Abstract
Abstract. In this paper, we study the effects of basal friction, sub-aqueous undercutting and glacier geometry on the calving process by combining six different models in an offline-coupled workflow: a continuum–mechanical ice flow model (Elmer/Ice), a climatic mass balance model, a simple subglacial hydrology model, a plume model, an undercutting model and a discrete particle model to investigate fracture dynamics (Helsinki Discrete Element Model, HiDEM). We demonstrate the feasibility of reproducing the observed calving retreat at the front of Kronebreen, a tidewater glacier in Svalbard, during a melt season by using the output from the first five models as input to HiDEM. Basal sliding and glacier motion are addressed using Elmer/Ice, while calving is modelled by HiDEM. A hydrology model calculates subglacial drainage paths and indicates two main outlets with different discharges. Depending on the discharge, the plume model computes frontal melt rates, which are iteratively projected to the actual front of the glacier at subglacial discharge locations. This produces undercutting of different sizes, as melt is concentrated close to the surface for high discharge and is more diffuse for low discharge. By testing different configurations, we show that undercutting plays a key role in glacier retreat and is necessary to reproduce observed retreat in the vicinity of the discharge locations during the melting season. Calving rates are also influenced by basal friction, through its effects on near-terminus strain rates and ice velocity.
Highlights
Accelerated discharge of ice into the oceans from land ice is a major contributor to sea level rise, and constitutes the largest source of uncertainty in sea level predictions for the twenty-first century and beyond (Church et al, 2013)
The high computational expense of the plume model used here means that it is not yet feasible to run the model on the timescales necessary to understand this variability, nor to run sufficient representative profiles to provide a useful understanding of the response
Previous work has suggested that intra-annual changes in the ambient stratification are small enough that plumes are relatively insensitive to these changes (Slater et al, 2017b) and that plume models forced with variations in runoff and a constant ambient stratification can qualitatively reproduce observations (Stevens et al, 2016)
Summary
Accelerated discharge of ice into the oceans from land ice is a major contributor to sea level rise, and constitutes the largest source of uncertainty in sea level predictions for the twenty-first century and beyond (Church et al, 2013). It has been suggested that ocean warming could play an important role in determining glacier calving rate and acceleration, by impacting submarine melt rates Straneo and Heimbach (2013) proposed two mechanisms responsible for the increase of submarine melt rates at the ice–ocean interface in Greenland: a warmer and thicker layer of Atlantic water in the fjords and an increase in subglacial discharge mainly during summer and autumn. Buoyant meltwater plumes entrain warm ocean water (Jenkins, 2011) and are thought to enhance melt undercutting (Slater et al, 2015) at the ice cliff triggering collapse of the ice above. Buoyant meltwater plumes entrain warm ocean water (Jenkins, 2011) and are thought to enhance melt undercutting (Slater et al, 2015) at the ice cliff triggering collapse of the ice above. Luckman et al (2015) investigated controls on seasonal variations in calving rates and showed that calving variations at Kronebreen, Published by Copernicus Publications on behalf of the European Geosciences Union
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