Preprints
https://doi.org/10.5194/tc-2020-318
https://doi.org/10.5194/tc-2020-318

  07 Dec 2020

07 Dec 2020

Review status: a revised version of this preprint was accepted for the journal TC and is expected to appear here in due course.

The temperature change shortcut: effects of mid-experiment temperature changes on the deformation of polycrystalline ice

Lisa Craw1, Adam Treverrow1, Sheng Fan2, Mark Peternell3, Sue Cook4, Felicity McCormack5, and Jason Roberts6,4 Lisa Craw et al.
  • 1Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, TAS, Australia
  • 2Department of Geology, University of Otago, Dunedin, New Zealand
  • 3Department of Earth Sciences, University of Gothenburg, Gothenburg, Sweden
  • 4Australian Antarctic Program Partnership, Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, TAS, Australia
  • 5School of Earth, Atmosphere & Environment, Monash University, Melbourne, VIC, Australia
  • 6Australian Antarctic Division, Hobart, TAS, Australia

Abstract. It is vital to understand the mechanical properties of flowing ice to model the dynamics of ice sheets and ice shelves, and to predict their behaviour in the future. We can do this by performing deformation experiments on ice in laboratories, and examining its mechanical and microstructural responses. However, natural conditions in ice sheets and ice shelves extend to low temperatures (< −5 °C), and high octahedral strains (> 0.08), and emulating these conditions in laboratory experiments can take an impractically long time. It is possible to accelerate an experiment by running it at a higher temperature in the early stages, and then lowering the temperature to meet the target conditions once the tertiary creep stage is reached. This can reduce total experiment run-time by > 1000 hours, however it is not known if this could affect the final strain rate or microstructure of the ice and potentially introduce a bias into the data. We deformed polycrystalline ice samples in uniaxial compression at −2 °C before lowering the temperature to either −7 °C or −10 °C, and compared the results to constant temperature experiments. Tertiary strain rates adjusted to the change in temperature very quickly (within 3 % of the total experiment run-time), with no significant deviation from strain rates measured in constant-temperature experiments. In experiments with a smaller temperature step (−2 °C to −7 °C) there is no observable difference in the final microstructure between changing-temperature and constant-temperature experiments which could introduce a bias into experimental results. For experiments with a larger temperature step (−2 °C to −10 °C), there are quantifiable differences in the microstructure. These differences are related to different recrystallisation mechanisms active at −10 °C, which are not as active when the first stages of the experiment are performed at −2 °C. For studies in which the main aim is obtaining tertiary strain rate data, we propose that a mid-experiment temperature change is a viable method for reducing the time taken to run low stress and low temperature experiments in the laboratory.

Lisa Craw et al.

 
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Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Printer-friendly Version - Printer-friendly version Supplement - Supplement

Lisa Craw et al.

Data sets

Mechanical and microstructural data from ice deformation experiments with a change in temperature partway Lisa Craw, Adam Treverrow, Sheng Fan, and Mark Peternell https://doi.org/10.4225/15/58eedf0d72be9

Lisa Craw et al.

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Short summary
Ice sheet and ice shelf models rely on data from experiments to accurately represent the way ice moves. Performing experiments at the temperatures and stresses that are generally present in nature takes a long time, and so there are few of these datasets. Here, we test the method of speeding up an experiment by running it initially at a higher temperature, before dropping to a lower target temperature to generate the relevant data. We show that this method can reduce experiment time by 55 %.