Theses - British Antarctic Survey


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  • ItemOpen Access
    Modelling the Exposure of Satellites in Medium Earth Orbit to Proton Belt Radiation
    Lozinski, Alexander; Lozinski, Alexander [0000-0002-6508-487X]
    Geomagnetically trapped protons forming Earth's proton radiation belt pose a hazard to orbiting spacecraft. In particular, solar cells are prone to degradation caused by non-ionising collisions with protons in the energy range of several megaelectron volts, which can ultimately shorten the lifespan of a mission. Dynamic enhancements in trapped proton flux following solar energetic particle events have been observed to last several months, and there is a strong need for physics‐based modelling in order to predict the impact these changes may have on orbiting spacecraft. This thesis addresses the need for physics-based modelling by presenting an investigation into inner proton belt variability with a 3D numerical model created from scratch, and by quantifying the impact that variability has on the solar cell degradation of orbiting satellites. After a review of background concepts in Chapter 1, Chapter 2 presents a case study on satellites undergoing electric orbit raising to geostationary orbit. The increase in solar cell degradation that can occur during a period of proton belt enhancement is calculated for three example orbits. It is found that a large enhancement can cause an additional degradation in solar cell output power by up to ~5% over the course of orbit raising, and further changes of a few percent are shown to occur based on the choice of trajectory, or for a 50μm change in solar cell coverglass shielding thickness. In Chapter 3 a physics-based numerical model is constructed, solving for proton phase space density in terms of the first, second and third adiabatic invariants μ, K and L. This chapter demonstrates how key processes can be quantified, including transport via radial diffusion, the cosmic ray albedo neutron decay source and coulomb collisional loss. In Chapter 4, a 2D version of the model is applied to derive proton radial diffusion coefficients for a period of solar maximum. This is achieved by varying parameters controlling the rate of radial diffusion in order to optimise the fit between model and data from the CRRES satellite, under the assumption of steady state. Results are compared with diffusion coefficients derived in other literature, and the validity of the steady state assumption underlying this technique is discussed. In Chapter 5, the 3D numerical model is applied to investigate time variability at energies of 1-10 megaelectron volts, a crucial energy range for solar cell degradation. Three sets of diffusion coefficients from previous literature are applied to model the time evolution of proton phase space density over the four year period 2014-2018. The sensitivity of modelling results to the choice of diffusion coefficients is discussed, including the effect on the anisotropy of proton pitch angle distributions. In the final research chapter of this thesis, Chapter 6, these modelling results are then applied to calculate solar cell degradation over the modelling period for an example satellite in 1200km inclined circular orbit. This demonstrates the final step in an end-to-end physics-based calculation of solar cell degradation.
  • ItemOpen Access
    Physiological and metabolic characteristics of polar diatoms: insights into cold adaptation and potential for biotechnology
    Coffin, Sam; Coffin, Sam [0000-0003-1943-4717]
    The polar regions represent two of the most extreme environments on Earth, with sub-zero temperatures, sustained light in the summer and complete darkness in the winter. Marine diatoms are prevalent in the polar oceans, significantly contributing to primary productivity and ecosystem functioning. They are characterized by having optimal growth at low temperatures (<10°C) and have developed various genetic adaptations to cope with these extreme environments. The polar regions, however, are experiencing unprecedented environmental changes because of regional climate change. We currently lack detailed knowledge on polar diatom ecophysiology and metabolism, which means we do not know how these species may be impacted by future environmental changes. One barrier to our understanding of polar diatoms is the availability of living strains for experimental study. The number of polar diatom strains in public collections is low and of those that are available, many have been kept in culture for many decades. Hence, there is an urgent requirement to isolate new environmental strains that have not been exposed to artificial conditions for many decades and also to increase the number and diversity of species available. In this project I conducted fieldwork in Antarctica to isolate several new Antarctic strains and used these alongside Arctic and Antarctic strains from culture collections to study whether physiological and metabolic characteristics are conserved between diatoms from the two regions. My studies focused primarily on the response to temperature with the aim of predicting the effects of future climate change on polar diatom physiology