Glaciers and ice caps are recognised as an important component of the global carbon cycle. Carbon within glacial systems exists in organic and inorganic forms, across supraglacial, englacial and subglacial realms. It is often difficult to detach cryospheric carbon cycling from hydrology, with the transfer of carbon between glacial inventories relying upon meltwater flows. Classical glacial hydrology consists of distributed drainage delivering delayed flow meltwaters, throughout the accumulation season, superseded by quick flow, aerated channelized drainage during increased ablation. It is upon this template that most existing studies have addressed the dynamics of carbon within glaciated catchments. However, Icelandic glacial systems provide an opportunity to investigate the role of subglacial volcanism in driving carbon dynamics. Hydrochemical properties of Sόlheimajökull bulk meltwaters indicate untraditional redox conditions, with discharge of reduced, anoxic meltwaters in Summer, when expansion of subglacial drainage intersects the Katla geothermal zone. This unique hydrological regime generates profound effects upon the solute flux from the glacier, particularly with regard to the carbon budget. Dissolved inorganic carbon dynamics are dominated by weathering of basaltic bedrocks and accessory hydrothermal calcites, fuelled by subglacial geothermal proton supply. Widespread basal anoxia during summer facilitates methanogenesis resulting in large quantities of methane being discharged from beneath the glacier (flux range between 9,179 to 22,551 tonnes per year). Evidence suggests subglacial microbial acetoclastic methanogenesis is responsible with δ13C and δD CH4 values of ~60‰ and -320‰ respectively, supported by laboratory identification of methanogenesis in Sόlheimajökull subglacial sediments. The organic counterpart to the carbon cycle is invoked to serve as the energy source for microbial metabolism. Such direct measurements of subglacial methane have rarely been achieved at contemporary ice margins. This study therefore provides an exciting opportunity to identify methane sources and carbon cycling in areas subjected to subglacial volcanism and to consider these within the broader context of global carbon dynamics.

No description available.

Pine Island Ice Shelf (PIIS), in the Amundsen Sea, is losing mass due to warm ocean waters melting the ice from below. The glacial meltwater appears as a warmer and more saline water mass (with lower O2 concentration) than theWinterWater. Tracing meltwater pathways from ice shelves is important for identifying the regions most affected by the increased input of this water type. Water mass characteristics (temperature, salinity, O2 concentration) are used to calculate glacial meltwater fractions (MW). The observations from the Amundsen Sea show a plume of MW travelling away from PIIS along ¾ = 27.7 kg m¡3, out to the continental shelf edge. We investigate the reliability of the interpretation of the observations as a signature of MW. Physical and biological processes can affect the calculated apparentMWby causing variations in the water mass characteristics. In theWeddell Sea, iceberg meltwater was found to enhance biological productivity. In the Amundsen Sea, the biological productivity was seen to artificially decrease the apparentMWsignature. We analyse the effects of these processes on the reliability of the calculated meltwater fractions using a modified one-dimensional ocean model. The model simulates the effects of an increase in sea ice production and an influx of Lower CDW, as well as biological activity. These processes are found to result in an observation that can conventionally be interpreted as a meltwater signature, similar to the plume observed at the continental shelf edge. Recommendations are made to improve the reliability of MW calculations, including the identification of a ‘pseudo’-CDW endpoint and to increase the uncertainty associated with the O2 concentrations. A meltwater pathway leading to the west of PIIS, along the coastline, is observed. This has implications for water mass characteristics further to the west and ultimately AABW formation in the Ross Sea.

