Scientists Detect Huge Carbon 'Burp' That Helped End Last Ice Age

Scientists have found the possible source of a huge carbon dioxide 'burp' that happened some 18,000 years ago and which helped to end the last ice age.

The results provide the first concrete evidence that carbon dioxide (CO2) was more efficiently locked away in the deep ocean during the last ice age, turning the deep sea into a more 'stagnant' carbon repository -- something scientists have long suspected but lacked data to support.

Working on a marine sediment core recovered from the Southern Ocean floor between Antarctica and South Africa, the international team led by Dr Luke Skinner of the University of Cambridge radiocarbon dated shells left behind by tiny marine creatures called foraminifera (forams for short).

By measuring how much carbon-14 (14C) was in the bottom-dwelling forams' shells, and comparing this with the amount of 14C in the atmosphere at the time, they were able to work out how long the CO2 had been locked in the ocean.

By linking their marine core to the Antarctic ice-cores using the temperature signal recorded in both archives, the team were also able compare their results directly with the ice-core record of past atmospheric CO2 variability.

According to Dr Skinner: "Our results show that during the last ice age, around 20,000 years ago, carbon dioxide dissolved in the deep water circulating around Antarctica was locked away for much longer than today. If enough of the deep ocean behaved in the same way, this could help to explain how ocean mixing processes lock up more carbon dioxide during glacial periods."

Throughout the past two million years (the Quaternary), the Earth has alternated between ice ages and warmer interglacials. These changes are mainly driven by alterations in the Earth's orbit around the sun (the Milankovic theory).

But changes in Earth's orbit could only have acted as the 'pace-maker of the ice ages' with help from large, positive feedbacks that turned this solar 'nudge' into a significant global energy imbalance.

Changes in atmospheric CO2 were one of the most important of these positive feedbacks, but what drove these changes in CO2 has remained uncertain.

Because the ocean is a large, dynamic reservoir of carbon, it has long been suspected that changes in ocean circulation must have played a major role in motivating these large changes in CO2. In addition, the Southern Ocean around Antarctica is expected to have been an important centre of action, because this is where deep water can be lifted up to the sea surface and 'exhale' its CO2 to the atmosphere.

Scientists think more CO2 was locked up in the deep ocean during ice ages, and that pulses or 'burps' of CO2 from the deep Southern Ocean helped trigger a global thaw every 100,000 years or so. The size of these pulses was roughly equivalent to the change in CO2 experienced since the start of the industrial revolution.

If this theory is correct, we would expect to see large transfers of carbon from the ocean to the atmosphere at the end of each ice age. This should be most obvious in the relative concentrations of radiocarbon (14C) in the ocean and atmosphere; 14C decays over time and so the longer carbon is locked up in the deep sea, the less 14C it contains.

As well as providing evidence for rapid release of carbon dioxide during deglaciation, the research illustrates how the ocean circulation can change significantly over a relatively short space of time.

"Our findings underline the fact that the ocean is a large and dynamic carbon pool. This has implications for proposals to pump carbon dioxide into the deep sea as a way of tackling climate change, for example. Such carbon dioxide would eventually come back up to the surface, and the question of how long it would take would depend on the state of the ocean circulation, as illustrated by the last deglaciation," says Dr Skinner.

The results are published in Science.

The research was funded by the Royal Society and the Natural Environment Research Council.
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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of Cambridge.

Journal Reference:
Skinner, L.C., Fallon, S. Waelbroeck, C., Michel, E. and Barker S. Ventilation of the deep Southern Ocean and deglacial CO2 rise. Science, 2010; 328 (5982): 1147-1151 DOI: 10.1126/science.1183627

Big Freeze Plunged Europe Into Ice Age in Months

New research shows that switching off the North Atlantic circulation can force the Northern hemisphere into a mini 'ice age' in a matter of months. Previous work has indicated that this process would take tens of years. (Credit: iStockphoto/Trevor Hunt)

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In the film The Day After Tomorrow, the world enters the icy grip of a new glacial period within the space of just a few weeks. Now new research shows that this scenario may not be so far from the truth after all.

William Patterson, from the University of Saskatchewan in Canada, and his colleagues have shown that switching off the North Atlantic circulation can force the Northern hemisphere into a mini 'ice age' in a matter of months. Previous work has indicated that this process would take tens of years.

Around 12,800 years ago the northern hemisphere was hit by a mini ice-age, known by scientists as the Younger Dryas, and nicknamed the 'Big Freeze', which lasted around 1300 years. Geological evidence shows that the Big Freeze was brought about by a sudden influx of freshwater, when the glacial Lake Agassiz in North America burst its banks and poured into the North Atlantic and Arctic Oceans. This vast pulse, a greater volume than all of North America's Great Lakes combined, diluted the North Atlantic conveyor belt and brought it to a halt.

