̽��ֱ�� of Cambridge - polar

Thriving Antarctic ecosystems found following iceberg calving

Anonymous — Tue, 25 Mar 2025 10:22:45 +0000

An international team of scientists have uncovered a thriving underwater ecosystem off the coast of Antarctica that had never before been accessible to humans.

̽��ֱ��team, including researchers from the ̽��ֱ�� of Cambridge, were working in the Bellingshausen Sea off the coast of Antarctica when a massive iceberg broke away from the George VI Ice Shelf in January of this year.

̽��ֱ��team, on board Schmidt Ocean Institute’s R/V Falkor (too), changed their plans and reached the newly exposed seafloor 12 days later, becoming the first to investigate the area.

Their expedition was the first detailed study of the geology, physical oceanography, and biology beneath such a large area once covered by a floating ice shelf. ̽��ֱ��A-84 iceberg was approximately 510 square kilometres (209 square miles) in size, and revealed an equivalent area of seafloor when it broke away from the ice shelf.

"We seized upon the moment, changed our expedition plan, and went for it so we could look at what was happening in the depths below," said expedition co-chief scientist Dr Patricia Esquete from the ̽��ֱ�� of Aveiro, Portugal. "We didn't expect to find such a beautiful, thriving ecosystem. Based on the size of the animals, the communities we observed have been there for decades, maybe even hundreds of years.”

Using Schmidt Ocean Institute’s remotely operated vehicle, ROV SuBastian, the team observed the deep seafloor for eight days and found flourishing ecosystems at depths as great as 1300 meters.

Their observations include large corals and sponges supporting an array of animal life, including icefish, giant sea spiders, and octopus. ̽��ֱ��discovery offers new insights into how ecosystems function beneath floating sections of the Antarctic ice sheet.

Little is known about what lies beneath Antarctica’s floating ice shelves. In 2021, British Antarctic Survey researchers first reported signs of bottom-dwelling life beneath the Filchner-Ronne ice shelf in the Southern Weddell Sea. ̽��ֱ��current expedition was the first to use an ROV to explore this remote environment.

̽��ֱ��team was surprised by the significant biomass and biodiversity of the ecosystems and suspect they have discovered several new species.

Deep-sea ecosystems typically rely on nutrients from the surface slowly raining down to the seafloor. For centuries, the ecosystems under the ice shelf have been covered by ice almost 150 metres thick, completely cutting them off from surface nutrients. " ̽��ֱ��fact that we found long-living species suggests that the lateral transport, which mostly consists of glacial meltwater from the ice shelf, could be the source of the nutrients to sustain the life we found," said team member Dr Laura Cimoli, from Cambridge’s Department of Applied Mathematics and Theoretical Physics.

̽��ֱ��newly exposed Antarctic seafloor also allowed the team, with scientists from Portugal, the United Kingdom, Chile, Germany, Norway, New Zealand, and the United States, to gather critical data on the past behaviour of the larger Antarctic ice sheet. ̽��ֱ��ice sheet has been shrinking and losing mass over the last few decades due to climate change.

“ ̽��ֱ��ice loss from the Antarctic Ice Sheet is a major contributor to sea level rise worldwide,” said expedition co-chief scientist Sasha Montelli of ̽��ֱ�� College London (UCL). “Our work is critical for providing longer-term context of these recent changes, improving our ability to make projections of future change — projections that can inform actionable policies. We will undoubtedly make new discoveries as we continue to analyse this data.”

“We were thrilled by the opportunity to explore the newly exposed seafloor,” said team member Dr Svetlana Radionovskaya from Cambridge’s Department of Earth Sciences. “ ̽��ֱ��research will provide key insights into ice sheet dynamics, oceanography and sub-ice shelf ecosystems. At a time when the West Antarctic Ice Sheet is melting at an alarming rate, understanding these dynamics and their impacts is crucial.”

photo1_fkt250110-20250117-gliderdeploymentzodiac-ingle-2717.jpg

̽��ֱ��oceanography team, led by Cimoli in collaboration with the ̽��ֱ�� of East Anglia and the British Antarctic Survey, used autonomous underwater vehicles to characterise the ocean circulation of the region and study the impacts of glacial meltwater on the physical and chemical seawater properties. "Antarctica and the Southern Ocean are a nexus point for ocean circulation, so changes that happen around Antarctica can affect global ocean circulation and global climate," said Cimoli.

