探花直播 of Cambridge - ice age

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

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

探花直播evidence, contained within an ice core, shows that in one location the ice sheet thinned by 450 metres 鈥� that鈥檚 more than the height of the Empire State Building 鈥� 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鈥檚 rising temperatures might destabilize parts of the West Antarctic Ice Sheet in the future, potentially passing a tipping point and inducing a runaway collapse. 探花直播study, published in Nature Geoscience, sheds light on how quickly Antarctic ice could melt if temperatures continue to soar.

鈥淲e now have direct evidence that this ice sheet suffered rapid ice loss in the past,鈥� said Professor Eric Wolff, senior author of the new study from Cambridge鈥檚 Department of Earth Sciences. 鈥淭his scenario isn鈥檛 something that exists only in our model predictions and it could happen again if parts of this ice sheet become unstable.鈥�

From west to east, the Antarctic ice sheets contain enough freshwater to raise global sea levels by around 57 metres. 探花直播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鈥檚 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.

鈥淲e 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,鈥� said Dr Isobel Rowell, study co-author from the British Antarctic Survey. 鈥淯sing ice cores we can go back to that time and estimate the ice sheet鈥檚 thickness and extent.鈥�

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鈥檚 snowfall 鈥� providing clues as to the changing climate and ice extent.

探花直播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. 鈥淥nce the ice thinned, it shrunk really fast,鈥� said Wolff, 鈥渢his was clearly a tipping point 鈥� a runaway process.鈥�

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.聽

探花直播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.

鈥淲e already knew from models that the ice thinned around this time, but the date of this was uncertain,鈥� said Rowell. Ice sheet models placed the retreat anywhere between 12,000 and 5,000 years ago and couldn鈥檛 say how quickly it happened. 鈥淲e now have a very precisely dated observation of that retreat that can be built into improved models,鈥� said Rowell.

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

Reference

Grieman et al. (2024)聽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 探花直播 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.

探花直播 of Cambridge / British Antarctic Survey

Tents at Skytrain Ice Rise

探花直播text in this work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. Images, including our videos, are Copyright 漏探花直播 of Cambridge and licensors/contributors as identified. All rights reserved. We make our image and video content available in a number of ways 鈥� 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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Mysterious 11,000-year-old skull headdresses go on display in Cambridge

sjr81 — Thu, 21 Jun 2018 08:21:37 +0000

探花直播headdresses are the star exhibits in A Survival Story 鈥� Prehistoric Life at Star Carr which gives visitors a fascinating glimpse into life in Mesolithic-era Britain following the end of the last Ice Age.

At the time people were building their homes on the shore of Lake Flixton, five miles inland from what is now the North Yorkshire coast, Britain was still attached to Europe with climates warming rapidly.

As well as the spectacular headdresses, made of red deer skull and antlers, the exhibition features other Mesolithic-era objects such as axes and weapons used to hunt a range of animals such as red deer and elk.

Also going on display is a wooden paddle 鈥� used to transport settlers around the lake 鈥� as well as objects for making fire. Beads and pendants made of shale and amber also provide evidence of how people adorned themselves, as do objects used for making cloths from animal skins.

Most of the objects on display are from MAA. They were recovered from excavations conducted at the site by Cambridge archaeologist Professor Grahame Clark. More recently, excavations have been conducted by the archaeologists from the Universities of Chester, Manchester and York.

It is also the first time so many of the artefacts belonging to MAA have been on display side-by-side. Many of the objects are very fragile and can鈥檛 be moved, meaning it is a unique opportunity to see such a wide selection of material from the Star Carr site.

Exhibition curator Dr Jody Joy said: 鈥淪tar Carr is unique. Only a scattering of stone tools normally survive from so long ago; but the waterlogged ground there has preserved bone, antler and wooden objects. It鈥檚 here that archaeologists have found the remains of the oldest house in Britain, exotic jewellery and mysterious headdresses.

鈥淭his was a time before farming, before pottery, before metalworking 鈥� but the people who made their homes there returned to the same place for hundreds of years.

