Retreat of Thwaites Glacier, West Antarctica, over the next 100 years using various ice flow models, ice shelf melt scenarios and basal friction laws

Abstract

Abstract. Thwaites Glacier (TG), West Antarctica, experiences rapid, potentially irreversible grounding line retreat and mass loss in response to enhanced ice shelf melting. Several numerical models of TG have been developed recently, showing a large spread in the evolution of the glacier in the coming decades to a century. It is, however, not clear how different parameterizations of basal friction and ice shelf melt or different approximations in ice stress balance affect projections.Here, we simulate the evolution of TG using different ice shelf melt, basal friction laws and ice sheet models of varying levels of complexity to 5 quantify the effect of these model configurations on the results. We find that the grounding line retreat and its sensitivity to ocean forcing is enhanced when a full-Stokes model is used, ice shelf melt is applied on partially floating elements, and a Budd friction is used. Initial conditions also impact the model results. Yet, all simulations suggest a rapid, sustained retreat along the same preferred pathway. The highest retreat rate occurs on the eastern side of the glacier and the lowest rate on a subglacial ridge on the western side. All the simulations indicate that TG will undergo an accelerated retreat once it retreats past the 10 western ridge. Combining the results, we find the uncertainty is small in the first 30 years, with a cumulative contribution to sea level rise of 5 mm, similar to the current rate. After 30 years, the mass loss depends on the model configurations, with a 300% difference over the next 100 years, ranging from 14 to 42 mm. IntroductionThwaites Glacier (TG), located in the Amundsen Sea Embayment (ASE) sector of West Antarctica, is one of the largest ice 15 dischargers in Antarctica, with a potential to raise global mean sea level by 59 cm, and one of the largest contributors to the mass loss from Antarctica (Holt et al., 2006;Mouginot et al., 2014). With a maximum speed over 4,000 m/yr and a width of nearly 120 km (Fig. 1a), the glacier discharged 126 Gt of ice into the ocean in 2014 , nearly three times as much as Jakobshavn Isbrae, the largest discharger of ice in Greenland (Howat et al., 2011). Over the past decade, the rate of mass loss of TG has increased from 28 Gt/yr in 2006 to 50 Gt/yr in 2014 (Medley et al., 2014;Mouginot et al., 2014; Rignot, 20 2008). The grounding line of TG has retreated by 14 km from 1992 to 2011 along its fast flowing main trunk . The surface has thinned at a rate of about 4 m/yr near the grounding line and more than 1 m/yr about 100 km inland (Pritchard et al., 2009). The rate of change in mass loss increased from 2.7 Gt/yr 2002. If these rates were to maintain over the coming decades, they would raise global sea level by, respectively, 41, 48 and 81 mm by 2100.The rapid mass loss and grounding line retreat of TG have been attributed to an increase in ice shelf melt rate induced by warmer ocean conditions (Rignot, 2001; Joughin et al., 2014;Seroussi et al., 2017). The strengthening of westerlies around the Antarctic ...

Impact of Iceberg Calving on the Retreat of Thwaites Glacier, West Antarctica Over the Next Century With Different Calving Laws and Ocean Thermal Forcing

“…Prior high-resolution modeling of TG focused on the impact of ice shelf melt (Joughin et al, 2010;Seroussi et al, 2017;Yu et al, 2018) with only coarse resolution models including both ice shelf and calving (DeConto & Pollard, 2016). Current satellite observations showed that the ice shelf of TG is highly damaged (MacGregor et al, 2012).…”

“…We model the evolution of TG over the next century using a shallow shelf approximation (SSA) (Morland & Zainuddin, 1987;MacAyeal, 1989). Our prior study showed that with the full Stokes simulations the grounding line retreats more rapidly but the pattern of retreat is well reproduced with SSA (Yu et al, 2018). We conclude on the importance and uncertainty of calving processes in controlling the retreat of TG.…”

“…We use a linear Weertman friction law (MacAyeal, 1989;Weertman, 1957). Using a nonlinear friction law might produce a more realistic response of the glacier, but our main focus is to evaluate the impact of calving on the evolution of TG, not the impact of a friction law as done previously (Yu et al, 2018). Ice shelf melt is applied when a floating section is present in the model.…”

“…The rapid retreat of TG has been attributed to high melt by the ocean beneath its ice shelf (Joughin et al, 2010;Seroussi et al, 2017;Yu et al, 2018). As the westerly winds continue to strengthen, more warm Circumpolar Deep Water will be allowed to intrude on the continental shelf, reach the ice shelves, and melt them from below.…”

“…Here, we extend a prior, high-resolution, modeling study of TG that is conditioned only by ice shelf melt, that is, without calving or frontal melt (Yu et al, 2018). In this study, we remove the ice shelf at the beginning of the experiment and apply iceberg calving and frontal melt by the ocean.…”