The main aim of this research project was to improve our understanding of the diversity, function and ecology of glacial microbiomes. Snow and ice algae are critical players in supraglacial habitats and form extensive blooms in spring and summer. Here I present results on the diversity and the function of snow and ice algae on 21 glaciers in 4 Arctic settings: Greenland, Iceland, Svalbard and Sweden. For the first time, I have evaluated the full microbial community composition (i.e., algae, bacteria, archaea) in the main supraglacial habitats, namely green snow, red snow, biofilms, dirty ice, and cryoconite holes. I have cross-correlated these data with metabolic analyses (i.e., metabolomics, pigments, fatty acids) and critical physico-chemical parameters. I found that snow and ice algae were the first communities to appear after the onset of melting and they showed positive net photosynthetic rates indicating accumulation of organic matter. Furthermore, for the first time I have described these communities in Iceland. My data reveal that red pigmented snow algae are cosmopolitan, and independent of location specific geochemical and mineralogical factors. Only six taxa made up >99% of the algal communities: two uncultured Chlamydomonadaceae, Chloromonas polyptera, Chloromonas nivalis, Chloromonas alpina and Raphidonema sempervirens. In contrast, the composition of green snow varied between the studied locations with higher relative abundance of Raphidonema sempervirens and Microglena sp. in Svalbard, and Chloromonas polyptera in Sweden. Furthermore, I show that green and red snow are not successive stages but two independent phenomena with different adaptation strategies. In all sites, bacteria were mostly represented by the phyla Bacteriodetes, Proteobacteria and Cyanobacteria. The bacterial community composition varied between the different habitats on the phylum level, whereas on the class level they also showed strong biogeography. Archaea showed overall low species diversity. The synthesis of pigments and fatty acids in snow and ice algae were mainly driven by nitrogen and less so by phosphorus limitation. This is especially important for pigments which cause a darkening of glacial surfaces. I show that snow and ice algae dramatically decrease surface albedo which will eventully result in higher melting rates of glaciers.

Recent climatic amelioration during the 20th and 21st centuries has stimulated the recession of glaciers world-wide. Moraines developed by valley glaciers provide a sedimentary record of their past response to climatic forcing. Despite the use of moraines for understanding the character and behaviour of former glaciers, our understanding of moraine development is lacking largely due to limited opportunities to study active moraine formation. This thesis reports on internal structure and sedimentary composition of lateral-frontal moraine at two Arctic (Austre Lovénbreen, Svalbard and Isfallsglaciären, Sweden) glaciers and one Alpine (Schwarzberggletscher, Switzerland) glacier and aids understanding of their palaeo-environmental significance. The internal structure and sedimentary architecture of Arctic lateral-frontal moraine is documented using ground penetrating radar (GPR) and via shallow excavation. Lateral-frontal moraine at both Arctic sites are shown to contain buried ice within their lateral zones, but not within their frontal zones, although the volumetric content of the buried ice and potential origin varies between sites. Frontal zones are therefore likely to be better preserved in the geomorphological record following complete de-icing, whereas lateral zones, which may also be subject to de-icing and external censoring from slope processes, may be poorly preserved. As the internal structure is dissimilar across Arctic sites, it is argued that the processes involved in the development of landforms by Arctic polythermal glaciers vary between high-Arctic and continental Scandinavian settings. Arctic lateral-frontal moraine are also distinct from those found at Alpine sites which are organised into stacked diamicton units that dip away from the lateral margin of the glacier. The sedimentary signature of Arctic and Alpine lateral-frontal moraine are investigated and compared. All moraines investigated exhibit clast-form gradients which is interpreted to relate to the relative significance and spatial variation of ‘active’ and ‘passive’ debris transport mechanisms within Arctic and Alpine valley glacier landsystems. However, the climatic, glaciological, and topographic regimes in which the moraines form influence the resulting character of the landform. The evolution of a degrading ice-cored moraine at Austre Lovénbreen is investigated using repeat photogrammetric topographic surveys. Relict glacier ice is undergoing moderate rates of degradation, predominately via down-wastage and could potentially be preserved as an archive of former high-Arctic glacier characteristics. This thesis also contributes to the wider body of knowledge in relation to the use of unmanned aerial vehicles (UAVs) and ‘Structure-from-Motion’ (SfM) photogrammetry for geomorphological research. The multi-technique approach employed by this research has allowed for the glaciological significance of subsets of lateral-frontal moraine (‘Controlled’, ‘Østrem’ and ‘Alpine’ type) within in glaciated valley landsystem to be better understood. Conceptual models accounting for landform development are presented and aid Quaternary studies that seek to identify and use lateral-frontal moraine for dating past glacier activity and determining palaeo-glacier characteristics.