̽��ֱ��researchers are also investigating how the iceberg calving event has contributed to mix the upper ocean, not just in the recently exposed area, but also further downstream as the iceberg floats away. As the giant iceberg drifts, it can generate turbulence that mixes water properties and could potentially mix the deep nutrient-rich water with the surface waters, fuelling biological productivity.

̽��ֱ��expedition was part of Challenger 150, a global cooperative focused on deep-sea biological research and endorsed by the Intergovernmental Oceanographic Commission of UNESCO (IOC/UNESCO) as an Ocean Decade Action.

“ ̽��ֱ��science team was originally in this remote region to study the seafloor and ecosystem at the interface between ice and sea,” said Schmidt Ocean Institute Executive Director, Dr Jyotika Virmani. “Being right there when this iceberg calved from the ice shelf presented a rare scientific opportunity. Serendipitous moments are part of the excitement of research at sea – they offer the chance to be the first to witness the untouched beauty of our world.”

Svetlana Radionovskaya is a Junior Research Fellow at Queens’ College, Cambridge. Laura Cimoli is a Research Fellow at the Institute of Computing for Climate Science, Department of Applied Mathematics and Theoretical Physics at the ̽��ֱ�� of Cambridge.

Adapted from a media release by the Schmidt Ocean Institute.

Inset image: Dr Cimoli (right) and Dr Meyer (UEA, left) prepare an underwater glider for deployment. Credit: Alex Ingle/Schmidt Ocean Institute.

Scientists explore a seafloor area newly exposed by iceberg A-84; discover vibrant communities of ancient sponges and corals.

ROV SuBastian / Schmidt Ocean Institute

Deep-sea coral at a depth of 1200 metres

̽��ֱ��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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Why do climate models underestimate polar warming? ‘Invisible clouds’ could be the answer

sc604 — Wed, 08 Nov 2023 16:06:47 +0000

̽��ֱ��Earth’s average surface temperature has increased drastically since the start of the Industrial Revolution, but the warming effect seen at the poles is even more exaggerated. While existing climate models consider the increased heating in the Arctic and Antarctic poles, they often underestimate the warming in these regions. This is especially true for climates millions of years ago, when greenhouse gas concentrations were very high.

This is a problem because future climate projections are generated with these same models: if they do not produce enough warming for the past, we might underestimate polar warming – and therefore the associated risks, such as ice sheet or permafrost melting – for the future.

“During my PhD, I was drawn to the fact that the climate models we are using do not represent the magnitude of warming that happens in the Arctic,” said lead author Dr Deepashree Dutta from Cambridge’s Department of Geography, who carried out the work during her PhD at UNSW. “At the same time, we knew that the majority of these models do not represent the upper layers of the atmosphere very well. And we thought this might be a missing link.”

̽��ֱ��team turned their focus to a key atmospheric element that is missing in most models — polar stratospheric clouds — and found that they can explain a large part of the missing warming in models.

Their results, published in the journal Nature Geoscience, show that there is still much to learn about the climate of the past, present and future.

Climate models are computer simulations of our global climate system that are built using our theoretical understanding of how the climate works. They can be used to recreate past conditions or predict future climate scenarios.

Climate models incorporate many factors that influence the climate, but they cannot include all real-world processes. One consequence of this is that generally, climate models simulate polar climate change that is smaller than actual observations.

“ ̽��ֱ��more detail you include in the model, the more resources they require to run,” said co-author Dr Martin Jucker from UNSW. “It’s often a toss-up between increasing the horizontal or vertical resolution of the model. And as we live down here at the surface of the earth, the detail closer to the surface is often prioritised.”

In 1992, American paleoclimatologist Dr Lisa Sloan first suggested that the extreme warming at high latitudes during past warm periods may have been caused by polar stratospheric clouds.

Polar stratospheric clouds form at very high altitudes (15-25 km above the Earth's surface), and at very low temperatures (over the poles). They are also called nacreous or mother-of-pearl clouds because of their bright and sometimes luminous hues, although they are not normally visible to the naked eye.

These polar stratospheric clouds have a similar effect on climate as greenhouse gases – they trap heat that would otherwise be lost to space and warm the surface of the Earth.

