̽��ֱ�� of Cambridge - Greenland

Medieval monks accidentally recorded some of history’s biggest volcanic eruptions

sc604 — Wed, 05 Apr 2023 14:58:42 +0000

An international team, including researchers from the ̽��ֱ�� of Cambridge, drew on readings of medieval texts, along with ice core and tree ring data, to accurately date some of the biggest volcanic eruptions the world has ever seen. Their results, reported in the journal Nature, uncover new information about one of the most volcanically active periods in Earth’s history, which some think helped to trigger the Little Ice Age, a long interval of cooling that saw the advance of European glaciers.

It took the researchers, led by the ̽��ֱ�� of Geneva (UNIGE), almost five years to examine hundreds of annals and chronicles from across Europe and the Middle East, in search of references to total lunar eclipses and their colouration.

Total lunar eclipses occur when the moon passes into the Earth’s shadow. Typically, the moon remains visible as a reddish orb because it is still bathed in sunlight bent round the Earth by its atmosphere. But after a very large volcanic eruption, there can be so much dust in the stratosphere – the middle part of the atmosphere starting roughly where commercial aircraft fly – that the eclipsed moon almost disappears.

Medieval chroniclers recorded and described all kinds of historical events, including the deeds of kings and popes, important battles, and natural disasters and famines. Just as noteworthy were the celestial phenomena that, to the chroniclers, might foretell such calamities. Mindful of the Book of Revelation, a vision of the end times that speaks of a blood-red moon, the monks were especially careful to take note of the moon’s colouration.

Of the 64 total lunar eclipses that occurred in Europe between 1100 and 1300, the chroniclers had faithfully documented 51. In five of these cases, they also reported that the moon was exceptionally dark.

Asked what made him connect the monks’ records of the brightness and colour of the eclipsed moon with volcanic gloom, the lead author of the work, UNIGE’s Sébastien Guillet said: “I was listening to Pink Floyd's Dark Side of the Moon album when I realised that the darkest lunar eclipses all occurred within a year or so of major volcanic eruptions. Since we know the exact days of the eclipses, it opened the possibility of using the sightings to narrow down when the eruptions must have happened.”

̽��ֱ��researchers found that scribes in Japan took equal note of lunar eclipses. One of the best known, Fujiwara no Teika, wrote of an unprecedented dark eclipse observed on 2 December 1229: ‘the old folk had never seen it like this time, with the location of the disk of the Moon not visible, just as if it had disappeared during the eclipse... It was truly something to fear.’

̽��ֱ��stratospheric dust from large volcanic eruptions was not only responsible for the vanishing moon. It also cooled summer temperatures by limiting the sunlight reaching the Earth’s surface. This in turn could bring ruin to agricultural crops.

“We know from previous work that strong tropical eruptions can induce global cooling on the order of roughly 1°C over a few years,” said Markus Stoffel from the ̽��ֱ�� of Geneva, a specialist in converting measurements of tree rings into climate data, who co-designed the study. “They can also lead to rainfall anomalies with droughts in one place and floods in another.”

Despite these effects, people at the time could not have imagined that the poor harvests or the unusual lunar eclipses had anything to do with volcanoes – the eruptions themselves were all but one undocumented.

“We only knew about these eruptions because they left traces in the ice of Antarctica and Greenland,” said co-author Professor Clive Oppenheimer from Cambridge’s Department of Geography. “By putting together the information from ice cores and the descriptions from medieval texts we can now make better estimates of when and where some of the biggest eruptions of this period occurred.”

To make the most of this integration, Guillet worked with climate modellers to compute the most likely timing of the eruptions. “Knowing the season when the volcanoes erupted is essential, as it influences the spread of the volcanic dust and the cooling and other climate anomalies associated with these eruptions,” he said.

As well as helping to narrow down the timing and intensity of these events, what makes the findings significant is that the interval from 1100 to 1300 is known from ice core evidence to be one of the most volcanically active periods in history. Of the 15 eruptions considered in the new study, one in the mid-13th century rivals the famous 1815 eruption of Tambora that brought on ‘the year without a summer’ of 1816. ̽��ֱ��collective effect of the medieval eruptions on Earth’s climate may have led to the Little Ice Age, when winter ice fairs were held on the frozen rivers of Europe.

“Improving our knowledge of these otherwise mysterious eruptions, is crucial to understanding whether and how past volcanism affected not only climate but also society during the Middle Ages,” said Guillet.

̽��ֱ��research was supported in part by the Swiss National Science Foundation.

Reference:
Sébastien Guillet et al. ‘Lunar eclipses illuminate timing and climate impact of medieval volcanism.’ Nature (2023). DOI: 10.1038/s41586-023-05751-z

By observing the night sky, medieval monks unwittingly recorded some of history’s largest volcanic eruptions, according to a new analysis of 12th and 13th century European and Middle Eastern chronicles.

Recueil de poésies françaises. Consolation de Boèce, Ms. 822, fol. 61v, Bibliothèque Municipale de Toulouse /Gallica, BnF

An illuminated manuscript from the late 14th to the early 15th century, depicting two individuals observing a lunar eclipse

̽��ֱ��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.