and metabolism. The project also aimed to identify potential candidate strains for biotechnological exploitation. Conducting fieldwork on the Western Antarctic Peninsula, I isolated 36 strains encompassing 12 different species of polar diatoms. These have been genetically and morphologically identified and representatives deposited in the Culture Collection for Algae and Protozoa. I investigated the ecophysiology of two diatom species found in both polar regions, Fragilariopsis cylindrus and Porosira glacialis. My results showed how the thermal tolerance differed between Arctic and Antarctic strains with optimal growth temperatures of the Arctic F. cylindrus being 3°C higher than the Antarctic strain. On the contrary, P. glacialis from the Arctic had an optimal growth temperature 5.5°C lower than the Antarctic strain. In addition, the thermal tolerance of newly isolated strains of F. cylindrus was investigated and found to be similar to the laboratory strain except for one, which was able to grow at 12°C. The difference in temperature tolerance between the Arctic and Antarctic F. cylindrus strains led me to investigate the vitamin B12 requirements of these strains. Previously it had been suggested that there are links between B12 dependency and temperature tolerance, and the Antarctic F. cylindrus was previously found to be B12 independent. My results demonstrated that all three Arctic F. cylindrus strains had an obligate requirement for exogenous vitamin B12, whereas all three Antarctic strains did not. Further investigation failed to isolate and identify the B12-independent methionine synthase gene (METE) in Arctic strains, but this gene was identified in Antarctic strains. In contrast, the B12-dependent methionine synthase gene (METH) was identified and partially sequenced in all strains. Several single nucleotide polymorphisms were identified in the Arctic strains which are hypothesised to be non-deleterious. These results provide a potential explanation for the B12 dependency in Arctic isolates, and reasons for how this might have arisen are considered. Lastly, polar diatoms are thought to offer a unique resource for biotechnology offering potentially novel metabolites or increased biomass production during winter months when temperatures decrease. Pilot experiments indicate that there is no advantage in growth over a temperate strain during the winter months in the UK, but further work focusing on optimisation is needed.
  • ItemOpen Access
    Liverwort-Fungal Associations: Novel Symbioses In Polar Regions?
    (2020-05-16) Foot, George William
    Symbioses between plants and fungi are ubiquitous in terrestrial ecosystems, in which they play key roles in plant nutrient acquisition and the cycling of elements. The plant host provides carbon fixed in photosynthesis to the fungi, which in return provide the host with limiting nutrients such as nitrogen and phosphorus. These associations, referred to as mycorrhiza, are hypothesised to have been a key factor in the colonisation of the land by plants. However, we still know very little about fungal symbioses in one of the most ancient groups of land plants — the liverworts — and in the bryophyte enriched floras of the polar regions. This study provides the first large-scale survey of fungal colonisation of liverworts on Svalbard in the High Arctic and on South Georgia in sub-Antarctica, increasing current knowledge of these symbioses from three to 35 liverwort species across both polar regions. Fungal DNA was sequenced to establish the identity of the mycobionts present, with ​in planta FISH and light microscopy being used to determine the distribution of fungal structures. Furthermore, elemental and isotopic concentrations of liverwort tissues were measured to explore whether mycobionts might be associated with liverwort nutrition. To isolate the fungal contribution to liverwort N nutrition and test whether fungi receive C from their liverwort host, a dual 1​ 5​N and 1​ 4​C isotope labelling experiment was established, with NanoSIMS being utilized to visualise the flow of N into liverwort tissue. I found that fungal colonisation was frequent in the liverworts surveyed, with species from the Serendipitaceae being among the most abundant fungal taxa recorded. Interestingly, all of the mycobionts identified (apart from ​Rhizoscyphus ericae​) were endemic to either the Arctic or Antarctic. Blue staining hyphal coils and dark septate endophytes were frequently observed, with the former correlating positively with plant N concentration, suggesting that mycobionts might enhance the acquisition of this element by their liverwort hosts. Stable isotope labelling combined with NanoSIMS demonstrated that 1​ 5​N is transferred ​via mycobiont hyphae into liverwort tissues, where it is incorporated. However, I did not observe a reciprocal transfer of 14​C from liverwort to mycobionts. This research suggests that the distribution and function of liverwort-fungal associations varies considerably with latitude. The findings are important for understanding C and N cycling in polar soils, how climate change might alter the magnitude of these nutrient fluxes and, more broadly, the evolution of liverwort-fungal associations.