鈥� 探花直播most mysterious objects found at Star Carr are 33 deer skull headdresses. Only three similar objects have been discovered elsewhere 鈥� all in Germany. Someone has removed parts of the antlers and drilled holes in the skulls, but archaeologists don鈥檛 know why. They may have been hunting disguises, they may have been used in ceremonies or dances. We can never know for sure, but this is why Star Carr continues to intrigue us.鈥�

As well as the headdresses, archaeologists have also discovered scatters of flint showing where people made stone tools, and antler points used to hunt and fish. 227 points were found at Star Carr, more than 90pc of all those ever discovered in Britain.

Closer to what was the lake edge (Lake Flixton has long since dried up), there is evidence of Mesolithic-era enterprise including wooden platforms used as walkways and jetties (the earliest known examples of carpentry in Europe) 鈥� where boats would have given access to the lake and its two islands.

First discovered in 1947 by an amateur archaeologist, work at Star Carr continues to this day. Unfortunately, recent artefacts are showing signs of decay as changing land use around the site causes the peat where many artefacts have been preserved naturally for millennia to dry out. It is now a race against time for archaeologists to discover more about the site before it is lost.

鈥淪tar Carr shows that although life was very different 11,500 years ago, people shared remarkably similar concerns to us,鈥� added Joy. 鈥淭hey needed food, warmth and comfort. They made sense of the world through ritual and religion.

鈥� 探花直播people of Star Carr were very adaptable and there is much we can learn from them as we too face the challenges of rapid climate change. There are still many discoveries to be made, but these precious archaeological remains are now threatened by the changing environment.

鈥淎s they are so old, the objects from Star Carr are very fragile and they must be carefully monitored and stored. As a result, few artefacts are normally on display. This is a rare opportunity to see so many of these objects side-by-side telling the story of this extraordinary site.鈥�

A Survival Story 鈥� Prehistoric Life at Star Carr is on display at the Li Ka Shing Gallery at the Museum of Archaeology and Anthropology, Downing Street, Cambridge, from June 21 to December 30, 2019. Entry is free.

Three 11,500-year-old deer skull headdresses 鈥� excavated from a world-renowned archaeological site in Yorkshire 鈥� will go on display, one for the first time, at Cambridge 探花直播鈥檚 Museum of Archaeology and Anthropology (MAA) from today.

探花直播most mysterious objects found at Star Carr are 33 deer skull headdresses. Only three similar objects have been discovered elsewhere 鈥� all in Germany.

Jody Joy

Museum of Archaeology and Anthropology

One of the three Mesolithic deer skull headdresses from the new exhibition

探花直播text in this work is licensed under a Creative Commons Attribution 4.0 International License. Images, including our videos, are Copyright 漏探花直播 of Cambridge and licensors/contributors as identified.聽 All rights reserved. We make our image and video content available in a number of ways 鈥� 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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Silent witnesses: how an ice age was written in the trees

lw355 — Tue, 27 Feb 2018 12:00:35 +0000

Researchers use聽tree rings to unravel past climates and their聽impact on civilisations.聽

READ THE STORY HERE

What connects a series of volcanic eruptions and severe summer cooling with a century of pandemics, human migration and the rise and fall of civilisations? Tree rings, says Ulf B眉ntgen, who leads Cambridge鈥檚 first dedicated tree-ring laboratory in the Department of Geography.

Once you embark on these integrative approaches you can ask questions like how did complex societies cope with climate change? That鈥檚 when it starts to get really exciting.

Ulf B眉ntgen

Hrafn 脫skarsson

Subfossil trees preserved in Iceland

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Textbook story of how humans populated America is 鈥渂iologically unviable鈥�, study finds

tdk25 — Wed, 10 Aug 2016 17:00:08 +0000

探花直播established theory about how Ice Age peoples first reached the present-day United States has been challenged by an unprecedented study which concludes that their supposed entry route was 鈥渂iologically unviable鈥�.

探花直播first people to reach the Americas crossed via an ancient land bridge between Siberia and Alaska but then, according to conventional wisdom, had to wait until two huge ice sheets that covered what is now Canada started to recede, creating the so-called 鈥渋ce-free corridor鈥� which enabled them to move south.

In a new study published in the journal Nature, however, an international team of researchers used ancient DNA extracted from a crucial pinch-point within this corridor to investigate how its ecosystem evolved as the glaciers began to retreat. They created a comprehensive picture showing how and when different flora and fauna emerged and the once ice-covered landscape became a viable passageway. No prehistoric reconstruction project like it has ever been attempted before.

