to the model, topographic basins, particularly the low albedo basin floors, played a prominent role in runoff production. Smooth glacier surfaces exhibited low melt rates, but were important during high melt conditions due to their large surface area. Estimated runoff contributions from cliffs and cryoconite holes was somewhat smaller than suggested in previous studies. Spatial and temporal variability in albedo due to snow and debris played a dominant role in flow variations between streams and seasons. In general, the model supported the existing assumption that snowmelt is insignificant, but in extreme melt years snowmelt in the accumulation area may contribute significantly to runoff in some locations.

The Devonian Taylor Group, in the Olympus Range area, southern Victoria Land (SVL), Antarctica, is separated from the basement by a regional nonconformity (Kukri Erosion Surface). A second localized unconformity within the Taylor Group called the Heimdall Erosion Surface separates the New Mountain Sandstone and older units from the younger Altar Mountain Formation. The depositional environment of the New Mountain Sandstone has long been under contention. The New Mountain Sandstone Formation is a predominantly quartzose cross-bedded sandstone. Its newly defined Mt Jason Member is a coarse arkosic small scale cross-bedded pebbly sandstone that grades up section into the rest of the quartzose New Mountain Sandstone with large scale cross beds. The New Mountain Sandstone has been divided into five lithofacies including the Basal Conglomerate Lithofacies, Pebbly Sandstone Lithofacies, Granule Cross-bedded Lithofacies, Pinstripe Cross-bedded Lithofacies and Cross-bedded Sandstone Lithofacies. Deposition was in a shoreface environment with minor coastal aeolian deposition. The environment changed from upper shoreface to lower shoreface up section, forming transgressive to highstand systems tracts. The Heimdall Erosion Surface truncates the Cross-bedded Sandstone Lithofacies and the Pinstripe Cross-bedded Lithofacies and was formed due to relative sea level fall leading to exposure and erosion of underlying sedimentary and basement rocks. It forms a type 1 sequence boundary. The New Mountain Sandstone was partially or totally lithified before erosion as shown by the jagged morphology of the eroded cross beds on the surface. It is not known when cementation of the NMS took place or how much of the formation has been eroded. The Heimdall Erosion Surface and Kukri Erosion Surface converge locally due to erosion on the Heimdall Erosion Surface and relief on the Kukri Erosion Surface. The Heimdall Erosion Surface became a shore platform and the site of deposition as relative sea level rose. The Altar Mountain Formation with its Odin Member is a cross-bedded, massive and bedded feldspathic and quartzose sandstone that fines up section and is deposited on the erosion surface. The Altar Mountain Formation is divided into four lithofacies including the Conglomerate Lithofacies, Trough Cross-bedded Lithofacies, Cross-bedded Bioturbated Lithofacies and Bedded Fine Lithofacies. Deposition was in a shoreface environment, changing up section to an inner shelf environment with minor estuarine/tidal influence near the top of the section forming transgressive to highstand to regressive system tracts. The sedimentary rocks are derived mainly from the Granite Harbour Intrusives and Koettlitz Group, which underlie the sandstones, but were exposed elsewhere in SVL. The sandstone clasts within the Conglomerate Lithofacies could be derived from underlying older Taylor Group rocks or exotic sources from outside the field area. Correlation with data from adjacent areas suggests deposition of the New Mountain Sandstone occurred in a shallow sea that existed from the Olympus Range, southwards into the Asgard Range and included Vashka Crag. The area around Sponsors Peak and to the north was exposed and supplying feldspathic and quartzose sediment and pebbles into the depositional basin. As relative sea level fell due to either tectonic uplift or eustatic processes a large area of southern Victoria Land was exposed including the Olympus and Asgard Ranges and Bull Pass-St Johns Range area. This lead to erosion of the New Mountain Formation and basement rocks. Deposition of the New Mountain Sandstone continued further south shown by the gradational contact between it and the overlying Altar Mountain Formation. Relative sea level rise led to deposition of the Altar Mountain Formation. Shallow seas once more dominated the southern Victoria Land with deltas in the east (in the Bull Pass-St Johns Range area) feeding feldspathic sediment into the depositional basin (Odin Member). Further sea level rise drowned the delta region and a shallow marine to inner shelf environment led to deposition of the rest of the Altar Mountain Formation.