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Physical Geography / Environmental Science PhD Opportunities

Research clusters, groups and topics

Physical Geography / Environmental Science research at the Department of Geography is divided into two broad research clusters: 1) Glaciology and Quaternary and 2) Environmental Processes. Within each of these large clusters, there are several distinct research groups advertising PhD topics suitable for studentships. If you have other ideas for topics that fall within the interests of these research groups, then we would be pleased to discuss them with you. To find out more about the topics or to discuss your own research ideas with a potential supervisor, please contact the relevant supervisor by e-mail.

Enquiries, applications and admissions

We welcome enquiries and applications from those with backgrounds in Physical Geography or Environmental Science, or in any other related and relevant discipline (e.g. Biology, Chemistry, Climatology, Computing, Engineering, Geology, Mathematics, Oceanography or Physics). Applicants should hold, or expect shortly to obtain, at least an Upper Second Class Honours Degree or equivalent.

  • UK / EU nationals who wish to be considered for a Natural Environment Research Council (NERC) studentship or a Cambridge Home and EU Scholarship Scheme (CHESS) award. Deadline: Friday, 11 January 2013. Read further details.
  • Non UK nationals who wish to be considered for a scholarship administered by the University of Cambridge for an October 2013 start: deadline 16 October 2012 for students from USA and 4 December 2012 for students from all other countries. Read further details.
  • Anyone who has secured full funding already. Please apply as soon as possible and at least 3 months before the start date, i.e. by 28 March 2013 for October 2013 start. Read further details.

1. Glaciology and Quaternary - www.geog.cam.ac.uk/research/gqc/

A. Glaciology

A1. Mass balance of Icelandic Glaciers

Supervisors: Ian Willis, Neil Arnold and Gareth Rees

Iceland is especially sensitive to global warming since its climate is affected by the confluence of warm and cold oceanic currents (a branch of the Gulf Stream and the East Greenland current respectively), and the tracks of most N. Atlantic depressions. Small changes in ocean or atmospheric circulation will have large effects on climatic variables such as air temperature, cloudiness and precipitation. Currently, about 11% (11 200km2) of Iceland is covered by ice, mostly contained within extensive plateau ice caps ranging in size from Hofsjökull i Loni (8 km2) to Vatnajökull (8175 km2). The maritime climate means these ice caps receive up to ~4 m w.e. a-1 of snowfall in their accumulation zones and lose up to ~10m w.e. a-1 of ice in their ablation areas. This, together with the fact they are temperate, means they are dynamically responsive to small climatically-induced mass balance changes.

The principal objective of this project is to develop a distributed mass balance – dynamics model for Iceland's glaciers that can be used to calculate spatial variations in accumulation and ablation and predict the likely response of the glaciers' mass balance to future scenarios of climate change. The mass balance component of the model has been used already to simulate surface mass balance variations across Haut Glacier d'Arolla, Switzerland and Midre Lovénbreen, Svalbard and is currently being used to calculate surface mass balance changes across large regions of Svalbard.

A major component to the project would be to couple the current mass balance model to an ice dynamics model. The model will first be developed, applied and tested using data collected on Langjökull, Iceland's second largest icecap (925km2). We have a range of data sets already for this ice mass including surface DEMs (derived from a range of ground dGPS traverse (1997), airborne photogrammetry (2001), and airborne LiDAR (2006)), a bed DEM, and weather station and point mass balance data available since 1996. Airborne Thematic Mapper multispectral data will be used together with Landsat and ground-based reflectance data to develop parameterisations in order to calculate spatial and temporal variations in albedo. 2m resolution airborne LiDAR surface topography data of most of the ice cap and 10cm resolution Terrestrial Laser Scanner surface topography data will be used to parameterise surface roughness. Statistically downscaled ERA-40 reanalysis data and GCM output will be used to drive the model for the past and future respectively. The model will be tested/calibrated against the point mass balance measurements and estimates of volume changes derived from surface DEM comparison. The project will involve further fieldwork in Iceland and benefits from collaboration with Professor Helgi Björnsson, Finnur Pálsson and Sverrir Gudmundsson (University of Iceland) and Dr Richard Hodgkins (University of Loughborough).

  • Björnsson, H. Palsson, F. Adalgeirsdottir, G. Gudmundsson, S. 2005. Mass balance of Vatnajökull (1991-2004) and Langjökull (1996-2004) ice caps, Iceland. Geophysical Research Abstracts, 7, 06485. Poster presented at EGU, April 2005 [http://www.raunvis.hi.is/~sg/EGU05_A_06485.pdf].

A2. Hydrology of polythermal glaciers

Supervisors: Ian Willis, Neil Arnold, Andy Hodson (Sheffield) & Jack Kohler (NVE, Norway)

It is now widely recognised that the hydrology of glaciers controls their dynamics and sediment/solute transfer processes, and the overall river flow regime of glacierised catchments, including the incidence of flooding. Whilst considerable progress has been made in understanding the hydrology of temperate glaciers and incorporating key processes into time dependent hydrological models, research into the hydrology of polythermal glaciers is still in its infancy and there has been little attempt to study the main processes within a numerical modelling context.

The overall aim of this project is to adapt and build on an existing physically-based distributed model of glacier hydrology. Currently, the model calculates distributed meltwater inputs to a glacier surface using standard energy balance theory and routes the water vertically and laterally through the unsaturated and saturated snowpack using standard snow hydrology theory. Variations in water routing through a network of englacial and subglacial channels in response to variations in surface water inputs are also treated in a physical way.

The model has so far been developed and tested using data from a temperate glacier in Switzerland but will be applied to a polythermal glacier in Svalbard for this project. There will be two main stages of model development. First, the surface energy balance and snow hydrology components of the model will be adapted to ensure they correctly calculate snowpack temperatures, melt rates, conduction within the snowpack and refreezing within the snowpack. Second, the subglacial hydrology component of the model will be adapted to include the effects on water routing of a distributed subglacial drainage system comprising a thin film and/or linked cavities, to account for interactions between the distributed and channelised components, and to incorporate the evolution of the subglacial drainage system to allow for the storage and subsequent release of water, which seems to be a charcateristics of many polythermal glaciers. Existing data sets will be used to develop and test the model, but the project is also likely to contain a fieldwork component at Midre Lovenbreen or Austre Lovenbreen, Svalbard to collect new data.

  • Arnold, N., Richards, K, Willis, I. and Sharp, M. 1998. Initial results from a semi-distributed, physically-based model of glacier hydrology. Hydrological Processes, 12, 191-219.
  • Arnold, N.S., Rees, W.G., Hodson, A.J. and Kohler, J. (2006) Topographic controls on the surface energy balance of a high Arctic valley glacier. Journal of Geophysical Research 111 F02011, doi:10.1029/2005JF000426 (15 pp).
  • Rippin, D., Willis, I., Arnold, N., Hodson, A., Moore, J., Kohler, J. and Bjornsson, H. 2003. Changes in geometry and sub-glacial drainage of Midre Lovénbreen, Svalbard, determined from digital elevation models. Earth Surface Processes and Landforms, 28, 273-298.

A3. Surface energy-balance and melt modelling of debris-covered glaciers

Supervisors: I. Willis, N. Arnold and B. Brock (Dundee)

As alpine glaciers retreat, debris, ranging in size from boulders to dust is increasingly concentrated onto their surfaces. Several studies at specific locations on a few glaciers have shown that thin layers of debris may enhance surface melt rates by lowering albedo but that thicker debris layers may reduce ablation by shading. Distributed glacier surface energy balance models do not adequately account for the effects of debris cover and its potential change in the future on patterns of melt and runoff, and yet this is likely to play an increasingly important role over the next few decades with important implications for glacier mass balance and the hydrology of glacier fed streams.

