An introduction to the Greenland Ice Sheet

Map of the Greenland Ice Sheet and its surrounding oceans, towns and glaciers
Map of Greenland and its major towns, glaciers and surrounding oceans (NSIDC)

The Greenland Ice Sheet is one of two continent-scale ice masses on Earth, with the other being the Antarctic Ice Sheet. The Greenland Ice Sheet is the largest ice mass in the Northern Hemisphere. It lies from 71°N northwards, between the Atlantic and the Arctic Ocean [1]. Almost 80% of Greenland’s landmass is covered by the ice sheet, expanding an area over 1.7 million km2. The ice from the centre flows through a series of drainage networks with both outlet glaciers and ice streams, all flowing towards the ocean, with some ending in glacial ice tongues [2].

Unlike Antarctica, which has almost 75% of its coastline dominated by floating ice shelves, Greenland has only ice tongues. They are fewer in number and are constrained to fjords [3].

BedMachine: Greenland’s Bedrock Topography

Greenland BedMachine
Greenland’s bed topography from BedMachine v3, from Morlinghem et al (2017)
Greenland ice sheet ice thickness
Greenland’s ice thickness map. Morlinghem et al (2017)

Over the past few years, there has been an increase in the understanding on the topography beneath the ice sheet from the development of BedMachine v3 [4]. This was created using a series of remote sensing techniques and bathymetric data from the surrounding oceans. This dataset has now allowed the visualisation and quantification of the volume of ice present on the ice sheet, the bed topography, and the thickness of ice. BedMachine has showed that Greenland’s topography has a saucerlike basin in the centre, with much of it at, or below current sea levels [1,4].

The data from BedMachine has shows that some of the central parts of the ice sheet has an ice thickness average of >3000 m. This understanding has enabled the calculation of the global sea level rise potential of the Greenland Ice Sheet. This is now calculated to be 7.4 m [2,4]. This means that if all the ice in Greenland melted, global sea levels would rise by 7.4 m on average globally.

The Greenland Ice Sheet through the Quaternary

Ice sheets play an integral role in the global climate system, thus it is important to understand how they have responded in the past. This better prepares us for future changes to both the climate, and global sea level rise [5,6].

During the Quaternary Period (last 2.6 Ma), the Greenland Ice Sheet was one of a series of ice sheets dominating the Northern Hemisphere high latitudes. This included an ice sheet over North America (the Laurentide Ice Sheet) and over Europe, including Britain (the Eurasian Ice Sheet). The Greenland Ice Sheet held an additional 4.1 m sea level equivalent of ice during the global Last Glacial Maximum [10].

However, since start of the current interglacial period, around 11,700 years ago, the Greenland Ice Sheet is the only one to remain. During these glacial periods, the Greenland Ice Shelf was larger than its present extent, whereas in past interglacials, evidence shows that Greenland had significantly less ice than its present day distribution [7].

How is the Greenland Ice Sheet Changing today?

Greenland’s surface mass balance relative to the 1981 to 2010 reference period (NSIDC, 2020).

Over recent decades, the increase in air and ocean temperatures has resulted in the mass loss of ice through iceberg calving, meltwater runoff, and ocean-driven melting, all contributing a negative surface mass balance [2,5]. The figure here demonstrates that over the recent years, Greenland’s melting season has fallen well below the 1981-2020 mean with most of the melt occurring in the Northern Hemisphere summer [1].

This loss of ice from the Greenland Ice Sheet is directly influencing the global mean sea level. Current observations show that it is raising global sea levels by ~0.69 mm yr-1 [5] which is greater than the contribution from the Antarctic ice sheets combined [5]. Satellite measurements from the early 1990s to 2018 recorded a mass loss of 3800 ± 339 billion tonnes of ice, altogether, contributed 10.6 ± 0.9 mm to global sea levels.

A large proportion of ice loss from this ice sheet occurs where the ice is in contact with the warming ocean [2,8], specifically in fjords [9]. Warm ocean water infiltrates beneath the glacier tongue of ice shelf on the coastline of Greenland, resulting in undercutting of the ice, removing mass from the ice shelf [9].

The Future of the Greenland Ice Sheet

A range of models have been used to predict what may happen to this ice sheet in the future. The findings clearly show that the current net loss seen in Greenland will continue into the future, even under different emission scenarios[2,8].

References

1. NSIDC (2021) Greenland Ice Sheet today. Available at: http://nsidc.org/greenland-today/.

2. The IMBIE Team (2019) Mass balance of the Greenland Ice Sheet from 1992 to 2018. Nature. 579.

3. Dowdeswell, J.A., and Jeffries, M.O. (2017) Arctic Ice Shelves: An Introduction. in: Arctic Ice Shelves and Ice Islands. Springer. Polar Sciences.

4. Morlighem M. et al., (2017), BedMachine v3: Complete bed topography and ocean bathymetry mapping of Greenland from multi-beam echo sounding combined with mass conservation, Geophys. Res. Lett., 44, doi:10.1002/2017GL074954

5. Bamber, J.L. et al., (2018) The land ice contribution to sea level during the satellite era. Env. Res. Lett. 13. 063008

6. Batchelor, C.L. et al., (2019) The configuration of Northern Hemisphere ice sheets through the Quaternary. Nature Comms. 10. 3713.

7. Alley, R. B. et al., (2010) History of the Greenland ice sheet: Paleoclimatic insights. Quaternary Science Reviews 29, 1728-1756.

8. Goelzer, H. et al., (2020) The future sea-level contribution of the Greenland ice sheet: a multi-model ensemble study of ISMIP6. The Cryosphere. 14.

9. Wood, M. et al., (2021) Ocean forcing drives glacier retreat in Greenland. Science Advances. 7(1).

10. Simms, A. R., Lisiecki, L., Gebbie, G., Whitehouse, P. L. & Clark, J. F. Balancing the last glacial maximum (LGM) sea-level budget. Quat. Sci. Rev. 205, 143–153 (2019).

Further reading

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