“These clouds form under complex conditions, which most climate models cannot reproduce. And we wondered if this inability to simulate these clouds may result in less surface warming at the poles than what we’ve observed in the real world,” said Dutta.

Thirty years after Sloan’s research, Dutta wanted to test this theory using one of the few atmospheric models that incorporates polar atmospheric clouds, to see if it might explain the disparities in warming between observational data and climate models.

“I wanted to test this theory by running an atmospheric model that includes all necessary processes with conditions that resembled a time period over 50 million years ago, known as the early Eocene. It was a period of Earth’s history when the planet was very hot and the Arctic was ice-free throughout the year,” said Dutta.

̽��ֱ��Eocene was also a period characterised by high methane content, and the position of continents and mountains was different to today.

“Climate models are far too cold in the polar regions, when simulating these past hot climates, and this has been an enigma for the past thirty years,” said Jucker. “ ̽��ֱ��early Eocene was a period in the Earth’s climate with extreme polar warming, so presented the perfect test for our climate models.”

̽��ֱ��team found that the elevated methane levels during the Eocene resulted in an increase in polar stratospheric cloud formation. They found that under certain conditions, the local surface warming due to stratospheric clouds was up to 7 degrees Celsius during the coldest winter months. This temperature difference significantly reduces the gap between climate models and temperature evidence from climate archives.

By comparing future simulations to simulations of the Eocene, the researchers also discovered that it isn’t just methane that was needed to produce polar stratospheric clouds. “This is another key finding of this work,” said Dutta. “It’s not just methane, but it's also the Earth’s continental arrangement, which plays an important role in forming these stratospheric clouds. Because if we input the same amount of methane for our future climate, we do not see the same increase in stratospheric clouds.”

̽��ֱ��research has provided some of the answers to questions about the climate of the deep past, but what does that mean for future projections?

“We found that stratospheric clouds account for the accelerated warming at the poles that is often left out of our climate models, and of course this could potentially mean that our future projections are also not warm enough,” said Jucker. “But the good news is that these clouds are more likely to form under the continental arrangement that was present tens of millions of years ago, and is not found on Earth now. Therefore, we don’t expect such large increases in stratospheric clouds in the future.”

This new research has not only helped to provide a piece of the puzzle as to why temperature recordings in the Arctic are always warmer than climate models – it has also provided new insights into the Earth’s past climate.

“Our study shows the value of increasing the detail of climate models, where we can,” said Dutta. “Although we already know a lot about these clouds theoretically, until we include them in our climate models, we won’t know the full scale of their impact.”

Reference:
Deepashree Dutta et al. ‘Early Eocene low orography and high methane enhance Arctic warming via polar stratospheric clouds.’ Nature Geoscience (2023). DOI: 10.1038/s41561-023-01298-w

Adapted from a UNSW press release.

Stratospheric clouds over the Arctic may explain the differences seen between the polar warming calculated by climate models and actual recordings, according to researchers from the ̽��ֱ�� of Cambridge and UNSW Sydney.

Our study shows the value of increasing the detail of climate models where we can

Deepashree Dutta

Cavan Images / Per-Andre Hoffmann via Getty Images

Mother of pearl clouds (nacreous clouds), Polar Stratospheric Clouds.

̽��ֱ��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 – 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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Ice sheets can collapse faster than previously thought possible

sc604 — Wed, 05 Apr 2023 14:59:35 +0000

An international team of researchers used high-resolution imagery of the seafloor to reveal just how quickly a former ice sheet that extended from Norway retreated at the end of the last Ice Age, about 20,000 years ago.

̽��ֱ��team, including researchers from the ̽��ֱ�� of Cambridge, mapped more than 7,600 small-scale landforms called corrugation ridges across the seafloor. ̽��ֱ��ridges are less than 2.5 metres high and are spaced between about 25 and 300 metres apart.

These landforms are understood to have formed when the ice sheet’s retreating margin moved up and down with the tides, pushing seafloor sediments into a ridge every low tide. Given that two ridges would have been produced each day, the researchers were able to calculate how quickly the ice sheet retreated.

Their results, reported in the journal Nature, show the former ice sheet underwent pulses of rapid retreat at a speed of 50 to 600 metres per day. This is much faster than any ice sheet retreat rate that has been observed from satellites or inferred from similar landforms in Antarctica.

