Abstract
Tunabreen is a 26-km long tidewater glacier. It is the most frequently surging glacier in Svalbard, with four documented surges in the past hundred years. We have modelled the evolution of this glacier with a Minimal Glacier Model (MGM), in which ice mechanics, calving and surging are parameterized. The model geometry consists of a flow band to which three tributaries supply mass. The calving rate is set to the mean observed value for the period 2012–2019, and kept constant. For the past 120 years, a smooth Equilibrium Line Altitude (ELA) history is reconstructed by finding the best possible match between observed and simulated glacier length. There is a modest correlation between this ELA history and meteorological observations from Longyearbyen. The simulated glacier retreat is in good agreement with observations. Runs with and without surging show that the effect of surging on the long term glacier evolution is limited. Due to the low surface slope and associated strong height -mass balance feedback, Tunabreen is very sensitive to changes in ELA. For a constant future ELA equal to the reconstructed value for 2020, the glacier front will retreat by 8 km during the coming hundred years. For an increase of the ELA of 2 m per year, the retreat is projected to be 13 km and Tunabreen becomes a land-based glacier around 2100. The calving rate is an important parameter: increasing its value by 50 % has about the same effect as a 50 m increase in the ELA, the corresponding equilibrium glacier length being 18 km (as compared to 25.8 km in the reference state). Response times vary from 150 to 400 years, depending on the forcing and on the state of the glacier (tidewater or land-based).
Highlights
Tunabreen is a 26-km long tidewater glacier in central Spitsbergen (Figure 1)
We have modelled the evolution of this glacier with a Minimal Glacier Model (MGM), in which ice mechanics, calving and surging are parameterized
For the past 120 years, a smooth Equilibrium Line Altitude (ELA) history is reconstructed by finding the best possible match between observed and simulated glacier length
Summary
Tunabreen is a 26-km long tidewater glacier in central Spitsbergen (Figure 1) It is the most frequently surging glacier in Svalbard, with four documented surges during the past hundred years (Flink et al, 2015; Luckman et al, 2015). The model we used is a so-called Minimal Glacier Model (MGM, Oerlemans 2011), in which dynamic processes are parameterized In this class of models, ice mechanics are not explicitly considered, but a number of essential feedback mechanisms can be dealt with (height - mass balance feedback, effect of reversed bed slopes, variable calving rates, effect of regular surging on the long-term mass budget, inclusion of tributary glaciers and basins). In the lumped-parameter model the focus is more on the details of local mechanical processes and their interaction with hydrology and thermodynamics - the large-scale glacier parameters are specified
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