Ice shelf study

In late November 2008 Dr Bryn Hubbard from the Institute of Geography and Earth Sciences at Aberystwyth University set out on a four week expedition to study the ice shelves of eastern Antarctica.

Six hours after departing from Cape Town the scheduled flight, a rather noisy affair in barely furnished Russian built Ilyushin aircraft, landed at the Novolazarevskaya polar station. The temperature was a summery minus 17 degrees celsius.

Some of those on board were Russian holidaymakers seeking the pleasures of the Antarctic summer. Dr Hubbard, on the other hand was there as part of a Belgian expedition to study the ice shelves of Dronning Maud Land, a region of Antarctica directly adjacent to the southern tip of Africa.

When the Larsen B Ice Shelf in Antarctica collapsed in 2002, the event appeared to be a sudden response to climate change. The long, fringing ice shelf in the north west part of the Weddell Sea was assumed to be the latest in a long line of victims of Antarctic summer heat waves linked to global warming.

However, a study published in 2008 by Professor Neil Glasser, a colleague of Dr Hubbard's at Aberystwyth, revealed that there was more to the demise of Larsen B than was at first believed.

Professor Glasser argued that the ice shelf had been deteriorating over a much longer period and that global warming was not the only reason for its spectacular break-up. Fault lines present in the ice shelf for many years were also contributing factors.

For many glaciologists, including Dr Hubbard and his Belgian colleagues, these findings posed an important question. All ice shelves have fault lines. So why aren't they all breaking up in the same way?

Glaciologists have known for some time that sea water under ice shelves gradually freezes and becomes incorporated in to the ice. Dr Hubbard’s mission was to study this phenomenon and determine whether this new ice can make an ice shelf stronger and act, as he puts it, ‘as polyfilla’.

Base camp for the 5 man team was the newly built Princess Elisabeth Station – a space-like polar outpost described by its architect as the continent’s first “zero emission” research station.

180 km north from the Princes Elizabeth Station they set about studying the ice shelf. Using an ice drill they pierced the ice shelf at five locations, extracting cores that extended down until they reached the sea below.

Cores taken near the surface are characterised by the large number of air bubbles trapped in the ice. These air bubbles provide a valuable record of carbon dioxide levels in the atmosphere extending back over thousands of years.

In contrast, cores extracted from recently frozen sea water at the base of the ice shelf have a light turquoise tinged glass-like appearance. Known as marine ice, it is devoid of air pockets, having frozen on from the sea water at the base of the ice shelf.

Dr Hubbard was invited on to the expedition for his expertise in operating the ice corer and an Optical Televiewer, a small camera developed by geologists to study rock formations in the search for valuable mineral deposits.

As it was lowered into the borehole the camera created a visual record of the changing characteristics of the ice. This work provided some of the very first images ever taken of marine ice and revealed a feature little-known to glaciologists until now, metres and metres of slush where the underlying sea water gradually freezes to form the marine ice.

For Dr Hubbard a study of this kind provides valuable data on how ice shelves form and break-up. Over many years he has been working on mathematical models developed to represent the flow of ice in glaciers in areas such as the Andes, the Himalayas and the Alps. 

Increasingly these models are being used to try to predict changes to large bodies of ice as a result of global warming.  However, they don’t explain why the ice shelf in Dronning Maud Land has not broken up as Larsen B did.

When asked about the implications of ice shelf break-up for rising sea levels, Dr Hubbard explains that there is good and bad news.

“On the positive side, a floating ice-shelf already displaces its weight in water, so the effect of its break-up will be negligible. However, on the down side these ice shelves provide an important buffer zone between the sea and some of the world’s largest glaciers.”

“In theory, the break-up of an ice shelf could expose a glacier to the sea, causing it to accelerate and release large amounts of ice into the world’s oceans, which in turn would cause sea levels to rise further – above the rates currently predicted”, he added.

This remains to be proven. No doubt it will become the focus for another mission to one of the world’s most inhospitable yet beautiful regions.