“Our research provides a warning from the past about the speeds that ice sheets are physically capable of retreating at,” said Dr Christine Batchelor from Newcastle ̽��ֱ��, who led the research. “Our results show that pulses of rapid retreat can be far quicker than anything we’ve seen so far.”

Information about how ice sheets behaved during past periods of climate warming is important to inform computer simulations that predict future ice sheet and sea-level change.

“This study shows the value of acquiring high-resolution imagery about the glaciated landscapes that are preserved on the seafloor,” said co-author Dr Dag Ottesen from the Geological Survey of Norway, who is involved in the MAREANO seafloor mapping programme that collected the data.

̽��ֱ��new research suggests that periods of such rapid ice-sheet retreat may only last for short periods of time: from days to months.

“This shows how rates of ice-sheet retreat averaged over several years or longer can conceal shorter episodes of more rapid retreat,” said co-author Professor Julian Dowdeswell from Cambridge’s Scott Polar Research Institute. “It is important that computer simulations are able to reproduce this ‘pulsed’ ice-sheet behaviour.”

̽��ֱ��seafloor landforms also shed light into the mechanism by which such rapid retreat can occur. ̽��ֱ��researchers found that the former ice sheet had retreated fastest across the flattest parts of its bed.

“An ice margin can unground from the seafloor and retreat near-instantly when it becomes buoyant,” said co-author Dr Frazer Christie, also from the Scott Polar Research Institute. “This style of retreat only occurs across relatively flat beds, where less melting is required to thin the overlying ice to the point where it starts to float.”

̽��ֱ��researchers conclude that pulses of similarly rapid retreat could soon be observed in parts of Antarctica. This includes at West Antarctica’s vast Thwaites Glacier, which is the subject of considerable international research due to its potential susceptibility to unstable retreat. ̽��ֱ��authors of this new study suggest that Thwaites Glacier could undergo a pulse of rapid retreat because it has recently retreated close to a flat area of its bed.

“Our findings suggest that present-day rates of melting are sufficient to cause short pulses of rapid retreat across flat-bedded areas of the Antarctic Ice Sheet, including at Thwaites”, said Batchelor. “Satellites may well detect this style of ice-sheet retreat in the near future, especially if we continue our current trend of climate warming.”

Other co-authors are Dr Aleksandr Montelli and Evelyn Dowdeswell at the Scott Polar Research Institute, Dr Jeffrey Evans at Loughborough ̽��ֱ��, and Dr Lilja Bjarnadóttir at the Geological Survey of Norway. ̽��ֱ��study was supported by Peterhouse, Cambridge, the Faculty of Humanities and Social Sciences at Newcastle ̽��ֱ��, the Prince Albert II of Monaco Foundation, and the Geological Survey of Norway.

Reference:
Christine L Batchelor et al. ‘Rapid, buoyancy-driven ice-sheet retreat of hundreds of metres per day’. Nature (2023), DOI: 10.1038/s41586-023-05876-1

Adapted from a press release by Newcastle ̽��ֱ��.

Ice sheets can retreat up to 600 metres a day during periods of climate warming, 20 times faster than the highest rate of retreat previously measured.

Copernicus EU/ESA, processed by Dr Frazer Christie

Sentinel-1 image composite depicting the highly fractured and fast-flowing frontal margin of the Thwaites and Crosson ice shelves

̽��ֱ��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 – 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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Researchers build more detailed picture of the movement of Greenland Ice Sheet

sc604 — Fri, 10 Feb 2023 15:14:39 +0000

Researchers have found that the movement of glaciers in Greenland is more complex than previously thought, with deformation in regions of warmer ice containing small amounts of water accounting for motion that had often been assumed to be caused by sliding where the ice meets the bedrock beneath.

Fibre-optics used to take the temperature of Greenland Ice Sheet

sc604 — Fri, 14 May 2021 17:09:27 +0000

Scientists have used fibre-optic sensing to obtain the most detailed measurements of ice properties ever taken on the Greenland Ice Sheet. Their findings will be used to make more accurate models of the future movement of the world’s second-largest ice sheet, as the effects of climate change continue to accelerate.

