Dynamic regimes of the Greenland Ice Sheet emerging from interacting melt-elevation and glacial isostatic adjustment feedbacks

Abstract

Abstract. The stability of the Greenland Ice Sheet under global warming is governed by a number of dynamic processes and interacting feedback mechanisms in the ice sheet, atmosphere and solid Earth. Here we study the long-term effects due to the interplay of the competing melt-elevation and glacial isostatic adjustment (GIA) feedbacks for different temperature step forcing experiments with a coupled ice-sheet and solid-Earth model. Our model results show that for warming levels above 2 °C, Greenland could become essentially ice-free on the long-term, mainly as a result of surface melting and acceleration of ice flow. These ice losses can be mitigated, however, in some cases with strong GIA feedback even promoting the partial recovery of the Greenland ice volume. We further explore the full-factorial parameter space determining the relative strengths of the two feedbacks: Our findings suggest distinct dynamic regimes of the Greenland Ice Sheets on the route to destabilization under global warming – from recovery, via quasi-periodic oscillations in ice volume to ice-sheet collapse. In the recovery regime, the initial ice loss due to warming is essentially reversed within 50,000 years and the ice volume stabilizes at 61–93 % of the present-day volume. For certain combinations of temperature increase, atmospheric lapse rate and mantle viscosity, the interaction of the GIA feedback and the melt-elevation feedback leads to self-sustained, long-term oscillations in ice-sheet volume with oscillation periods of tens to hundreds of thousands of years and oscillation amplitudes between 15–70 % of present-day ice volume. This oscillatory regime reveals a possible mode of internal climatic variability in the Earth system on time scales on the order of 100,000 years that may be excited by or synchronized with orbital forcing or interact with glacial cycles and other slow modes of variability. Our findings are not meant as scenario-based near-term projections of ice losses but rather providing insight into of the feedback loops governing the "deep future" and, thus, long-term resilience of the Greenland Ice Sheet.

Solid Earth Uplift Due To Contemporary Ice Melt Above Low‐Viscosity Regions of the Upper Mantle

“…When ice melts, the surface elevation decreases and the ice is subjected to warmer temperatures and larger melt rates, leading to further ice melt, and potential ice sheet destabilization (Levermann et al., 2013). However, GIA counteracts this feedback by increasing the surface elevation when ice melts (Zeitz et al., 2022), and fast uplift above LV regions can amplify this feedback. For marine terminating glaciers, GIA can stabilize the grounding line.…”

Overshooting the critical threshold for the Greenland ice sheet

“…Recently, it has been shown that, to some extent, the glacial isostatic adjustment can counteract the positive feedbacks that are believed to cause a hysteresis of the Greenland ice sheet with global warming [21]. While the uplifting of the bedrock due to decreasing ice load with increasing temperatures slows down the ice loss, a regrowth of the ice sheet is only facilitated when the temperature decreases again.…”

“…However, the time scale of this feedback is still debated [22,23] and is often neglected on sub-millennial time scales [7]. The simulated oscillations of the ice sheet on a decamillennial time scale are believed to be the consequence of an interplay between bedrock uplift and melt-elevation feedback in PISM [21]. We find that the intermediate states are at least partially caused by the interplay between the isostatic glacial adjustment and melt-elevation feedback and we find fewer intermediate states without bedrock uplifting (Fig.…”

The stability of present-day Antarctic grounding lines – Part B: Possible commitment of regional collapse under current climate

“…This is also underlined by our control run experiments which show convergence of their ice volume towards steady states rather than large scale cyclic behaviour. Other feedbacks and processes than MISI might influence the stability regime of grounding lines, e.g., bedrock uplift and the melt-elevation feedback can lead to cyclic behaviour (Zeitz et al, 2021). We here exclude those feedbacks and only focus on MISI.…”