探花直播researchers conclude that while people may well have travelled this corridor after about 12,600 years ago, it would have been impassable earlier than that, as the corridor lacked crucial resources, such as wood for fuel and tools, and game animals which were essential to the hunter-gatherer lifestyle.

If this is true, then it means that the first Americans, who were present south of the ice sheets long before 12,600 years ago, must have made the journey south by another route. 探花直播study鈥檚 authors suggest that they probably migrated along the Pacific coast.

Who these people were is still widely disputed. Archaeologists agree, however, that early inhabitants of the modern-day contiguous United States included the so-called 鈥淐lovis鈥� culture, which first appear in the archaeological record over 13,000 years ago. And the new study argues that the ice-free corridor would have been completely impassable at that time.

探花直播research was led by Professor Eske Willerslev, an evolutionary geneticist in the Department of Zoology and Fellow of St John鈥檚 College, 探花直播 of Cambridge, who also holds posts at the Centre for GeoGenetics, 探花直播 of Copenhagen, and the Wellcome Sanger Institute in Cambridge.

鈥� 探花直播bottom line is that even though the physical corridor was open by 13,000 years ago, it was several hundred years before it was possible to use it,鈥� Willerslev said.

鈥淭hat means that the first people entering what is now the US, Central and South America must have taken a different route. Whether you believe these people were Clovis, or someone else, they simply could not have come through the corridor, as long claimed.鈥�

Mikkel Winther Pedersen, a PhD student at the Centre for GeoGenetics, 探花直播 of Copenhagen, who conducted the molecular analysis, added: 鈥� 探花直播ice-free corridor was long considered the principal entry route for the first Americans. Our results reveal that it simply opened up too late for that to have been possible.鈥�

探花直播corridor is thought to have been about 1,500 kilometres long, and emerged east of the Rocky Mountains 13,000 years ago in present-day western Canada, as two great ice sheets 鈥� the Cordilleran and Laurentide, retreated.

On paper, this fits well with the argument that Clovis people were the first to disperse across the Americas. 探花直播first evidence for this culture, which is named after distinctive stone tools found near Clovis, New Mexico, also dates from roughly the same time, although many archaeologists now believe that other people arrived earlier.

鈥淲hat nobody has looked at is when the corridor became biologically viable,鈥� Willerslev said. 鈥淲hen could they actually have survived the long and difficult journey through it?鈥�

探花直播conclusion reached by Willerslev and his colleagues is that the journey would have been impossible until about 12,600 years ago. Their research focused on a 鈥渂ottleneck鈥�, one of the last parts of the corridor to become ice-free, and now partly covered by Charlie Lake in British Columbia, and Spring Lake, Alberta 鈥� both part of Canada鈥檚 Peace River drainage basin.

探花直播team gathered evidence including radiocarbon dates, pollen, macrofossils and DNA taken from lake sediment cores, which they obtained standing on the frozen lake surface during the winter season. Willerslev鈥檚 own PhD, 13 years ago, demonstrated that it is possible to extract ancient plant and mammalian DNA from sediments, as it contains preserved molecular fossils from substances such as tissue, urine, and faeces.

Having acquired the DNA, the group then applied a technique termed 鈥渟hotgun sequencing鈥�. 鈥淚nstead of looking for specific pieces of DNA from individual species, we basically sequenced everything in there, from bacteria to animals,鈥� Willerslev said. 鈥淚t鈥檚 amazing what you can get out of this. We found evidence of fish, eagles, mammals and plants. It shows how effective this approach can be to reconstruct past environments.鈥�

This approach allowed the team to see, with remarkable precision, how the bottleneck鈥檚 ecosystem developed. Crucially, it showed that before about 12,600 years ago, there were no plants, nor animals, in the corridor, meaning that humans passing through it would not have had the聽resources that were聽essential for聽their survival.

Around 12,600 years ago, steppe vegetation started to appear, followed quickly by animals such as bison, woolly mammoth, jackrabbits and voles. Importantly 11,500 years ago, the researchers identified a transition to a 鈥減arkland ecosystem鈥� 鈥� a landscape densely populated by trees, as well as moose, elk and bald-headed eagles, which would have offered crucial resources for migrating humans.