Surface lakes cause Antarctic ice shelves to ‘flex’

sc604 — Wed, 13 Feb 2019 10:00:00 +0000

A team of British and American researchers, co-led by the ̽��ֱ�� of Cambridge, has measured how much the McMurdo ice shelf in Antarctica flexes in response to the filling and draining of meltwater lakes on its surface. This type of flexing had been hypothesised before and simulated by computer models, but this is the first time the phenomenon has been measured in the field. ̽��ֱ��results are reported in the journal Nature Communications.

̽��ֱ��results demonstrate a link between surface melting and the weakening of Antarctic ice shelves and support the idea that recent ice shelf breakup around the Antarctic Peninsula may have been triggered, at least in part, by large amounts of surface meltwater produced in response to atmospheric warming.

As the climate continues to warm, more and more ice shelves may become susceptible to flex, fracture and break up over the coming century.

Most of the Antarctic continent is covered by the Antarctic Ice Sheet, which is up to four kilometres thick and contains enough ice to raise global sea levels by about 58 metres. Over most of the continent and for most of the year, air temperatures are well below zero and the ice surface remains frozen. But around 75% of the ice sheet is fringed by floating ice shelves, which are up to a kilometre thick, mostly below sea level, but with tens of metres of their total height protruding above the water. In the summer months, when air temperatures rise above freezing, the surfaces of these ice shelves are susceptible to melting.

“Surface water on ice shelves has been known about for a long time,” said co-author Dr Ian Willis from Cambridge’s Scott Polar Research Institute. “Over 100 years ago, members of both Shackleton’s Nimrod team and the Northern Party team of Scott’s British Antarctic Expedition mapped and recorded water on the Nansen Ice Shelf, around 300 kilometres from where we did our study on the McMurdo Ice Shelf. For the last few decades, it has also been possible to see widespread surface meltwater forming on many ice shelves each summer from satellite imagery.”

What is not fully known is the extent to which surface water might destabilise an ice shelf, especially in warmer summers when more meltwater is produced. If the slope of the ice shelf is sufficiently steep, the water may flow off the ice shelf to the ocean in large surface rivers, mitigating against any potential instability.

̽��ֱ��danger comes if water pools up in surface depressions on the ice shelf to form large lakes. ̽��ֱ��extra weight of the water will push down on the floating ice, causing it to sink a bit further into the sea. Around the edge of the lake, the ice will flex upwards to compensate. “If the lake then drains, the ice shelf will now flex back, rising up where the lake used to be, sinking down around the edge,” said lead author Dr Alison Banwell, also from SPRI. “It is this filling and draining of lakes that causes the ice shelf to flex, and if the stresses are large enough, fractures might also develop.”

Banwell and co-author Professor Doug MacAyeal from the ̽��ֱ�� of Chicago had previously suggested that the filling and draining of hundreds of lakes might have led to the catastrophic breakup of the Larsen B Ice Shelf 2002 when 3,250 square kilometres of ice was lost in just a few days.

“We had been able to model the rapid disintegration of that ice shelf via our meltwater loading-induced fracture mechanism,” said Banwell. “However, the problem was that no one had actually measured ice shelf flex and fracture in the field, and so we were unable to fully constrain the parameters in our model. That’s partly why we set out to try to measure the process on the McMurdo ice shelf.”

Using helicopters, snow machines and their own two feet, the researchers set up a series of pressure sensors to monitor the rise and fall of water levels in depressions which filled to become lakes, and GPS receivers to measure small vertical movements of the ice shelf.

“It was a lot of work to obtain the data, but they reveal a fascinating story,” said MacAyeal. “Most of the GPS signal is due to the ocean tides, which move the floating ice shelf up and down by several metres twice a day. But when we removed this tidal signal we found some GPS receivers moved down, then up by around one metre over a few weeks whereas others, just a few hundred metres away, hardly moved at all. ̽��ֱ��ones that moved down then up the most were situated where lakes were filling and draining, and there was relatively little movement away from the lakes. It is this differential vertical motion that shows the ice shelf is flexing. We’d anticipated this result, but it was very nice when we found it.”

̽��ֱ��team hope that their work will inspire others to look for evidence of flex and fracture on other ice shelves around Antarctica. Their work will also help in developing ice sheet scale models that could be used to predict the stability of ice shelves in the future and to understand the controls on ice shelf size since they act as buffers against fast-moving ice from the continent. As ice shelves shrink, glaciers and ice streams behind them flow more rapidly to the ocean, contributing to global sea level rise.

