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Seligman Crystal awarded to David Sugden

In September 2012, Professor David Sugden was awarded the International Glaciological Society's prestigious Seligman Crystal.

'The Seligman Crystal shall be awarded from time to time to one who has made an outstanding scientific contribution to glaciology so that the subject is now enriched'.

Prof. Sugden's Acceptance Address

I am humbled but very honoured to receive the Seligman Crystal. There is nothing more precious than to be honoured by one’s own community. This is especially so when that community is international, cross-disciplinary, and studying a topic of such importance for humanity as glaciology.

What I would like to do in this lecture is first, to take you back to what it was like to start in glaciology in the 1960s, second, to look at highlights of discoveries made by a series of research students and post docs with whom I. have been fortunate to work, and finally, to relate a few key discoveries, even ‘eureka moments’, of a field scientist in both East and West Antarctica.

Figure 1
Figure 1. Dropping freight parachutes from a DC3 in inner Scoresby Sund and Jameson Land on a student expedition to East Greenland in 1962.

I first caught the glacier bug whilst as a sixteen-year-old I participated in a Brathay survey of Tunsbergdalsbreen in Norway and followed it up with student expeditions to Iceland and Greenland. I marvel at the different attitude to Health and Safety in those days. On the 1962 Oxford University Expedition to East Greenland, organised with Brian John, we dropped supplies and two folding kayaks by parachute to near Syd Kap in inner Scoresby Sund (Figure 1). We chartered a DC3 from Icelandair and, flying from Mestersvig with no door and no seats, we followed the advice given to us when borrowing the parachutes from the Royal Air Force in Brize Norton, namely, tie the rip cord firmly to the plane. Out went the first load and, one second later, so also did the whole luggage rack to which it was attached! The remaining loads were then attached (at the pilots request), to his seat!

It was on this expedition that I got news that I had been offered a Department of Science and Industrial Research studentship; the telegram was dropped from an Erzberg mine plane weighted with a slab of butter. This led to a thesis on glacial erosion in the Cairngorm Mountains in Scotland. My supervisor, Marjorie Sweeting, an expert on karst, did suggest that the study of erosion would be impossible to date and thus limiting. Looking back I see that my thesis was classic landscape evolution, following in the mould of the geomorphological paradigm of William Morris Davis. There was little on processes or why the landscape of upland tors and clean troughs had been dissected in such a selective manner by glaciers.

In the early years as a lecturer in the University of Aberdeen, I tried to compensate by reading all back issues of the Journal of Glaciology to try and understand more about glacial processes. So did Brian John at Durham, and it was John Davey at Edward Arnold who encouraged us to refine and publish our early lecture notes together as Glaciers and Landscape in 1976. Others, such as Geoffrey Boulton, were discovering the significance of basal thermal regime in controlling processes of glacial deposition and it was logical to expand this to landscapes, first in Greenland with the aid of air photographs in the Geodetic Institute in KÝbenhavn, and then, at the encouragement of John Andrews, to the Laurentide Ice sheet, where Molly Mahaffy had developed an early ice-sheet model under his supervision. Most of you in this room will find it difficult to imagine the construction of a computer model in the 1970s. Every evening I would go across campus to the computer centre with my armful of punch cards. The programme ran overnight and for at least a month my results came through with error messages. With the help of my room mates, Giff Miller and Jim Clark, the program eventually worked and it was then possible to compare the pattern of basal thermal regime with the distribution of landscape types and thus begin to relate landscape to process.

Perhaps the best thing about a university post is the joy of working with bright young scientists brimming with optimism and new skills. It is impossible to mention all, but a few examples will make the point. Martin Sharp was one such postgraduate who came to work on surging glaciers in 1978/9. Chalmers Clapperton and I clearly remember four classes he offered to give to our class on glacier processes. These took up a challenge clearly posed by W.S.B.Paterson in The Physics of Glaciers (1969) and showed how glacier theory could be tested and refined by well posed field observations. Working with Roland Souchez, Reggie Lorraine and Jean-Louis Tison from Bruxelles, Peter Knight examined the debris and isotopic characteristics of regelation ice exposed at the margin of the Greenland Ice Sheet. We were puzzled by the discovery of refrozen clear ice with an isotopic signature close to average for Greenland, no fractionation, and widely-spaced clots of fine debris, which indicated refreezing en masse in a closed system, perhaps in the interior. In the light of modern hydrological studies, could these be formed by the freezing of surface lake drainage to the base when the discharge does not connect with subglacial drainage routes? It would help explain the puzzling characteristics.