The overall aims of this project are to: i) use a combination of field work and remote sensing image classification techniques to quantify the debris cover changes of certain glaciers of the last few decades; ii) undertake field work on several glaciers to collect data necessary to calculate the energy and mass fluxes between the atmosphere and different types of debris covered ice surface and how these vary during an ablation season; iii) adapt an existing distributed energy balance / melt model to incorporate the effects of debris cover and test/calibrate the model against field measurements; iv) use the model to investigate the sensitivity of glacier mass balance and runoff to different debris covers and different formulations of debris cover processes; and v) use the model to evaluate how the debris covers and geometries of glaciers will evolve in the future to different scenarios of climate change.

The project will likely involve fieldwork in the European Alps but also possibly the Southern Alps, New Zealand or Alaska, USA.

  • Brock, B.W., Willis, I.C. Sharp, M.J. and Arnold, N.S. 2000. Modelling seasonal and spatial variations in the surface energy balance of Haut Glacier d'Arolla, Switzerland. Annals of Glaciology, 31, 53-62. E2. Mass balance of ice caps.
  • Willis, I., Arnold, N. and Brock, B. 2002. Modelling energy balance, melt and runoff in a small supraglacial catchment. Hydrological Processes 16(14) 2721-2749.
  • Arnold, N.S., Rees, W.G., Hodson, A.J. and Kohler, J. 2006. Topographic controls on the energy balance of a high Arctic glacier. In Press, Journal of Geophysical Research. Journal Of Geophysical Research, 111, F02011, doi:10.1029/2005jf000426.

A4. Using airborne and spaceborne remote sensing to investigate glacier geomorphic processes

Supervisors: Ian Willis, Gareth Rees and Neil Arnold

Airborne and spaceborne remote sensing techniques are widely used in glaciology to map the former extent of ice masses, and the geomophological features they have left behind. Such data are increasingly being used to infer the dynamic processes of former ice masses, in particular the distribution of warm and cold based ice, the locations of fast and slow flow, and the regions of basal sliding vs. sediment deformation. In a similar way, the technique of swath bathymetry is increasingly being used to map the geomorphology and reconstruct processes of former ice masses that terminated in shallow marine environments.

This project will use a combination of airborne and spaceborne remotely sensed imagery, together with airborne topopgraphic LiDAR data to investigate the geomorphology and retreat history of formerly glaciated terrain. We already have such data collected from several Svalbard glaciers in 2003 and 2005, several Icelandic glaciers in 2007, and hope to supplement these with flights in the Scottish Highlands in 2009. The LiDAR data have a horizontal resolution of ~1m and a vertical accuracy of ~0.1m and so the data have the potential to reveal detailed glacial geomorphic processes at a scale not previously possible with other remote sensing techniques.

The work will involve a variety of image analysis techniques but there will also be the opportunity for fieldwork in Svalbard and Iceland and (hopefully) the Scottish Highlands involving ground surveying, geomorphic mapping, and sediment logging, for ground-truthing purposes.

  • Smith, M.J., Rose, J. and Booth, S. 2006. Geomorphological mapping of glacial landforms from remotely sensed data: An evaluation of the principal data sources and an assessment of their quality. Geomorphology, 76 148- 165.

A5. Investigating flow sensitivity of Greenland outlet glaciers

Supervisors: Poul Christoffersen and Andreas Vieli (Durham)

Remote sensing of the Greenland Ice Sheet has revealed a net increase in ice-mass loss from 50 to 100 cubic km per year between 1995 and 2000 due to widespread acceleration of ice flow below 66°N. In 2005, the mass loss may have increased to more than 200 km3/year as the geographical boundary of speed-up appeared to migrate to 70°N (Rignot and Kanagaratnam, 2006). The sudden increase in sea-level-rise contribution from Greenland glaciers captured the attention of scientists, policymakers and the general public and the need for a better understanding of dynamic controls on ice sheet mass balance is one of the key conclusions in the Fourth Assessment Report by the Intergovernmental Panel on Climate Change (IPCC, 2007).

It is important to identify the driver of ice sheet mass-loss because an annual ice mass loss of 220 Gt corresponds to sea-level rise in excess of 0.6 mm/year. Zwally et al. (2002) measured surface velocities on 1-km-thick ice in West Greenland and proposed that speed-up events were caused by basal lubrication induced by penetration of surface meltwater to the bed. This mechanism may provoke a precarious positive feedback because accelerated ice flow leads to thinning, which in turn may lead to an increase in surface melt since a larger part of the ice-sheet moves into lower and therefore warmer elevations. Recent studies have confirmed this mechanism, but significant impacts are confined to the slow-moving, land-terminating parts of the ice sheet (Das et al., 2008; Joughin et al., 2008). Surface melt-induced basal lubrication does not significantly influence the fast flow of marine outlet glaciers (Joughin et al., 2008). Even on the land-terminating margin, its occurrence appears to have a very limited impact on the annual rate of ice flow (van de Wal et al., 2008). These observations are consistent with mapped ice margins, which show widespread, synchronous recession in 2000-2006 for glaciers terminating in the ocean and no detectable change for glaciers terminating on land (Moon and Joughin, 2008). Since 2006, the marine-terminating outlet glaciers appear to have stabilized, but cause of stabilization is not known.

The aim of this project is to examine the cause of discharge fluctuations from major outlet glaciers in Greenland. The project will include development and application of a numerical flow model where calving dynamics are influenced by ocean properties (Holland et al., 2008). The simulation may be based on application of a novel 3D higher order model currently used to simulate Antarctic ice streams. The robustness of the numerical experiments will be tested on the basis of datasets including (i) meteorological data acquired from automatic weather stations, (ii) time series of speed and calving front position, and (iii) oceanographic data from marine-geophysical cruises. The model will be used to explore the nature of ice-ocean-climate interactions and to predict sea-level rise associated with glacial discharge from two of Greenland's most significant drainage basins.

  • Howat, I. M., I. Joughin, S. Tulaczyk, and S. Gogineni, Rapid retreat and acceleration of Helheim Glacier, east Greenland, Geophysical Research Letters, 32, 2005.
  • Holland, D.M., Thomas, R.H., de Young, Ribergaard, M.H., Lyberth, B., 2008. Acceleration of Jakobshavn Isbrae triggered by warm subsurface ocean waters. Nature Geoscience. 1: 659-664.
  • Joughin, I., S. B. Das, M. A. King, B. E. Smith, I. M. Howat, and T. Moon (2008a), Seasonal speedup along the western flank of the Greenland Ice Sheet, Science, 320, 781-783.
  • Moon, T., and I. Joughin (2008), Changes in ice front position on Greenland's outlet glaciers from 1992 to 2007, Journal of Geophysical Research, 113, F02022, doi:10.1029/2007JF000927.
  • Rignot, E., and P. Kanagaratnam, Changes in the Velocity Structure of the Greenland Ice Sheet, Science, 311, 986-990, 2006.
  • van de Wal, R. S. W., W. Boot, M. R. van den Broeke, C. J. P. P. Smeets, C. H. Reijmer, J. J. A. Donker, and J. Qoerlemans (2008), Large and rapid melt-induced velocity changes in the Ablation zone of the Greenland Ice Sheet, Science, 321, 111-113.
  • Zwally, H. J., W. Abdalati, T. Herring, K. Larson, J. Saba, and K. Steffen, Surface melt-induced acceleration of Greenland ice-sheet flow, Science, 297, 218-220, 2002.

