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Massive amounts of carbon dioxide released from the deep ocean brought an end to the last ice age, according to new research.

A study examining fluctuations in ocean acidity recorded in the shells of ancient marine animals has shown how levels of carbon dioxide soared around 16,000 to 7,500 years ago.

The scientists behind the research found the gas appears to have been released from hot spots in the Southern Atlantic Ocean and eastern equatorial Pacific Ocean, carried to the surface by currents welling up from the deep ocean. 

Carbon dioxide from the deep sea may have led glaciers, like the one above, melting at the end of the ice age

They say this release of carbon dioxide from where it was trapped in the deep ocean is likely to have played a major role in the warming that lead to the melting of the ice sheets that covered much of the world.

The findings help to provide new clues about how the world was transformed from being largely locked in ice to the milder climate that exists today.

However, it is still unclear exactly what triggered the release of the gas from the ocean floor in the first place.

Researchers claim that it could also provide insight into how the oceans can affect the climate.

Dr Miguel Martinez-Boti, a paleoceanographer who led the study at the University of Southampton, said: 'The magnitude and rapidity of the swings in atmospheric CO2 across the ice age cycles suggests that changes in ocean carbon storage are important drivers of natural atmospheric CO2 variations.

'Our findings support the theory that a series of processes operating in the southernmost sector of the Atlantic, Pacific and Indian Oceans, a region known as the 'Southern Ocean', changed the amount of carbon stored in the deep-sea.

'While a reduction in communication between the deep-sea and the atmosphere in this region potentially locks carbon away from the atmosphere into the abyss during ice ages, the opposite occurs during warm interglacial periods.'

The study, which is published in the journal Nature, examined the levels of boron isotopes in the fossils of microscopic plankton obtained from deep sea drilling samples.

This allowed them to calculate the acidity of the ocean the plankton lived in at the time - something that is affected by astmospheric carbon dioxide levels.

They found that around 16,000 to 7,500 years ago the carbon dioxide levels in surface water of the oceans southern Atlantic and eastern equatorial Pacific Ocean increased signifcantly.

The scientists studied the isotope levels in the shells of fossilised plankton like Globigerina bulloides above

This graph shows how dissolved carbon dioxide levels have changed from the ice age (blue dot) to the end of the ice age (red dots). EEP denotes the equatorial Pacific Ocean, SA is the South Atlantic Ocean. The solid lines show a various modern data for carbon dioxide levels found in the the world's oceans

The surface waters at these locations are known to come from water in the deep ocean upwelling.

Atmospheric carbon dioxide levels are known to have increased at around this time from 185 parts per million but then increased to around 280 parts per million.

This, say the scientists, is because the carbon dioxide welling up in water from the deep ocean was being released into the atmosphere.

This would have helped to warm the climate and cause the ice trapped on the land in glaciers to melt.

Dr Gavin Foster, a reader in geochemistry at the University of Southampton who was a co-author in the study, said the findings could help to explain how the ocean is effecting the climate today.

Climate change scientists estimate that the deep oceans have been absorbing much of the carbon dioxide released into the atmosphere by human activity.

The above map shows modern annual average carbon dioxide levels in the world's oceans and the locations where the core samples containing the fossilised plankton were obtained that the researchers studied

This has been used to partly explain the 'pause' in global warming that has occured over the past decade.

Dr Foster said: 'Just like the way the oceans have stored around 30% of humanity's fossil fuel emissions over the last 100 years or so, our new data confirms that natural variations in atmospheric CO2 between ice ages and warm interglacials are driven largely by changes in the amount of carbon stored in our oceans.

'While our results support a primary role for the Southern Ocean processes in these natural cycles, we don't yet know the full story and other processes operating in other parts of the ocean, such as the North Pacific, may have an additional role to play.'

Dr Katherine Allen, from the department of marine and coastal sciences at Rutgers University in New Jersey, said more work was needed to understand what caused these changes in carbon dioxide in the ocean.

She said: 'Somehow, during the descent into the last ice age, the CO2 balance between ocean and atmosphere was tipped in favour of the ocean. After the ice age, CO2 levels rose again, implying that the balance must have tipped back.

'These exciting hints regarding ocean–atmosphere carbon exchange raise further questions.

'Additional records are now needed to cover the other half of the glacial cycle: the descent into the ice age.'