A number of research students and postdocs developed ice-sheet models that helped develop the links between landscape, climate and ice-sheet behaviour. The research students gained invaluable experience, firstly from Bill Budd in Australia and then from Hans Oerlemans, who ran a series of European-wide modelling courses. There are several highlights that changed the scientific questions we ask. Tony Payne showed how topography could introduce sensitive tipping points in the growth of an ice sheet, determining for example whether the ice would remain in the mountains or, exposed to a slightly colder climate, expand to its maximum extent. Nick Hulton showed that the southern westerlies must have moved north during glaciations in order to simulate the known extent of the Patagonian ice sheet; further, both the present ice fields and a large ice sheet could survive in equilibrium with the present-day climate, a theme followed up in Iceland by Andrew Mackintosh. Alun Hubbard introduced longitudinal stress into the models and was able to represent ice-sheet behaviour at the resolution of individual valleys. The importance of this is that there is a wealth of observational information at such a scale on the beds of the former northern hemisphere, mid-latitude ice sheets that can be used to refine ice-sheet models. Nick Golledge used this approach to show how modelled ice velocities beneath the Younger Dryas ice-sheet in Scotland correlated with a radial pattern of intermediate-sized troughs. A further step is to separate out those erosional forms associated with larger ice sheets, for example the remarkable assemblage of landforms identified by Tom Bradwell caused by a major ice stream flowing from northwestern Scotland to the ‘delta’ at the edge of the continental shelf.

A modelling approach can also be used to predict the landforms beneath current ice sheets. Stewart Jamieson modelled the extent and basal thermal regime of the Antarctic ice sheet at various stages of its evolution, making it possible, for example, to identify landscapes starting with alpine glaciation and later becoming protected beneath cold-based ice, landscapes associated with the same direction of ice flow during minimum and maximum glacial stages, and those landscapes where ice flow changes direction from stage to stage and may even concentrate deposits. As our understanding of the bed of the Antarctic ice-sheet advances through boreholes and remote sensing, this approach will do much to aid interpretation and the effect of the bed on ice-sheet dynamics.

Figure 2
Figure 2. Brian John and I worked with the Whirlwind helicopters of HMS Protector in the South Shetland Islands in 1965/66.
Figure 3
Figure 3. Beacon Valley in the McMurdo Dry Valleys, Transantarctic Mountains. Here basal ice beneath a thin cover of regolith has survived for over 8 and probably 13 million years. Taylor Glacier, an outlet of the East Antarctic Ice Sheet, flows into the mouth of the valley.

I have been fortunate to work in the field in Antarctica on some 15 occasions, first with Brian John and Chalmers Clapperton in South Georgia, the South Shetlands and Antarctic Peninsula, and then in the Transantarctic Mountains with George Denton and with others in inner West Antarctica (Figure 2). Perhaps I can take the opportunity to share two ‘eureka moments’ associated with the case that the East Antarctic Ice Sheet must have existed in approximately its present state for 14 million years. The first, working with David Marchant, was the discovery of glacier ice in Beacon Valley consisting of regelation ice with striated stones (Figure 3). This was a surprise since we assumed the ice had come from a local valley head where the mean annual temperature is currently around -30 degrees C; as a result all the ice would be below the pressure melting point and unable to striate stones. The ice is protected beneath a thin rock debris cover with wedges of tundra polygons filled with volcanic ash, later found to be ~ 8 million years old. Subsequent analysis of the sediment in the ice revealed erratics from outside the local valley and this implied that ice must have moved up-valley from a thicker Taylor Glacier rather than down-valley from a local source. A few days later Roland Souchez, who was analysing the ice in the core, queried whether my orientation of the core could have been the wrong way round. He had found that the foliation in the ice indicated ice flow up-valley, confirming our new interpretation! Others have worked on Beacon Valley subsequently and we now believe this thicker ice dates from ~13 million years ago, the oldest glacier ice yet discovered. Its survival surely suggests that the East Antarctic Ice Sheet and its polar climate have remained essentially intact for the same length of time.

