ScotIce - How fast could ice caps collapse?

Lead Research Organisation: Scottish Universities Environmental Research Centre (SUERC)
Department Name: SUERC

Abstract

Average surface air temperatures have been rising everywhere on Earth over the last century and are predicted to continue to rise for at least the next century. One of the clearest indicators of this warming is the shrinking of glaciers and the marked reduction of sea ice in the Arctic, where atmospheric warming is most pronounced. Melting of sea ice does not contribute to sea level rise, but meltwater from land-based glaciers and ice caps ends up in the oceans and is a major contributor to sea level rise. How fast will glaciers and ice caps melt? Will they disappear in decades, adding all of their water rapidly to the oceans, or will the melting occur over a longer time span, with a less rapid but ultimately the same amount of sea level rise. For the 150 million people living within 1 m of high tide, and those concerned about maintaining trillions of pounds worth of global coastal infrastructure, answering the question of how fast glaciers and ice caps will melt and contribute to sea level rise is important.

ScotIce will determine how fast ice caps can melt by analysing the collapse of the ice cap that existed in Scotland about 11600 years ago and disappeared at a time when temperatures rose by 8C, the same as the temperature rise predicted for the Arctic by 2100. By measuring how quickly the ice cap disappeared we will learn how fast present day equivalent sized ice masses subjected to similar warming could disappear, thus providing data needed for sea level rise models to make more informed predictions.

To quantify how fast the Scottish ice cap collapsed we need to be able to determine the rate of change of the former ice mass. We will use surface exposure dating with the cosmogenic nuclides 10Be and 26Al produced in the mineral quartz in rock by cosmic rays, that is, when the rock is exposed to the sky. Conversely, the production of the nuclides in quartz stops when the rocks are covered by a few metres of ice. Surface exposure dating is the only technique available to directly date when landforms become exposed as ice melts. We will measure the concentration of these nuclides in glacially abraded and plucked rock surfaces and glacially transported boulders, located at the maximum, intermediate and minimum extent of the ice cap. Because we know how fast the cosmogenic nuclides are produced in quartz, we can use the measured cosmogenic nuclide concentration to determine when the sampled rock surface became exposed from under the ice. In other words, we can determine when the ice disappeared from the sample site. The age difference between the maximum and minimum ice extent provides the retreat rate which will be integrated with independently dated climate proxy archives to look for causal relationships.

To be able to test the hypothesised rapid collapse of the Scottish ice cap we first need to improve the surface exposure dating technique from the current routine 2-3% to 1% or better measurement precision for 10Be and 26Al. Analytical improvements to the accelerator mass spectrometry (AMS) that is currently used to measure 10Be and 26Al will allow us to resolve the rate of ice cap collapse. However, there are some questions for which AMS is unlikely to provide the necessary precision. To resolve if the decline of the ice cap was steady or episodic requires the development of an entirely new methodology for measuring 26Al by positive ion mass spectrometry (PIMS) being pioneered at the Scottish Universities Environmental Research Centre (SUERC). Developing Al PIMS has the potential for leading to a paradigm shift in how Earth and Environmental scientists determine the rate of natural processes and date landscapes.

ScotIce empirical data on ice cap collapse will inform predictive sea level models, while improved AMS precision and new Al-PIMS has the potential to revolutionise surface exposure dating and open up new fields of research for the UK and international science community.

Planned Impact

Who are the beneficiaries and how will they benefit from ScotIce?

Climate and Sea Level Change mitigation and adaptation: ScotIce aims to constrain the rate at which existing ice caps can collapse. More precise estimates of ice mass loss will enable improved input parameterisation in climate change impact modelling. This will reduce the uncertainties currently implicit in simulations of future ice mass behaviour and predictions of global sea-level change. Constraining the rate of glacier and ice cap demise is one of the problematic factors when implementing climate/ice feedback loops to coupled ice-sheet GCMs that drive our climate forecasting for the near and distant future. Improved predictive capability is critical for policy makers concerned with the impacts on trillions of pounds worth of global coastal infrastructure and the 150 million people living within 1 m of high tide.

Dating community: The higher precision dating we will develop as part of ScotIce will have impact in all of the diverse application fields of cosmogenic isotope dating. Examples of additional impact of future application would be:
Tectonics - improved understanding of recent faults histories, fault mechanics, and along and across fault interactions will lead to improved modelling and more accurate hazard mapping. In turn this will inform policy makers, and insurers, and ultimately lead to better public safety.
Burial Dating - this relies on high precision of both Be and Al measurement. Burial dating has been utilised for dating early hominid sites, but currently suffers from relatively large uncertainties resulting in as yet unresolved questions about the timing of hominid evolution. Improvements in this application will solve some of these resolution issues leading to improved understanding of early human migration.

We aim to raise awareness about how geoscientists and physicists work together towards reducing uncertainty in generating predictive scenarios and thus how science is central to a sustainable society.

Industrial impact
The SUERC AMS facility has an existing and long-term industrial research partnership with NEC (leaders in commercial AMS and PIMS instruments) and Pantechnik (leaders in commercial ECR plasma ion sources). The SUERC AMS instrument is commercially available from NEC. Our work validating the high precision ability will allow them to market their system as being able to perform to this standard. This can create commercial success from multiple routes: 1) by giving them high performance superior technology during tendering process increasing likelihood of sales 2) contracts for modification of other people's system to match ours, and 3) training of customers to operate the machinery with our new method. This impact will be immediately available to NEC and will also have impact for all AMS companies as they learn to apply our technique to their systems.

The biggest industrial impact will come through Al-PIMS (see Pantechnik and NEC letters of support). Equalling the performance of PIMS compared to conventional AMS, will allow users to perform cosmogenic isotope analysis on a compact system. This will be a step change in the way these isotopes can be measured. The compact PIMS system is much simpler to use than conventional AMS, with no particle accelerator and no high energy particle beams; it is effectively just a large mass spectrometer. In addition, the PIMS has around 20% the foot print and 20% the cost of large AMS system such as the 5MV AMS at SUERC. This reduction in cost, size and complexity will mean large scale national facilities for the conventional technology will no longer be needed and individual laboratories will be able to have their own compact rare isotope mass spectrometer, in turn increasing the volume of science that can be done.

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