How fast can an ice cap collapse? Pushing the limits of geochronology with large particle accelerators

Overview

How fast will terrestrial glaciers and ice caps melt in response to global warming? 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 similar amount of sea level rise. For the millions of people living on coastal lowlands, 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.

To determine how fast ice caps can melt requires access to their beds, which is not possible for present day ice caps. Hence we will determine the rate of retreat of the former Scottish ice cap about 11600 years ago when temperatures rose rapidly by 6-8°C, similar to the temperature rise predicted for the Arctic by 2100. By measuring how quickly the Scottish ice cap disappeared you will establish how quickly equivalent sized ice masses could disappear, providing empirical data for predictive sea level rise models.

The dating technique of choice in many palaeo-glaciological studies is surface exposure dating because it allows direct determination of ice retreat from glacial landforms. However, the precision of the technique is currently insufficient to resolve the rate of retreat of the Scottish ice cap, or to correlate the retreat to high resolution climate proxies.

Key research questions: Can surface exposure dating with 10Be and 26Al using accelerator mass spectrometry (AMS) and/or positive ion mass spectrometry (PIMS) provide 1% precision routinely? When and how fast did the Scottish ice cap disappear? Was the retreat of the ice cap steady or intermittent?

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Image Captions

Picture 1.jpg “(left) Multi-Cathode Source of Negative Ions by Caesium Sputtering (MC-SNICS) to produce ion beams from cosmogenic nuclide samples, (middle) 5 million volt accelerator to break up molecular interferences, and (right) positive mass spectrometry (PIMS) ion source.”

Methodology

To quantify how fast the Scottish ice cap collapsed you will use the in situ produced terrestrial cosmogenic nuclides 10Be and 26Al in quartz to determine the surface exposure ages of glacial landforms located at the maximum, intermediate and minimum extent of the ice cap. Because we know how fast the cosmogenic nuclides are produced in quartz exposed at the Earth’s surface, we can use the measured cosmogenic nuclide concentration to determine when the sampled rock surface became exposed from under the ice. 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 investigate causal relationships. To test the hypothesised rapid collapse of the Scottish ice cap we need to improve surface exposure dating measurement precision from the current 2-3% to 1% or better. 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. To resolve if the decline of the ice cap was steady or intermittent requires the development of an entirely new methodology for measuring 26Al by positive ion mass spectrometry (PIMS) invented and being pioneered at the Scottish Universities Environmental Research Centre (SUERC).

Pushing the boundaries of conventional AMS and developing Al-PIMS has the potential for leading to a paradigm shift in how Earth and Environmental scientists determine exposure ages and process rates.

Project Timeline

Year 1

Refining key research questions and establishing hypotheses; select sample sites; (± fieldwork); training in core geochemistry, accelerator mass spectrometry skills, and PIMS skills; testing AMS ion source operation using different sample matrices and AMS cathode configurations; PhD progression presentation.

Year 2

AMS and PIMS ion source optimisation; field sample preparation; data analysis; statistical modelling; presentation at national conference.

Year 3

Further data analysis; lead authorship of key manuscript(s); presentation at international conference (e.g. AGU, EGU);

Year 3.5

Thesis preparation and write-up; thesis submission for examination.

Training
& Skills

A comprehensive training programme will be provided comprising both specialist scientific training and generic transferable and professional skills. This is a unique PhD opportunity for an analytically minded candidate, offering direct access to unique technologies and providing highly desirable specialist and complementary interdisciplinary skills. Training will be provided by internationally recognised experts, mostly the project supervisors. Specifically, training in geochemical sample preparation; cosmogenic-nuclide analysis by AMS and PIMS; data reduction; numerical data interpretation and statistical modelling. Training in field sampling for surface exposure dating can be provided, but fieldwork is not suitable/desirable for everyone and is not a requirement for this project. Preparation of samples for 10Be and 26Al will be carried out under the guidance of Dr Derek Fabel in the SUERC cosmogenic isotope laboratories. Measurement of isotopic ratios at the SUERC AMS Laboratory will be under the guidance of Dr Richard Shanks and Dr Derek Fabel. The student will gain access to University of Glasgow taught courses and NERC run training course depending on skill of the candidate. The skills developed in this project will make the candidate an expert in cosmogenic nuclide dating, AMS, and PIMS analytical techniques. Any one of these skills will create many opportunities for a highly successful research career.

References & further reading

Balco, G. 2011. Contributions and unrealized potential contributions of cosmogenic-nuclide exposure dating to glacier chronology 1990-2010. Quaternary Science Reviews, 20, 3-27.

Dunai, T. 2010. Cosmogenic Nuclides: Principles, Concepts and Applications in the Earth Surface Sciences. Cambridge University Press, Cambridge, UK.

Freeman et al. 2015. Radiocarbon positive-ion mass spectrometry. Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 361, 229-232.

Further Information

Applications: to apply for this PhD please use the url: https://www.gla.ac.uk/study/applyonline/?CAREER=PGR&PLAN_CODES=CF18-7316

For further information, or informal enquiries, contact:
Dr Richard Shanks richard.shanks@glasgow.ac.uk
or Dr Derek Fabel derek.fabel@glasgow.ac.uk

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