  • ItemOpen Access
    Investigating Volcanic and Glacial Processes Using Microseismicity
    (2019-11-30) Hudson, Thomas Samuel; Hudson, Thomas Samuel [0000-0003-2944-883X]
    Volcanoes and glaciers can both pose a significant threat to life and property. Volcanoes can erupt suddenly, without warning, causing injury, death and damage to property. Glaciers generally present a hazard over longer timescales, melting or sliding into the oceans and contributing to sea-level rise. The movement of melt at volcanoes, and ice at and near the Earth′s poles, can be investigated using microseismicity, emitted when these fluids and bodies release kinetic energy as they move. I use this microseismicity to study: melt moving from the deep crust and feeding Bardarbunga volcano, Iceland, before and after an eruption; icequakes at the bed of glaciers and ice sheets to study and constrain the physics of glacial sliding; and surface icequakes caused by crevassing, to see whether or not the crevasses observed are induced by hydrofracture. I use a combination of seismic observations and simple physical models to investigate these fundamental geophysical processes. Understanding the magmatic plumbing of a volcano is important for attempting to improve eruption forecasting. I analyse microseismicity before and after the Bardarbunga volcanic eruption, the largest eruption in Iceland in 230 years, to study possible pathways of melt from the deep crust to the shallow melt storage region. The seismicity and earthquake source mechanisms suggest that melt travels along a pathway that is approximately vertical, and laterally offset from the main shallow melt storage region by 12 km. However, it is also likely that an aseismic melt feed exists directly under Bardarbunga that we do not observe. These observations imply that volcanoes can be fed from depth, with lateral offsets of 10s kms, and that it is not adequate to monitor such volcanoes using seismicity alone. One critical process for constraining sea-level rise projections is glacial sliding. I describe how to detect and locate icequakes that originate at the bed of glaciers, which can be used to study glacial sliding. I analyse icequake source mechanisms for several glacial settings, comprising a range of spatial scales, in an attempt to unify the theory of stick-slip icequake failure, what it can tell us about glacial slip, and how such icequakes can be used to provide the first remotely measured values of bed shear modulus. The method used to remotely measure bed shear modulus will help constrain ice dynamics models and inform future passive cryoseismology studies of the Earth′s ice sheets. Another poorly understood process is surface crevassing. Again, I analyse the source mechanisms of surface crevassing icequakes and show that they are tensile cracks, opening in the shallow subsurface. I present a novel method of obtaining depth estimates for these crevasse icequakes. Deriving crevasse depth is important since crevasse depth is usually limited by the stress distribution within the ice column, unless they are filled with water that can allow deeper propagation via hydrofracture. This mechanism is a possible pathway of meltwater propagating from surface to bed, lubricating the bed and exacerbating the movement of ice into the ocean. The same mechanism is also important for understanding how ice shelves, such as the Larson B ice shelf, break up, releasing onshore ice to flow unperturbed into the ocean. Such observations of crevasse fracture are therefore of great relevance for understanding key instabilities that could contribute to future sea-level changes. My results help inform our understanding of the aforementioned processes, which are critical for forecasting volcanic eruptions better, and informing and constraining ice dynamics models used for sea-level rise projections.
