Preprints
https://doi.org/10.5194/egusphere-2022-236
https://doi.org/10.5194/egusphere-2022-236
 
23 May 2022
23 May 2022
Status: this preprint is open for discussion.

Geothermal heat flux is the dominant source of uncertainty in englacial-temperature-based dating of ice-rise formation

Aleksandr Montelli1,2 and Jonathan Kingslake1 Aleksandr Montelli and Jonathan Kingslake
  • 1Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York, USA
  • 2Scott Polar Research Institute, University of Cambridge, Cambridge, UK

Abstract. Ice rises are areas of locally grounded, slow-moving ice adjacent to floating ice shelves. Temperature profiles measured through ice rises contain information regarding changes to their dynamic evolution and external forcings, such as past surface temperatures, past accumulation rates and geothermal heat flux. While previous work has used borehole temperature-depth measurements to infer one or two such parameters, there has been no systematic investigation of parameter sensitivity to the interplay of multiple external forcings and dynamic changes. A one-dimensional vertical heat flow forward model developed here examines how changing forcings affect temperature profiles. Further, using both synthetic data and previous measurements from the Crary Ice Rise in Antarctica, we use our model in a Markov Chain Monte-Carlo inversion to demonstrate that this method has potential as a useful dating technique that can be implemented at ice rises across Antarctica. However, we also highlight the non-uniqueness of previous ice rise formation dating based on temperature profiles, showing that using nominal values for forcing parameters, without taking into account their realistic uncertainties, can lead to underestimation of dating uncertainty. In particular, geothermal heat flux represents the dominant source of uncertainty in ice-rise age estimation. For instance, in Crary Ice Rise higher heat flux values (i.e., about 90 mW m-2) yield grounding timing of 1400±800 years, whereas lower heat flux of around 60 mW m-2 implies earlier ice rise formation and lower uncertainties in the ice rise age estimations (500±250 years). We discuss the utility of this method in choosing future ice drilling sites and conclude that integrating this technique with other indirect dating methods can provide useful constraints on past forcings and changing boundary conditions from in-situ temperature-depth measurements.

Aleksandr Montelli and Jonathan Kingslake

Status: open (until 18 Jul 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Review of Montelli and Kingslake', Anonymous Referee #1, 21 Jun 2022 reply
  • RC2: 'Comment on egusphere-2022-236', Anonymous Referee #2, 26 Jun 2022 reply

Aleksandr Montelli and Jonathan Kingslake

Aleksandr Montelli and Jonathan Kingslake

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Short summary
Thermal modelling and Bayesian inversion techniques are used to evaluate the uncertainties inherent in inferences of ice-sheet evolution from borehole temperature measurements. We show that the same temperature profiles may result from a range of parameters, of which geothermal heat flux through underlying bedrock plays a key role. Careful model parametrization and evaluation of heat flux are essential for inferring past ice-sheet evolution from englacial borehole thermometry.