Natural products continue to be a valuable source of compounds in research involving chemical ecology and drug discovery. Secondary metabolites are biosynthesized to benefit the host organism in its environment (feeding deterrence from predators, antibiotic properties to avoid infection, etc.) but these compounds also serve as useful scaffolds in drug discovery applications. The research herein describes both aspects of these two branches of natural products chemistry. The Antarctic sponge Dendrilla membranosa produces diterpenes, of which membranolide A, deters feeding of the predatory amphipod Gondogenia antarctica. A metabolomic study of several sponges was undertaken to determine environmental factors that govern the metabolism of D. membranosa. Habitat specificity, above or below the algal canopy, was a significant factor for the chemical clustering of sponges as well as the abundance of potential amphipod predators that are prevalent within the canopy. Another D. membranosa diterpene, aplysulphurin, undergoes degradation upon methanolic treatment to form the methoxy membranolides B-H. An investigation of these artifacts reveals potent activity against the leishmaniasis-causing parasite Leishmania donovani. Microorganisms also generate a significant number of bioactive natural products. Biotic and abiotic culture stressors such as co-culturing and epigenetic modification, respectively, will be explored to turn on cryptic biosynthetic pathways. These techniques are shown to produce unique secondary metabolites from cultures and further reinforce the one strain many compounds approach to the versatile and formidable microbial domain.

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.

The investigation presented in this thesis examined the microbial and functional diversity of the meltwater ponds Fresh, Orange and Salt Ponds on the McMurdo Ice Shelf, near Bratina Island, Antarctica. These sites were chosen because of the ecological importance and absence of detailed characterisations of their diversity and function as part of Antarctica?s largest wetland. Particular focus was on cyanobacterial diversity, nitrogen fixation and secondary metabolite production. Using 16S rRNA gene and morphological analysis a large diversity of cyanobacteria (more than 22 phylotypes) was identified with high phylogenetic similarities (up to 99% sequence identity) to cyanobacteria from mats in other regions of Antarctica. In addition biogeographical distributions were identified including potentially endemic and cosmopolitan cyanobacteria. High salinities were also connected to the change and reduction of diversity. Lipid marker analyses were performed targeting hydrocarbons, ether-linked hydrocarbons, methylated fatty acid esters (FAME), wax esters, hopanols and sterols. Lipid biomarker profiles were similar to typical cyanobacteria dominated mats with major input from microorganisms including oxygenic and anoxygenic phototrophs, obligate aerobic and anaerobic heterotrophs that conduct the metabolic processes of fermentation, sulphate reduction, sulphate and iron-oxidation, methanogeneses. Signature lipids indicative of Chloroflexus and archaea, as well as branched aliphatic alkanes with quaternary substituted carbon atoms (BAQCs), were identified for the first time in Fresh, Orange and Salt Ponds. Based on nifH gene analysis, the nitrogen fixing diversity characterised in Orange Pond consisted of cyanobacterial Nostoc sp. as well as firmicutes, beta-, gamma- and delta-proteobacteria. Acetylene reduction assays and nifH gene RNA transcript diversity identified Nostoc sp. as a main contributor of nitrogenase activity in these ponds. Furthermore, analytical methods were used to identify the cyanobacterial secondary metabolites microcystins, although the genetic basis for this production and the toxin producer could not been identified. However non-ribosomal peptide synthetases (NRPS) and polyketide synthases (PKS) genes were identified which could be the genetic basis for novel bioactives. The use of a multi-disciplinary approach synthesis and subsequent results significantly increased our understanding of the diversity and function of microbial mat communities in the unique meltwater ponds of the McMurdo Ice shelf, Antarctica.

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.

Atmospheric turbulence results taken on the Antarctic plateau are presented in this thesis. Covering two high sites: South Pole and Dome C, this work describes their seeing and meteorological conditions. Using an acoustic sounder to study the turbulence profile of the first kilo- metre of the atmosphere and a Differential Image Motion Monitor (DIMM) to investigate the integrated seeing we are able to deduce important at- mospheric parameters such as the Fried parameter (r0) and the isoplanatic angle (??0). It was found that at the two sites, the free atmosphere (above the first kilometer) was extremely stable and contributed between 0.2" and 0.3" of the total seeing with no evidence of jet or vortex peaks of strong turbulence. The boundary layer turbulence is what differentiates the two sites. Located on the Western flank of the plateau, the South Pole is prone to katabatic winds. Dome C on the other hand is on a local maximum of the plateau and the wind conditions are amongst the calmest in the world. Also linked to the topography is the vertical extent of the temperature in- version that is required to create optical turbulence. At the South Pole the inversion reaches 300 m and only 30 m at Dome C. This difference results in relatively poor seeing conditions at the South Pole (1.8") and excellent at Dome C (0.27"). The strong correlation between the seeing and the ground layer meteorological conditions indicates that even better seeing could be found at Dome A, the highest point of the plateau. Having most of the turbulence near the ground is also incredibly ad- vantageous for adaptive optics. The isoplanatic angle is respectively 3.3" and 5.7" for the South Pole and Dome C. This is significantly larger than at temperate sites where the average isoplanatic angle rarely exceeds 2". This means that wider fields can be corrected without the complication of conjugation to specific layers. For such purpose the potential is even more interesting. We show that ground conjugated adaptive optics would decrease the natural seeing to 0.22" for a wide field of 10 and 0.47" for a field of 1" at the South Pole. At Dome C the results are less impressive due to the already excellent seeing, but a gain of 0.1&quote can still be achieved over 1&quote. These results show that high angular resolution observations can be done better on the Antarctic plateau than any other known site.

