Martin Siegert - Beneath the polar ice sheets

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Martin Siegert, Deputy Vice-Chancellor at the University of Exeter and an antarctic glaciologist, examines the changes in the Antarctic.

About Martin Siegert

"I am Deputy Vice-Chancellor at the University of Exeter and was Co-Director of the Grantham Institute, Imperial College London.

I am an Antarctic glaciologist who studies how the ice sheets have changed in the past, how they are changing now, and how they will change in the future."

Measuring polar ice sheets

The polar ice sheets are changing, which is a very concerning issue. As a glaciologist, I study how the Antarctic ice sheet flows and what’s underneath the ice. I predominantly use geophysics – my preferred geophysical technique is radar. The reason I use radar is because radio waves travel straight through cold ice, but they bounce off the bottom of the ice sheet so we can measure the two-way travel time of the radio wave; that is, we know the velocity of the radio wave in ice, so we can measure the ice thickness. If we know the ice thickness, we can measure the topography underneath the ice. Greenland and Antarctica have a 3,000- and 4,000-metre thick ice sheet, respectively, and underneath each one hides a very complex landscape.

Antarctica’s ice sheet is divided into the West Antarctic ice sheet and the East Antarctic ice sheet. The East Antarctic ice sheet is by far the biggest of the two, and most of it is resting on land above the level of the sea. Underneath, there are amazing mountains, valleys and landscapes. The last mountain range to ever be discovered was the Gamburtsev subglacial mountains in the middle of the East Antarctic continent. West Antarctica is a different situation. It’s still a continent, but it lies below the sea level. Unusually, the ice sheet that covers it is also grounded below sea level, reaching over two kilometres below sea level in some parts.

Key Points

• Greenland and Antarctica have a 3,000- and 4,000-metre thick ice sheet, respectively, and underneath each one hides a very complex landscape. Both the ice sheets are now experiencing significant amounts of mass loss.
• Most of the 20 centimetres of sea level rise that we’ve seen since 1850 is due to the thermal expansion of the ocean and the subsequent melting of valley glaciers all around the world.
• Future sea level change is likely to be dominated by melting of the polar ice sheets. On its own, East Antarctica has enough ice to raise sea level by approximately 57 metres. A tenth of the planet’s population live close to the edge of the ocean.
• The increase in carbon dioxide and other greenhouse gases into the atmosphere has a warming effect. If we don’t reduce emissions to zero in 30 years’ time, the ice sheets will start to melt even more rapidly than they are now.
• We have to use ice sheet models to understand how Antarctica is likely to change in the future but we have no measurements as Antarctica has the last few parts of land surface of our planet that have not been measured. It's an imperative job to do.