Somewhere in between, the lakes in the area were populated by fish, including several identifiable species such as pike and perch. Finally, about 10,000 years ago, the area transitioned again, this time into boreal forest, characterised by spruce and pine.

探花直播fact that Clovis was clearly present south of the corridor before 12,600 years ago means that they could not have travelled through it. David Meltzer, an archaeologist at Southern Methodist 探花直播 and a co-author on the study, said: 鈥淭here is compelling evidence that Clovis was preceded by an earlier and possibly separate population, but either way, the first people to reach the Americas in Ice Age times would have found the corridor itself impassable.鈥�

鈥淢ost likely, you would say that the evidence points to their having travelled down the Pacific Coast,鈥� Willerslev added. 鈥淭hat now seems the most likely scenario.鈥�

探花直播paper Postglacial viability and colonization in North America's ice-free corridor is published in the journal Nature on 10. August 2016. DOI: 10.1038/nature19085

鈥婭nset images:聽Map outlining the opening of the human migration routes in North America revealed by the results presented in this study. /聽Mikkel W. Pedersen and colleague preparing for coring of the lake sediments. All images聽provided by Mikkel Winther Pedersen, Centre for GeoGenetics, Natural History Museum of Denmark, 探花直播 of Copenhagen.

Using ancient DNA, researchers have created a unique picture of how a prehistoric migration route evolved over thousands of years 鈥� revealing that it could not have been used by the first people to enter the Americas, as traditionally thought.

探花直播first people entering what is now the US, Central and South America must have taken a different route to the one that has long been claimed

Eske Willerslev

Mikkel Winther Pedersen, Centre for GeoGenetics, Natural History Museum of Denmark, 探花直播 of Copenhagen

探花直播fieldwork was conducted during the winter because the frozen lake surface provided the researchers with a solid (but freezing) platform for drilling into the sediment

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Super-slow circulation allowed world鈥檚 oceans to store huge amounts of carbon during the last ice age

sc604 — Mon, 27 Jun 2016 09:00:00 +0000

Using the information contained within the shells of tiny animals known as foraminifera, the researchers, led by the 探花直播 of Cambridge, looked at the characteristics of the seawater in the Atlantic Ocean during the last ice age, including its ability to store carbon. Since atmospheric CO₂ levels during the period were about a third lower than those of the pre-industrial atmosphere, the researchers were attempting to find if the extra carbon not present in the atmosphere was stored in the deep ocean instead.

They found that the deep ocean circulated at a much slower rate at the peak of the last ice age than had previously been suggested, which is one of the reasons why it was able to store much more carbon for much longer periods. That carbon was accumulated as organisms from the surface ocean died and sank into the deep ocean where their bodies dissolved, releasing carbon that was in effect 鈥榯rapped鈥� there for thousands of years. Their results are reported in two separate papers in Nature Communications.

探花直播ability to reconstruct past climate change is an important part of understanding why the climate of today behaves the way it does. It also helps to predict how the planet might respond to changes made by humans, such as the continuing emission of large quantities of CO₂ into the atmosphere.

探花直播world鈥檚 oceans work like a giant conveyer belt, transporting heat, nutrients and gases around the globe. In today鈥檚 oceans, warmer waters travel northwards along currents such as the Gulf Stream from the equatorial regions towards the pole, becoming saltier, colder and denser as they go, causing them to sink to the bottom. These deep waters flow into the ocean basins, eventually ending up in the Southern Ocean or the North Pacific Ocean. A complete loop can take as long as 1000 years.

鈥淒uring the period we鈥檙e looking at, large amounts of carbon were likely transported from the surface ocean to the deep ocean by organisms as they died, sunk and dissolved,鈥� said Emma Freeman, the lead author of one of the papers. 鈥淭his process released the carbon the organisms contained into the deep ocean waters, where it was trapped for thousands of years, due to the very slow circulation.鈥�

Freeman and her co-authors used radiocarbon dating, a technique that is more commonly used by archaeologists, in order to determine how old the water was in different parts of the ocean. Using the radiocarbon information from tiny shells of foraminifera, they found that carbon was stored in the slowly-circulating deep ocean.

