How important are ice streams in accelerating ice sheet deglaciation?

It is widely accepted that the Earth's climate is warming and that glaciers are losing mass and increasing sea level. Small glaciers are particularly susceptible but only represent a fraction of the Earth's freshwater stored as ice. In contrast, the huge ice sheets in Greenland and Antarctica store several 10s of metres of equivalent sea level and recent studies suggest that they, too, are losing mass and that this appears to be accelerating.

Ice sheets transfer ice to the oceans via numerous fast flowing glaciers called 'ice streams'. It has been discovered that ice streams can speed up, slow down, and even stop altogether; as well as switch their position. These changes can occur relatively rapidly (over a few years) but it is not clear whether they are part of a long-term trend of ice sheet shrinkage (over centuries to millennia) or simply reflect their natural variability. Another possibility is that the recent acceleration and thinning is the beginning or 'pre-cursor' of an episode of widespread mass loss but the question remains: how important are ice streams in accelerating ice sheet deglaciation, e.g. beyond that which might be excepted from climate forcing alone?

In order to assess the significance of these short-term changes, we need to understand how ice streams operate over time-scales longer than current measurements allow and we also need to view ice streams as an integrated pattern of drainage within the ice sheet that evolves over several millennia. This can be achieved through investigation of past ice stream behaviour. Past-ice streams can be identified because, compared to slow-flowing ice, their rapid flow creates distinctive glacial landforms on the now-exposed ice sheet bed. We can locate these ice stream 'footprints' on past ice sheet beds very easily (e.g. in the UK or North America) and then use dating techniques (e.g. radiocarbon dating) and other evidence related to ice sheet flow patterns to estimate when and for how long they existed. This approach has been taken by scientists and has increased our understanding of their behaviour over long time-scales but studies have tended to focus on just one ice stream or specific regions. What we really want is information on the activity of lots of ice streams from across an entire ice sheet and, ideally, from as long a time-span as possible i.e. from a complete deglaciation, when the ice sheet shrinks from its maximum extent and disappears altogether.

This aim of this project, therefore, is to produce a ground-breaking dataset that reconstructs the spatial and temporal activity of every ice stream in the North American Laurentide Ice Sheet (which was similar in size to Antarctica) from its maximum extent around 21,000 yrs ago to its near-disappearance around 5,000 yrs ago. We will map all the flow patterns on the ice sheet bed, including ice streams, and date these using an existing database of ~4,000 radiocarbon dates (and other published dates). A recent pilot study shows that we can date the duration of individual ice streams to within 250-500 yrs. This will allow us to see how an entire drainage network of ice streams evolves during deglaciation and whether their combined activity caused major episodes of significant mass loss. It will also reveal the extent to which ice stream activity is linked to abrupt climate and sea level changes in the past, e.g. abrupt warming or cooling and rapid changes in sea level. Taken together, this will provide a firm context with which to model and predict the future response and likely magnitude of changes in modern-day ice sheets, e.g. for the next IPCC Report.

Policymakers and International Scientific Panels/Groups: our project targets current limitations identified in the 4th IPCC report concerning our ability to accurately predict sea level contributions from ice sheets. We will discover whether dynamic changes in ice streams led to rapid acceleration(s) in mass loss and the likely magnitude and time-scales over which these episodes occurred, thereby improving IPCC predictions of future sea level change (see LoS from Tony Payne, lead author of 5th IPCC report: 'Sea Level Change'). IPCC draws consensus from scientific papers but we will also target policymakers through contributions such as NERC Planet Earth, NERC Science Days, and invitations to local MPs, e.g. Stokes has previously been invited to present results of his research at the House of Commons. Our project will also contribute to several international working groups. It is central to the INQUA project 'Meltwater Routing and Ocean-Cryopshere-Atmosphere response' (MOCA), led by Project Partner Tarasov, which aims 'to establish a constrained regional meltwater and iceberg discharge chronology for the northern hemisphere'. MOCA is also linked to the 'Paleo Model Intercomparison Project' (PMIP II), and we will contribute to their aim of developing improved palaeo-environmental datasets. Ice sheet modellers will also benefit from our dataset, which can be used to test/validate models of ice stream/ice sheet behaviour. Our regional analyses of marine-based ice streams is also relevant to the Marine Ice Sheet Intercomparison Project (MISMIP), which is focused on evaluating agreement between marine-ice sheet models and 'real' ice sheet behavior (see LoS from Hindmarsh/Payne). In other disciplines, palaeo-oceanographers will benefit from new knowledge of the likely magnitude and timing of iceberg discharge events and meltwater pulses from ice streams; and palaeo-climatologists will benefit from a new understanding of the links between ice sheet dynamics, palaeo-climate and palaeo-oceanography (e.g. see LoS from Anders Carlson).

Teachers, educators, schoolchildren: this group will benefit from our involvement in the Climate Change for Schools Project (CCSP), which aims to put climate change at the heart of the national curriculum and make schools 'beacons' for positive action in their local communities. Following consultation with Project Manager Dr Krista McKinzey (see LoS) as to how we can best contribute, we propose to run 5 x 1 day workshops for secondary school teachers. The purpose of these will be to disseminate scientific knowledge on glaciers and climate change and devise new resources/schemes of work on this topic for the curriculum. The project website will have pages specifically designed for different educational groups (primary, secondary, tertiary), including resources for teachers to download with suggested activities. We also plan to continue existing activities in secondary/tertiary education where Stokes has given talks in schools and at education conferences (e.g. Philip Allan AS/A2 Physics Conference; British Association Science Festival, South African Science Festival) and written articles (e.g. 'Physics Review' A-level magazine).

General Public: the behaviour of large polar ice sheets has the potential to engender a wider public interest. Following consultation with the Director for Science Communication at the award-winning 'Life' Science Centre, Newcastle (see LoS from Ian Simmons), we propose to improve understanding and raise awareness of these issues through a series of 'Meet the Scientist' days. We will hold an exhibit on 'Glaciers and Climate Change' and provide computer portals for exercises and mapping of glacier change, and take-away resources/fact-sheets, etc. As with previous outputs that have been covered in a variety of national and international media (e.g. the Co-I's recent appearance on national television), newsworthy results will be disseminated through University press releases.