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Heterotrophic protists, consisting largely of the Cercozoa, Amoebozoa, Ciliophora, Discoba and some Stramenopiles, are a poorly characterized component of life on Earth. They play an important ecological role in soil communities and provide key insights into the nature of one of life’s most enigmatic evolutionary transitions: the development of the complex unicell. Soil ecosystems are crucial to the functioning of global biogeochemical cycles (e.g. carbon and nitrogen) but are at risk of drastic change from anthropogenic climate change. Heterotrophic protists are the primary regulators of bacterial diversity in soils and as such play integral roles in biogeochemical cycling, nutrient mobilization, and trophic cascades in food webs under stress. Understanding the nature of these changes requires examining the rates, diversity, and resiliency of interactions that occur between soil organisms. However, soils are the most taxonomically diverse ecosystems on Earth and disentangling the complexities of dynamic and varied biotic interactions in them requires a unique model system. The McMurdo Dry Valleys of Antarctica, one of the harshest terrestrial environments on Earth, serve as a model soil ecosystem owing to their highly reduced biological diversity. Exploring the functioning of heterotrophic protists in these valleys provides a way to test the applicability of this model system to other soil food webs. However, very little is known about their taxonomic diversity, which is a strong predictor of function. Therefore, I reviewed the Antarctic literature to compile a checklist of all known terrestrial heterotrophic protists in Antarctica. I found significant geographical, methodological, and taxonomic biases and outlined how to address these in future research programs. I also conducted a molecular survey of whole soil communities using 18 shotgun metagenomes representing major landscape features of the McMurdo Dry Valleys. The results revealed the dominance of Cercozoa and point to an Antarctic heterotrophic protist soil community that is taxonomically diverse and reflects the structure and composition of communities at lower latitudes. To investigate whether biotic interactions or abiotic factors were a larger driver for Antarctic heterotrophic protists, I conducted variation partitioning using environmental data (e.g. moisture, pH and electrical conductivity). Biotic variables were more significant and accounted for more of the variation than environmental variables. Taken together, it is clear that heterotrophic protists play key ecological roles in this ecosystem. Deeper insights into the ecology of these organisms in the McMurdo Dry Valleys also have implications for the search for complex unicellular life in our universe. I discuss the theoretical underpinnings of searching for these forms of life outside of Earth, conclude that they are likely to occur, and postulate how future missions could practically search for complex unicells.

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This thesis examines the utility of the Rényi entropy (RE), a measure of the complexity of probability density functions, as a tool for finding physically meaningful patterns in geophysical data. Initially, the RE is applied to observational data of long-lived atmospheric tracers in order to analyse the dynamics of stratospheric transitions regions associated with barriers to horizontal mixing. Its wider applicability is investigated by testing the RE as a method for highlighting internal boundaries in snow and ice from ground penetrating radar (GPR) recordings. High-resolution 500 MHz GPR soundings of dry snow were acquired at several sites near Scott Base, Antarctica, in 2008 and 2009, with the aim of using the RE to facilitate the identification and tracking of subsurface layers to extrapolate point measurements of accumulation from snow pits and firn cores to larger areas. The atmospheric analysis focuses on applying the RE to observational tracer data from the EOS-MLS satellite instrument. Nitrous oxide (N2O) is shown to exhibit subtropical RE maxima in both hemispheres. These peaks are a measure of the tracer gradients that mark the transition between the tropics and the mid-latitudes in the stratosphere, also referred to as the edges of the tropical pipe. The RE maxima are shown to be located closer to the equator in winter than in summer. This agrees well with the expected behaviour of the tropical pipe edges and is similar to results reported by other studies. Compared to other stratospheric mixing metrics, the RE has the advantage that it is easy to calculate as it does not, for example, require conversion to equivalent latitude and does not rely on dynamical information such as wind fields. The RE analysis also reveals occasional sudden poleward shifts of the southern hemisphere tropical pipe edge during austral winter which are accompanied by increased mid-latitude N2O levels. These events are investigated in more detail by creating daily high-resolution N2O maps using a two-dimensional trajectory model and MERRA reanalysis winds to advect N2O observations forwards and backwards in time on isentropic surfaces. With the aid of this ‘domain filling’ technique it is illustrated that the increase in southern hemisphere mid-latitude N2O during austral winter is probably the result of the cumulative effect of several large-scale, episodic leaks of N2O-rich air from the tropical pipe. A comparison with the global distribution of potential vorticity strongly suggests that irreversible mixing related to planetary wave breaking is the cause of the leak events. Between 2004 and 2011 the large-scale leaks are shown to occur approximately every second year and a connection to the equatorial