A6. Assessing state and dynamics of Arctic ice caps

Supervisors: Poul Christoffersen and Julian Dowdeswell

The body of scientific evidence for significant anthropogenic impacts on the global climate is growing and public concern underscores a need for better assessments of contemporary environmental changes in regions such as the Arctic. Although the vast majority of ice on Earth is stored in Greenland and Antarctica, it is important to keep in mind that 70% of the cryospheric contribution to 20th century sea-level rise was attributed to the retreat of mountain glaciers and ice caps (Dyurgerov and Meier, 2000; Meier and et al., 2007). Arctic ice masses are an important component of global change, especially as Arctic temperatures are increasing at almost twice the global average (IPCC, 2007).

The aim of this project is to investigate the response of Arctic ice caps to seasonal, interannual and decadal variations in air and ocean temperatures. The glaciological investigation will include delineation of calving ice fronts in time series and determination of surface velocity using InSAR and feature tracking techniques. Glaciological investigations may also include application of a 3D higher order ice flow model, which is currently used by the Scott Polar Research Institute in collaborative projects with partners in the UK and the USA. Datasets of environmental variables will be developed from meteorological records, satellite sensors and outputs from global ocean and climate models. The anticipated outcomes from this interdisciplinary project include integrated assessments of atmospheric vs. oceanic forcings and physical understanding of the response of ice caps to weather cycles vs. climate trends. The project can be designed so that it focuses on a specific Arctic ice cap, a selection of Arctic ice caps or the Greenland Ice Sheet. The studentship may be integrated with activities and outcomes from NERC-funded research projects aiming to elucidate ice flow and basal conditions on Vestfonna Ice Cap and the Greenland Ice Sheet.

  • Dyurgerov, M. B. and Meier, M. F., 2000, Twentieth century climate change: Evidence from small glaciers, Proceedings of the National Academy of Sciences of the United States of America, 97, 1406-1411.
  • IPCC (2007), Climate change 2007: The Physical Science Basis. Contributions of Working Group 1 to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Edited by S. Solomon et al., 996 pp., Cambridge University Press, Cambridge, UK, and New York, USA.
  • Meier, MF; Dyurgerov, MB; Rick, UK, et al., 2007, Glaciers dominate Eustatic sea-level rise in the 21st century, Science, 317, 1064-1067.

A7. Investigating ice flow and meltwater hydraulics on the Greenland Ice Sheet

Supervisor: Poul Christoffersen and Ian Willis

The Greenland Ice Sheet rests on bedrock above or close to sea level. Glaciologists have for years assumed that such position would be stable and that demise of the ice sheet would require thousands of years even under global warming scenarios. This assumption needs urgent revision. It was recently shown that surface meltwater can penetrate to the base of the Greenland Ice Sheet and cause ice-flow speed-up due to faster basal sliding (Zwally et al., 2003; Das et al., 2008; Joughin et al., 2008). This mechanism is potentially dangerous because accelerated ice flow leads to thinning, which in turn leads to an increase in surface melt since a larger part of the ice sheet moves into lower and warmer elevations.

Surface meltwater-induced basal mechanics are poorly understood and they are not present in the current generation of ice sheet models used to forecast future sea-level change. As highlighted in the Fourth Assessment Report by the Intergovernmental Panel on Climate Change (IPCC, 2007), it is essential that glaciologists provide a theoretical means to quantitatively evaluate: (1) linkages between surface, interior and basal water systems and their impacts on dynamic processes, and (2) the extent to which Arctic warming will affect the spatial and temporal characteristics of meltwater-induced glacial dynamics.

This project will address the above shortcomings by development and application of a numerical model that integrates ice flow and meltwater drainage in a land-terminating catchment on the western flank of the Greenland Ice Sheet. The project is designed so that it interacts with a multifaceted research project funded by the Natural Environment Research Council (2009-2012). The project may thus involve glaciological investigations with deep-looking (low frequency) radar, automatic weather stations and survey-quality GPS receivers.

  • Das, S. B., I. Joughin, M. D. Behn, I. M. Howat, M. A. King, D. Lizarralde, and M. P. Bhatia (2008), Fracture propagation to the base of the Greenland Ice Sheet during supraglacial lake drainage, Science, 320, 778-781.
  • IPCC (2007), Climate change 2007: The Physical Science Basis. Contributions of Working Group 1 to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Edited by S. Solomon et al., 996 pp., Cambridge University Press, Cambridge, UK, and New York, USA.
  • Joughin, I., S. B. Das, M. A. King, B. E. Smith, I. M. Howat, and T. Moon (2008), Seasonal speedup along the western flank of the Greenland Ice Sheet, Science, 320, 781-783.
  • Zwally, H. J. et al. Surface melt-induced acceleration of Greenland ice-sheet flow. Science, 297, 218-222 (2002).

A8. Processes and patterns of glacier-influenced sedimentation on Arctic and Antarctic continental margins

Supervisor: Julian Dowdeswell

During Quaternary glacial periods, glaciers and ice sheets expanded along fjords and across continental shelves, sometimes reaching the shelf edge, on many high-latitude margins in the Arctic and Antarctic (e.g. Dowdeswell et al., 2002; Ottesen et al., 2005; Dowdeswell et al., 2006). Submarine landforms, produced by the action of these ice masses, contain a record of the past extent, flow direction and processes that took place at the ice-bed interface. The basal boundary of glaciers and ice sheets is of considerable significance to our understanding of glaciological processes, but it is a location hidden by a kilometre or more of ice in modern polar settings. Glacier and ice sheet retreat after the last glacial period has both revealed suites of submarine landforms produced at the base of former ice masses, and marine waters have protected them from much of the subsequent erosion to which sub-aerial landforms have been subjected.

We hold a large number of geophysical and geological datasets concerning continental shelf, slope and deep-marine high-latitude settings that have been influenced intermittently by the growth and decay of ice masses. These datasets include swath bathymetry, shallow acoustic profiles and core material, that can be used to reconstruct the past form and flow of ice sheets. The candidate would work with several of these datasets, using digital image analysis tools in order to understand the details of past ice flow extent, direction and basal processes. Data are available from the Arctic (Greenland, Svalbard and Norwegian margins) and from West Antarctica and the Antarctic Peninsula. These datasets have been collected over the past decade or so on a series of research cruises of the British ice-strengthened research vessel James Clark Ross, and there will be a further cruise this summer. The successful candidate may be able to take part in this cruise to West Greenland.

  • Dowdeswell, J.A., Ó Cofaigh, C., Taylor, J., Kenyon, N.H., Mienert, J. and Wilken, M., 2002. On the architecture of high-latitude continental margins: the influence of ice-sheet and sea-ice processes in the Polar North Atlantic. In Dowdeswell, J.A. and Ó Cofaigh, C., (Editors), Glacier-Influenced Sedimentation on High-Latitude Continental Margins, Geological Society, London, Special Publication, 203, p. 33-54.
  • Dowdeswell, J.A., Evans, J., Ó Cofaigh, C. and Anderson, J.B., 2006. Morphology and sedimentary processes on the continental slope off Pine Island Bay, Amundsen Sea, West Antarctica. Geological Society of America, Bulletin, v. 118, p. 606-619.
  • Ottesen, D., Dowdeswell, J.A. and Rise, L., 2005. Submarine landforms and the reconstruction of fast-flowing ice streams within a large Quaternary ice sheet: the 2,500 km-long Norwegian-Svalbard margin (57º to 80ºN). Geological Society of America, Bulletin, v. 117, p. 1033-1050.

A9. Ice-Ocean interactions in the Arctic

Supervisors: Poul Christoffersen and Julian Dowdeswell

Arctic warming is predicted to be almost twice the global average and temperature increases of 4-7°C are forecast during the 21st century (IPCC, 2007; ACIA, 2004). Arctic ice masses are therefore expected to diminish at an accelerated pace with major impact on global sea levels (Bamber et al., 2007).