̽��ֱ��work was funded by the US National Science Foundation, the Leverhulme Trust, NASA, and CIRES, ̽��ֱ�� of Colorado, Boulder.

Reference:
Alison F. Banwell et al. ‘Direct Measurements of Ice-Shelf Flexure caused by Surface Meltwater Ponding and Drainage.’ Nature Communications (2019). DOI: 10.1038/s41467-019-08522-5

A bold response to the world’s greatest challenge
̽��ֱ�� ̽��ֱ�� of Cambridge is building on its existing research and launching an ambitious new environment and climate change initiative. Cambridge Zero is not just about developing greener technologies. It will harness the full power of the ̽��ֱ��’s research and policy expertise, developing solutions that work for our lives, our society and our biosphere.

̽��ֱ��filling and draining of meltwater lakes has been found to cause a floating Antarctic ice shelf to flex, potentially threatening its stability.

Filling and draining of lakes causes the ice shelf to flex, and if the stresses are large enough, fractures might also develop

Alison Banwell

Surface lakes on the McMurdo Ice Shelf

̽��ֱ��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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̽��ֱ��search for Endurance

sc604 — Thu, 24 Jan 2019 16:27:46 +0000

Update - 14 February 2019: ̽��ֱ��Weddell Sea Expedition reached the wreck site, but deteriorating weather and ice conditions forced searchers to abandon the quest... for now.

Professor Julian Dowdeswell, Director of the Scott Polar Research Institute, is chief scientist on the ambitious expedition, which will use drones, satellites and autonomous underwater vehicles to study ice conditions in the Weddell Sea in unprecedented detail.

̽��ֱ��Weddell Sea is also the site of one of the most famous stories from the ‘Heroic Age’ of polar exploration.

̽��ֱ��Imperial Trans-Antarctic Expedition 1914-17 set out to cross Antarctica via the South Pole. However, in November 1915, Shackleton and his 28-man crew were confronted with one of the worst disasters in Antarctic history when Endurance was trapped, crushed and sunk by pack ice. ̽��ֱ��outside world was unaware of their predicament or location, food was scarce and the chance of survival was remote.

In this film, Professor Dowdeswell tells the incredible story of Endurance, and how he and the other members of the Weddell Sea expedition hope to locate the wreckage of one of the most iconic vessels in polar exploration.

In early January, a team of Cambridge scientists set out on an expedition to study and map the Larsen C ice shelf in western Antarctica, and – ice conditions permitting – search for the wreckage of Sir Ernest Shackleton’s Endurance.

̽��ֱ��Search for Endurance

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New insights into the dynamics of past climate change

sc604 — Wed, 14 Oct 2015 07:05:16 +0000

A new study of the relationship between ocean currents and climate change has found that they are tightly linked, and that changes in the polar regions can affect the ocean and climate on the opposite side of the world within one to two hundred years, far quicker than previously thought.

̽��ֱ��study, by an international team of scientists led by the ̽��ֱ�� of Cambridge, examined how changes in ocean currents in the Atlantic Ocean were related to climate conditions in the northern hemisphere during the last ice age, by examining data from ice cores and fossilised plankton shells. It found that variations in ocean currents and abrupt climate events in the North Atlantic region were tightly linked in the past, and that changes in the polar regions affected the ocean circulation and climate on the opposite side of the world.

̽��ֱ��researchers determined that as large amounts of fresh water were emptied into the North Atlantic as icebergs broke off the North American and Eurasian ice sheets, the deep and shallow currents in the North Atlantic rapidly slowed down, which led to the formation of sea ice around Greenland and the subsequent cooling of the Northern Hemisphere. It also strongly affected conditions in the South Atlantic within a matter of one to two hundred years. ̽��ֱ��results, published in the journal Nature Geoscience, show how climate events in the Northern Hemisphere were tightly coupled with changes in the strength of deep ocean currents in the Atlantic Ocean, and how that may have affected conditions across the globe.

During the last ice age, which took place from 70,000 to 19,000 years ago, the climate in the Northern Hemisphere toggled back and forth between warm and cold states roughly every 1000 to 6000 years. These events, known as Dansgaard-Oeschger events, were first identified in data from Greenland ice cores in the early 1990s, and had far-reaching impacts on the global climate.