quasi-biennial oscillation is found to be likely, though this cannot be established conclusively due to the relatively short data set. Identification and tracking of subsurface boundaries, such as ice layers in snow or the bedrock of a glacier, is the focus of the cryospheric part of this project. The utility of the RE for detecting amplitude gradients associated with reflections in GPR recordings is initially tested on a 25 MHz sounding of an Antarctic glacier. The results show distinct regions of increased RE values that allow identification of the glacial bedrock along large parts of the profile. Due to the low computational requirements, the RE is found to be an effective pseudo gain function for initial analysis of GPR data in the field. While other gain functions often have to be tuned to give a good contrast between reflections and background noise over the whole vertical range of a profile, the RE tends to assign all detectable amplitude gradients a similar (high) value, resulting in a clear contrast between reflections and background scattering. Additionally, theoretical considerations allow the definition of a ‘standard’ data window size with which the RE can be applied to recordings made by most pulsed GPR systems and centre frequencies. This is confirmed by tests with higher frequency recordings (50 and 500 MHz) acquired on the McMurdo Ice Shelf. However, these also reveal that the RE processing is less reliable for identifying more closely spaced reflections from internal layers in dry snow. In order to complete the intended high-resolution analysis of accumulation patterns by tracking internal snow layers in the 500 MHz data from two test sites, a different processing approach is developed. Using an estimate of the emitted waveform from direct measurement, deterministic deconvolution via the Fourier domain is applied to the high-resolution GPR data. This reveals unambiguous reflection horizons which can be observed in repeat measurements made one year apart. Point measurements of average accumulation from snow pits and firn cores are extrapolated to larger areas by identifying and tracking a dateable dust layer horizon in the radargrams. Furthermore, it is shown that annual compaction rates of snow can be estimated by tracking several internal reflection horizons along the deconvolved radar profiles and calculating the average change in separation of horizon pairs from one year to the next. The technique is complementary to point measurements from other studies and the derived compaction rates agree well with published values and theoretical estimates.

The distribution of massive ground ice in the ground in Taylor Valley of the McMurdo Dry Valleys, Antarctica, is quite unknown, and could provide answers to questions such as where the ice comes from, if it has been affected and removed by proglacial lakes and how landscapes underlain by massive ground ice responds to climate change. It could also be a source for atmospheric information in the past and hence a key in climate research. The main goal with this project was therefore to map the distribution of massive ground ice mainly in Taylor Valley, but also in the adjacent Salmon Valley and Wright Valley, using ground penetrating radar to see how the distribution varied and if there was any spatial patterns. The technical computing programme MATLAB was used for editing of the raw radar data, merging of GPR profiles and digitalization of reflectors for possible massive ground ice and several compilations of different files. The data obtained from MATLAB was imported and interpreted using the geographic information system ArcGIS. A series of histograms showing the distribution of massive ground ice depending on the parameters elevation, slope and aspect were made by using the spreadsheet application Microsoft Excel. The results showed that the distribution of massive ground ice was more common at elevations up to 200 m, at the mouth of the valleys and also more frequent in Taylor Valley than in Wright Valley. There was a slightly higher amount of massive ground ice at northeast-east aspects, probably due to different incoming solar radiation. The lack of, or not that prominent, differences for slope and aspect can be due to lack of data, a not enough detailed digital elevation model or that it have existed for a too short period of time to display big differences caused by effects from these parameters. The higher frequency of massive ground ice in Taylor Valley can be due to a thicker sediment cover when compared with the situation in Wright Valley. The distribution of massive ground ice at different slopes seems to follow the distribution of radar measurements, whereas the origin of the massive ground ice and sediment cover can be responsible for the distribution across different elevations. The reason why massive ground ice still occurs despite the existence of Glacial Lake Washburn that previously occupied Taylor Valley could be that the glacial lake did not remain for a sufficiently long time to melt all the massive ice. Massive ground ice is very common in a zone that is believed to be very susceptible for future warming, which means that changes that already have been observed in areas rich in massive ground ice can continue to happen and changes in other areas with massive ice can be enabled. The ice can thus play a major role in the development of the landscape in the McMurdo Dry Valleys depending on the amount of warming. / Markis kan hittas i mark som har temperaturer under 0°C under åtminstone 2 år i följd och därav klassas som permafrost, skillnaden mellan markis och permafrost är däremot att permafrost inte behöver vara just is utan kan enbart vara kall mark. För att markis ska klassas som massiv is så ska andelen is i marken vara minst 250 % jämfört