  • ItemOpen Access
    Wind and temperature in a glacierised Himalayan valley, and their controlling mechanisms
    (2019-11-30) Potter, Emily Ruth; Potter, Emily Ruth [0000-0001-5273-1292]
    The Hindu-Kush Karakoram Himalaya (HKKH) contains the third largest quantity of snow and ice in the world, after the Polar Regions. Meltwater from this snow and ice feeds many of the major rivers in Asia, which ultimately provide water for 1.9 billion people. Due to its complex and rugged terrain, as well as a scarcity of in-situ measurements and fine-scale numerical modelling studies, important factors influencing melt and precipitation, such as the local valley wind regimes and the lapse rates of near-surface temperatures, are poorly understood in the HKKH. This thesis aims to improve understanding of the valley wind regime and temperature lapse rate for the glacierised Dudh Koshi River Basin in the Nepalese Himalaya, which includes the Khumbu Glacier, by utilising results from a high-resolution atmospheric model and measurements from a field campaign. First, the mechanisms controlling the local wind regime in the Dudh Koshi Valley are investigated, by running the Weather Research and Forecasting (WRF) model at 1 km horizontal resolution for one month in the summer and one month in the winter. The WRF model output is found to well represent the diurnal cycle of the wind when compared to existing in-situ observations, which is characterised by strong up-valley near-surface winds during the day and weak (predominantly up-valley) winds at night in both months. A momentum budget analysis reveals that the predominant physical drivers of the near-surface wind acceleration are the pressure gradient, advection and turbulent vertical mixing, which are extremely spatially variable over the valley. The results also show that the local wind regime and its drivers are strongly affected by the presence of glaciers, which act to weaken the up-valley flow. Second, as the Khumbu Glacier is largely debris-covered (along with many glaciers in the HKKH), a new debris-cover category is added into the WRF model. This enhancement is found to improve the model representation of near-surface temperature, relative humidity, wind speed and radiation, in comparison to the default category of clean-ice glaciers. The addition of the new debris-cover category, and the resulting change in near-surface temperature and wind speed are found to have consequent effects on water vapour, hydrometeors and ultimately snow cover. Third, to investigate the temperature lapse rate, a series of temperature sensors was installed throughout the Dudh Koshi Valley and over the Khumbu Glacier for 18 days during the pre-monsoon season in 2017, and the entire monsoon season. Lapse rates are found to vary considerably, both diurnally and over the pre-monsoon and monsoon periods. Temperature budget analysis based on output from the WRF model reveals that (both off-glacier and on the debris-covered glacier) the near-surface temperature during the day is warmed by turbulent vertical mixing and cooled by advection. Furthermore, at night a relationship is identified between strong downslope winds on the glacier and shallow lapse rates, due to warming from advection and cooling from turbulent vertical mixing. In addition, in the monsoon season there is a substantial contribution from latent cooling during the day. This is the first work to provide a full momentum and temperature budget analysis for a valley in the HKKH region. It is hoped that the advances made in this thesis may ultimately help inform developments to weather and climate models over the region, including highlighting the need for debris-covered glaciers to be represented in atmospheric models.
