Improved representation of the contemporary Greenland ice sheet firn layer by IMAU-FDM v1.2G

Abstract

Abstract. The firn layer that covers 90 % of the Greenland ice sheet (GrIS) plays an important role in determining the response of the ice sheet to climate change. Meltwater can percolate into the firn layer and refreeze at greater depths, thereby temporarily preventing mass loss. However, as global warming leads to increasing surface melt, more surface melt may refreeze in the firn layer, thereby reducing the capacity to buffer subsequent episodes of melt. This can lead to a tipping point in meltwater runoff. It is therefore important to study the evolution of the Greenland firn layer in the past, present and future. In this study, we present the latest version of our firn model, IMAU-FDM (Firn Densification Model), with an application to the GrIS. We improved the density of freshly fallen snow, the dry-snow densification rate and the firn's thermal conductivity using recently published parameterizations and by calibrating to an extended set of observations of firn density, temperature and liquid water content at the GrIS. Overall, the updated model settings lead to higher firn air content and higher 10 m firn temperatures, owing to a lower density near the surface. The effect of the new model settings on the surface elevation change is investigated through three case studies located at Summit, KAN-U and FA-13. Most notably, the updated model shows greater inter- and intra-annual variability in elevation and an increased sensitivity to climate forcing.

Characteristics of the contemporary Antarctic firn layer simulated with IMAU-FDM v1.2A (1979–2020)

“…The updated parameterization has a similar bias and RMSE to surface snow density observations compared to the SNOWPACK model and the Community Firn Model (CFM) (Keenan et al, 2021;Medley et al, 2020). The fresh snow density parameterization for Greenland used in FDM v1.2G, is only a function of yearly temperature (Brils et al (2021). This is in contrast with Antarctica, where we found a strong dependency with instantaneous wind speed and temperature, which is in line with previous work (Keenan et al, 2021;Lenaerts et al, 2012;van Kampenhout et al, 2017), and likely owing to the larger range in temperature and wind speed conditions during snow deposition in Antarctica.…”

“…The model was originally developed by Helsen et al (2008), and updated by Ligtenberg et al (2011) to a version abbreviated here to FDM v1.1. Brils et al (2021) recently improved IMAU-FDM applied to the Greenland ice sheet by including a refined parameterization of the thermal conductivity to version FDM V1.2G. The various versions of IMAU-FDM have been extensively evaluated against firn density and temperature observations from both Greenland and Antarctica (Ligtenberg et al, 2011;Kuipers Munneke et al, 2015;Brils et al, 2021).…”

“…( 3) is used without correction fits. Ligtenberg et al (2011) and Brils et al (2021) used logarithmic correction functions, thus:…”

“…To capture the percolation and refreezing of meltwater more accurately, the model timestep is reduced from 3600 to 300 s for locations with the significant melt. Further details and evaluation of heat conduction, percolation and refreezing are provided by Brils et al (2021).…”

Major Modes of Climate Variability Dominate Nonlinear Antarctic Ice‐Sheet Elevation Changes 2002–2020

“…Data presented here are available at King and Christoffersen (2024) and King et al (2023a). All underlying data are openly available (Brils et al, 2021;Haran et al, 2014Haran et al, , updated 2019Howat, 2022;Medley et al, 2022a;Morlighem, 2022;Nilsson et al, 2023;Rignot et al, 2017;Sasgen et al, 2020). The software of Wu, 2023 was used for multivariate EOF analysis.…”