In a separate study led by Jake Howe, also from Cambridge鈥檚 Department of Earth Sciences, researchers studied the neodymium isotopes contained in the foraminifera shells, a method which works like a dye tracer, and came to a similar conclusion about the amount of carbon the ocean was able to store.

鈥淲e found that during the peak of the last ice age, the deep Atlantic Ocean was filled not just with southern-sourced waters as previously thought, but with northern-sourced waters as well,鈥� said Howe.

What was previously interpreted to be a layer of southern-sourced water in the deep Atlantic during the last ice age was in fact shown to be a mixture of slowly circulating northern- and southern-sourced waters with a large amount of carbon stored in it.

鈥淥ur research looks at a time when the world was much colder than it is now, but it鈥檚 still important for understanding the effects of changing ocean circulation,鈥� said Freeman. 鈥淲e need to understand the dynamics of the ocean in order to know how it can be affected by a changing climate.鈥�

探花直播research was funded in part by the Natural Environment Research Council (NERC), the Royal Society and the Isaac Newton Trust.

Reference:
Jacob Howe et al. 鈥�North Atlantic Deep Water Production during the Last Glacial Maximum.鈥� Nature Communications (2016): DOI: 10.1038/ncomms11765

Emma Freeman et al. 鈥�Radiocarbon evidence for enhanced respired carbon storage in the Atlantic at the Last Glacial Maximum.鈥� Nature Communications (2016). DOI: 10.1038/ncomms11998

探花直播way the ocean transported heat, nutrients and carbon dioxide at the peak of the last ice age, about 20,000 years ago, is significantly different than what has previously been suggested, according to two new studies. 探花直播findings suggest that the colder ocean circulated at a very slow rate, which enabled it to store much more carbon for much longer than the modern ocean.

We need to understand the dynamics of the ocean in order to know how it can be affected by a changing climate.

Emma Freeman

Psammophile

Foraminifera "Star sand" Hatoma Island - Japan

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Increase in volcanic eruptions at the end of the ice age caused by melting ice caps and glacial erosion

sc604 — Tue, 02 Feb 2016 06:00:00 +0000

探花直播combination of erosion and melting ice caps led to a massive increase in volcanic activity at the end of the last ice age, according to new research. As the climate warmed, the ice caps melted, decreasing the pressure on the Earth鈥檚 mantle, leading to an increase in both magma production and volcanic eruptions. 探花直播researchers, led by the 探花直播 of Cambridge, have found that erosion also played a major role in the process, and may have contributed to an increase in atmospheric carbon dioxide levels.

鈥淚t鈥檚 been established that melting ice caps and volcanic activity are linked 鈥� but what we鈥檝e found is that erosion also plays a key role in the cycle,鈥� said Dr Pietro Sternai of Cambridge鈥檚 Department of Earth Sciences, the paper鈥檚 lead author, who is also a member of Caltech鈥檚 Division of Geological and Planetary Science. 鈥淧revious attempts to model the huge increase in atmospheric CO₂ at the end of the last ice age failed to account for the role of erosion, meaning that CO₂ levels may have been seriously underestimated.鈥�

Using numerical simulations, which modelled various different features such as ice caps and glacial erosion rates, Sternai and his colleagues from the 探花直播 of Geneva and ETH Zurich found that erosion is just as important as melting ice in driving the increase in magma production and subsequent volcanic activity. 探花直播results are published in the journal Geophysical Research Letters.

Although the researchers caution not to draw too strong a link between anthropogenic (human-caused) climate change and increased volcanic activity as the timescales are very different, since we now live in a period where the ice caps are being melted by climate change, they say that the same mechanism will likely work at shorter timescales as well.

Over the past million years, the Earth has gone back and forth between ice ages, or glacial periods, and interglacial periods, with each period lasting for roughly 100,000 years. During the interglacial periods, such as the one we live in today, volcanic activity is much higher, as the lack of pressure provided by the ice caps means that volcanoes are freer to erupt. But in the transition from an ice age to an interglacial period, the rates of erosion also increase, especially in mountain ranges where volcanoes tend to cluster.

Glaciers are considered to be the most erosive force on Earth, and as they melt, the ground beneath is eroded by as much as ten centimetres per year, further decreasing the pressure on the volcano and increasing the likelihood of an eruption. A decrease in pressure enhances the production of magma at depth, since rocks held at lower pressure tend to melt at lower temperatures.

