Simulated retreat of Jakobshavn Isbræ during the 21st century

Abstract

The early 21st century retreat of Jakobshavn Isbrae into its overdeepened bedrock trough was accompanied by acceleration to unprecedented ice stream speeds. Such dramatic changes suggested the possibility of substantial mass loss over the rest of this century. Here we use a threedimensional ice sheet model with parameterizations to represent the effects of ice mélange buttressing, crevasse-depthbased calving and submarine melting to adequately reproduce its recent evolution. We are the first study on Jakobshavn Isbrae that solves for three-dimensional ice flow coupled with representations of hydro-fracturing-induced calving and mélange buttressing. Additionally, the model can accurately replicate interannual variations in grounding line and terminus position, including seasonal fluctuations that emerged after arriving at the overdeepened basin and the disappearance of its floating ice shelf. Our simulated ice viscosity variability due to shear margin evolution is particularly important in reproducing the large observed interannual changes in terminus velocity. We use this model to project Jakobshavn's evolution over this century, forced by ocean temperatures from seven Earth system models and surface runoff derived from RACMO, all under the IPCC RCP4.5 climate scenario. In our simulations, Jakobshavn's grounding line continues to retreat ∼ 18.5 km by the end of this century, leading to a total mass loss of ∼ 2068 Gt (5.7 mm sea level rise equivalent). Despite the relative success of the model in simulating the recent behavior of the glacier, the model does not simulate winter calving events that have become relatively more important.Published by Copernicus Publications on behalf of the European Geosciences Union.

Twenty-first century response of Petermann Glacier, northwest Greenland to ice shelf loss

“…Crucially, this stabilization limits the sea level rise contribution of PG to <1 mm over the next 100 years. This is much smaller than projections from Jakobshavn Isbræ (2.77–5.7 mm) by 2100 (Bondzio and others, 2017; Guo and others, 2019) and Zachariæ Isstrøm (up to 16 mm in an extreme case: Choi and others, 2017) but is similar to the lowest emissions scenario (A1B) projections at Petermann and Kangerdlugssuaq (~ 1 mm: Nick and others, 2013). We now discuss several factors limiting grounding-line migration and ice loss.…”

“…The question still remains as to the future stability of PG if the entire ice shelf collapses, and calving then occurs from a grounded terminus. However, unlike glaciers with former ice shelves elsewhere in Greenland (Zachariæ Isstrøm and Jakobshavn Isbræ/Sermeq Kujalleq), where deep retrograde beds and widening fjords allowed for sustained retreat after ice shelf collapse (Mouginot and others, 2015; Choi and others, 2017; Guo and others, 2019), PG's inland geometry (steep prograde bed and narrow fjord: Fig. 6) does not suggest that grounded ice calving will force rapid unstable retreat in the future.…”

“…Elsewhere in Greenland, deep bed topography has allowed runaway grounding line retreat after ice shelf collapse. For example, the collapse of Jakobshavn Isbræ's ice shelf was followed by grounding line retreat and acceleration (Joughin and others, 2008, 2014), which is projected to continue throughout the 21st century due to deep bed topography further inland (Bondzio and others, 2017; Guo and others, 2019). Similarly, at Zachariæ Isstrøm, collapse of the ice shelf by 2012 was followed by acceleration, thinning and grounding line retreat down a retrograde bedslope (Mouginot and others, 2015; Hill and others, 2018 a ).…”

Greenland Ice Sheet Response to Stratospheric Aerosol Injection Geoengineering

“…Ocean temperatures have been shown to explain much of the recent retreat and inter‐annular variability in terminus position of outlet glaciers (Bondzio et al, ; Cowton et al, ). We estimate the potential impact of SAI on dynamical process by considering the three‐dimensional BISICLES ice dynamics model (Guo et al, ) of Jakobshavn Isbrae (Figure ), the fastest and largest individual contributor of Greenland's outlets to recent sea level rise (McMillan et al, ). The model has parameterizations to represent the effects of ice mélange buttressing, crevasse‐depth‐based calving, and submarine melting and reproduces well the glacier's recent evolution (Guo et al, ).…”

“…We estimate the potential impact of SAI on dynamical process by considering the three‐dimensional BISICLES ice dynamics model (Guo et al, ) of Jakobshavn Isbrae (Figure ), the fastest and largest individual contributor of Greenland's outlets to recent sea level rise (McMillan et al, ). The model has parameterizations to represent the effects of ice mélange buttressing, crevasse‐depth‐based calving, and submarine melting and reproduces well the glacier's recent evolution (Guo et al, ). We find (Figure ) that dynamic ice losses are 15 ± 1% (95% confidence interval, N = 200) lower under G4 than under RCP4.5 by 2070.…”