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

Abstract

Abstract. Firn simulations are essential for understanding Antarctic ice sheet mass change, as they enable us to convert satellite altimetry observed volume changes to mass changes and column thickness to ice thickness and to quantify the meltwater buffering capacity of firn. Here, we present and evaluate a simulation of the contemporary Antarctic firn layer using the updated semi-empirical IMAU Firn Densification Model (IMAU-FDM) for the period 1979–2020. We have improved previous fresh-snow density and firn compaction parameterizations and used updated atmospheric forcing. In addition, the model has been calibrated and evaluated using 112 firn core density observations across the ice sheet. We found that 62 % of the seasonal and 67 % of the decadal surface height variability are due to variations in firn air content rather than firn mass. Comparison of simulated surface elevation change with a previously published multi-mission altimetry product for the period 2003–2015 shows that performance of the updated model has improved, notably in Dronning Maud Land and Wilkes Land. However, a substantial trend difference (>10 cm yr−1) remains in the Antarctic Peninsula and Ellsworth Land, mainly caused by uncertainties in the spin-up forcing. By estimating previous climatic conditions from ice core data, these trend differences can be reduced by 38 %.

Determining the Freshwater Fluxes from Antarctica with Earth Observation Data, Models, and In Situ Measurements: Uncertainties, Knowledge Gaps, and Prospects for New Advances

“…Underestimates in basal topography also extend to estimates of ocean depth, with similar consequences for mass flux estimates, ice sheet modelling and ocean forcing estimates on the ice shelves. Finally, there is uncertainty related to the firn air correction applied to convert elevation to ice thickness (Veldhuijsen et al, 2023).…”

Evolution of Antarctic firn air content under three future warming scenarios

“…An equilibrium initial firn column is obtained by looping over a reference climate until the entire firn column is refreshed. For further details of the model setup we refer to Veldhuijsen et al (2023a) and Brils et al (2022). Version v1.2A of IMAU-FDM (referred as FDM v1.2A) has been extensively evaluated over Antarctica against in situ observations of firn density and temperature, and remote sensing altimetry measurements (Veldhuijsen et al, 2023a).…”

“…For further details of the model setup we refer to Veldhuijsen et al (2023a) and Brils et al (2022). Version v1.2A of IMAU-FDM (referred as FDM v1.2A) has been extensively evaluated over Antarctica against in situ observations of firn density and temperature, and remote sensing altimetry measurements (Veldhuijsen et al, 2023a). In this study we update the model to version IMAU-FDM v1.2AD (referred to as FDM v1.2AD) by implementing a densification expression that is suitable for transient climate change experiments, as is described in the next sections.…”

“…Firn models forced by outputs of regional climate models or reanalysis datasets, have been used to simulate the current (1979 till present) AIS firn layer (Gardner et al, 2023;Keenan et al, 2021;Medley et al, 2022;Veldhuijsen et al, 2023a). Firn models have also been forced by outputs of regional climate models to simulate FAC evolution in response to climate change scenarios (Ligtenberg et al, 2014;Munneke et al, 2014).…”

“…Here, we use the IMAU Firn Densification Model (IMAU-FDM) for Antarctica, which has previously been evaluated for the contemporary climate (Veldhuijsen et al, 2023a). IMAU-FDM is driven by realizations of CESM2 of the scenarios SSP1-2.6, SSP2-4.5 and SSP5-8.5 for the period 1950-2100, dynamically downscaled to 27 km resolution with RACMO2.3p2.…”