Warm saline water from the Atlantic plays a key role in the Arctic climate system. Atlantic Water is carried by the North Atlantic Current, which bifurcates near Iceland. The main branch of the North Atlantic Current enters the Nordic Seas and follows the Norwegian coast before it bifurcates again, flowing either west into the Barents Sea or north into the Arctic Ocean west of Spitsbergen. The second branch enters the Irminger Sea where warm Atlantic Water meets cold polar water from the East Greenland Current. The Irminger Sea forms a part of the sub-polar North Atlantic and is a critical component of Earth's global climate system as deep water formation at this location drives thermohaline circulation (Dickson and Brown, 1994). It is also a location where the Greenland Ice Sheet is exposed to warm ocean temperatures and this exposure has recently caused widespread retreat and acceleration of outlet glaciers terminating in fjords (Moon and Joughin, 2008; Joughin et al., 2008; Holland et al., 2008).

The fundamental aim of the project is to assess cryopsheric impacts of atmospheric warming and changes in the flow of Atlantic water in the Arctic and sub-Arctic seas. The investigation will be quantitative and focused on cryospheric impacts in target areas proximal to major ocean currents. Research objectives include use of: (i) climate reanalysis data, (ii) atmospheric weather records; (iii) outputs from global ocean models, (iv) hydrographic ocean datasets; (v) satellite-derived changes in front position and flow speed of a selection of target glaciers. The project may also include numerical modeling of marine-terminating glaciers.

  • ACIA, 2004. Impact of a warming Arctic, Arctic Climate Impact Assessment, Cambridge University Press.
  • Holland, D.M., Thomas, R.H., de Young, Ribergaard, M.H., Lyberth, B., 2008. Acceleration of Jakobshavn Isbrae triggered by warm subsurface ocean waters. Nature Geoscience. 1: 659-664.
  • IPCC (2007), Climate change 2007: The Physical Science Basis. Contributions of Working Group 1 to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Edited by S. Solomon et al., 996 pp., Cambridge University Press, Cambridge, UK, and New York, USA.
  • Joughin, I., S. B. Das, M. A. King, B. E. Smith, I. M. Howat, and T. Moon (2008a), Seasonal speedup along the western flank of the Greenland Ice Sheet, Science, 320, 781-783.
  • Moon, T., and I. Joughin (2008), Changes in ice front position on Greenland's outlet glaciers from 1992 to 2007, Journal of Geophysical Research, 113, F02022, doi:10.1029/2007JF000927.

A10. Response of calving glaciers to sea ice formation and water circulation in fjords

Supervisors: Poul Christoffersen and Tony Payne (Bristol)

Satellite observations show that a deficit in the mass balance of the Greenland Ice Sheet grew from -91 cubic km/year in 1996 to -140 cubic km/year in 2000 due to widespread acceleration of outlet glaciers terminating in fjord. In 2005, the imbalance increased to about -220 cubic km/year. More than 70% of the ice mass loss in 2005 came from glaciers on the East Coast and the largest contributor to sea-level rise was Kangerdlugssuaq Glacier whose net volume loss increased from -5 cubic km/year in 2000 to -40 cubic km/year in 2005 (Rignot and kanagaratnam, 2006).

It is important to identify the driver of ice sheet mass-loss because an annual ice mass loss of 220 cubic km/year corresponds to sea-level rise in excess of 0.6 mm/year. Scientists have for some years measured surface velocities along the western flank of the Greenland Ice Sheet and it was proposed that speed-up events were caused by basal lubrication induced by penetration of surface meltwater to the bed (Zwally et al., 2002). This mechanism may provoke a precarious positive feedback because accelerated ice flow leads to thinning, which in turn may lead to an increase in surface melt since a larger part of the ice-sheet moves into lower and therefore warmer elevations. Recent studies have confirmed this mechanism (Das et al., 2008), but significant impacts seem to be confined to the slow-moving, land-terminating parts of the ice sheet (Joughin et al., 2008). Surface melt-induced basal lubrication does not significantly influence the fast flow of marine outlet glaciers. Even on the land-terminating margin, its occurrence appears to have a very limited impact on the annual rate of ice flow (van de Wal, 2008). These observations are consistent with mapped ice margins, which show widespread, synchronous recent recession for glaciers terminating in the ocean and no detectable change for glaciers terminating on land (Moon and Joughin, 2008).

The rapid increase in ice mass-loss from the Greenland Ice Sheet by fast flowing outlet glaciers terminating in fjords has captured the attention of scientists, policymakers and the general public. The need for better theoretical understanding of dynamic controls on ice sheet evolution is one of the key conclusions in the Fourth Assessment Report by the Intergovernmental Panel on Climate Change (IPCC, 2007).

This project will elucidate oceanic controls on the observed rate of ice loss from the Greenland Ice Sheet. The fundamental aim is to test the hypothesis that sea-ice formation and fjord circulation are the main controls on calving glacier dynamics. To test the hypothesis, a numerical model of water circulation in Kangerdlugssuaq Fjord will be coupled to a higher-order ice flow model for Kangerdlugssuaq Glacier and its catchment. The project can be expanded to include other tidewater glaciers, but Kangerdlugssuaq Glacier is the ideal starting point because it is one of Greenland's fastest glaciers and because the Scott Polar Research Institute has extensive datasets for this prominent glacier.

  • IPCC (2007), Climate change 2007: The Physical Science Basis. Contributions of Working Group 1 to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Edited by S. Solomon et al., 996 pp., Cambridge University Press, Cambridge, UK, and New York, USA.
  • Joughin, I., S. B. Das, M. A. King, B. E. Smith, I. M. Howat, and T. Moon (2008a), Seasonal speedup along the western flank of the Greenland Ice Sheet, Science, 320, 781-783.
  • Moon, T., and I. Joughin (2008), Changes in ice front position on Greenland's outlet glaciers from 1992 to 2007, Journal of Geophysical Research, 113, F02022, doi:10.1029/2007JF000927.
  • Rignot, E., and P. Kanagaratnam, Changes in the Velocity Structure of the Greenland Ice Sheet, Science, 311, 986-990, 2006.
  • van de Wal, R. S. W., W. Boot, M. R. van den Broeke, C. J. P. P. Smeets, C. H. Reijmer, J. J. A. Donker, and J. Qoerlemans (2008), Large and rapid melt-induced velocity changes in the Ablation zone of the Greenland Ice Sheet, Science, 321, 111-113.

A11. Sedimentary processes and flow of Antarctic ice streams A11

Supervisor: Poul Christoffersen and Julian Dowdeswell

Satellite remote sensing has provided much new information about the contemporary changes occurring in the Antarctic Ice Sheet. Although the quality of satellite sensors are improving rapidly, these remotely sensed data are ultimately snapshots in time, as coverage is limited to only a few decades. The geological record of the Antarctic continental shelf has been used to infer the history of the Antarctic Ice Sheet, but this approach does not include the Quantitative constraints offered by e.g. numerical modelling techniques.

The aim of this project is to integrate geological processes in a numerical ice flow model (Bougamont et al., 2003; Christoffersen and Tulaczyk, 2003). The integrated model will be applied to the Ross ice streams and outlet glaciers draining the East Antarctic Ice Sheet. The model will be used to reconstruct ice flow and sediment transfer from the Antarctic continent to the Antarctic continental shelf. Model results will be validated using geological records from the Cape Roberts and ANDRILL projects (Mosola et al., 2006; McKay et al., 2008; 2009).

