Dr. Terence J. Hughes
Department of Earth Sciences/Climate Change Institute/University of Maine
Orono, ME 04469-5790, USA
1 April 2006

1975-1980
The University of Maine (UM) hired me in 1974, with a joint appointment in the Institute for Quaternary Studies (now the Climate Change Institute) and the Department of Geological Sciences (now the Department of Earth Sciences). I arrived in January of 1975, after my tenure at NCAR. My ISCAP bulletins had caught the attention of Harold Borns, who was both Institute director and Department chairman, and George Denton, who had acquired a large slice of a major project of the International Decade of Ocean Exploration (IDOE) called Climate: Long-range Investigation, Mapping, and Prediction (CLIMAP). I wrote my fourth and last ISCAP bulletin (on West Antarctic ice streams) at UM in 1975, and then committed myself to CLIMAP. The UM contribution was to produce computer reconstructions of ice sheets at the last glacial maximum 18,000 years ago as its primary mission, and a computer disintegration of the West Antarctic Ice Sheet during the last interglacial maximum 125,000 years ago as a secondary mission. Modeling this disintegration for the present interglaciation was the ultimate objective of my ISCAP bulletins. We showed that ice downdrawn by Thwaites Glacier and Pine Island Glacier into Pine Island Bay made it the “weak underbelly” of the ice sheet. A mathematician from Wisconsin, Dave Schilling, and our own Jim “Shamis” Fastook assisted me. Our work was largely complete by 1979, and we presented it at the Symposium on Dynamics of Large Ice Masses held by the International Glaciological Society. All of our manuscripts but the one with our West Antarctic disintegration were rejected. Too topsy-turvy? George Denton arranged for Wiley Interscience to publish our work in 1981 as The Last Great Ice Sheets. It's now a classic.

We presented two reconstructions of former Northern Hemisphere ice sheets, a minimum model in which ice sheets ended near present-day shorelines and a maximum model in which these ice sheets extended to the edge of arctic and sub-arctic continental shelves. The two models were based on different interpretations of so-called "weathering zones" along fjordland coastlines of North America and Europe. The conventional view was that these zones represented former ice-sheet surface elevations existing at different times during Quaternary glaciation cycles. After observing them on the Gaspe Peninsula of Quebec, I concluded they were basal thermal zones produced under the ice sheets during the last glacial maximum, zones in which the bed was either frozen, thawed, or a mosaic of frozen and thawed patches. It was topsy-turvy from the prevailing view. I developed a "bottom up" scheme for reconstructing former ice sheets to produce two models, based on the two interpretations of "weathering zones" and of glacial geology in general.

My “bottom-up” approach was topsy-turvy from the conventional "top down" approach that relied on reconstructing former ice sheets based on a specified (but largely unknown) mass-balance pattern of ice accumulation and ablation rates over ice-sheet surfaces. Top-down models produced patterns of basal frozen and thawed regions, and therefore variations in basal traction, that were extremely sensitive to the surface mass balance. Small mass-balance variations resulted in big differences in ice elevations calculated from bed traction. My bottom-up approach was insensitive to the surface mass balance, being based on the idea that glacial geology revealed where the bed was frozen and thawed, providing more (frozen bed) or less (thawed bed) traction that required higher or lower ice to overcome the basal resistance to flow. Our “maximum” and “minimum” models, both based on the bottom-up approach, spurred an ongoing search for the "marine" ice sheets on continental shelves generated in the maximum model. The maximum model won out when exposure-age dating techniques were developed and applied to date glacial erratics and exposed bedrock in the fjordlands.

In 1977, I began a three-decade collaboration with Mikhail (Misha) Grosswald of the Institute of Geography, USSR (now Russian) Academy of Sciences, in Moscow. Misha, George Denton and I took an idea from John Mercer in 1970 and postulated in Nature that a single “Arctic Ice Sheet” behaving as a unified dynamic system existed at the last glacial maximum. It had an ice shelf floating in its center and it disintegrated from the inside out. This was topsy-turvy from the ice-free Arctic Ocean proposed by Maurice Ewing and William Donn in Science from 1956 to 1966. In 1968, Misha, along with Swedish and Canadian colleagues Valter Schytt, Gunnar Hoppe, and Weston Blake, had proposed a marine ice sheet in the Barents Sea north of Scandinavia. In 1970, Blake showed that a marine “Innuitian Ice Sheet” had also covered the Canadian Queen Elizabeth Islands. Since then, Misha found evidence for a marine “Eurasian Ice Sheet” extending from Spitzbergen to Alaska that transgressed onto the Russian mainland from the arctic continental shelf. I reconstructed its vertical elevation, based on his glacial geology. This has triggered ongoing fieldwork in the Eurasian Arctic that has confirmed a former marine ice sheet in the Chukchi Sea and a thick ice shelf in the Arctic Ocean. The ice shelf, these marine ice sheets, and their landward extensions were an Arctic Ice Sheet.

Resistance to our ideas about vast former ice sheets in the Arctic inspired my 1980 letter in Boreas, “Genes and glacial history.” I floated the topsy-turvy idea that resistance was based on genetics, not field evidence. During the last glaciation, some Europeans adapted to the advancing ice sheets whereas others fled to Africa. After the ice sheets were gone, they came seeping back into Europe and mingled with those who toughed it out. Today, genetic recombinations replicate both types in certain individuals. Misha and I have the genes of those who grew to Love The Ice. As for the others, they can’t stand ice anywhere. They barely tolerate half-vast ice sheets, and we all know Who They Are.

In 1980, I concluded my forays into plate tectonics after I was invited to attend the International Conference on Mathematical Problems of the Thermal and Dynamic State of the Earth held at Lake Arrowhead in California. There I met all the "heavy lifters" in plate tectonics and mantle dynamics. I presented a theoretical model for thermal convection in Earth's mantle that turned on and off when the thermal buoyancy stress rose above and fell below a "yield stress" for crystalline mantle rocks, with narrow hot curtains rising rapidly under plate boundaries and broad cold plugs sinking slowly under the plates. That's where I met Dick Peltier, who had developed models of mantle viscosity based on rates of post glacial crustal adjustments to the changing distribution of ice and water on Earth's surface since the last glacial maximum. We both argued for mantle-wide convection. I wrote a paper on lithosphere deformation by continental ice sheets, using my viscoplastic yield stress criterion, which was topsy-turvy from viscous deformation. The Royal Society of London published it in 1981 in its Proceedings.