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SPRI Physical Sciences Seminar Series 2007-8

SPRI Physical Sciences Seminar Series 2007-8

Talks will be held in the main lecture theatre at the Scott Polar Research Institute and will start at 16.30. Some seminar dates may be subject to change. Please contact Dr Poul Christoffersen for more details.

An archive of previous seminars is available.

Michaelmas Term

Wednesday 31st October 2007
Joy Singarayer (Department of Geographical Sciences, University of Bristol)
Insights from modelling spatial and temporal variations in marine radiocarbon ages
Variations in marine radiocarbon reservoir ages have the potential to provide important information about past ocean circulation and climate changes. They are likely to have displayed a large amount of spatial variability on millennial and shorter timescales. This variability is valuable for reconstructing climate changes. However, it is also potentially problematic for using marine-based data to produce radiocarbon calibration curves. Deconvolving different factors such as ocean circulation and production changes is difficult from data alone, even when using complementary records. Modelling can play a crucial role in improving our interpretations of the radiocarbon record. The GENIE (Grid ENabled Integrated Earth system) model used here is a fast, 3D intermediate complexity model, which combines a dynamic ocean model, thermodynamic sea-ice scheme, energy/moisture-balance atmosphere, terrestrial vegetation, marine biogeochemical cycling and ocean sedimentation. Representation of carbon isotopes is incorporated in all relevant components of the model. The model imposes a global average radiocarbon production rate as a time-varying function of solar activity and geomagnetic field intensity. The GENIE model has been used to assess the spatial and temporal variation of marine reservoir ages during the Younger Dryas and the deglaciation. A series of transient model simulations have been performed that include variations in geomagnetic intensity and freshwater 'hosing' experiments to simulate meltwater input. The sensitivity of modelled reservoir ages to ocean circulation and radiocarbon production has been analysed. Additionally, we reconstruct modelled atmospheric radiocarbon 'calibration curves' based on surface marine radiocarbon content from various modelled ocean regions. These reconstructions highlight spatially-dependent discrepancies that may be introduced by assuming constant reservoir ages, as has previously been assumed. However, preliminary results suggest that possible discrepancies in records from different locations may also have the potential to give useful insights into the relative magnitude of the impacts of climate changes and production rate changes.
Wednesday 14th November 2007
Richard Hindmarsh (British Antarctic Survey)
What's to be scared of in modelling Antarctic deglaciation?
After thirty years of discussion of the marine ice-sheet instability and its possible consequences of 15-20ft of sea-level rise, quantitative modelling of this notion has apparently advanced very little. This talk will examine the problems; (i) the shortage of data, and a presentation of a new glaciological dating technique; (ii) what we know about the grounding line instability, and some significant advances made in the past two years; and (iii) how close are models are to explaining the geomorphological features (drumlins etc.) which characterise ice-sheet activity. The talk will finish with some comments on possible rates of sea-level rise.
Wednesday 28th November 2007
Steve Price (Bristol Glaciology Centre, University of Bristol)
Using higher-order flow models to understand the dynamics of the Greenland ice sheet
Recent observations indicate that numerous large outlet glaciers draining the Greenland ice sheet are accelerating, thinning rapidly, and retreating. Two mechanisms put forth to explain this behavior are (1) a change in longitudinal force balance as a result of thinning and retreat of floating, marginal ice, and (2) increases in basal lubrication and sliding speed as a result of increased surface melt generation, extent, and/or access to the ice sheet bed. These two mechanisms imply very different forcings - ocean warming versus atmospheric warming, respectively - and very different long-term responses of the ice sheet to that forcing. This talk will discuss how "higher-order" ice flow models and observations are being used to test these differing hypotheses, with the goal of clarifying the cause of recent changes and their likely future coarse.

Lent Term

Wednesday 6th February 2008 [in the Museum]
Susan Solomon (NOAA Aeronomy Laboratory, USA)
The Coldest March: Scott's Fatal Antarctic Expedition
Antarctica is a place of unique beauty and history. The experiences of the speaker in probing the spectacular ozone hole that now forms in Antarctica led to an interest in using science to better understand the experiences of some of the first men who explored the continent ninety years ago. It will be shown that Robert Falcon Scott and his companions were struck down on their return journey from the Pole by weather conditions that can now be shown to be highly unusual (Solomon, The Coldest March, Yale University Press, 2001). Solomon uses the tools and knowledge of modern science to reveal a host of fresh insights into the lives, characters, and deaths of Scott and his men, providing a firmer basis from which to consider their legacies.
Wednesday 20th February 2008
Bob Hawley (Scott Polar Research Institute and University of Washington, USA)
Density, densification, and stratigraphy: a descent into the shallow depths of firn profiling

The transformation of snow into ice is of fundamental importance to glaciology. Measurements of firn densification in-situ are rare, due to the logistical difficulties involved. But in the course of measuring densification, many other useful information can be obtained. This talk will center around the effort to measure firn compaction in-situ using a new technique called Borehole Optical Stratigraphy, and the things we've learned along the way, including how we can rapidly determine the depth-age scale in the shallow region, and what optical stratigraphy can tell us about the existing density profile.

Wednesday 5th March 2008
Chris Stokes (Department of Geography, University of Durham)
Episodic ice streaming into the Arctic Ocean from the north-western margin of the Laurentide Ice Sheet
Previous work suggests that large marine-based ice streams drained the north-western sector of the Laurentide Ice Sheet, similar to those observed in present-day ice sheets. They were comparable in size to the Hudson Strait ice stream, which has been cited as a source of the North Atlantic's Heinrich events, but have traditionally attracted much less attention. More recently, however, they have been invoked as a possible source for several major ice export events to the Arctic Ocean and for a grounded Arctic ice shelf or ice sheet during the Late Pleistocene. The large ice/meltwater flux from the north-western margin of the Laurentide ice sheet has also been hypothesized as a potential trigger for the Younger Dryas cold interval. This talk reviews the evidence for ice streaming in this sector of the ice sheet and presents a new reconstruction of their activity during deglaciation. The results indicate spatial and temporal switches in ice streaming and major reorganisations in ice sheet dynamics. This has important implications for Arctic Ocean palaeoceanography and the behaviour of ice streams in contemporary ice sheets.

Easter Term

Wednesday 23rd April 2008
Julian Murton (Department of Geography, University of Sussex)
Bedrock fracture and permafrost landscape development
In permafrost regions underlain by high-porosity fine-grained bedrock, the growth of segregated ice is a fundamental process of rock fracture and regolith production. Fracture occurs when water migrates down into the permafrost, nourishing ice-lens growth. Over decades to millennia, this process produces an ice-rich layer of fractured bedrock that underlies the active layer. The growth and thaw of this icy permafrost layer is thought to be an important process of landscape development in permafrost lowlands in Svalbard and Canada. Evidence for Quaternary ice segregation in bedrock is widespread in the Mesozoic sedimentary rocks of northwest Europe, consistent with valley development by alternating ice segregation and thermal erosion.
Wednesday 7th May 2008
Alfred McLaren (Talk and book signing)
Unknown waters: a firsthand account of the historic under-ice survey of the Siberian continental shelf
See the lectures page for more information.