Abstract
Abstract. In this study the dynamics and sensitivity of Hans Tausen Iskappe (western Peary Land, Greenland) to climatic forcing is investigated with a coupled ice flow–mass balance model. The surface mass balance (SMB) is calculated from a precipitation field obtained from the Regional Atmospheric Climate Model (RACMO2.3), while runoff is calculated from a positive-degree-day runoff–retention model. For the ice flow a 3-D higher-order thermomechanical model is used, which is run at a 250 m resolution. A higher-order solution is needed to accurately represent the ice flow in the outlet glaciers. Under 1961–1990 climatic conditions a steady-state ice cap is obtained that is overall similar in geometry to the present-day ice cap. Ice thickness, temperature and flow velocity in the interior agree well with observations. For the outlet glaciers a reasonable agreement with temperature and ice thickness measurements can be obtained with an additional heat source related to infiltrating meltwater. The simulations indicate that the SMB–elevation feedback has a major effect on the ice cap response time and stability. This causes the southern part of the ice cap to be extremely sensitive to a change in climatic conditions and leads to thresholds in the ice cap evolution. Under constant 2005–2014 climatic conditions the entire southern part of the ice cap cannot be sustained, and the ice cap loses about 80 % of its present-day volume. The projected loss of surrounding permanent sea ice and resultant precipitation increase may attenuate the future mass loss but will be insufficient to preserve the present-day ice cap for most scenarios. In a warmer and wetter climate the ice margin will retreat, while the interior is projected to thicken, leading to a steeper ice cap, in line with the present-day observed trends. For intermediate- (+4 °C) and high- warming scenarios (+8 °C) the ice cap is projected to disappear around AD 2400 and 2200 respectively, almost independent of the projected precipitation regime and the simulated present-day geometry.
Highlights
Glaciers and ice caps (GICs) made an important contribution to sea level rise in the 20th century
For slightly warmer conditions the collapse threshold of the southern part of the ice cap is crossed, and eventually, after thousands of years, the entire southern part of the ice cap is lost. This is for instance the case under the 2005–2014 climatic conditions, which are around 1.6 ◦C warmer than the 1961–1990 average conditions over Hans Tausen Iskappe (6 % higher precipitation than 1961–1990 mean) and for which the specific surface mass balance (SMB) of the present-day ice cap is very negative (−0.39, −0.32 and −0.32 m w.e. a−1 in MAR3.5.2, RACMO2.3 and PDD melt–retention approach respectively)
In this study a SMB–thermomechanical ice flow model was developed for Hans Tausen Iskappe, the world’s northernmost ice cap, and tested for various parameter settings and model complexities
Summary
Glaciers and ice caps (GICs) made an important contribution to sea level rise in the 20th century. In order to resolve the ice flow in the many outlet glaciers accurately, a higher-order (HO) approximation to the full force balance is used This differs from other detailed ice cap and ice field modelling studies (Aðalgeirsdóttir et al, 2005, 2006; Flowers et al, 2005, 2007, 2008; Giesen and Oerlemans, 2010; Hannesdóttir et al, 2015; Ziemen et al, 2016; Åkesson et al, 2017) that are based on the SIA or similar approaches. Thresholds are analysed that could inhibit ice cap growth or decay, followed by the sensitivity of the ice cap to changes in climatic conditions and their implications for the future ice cap evolution (Sect. 6)
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