One of the key objectives of this project is to elucidate spatial and temporal characteristics of sediment entrainment and transfer by Antarctic ice streams during the Quaternary and possibly late Cenozoic periods. The ice-flow/sediment-transfer model will be used as a means to quantitatively assess the formation of subglacial landforms and the influence of landform assemblages on ice sheet dynamics (Dowdeswell et al., 2008; Christoffersen et al., 2009). The anticipated outcomes from the project will contribute to a better understanding of past and future behaviour of the Antarctic Ice Sheet.

  • Bougamont M. and S. Tulaczyk, 2003, Glacial erosion beneath ice streams and ice-stream tributaries: constraints on temporal and spatial distribution of erosion from numerical simulations of a West Antarctic ice stream, Boreas, 32, 178-190.
  • Christoffersen P. and S. Tulaczyk, 2003, Response of subglacial sediments to basal freeze-on: 1. Theory and comparison to observations from beneath the West Antarctic Ice Sheet, Journal of Geophysical Research Solid Earth, 108 (B4), 2222.
  • Christoffersen P., S. Tulaczyk and A. Behar, 2009, Basal ice sequences in Antarctic ice stream expose past hydrologic conditions and a principal mode of sediment transfer, Journal of Geophysical Research, submitted.
  • Dowdeswell, JA; Ottesen, D; Evans, J, et al., 2008, Submarine glacial landforms and rates of ice-stream collapse, Geology, 36, 819-822.
  • Mosola A. B. and J. B. Anderson, 2006, Expansion and rapid retreat of the West Antarctic Ice Sheet in eastern Ross Sea: possible consequence of over-extended ice streams?, Quaternary Science Reviews, 25, 2177-2196.
  • McKay, R.M., Dunbar, G. B. Naish, T. R. Barrett, P. J. Carter, L. and Harper, M., 2008, Retreat history of the Ross Ice Sheet (Shelf) since the Last Glacial Maximum from deep-basin sediment cores around Ross Island, Palaeogeography, Palaeoclimatology, Palaeoecology, 260, 245–261.
  • McKay, R., Browne, G., Carter, L., Cowan, E., Dunbar, G., Krissek, L., Naish, T., Powell, R., Reed, J., Talarico, F., Wilch, T., 2009. The stratigraphic signature of the late Cenozoic Antarctic Ice Sheets in the Ross Embayment. Geological Society of America Bulletin 121: 1537-1561.

A12. Investigating Arctic permafrost decay

Supervisor: Poul Christoffersen and Julian Dowdeswell

The Arctic is changing at a greater rate than any other environment on Earth. Surface temperatures are warming and permafrost is degrading, and ecosystems are adapting to new environmental conditions. New extreme and seasonal surface conditions are evident, hydrological and biogeochemical cycles are shifting, and more regularly social systems are being affected. The Arctic warms faster than the global mean because recession of reflective sea-ice and snow cover leads to increased absorption of solar energy by exposure of darker land and ocean surfaces, and limited evaporation (compared to the tropics) means that a high fraction of the solar energy goes directly into warming the atmosphere (ACIA, 2004). Even though the Arctic zone of continuous permafrost has relatively cold mean annual air temperatures, a large increase in the extent of permafrost degradation, for instance in northern Alaska, is associated with record warm temperatures since 1990 (Hinzman et al., 2005; Jorgensen et al., 2006).

The aim of this project is to develop spatial and temporal understanding of permafrost decay through analyses and interpretation of satellite imagery of the Alaskan and Siberian Arctic. The investigations will include assessment of changes in hydrological cycles and development of thermokarst lakes in response to permafrost decay. Project outcomes may be integrated with numerical experiments with the Joint UK Land Environment Simulator (JULES).

  • ACIA, 2004. Impact of a warming Arctic, Arctic Climate Impact Assessment, Cambridge University Press.
  • Hinzman L. D. and 34 others, 2005. Evidence and implications of recent climate change in northern Alaska and other arctic regions, Climatic Change, 72, 251-298. doi:10.1007/s10584-005-5352-2
  • Jorgenson M.T. and 2 others, 2006. Abrupt increase in permafrost degradation in Arctic Alaska, Geophysical Research Letters, L02503. doi:10.1029/2005GL024960

B. Quaternary Palaeoenvironments - www.qpg.geog.cam.ac.uk

Quaternary Palaeoenvironments projects are listed on the QPG website.

2. Environmental Processes - www.geog.cam.ac.uk/research/ep/

C. Cambridge Coastal Research Unit - www.ccru.geog.cam.ac.uk

C1. The decadal morphodynamic change of cuspate forelands: case studies from East Anglia

Supervisors: I Möller, T Spencer and SM Brooks (Birkbeck College, University of London)

(N.B. This topic may not be available for October 2013 admission)

An adequate understanding of, and ability to predict, geomorphological processes that govern the long-term natural and/or human induced changes of large-scale sedimentary features, such as cuspate forelands, is essential to the successful management of shorelines. It has been speculated that some large-scale (km scale) nearshore sedimentary features, the nesses or cuspate forelands, of the UK East Coast are inextricably linked to offshore tidal sand banks and thus to the regional sediment transport on the shores of the southern North Sea as a whole. The highly dynamic nature of these nesses has led to the migration of large amounts of sediment alongshore and resulted in changes of beach width of >100 m over time-spans of less than 40 years (Robinson, 1980). Furthermore, ness migration has led to the 'switch on' and 'switch off' of cliff erosion in weakly cemented Plio-Pleistocene deposits and thus to changing foci for sediment inputs to the nearshore zone. Coastal managers are thus faced with the challenge to understand the link between the dynamics of the nesses and sediment transport on a larger scale within the Southern North Sea. Furthermore, the ability to predict the morphological evolution of such features is required if direct and indirect coastal management problems linked to the movement of nesses are to be anticipated.

The coastal management of sedimentary shorelines requires that the maximum amount of morphodynamic information is extracted from existing datasets. In particular, management applications increasingly require information on sediment volumes (for the determination of sediment budgets) rather than beach plan-form or cross-sectional change. In their attempt to reconstruct ness behaviour, early studies (e.g. McCave, 1978 and Robinson, 1966; 1980) had to rely on topomaps produced infrequently over the past century (with periods of up to several decades between individual surveys) and with a limited resolution for the analysis of beach planform shape parameters. These shortcomings resulted in several, often contradictory, theories as to the evolution and dynamics of these features. Since the early 1990s, annual 1:5,000 aerial stereo-pair photographs have become available that now provide scope for a much more in-depth study of the annual to decadal dynamics of the ness features of the UK East Coast. In addition, new digital methods for the analysis of spatial data (such as digital photogrammetry and the DSAS extension to ArcMap) have become available. Previous work in Cambridge and London, funded through the EU and UK The Crown Estates respectively, has shown that such methods can successfully be used to extract three-dimensional morphodynamic information from repeat photography. This in turn has allowed a re-evaluation of existing theories of ness dynamics and evolution.

This project will build upon, and extend i) the analysis of aerial photography of i) Winterton Ness, Norfolk coast, 1998 – 2001 with new data from ii) Caister Ness and iii) Benacre Ness, Suffolk coast, to encompass the full 15-year time period (1992 - present) now available. Images, acquired from an agreed collaboration with the UK Environment Agency, will be georeferenced by ground control data acquired by differential GPS (dGPS) field survey. The position of cliff top edge, dune edge and other beach plan-form features will be identified, mapped, and converted into computer-animated time-series. Digital photogrammetry and GIS techniques will be applied to those images available in digital format to generate digital elevation models (DEMs). The accuracy of the DEMs will be determined through field surveys using ground-based LiDAR and dGPS. The results will be used to construct animations and quantitative estimates of the morphological change that have characterised these Nesses over the 15-year time-scale. This information will then be set in the context of available information on wave/tide circulation patterns and other ongoing research on the UK East Coast and further afield to revise and extend existing models of the evolution of cuspate forelands in general and assess the impact of human interference with long-shore transport along this coast in particular.

