FIFTY YEARS OF ADVANCES IN UNDERSTANDING ICE SHEET-CLIMATE INTERACTIONS

One can chart a steady trajectory in the direction that glacial geology has taken over the last 50 years and its influence on our understanding of ice-sheet dynamics and interactions of ice sheets with the climate system. Two early developments paved the way for the major advances in this understanding: the advent of radiocarbon dating, which provided the ability to develop robust chronologies, and the recognition of the potential complexity of ice-sheet sedimentary environments. Pioneering studies in the 1950’s and 1960’s used new radiocarbon constraints to associate the record of the Laurentide Ice Sheet (LIS) in the central-eastern Great Lakes region with the newly developed deep-sea oxygen isotope record. The resulting subdivision of the last glaciation into an early, middle, and late Wisconsinan supported a largely ice-volume signal for the oxygen isotope record. Moreover, the identification of multiple stadial and interstadial events during the middle and late Wisconsinan preceded by over two decades the evidence for millennial-scale ice-sheet variability during isotope stages 2 and 3 recognized from deep-sea cores, and posed new challenges to understanding ice-sheet dynamics and its relation to climate change. At the same time, work in the eastern Canadian Arctic revealed important new information regarding the inception of the LIS following the last interglaciation and its subsequent history of advance and retreat. Combined, this work provided a broad perspective on ice-sheet history and its relation to climate change. New studies of relative sea level change and its implications for glacial isostatic adjustment also strongly influenced development of sophisticated models of the solid Earth’s response to ice-sheet loading. From the sedimentological perspective, two novel ideas in the early 1960’s helped usher in an improved understanding of the glacial geologic record, with implications for ice-sheet history and dynamics: the recognition that some diamictons may be deposited in a glacial environment as debris flows, and that some sediments were deformed subglacially. Process-based understanding the glacial geologic record has provided the basis for several reconstructions of the LIS, with large differences between the reconstructions having important implications for climate change.