Ice age carbon hid in the deep Atlantic

Benthic Foraminifera fossils, 0.3 mm across
A huge reservoir of carbon developed in the deep Atlantic Ocean during the last ice age, according to research led by the Australian National University (ANU).

Within 10,000 years the sea level dropped 60 metres, and the atmosphere lost 60 gigatonnes of carbon, equivalent to a drop of about 30 parts per million of CO2.

And as the study reveals, as ocean currents changed over 10,000 years, an extra 50 gigatonnes of carbon was stored at the bottom of the Atlantic Ocean.

The research team from ANU, University of New South Wales, Chinese Academy of Sciences, and several other partner institutions 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 CO2 in the ocean more than three kilometres under the surface.

The team found that this change in CO2 matched closely with changes in the ocean circulation, which caused a large body of carbon-laden water in the southern Atlantic to spread northward and upward.

The researchers believe that these insights into past climate change events will help scientists better understand the complex interactions between the atmosphere and the ocean that may occur with the current rise in atmospheric CO2 levels.

In the past 150 years, atmospheric CO2 has risen from below 300 parts per million to 400 parts per million.

The study was published in the journal Nature Geoscience.

Story based on a media release provided by the Australian National University