The drainage of ice-dammed lakes produces floods that can pose hazards, waste water resources and modulate ice flow. In this thesis I investigate several aspects of ice-dammed lake drainage through the development and analysis of mathematical models. After an introduction in the first chapter and a description of the mathematical background to the thesis in the second, the third chapter investigates the mechanisms behind observed variability in the size and timing of subglacial floods from ice-dammed lakes. In particular, I examine how environmental controls like the weather and the shape of glaciers affect floods. In the next chapter, I quantify how well simple models can predict the dates of floods from an ice-marginal lake in Kyrgyzstan. I find that incorporating environmental controls into models improves their prediction ability. Next I investigate the coupling between subglacial drainage and glacier motion during ice-dammed lake drainage by developing and analysing a model which couples a marginal lake, glacier sliding, subglacial drainage through a channel and subglacial drainage through a distributed system of cavities. I show how changes in lake level cause the rate at which a glacier slides to increase during the first half of floods and decrease during the second half. The next two chapters are concerned with two lake-drainage scenarios that involve water flowing as an open stream: firstly, the subglacial open-channel flow that occurs after a marginal lake drains completely during a flood, and secondly, the drainage of supraglacial lakes across the surface of ice sheets. I end the thesis with a summary of my findings and some suggestions of theoretical and field-based investigations that are worthwhile pursing in the future.

Supraglacial lakes (SGLs) form when runoff (meltwater + rain) pools in depressions on the Greenland ice sheet (GrIS). SGLs can collectively affect seasonal ice sheet flow rates when they drain episodically; although the net impact on flow speed is uncertain. In this thesis: 1) a new model of SGL Initiation and Growth (the SLInG model) is presented, 2) existing SGL observations are evaluated and combined to form a single optimised dataset, 3) these data are used to evaluate the model and 4) this model is used to investigate past trends in SGL evolution in south west Greenland. SLInG is a 2-dimensional transient hydrology model which routes runoff, which has been simulated using a regional climate model, over a digital elevation model (DEM) of the ice sheet surface. Water is routed using Darcy’s law for flow through a porous medium and Manning’s equation for open channel flow, and is allowed to collect in depressions in the DEM, thus forming SGLs. Observations of SGLs can be temporally sparse and variation in reported lake frequency can be significant between datasets. Three observational datasets of SGLs, automatically derived from satellite data, were found to omit a sizeable (29 to 48%) fraction of lakes identified manually. These datasets were combined using a hierarchical scheme, leading to a 67% increase in the number of lakes reported. By comparison with satellite observations, SLInG is found to be 19 times more likely to correctly predict the location, or absence, of a lake, than not. In addition, simulated and observed lake onset dates are highly correlated (r= ~0.8) and model estimates of the rate of growth of lake covered area are, on average, just 14% greater than observed values. SLInG was forced with 40 years of reanalysis data in order to investigate historical variation in the temporal evolution of SGLs. SLInG shows that SGLs have responded to recent dramatic changes in local climate by migrating inland by 150 m a.s.l. (3.75 m a.s.l. per year) during 1971-2010. This modelled trend is in good agreement with recent satellite observations and suggests that SGLs, by forming and draining at higher elevations, where pre-existing surface-bed conduits such as moulins and crevasses are rare, may contribute more significantly to ice sheet dynamics in the future.

No description available.

