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How ice age carbon hid in the deep Atlantic

New research reported in Nature Geoscience

How ice age carbon hid in the deep Atlantic

New research, involving Dr David Thornalley (UCL Geography), published this week in Nature Geoscience has found that a huge reservoir of carbon developed in the deep Atlantic Ocean during the last ice age. As ocean currents changed over 10,000 years, an extra 50 gigatonnes of carbon became stored at the bottom of the Atlantic Ocean.

In this work, David collaborated with lead researcher Dr Jimin Yu of The Australian National University (ANU), who describes the change as a major climate transition period for the Earth:

“During 10,000 years the sea level fell by 60 metres, and the atmosphere lost 60 gigatonnes of carbon, equivalent to a drop of about 30 parts per million of carbon dioxide. This research helps us understand the fate and impact of that carbon.”

The research team studied the chemical makeup in fossils of tiny animals called benthic foraminifera that live in the deepest parts of the Atlantic Ocean. During the slide into an ice age, about 70,000 years ago, the ratio of boron to calcium in the fossils decreased, reflecting an increase in the amount of carbon dioxide in the ocean more than three kilometres below the surface.

It was found that these carbon dioxide changes closely matched changes in the ocean circulation. A large body of carbon-laden water in the Southern Atlantic, accumulated over hundreds of years from sinking dead plankton, spread northward and upward.

The research helps us understand the complex interactions between the atmosphere and the ocean that may be accompanying the current growth in atmospheric carbon dioxide, from around 300 to 400 parts per million in the past 150 years, blamed for global warming.

David explains, “To improve our understanding of climate change in the future we must look at what happened in the past.”.

The research is published in Nature Geoscience :



Illustration: During the transitions into a cold climate, carbon storage in the deep ocean lowers deep water pH and causes carbonate dissolution on the seafloor (dark colour). The chemical compositions of micro fossils helps quantify deep-sea carbon sequestration.


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