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Quaternary Discussion Group (QDG)

A series of 50 minute lectures, followed by discussion, on the broad topic of environmental evolution, climate, ecological and human change during the Quaternary (the last ~2.6 million years). The lectures are aimed at a broad audience (including geoscientists, glaciologists, environmental scientists, atmospheric chemists, biologists, anthropologists and archaeologists).

Seminars are usually held on Thursdays starting at 17:30 in Clare College in the Thirkill Room (far left corner of first court) or the Latimer Room (on the left in the first court).

Wine is usually served after the talks and there is time for discussion over drinks and/or dinner after the seminar, which should last approximately 1 hour. The meetings are currently organised by Rachael Rhodes (rhr34@cam.ac.uk; Godwin Laboratory for Palaeoclimate Research, Department of Earth Sciences), and Della Murton (dkf20@cam.ac.uk; Department of Zoology). Please feel free to contact the organisers with queries and suggestions.

A map showing the position of Clare College is available at http://www.clare.cam.ac.uk/Maps-and-Directions/

Please remember to check regularly for updates.

View the archive of previous seminars.

# Thursday 4th May 2017, 5.30pm - Chris Stokes, Durham University
How ice sheets collapse: a lesson from the Laurentide Ice Sheet
Venue: Cripps Auditorium, Cripps Court, Magdalene College

The contribution of the Greenland and West Antarctic ice sheets to sea level has increased in recent decades, largely due to the thinning and retreat of rapidly-flowing outlet glaciers and ice streams. This ‘dynamic’ loss is a serious concern, with some modelling studies suggesting that the collapse of a major ice sheet could be imminent or potentially underway in West Antarctica, but others predicting a more limited response. A major problem is that observations used to initialize and calibrate models typically span only a few decades and, at the ice-sheet scale, it is unclear how the entire drainage network of ice streams evolves over longer timescales. This represents one of the largest sources of uncertainty when predicting the contributions of ice sheets to sea-level rise. A key question is whether ice streams might increase and sustain rates of mass loss over centuries or millennia, beyond those expected for a given ocean–climate forcing. In this paper, we utilise a unique Quaternary record of 117 ice streams that operated at various times during deglaciation of the Laurentide Ice Sheet from about 22,000 to 7,000 years ago). We show that as they activated and deactivated in different locations, their overall number decreased, they occupied a progressively smaller percentage of the ice sheet perimeter and their total discharge decreased. The underlying geology and topography clearly influenced ice stream activity, but— at the ice-sheet scale—their drainage network adjusted and was strongly linked to changes in ice sheet volume. It is unclear whether these findings can be directly translated to modern ice sheets. However, contrary to the view that sees ice streams as unstable entities that can accelerate ice-sheet deglaciation, we conclude that ice streams exerted progressively less influence on ice sheet mass balance during the retreat of the Laurentide Ice Sheet.

# Thursday 18th May 2017, 4.00pm - Shaun Marcott, University of Wisconsin-Madison
The timing of cirque glaciation in western North America revisited: No Neoglacial in the U.S. Cordillera?
Venue: Castlereagh Room, Fisher Building, St John's College

Glaciers are intrinsically linked to climate, and given the sensitivity of small alpine glaciers to climate change, accurate and precise chronologies of their fluctuations are important in elucidating both the temporal and spatial structure of climate variability. Despite nearly a century of research, the timing of latest Pleistocene and Holocene alpine glaciation in much of western North America remains poorly constrained. I will present ~125 10Be ages from ~20 cirque moraines in 10 mountain ranges across western North America that were previously interpreted as mid- to late Holocene in age. Our new 10Be glacial chronology indicates that these moraines were deposited during the latest Pleistocene to earliest Holocene, requiring a refined interpretation of Holocene glacial activity in western North America and the associated climate forcing. Although alpine glaciers may have continued to fluctuate during the Holocene, they never advanced beyond their Little Ice Age maximum limit. Instead, cirque glacier activity in western North America has followed in near step with late Pleistocene high and mid latitude climate with alpine glaciers retreating to high altitude cirques early during the last deglaciation.