During the last 20 years, West Antarctica has experienced enhanced ice discharge to the ocean due to loss of buttressing from melting and collapsing ice shelves. On the other hand, increases in precipitation have been reported in East Antarctica in line with an expected wetter atmosphere in a warming climate. The big questions that still lie ahead are therefore: (i) Will the enhanced precipitations in East Antarctica compensate the dynamic mass losses observed in West Antarctica in the future? (ii) And what will be the resulting contribution to sea level rise (SLR)? To answer those questions we need to have a firm grip on the present day mass balance (MB) of Antarctica and on the mechanisms that govern both the surface mass balance (SMB) and the ice discharge (D) into the ocean. This thesis investigates the MB of Antarctica using the input-output method (10M) allowing for a direct diagnoses of local, regional and global MB in Antarctica. It does this for both the Antarctic Ice Sheet (AIS) and the ice shelves. Because the mass imbalance of AIS is of the order of 5-10% of both accumulation and attrition terms of the mass budget (~2000 Gt yr-1), all glaciers around Antarctica as well as each assumption made require precise attention. This thesis starts with a chapter exploring the grounding zone (Chapter 2), and then goes on to the actual mass balance calculations of the AIS in Chapter 3 and of the Antarctica ice shelves in Chapter 4. The Grounding lines (GL) of Antarctica have been widely studied using various techniques at a local and regional scale. In recent years GL datasets aiming for circumpolar coverage have been published using different approaches. However these datasets still bear unexplained discrepancies of up to tens of kilometres in numerous places around Antarctica. In Chapter 2 four recent datasets are compared which track either the surface break of slope (h) or the inward limit of tidal flexure (F) as proxies for the grounding point (G). From visual examination and from a particle tracking scheme (PTS), it is found that all GL datasets agree within 1-2 km on slow moving ice and on the sides of fast flowing features (FFFs). However it is confirmed that h, obtained from photogrametry or photo clinometry, is not a reliable proxy in central parts of FFFs because of multiple breaks-in-slope and artefacts. It is further confirmed that the most reliable methods to map G in such places are those tracking F. In addition, a gravitational driving stress (td) is computed from a 1 km Antarctic digital model elevation (DEM) and leads to the finding that driving stress mapping (DSM) supports dynamic approaches in grounding line location. This reconciles static and dynamic grounding line methods by showing that they map the same features providing that altimetry is used rather than imagery for static methods. Guided by these analyses a new, up-to-date, and complete grounding line of Antarctica is compiled. The potential of DSM is successfully tested on a grounding line migration case study in West Antarctica. To investigate the grounding zone around Antarctica and its ice dynamics, DSM is further used. DSM allows to map sharp transitions across G for slow moving ice, as well as complicated transitions on fast flowing features (FFFs). Complicated transitions on FFFs contradict the idea of there being an ideal transition occurring at G, whereby the ice flow regime switches from basal drag-dominated to lateral drag-dominated. Rather, it is found that acceleration occurs upstream of G and that deceleration occurs downstream of G. This changes the understanding of the grounding zone ice dynamics, where ice was believed to accelerate at G due to loss of basal drag. Using DSM in combination with ice penetrating radar (lPR), reported and new ice plains (i .e. lightly grounded areas) are detected and mapped. They extents cover ~55,000 km2 around the Ross, the Filchner-Ronne, and the Larsen C ice shelves. These findings have implications for our understanding of ice sheet stability since ice plains are particularly prone to grounding line migration and can stretch up to ~300 km inland of G. In Chapter 3 the MB of the AIS is assessed using the input-output method (lOM). The grounding line fluxes (GLF) and 5MB are estimated for 110 drainage basins covering the whole AIS. The GLF is computed using up to date grounding lines and additional radar ice thicknesses data compared to previous 10M studies. 5MB values are re-evaluated in light of new drainage basins defined from an ice velocity field rather than from topography. 5MB is taken as the 30 years mean of three regional climate models. Due to a number of improvements in the GLF methodology, an unprecedented 94% of the ice sheet area is surveyed, i.e. an increase of + 13% from the latest 10M study. Un-surveyed areas are accounted for using mass trends (MT) from a Bayesian hierarchical modelling solution from the RATES (Resolving Antarctic ice mass TrEndS) project. The integrated AIS mass balance is -63 ± 83 Gt yr- I and divides into -22 ± 28, -62 ± 45, and 22 ± 64 Gt yr- I for the Antarctic Peninsula (AP), the West Antarctic Ice Sheet (WAIS), and the East Antarctic Ice Sheet (EAIS), respectively. The integrated MB is therefore a lower 10M estimate compared to previous 10M studies and reconciles the 10M with the other MB methods of satellite gravimetry and altimetry. Because the stability of the AIS is intimately linked to the stability of ice shelves, Chapter 4 finally focuses on the mass balance of ice shelves around Antarctica, giving the partition between calving fluxes (CF) and basal mass balance (BMB), the main processes by which Antarctic ice is lost. Before this study, iceberg calving had been assumed the dominant cause of mass loss for the Antarctic ice sheet, with previous estimates of the calving flux exceeding 2,000 Gt yr- I . More recently, the importance of melting by the ocean had been demonstrated close to the grounding line and near the calving front. So far, however, no study had reliably quantified the calving flux and the BMB (the balance between accretion and ablation at the ice-shelf base) for the whole of Antarctica. The distribution of fresh water in the Southern Ocean and its partitioning between the liquid and solid phases was therefore poorly constrained. Here, a first estimate of the mass balance components for all ice shelves in Antarctica is produced using calving flux and grounding-line flux from satellite and airborne observations, modelled ice-shelf snow accumulation rates, and a regional scaling that accounts for un-surveyed areas. The total CF is 1321 ± 144 Gt yr- I and the total BMB is -1454 ± 174 Gt yr-1 . These numbers mean that about half of the ice-sheet surface mass gain is lost through oceanic erosion before reaching the ice front, and that the calving flux is about 34% less than previous estimates derived from iceberg tracking. In addition, the fraction of mass loss due to basal processes varies from about 10 to 90 % between ice shelves. A significant positive correlation between BMB and surface elevation change is found for ice shelves experiencing surface lowering and enhanced discharge. It is therefore suggested that basal mass loss is a valuable metric for predicting future ice-shelf vulnerability to oceanic forcing.