C2. Vegetation surface roughness quantification and relationships to flow attenuation over intertidal surfaces

Supervisors: I. Möller & T. Spencer

Successful coastal management in the face of global environmental change (sea level rise and storminess) will require better tools to assess the natural wave/tide 'buffering' function of the intertidal zone. Previous studies have shown that intertidal salt marsh environments in a variety of physical settings can cause significant attenuation of waves (e.g. Möller et al., 2001 and Möller and Spencer, 2003) and currents (e.g. Leonard and Reed, 2002). This research has focussed on either the 'marsh-wide' scale of the complex canopy of mixed vegetation type (100s metre) or on the scale of individual plants and their structure (<1m scale) , involving detailed, time-consuming, and costly field measurements at specific sites. More accurate numerical models of wave and tide propagation across vegetated surfaces would allow for a more generic assessment of the varying sea defence function of the intertidal zone, as is required for the design of scientifically-informed regional coastal management strategies. Currently, however, existing numerical models perform with limited accuracy due to the poor representation of vegetation-induced surface roughness and associated flow retardation.

Many saltmarsh plant species, such as Atriplex portulacoides, present on most UK East coast marshes, not only exhibit a high degree of structural complexity, but are also subject to seasonal changes in growth that may affect their wave/current attenuation potential (Möller and Spencer, 2002). To represent such vegetation simply as an array of rigid cylinders obstructing the flow (Knutson et al. 1982), or to merely quantifying the drag force acting on the plant (Dalrymple et al. 1984, Kobayashi et al. 1993), does thus not suffice as an adequate assessment of hydrodynamic roughness. Furthermore, the flexible and buoyant nature of the intertidal vegetation canopy provides additional challenges when quantifying its hydrodynamic behaviour.

Side-on digital photography (as developed for grasslands by Zehm et al. (2003) and adapted for salt marsh vegetation by Möller (2006)) and ground-based LiDAR offers the possibility of developing more complex statistical summary parameters that represent those characteristics of the vegetation canopy that relate most closely to flow attenuation by the canopy. This study will use both these techniques in a controlled laboratory environment, where the attenuation of uni-directional (and, if feasible, bi-directional) currents will be recorded through a series (e.g. Spartina alterniflora and Atriplex portulacoides) of mono-specific salt-marsh canopies. For each species, the vegetation density and height will be varied between individual experiments and the spatial structure of the canopy will be recorded each time using side-on digital photography of a 30-100 cm wide section of the canopy (giving an effective sampling interval of the order of 0.1 mm) and near-vertical ground-based LiDAR of the entire canopy with an average point-spacing of approximately 5 cm. Variations in canopy height as well as canopy density or 'porosity' metrics will be analysed using a series of statistical approaches, including an investigation of possible self-affine ('fractal') patterns common to natural surfaces (i.e. evidence of a power-law dependancy of the Fourier transform of the spatial measurement (e.g. the canopy height profile)). Such methods have, e.g., successfully been used to characterise the aerodynamic roughness elements of glacier surfaces (Rees and Arnold, 2006). The statistical relationship between the various 'roughness' and 'porosity' metrics on the one hand, and the degree of flow attenuation on the other hand, will then be investigated, with the aim of identifying which metric can most reliably be used as an indication of hydrodynamic roughness of the canopy.

It is hoped that this project will be a collaboration between CCRU and HR Wallingford Ltd and will be accompanied by a CASE award to the student. Whilst the student will be based in Cambridge, s/he will spend some research time at HR Wallingford Ltd, working alongside staff there.

C3. Decadal-scale morphodynamics of cohesive intertidal open coasts

Supervisors: I. Möller & T. Spencer

The behaviour of cohesive intertidal shores, characterised, in NW Europe, by mudflat and saltmarsh environments, is governed largely by the physical drivers of sea level, wave energy level, and sediment supply. While all three of these factors are expected to change as a result of longer-term (50-100 year scale) climatic changes (IPCC, 2007), the annual to decadal scale variability within these controls is likely to result in morphological changes of the intertidal zone over similar time-scales (see e.g. Allen (2000)). Moreover, it is likely, that the response of the intertidal zone to these physical stimuli is highly non-linear, controlled by thresholds, and characterised by morphodynamic feedback and lag-times.

This project aims to make use of extensive morphological and hydrodynamic datasets for a series of open coast or outer estuarine saltmarsh sites on the East coast of the UK (including The Wash (Lincolnshire), Wells/Stiffkey (North Norfolk), Dengie (Essex), and Medway (Kent)) to statistically evaluate the relationship between these physical drivers and the morphological response of the saltmarsh-mudflat interface. Morphological data will consist of cross-shore intertidal profiles and 1:5,000 aerial photographs held by the UK Environment Agency and available at annual intervals for the period 1991/2 to present (i.e. at least the last 16 years). Hydrodynamic datasets will be gathered from a range of sources, including hindcast model outputs of wave / water levels and water level records held at the Environment Agency and the British Oceanographic Data Centre. A series of statistical approaches will be used to investigate a range of possible non-linear statistical relationships between hydrodynamic forcing and morphological response with the aim of building a stochastic model to simulate horizontal erosion/accretion 'behaviour' of intertidal open coast wetlands on the UK East Coast.

D. Hydrology, Water and Landscape - www.geog.cam.ac.uk/research/ep/hwl/

D1. Discrete element modelling of sediment transport systems

Supervisors: Keith Richards, Mike Bithell & Dongfang Liang (Engineering)

Discrete element methods are proving to be an invaluable means of understanding a range of particle interaction processes. They are well-developed in certain fields (eg, chemical engineering, powder technology), but their potential has yet to be fully exploited in environmental sciences. The aim of this project will be to develop such an application, with reference to one of a number of phenomena (bedload transport in rivers, scree sorting processes, long-runout debris avalanches). For example, classic examples of long runout landslides (eg, Franks, Blackhawk, Ulm) could be re-assessed, by reconstructing the pre-failure topography and the failed mass, and seeking to replicate the long runout behaviour of the slide debris. This will give insights into the rheology, and permit improvements to be made simplified macro-scale models of the process. A particular focus of this research is thus to extract key patterns of larger-scale behaviour from these micro-scale models, such as the distribution of shear, the potential for particle wear, the depositional characteristics and the effects of topographic features (and of structural protection measures). The project will employ a combination of terrain modelling and remote sensing to construct the topography, and scaled laboratory modelling and field monitoring in order to parameterize and test the models developed. It will be of interest to students with backgrounds in engineering, earth science, computing, applied mathematics and physical geography.

D2. Interactions of hydrology, vegetation and land use

Supervisors: Mike Bithell & Keith Richards

Temporal fluctuations in rainfall, on timescales from annual through to decadal and longer, change the spatial distribution of ground water availability, mediated by the soil-type, slope and landcover. This in turn determines the locations within the landscape that can support agriculture. Interception of rainfall and its infiltration into and movement through the soil is dependent both on vegetation and land-use - natural forest, actively harvested forest and farmland all have differing hydrological characteristics. The resulting soil moisture distribution and runoff rates affect soil erodibility and landslide probabilities, irrigation possibilities and rain-fed crop yields, flood frequency and stream discharge. New techniques in computational modelling now allow us to build models that represent some of the complexity of human behaviour and social interaction, and to couple these to ecological and physical models. This project will build on an existing environmental model that incorporates an agent-based model of a farming community, an individual-based forest model and spatially distributed hydrological model to investigate interplay between human decision-making, land-use change, vegetation dynamics and hydrology. In this way we can study the implications for biodiversity and the sustainability of various farming practices at the catchment scale. This inter-disciplinary project will be of interest to students with backgrounds in land use change, ecology or hydrology, or interests in interface between social and environmental systems. A grounding in applied mathematics, GIS or numerical computation would also be an advantage.