Accelerating melt rate makes Greenland Ice Sheet world’s largest ‘dam’

sc604 — Mon, 21 Feb 2022 19:47:29 +0000

̽��ֱ��world’s second-largest ice sheet is melting from the bottom up – and generating huge amounts of heat from hydropower.

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.

Lakes on Greenland Ice Sheet can drain huge amounts of water, even in winter

sc604 — Wed, 31 Mar 2021 23:19:20 +0000

̽��ֱ��researchers, from the ̽��ֱ�� of Cambridge, used radar data from a European Space Agency satellite to show that even when the heat from the Sun is absent, these lakes can discharge large amounts of water to the base of the ice sheet. These ‘drainage events’ are thought to play a significant role in accelerating the movement of the ice by lubricating it from below.

Previous studies of draining lakes have all been carried out during the summer months, through a combination of direct field observations and optical satellite data, which requires daylight.

̽��ֱ��approach developed by the Cambridge researchers uses the radar ‘backscatter’ – the reflection of waves back to the satellite from where they were emitted – to detect changes in the lakes during the winter months, when Greenland is in near-total darkness.

̽��ֱ��results, reported in the journal ̽��ֱ��Cryosphere, imply that the ‘plumbing’ system beneath the Greenland Ice Sheet doesn’t just slowly leak water from the previous summer, but even in the depths of the Arctic winter, it can be ‘recharged’, as large amounts of surface lake water cascade to the base of the ice sheet.

Many previous studies have shown that the Greenland Ice Sheet is losing mass, and the rate of loss is accelerating, due to melting and runoff.

“One of the unknowns in terms of predicting the future of the ice sheet is how fast the glaciers move – whether they will speed up and if so, by how much,” said co-author Dr Ian Willis from Cambridge’s Scott Polar Research Institute (SPRI). “ ̽��ֱ��key control on how fast the glaciers move is the amount of meltwater getting to the bottom of the ice sheet, which is where our work comes in.”

Lakes form on the surface of the Greenland ice sheet each summer as the weather warms. They exist for weeks or months but can drain in a matter of hours due to hydrofracturing, transferring millions of cubic metres of water and heat to the base of the ice sheet. ̽��ֱ��affected areas include sensitive regions of the ice sheet interior where the impact on ice flow is potentially large.

“It’s always been thought that these lakes drained only in the summer, simply because it’s warmer and the sun causes the ice to melt,” said co-author Corinne Benedek, also from SPRI. “In the winter, it’s dark and the surfaces freeze. We thought that the filling of the lakes is what caused their eventual drainage, but it turns out that isn’t always the case.”

Benedek, who is currently a PhD candidate at SPRI, first became interested in what happens to surface lakes in the winter while she was a Master’s student studying satellite thermal data.

“ ̽��ֱ��thermal data showed me that liquid water can survive in the lakes throughout the winter,” she said. “Previous studies using airborne radar had also identified lakes buried a few metres beneath the surface of the ice sheet in the summer. Both of these things got me thinking about ways to observe lakes all year long. ̽��ֱ��optical satellite imagery we normally use to observe the lakes isn’t available in winter, or even when it’s cloudy.”

Benedek and Willis developed a method using data from the Sentinel-1 satellite, which uses a type of radar called synthetic aperture radar (SAR). SAR functions at a wavelength that makes it possible to see through clouds and in the dark. Ice and water read differently using SAR, and so they developed an algorithm that tracks when sudden changes in SAR backscatter occur.

Over three winters, they identified six lakes that appeared to drain over the winter months. These lakes were buried lakes or surface lakes that were frozen over. ̽��ֱ��algorithm was able to identify where the backscatter characteristics of the lake changed markedly between one image and the next one recorded 12 days later.

̽��ֱ��SAR data was backed up with additional optical data from the previous autumn and subsequent spring, which confirmed that lakes areas shrank considerably for the six drained lakes. For three of the lakes, the optical data, as well as data from other satellites, was used to show the snow- and ice-covered lakes collapsed, dropping by several metres, again confirming the water had drained.

“ ̽��ֱ��first lake I found was surprising,” said Benedek. “It took me a while to be sure that what I thought I was seeing was really what I was seeing. We used surface elevation data from before and after the events to confirm what we were thinking. We know now that drainage of lakes during the winter is something that can happen, but we don’t yet know how often it happens.”

“Glaciers slow down in the winter, but they’re still moving,” said Willis. “It must be this movement that causes fractures to develop in certain places allowing some lakes to drain. We don’t yet know how widespread this winter lake drainage phenomenon is, but it could have important implications for the Greenland Ice Sheet, as well as elsewhere in the Arctic and Antarctic.”

Reference:
Corinne L. Benedek and Ian C. Willis. ‘Winter drainage of surface lakes on the Greenland Ice Sheet from Sentinel-1 SAR imagery.’ ̽��ֱ��Cryosphere (2021). DOI: 10.5194/tc-15-1-2021

Using satellite data to ‘see in the dark’, researchers have shown for the first time that lakes on the Greenland Ice Sheet drain during winter, a finding with implications for the speed at which the world’s second-largest ice sheet flows to the ocean.