Uncertainty over future sea level rise is of great concern to society. One useful analogue for future sea levels is the Last Interglaciation (~130-118ka), when global sea level was around 6m higher than present. While most of the expected components to this are well simulated, the magnitude and location of the Antarctic contribution is poorly understood. Here, I perform a variety of ice sheet sensitivity tests to determine constraints on the extent/geometry of the Antarctic ice sheet during the Last Interglaciation in comparison with Antarctic ice core δ180 data and far-field relative sea level data, raised beaches and fossil corals from Patagonia and Australia. The effect of changes in solid earth deformation at ice core sites are simulated using a glacial isostatic adjustment model, and show minimal impact from plausible ice sheet collapses at any considered data sites, and that the ongoing deglacial uplift effects are likely to form a significant component of solid earth elevation around the Ross and Weddell Seas. I use the coupled atmosphere-ocean climate model, HadeM3, to simulate 2kyr snapshot runs for each ice sheet scenario (132-118ka). Precipitation seasonality is very poorly simulated over inland East Antarctica. Modelled changes in temperature between LIG and preindustrial show most similarity to ice core 8180 data when changes in precipitation seasonality are not accounted for. In the event of collapse of any of the marine based West Antarctic, Wilkes, and Aurora basins, cyclonic conditions would dramatically alter local climate, which is not observed in any data, indicating the ice sheet to be in similar to present geometry. Finally, I investigate the effect of glacial-isostasy on the nearest far-field relative sea level data, from Patagonia and Australia. Australian data suggests that there would have to be continual gradual sea level input throughout the Interglaciation. Although a unique fingerprint of West Antarctic collapse might be seen in Patagonian data, uncertain tectonic uplift and deglaciation history means this would be practically impossible to determine. Overall, I am able to determine that the Wilkes or Aurora subglacial basins did not significantly retreat. There remains no data suggesting a West Antarctic collapse in the Last Interglaciation, although the magnitude of global sea level strongly implies some Antarctic contribution.