Unravelling the history of ice sheet change and glacio-isostatic uplift of sub-Antarctic South Georgia.

Overview

South Georgia is an island in the Southern Ocean, close to the one of the major climate boundaries of the planet, the oceanic Polar Front. It is amongst the largest of the sub-Antarctic islands and is heavily glacierised with most of the island ice-covered and ice-free areas concentrated on the peninsulas of the north-east coast (Figure 1). Recent work has begun to unravel the glacial history of the island, including during deglaciation from the Last Glacial Maximum (Bentley et al., 2007; Graham et al., 2017) and more recent decadal retreat (Cook et al., 2010; Figure 1). Other work has explored the potential relative influence of glacial history and tectonics on the evolution of the island over longer timescales (Barlow et al., 2016). All of this works points to a complex interplay between ice cap and glacier behaviour, local and regional tectonic uplift, glacio-isostatic adjustment (GIA), and sea level.

The aim of this project is therefore to understand the interactions between, and controls upon, past ice cap/glacier evolution and GIA in South Georgia.

This project will be a collaboration with US and Luxembourg collaborators who installed a network of GPS receivers on the island. Their preliminary datasets suggest quite high rates of vertical uplift but that the relative influence of tectonics vs. ongoing GIA induced by past glacial (un)loading is still not clear and requires better understanding of the past extent and thickness of the South Georgia ice cap.

In this project we propose to develop a numerical model of the South Georgia ice cap to explore a series of related research questions including:
1. Using the geomorphological record can we determine a glacial history of the island?
2. What climate shifts were needed to cause past glacier fluctuations, on both millennial timescales and in recent decades?
3. Can we simulate the future behaviour of South Georgia glaciers?
4. What is the ongoing rate of deformation of the islands that can be attributed to GIA? (and by implication the residual GPS-measured rates to tectonics)
5. Are there implications for management of the island’s natural resources, where glacier retreat can have implications for faunal distributions and for tourism?
The work may also be extended to other sub-Antarctic islands, where appropriate.

Click on an image to expand

Image Captions

Figure 1: Map of South Georgia – the coloured lines representing recent glacier retreat, but in the past, ice extended further onto the continental shelf. The retreat history and GIA response of this behaviour will be the focus of this project.

Methodology

The primary approach adopted will be use of a numerical model, the Parallel Ice Sheet Model (PISM). An initial component of the project will be to develop datasets for the key boundary conditions, and forcings required for the simulations including: 1) generating a new DEM compilation of the island of South Georgia, incorporating new bathymetric data, and determining the sub-ice topography of the island using inversions of ice velocity (working with collaborators); 2) building a library of climate forcing scenarios as developed from existing climate model runs, and from climate records on the island; and 3) Producing a synthesis of glacier fluctuations from geomorphology, marine geology and historical and remote sensing observations. The glacier models will be run on the new South Georgia topography, using the climate library, and tested against the geological and observational constraints. Once the model simulations have been established they will be used as input to a regional Glacial-isostatic adjustment model that will be used to determine the impact of glacier loading and unloading on rates and patterns of uplift measured by GPS. Working with US collaborators the implications for the glacial, sea level, GIA and tectonic history of the island will therefore be explored.

Project Timeline

Year 1

Year 1: Develop compilation of glacial history of the island from geomorphology, marine geology, and historical observations. Determine a digital elevation model of the island from published sources, new bathymetric compilations, and by conducting an ice velocity bed inversion over currently ice-covered areas. Learn numerical modelling techniques.

Year 2

Year 2: Conduct numerical modelling of South Georgia ice cap. Explore LGM-to-present behaviour, and decadal-scale behaviour. Supplement analysis with further remote sensing to understand change in last decade.

Year 3

Year 3: interpretation of modelling results and integration with ongoing work on GIA modelling using ice loads from the models. Consideration of implications of tectonic history on glacial history and on GPS-measured deformation rates.

Year 3.5

Year 3.5 – write up of final thesis and papers.

Training
& Skills

IAPETUS2 provides a wide range of training opportunities to its students. In respect of this project, two of the most relevant are the ‘Introduction to modelling in Python’ and ‘Advanced statistics in R’ modules, but we will discuss the student’s needs and interests at the outset of the project. In addition, training in RES data analysis and interpretation will be provided within the project, as well as the use of a wide range of glacial geological, glaciological, climate and GPS datasets. The student will gain specific skills in modelling using the Parallel Ice sheet Model (PISM). Environmental modelling skills are highly sought after by environmental and engineering consultancies. This project will also provide training in how to process large quantitative datasets such as DEMs as well as Python programming for modelling scripts. The student will gain experience in efficiently analysing large and complex datasets.
Throughout: The student will be encouraged to write papers for publication throughout the duration of the project. This will benefit their career and will enable us to support the development in writing skills and in going through the publication process.

References & further reading

Barlow NLM, Bentley MJ, Spada G, Evans DJA, Hansom JD, Brader MD, White DA, Zander A, Berg S 2016. Testing models of ice cap extent, South Georgia, sub-Antarctic, Quaternary Science Reviews, 154, pp.157-168. doi: 10.1016/j.quascirev.2016.11.007
Bentley, M.J., Evans, D.J.E., Fogwill, C.J., Hansom, J. and Kubik, P.W. 2007. Glacial Geomorphology and Chronology of Deglaciation, South Georgia, Sub-Antarctic, Quaternary Science Reviews, 26, 644-677. doi: 10.1016/j.quascirev.2006.11.019.
Cook, A., Poncet, S., Cooper, A.P.B., Herbert, D., Christie, D. 2010. Glacier retreat on South Georgia and implications for the spread of rats, Antarctic Science 22(03):255 – 263, doi: 10.1017/S0954102010000064.
Graham et al., 2017. Major advance of South Georgia glaciers during the Antarctic Cold Reversal following extensive sub-Antarctic glaciation, Nature Communications,8, 14798.

Further Information

Prof. Mike Bentley
Department of Geography
Durham University
https://www.dur.ac.uk/geography/staff/geogstaffhidden/?id=329
Email: m.j.bentley@durham.ac.uk
Tel: +44 (0) 191 334 1859

Dr Stewart Jamieson
Department of Geography
Durham University
https://www.dur.ac.uk/geography/staff/geogstaffhidden/?id=8469
Email: Stewart.Jamieson@durham.ac.uk
Tel: +44 (0) 191 3341990

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