CO2 in oceans said to have played role in ending last ice age

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Carbon dioxide from deep oceans is said to be responsible for ending the last ice age, a new research carried out by University of Southampton claims. The research, which gives insight into how oceans affect climate change, is published in journal Nature.

The study shows that carbon stored in an isolated reservoir deep in the Southern Ocean re-connected with the atmosphere, driving a rise in atmospheric CO2 and an increase in global temperatures.

Atmospheric CO2 levels fluctuate from about 185 parts-per-million (ppm), during ice ages, to around 280 ppm, during warmer periods like today (termed interglacials). The oceans currently contain approximately sixty times more carbon than the atmosphere and that carbon can exchange rapidly (from a geological perspective) between these two systems (atmosphere-ocean), researchers said.

Joint lead author Dr Miguel Martinez-Boti from the University of Southampton said that the magnitude and rapidity of the swings in atmospheric CO2 across the ice age cycles indicate that changes in ocean carbon storage are an important driver of natural atmospheric CO2 variations.

“We found that very high concentrations of dissolved CO2 in surface waters of the Southern Atlantic Ocean and the eastern equatorial Pacific coincided with the rises in atmospheric CO2 at the end of the last ice age, suggesting that these regions acted as sources of CO2 to the atmosphere,” said joint lead author Dr Gianluca Marino, from Australian National University (ANU).

“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,” said Marino, who was previously at Universitat Autonoma de Barcelona (UAB).

“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,” said Marino.

The international team studied the composition of the calcium carbonate shells of ancient marine organisms that inhabited the surface of the ocean thousands of years ago in order to trace its carbon content.

“Just like the way the oceans have stored around 30 per cent 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,” co-author Dr Gavin Foster from the University of Southampton added.