When volcanoes erupt, they release more carbon dioxide into the atmosphere, creating a cycle that speeds up the warming process. Previous models that attempted to explain the increase in atmospheric CO₂ during the end of the last ice age accounted for the role of deglaciation in increasing volcanic activity, but did not account for erosion, meaning that CO₂ levels may have been significantly underestimated.

A typical ice age lasting 100,000 years can be characterised into periods of advancing and retreating ice 鈥� the ice grows for 80,000 years, but it only takes 20,000 years for that ice to melt.

鈥淭here are several factors that contribute to climate warming and cooling trends, and many of them are related to the Earth鈥檚 orbital parameters,鈥� said Sternai. 鈥淏ut we know that much faster warming that cooling can鈥檛 be caused solely by changes in the Earth鈥檚 orbit 鈥� it must be, at least to some extent, related to something within the Earth system itself. Erosion, by contributing to unload the Earth鈥檚 surface and enhance volcanic CO₂ emissions, may be the missing factor required to explain such persistent climate asymmetry.鈥�

Reference:
Pietro Sternai et al. 鈥�Deglaciation and glacial erosion: a joint control on magma productivity by continental unloading.鈥� Geophysical Research Letters (2016). DOI: 10.1002/2015GL067285

鈥婭nset image:聽3D model simulation of a glaciation on the Villarrica Volcano (Chile). Credit: Pietro Sternai

Researchers have found that glacial erosion and melting ice caps both played a key role in driving the observed global increase in volcanic activity at the end of the last ice age.聽

It鈥檚 been established that melting ice caps and volcanic activity are linked 鈥� but what we鈥檝e found is that erosion also plays a key role in the cycle.

Pietro Sternai

Matthew.landry at English Wikipedia

Arenal Volcano in November 2006

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Melting of massive ice 鈥榣id鈥� resulted in huge release of CO2 at the end of the ice age

sc604 — Mon, 04 Jan 2016 20:00:00 +0000

A new study reconstructing conditions at the end of the last ice age suggests that as the Antarctic sea ice melted, massive amounts of carbon dioxide that had been trapped in the ocean were released into the atmosphere.

探花直播study includes the first detailed reconstruction of the Southern Ocean density of the period and identified how it changed as the Earth warmed. It suggests a massive reorganisation of ocean temperature and salinity, but finds that this was not the driver of increased concentration of carbon dioxide in the atmosphere. 探花直播study, led by researchers from the 探花直播 of Cambridge, is published in the journal Proceedings of the National Academy of Sciences.

探花直播ocean is made up of different layers of varying densities and chemical compositions. During the last ice age, it was thought that the deepest part of the ocean was made up of very salty, dense water, which was capable of trapping a lot of CO₂. Scientists believed that a decrease in the density of this deep water resulted in the release of CO₂ from the deep ocean to the atmosphere.

However, the new findings suggest that although a decrease in the density of the deep ocean did occur, it happened much later than the rise in atmospheric CO₂, suggesting that other mechanisms must be responsible for the release of CO₂ from the oceans at the end of the last ice age.聽

鈥淲e set out to test the idea that a decrease in ocean density resulted in a rise in CO₂ by reconstructing how it changed across time periods when the Earth was warming,鈥� said the paper鈥檚 lead author Jenny Roberts, a PhD student in Cambridge鈥檚 Department of Earth Sciences who is also a member of the British Antarctic Survey. 鈥淗owever what we found was not what we were expecting to see.鈥�

In order to determine how the oceans have changed over time and to identify what might have caused the massive release of CO₂, the researchers studied the chemical composition of microscopic shelled animals that have been buried deep in ocean sediment since the end of the ice age. Like layers of snow, the shells of these tiny animals, known as foraminifera, contain clues about what the ocean was like while they were alive, allowing the researchers to reconstruct how the ocean changed as the ice age was ending.

They found that during the cold glacial periods, the deepest water was significantly denser than it is today. However, what was unexpected was the timing of the reduction in the deep ocean density, which happened some 5,000 years after the initial increase in CO₂, meaning that the density decrease couldn鈥檛 be responsible for releasing CO₂ to the atmosphere.