We don’t yet know how widespread this winter lake drainage phenomenon is, but it could have important implications for the Greenland Ice Sheet, as well as elsewhere in the Arctic and Antarctic

Ian Willis

Lake on the surface of the Greenland Ice Sheet

̽��ֱ��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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Over-hunting walruses contributed to the collapse of Norse Greenland

fpjl2 — Mon, 06 Jan 2020 12:30:00 +0000

Medieval Greenlanders may have chased dwindling walrus herds ever farther north in an effort to maintain their economy, when the value of walrus ivory tanked after the introduction of elephant tusks into European markets in the 1200s.

Drone images show Greenland Ice Sheet becoming more unstable as it fractures

sc604 — Tue, 03 Dec 2019 09:49:11 +0000

̽��ֱ��world’s second-largest ice sheet, and the single largest contributor to global sea level rise, is potentially becoming unstable because of fractures developing in response to faster ice flow and more meltwater forming on its surface.

Sea ice acts as ‘pacemaker’ for abrupt climate change

sc604 — Wed, 06 Mar 2019 19:00:00 +0000

An international study involving researchers from the UK, Norway, Germany Australia, South Korea and the US has confirmed that changes in sea ice cover in the Norwegian Sea played a key role in driving abrupt climate change events between 32,000 and 40,000 years ago, where global temperatures shifted as much as 15 degrees Celsius.

̽��ֱ��results, reported in the journal Science Advances, indicate that initial sea ice reduction started before the abrupt warming over Greenland, and that sea ice expansion started before the end of the warm periods in Greenland.

̽��ֱ��Arctic sea ice is a key element of the global climate system and the strong ongoing warming of the Arctic Ocean can have major impacts on the stability of the Greenland Ice Sheet, first and foremost accelerated sea level rise.

̽��ֱ��Nordic Sea system and its water column structure during the last glacial cycle is the closest analogue to the present-day Arctic Ocean, which makes it a perfect natural laboratory to understand the role of rapid disappearance of regional sea ice on abrupt warming on the Greenland Ice Sheet.

̽��ֱ��last glacial period, 10,000–100,000 years ago, was marked by repeated abrupt climate changes with global implications. Within a matter of decades, temperature shifts of as much as 15 degrees Celsius occurred around Greenland, but the mechanisms driving these changes –known as Dansgaard-Oeschger events – are not fully understood.

“One of the most challenging aspects of palaeoclimatology is to precisely resolve and reconstruct the exact timing of the events that took place across the major climate transitions of the last glacial cycle,” said co-author Dr Francesco Muschitiello, from the ̽��ֱ�� of Cambridge’s Department of Geography. “As a result, a detailed account of the temporal relationship between changes in sea-ice extent in the Nordic Seas, and North Atlantic ocean circulation and climate across Dansgaard-Oeschger events has been so far elusive.”

̽��ֱ��researchers investigated specific organic molecules in a sediment core from the southern Norwegian Sea, one of which was produced by algae that live in sea ice and others that were produced by organisms living in open, ice-free waters thousands of years ago.

̽��ֱ��new sea ice reconstruction based on organic molecules in marine sediments was also evaluated by means of results from a model simulation of past sea ice conditions.

“Our data suggest that there were substantial changes in the sea ice cover in the southern Norwegian Sea between 32,000 and 40,000 years ago,” said Henrik Sadatzki from the ̽��ֱ�� of Bergen and the paper’s first author. “Most extensive sea ice conditions occurred at the onsets and early parts of cold periods over Greenland and the most pronounced open-ocean conditions occurred at the onsets of the abrupt changes to warm periods over Greenland.”

̽��ֱ��results support that an enhanced sea ice cover contributed to insulation of the cold, high-latitude atmosphere from relatively warmer waters that were present in the Norwegian Sea beneath the sea ice lid.

In turn, sea ice reduction allowed for heat release from the exposed Norwegian Sea waters to the atmosphere, which was a prime ingredient in shaping the abrupt warming of the Dansgaard-Oeschger climate events in Greenland.

̽��ֱ��Dansgaard–Oeschger climate events have stirred interest in documenting that the climate system contains mechanisms that may lead to abrupt and surprising climate changes.

These findings clarify the series of events taking place in the high-latitude North Atlantic across the abrupt Dansgaard–Oeschger cycles of the last glacial period. However, further work is needed to ultimately identify the physical mechanisms linking the current sudden demise of Arctic sea ice to abrupt Greenland Ice Sheet changes.

̽��ֱ��research was funded in part by the European Research Council.

Reference:
Henrik Sadatzki et al. ‘Sea ice variability in the southern Norwegian Sea during glacial Dansgaard-Oeschger climate cycles.’ Science Advances (2019). DOI: 10.1126/sciadv.aau6174

Adapted from a ̽��ֱ�� of Bergen press release.

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Substantial variations in past sea ice cover in the Norwegian Sea were instrumental for several abrupt climate changes in large parts of the world, researchers have found.

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Icebergs in Ilulissat Icefjord, Greenland

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