Studies of deep-sea corals show that ocean currents did not cause a rise in carbon dioxide in the atmosphere.

Pioneering analysis of deep-sea corals has changed the idea that ocean currents helped increase atmospheric carbon dioxide over the past 11,000 years.

The research, led by the University of Bristol in the UK and Nanjing University in China, examined the history of ocean water to reveal a new interest in the history of ocean water.

Understanding the causes of the pre-industrial rise in carbon dioxide (CO₂) during the Holocene, which began 11,700 years ago, is a source of scientific controversy. Another theory suggests an increase in deep water with a high carbon content in the surface of the Southern Ocean, in other words a change in the surface circulation of the oceans, may have caused the release of oceanic gases into the atmosphere, although this is not all. he understood.

Lead author Tianyu Chen, Professor of Marine Geochemistry at the University of Nanjing and the University of Bristol, said: “Our research challenges assumptions about the role of oceans in climate change during the Holocene. We pave the way for a deeper understanding of the complex relationship between oceans and climate. of the Earth.

The Holocene, which followed the retreat of the ice sheets in the Northern Hemisphere, is the most recent epoch on Earth and has attracted the attention of scientists who study the Earth’s recent climate. The most important factor at this time is the rise in atmospheric CO₂ levels. Initially, at the beginning of the Holocene, CO₂ levels were about 260 parts per million by volume (ppmv). However, over the course of about 5,000 years it rose by 20 ppmv, equivalent to about 150 gigatons of CO.₂.

Corals are fascinating organisms, having thrived along the coast during the Holocene. An international team of researchers carefully recorded deep ocean data from the Drake Passage, which lies between South America and Antarctica, and the Reykjanes Ridge, south of Iceland, from this period. Corals live in deep waters stretching up to 1,900 meters within the Antarctic circumpolar waters and the North Atlantic Deep Water.

Surprisingly, the radiocarbon data indicated that oxygen levels in the surrounding Antarctic and North Atlantic Deep Water remained stable.

The results, published in Nature Geoscience, shows the long-term mixing of the polar ocean between surface and deep water, on a millennial scale, has not experienced significant disturbances. Therefore, it shows that the expansion of the North Atlantic and Southern Ocean alone did not cause the rise in CO emissions.₂ during the Holocene. Instead, the researchers think biogeochemical cycles that redistribute nutrients and carbon into oceans and land may have caused this rise.

Another co-author Dr. Joseph Stewart, Research Fellow in Geochemistry at the University of Bristol, said, “Because of the decay of radioactive isotopes within their bones, deep-sea corals have two ‘clocks’. Track the concentration of uranium-238 within corals slowly decay to thorium-230 allowing us to accurately assess their age by measuring the ratio of this isotope.

“The second clock, radiocarbon (carbon-14) also decays slowly, but it enters the ocean more through the atmosphere. Therefore, the radiocarbon-dated rocks tell us how long the deep water that has been exposed to radiocarbon has not been affected by the radiocarbon-rich. Using both ‘clocks’ together we were able to determine the amount of oxygen in the ocean during this important period.”

This study represents an important step forward in unraveling the relationship between ocean circulation, carbon cycling, and climate change during the Holocene. A detailed future understanding of natural and anthropogenic changes in carbon fluxes is necessary to better understand the carbon budget of the Holocene atmosphere.

Co-author Laura Robinson, Professor of Geochemistry at the University of Bristol, added, “These findings contribute to the increase of knowledge in this field and emphasize the need to further investigate the mechanism that prevents the biogeochemical cycle and the expansion of the ocean during the crisis. Holocene.”