Preprints
https://doi.org/10.5194/egusphere-2023-54
https://doi.org/10.5194/egusphere-2023-54
30 Jan 2023
 | 30 Jan 2023
Status: this preprint is open for discussion.

Modelling the development and decay of cryoconite holes in Northwest Greenland

Yukihiko Onuma, Koji Fujita, Nozomu Takeuchi, Masashi Niwano, and Teruo Aoki

Abstract. Cryoconite holes (CHs) are water-filled cylindrical holes with cryoconite (dark-coloured sediment) deposited at their bottoms, forming on ablating ice surfaces of glaciers and ice sheets worldwide. Because the collapse of CHs may disperse cryoconite on the ice surface, thereby decreasing the ice surface albedo, accurate simulation of the temporal changes in CH depth is essential for understanding ice surface melt. We established a novel model that simulates the temporal changes in CH depth using heat budgets calculated independently at the ice surface and CH bottom based on hole-shape geometry. We evaluated the model with in situ observations of the CH depths on the Qaanaaq ice cap in Northwest Greenland during the 2012, 2014, and 2017 melt seasons. The model reproduced well the observed depth changes and timing of CH collapse. Although earlier models have shown that CH depth tends to be deeper when downward shortwave radiation is intense, our sensitivity tests suggest that deeper CH tends to form when the diffuse component of downward shortwave radiation is dominant, whereas CHs tend to be shallower when the direct component is dominant. In addition, the total heat flux to the CH bottom is dominated by shortwave radiation transmitted through ice rather than that directly from the CH mouths when the CH is deeper than 10 cm. Furthermore, the tests highlight that the ice surface albedo is a key parameter for accurately reproducing the timing of CH collapse because 0.1 decrease in albedo induces the CH collapse one day earlier. Heat component analysis suggests that CH depth is governed by the balance between the intensity of the diffuse component of downward shortwave radiation and the wind speed. Therefore, these meteorological conditions may be important factors contributing to the recent surface darkening of the Greenland ice sheet and other glaciers via the redistribution of CHs. Coupling the CH model proposed in this study with a climate model should improve our understanding of glacier-surface darkening.

Yukihiko Onuma et al.

Status: open (until 27 Mar 2023)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-54 (Yukihiko Onuma et al.)', David Chandler, 16 Mar 2023 reply
  • RC2: 'Comment on egusphere-2023-54', Anonymous Referee #2, 20 Mar 2023 reply

Yukihiko Onuma et al.

Data sets

Codes and data set for Cryoconite hole model (CryHo) Yukihiko Onuma, Koji Fujita, Nozomu Takeuchi, Masashi Niwano and Teruo Aoki https://doi.org/10.5281/zenodo.7539526

Model code and software

Codes and data set for Cryoconite hole model (CryHo) Yukihiko Onuma, Koji Fujita, Nozomu Takeuchi, Masashi Niwano and Teruo Aoki https://doi.org/10.5281/zenodo.7539526

Yukihiko Onuma et al.

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Short summary
We established a novel model that simulates the temporal changes in cryoconite hole (CH) depth using heat budgets calculated independently at the ice surface and CH bottom based on hole-shape geometry. The simulations suggest that CH depth is governed by the balance between the intensity of the diffuse component of downward shortwave radiation and the wind speed. The meteorological conditions may be important factors contributing to the recent ice surface darkening via the redistribution of CHs.