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.

Numerous recent studies have documented dynamic changes in the behaviors of large marine-terminating outlet glaciers and ice streams in Greenland, the Antarctic Peninsula, and West Antarctica. However, fewer observations of outlet glaciers and ice shelves exist for the East Antarctic Ice Sheet. In addition, most recent surface velocity mappings of the Lambert Glacier-Amery Ice Shelf system (LAS) are derived for the time period of 1997-2000. From this research, surface velocity measurements provide a more extended view of the behavior and stability of the LAS over the past two decades than can be gleaned from a single observational period. This study uses remote sensing to investigate whether significant changes in velocities have occurred from the late 1980’s through the late 2010’s and assesses the magnitude of mass balance changes observed at the grounding line. To accomplish this goal, surface velocities of the LAS from late 1980’s to late 2010’s for three separate time periods are measured. The observed surface velocities of the LAS ranged from 0 to 1300 m yr^-1 during 1988-1990. A slight slowing down is detected in the central Amery Ice Shelf front by analyzing the surface velocity measurements made along the centerlines. The mass balance is the difference between snow accumulation and the outflux of the grounded LAS and is calculated for individual sub-basin during the three time intervals of 1988-1990, 1999-2004, and 2007-2011 to illustrate the mass balance variation under sub-basin level. The flux gates of the Lambert Glacial sub-basin combined with the Mellor Glacial and the Fisher Glacial sub-basin appear to be the largest outlet of the grounded ice of the LAS. The ice mass transported from the interior region through the three flux gates in total is 43.58 Gt yr^-1, 36.72 Gt yr^-1, and 38.61 Gt yr^-1 respectively for the three time intervals above. The sub-basins in the eastern side appear differently than the western side. The outfluxes of the eastern sub-basins vary from 15.85 to 18.64 Gt yr^-1, while the western outfluxes vary from 15.85 to 18.64 Gt yr^-1. The grounded LAS has discharged ice from 84.55 to 81.60 Gt yr^-1 and to 79.20 Gt yr^-1 during 1980s-1990s and 1990s-2000s. Assuming the snow accumulation distribution is stable, the grounded LAS mass lose has increased 2.95 Gt yr^-1 from 1980s to 1990s and 2.40 Gt yr^-1 from 1990s to 2000s. These results indicate insight into the stability of the Amery Ice Shelf over the last few decades.

No description available.

Despite extensive studies on Weddell seals (Leptonychotes weddellii) in McMurdo Sound since the 1960s, uncertainty still remains regarding female foraging habits during the lactation period. Based on their large body mass at the start of lactation and large relative mass loss at the end, the current hypothesis is that Weddell seals fast or feed to a neglible extent during lactation. However, this hypothesis has not been fully tested to date, as evidence for foraging is indirect and is based primarily on dive behaviour. The work presented in this thesis describes the development of a new dietary method, the biomarker method, and its application for studying the foraging behaviour of female Weddell seals during lactation. Biomarkers were used to (1) monitor the onset of feeding in individual animals, and (2) determine what prey females were feeding on using characteristic/taxon-specific biomarker patterns. Proton nuclear magnetic resonance spectroscopy (1H NMR) and liquid chromatography-tandem mass spectrometry (LC-MS/MS) assays were developed to detect and quantify dietary biomarkers in biological samples, mainly tissues, serum and plasma. Trimethylamine N-oxide, arsenobetaine, dimethylsulfoniopropionate, homarine and glycine betaine were first measured in thirty-three prey and potential prey species of Weddell seals collected from the Ross Sea and McMurdo Sound regions of Antarctica. These same compounds were then measured in the plasma of twelve female Weddell seals over the lactation period at the Hutton Cliffs seal colony, McMurdo Sound in 2006. Time-depth recorders monitored seal dive activity over the same period. The data obtained from both NMR and LC-MS/MS assays showed that biomarkers in Antarctic species varied both in content and concentration. The compound homarine, which occurs primarily in cephalopods, is suitable for distinguishing between major food groups of known prey of Weddell seals (i.e., fishes versus cephalopods). DMSP, a compound that occurs primarily in fish common in McMurdo Sound (e.g., Trematomus bernacchii and Pagothenia borchgrevinki) but not in significant amounts in Dissostichus mawsoni or Pleuragramma antarcticum, two main prey items for Weddell seals, may also be a suitable biomarker for distinguishing between major and minor prey types. The detection of plasma TMAO, AsB and homarine indicated that 75% of Weddell seals studied fed during lactation. The presence of these three compounds indicates the seals were preying upon a combination of fish and cephalopods. Two lactating females started foraging as early as 9 to 12 days postpartum and elevated biomarker levels were concurrent with increased dive activity. The onset of foraging and dive behaviour amongst individuals was highly variable; however, the results suggests that the number of females who feed during lactation may be more prevalent and initiated at an earlier stage than previously thought. This may have implications for future reproductive success given effects of climate change on sea ice abundance and resource availability. Overall, the work presented in this thesis provides new insights into the foraging behaviour of female Weddell seals during lactation and has added to the current knowledge of the biomarker distribution within the Antarctic ecosystem.

No description available.