鈥淏efore this study there were these two observations, the first was that glacial deep water was really salty and dense, and the second that it also contained a lot of CO₂, and the community put two and two together and said these two observations must be linked,鈥� said Roberts. 鈥淏ut it was only through doing our study, and looking at the change in both density and CO₂ across the deglaciation, that we found they actually weren鈥檛 linked. This surprised us all.鈥�

Through examination of the shells, the researchers found that changes in CO₂ and density are not nearly as tightly linked as previously thought, suggesting something else must be causing CO₂ to be released from the ocean.

Like a bottle of wine with a cork, sea ice can prevent CO₂-rich water from releasing its CO₂ to the atmosphere. 探花直播Southern Ocean is a key area of exchange of CO₂ between the ocean and atmosphere. 探花直播expansion of sea ice during the last ice age acted as a 鈥榣id鈥� on the Southern Ocean, preventing CO₂ from escaping. 探花直播researchers suggest that the retreat of this sea ice lid at the end of the last ice age uncorked this 'vintage' CO₂, resulting in an increase in carbon dioxide in the atmosphere. 聽

鈥淎lthough conditions at the end of the last ice age were very different to today, this study highlights the importance that dynamic features such as sea ice have on regulating the climate system, and emphasises the need for improved understanding and prediction as we head into our ever warming world,鈥� said Roberts.聽

Reference:
Roberts, J. et. al. 鈥�Evolution of South Atlantic density and chemical stratification across the last deglaciation.鈥� PNAS (2016). DOI: 10.1073/pnas.1511252113

聽

A new study of how the structure of the ocean has changed since the end of the last ice age suggest that the melting of a vast 鈥榣id鈥� of sea ice caused the release of huge amounts of carbon dioxide into the atmosphere.

Although conditions at the end of the last ice age were very different to today, this study highlights the importance that dynamic features such as sea ice have on regulating the climate system.

Jenny Roberts

Foraminifera

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

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鈥楩ourth strand鈥� of European ancestry originated with hunter-gatherers isolated by Ice Age

fpjl2 — Mon, 16 Nov 2015 10:33:13 +0000

探花直播first sequencing of ancient genomes extracted from human remains that date back to the Late Upper Palaeolithic period over 13,000 years ago has revealed a previously unknown 鈥渇ourth strand鈥� of ancient European ancestry.

This new lineage stems from populations of hunter-gatherers that split from western hunter-gatherers shortly after the 鈥榦ut of Africa鈥� expansion some 45,000 years ago and went on to settle in the Caucasus region, where southern Russia meets Georgia today.

Here these hunter-gatherers largely remained for millennia, becoming increasingly isolated as the Ice Age culminated in the last 鈥楪lacial Maximum鈥� some 25,000 years ago, which they weathered in the relative shelter of the Caucasus mountains until eventual thawing allowed movement and brought them into contact with other populations, likely from further east.

This led to a genetic mixture that resulted in the Yamnaya culture: horse-borne Steppe herders that swept into Western Europe around 5,000 years ago, arguably heralding the start of the Bronze Age and bringing with them metallurgy and animal herding skills, along with the Caucasus hunter-gatherer strand of ancestral DNA 鈥� now present in almost all populations from the European continent.

探花直播research was conducted by an international team led by scientists from Cambridge 探花直播, Trinity College Dublin and 探花直播 College Dublin. 探花直播findings are published today in the journal Nature Communications.聽聽聽聽聽聽聽

鈥� 探花直播question of where the Yamnaya come from has been something of a mystery up to now,鈥� said one of the lead senior authors Dr Andrea Manica, from Cambridge鈥檚 Department of Zoology.

鈥淲e can now answer that as we鈥檝e found that their genetic make-up is a mix of Eastern European hunter-gatherers and a population from this pocket of Caucasus hunter-gatherers who weathered much of the last Ice Age in apparent isolation. This Caucasus pocket is the fourth major strand of ancient European ancestry, one that we were unaware of until now,鈥� he said聽聽聽

Professor Daniel Bradley, leader of the Trinity team, said: 鈥淭his is a major new piece in the human ancestry jigsaw, the influence of which is now present within almost all populations from the European continent and many beyond.鈥�

Previously, ancient Eurasian genomes had revealed three ancestral populations that contributed to contemporary Europeans in varying degrees, says Manica.