Without the warming influence of this ocean circulation temperatures across the Northern hemisphere plummeted, ice sheets grew and human civilisation fell apart.

Previous evidence from Greenland ice cores has indicated that this sudden change in climate occurred over the space of a decade or so. Now new data shows that the change was amazingly abrupt, taking place over the course of a few months, or a year or two at most.

Patterson and his colleagues have created the highest resolution record of the 'Big Freeze' event to date, from a mud core taken from an ancient lake, Lough Monreach, in Ireland. Using a scalpel layers were sliced from the core, just 0.5mm thick, representing a time period of one to three months.

Carbon isotopes in each slice reveal how productive the lake was, while oxygen isotopes give a picture of temperature and rainfall. At the start of the 'Big Freeze' their new record shows that temperatures plummeted and lake productivity stopped over the course of just a few years. "It would be like taking Ireland today and moving it up to Svalbard, creating icy conditions in a very short period of time," says Patterson, who presented the findings at the European Science Foundation BOREAS conference on humans in the Arctic, in Rovaniemi, Finland.

Meanwhile, their isotope record from the end of the Big Freeze shows that it took around two centuries for the lake and climate to recover, rather than the abrupt decade or so that ice cores indicate. "This makes sense because it would take time for the ocean and atmospheric circulation to turn on again," says Patterson.

Looking ahead to the future Patterson says there is no reason why a 'Big Freeze' shouldn't happen again. "If the Greenland ice sheet melted suddenly it would be catastrophic," he says.

This study was part of a broad network of 38 individual research teams from Europe, Russia, Canada and the USA forming the European Science Foundation EUROCORES programme 'Histories from the North -- environments, movements, narratives' (BOREAS). This highly interdisciplinary initiative brought together scientists from a wide range of disciplines including humanities, social, medical, environmental and climate sciences.

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Adapted from materials provided by European Science Foundation.

When Did Humans Return After Last Ice Age?

Gough's Cave. (Credit: Copyright Natural History Museum)

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The Cheddar Gorge in Somerset was one of the first sites to be inhabited by humans when they returned to Britain near the end of the last Ice Age. According to new radio carbon dating by Oxford University researchers, outlined in the latest issue of Quaternary Science Review, humans were living in Gough's Cave 14,700 years ago.

A number of stone artefacts as well as human and animal bones from excavations, spread over more than 100 years, shed further light on the nature as well as the timing of people to the cave.

Technological advances have allowed researchers at Oxford University and London's Natural History Museum to date the bones more accurately. Previous radiocarbon dates suggested a wide span of occupation of within 1000-1500 years. The new dates show a much narrower range of dates, corresponding precisely to climate warming, providing evidence that the archaeological material in the cave could have accumulated over perhaps as little as two to three human generations, centred on 14,700 years ago.

Dr Tom Higham, Deputy Director of the Oxford Radiocarbon Accelerator Unit, commented: 'In the past, radiocarbon dates have often been influenced by contamination that modern techniques can remove much more effectively. The new results have transformed our understanding of this site because at last we have a chronology we can rely on and which we can link to climatic events here and in the wider world.'

Dr Roger Jacobi, of the British Museum and the Natural History Museum, who led the research, said: 'This is the biggest advance which we have made in understanding the story of the Palaeolithic use of this remarkable cave, and it is one which has implications for our understanding of many other British archaeological sites.'

Many of the human remains bear patterns of cutmarks, which have been interpreted as evidence of cannibalism. These were previously thought to have belonged to a more recent period of activity than that associated with the hunting of horses and red deer.

Professor Chris Stringer, Natural History Museum Palaeontologist, commented: ' We were puzzled that the human bones we excavated in Gough's Cave about 20 years ago, including those that may have been cannibalised, seemed to be up to a thousand years different in age. The new dating methods show instead that the butchery and consumption of both horses and humans occurred in a very short space of time, about 14,700 years ago. So as Europe rapidly defrosted, family groups probably followed herds of horses into Britain across grasslands where the North Sea is today.'

Further sites will be re-examined using the same approach to test whether humans returned to Britain at the time of climate warming or whether they came back before this period. More accurate dating might be possible through applying isotopic methods directly to the human teeth from the site, as well as to those of the prey animals, because this will allow a better assessment of whether the animals were hunted in a warmer or colder period. At present, the radiocarbon dates are not sufficiently precise enough to answer this key question. The work is part of the Ancient Human Occupation of Britain project, funded by the Leverhulme Trust.
Adapted from materials provided by University of Oxford.