̽��ֱ�� of Cambridge - Eric Wolff

Ice cores provide first documentation of rapid Antarctic ice loss in the past

cmm201 — Thu, 08 Feb 2024 10:00:00 +0000

̽��ֱ��evidence, contained within an ice core, shows that in one location the ice sheet thinned by 450 metres — that’s more than the height of the Empire State Building — in just under 200 years.

This is the first evidence anywhere in Antarctica for such a fast loss of ice. Scientists are worried that today’s rising temperatures might destabilize parts of the West Antarctic Ice Sheet in the future, potentially passing a tipping point and inducing a runaway collapse. ̽��ֱ��study, published in Nature Geoscience, sheds light on how quickly Antarctic ice could melt if temperatures continue to soar.

“We now have direct evidence that this ice sheet suffered rapid ice loss in the past,” said Professor Eric Wolff, senior author of the new study from Cambridge’s Department of Earth Sciences. “This scenario isn’t something that exists only in our model predictions and it could happen again if parts of this ice sheet become unstable.”

From west to east, the Antarctic ice sheets contain enough freshwater to raise global sea levels by around 57 metres. ̽��ֱ��West Antarctic Ice Sheet is considered particularly vulnerable because much of it sits on bedrock below sea level.

Model predictions suggest that a large part of the West Antarctic Ice Sheet could disappear in the next few centuries, causing sea levels to rise. Exactly when and how quickly the ice could be lost is, however, uncertain.

One way to train ice sheet models to make better predictions is to feed them with data on ice loss from periods of warming in Earth’s history. At the peak of the Last Ice Age 20,000 years ago, Antarctic ice covered a larger area than today. As our planet thawed and temperatures slowly climbed, the West Antarctic Ice Sheet contracted to more or less its current extent.

“We wanted to know what happened to the West Antarctic Ice Sheet at the end of the Last Ice Age, when temperatures on Earth were rising, albeit at a slower rate than current anthropogenic warming,” said Dr Isobel Rowell, study co-author from the British Antarctic Survey. “Using ice cores we can go back to that time and estimate the ice sheet’s thickness and extent.”

Ice cores are made up of layers of ice that formed as snow fell and was then buried and compacted into ice crystals over thousands of years. Trapped within each ice layer are bubbles of ancient air and contaminants that mixed with each year’s snowfall — providing clues as to the changing climate and ice extent.

̽��ֱ��researchers drilled a 651-metre-long ice core from Skytrain Ice Rise in 2019. This mound of ice sits at the edge of the ice sheet, near the point where grounded ice flows into the floating Ronne Ice Shelf.

After transporting the ice cores to Cambridge at -20C, the researchers analysed them to reconstruct the ice thickness. First, they measured stable water isotopes, which indicate the temperature at the time the snow fell. Temperature decreases at higher altitudes (think of cold mountain air), so they could equate warmer temperatures with lower-lying, thinner ice.

They also measured the pressure of air bubbles trapped in the ice. Like temperature, air pressure also varies systematically with elevation. Lower-lying, thinner ice contains higher-pressure air bubbles.

These measurements told them that ice thinned rapidly 8,000 years ago. “Once the ice thinned, it shrunk really fast,” said Wolff, “this was clearly a tipping point — a runaway process.”

They think this thinning was probably triggered by warm water getting underneath the edge of the West Antarctic Ice Sheet, which normally sits on bedrock. This likely untethered a section of the ice from bedrock, allowing it to float suddenly and forming what is now the Ronne Ice Shelf. This allowed neighbouring Skytrain Ice Rise, no longer restrained by grounded ice, to thin rapidly.

̽��ֱ��researchers also found that the sodium content of the ice (originating from salt in sea spray) increased about 300 years after the ice thinned. This told them that, after the ice thinned, the ice shelf shrunk back so that the sea was hundreds of kilometres nearer to their site.

“We already knew from models that the ice thinned around this time, but the date of this was uncertain,” said Rowell. Ice sheet models placed the retreat anywhere between 12,000 and 5,000 years ago and couldn’t say how quickly it happened. “We now have a very precisely dated observation of that retreat that can be built into improved models,” said Rowell.

Although the West Antarctic Ice Sheet retreated quickly 8,000 years ago, it stabilised when it reached roughly its current extent. “It’s now crucial to find out whether extra warmth could destabilise the ice and cause it to start retreating again,” said Wolff.

Reference

Grieman et al. (2024) Abrupt Holocene ice loss due to thinning and ungrounding in the Weddell Sea Embayment. Nature Geoscience. DOI: 10.1038/s41561-024-01375-8

Researchers from the ̽��ֱ�� of Cambridge and the British Antarctic Survey have uncovered the first direct evidence that the West Antarctic Ice Sheet shrunk suddenly and dramatically at the end of the Last Ice Age, around 8,000 years ago.

̽��ֱ�� of Cambridge / British Antarctic Survey

Tents at Skytrain Ice Rise

̽��ֱ��text in this work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. Images, including our videos, are Copyright © ̽��ֱ�� of Cambridge and licensors/contributors as identified. All rights reserved. We make our image and video content available in a number of ways – on our main website under its Terms and conditions, and on a range of channels including social media that permit your use and sharing of our content under their respective Terms.

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Exploring Antarctica in Cambridge

zs332 — Fri, 01 Apr 2022 11:08:48 +0000

In its inaugural year in 2021, the Cambridge Festival managed to reach every continent on Earth - except Antarctica. So, for 2022, we’ve brought Antarctica to Cambridge. While you're here, learn about some of the world-leading research happening here in Cambridge.