D3. Discrete element modelling of scree slope development

Supervisors: Mike Bithell & Keith Richards

Discrete element modelling is a computational technique that simulates the dynamics of particle assemblages by computing explicitly the trajectory of every particle under the forces of gravity and the effects of collisions with other particles or with solid surfaces. It is proving to be an invaluable means of understanding a range of particle interaction processes. It is well-developed in certain fields (e.g. chemical engineering, powder technology), but the potential has yet to be fully exploited in environmental sciences. The aim of this project will be to develop such an application, with reference to one of a number of scree sorting processes. The development of a scree may take place through infrequent falls of individual particles through to large scale multiple rock-fall events. The shape of the resulting slope is thought to be a result of the combination of large scale factors such as cliff retreat, energy of supply of the falling rocks, local slope characteristics and rate of removal of the resulting scree material, and individual particle properties such as size range, shape, surface friction and internal dissipation. The project will employ a combination of terrain modelling and remote sensing to construct the topography, and scaled laboratory modelling and field monitoring in order to parameterize and test the models developed.

D4. Modelling channel, floodplain and floodplain ecosystem dynamics

Supervisors: Keith Richards & Mike Bithell

Reduced complexity models (in which the hydrodynamics are treated in a simplified manner) are of increasing value in simulating longer-term evolution of fluvial systems at larger length scales (101-103 years, 103-106 metres). In particular, they have the potential to simulate evolution where significant change occurs in the boundary conditions for the flow, and therefore strong feedbacks occur amongst flow, sediment transport and topographic change. They could also allow interactions of hydrological, geomorphological and ecological dynamics to be studied, and therefore could be useful tools in the management of river-floodplain systems. Nevertheless, the potential is not easy to realize, because is it not always clear that the simplifications adopted allow realistic coupling of sub-models (eg of flow and sediment transport). The Department has a long term research programme to apply this class of models to floodplain dynamics, and projects have thus far explored flow models, simplified transport models, and simple models for ecological change. There remains scope for a variety of contributions to this programme, for example in coupling flow and sediment transport to derive predictions of channel change, in developing a model structure that allows simulation of channel pattern and defines the conditions when meandering or braiding occur, and in individual-based modelling of floodplain ecosystem structure and it feedback to the physical processes of flow and sediment transport. These projects would suit individuals with a variety of backgrounds, with experience in numerical modelling, computation and GIS and remote sensing being particularly relevant.

E. Atmospheric Processes - www.geog.cam.ac.uk/research/ep/ap/

E1. Implementation and Testing of a Convective Cloud Field Model for use in Global Climate Models

Supervisors: Prof. Hans-F Graf and Dr. Michael Herzog

Convective clouds are a challenging problem in atmospheric modelling at the scale of global climate models since they have spatial scales that cannot explicitly be resolved. In most cases the current parameterisations reduce the cloud spectra to a single mean cloud. This produces problems not only for the simulation of precipitation, but also for convective transport and latent heat release. While it is possible to parameterise these cloud spectra by cloud resolving sub-models, this is computationally by far too expensive for long climate simulations. The aim of this project is to implement a new Convective Cloud Field Model (CCFM) into a climate model after rigorous testing against observations and cloud resolving models, optimisation with respect to microphysics and initialisation, and adaptation. The use of CCFM allows to explicitly simulating cloud spectra without prescribing the spectrum properties from observations or cloud resolving models. It results also in explicit convective transport, microphysics inclusive the fate of soluble and non-soluble species and the effects of aerosols on cloud properties. The work will concentrate on i) a climate control run with CCFM which will be evaluated against the standard climate model and observations, both satellite and ground based, ii) a GCM simulation of the effects of different aerosols on convective clouds and climate, iii) implementing a convection transport scheme for atmospheric tracers and iv) providing a tested module for the parameterisation of convective cloud fields for use in climate models. Good mathematical/physical training is essential.

E2. Comparison of deep convection in single column and cloud resolving model using observed and idealized cases

Supervisors: Dr. Michael Herzog and Prof. Hans-F. Graf

Convection and its parameterisation are a major challenge in climate research. A recently developed convective cloud field model CCFM used in exchange of bulk mass flux schemes in climate models will be tested against the really cloud resolving model ATHAM and observations. It will be necessary to further develop a module of surface energy fluxes (soil model) for ATHAM. Extensive numerical simulations will be performed on the Darwin Supercomputer and the results be evaluated against campaign observations. The project will focus on process oriented research. Good mathematical/physical training is essential.

E3. Simulating co-ignimbrite eruptions with the plume model ATHAM

Supervisors: Dr. Michael Herzog, Prof. Hans-F. Graf and Dr. Clive Oppenheimer

Big explosive volcanic eruptions of the caldera forming type very probably are characterized by the formation of secondary eruption columns, the co-ignimbrite plumes. Explosive volcanic eruptions form buoyant plumes after sufficient entrainment has taken place. If a (buoyant) Plinian eruption plume cannot be formed, the eruption column will collapse. A secondary, so called co-ignimbrite plume can be formed from the developing pyroclastic flow. In previous work the behaviour of such co-ignimbrite eruptions has been studied by one-dimensional plume models based on the assumption that they can be regarded point sources. So far we used the three-dimensional plume model ATHAM in an idealized setup to investigate the impact of this assumption on the plume development. Clearly, Neutral Buoyancy Heights are overestimated when one-dimensional stationary top hat models are applied. Entrainment and wind shear have strong influence on the plume development. Co-ignimbrite plumes can be realistically represented only in a fully three dimensional model. The goal of the project is a more realistic representation of pyroclastic flows and the formation of the co-ignimbrite plume in the model ATHAM. The project includes some model development: implementation of terrain following coordinate system and a simple soil model. The results will be of theoretical nature and be based on comparing forcing and effects from idealized to more realistic configurations of the model. Specific observed cases will be simulated and evaluated. The sedimentation of ashes will be in the centre of the investigation and an intense evaluation of the classical sedimentation theory. ATHAM results and surface observations will be compared. Good mathematical/physical training is essential.

E4. Simulating radar signals for volcanic clouds: the ATHAM Radar Simulator

Supervisors: Dr. Michael Herzog and Prof. Hans-F. Graf

Volcanic eruptions pose a danger for aviation as ashes in the plume may destroy the turbines of jet engines, acids may destroy seals and ash may scratch windshields making them opaque. At several places, like in Sicily, Radar observations are used to monitor volcanic plumes but due to their changing nature the Radar signals are not easy to interpret. Hence, a first guess Radar signal is necessary that includes the varying composition of the plume. In collaboration with the University of l'Aquila, Italy, a module will be developed for the high resolution plume model ATHAM that allows simulating the RADAR reflectivity of a volcanic plume. Extensive comparison will be made against real observations. The module will further be developed into one that allows simulating the Radar signals of deep convective clouds. Good mathematical/physical training is essential.

E5. Stratospheric sulphur chemistry for volcanic injections

Supervisors: Prof. Hans-F. Graf and Dr. Michael Herzog (collaboration with Prof. John Pyle, Chemistry)

Volcanic eruptions, large wild fires and deep convective clouds can inject large mounts of solid material, tropospheric trace gases and ice into the lower stratosphere. While the very high resolving model ATHAM can simulate this injection, its time frame is too short to also simulate the fate of this material in the stratosphere. The PhD work will consist of simulations with ATHAM for a number of typical weather conditions of the stratospheric injection of SO2, water vapour and ice particles. These injected masses will then further be treated in a Chemistry-transport model TOMCAT (available at the Chemistry department) to simulate their fate over several days. This will, for the first time, allow to estimate the effective amount of direct stratospheric injection of tropospheric material into the stratosphere. Results will be evaluated against in situ and satellite observations. Good mathematical/physical training is essential.

