Please find details below about two potential (open competition) fully funded PhD projects at the University of Exeter. Further details of the projects, the NERC Doctoral Training Partnership and how to apply can be found on:
http://www.bristol.ac.uk/gw4plusdtp/projects/ - details of the two projects below are under the “Atmospheres, Ocean & Ice” theme.
Thanks,
Anne
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Dr. Anne Le Brocq
Lecturer, Geography
College of Life and Environmental Sciences
University of Exeter
http://www.exeter.ac.uk/geography
https://twitter.com/#!/exetergeography
+44 (0)1392 723833
“Ice-Shelf Signatures of Subglacial Hydrology in Antarctica and Greenland”
Supervisors:
Dr Anne Le Brocq (Department of Geography, University of Exeter) - Main supervisor
Dr Paul Holland (British Antarctic Survey)
Prof Martin Siegert (School of Geographical Sciences, University of Bristol)
Prof Carl Gladish (New York University, Abu Dhabi)
Project description: The nature of the subglacial hydrological system and its influence on ice flow is at the forefront of glaciological research for both the Antarctic and Greenland ice sheets. The flow of ice streams has a complex relationship with subglacial water depth and pressure, which is in turn a function of the nature of the hydrological system. The subglacial hydrological system has been characterised as having two states: distributed and channelised.
The traditional view of Antarctic subglacial hydrology is a distributed, spatially extensive hydrological system. However, linear features identified in satellite imagery of ice shelves, the floating extension of ice streams, suggest otherwise (Figure 1). Combined with radar sounding and laser altimetry measurements, and the results of a subglacial hydrological model, these features suggest that an active and focussed channelised system exists near the grounding lines of major ice streams [Le Brocq et al., in press].
The hypothesised physics of this situation are as follows: 1) subglacial meltwater exits the ice sheet grounding line at discrete locations; 2) its high buoyancy (freshness) triggers rapid ocean plumes; 3) vigorous plume turbulence mixes relatively warm ocean water towards the ice shelf; 4) deep channels are melted in the base of the ice; 5) the ice-shelf surface sags downwards in response because the ice is floating; 6) as the ice flows, the meltwater history at the grounding line is recorded in its surface and visible in satellite imagery.
The existence of channelised hydrology, and our ability to monitor it, has implications across many disciplines, including the prediction of ice-sheet flow, ice—ocean interaction, ice-shelf stability, and nutrient input to the ocean. This PhD will, therefore, investigate the controls on ice shelf channel formation in order to provide crucial insight into the nature of the otherwise inaccessible hydrological systems beneath the Antarctic and Greenland ice sheets.
The project will first utilise observations from Antarctica and Greenland. Satellite imagery will reveal surface features, satellite laser altimetry will allow investigation of temporal change in these features, and airborne ice-penetrating radar will reveal basal and surface morphology. Next, a coupled ice shelf/meltwater plume model [Gladish et al., 2012] will be used to investigate different scenarios of subglacial meltwater flux input to the sub-ice-shelf cavity.
“An experimental exploration of deep water formation under the Filchner Ice shelf, Antarctica”
Supervisors:
Prof Andrew Watson (Department of Geography, University of Exeter) – Main supervisor
Dr Marie-Jose Messias (Department of Geography, University of Exeter)
Dr Keith Nicholls (British Antarctic Survey)
Prof Mike Meredith (British Antarctic Survey)
Project description: Processes occurring beneath the ice shelves of Antarctica are critical to deep water formation, a major factor in the global climate system. A leading example is Filchner-Ronne Ice Shelf (FRIS) in the Weddell Sea; water interacts with the underside of the ice and the very cold, modified product makes a major contribution to Antarctic Bottom Water formation, the bottom water of most of the world’s oceans.
Our present understanding of these processes is limited by the extreme inaccessibility of the sub-ice shelf environment. We know little about the mixing processes undergone by the modified waters and their subsequent export into the deep ocean. A long-standing hypothesis is that, after being pre- processed beneath the neighbouring Ronne Ice Shelf, dense shelf waters recirculate within the Filchner Depression, a deep trough under the Filchner ice shelf. There they gradually mix with nearsurface waters from north of the ice front until they are light enough to pass the sill of the depression and cascade down the shelf slope (Nicholls et al, 2009). We aim to test this mechanism with a tracer release experiment under the ice. The tracer will be released by drilling through the ice shelf, and its distribution quantified by measurements at the ice front. This experiment will be proposed to NERC at the end of this year. The novel experiment, its high science payoff and value for money (it will be supported by already-planned field activities of BAS in 2015/16) give it a high chance of success. It will use the open ocean tracer release methodology that our group has utilized successfully over many years (e.g. see Watson et al, paper in Sep 19, 2013 , Nature).
During the first year the student will use a numerical model of the FRIS (e.g. Jenkins et al, 2004) to simulate the behaviour of the tracer under a variety of possible mixing and forcing scenarios. The results will advise the field activities, particularly the locations of the monitoring moorings. If the field experiment is funded, the student will participate in the field work and the interpretation of the results, during the second year. Further interpretation and writing will occupy the final 18 months of the studentship. If the project is not funded, the modelling study will be extended to a full-scale PhD project, exploiting existing datasets, both from beneath Ronne Ice Shelf, and from north of Filchner Ice Shelf.
