Colossal ‘doomsday’ glacier set to melt triggering ‘catastrophic sea level rise’

Worrying new evidence points to a vast ‘doomsday’ glacier approaching melting point.

Scientists have uncovered the strongest evidence yet that some of Antarctica’s most vulnerable glaciers, including the enormous Thwaites Glacier, are set to reach a tipping point soon.

Thwaites has been nicknamed the ‘doomsday’ glacier because its collapse could trigger catastrophic sea level rise. It is held in place by an ice shelf that acts like a cork, holding the colossal glacier back on the land and providing a vital defence against rising sea levels. But the ice shelf is extremely vulnerable as the ocean warms.

Findings from mud cores suggest much of the West Antarctic Ice Sheet (WAIS) has a historic tipping point, triggered by global temperatures similar to those experienced today.

The study, published in Nature Communications, could help researchers understand how the ice sheet might respond to continued global warming.

Scientists have long debated how the West Antarctic Ice Sheet responded to previous warm periods, known as interglacials.

Now, an international team led by the British Antarctic Survey (BAS) says it has found the answer in the cores drilled from the ocean floor off Antarctica.

The researchers identified a distinctive mineral called kaolinite, commonly known as china clay. It typically forms in warm, wet tropical climates or swampy environments, such as those that existed on the Antarctic continent more than 34 million years ago.

Today, ancient deposits of kaolinite lie buried in the bedrock beneath the West Antarctic Ice Sheet. The immense weight of glaciers such as Thwaites and neighbouring Pine Island grinds the mineral out, allowing it to be carried offshore by icebergs and ocean currents.

But sediment cores recovered from 4,000m below the sea surface on Antarctica’s continental margin reveal a striking pattern.

During every interglacial period over the past 800,000 years, levels of kaolinite in the sediment fell to almost zero.

‘When the kaolinite signal at our drill-core sites suddenly collapses, it tells us the marine-based ice in the Amundsen Sea sector of the West Antarctic – including Thwaites and Pine Island glaciers – must have melted and retreated far back into the continent’s interior,’ says Dr Claus-Dieter Hillenbrand, the BAS marine geologist who led the study.

‘It’s the only way to explain why the delivery of kaolinite-rich debris to the ocean floor stops.’ Establishing that the ice had retreated was only part of the investigation. The team also wanted to understand what had caused it.

The answer came from a second clay mineral, smectite.

Unlike clays formed from the weathering of Antarctic rocks and volcanoes, the particular magnesium-rich variety identified by researchers has a chemical signature associated with the deep Pacific Ocean floor, far to the north.

The scientists believe warm deep-water currents carried the mineral south towards Antarctica, depositing it in coastal sediments at the same time as the kaolinite signal disappeared.

Such currents would have brought warmer water on to the West Antarctic continental shelf, melting grounded ice and reducing the erosion responsible for producing the kaolinite-rich sediment.

To strengthen their findings, the researchers examined fossilised remains of diatoms – microscopic marine algae – preserved in the mud. Their shell-like structures take different forms depending on water temperature, providing further evidence of changing conditions.

The analysis revealed that waters around West Antarctica became significantly warmer than the global average during past interglacials.

While global temperatures were between 1C and 1.5C above pre-industrial levels – similar to today – or, in some cases, even lower, waters in front of the ice sheet reached between about 1C and 3C above today’s near-freezing baseline.

The researchers say the speed of the changes is a crucial difference between past and present conditions.

Under natural conditions, Dr Hillenbrand says, the disappearance of Thwaites Glacier could have taken several thousand years.

But human-caused greenhouse gas emissions are now warming the oceans at an unprecedented rate, potentially compressing a process that once took millennia into just centuries.

‘What we found, to my surprise, is that even under natural conditions we had at least a partial collapse of the West Antarctic Ice Sheet. What we are doing now is making it much worse,’ the geologist says.

A complete collapse of Thwaites Glacier would add about 65cm to global sea levels, while the neighbouring Pine Island Glacier could contribute a further 51cm.

If much wider areas of the West Antarctic Ice Sheet were to collapse, sea levels could rise by as much as three to five metres.

‘I’m personally convinced that future generations will see substantial sea-level rise,’ says Dr Rob Larter, a BAS marine geophysicist and co-author of the study.

‘How fast we’ll see that rise is really difficult to say. This study shows that even in past natural warm periods we had a lot of ice loss, but what we’re living in now is an interglacial on steroids.’

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