  • ItemOpen Access
    ‘Organics in ice’: Novel organic compounds in ice cores for use in palaeoclimate reconstruction
    (2019-10-26) King, Amy Constance Faith; King, Amy Constance Faith [0000-0002-1285-7568]
    The majority of current ice core studies focus on analysing the inorganic component of atmospheric aerosol, trapped and preserved in the ice as a record of past atmosphere. However, this does not fully represent the make-up of atmospheric aerosol, which can be up to 50% organic. This thesis aims to develop the understanding and quantification of a number of these organic compounds in ice core samples. A novel and promising area of ‘organics in ice’ research lies within the groups of primary and secondary compounds released from the terrestrial and marine biospheres; these compounds may help us to form a record of past biosphere emissions, with implications for biological productivity and atmospheric chemistry. A small selection of studies obtaining new records from these types of organic compounds in ice have demonstrated this concept, for example lipid compounds in snow layers dating back 450 years in Greenland, oxidation products of isoprene and monoterpenes in ice up to 350 years old in Alaska, and carboxylic acids and inorganic ions between 1942-1993 from Grenzgletscher (Monte Rosa Massif) in the southern Swiss Alps. Compound concentrations were related back to Northern Hemisphere temperature, atmospheric transport pathways and intensities, and biomass burning signals respectively. There are many terrestrial and marine biogenic compounds not yet investigated in ice core samples. Thus we are presented with an almost untapped reservoir of new climate information. Therefore, it is timely to produce a method of analysis for a long list of the most promising of these compounds (herein ‘target compounds’), namely fatty acids and secondary oxidation aerosol of terpenes (SOA), allowing quantification of these novel analytes in ice core samples to investigate the concept further. This project begins with an investigation in to the possible contamination sources of the target compounds in ice core samples. It attempts to quantify the threat of contamination throughout the drilling, storage and analyses processes. It finds there is substantial presence of organic compounds in media used during ice core processing, but the risk to target compounds is minor where clean-protocols are followed, and the threat is limited to outer surface ice of a solid ice core. Recommendations for ice core processing steps in preparation for organics analyses are outlined based on these results. A method of high performance liquid chromatography-mass spectrometry (HPLC-MS) including rotary evaporation preconcentration of samples is then optimised for detection of target compounds. The final method achieves good average recoveries of 80%, and reproducibility of 9% RSD. The method is reproducible on different instruments, based on an interlab comparison. An extension of this method, direct injection HPLC-MS analysis (where sample preconcentration is eliminated) is tested for the benefits of reducing sample volume and contamination introduced by preconcentration steps. The method is successful for SOA compounds (7% RSD) but not for fatty acids where background contamination is very high. The method of preconcentration HPLC-MS is then applied to samples from two ice cores; the marine-aerosol dominated Bouvet Island (sub-Antarctic) ice core, and the terrestrial-aerosol dominated Belukha Glacier (Russian Altai Mountains) ice core. Novel organic compounds are detected in both cores. Compound concentration time-series are investigated statistically by comparison to pre-existing inorganic compound records from the same cores and to historical climate data, and by application of back trajectory modelling using the Met Office's Numerical Atmospheric-dispersion Modelling Environment (NAME). In the case of Bouvet Island, the fatty acid oleic acid is found to have statistically significant correlations with the sea-ice marker methanesulfonic acid, and indeed with sea ice concentration during July to September in a geographical region extending westwards from the island along the maximum sea ice extent margin. The mechanism behind this correlation is suggested to be that of algal blooming during spring months, releasing oleic acid which is transported by strong westerly winds to the island. This highlights the prospects for a suite of marine biogenics in ice cores being used as sea ice markers. In the Belukha core, where sample records are available at sub-annual resolution, a suite of SOA compounds display summer-time peaks in concentrations. This seasonal variability is shown to be related to emission signals of these organic compounds, which is an exciting prospect for future work in improving our understanding of budgets of these aerosols in the atmosphere. The records detected demonstrate great promise for the use of organic compounds as environmental markers.
