Oceans burp CO2 into the atmosphere


Fossilized remains of ancient deep-sea corals offer a new understanding of the effect the ocean has on CO2 levels


Fossilized remains of ancient deep-sea corals can act as time machines that provide new knowledge about the effect of the ocean on increasing CO2 levels.

Corals and fossils to understand the oceans

This process helped end the last ice age, but the cause of this increase in CO2 has baffled scientists for decades. Using geochemical fossil coral fingerprints, an international team of scientists has found new evidence that this increase in CO2 was linked to extremely rapid changes in ocean circulation around Antarctica.

The team collected fossil remains of deep-sea corals that lived thousands of meters below the waves. By studying the radioactive disintegration of the small amounts of uranium found in these skeletons, they identified corals that grew at the end of the Ice Age about 15,000 years ago.

Taking additional geochemical footprints of these specimens, including radiocarbon measurements, allowed the team to reconstruct changes in ocean circulation and compare them to changes in the global climate at an unprecedented time resolution. The results were published in Science Advances.

Professor Laura Robinson, a professor of geochemistry at the University of Bristol's Faculty of Earth Sciences, who led the research team, said: "Data show that circulation in the ocean depths can change surprisingly quickly and that this can quickly release CO2 into the atmosphere."

Dr James Rae of St Andrew's School of Environmental and Earth Sciences added: "Corals act as a time machine, allowing us to see changes in ocean circulation that occurred thousands of years ago.

"They show that the ocean around Antarctica can suddenly change its circulation to release CO2 belching into the atmosphere."

Scientists suspect that the Southern Ocean played an important role in the end of the last ice age and the team's findings add weight to this idea.

Dr Tao Li of Nanjing University, lead author of the new study, said: "There is no doubt that Southern Ocean processes must have played a critical role in these rapid climate changes and fossil corals provide the only possible way to examine southern ocean processes within these timeframes."

The greenhouse effect killed most of life in the ice age

In another study published in Nature Geoscience this week, the same team highlighted recent speculation that the overall increase in CO2 at the end of the ice age may have been related to the release of geological carbon from deep-sea sediments.

Andrea Burke, of st Andrew's School of Earth and Environment Sciences, added: "There have been some suggestions that carbon deposits deep in the sea mud could bubble and add CO2 to the ocean and atmosphere, but we found no evidence of this in our coral samples."

Dr. Tianyu Chen of Nanjing University said:

"Our robust radiocarbon reconstructions at intermediate depths create powerful limitations in mixing between the depths and upper layers of the ocean, which is important for modeling changes in carbon circulation and cycle during the last end of the ice age."

James Rae added: "Although the increase in CO2 at the end of the ice age was dramatic in geological terms, the recent increase in CO2 due to human activity is much greater and faster. What the climate system will do in response is pretty scary."