Figure 4
Figure 4. The exposure ages (Helium-3) of two cobbles from the meltwater flood debris in the Coombs Hills have remarkably old exposure ages of 8.9-10.4 million years..
Figure 5
Figure 5. George Denton stands beside a coarse ripple of meltwater flood debris, Coombs Hills, Transantarctic Mountains.

The second revealing discovery came from the great age of meltwater flood debris associated with overriding ice in the Dry Valley area. In the Coombs Hills is an area of corrugated sandstone bedrock with coarse ripples of dolerite, linked to a subglacial suite of meltwater channels and plunge pools (Figure 4). George Denton and I picked up three dolerite clasts resting on flat sandstone bedrock in mid-valley which were part of the bedload of the meltwater event. Analysis of Helium-3 in the rocks by Helen Margerison (Quinn) revealed astonishing exposure ages of between 8 and 10 million years (Figure 5). Allowing for erosion of the clasts, puts the ages at ~ 13-14 million years. So, while the Mediterranean Sea formed, the isthmus of Panama joined up South and North America and the North Atlantic Ocean widened by almost a third, these brick-sized clasts have remained undisturbed. This reflects the extremely low erosion rates under the present polar climate. Any period of warmth in the last 14 million years would surely have weathered away the clasts. It is truly humbling to stand in such a landscape that is so old.

Figure 6
Figure 6. Exposure ages of erratics on the summits and slopes of the Sarnoff Mountains, Marie Byrd Land, show the ice sheet has thinned by over 800 m in the last 12,000 years.

I would like to tell you of our present research looking at blue-ice moraines in the Heritage Range, in the Ellsworth Mountains block. Earlier work with John Stone showed how in parts of Marie Byrd Land the West Antarctic Ice Sheet has been thinning for at least 12,000 years (Figure 6). However, work with Mike Bentley and Anne Le Brocq in the Ellsworth Mountains suggests limited thinning of the Weddell Sea sector since the Last Glacial Maximum. Subsequent exposure-age work with Chris Fogwill and Andy Hein in the Shackleton Range shows neither thickening of outlet glaciers at the Last Glacial maximum nor thinning subsequently. This includes major glaciers flowing into the Weddell Sea sector from the East Antarctic Ice Sheet. Perhaps their stability is related to the extreme depth of an offshore trough cut during earlier glaciations. The blue-ice moraines in the Heritage Range are associated with a puzzling mix of exposure ages up to ~ 400,000 years in age and, working with Andy Hein, John Woodward and Stuart Dunning, in 2012/15 we plan to study the moraine forming processes using radar, ice flow studies, an unmanned small aircraft and exposure ages. If we can understand the mix of ages, we may begin to unravel a rich history of ice-sheet behaviour over half a million years.

There are many people who I want to thank for the award of the Seligman Crystal. First, as the names I have already mentioned illustrate, I have enjoyed remarkable support from the community of the International Glaciological Society. We have a friendly and open approach which encourages ideas and cross-disciplinary collaboration. I particularly thank those who took the trouble to recommend and support me. Second, I owe so much professionally to young colleagues and there are many more significant contributions than I have not had space to mention. It is especially good to see so many young glaciologists in this room. Lastly, my wife Britta has been a staunch glaciology supporter. Though sometimes wishing I had specialised on coral reefs, she handled her business and three small children with aplomb during my too many absences in the field or in the study. It has been quite a journey since that day when she came to hear a lecture about our 1962 Greenland Expedition, which was the occasion when we first met!

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