Preprints
https://doi.org/10.5194/tc-2022-182
https://doi.org/10.5194/tc-2022-182
 
20 Sep 2022
20 Sep 2022
Status: this preprint is currently under review for the journal TC.

Observed and modeled moulin heads in the Pâkitsoq region of Greenland suggest subglacial channel network effects

Celia Trunz1,2, Kristin Poinar3, Lauren C. Andrews4, Matthew D. Covington1, Jessica Mejia3,5, Jason Gulley5, and Victoria Siegel6 Celia Trunz et al.
  • 1Geosciences Department, University of Arkansas, Fayetteville AR, USA
  • 2Department of Applied Geomatics, Université de Sherbrooke, Sherbrooke, QC, CA
  • 3Department of Geology, University at Buffalo, Buffalo NY, USA
  • 4Global Modeling and Assimilation Office, NASA Goddard Space Flight Center, Greenbelt MD, USA
  • 5Geosciences Department, University of South Florida, Tampa FL, USA
  • 6Sisu Field Solutions LLC, Austin, Texas, USA

Abstract. In the ablation zone of land-terminating areas of the Greenland Ice Sheet, water pressures at the bed control seasonal and daily ice motion variability. During the melt season, large amounts of surface meltwater access the bed through moulins, which sustain an efficient channelized subglacial system. Water pressure within these subglacial channels can be inferred by measuring the hydraulic head within moulins. However, moulin head data are rare, and subglacial hydrology models that simulate water pressure fluctuations require water storage in moulins or subglacial channels. Neither the volume nor the location of such water storage is currently well constrained. Here, we use the Moulin Shape (MouSh) model, which quantifies time-evolving englacial storage, coupled with a subglacial channel model to simulate head measurements from a moulin in the Pâkitosq region in Greenland. We force the model with surface meltwater input calculated using field-acquired weather data. Our first-order simulations of moulin hydraulic head either over-predict the diurnal range of oscillation of the moulin head or require an unrealistically large moulin size to produce realistic head oscillation ranges. We find that to accurately match field observations of moulin head, additional subglacial water must be added to the system. We hypothesize that this additional `baseflow' represents strong subglacial network connectivity throughout the channelized system and is ultimately sourced from basal melt and non-local surface water inputs upstream.

Celia Trunz et al.

Status: open (until 15 Nov 2022)

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Celia Trunz et al.

Data sets

Supraglacial stream discharge measurements from six catchments within the Pâqitsoq region of Sermeq Avannarleq, western Greenland Ice Sheet 2017 -2018 Trunz, C., Mejia, J., Covington, M., Siegel, V., Conlon, B., & Gulley, J. https://doi.org/10.18739/A2D21RK53

Model code and software

cctrunz/ModelRepo_pyMouShBaseflow_paper: Initial code for submission (v1.0.0) Trunz, C., Poinar, K., & Andrews, L. C. https://doi.org/10.5281/zenodo.7058365

Celia Trunz et al.

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Short summary
Models simulating water pressure variations at the bottom of glaciers must use large storage parameters to produce realistic results. Whether that storage occurs englacially (in moulins) or subglacially is a matter of debate. Here, we directly simulate moulin volume to constrain the storage there. We find it is not enough. Instead, subglacial processes, including basal melt and input from upstream moulins, must be responsible for stabilizing these water pressure fluctuations.