Testing the area–altitude balance ratio (AABR) and accumulation–area ratio (AAR) methods of calculating glacier equilibrium-line altitudes

Oien, Rachel P.; Rea, Brice R.; Spagnolo, Matteo; Barr, Iestyn D.; Bingham, Robert G.

Abstract

In this study, we compare equilibrium-line altitudes (ELAs) calculated using the area–altitude balance ratio (AABR) and the accumulation–area ratio (AAR) methods, with measured ELAs derived from direct field observations. We utilise a GIS toolbox to calculate the ELA for 64 extant glaciers by applying the AABR and AAR methods to DEMs and polygons of their geometry. The calculated ELAs (c-ELAs) are then compared to measured zero-net balance ELAs (znb-ELAs) obtained from mass-balance time series held by the WGMS for the same glaciers. The correlation between znb-ELAs and AABR (1.56)/AAR (0.58) c-ELAs is very strong, with an r2 = 0.99. The smallest median difference between znb-ELAs and c-ELAs (i.e. 65.5 m) is obtained when a globally representative AABR of 1.56 is used. When applied to palaeoglacier-climate applications, this difference translates to ~0.42°C, well within the uncertainty of palaeotemperature proxies used to determine mean summer temperature at the ELA. The more widely used mean AABR of 1.75 is shown to be statistically invalid due to the skewness of the dataset. On this basis, when calculating glacier ELAs, we recommend the use of a global AABR value of 1.56.

Citation

Oien, R. P., Rea, B. R., Spagnolo, M., Barr, I. D., & Bingham, R. G. (2022). Testing the area–altitude balance ratio (AABR) and accumulation–area ratio (AAR) methods of calculating glacier equilibrium-line altitudes. Journal of Glaciology, 68(268), 357-368. https://doi.org/10.1017/jog.2021.100

• Journal Article Type: Article
• Acceptance Date: Sep 21, 2021
• Online Publication Date: Sep 21, 2021
• Publication Date: 2022-04
• Deposit Date: Mar 25, 2024
• Journal: Journal of Glaciology
• Print ISSN: 0022-1430
• Electronic ISSN: 1727-5652
• Publisher: International Glaciological Society
• Peer Reviewed: Peer Reviewed
• Volume: 68
• Issue: 268
• Pages: 357-368
• DOI: https://doi.org/10.1017/jog.2021.100
• Keywords: Earth-Surface Processes
• Public URL: https://durham-repository.worktribe.com/output/2346468
• Additional Information: Copyright: Copyright © The Author(s), 2021. Published by Cambridge University Press; License: This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (http://creativecommons.org/licenses/by/4.0/). Access via https://doi.org/10.1017/jog.2021.100