COP26: Cambridge experts on their hopes for the high-stakes summit

sc604 — Tue, 26 Oct 2021 07:58:53 +0000

What will it take to make the high-stakes United Nations climate summit a success? We spoke with some of our researchers and asked them what they want to see at COP26, what some of the biggest challenges are in getting to zero carbon, and what gives them hope.

Abrupt changes in Earth’s past climate occurred synchronously

cmm201 — Thu, 20 Aug 2020 18:00:00 +0000

̽��ֱ��Last Glacial Period, between 115,000 and 11,700 years ago, was punctuated by a series of severe climate changes: warm periods where temperatures in Greenland spiked by 8-16°C over the course of a decade.

Data from the Greenland and Antarctic ice cores suggests that these warming events, known as Greenland Interstadials, occurred at least 25 times over this period. Their imprint has also been observed in climate records collected from mid to low latitudes, leading scientists to question whether these widespread changes were simultaneous, or whether warming in some regions lagged behind others.

But resolving this question has proved challenging because precisely dated records of past climate are relatively rare. And dating is key. If scientists could exactly pinpoint the relative timing of warming in different regions, they could answer whether the climate changed synchronously.

̽��ֱ��study, published in the journal Science and led by ̽��ֱ�� of Melbourne PhD student Ellen Corrick, uses detailed climate data from stalagmites (speleothems) to compare the timing of climate changes between regions. Stalagmites take in detailed information on regional temperature and rainfall as they grow, and they can also be dated accurately, often to decadal resolution, using the uranium-thorium technique.

Corrick compiled climate data from 63 speleothem records collected from caves across Asia, Europe and South America - a dataset amounting to 20 years’ of published research from scientific teams around the world. ̽��ֱ��onset of many Greenland Interstadials was clearly recognisable in the speleothem data, each event marked by a shift in the contents of stable oxygen isotope, δ18O.

To test if the changes were synchronous, the team used statistical methods to compare the age of onset for the interstadials. Once they were sure that intraregional changes were simultaneous, the team looked at the relative timing of interstadials between Asia, Europe and South America. ̽��ֱ��wider comparison showed that, out of the 25 interstadials studied, 23 were synchronous.

According to co-author Professor Eric Wolff from Cambridge’s Department of Earth Sciences, the findings “provide confirmation of a persistent but, until now, unsubstantiated assumption that climate changes between the tropics and the Arctic were synchronous.”

̽��ֱ��team went on to compare their speleothem data with model simulations of future abrupt climate changes. “An interesting feature of this study is how well the climate model outputs agree with the stalagmite data. This gives us increased confidence in the climate models we’ve built,” said co-authro Professor Xu Zhang from Lanzhou ̽��ֱ�� China, who conducted model experiments at the Alfred Wegener Institute in Germany.

̽��ֱ��findings shed light on the patterns and timing of these warming phases, also known as Dansgaard-Oeschger events. But their cause, whether external factors, such the ice sheet height, greenhouse gases, meltwater and volcanism, or internal oscillations in Atlantic Ocean circulation, remains, as yet, an open question.

Reference:
E. Corrick et al. ‘Synchronous timing of abrupt climate changes during the last glacial period.’ Science (2020). DOI: 10.1126/science.aay5538

Adapted from a press release by ̽��ֱ�� ̽��ֱ�� of Melbourne

A study from the Universities of Cambridge and Melbourne has found that the onset of past climate changes was synchronous over an area extending from the Arctic to the low latitudes.

These findings provide confirmation of a persistent but, until now, unsubstantiated assumption that climate changes between the tropics and the Arctic were synchronous

Eric Wolff

Ellen Corrick, ̽��ֱ�� of Melbourne

Speleothems in the Corchia Cave, Central Italy

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. Images, including our videos, are Copyright © ̽��ֱ�� of Cambridge and licensors/contributors as identified. All rights reserved. We make our image and video content available in a number of ways – as here, on our main website under its Terms and conditions, and on a range of channels including social media that permit your use and sharing of our content under their respective Terms.

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̽��ֱ��climate crisis: towards zero carbon

lw355 — Wed, 26 Feb 2020 07:35:22 +0000

If we are to avoid climate disaster we must sharply reduce our carbon dioxide emissions starting today – but how?

In a new film, Cambridge researchers describe their work on generating and storing renewable energy, reducing energy consumption, understanding the impact of climate policies, and probing how we can each reduce our environmental impact. Alumni Sir David Attenborough and Dr Jane Goodall DBE speak about the climate crisis and reasons for hope.

We hear about the ambitious new programme Cambridge Zero bringing together ideas and innovations to tackle the global challenge of climate catastrophe – and inspiring a generation of future leaders – and how the ̽��ֱ�� is looking at its own operations to develop a zero carbon pathway for the future.

Explore more:

Visit our spotlight on Sustainable Earth

Read our Horizons magazine: download a pdf; view on Issuu

Sir David Attenborough, Dr Jane Goodall DBE and leading Cambridge ̽��ֱ�� researchers talk about the urgency of climate crisis – and some of the solutions that will take us towards zero carbon.

There are huge opportunities to getting things right – the only way to operate is to believe we can do something about it – and I truly think we can.

Sir David Attenborough

̽��ֱ��Climate Crisis: Towards Zero Carbon

NASA

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