Scaling of instability time-scales of Antarctic outlet glaciers based on one-dimensional similitude analysis

Abstract

Abstract. Recent observations and ice-dynamic modeling suggest that a marine ice sheet instability (MISI) might have been triggered in West Antarctica. The corresponding outlet glaciers, Pine Island Glacier (PIG) and Thwaites Glacier (TG), showed significant retreat during at least the last two decades. While other regions in Antarctica have the topographic predisposition for the same kind of instability it is so far unclear how fast these instabilities would unfold if they were initiated. Here we employ the concept of similitude to estimate the characteristic time scales of several potentially MISI-prone outlet glaciers around the Antarctic coast. The proposed one-dimensional scaling approach combines observational and model data with a scaling analysis of the governing equations for fast ice flow. Evaluating outlet-characteristic ice and bed geometry, surface mass balance and basal friction in the relevant region near the grounding line, we assume that the inferred time scales correspond to the outlet-specific initial responses time to potential destabilization. Our results suggest that TG and PIG have the fastest responses time of all investigated outlets, with TG responding about 1.25 to 2 times as fast as PIG, while other outlets around Antarctica would be up to ten times slower if destabilized. These results have to be viewed in light of the strong assumptions made in their derivation. These include the absence of ice-shelf buttressing, the one-dimensionality of the approach and the uncertainty of the available data, meaning strong caveats of the approach. We argue however that the current topographic situation and the physical conditions of the MISI-prone outlet glaciers carry the information of their respective time scale and that this information can be partially extracted through a similitude analysis. The one-dimensional analysis is only a first step. Whether a two-dimensional analysis is possible is beyond the scope of this study.

Tipping elements and amplified polar warming during the Last Interglacial

“…With Arctic sea-ice extent consistently breaking previous record lows (Kwok, 2018), the shift toward an ice-free summer state becomes increasingly possible, with ecological, environmental, climatic and even geopolitical implications for the wider Arctic region (Melia et al, 2016;Post et al, 2013;Screen and Williamson, 2017). At the other end of the globe, the projected contribution of Antarctic ice-sheet melt to 21st Century global mean sea level under an unmitigated emissions scenario ranges from a few decimetres Golledge et al, 2019Golledge et al, , 2015Levermann and Feldmann, 2019;Ritz et al, 2015) to more than a metre (DeConto and Pollard, 2016). Due to positive feedbacks within the Earth system, these changes at either pole are not independent; ocean-atmosphere interactions mean that the tipping of one sub-system into a different state could trigger the collapse of an inter-connected sub-system (Lenton and Ciscar, 2013;Lenton and Williams, 2013;Levermann et al, 2012;Steffen et al, 2007).…”