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.

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.

Thesis (M.S.)--Bowling Green State University, 2008. / Document formatted into pages; contains xi, 221 p. : ill. (some col.), maps. Includes bibliographical references.

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

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Lake Vanda is a meromictic, permanently ice-covered lake in the McMurdo Dry Valleys. The McMurdo Dry Valleys are a polar desert in Southern Victorialand Antarctica. This area experiences very little rainfall and very cold average temperatures, around –20°C. Lake Vanda has an unusual limnological profile, with a sharp physical and chemical gradient at about 60 m where the water transitions from cold, oxic, and fresh, to warm, hypersaline, and sulfidic; CaCl2 rather than NaCl is the dominant salt. Aerobic enrichment techniques were used to isolate what turned out to be several strains of a species of Chromohalobacter, a genus of the Gammaproteobacteria, from Lake Vanda deep waters, while targeted enrichments for anaerobic and spore-forming bacteria were negative. The isolates were characterized for their temperature and pH optima, carbon and nitrogen nutrition, and salt tolerance and requirements. The results showed the organisms to be obligately aerobic with a broad pH range (optima pH 7). The isolates used some sugars and organic acids but not alcohols or fatty acids for energy and cell carbon, and showed a moderate requirement for NaCl but no requirement for CaCl2, even though CaCl2 is the predominant salt in their environment.

Detailed information on diet and foraging behavior is necessary for understanding predator-prey interactions and food-web dynamics. The primary objective of this dissertation was to gain a more complete understanding of the natural foraging behavior of Weddell seals (Leptonychotes weddellii) in McMurdo Sound, Antarctica using a video data recorder to document the seal's three-dimensional movements and encounters with prey. Seals exhibited a variety of dive types that could be sorted into five groups based on 18 dive descriptors. Three of these groups (deep aerobic, deep anaerobic, and shallow aerobic) were identified as foraging dives, the frequency of which varied with bathymetry. Deep aerobic foraging dives were similar in depth and duration to foraging dives in previous studies and were more common at offshore breathing holes. However, differences occurred between offshore free-ranging and isolated-hole dives in the behaviors involving descent and the frequency of certain behavioral transitions. These differences were responses by the seals to variations in prey abundance, rather than responses to a change in breathing hole availability. Even with an apparently homogenous sample of seals, there was significant individual variability in foraging success, behavior, diet, and foraging tactics. Dive depth, duration, distance, and energetic cost were important for explaining foraging success when seals dove in shallow areas where Antarctic silverfish (Pleuragramma antarcticum) were more difficult to reach and less abundant. However, the relationship between those variables was not the same for all individuals. Diet and foraging tactics also varied significantly among individuals diving near the coastline. Two coastal seals specialized on silverfish, while two others consumed silverfish and benthic prey. Although benthic prey were more accessible along the coastline than offshore, silverfish, which have a high lipid content, required less handling to consume. Thus, it may be energy-efficient for seals to specialize on silverfish at coastal locations despite the additional time and energy required to travel to depths where silverfish are located. These results helped us understand variability within Weddell seal populations and the basis upon which foraging decisions are made in response to changes in bathymetry, access to breathing holes, and prey abundance and availability.

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 aim of this research was to demonstrate the relationship between variations in summertime surface mass balance of the McMurdo Ice Shelf and atmospheric processes. The approach encompassed a broad range of techniques. An existing energy balance mass balance model was adapted to deal with debris-covered ice surfaces and modified to produce distributed output. Point based surface energy and mass balance for two key surfaces of the ice shelf were linked to different synoptic types that were identified using a manual synoptic classification. The distributed model was initialised with distributed parameters derived from satellite remote sensing and forced with data from a regional climate model. Patterns of summertime surface mass balance produced by the distributed model were assessed against stake measurements and with respect to atmospheric processes. During the summers of 2003-2004 and 2004-2005 an automatic weather station (AWS) was operated on bare and debris-covered ice surfaces of the McMurdo Ice shelf, Antarctica. Surface mass balance was calculated using the energy balance model driven by the data from the AWS and additional data from permanent climate stations. Net mass balance for the measurement period was reproduced reasonably well when validated against directly measured turbulent fluxes, stake measurements, and continuously measured surface height at the AWS. For the bare ice surface net radiation provided the major energy input for ablation, whereas sensible heat flux was a second heat source. Ablation was by both melt (70%) and sublimation (30%). At the debris-covered ice site investigated, it is inferred that the debris cover is sufficient to insulate the underlying ice from ablation. Synoptic weather situations were analysed based on AVHRR composite images and surface pressure charts. Three distinct synoptic situations were found to occur during the summers, these were defined as Type A, low pressure system residing in the Ross Sea Embayment; Type B, anticyclonic conditions across region; and Type C, a trough of low pressure extending into the Ross Sea Embayment. A dependence of surface energy fluxes and mass balance on synoptic situation was identified for the bare ice surface. The distributed model was found to produce spatial patterns of mass balance which compared well with stake measurements. Mass balance patterns show that the McMurdo Ice Shelf was generally ablating in the west, and accumulating in the east during summer. Areas of enhanced ablation were found which were likely to be caused by the surface conditions and topographic effects on the wind field. The mean summertime surface mass balance across the entire ice shelf for the 2003-2004 and 2004-2005 summers were –2.5 mm w.e. and –6.7 mm w.e. respectively. The differences between the two summers are inferred to be a result of more frequent type A conditions occurring during the summer of 2004-2005.