med vikten på torr jord. Utbredningen av sådan massiv is i Taylor Valley i McMurdos torrdalar på Antarktis är inte helt känd, och kunskapen om att veta vart den finns (om den finns) skulle kunna ge svar på frågor som vart den kommer ifrån, om den har påverkats och smält bort av isuppdämda sjöar och hur landskap som är grundade av massiv markis påverkas av klimatförändringar. Isen skulle även kunna vara en informationskälla för tidigare atmosfäriska förhållanden. Huvudsyftet med detta arbete var därför att kartlägga utbredningen av massiv is främst i Taylor Valley, men även i de närliggande dalarna Salmon Valley och Wright Valley, och undersöka hur utbredningen varierar beroende på olika landskapsegenskaper som påverkar dess förekomst. Datorprogrammet och programspråket MATLAB användes för att editera rådatat från radar-mätningarna i området, samt för att sammanföra och digitalisera horisonter för möjlig massiv markis i radarfigurerna och för ett antal sammanställningar av olika filer. Data erhållet från MATLAB importerades till det geografiska informationssystemet ArcGIS där det kunde visualiseras i kartor och tolkas. Ett antal histogram skapades i kalkylprogrammet Microsoft Excel för att visa frekvensen av massiv markis vid olika höjder, sluttningsvinklar och olika väderstrecksriktningar. Resultaten visade att det var mer vanligt med massiv is höjder upp till 200 m, vid mynningarna av dalarna samt i Taylor Valley jämfört med Wright Valley. Det var en aning mer vanligt med massiv markis vid nordöst-östliga sluttningsriktningar, vilket antagligen beror på olika mängder inkommande solstrålning till de olika riktningarna. Avsaknaden av, eller inte så märkbara, skillnader för olika sluttningsvinklar och riktningar kan bero på att mängden data var för liten, att höjdkartan inte var tillräckligt detaljerad eller att isen inte har funnits tillräckligt länge för att bli påverkad av dessa parametrar. Anledningen till att det finns mer massiv markis i Taylor Valley än i Wright Valley kan vara att det skyddande sedimenttäcket är tunnare i Wright Valley än i Taylor Valley. Frekvensen av massiv markis vid olika sluttningsvinklar verkar bero på det totala antalet mätningar gjorda, fler mätningar leder till en högre frekvens av markis, medan dess ursprung samt det antagna tunnare sedimenttäcket på högre höjder kan vara anledningen till de olika frekvenserna av massiv markis vid olika höjder. Anledningen till varför det fortfarande finns massiv markis trots existensen av den isuppdämda sjön Washburn som tidigare fanns i Taylor Valley, och att isen således inte helt har smält bort på grund av sjön, kan vara att den fanns under en för kort tid så att de långsamma termodynamiska processerna som skulle orsaka smältningen inte hann agera tillräckligt länge för att smälta all is. Den massiva markisen är vanlig i en zon som tros vara väldigt mottaglig för framtida uppvärmning, vilket betyder att landskapsförändringar som redan har observerats i områden med mycket massiv markis kan fortsätta att ske samtidigt som andra områden med massiv markis kan börja förändras. Isen kan därför spela en stor roll i landskapsutvecklingen i McMurdos torrdalar beroende på hur mycket varmare det blir i området.

The natural environments of organisms present a multitude of biotic and abiotic challenges that require both short-term ecological and long-term evolutionary responses. Though most environmental response studies have focused on effects at the ecosystem, community and organismal levels, the ultimate controls of these responses are located in the genome of the organism. Soil nematodes are highly responsive to, and display a wide variety of responses to changing environmental conditions, making them ideal models for the study of organismal interactions with their environment. In an attempt to examine responses to environmental stress (desiccation and freezing), genomic level analyses of gene expression during anhydrobiosis of the Antarctic nematode Plectus murrayi was undertaken. An EST library representative of the desiccation induced transcripts was established and the transcripts differentially expressed during desiccation stress were identified. The expressed genome of P. murrayi showed that desiccation survival in nematodes involves differential expression of a suite of genes from diverse functional areas, and constitutive expression of a number of stress related genes. My study also revealed that exposure to slow desiccation and freezing plays an important role in the transcription of stress related genes, improves desiccation and freezing survival of nematodes. Deterioration of traits essential for biological control has been recognized in diverse biological control agents including insect pathogenic nematodes. I studied the genetic mechanisms behind such deterioration using expression profiling. My results showed that trait deterioration of insect pathogenic nematode induces substantial overall changes in the nematode transcriptome and exhibits a general pattern of metabolic shift causing massive changes in metabolic and other processes. Finally, through field observations and molecular laboratory experiments the validity of the growth rate hypothesis in natural populations of Antarctic nematodes was tested. My results indicated that elemental stoichiometry influences evolutionary adaptations in gene expression and genome evolution. My study, in addition to providing immediate insight into the mechanisms by which multicellular animals respond to their environment, is transformative in its potential to inform other fundamental ecological and evolutionary questions, such as the evolution of life-history patterns and the relationship between community structure and ecological function in ecosystems.

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