  • ItemOpen Access
    Understanding how low energy electrons control the variability of the Earth's electron radiation belts
    (2019-07-20) Allison, Hayley Jane
    The electron radiation belts are regions of geomagnetically trapped electrons, surrounding the Earth, presenting hazards to operational satellites. On the timeframe of hours, both the energy and particle flux of the radiation belts can change by orders of magnitude. Variations in the high energy relativistic electron flux depend on transport, acceleration, loss processes, and importantly, on the lower energy seed (10s – 100s keV) population. Seed population electrons are supplied to the radiation belt region during geomagnetically active periods and can be accelerated to higher energies via a range of processes. Unlike the higher energy, $>$1 MeV electrons, the azimuthal drift of the seed population is strongly affected by the convection electric field. Using fourteen years of electron flux data from low Earth orbit (LEO) satellites, a statistical study was performed on the magnetic local time distribution of three seed population energies, across a range of activity levels, defined by the geomagnetic indices AE, AE*, Kp, the solar wind velocity, and V$_sw$B$_z$. During periods of high activity, dawn-dusk flux asymmetries of over an order of magnitude were observed for $>$30 and $>$100 keV electrons, due to increased flux in the dawn sector. For $>$300 keV electrons, magnetic local time asymmetries were also present, but arose primarily due to a decrease in the average dusk-side flux beyond L* $\sim$4.5. A novel method was developed that utilizes measurements from low altitude, polar orbiting POES and MetOp satellites to retrieve the seed population at a pitch angle of 90$^o$. The resulting dataset offers a high time resolution, across multiple magnetic local time planes, and was used to formulate event-specific low energy boundary conditions for the British Antarctic Survey Radiation Belt Model (BAS-RBM). This new low energy boundary condition from LEO data has a higher spatial and temporal resolution, and a broader L* coverage, than previous work. The impact of variations in the seed population on the 1 MeV flux level was explored using the 3-D BAS-RBM to solve a diffusion equation for the electron phase space density. For some periods, an enhancement in the seed population was vital to recreate observed 1 MeV flux enhancements. A series of idealised experiments with the 2-D BAS-RBM were performed which highlight a careful balance between losses and acceleration from chorus waves. Our results show that seed population enhancements alter this balance by increasing the phase space density gradient, and consequently, the rate of energy diffusion, allowing acceleration to surpass loss. Additionally, pre-existing energy gradients in the phase space density and the duration of chorus wave activity determine whether $>$500 keV electrons were enhanced due to local acceleration.
  • ItemOpen Access
    Remote sensing of penguin populations: Development and application of a satellite-based method
    (2018-07-21) Brown, Jennifer Anne
    Five penguin species breed in Antarctica: emperors, Adélies, chinstraps, gentoos and macaronis. These are important Antarctic mid-trophic level predators and under predicted climate change are believed threatened. Accurate monitoring of populations is therefore of growing importance owing to the changing environment in which they live, particularly on the Western Antarctic Peninsula where rapid warming is occurring. The inaccessibility and size of many colonies makes ground based monitoring difficult with remote sensing providing an alternative, relatively low cost, monitoring method. Advancing current monitoring methods will help improve estimates of population trajectories at a regional scale. Recent and future progress in remote sensing, with new satellite sensors and platforms, offers increased potential for accurate, consistent large-scale data collection. The work in this thesis focuses on difficult to monitor brush-tailed penguins (Adélies, chinstraps and gentoos), aiming to develop new techniques and algorithms to improve their monitoring by satellite imagery. Penguin detection in satellite imagery is based on the red/brown guano stains that colonies create, with these stains evident from space. Fieldwork undertaken in Antarctica (Nov 2014-Jan 2015) using a field spectroradiometer obtained the first in situ hyperspectral reflectance spectra of Adélie and chinstrap guano. These spectra are used to identify the features responsible for varying guano types and suggest new indices for differentiating these in satellite imagery. Satellite imagery coincident with the fieldwork, obtained from WorldView-3 (~40 cm resolution) and Landsat 8 (~15 m resolution), are used to trial the index derived from the field spectra. Analysis of the field data and satellite images includes examination of guano colour for different species and comparison of methods of guano detection, aiming to enhance species detection from satellite imagery. In addition, Landsat 8 imagery from further locations is used to produce time series of this index for colonies, examining how guano colour changes over the breeding season are seen in satellite imagery. This dissertation concludes with recommendations for future developments of satellite-based methods based on the results of these analyses. Such improvements should help improve our current understanding of penguin population and continuing population changes in relation to climate change.