E6. The "new" type of El Nino: Why recently the Central Pacific takes over?

Supervisor: Prof. Hans-F. Graf

Very recently there have been numerous reports on a "new" type of El Nino, which is characterized by predominantly positive sea surface temperature anomalies in the tropical Central Pacific rather than in the East Pacific. Central Pacific and East Pacific events are events driven solely by local surface wind anomalies not including the thermocline and events following the delayed oscillator theory, including deepening of the thermocline by propagating Kelvin waves, respectively.

The PhD project will study the effects the two different types of El Nino have on weather and climate in Europe and provide evidence for a mechanism that links Central Pacific SSTA with the atmospheric circulation over the North Atlantic and Europe quite efficiently in case of Central Pacific SSTA, much less efficient for East Pacific SSTA. This process leads to winter climate anomalies in Europe that are opposite in sign, so that, if all El Ninos are considered regardless of their type, statistically non-significant effects emerge. Another important aspect is if the "new" El Nino is due to the change in the mean state of the climate system due to anthropogenic warming or it is due to naturally occurring multi-decadal variability of the Pacific ocean. The main tools to be used are data analysis and global coupled ocean-atmosphere model simulations. The candidate shall have profound knowledge in atmospheric (e.g. wave propagation) and ocean dynamics and be able to handle large data sets as well as use complex climate models.

F. Volcanology

F1. Environmental controls on the composition, size and evolution of volcanic aerosol

Supervisors: Rob Martin and Clive Oppenheimer, Evgenia Ilyinskaya (BGS) & Philip Kyle (New Mexico Tech.)

Volcanic degassing is an important natural source of particles to the atmosphere. Volcanic particles enhance chemical reactivity in volcanic plumes, act as cloud condensation nuclei and transport toxic and nutrient trace elements into terrestrial environments. The size and composition of volcanic particles are key controls on their environmental behaviour. Micron-sized sulphates (e.g., H2SO4, Na2SO4, K2SO4) are widely thought to be the most abundant type of particle in ash-poor volcanic plumes. However, our recent studies have revealed that micron-sized chlorides (e.g., NaCl, KCl) are most abundant in the volcanic plumes of Mt. Erebus (Antarctica) (Ilyinskaya et al., 2010) and Eyjafjallajokull (Iceland) (Ilyinskaya et al., 2012). These marked compositional differences likely reflect the very low temperatures (<0 °C) during sampling. Elsewhere, volcanic particles may become richer in chloride during periods of high relative humidity (e.g., during the night or the wet season) due to particle uptake of HCl. To date, most measurements of volcanic particles have been made over a narrow range of atmospheric conditions (i.e., warm and dry) so the true nature of volcanic particles may be misrepresented.

The aim of this project is to develop a more complete understanding of particles in volcanic plumes. Field measurements will be designed to investigate systematically changes in volcanic particles (i.e., size and composition) in response to atmospheric conditions (i.e., temperature and relative humidity). Size-distributed particle samples will be collected using cascade impactors (e.g., Martin et al., 2008, 2011, 2012) over a range of atmospheric conditions. Results from field measurements will be investigated using equilibrium aerosol models (e.g., E-AIM). It is anticipated that fieldwork will be conducted at Masaya volcano (Nicaragua) and Kilauea (USA), where relative humidity changes significantly between the day and night. Fieldwork will also be conducted in Erebus (Antarctica) to examine more closely the characteristic features of volcanic plumes and particles in cold atmospheric settings.

The ideal candidate will have a background and keen interest in earth sciences/atmospheric chemistry, and be able to undertake careful laboratory work. The anticipated fieldwork is physically demanding and will involve sampling in cold conditions and during the night-time.

References (all available on request – contact Rob Martin, rsm45@cam.ac.uk):

  • Ilyinskaya, E., Oppenheimer, C., Mather, T.A., Martin, R.S., & Kyle, P., 2010, Size-resolved chemical composition of aerosol emitted by Erebus volcano, Antarctica, Geochemistry, Geophysics and Geosystems, 11, Q03017.
  • Ilyinskaya, E., Martin, R.S., Oppenheimer, C., 2012, Aerosol formation in basaltic lava fountaining: Eyjafjallajökull volcano, Iceland, Journal of Geophysical Research, 117, D00U27.
  • Martin, R. S., T. A. Mather, D. M. Pyle, M. Power, A. G. Allen, A. Aiuppa, C. J. Horwell, and E. P. W. Ward (2008), Composition-resolved size distributions of volcanic aerosols in the Mt. Etna plumes, J. Geophys. Res., 113, D17211.
  • Martin, R.S., Ilyinskaya, E., Sawyer, G.M., Tsanev, V.I. and Oppenheimer, C., 2011, A re-assessment of aerosol size distributions from Masaya volcano (Nicaragua), Atmospheric Environment, 45, 547–560.
  • Martin, R.S., Sawyer, G. M., Day, J. A., Le Blond, J. S., Ilyinskaya, E., and Oppenheimer, C., 2012, High resolution size distributions and emission fluxes of trace elements from Masaya volcano, Nicaragua, Journal of Geophysical Research, 117, B08206.

G. Landscape Ecology

G1: The role of ecosytem physiological processes in the historical global carbon cycle on land

Supervisor: Andrew Friend

Terrestrial ecosystems plays a key role in the global carbon cycle, as well as providing humans and other ecosystem trophic levels with essential services. However, we only have a very poor understanding of the global behaviour of their interaction with the atmosphere, including the surface carbon balance. This is despite numerous observational systems collecting data on ecosystem state and behaviour. These observations include in situ fluxes, tree rings, and structural parameters such as height, as well as remote sensing estimates of surface light absorption, leaf area, and atmospheric CO2 dynamics (which can be used to estimate surface fluxes). It is essential that we improve our understanding of past fluxes and their controls in order to inform future projections of both impacts and feedbacks with the atmosphere. Examples of controls on temporal and spatial variability include seasonal drought, temperatures extremes, and storm damage (e.g. across the Amazon rainforest in 2005).

This PhD project will address this problem using a dynamic global vegetation model (see References below). The model will be further developed, tested, and used to better understand the role of climate and atmospheric CO2 on the historical global terrestrial carbon balance. The model exists in different forms that allow the analysis of controls on ecosystem state as a result of climate variability in space and time. The model will be extended to incorporate land use change over the 1880-2009 period , and simulations will be made of the global distribution of carbon sources and sinks over this period. Comparisons will be made with satellite data (e.g. MODIS), in situ data such as from flux towers, and the dynamics of atmospheric CO2. In addition, collaborations with other research groups will be exploited to compare different model and remote-sensing based estimates of historical carbon fluxes. This will enable the quantification and attribution of uncertainty, and establish methodologies for further improving our understanding of controls on terrestrial ecosystem states and behaviour, particularly their roles in the global carbon cycle.

References:

  • Friend AD. 2010. Terrestrial plant production and climate change. Journal of Experimental Botany, doi: 10.1093/jxb/erq019
  • Friend, A.D. and Kiang, N.Y. 2005. Land-surface model development for the GISS GCM: Effects of improved canopy physiology on simulated climate. Journal of Climate 18, 2883-2902, doi:10.1175/JCLI3425.1.
  • Friend, A.D. and White, A. 2000. Evaluation and analysis of a dynamic terrestrial ecosystem model under preindustrial conditions at the global scale. Global Biogeochemical Cycles 14(4), 1173-1190.