An example from the past illustrates how suddenly and dramatically Antarctica’s mighty ice cap can disappear when climate changes: In less than 200 years, the West Antarctic ice sheet has become 450 meters thinner at one point, reports a research team in the specialist magazine “Nature Geoscience”. This shows that once a tipping point is reached, ice in Antarctica can disappear very quickly.
The group led by Eric Wolff from the University of Cambridge (Great Britain) used a 651 meter long ice core from the so-called Skytrain Ice Rise. This peninsula-shaped ice dome lies in West Antarctica’s Ellsworth Land. “We wanted to know what happened to the West Antarctic ice sheet at the end of the last ice age, when Earth’s temperatures were rising, albeit more slowly than the current anthropogenic warming,” said co-author Isobel Rowell of the British Antarctic Survey in Cambridge.
The ice sheet consists of layers that were formed by snowfall and compacted over thousands of years. Every layer of ice contains bubbles of old air and substances introduced back then. The ratio of certain molecules in the ice, the occurrence of certain substances and the air pressure within bubbles in the ice were now analyzed. In this way, the events of many thousands of years ago could be reconstructed.
“As soon as the ice became thinner, it shrank very quickly”
After the end of the last ice age around 8,200 years ago, the dome lost around 450 meters of ice in just 176 years. On average, the ice mass was shrinking by a good 2.5 meters per year.
The Skytrain Ice Rise lies on the edge of the Ronne ice shelf, where the bedrock lies below sea level. During the last ice age, the ice shelf was frozen to the bottom. When the air and sea became warmer after the Ice Age, the sea undermined parts of the ice shelf, the researchers suspect. The ice now floated on the water and the resistance to the glacier ice pushing down from the ice dome decreased. “As soon as the ice became thinner, it shrank very quickly,” Wolff explained. “This was clearly a tipping point – a process that got out of control.”
Researchers: tipping point could be exceeded
The scientists also found that between 7,700 and 7,300 years ago, the amount of sodium – which comes from the salt in sea spray – in the ice gradually increased. Taking into account previous studies, they concluded that during this time the sea moved about 270 kilometers closer to the ice dome because the ice shelf receded.
Overall, according to Wolff’s team, the new measurement data confirms that ice loss in Antarctica can occur relatively quickly. Scientists fear that current global warming could destabilize parts of the West Antarctic ice sheet, exceeding a tipping point and triggering a collapse. “This scenario does not only exist in our model predictions and it could happen again if parts of this ice sheet become unstable,” said Wolff.
The West Antarctic ice sheet is considered particularly vulnerable because a large part of it lies on rocks that lie below sea level. It is significantly smaller than East Antarctica, whose ice is considered to be more stable. According to the researchers, overall, the Antarctic ice sheets contain enough fresh water to raise global sea levels by around 57 meters.