Following the 鈥榦ut of Africa鈥� expansion, some hunter-gatherer populations migrated north-west, eventually colonising much of Europe from Spain to Hungary, while other populations settled around the eastern Mediterranean and Levant, where they would develop agriculture around 10,000 years ago. These early farmers then expanded into and colonised Europe.聽聽

Lastly, at the start of the Bronze Age around 5,000 years ago, there was a wave of migration from central Eurasia into Western Europe 鈥� the Yamnaya.

However, the sequencing of ancient DNA recovered from two separate burials in Western Georgia 鈥� one over 13,000 years old, the other almost 10,000 years old 鈥� has enabled scientists to reveal that the Yamnaya owed half their ancestry to previously unknown and genetically distinct hunter-gatherer sources: the fourth strand.

By reading the DNA, the researchers were able to show that the lineage of this fourth Caucasus hunter-gatherer strand diverged from the western hunter-gatherers just after the expansion of anatomically modern humans into Europe from Africa.聽聽

探花直播Caucasus hunter-gatherer genome showed a continued mixture with the ancestors of the early farmers in the Levant area, which Manica says makes sense given the relative proximity. This ends, however, around 25,000 years ago 鈥� just before the time of the last glacial maximum, or peak Ice Age.

At this point, Caucasus hunter-gatherer populations shrink as the genes homogenise, a sign of breeding between those with increasingly similar DNA. This doesn鈥檛 change for thousands of years as these populations remain in apparent isolation in the shelter of the mountains 鈥� possibly cut off from other major ancestral populations for as long as 15,000 years 鈥� until migrations began again as the Glacial Maximum recedes, and the Yamnaya culture ultimately emerges.聽

鈥淲e knew that the Yamnaya had this big genetic component that we couldn鈥檛 place, and we can now see it was this ancient lineage hiding in the Caucasus during the last Ice Age,鈥� said Manica.

While the Caucasus hunter-gatherer ancestry would eventually be carried west by the Yamnaya, the researchers found it also had a significant influence further east. A similar population must have migrated into South Asia at some point, says Eppie Jones, a PhD student from Trinity College who is the first author of the paper.

鈥淚ndia is a complete mix of Asian and European genetic components. 探花直播Caucasus hunter-gatherer ancestry is the best match we鈥檝e found for the European genetic component found right across modern Indian populations,鈥� Jones said. Researchers say this strand of ancestry may have flowed into the region with the bringers of Indo-Aryan languages.聽聽聽

探花直播widespread nature of the Caucasus hunter-gatherer ancestry following its long isolation makes sense geographically, says Professor Ron Pinhasi, a lead senior author from 探花直播 College Dublin. 鈥� 探花直播Caucasus region sits almost at a crossroads of the Eurasian landmass, with arguably the most sensible migration routes both west and east in the vicinity.鈥�

He added: 鈥� 探花直播sequencing of genomes from this key region will have a major impact on the fields of palaeogeneomics and human evolution in Eurasia, as it bridges a major geographic gap in our knowledge.鈥�

David Lordkipanidze, Director of the Georgian National Museum and co-author of the paper,聽said: 鈥淭his is the first sequence from Georgia 鈥� I am sure soon we will get more palaeogenetic information from our rich collections of fossils.鈥�

Inset image:聽the view from the Satsurblia cave in Western Georgia, where a human right temporal bone dating from over 13,000 years ago was discovered. DNA extracted from this bone was used in the new research.

Reference:
E.R. Jones聽et. al. 鈥�Upper Palaeolithic genomes reveal deep roots of modern Eurasians.鈥� Nature Communications (2015). DOI:聽10.1038/ncomms9912

Populations of hunter-gatherers weathered Ice Age in apparent isolation in Caucasus mountain region for millennia, later mixing with other ancestral populations, from which emerged the Yamnaya culture that would bring this Caucasus hunter-gatherer lineage to Western Europe.

This Caucasus pocket is the fourth major strand of ancient European ancestry, one that we were unaware of until now

Andrea Manica

Eppie Jones

DNA was extracted from the molar teeth of this skeleton, dating from almost 10,000 years ago and found in the Kotias Klde rockshelter in Western Georgia.

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

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