Response of the north-west Greenland Ice Sheet to recent and future climate change

Overview

The Arctic is warming rapidly and temperatures are forecast to rise by up to 8 °C by 2100, which is double the global average (IPCC, 2013). Consequently, ice loss from the Greenland Ice Sheet (GrIS) has increased more than four-fold in recent decades and continues to accelerate (Shepherd et al., 2012; Helm et al., 2014). This has resulted in 0.75 mm a-1 of sea level rise, and the ice sheet is predicted to contribute 9 cm by 2050 (Helm et al., 2014). Mass loss has occurred via both negative surface mass balance and accelerated discharge from marine-terminating outlet glaciers. These fast-flowing conveyor belts of ice allow the GrIS to respond rapidly to climate warming and transmit changes far into the interior (van de Broeke et al., 2009). Since the mid-2000s, outlet glaciers in north-west Greenland have become a major source of dynamic ice loss, glacier acceleration and retreat (e.g. Moon et al., 2012; Carr et al., 2013; Kahn et al., 2010). As such, understanding the controls on glacier dynamics in north-west Greenland is a key priority.

A number of external factors are thought to control glacier dynamics in north-west Greenland, including air temperatures (through hydro fracture and/or meltwater inputs to the bed), sea ice concentrations (via buttressing forces on the termini) and/or ocean temperatures (due to oceanic melting and enhancing calving). Previous work has categorised the seasonal velocity fluctuations of north-west Greenland glaciers according to their correspondence with some of these forcing factors, specifically modelled melt and terminus position (Vijay et al., 2019; Moon et al., 2014). However, these studies classified the same glaciers as having different seasonal velocity characteristics and covered a comparatively short time span position (Vijay et al., 2019; Moon et al., 2014). Thus, it is unclear whether these seasonal velocity categories hold long-term and if they have any impact on how these glaciers respond to climate change. As well as the impacts of surface melt, sea ice has been identified as an important control in north-west Greenland (Moon et al., 2015). However, it is unclear how its influence varies along the coast, with different fjord geometries, and how ‘strong’ the sea ice needs to be, in order to impact glacier behaviour. Thus, there is an urgent need to determine which factors are controlling north-west Greenland outlet glacier behaviour, to facilitate prediction.

Overall, north-west Greenland glaciers are changing dramatically, but there has been substantial temporal and spatial variability in their retreat rates (Bunce et al., 2018) and ice velocities (Moon et al., 2014). This has been linked to the characteristics of the glacier beds, particularly the bed slope and the fjord width (Carr et al., 2017; Bunce et al., 2018), which are diverse in north-west Greenland. As such, it is vital to understand how the bed geometry modulates the response of individual outlet glaciers to the forcing factors outlined above, in order to accurately predict glacier response to future climate changes.
The key research questions that this studentship will address are:
1. How do variations in melt water inputs and terminus position impact glacier dynamics longer-term?
2. To what extent does sea ice control glacier dynamics, and how does this vary with the different fjord configurations and sea ice properties observed in north-west Greenland?
3. How sensitive are north-west Greenland glacier to variations in oceanic melting?
4. How might north-west Greenland glaciers behave in the future, and to what extent is this influenced by their basal topography?

Click on an image to expand

Image Captions

Figure 1: North-west Greenland retreat rates 2000-2010 (circle size and colour), and basal topography: white = low elevation; brown = high elevation.

Methodology

The project will compile and extend current remotely sensed data on north-west Greenland glacier dynamics. Specifically, the project will determine sub-annual velocities from pre-existing velocity datasets (e.g. GoLive and MEaSURES). It will compile terminus positions from pre-existing datasets (e.g. Moon et al., 2014) and extend these where necessary. Surface elevation changes will be measured from IceSat data and Arctic DEM. Information on forcing factors will be determined from National and Naval Centre sea ice charts, the regional atmospheric climate model RACMO2.3and TOPAZ ocean reanalysis data. Together, these data will be used to assess relationships between dynamic changes and forcing factors, and as inputs for the model. The data on forcing factors will be used to constrain their likely range.

Numerical modelling will be used to assess glacier sensitivity to external controls and the influence of basal topography on future glacier behaviour. Specifically, the student will use a state-of-the art two horizontal dimensional numerical model, which has been developed by Dr. Gudmundsson (Northumbria University). This model has been proven effective for similar applications (e.g. deRydt et al., 2015) and will be set up initially using the remotely sensed data noted above. A particular focus of the numerical modelling component will be to investigate the impact of sea ice buttressing on glacier behaviour in north-west Greenland. The model incorporates an ice mélange (a seasonal ice shelf, composed of sea ice and icebergs), and includes related processes that have yet to be included in most models. We will also investigate how seasonal variations in basal slipperiness (representing changes in meltwater-induced increase in ice velocities) impact ice dynamics in the longer-term and assess glacier sensitivity to changes in oceanic melting. Finally, we will model the near-future evolution of north-west Greenland glaciers, with a particular focus on how their behaviour relates to the bedrock topography.

Project Timeline

Year 1

Compile remotely sensed data. Identify target glaciers and input datasets for numerical modelling.

Year 2

Training in model usage and gain experience in its application to the study glaciers. Assessment of sensitivity to forcing factors, with a particular focus on sea ice.

Year 3

Continuation of modelling. Investigation of potential future behaviour of north-west Greenland glaciers and assessment of the role of bedrock topography.

Year 3.5

Completion of analysis and thesis write-up.

Training
& Skills

The student will be given specific, focused training on the use of the numerical model by Dr. G. H. Gudmundsson, who has written and developed the model. The model is written in Matlab and so the student will be given training in the use of this software. This will be supported by the Karthaus numerical modelling summer school. The student will develop key skills in numerical modelling, GIS and remote sensing.

References & further reading

Bunce, C., Carr, J.R., et al, 2018 Ice front change of marine-terminating outlet glaciers in northwest and southeast Greenland during the 21st century. Journal of Glaciology, pp.1-13.

Carr, J.R., Stokes, C., & Vieli, A. 2017. Threefold increase in marine-terminating outlet glacier retreat rates across the Atlantic Arctic: 1992-2010. Annals of Glaciology, 1-20. doi:10.1017/aog.2017.3

De Rydt, J., et al. 2015. Modelling the instantaneous response of glaciers after the collapse of the Larsen B Ice Shelf. Geophys. Research Letters, 42. 5355-5363.

Moon, T., et al., 2014. Distinct patterns of seasonal Greenland glacier velocity. Geophysical research letters, 41(20), pp.7209-7216.

Moon, T. et al., 2015. Seasonal to multiyear variability of glacier surface velocity, terminus position, and sea ice/ice mélange in northwest Greenland. Journal of Geophysical Research: Earth Surface 120 (5) 818-833.

Vijay, S. et al., 2019. Resolving seasonal ice velocity of 45 Greenlandic glaciers with very high temporal details. Geophysical Research Letters, 46(3), pp.1485-1495.

Further Information

Dr. Rachel Carr
Newcastle University
Email: rachel.carr@newcastle.ac.uk
Tel: +44 (0) 191 208 6436

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