̽��ֱ��ocean, which covers 70% of the planet, is a huge reservoir of carbon dioxide and heat. It stores about 60 times more carbon than the atmosphere, and can release or take up carbon on both short and long timescales. As changes happen in the polar regions, they are carried around the world by ocean currents, both at the surface and in the deep ocean. These currents are driven by winds, ocean temperature and salinity differences, and are efficient at distributing heat and carbon around the globe. Ocean currents therefore have a strong influence on whether regions of the world are warm (such as Europe) or whether they are not (such as Antarctica) as they modulate the effects of solar radiation. They also influence whether CO2 is stored in the ocean or the atmosphere, which is very important for global climate variability.

“Other studies have shown that the overturning circulation in the Atlantic has faced a slowdown during the last few decades,” said Dr Julia Gottschalk of Cambridge Department of Earth Sciences, the paper's lead author. “ ̽��ֱ��scientific community is only beginning to understand what it would mean for global climate should this trend continue, as predicted by some climate models.”

Analysing new data from marine sediment cores taken from the deep South Atlantic, between the southern tip of South America and the southern tip of Africa, the researchers discovered that during the last ice age, deep ocean currents in the South Atlantic varied essentially in unison with Greenland ice-core temperatures. “This implies that a very rapid transmission process must have operated, that linked rapid climate change around Greenland with the otherwise sluggish deep Atlantic Ocean circulation,” said Gottschalk, who is a Gates Cambridge Scholar. Best estimates of the delay between these two records suggest that the transmission happened within about 100 to 200 years.

Digging through metres of ocean mud from depths of 3,800 metres, the team studied the dissolution of fossil plankton shells that was closely linked to the chemical signature of different water masses. Water masses originating in the North Atlantic are less corrosive than water masses from the South Atlantic.

“Periods of very intense North Atlantic circulation and higher Northern Hemisphere temperatures increased the preservation of microfossils in the sediment cores, whereas those with slower circulation, when the study site was primarily influenced from the south, were linked with decreased carbonate ion concentrations at our core site which led to partial dissolution,” said co-author Dr Luke Skinner, also from Cambridge's Department of Earth Sciences.

To better understand the physical mechanisms of rapid ocean adjustment, the data was compared with a climate model simulation which covers the same period. “ ̽��ֱ��data of the model simulation was so close to the deep ocean sediment data, that we knew immediately, we were on the right track,” said co-author Dr Laurie Menviel from the ̽��ֱ�� of New South Wales, Australia, who conducted the model simulation.

̽��ֱ��timescales of these large-scale adjustments found in the palaeoceanographic data agree extremely well with those predicted by the model. “Waves between layers of different density in the deep ocean are responsible for quickly transmitting signals from North to South. This is a paradigm shift in our understanding of how the ocean works,” said Axel Timmermann, Professor of Oceanography at the ̽��ֱ�� of Hawaii.

Although conditions at the end of the last ice age were very different to those of today, the findings could shed light on how changing conditions in the polar regions may affect ocean currents. However, much more research is needed in this area. ̽��ֱ��study's findings could help test and improve climate models that are run for both past and future conditions.

̽��ֱ��sediment cores were recovered by Dr Claire Waelbroeck and colleagues aboard the French research vessel Marion Dufresne.

̽��ֱ��research was supported by the Gates Cambridge Trust, the Natural Environmental Research Council of the UK, the Royal Society, the European Research Council, the Australian Research Council and the National Science Foundation of the United States of America.

Reference:
Gottschalk, J et. al. Abrupt changes in the southern extent of North Atlantic Deep Water during Dansgaard-Oeschger events. Nature Geoscience (2015). DOI: 10.1038/ngeo2558

A new study finds that changing climate in the polar regions can affect conditions in the rest of the world far quicker than previously thought.

Other studies have shown that the overturning circulation in the Atlantic has faced a slowdown during the last few decades. ̽��ֱ��scientific community is only beginning to understand what it would mean for global climate should this trend continue, as predicted by some climate models

Julia Gottschalk

Left: Marine sediment core sample from the South Atlantic with fossilised partially dissolved shells of planktonic organisms. Right: Well-preserved plankton shells.

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

Yes