Andrea Burke, University of St Andrews, School of Earth and Environmental Sciences, St Andrews, KY16, United Kingdom, James William Buchanan Rae, University of St Andrews, School of Earth and Environmental Sciences, St Andrews, United Kingdom, Rosanna Greenop, University of St Andrews, St Andrews, United Kingdom, Paula J Reimer, Queen's University Belfast, Belfast, BT9, United Kingdom and Tim Heaton, University of Sheffield, Sheffield, United Kingdom