  • ItemOpen Access
    The impact of tropical sea surface temperature perturbations on atmospheric circulation over north Canada and Greenland
    (2018-07-21) McCrystall, Michelle Roisin
    Identifying the drivers of Arctic climate variability is essential for understanding the recent rapid changes in local climate and determining the mechanisms that cause them. Remote tropical sea surface temperatures (SST) have been identified in previous studies as having contributed to the recent positive trends in surface temperature and geopotential height at 200 hPa over north Canada and Greenland (1979-2012) through poleward propagating Rossby waves. However, the source and direction of wave propagation on to north Canada and Greenland (NCG) differs across climate datasets indicating that there are still uncertainties surrounding the mechanisms for how the tropics influence the NCG climate. This thesis aims to further investigate the robustness of the trends over NCG and understand how circulation in this region responds to imposed tropical SST perturbations. The eddy 200 hPa geopotential height (Z200) trends over NCG are assessed in a number of different datasets and compared to the response of eddy Z200 over NCG to imposed tropical SST perturbations in a number of sensitivity studies using the HadGEM3 atmosphere-only model. These model experiments are forced with observed differences in SSTs from the beginning and end of the satellite record (1979-1988 and 2003-2012), with spatial perturbations for [i] the entire tropics, [ii] global SSTs, [iii] the tropical Pacific only, [iv] the tropical Atlantic SST only, [v] the tropical Indian Ocean only. The positive spatial trends of eddy Z200 over NCG from ERA-Interim reanalysis is largely captured in ensemble means of two available climate datasets, UPSCALE and AMIP, indicating that this is a robust climate pattern, however, these trends appear to be stronger in the latter part of the record specifically over the UPSCALE period (1985 to 2011). The model sensitivity studies show that a negative eddy Z200 anomaly over NCG was found in response to all imposed tropical SST perturbations (2003-2012) relative to a background state (1979-1988). This was due a stationary trough over the region that was able to intensify in response to a lack of a strong anomalous wave forcing from changes in mid-tropospheric temperature and zonal winds. The forcing from the tropical Atlantic, relative to the other tropical ocean basins, resulted in the largest eddy Z200 response over NCG, indicating its dominance in forcing the large scale tropical signal. The influence of extratropical SST perturbations relative to tropical SST perturbations were also investigated and it was demonstrated that this negative anomaly is largely driven by the change in tropical sea surface temperatures.
  • ItemOpen Access
    The Evolutionary History of the Antarctic Flora
    (2017-06-21) Biersma, Elisabeth Machteld; Biersma, Elisabeth Machteld [0000-0002-9877-2177]
    How long has the extant flora been present in the Antarctic? Glaciological reconstructions propose that most areas in Antarctica were covered by thick ice sheets throughout the Last Glacial Maximum (LGM; ~22-18 kya) as well as previous glaciations, suggesting terrestrial life must have been extremely limited during these periods. In contrast, recent biogeographic and genetic studies support most extant groups of Antarctic terrestrial fauna having survived past glaciations in situ. However, studies on the origin and age of the Antarctic flora remain sparse. Applying population genetic, phylogeographic and divergence time analyses I assessed the global biogeography, origin and age of several abundant Antarctic moss species, including: four Polytrichaceae mosses, characterised by having bipolar distributions, the most common (~45% of species) distribution pattern amongst Antarctic mosses; the globally widespread moss Ceratodon purpureus; the bank-forming moss Chorisodontium aciphyllum, also known for its old sub-fossils in Antarctica and long-term viability from revival experiments; and, lastly, the genus Schistidium, the most species-rich moss genus in Antarctica, including many endemic species. Genetic analyses revealed evidence of long-term (multi-million year) survival of plants in Antarctica (several species of Schistidium, Ceratodon purpureus, and possibly Polytrichum juniperinum). However, evidence for a likely more recent (<100 ky) arrival of Chorisodontium aciphyllum was also found. Some species revealed multiple separate dispersal events to the Antarctic, suggesting the region may be less isolated for spore-dispersed organisms than previously thought. Evidence for increased genetic diversity in the northern maritime Antarctic compared to other regions point at it including potential refugial areas. Furthermore, genetic patterns revealed geographic features that enable and limit the connectivity of bryophytes globally as well as in Antarctica. This study suggests that, despite the harsh polar climate during glaciation periods, many bryophytes have had a much longer presence in Antarctica than previously thought.