ScotIce – How fast could ice caps collapse?

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.