Ancient corals reveal secrets of the deep
Ancient deep-sea corals reveal that ocean currents propelled a huge rise in carbon dioxide levels 15,000 years ago.
Fossilised remains of coral, discovered at the bottom of Antarctica's Southern Ocean, provide evidence that rapid changes in ocean cir culation can boost CO 2 in the atmosphere, a new study has revealed.
Rising CO2 levels are known to have ended the Last Glacial Period around 15,000 years ago, but why this happened has remained a mystery until now.
Study co -author Dr James Rae, of the University of St Andrews, said: "The corals act as a time machine, allowing us to see changes in ocean circulation that happened thousands of years ago.
"They show that the ocean around Antarctica can suddenly switch its circulation to deliver burps of CO2 to the atmosphere."
Fossil remains of deep -sea corals, which lived thousands of metres beneath the waves, were collected by the scientists.
Radioactive decay of tiny amounts of uranium found in the coral skeletons helped determine which fossils lived at the end of the last ice age.
Next, a process known as geochemical fingerprinting, which measures radiocarbon, was used to map changes in the ocean's circulation.
Co-author Dr Tianyu Chen, of Nanjing University in China, said :" Our robust reconstructions of radiocarbon at intermediate depths yields powerful constraints on mixing between the deep and upper ocean, which is important for modelling changes in circulation and carbon cycle during the last ice age termination."
These current conversions were then compared with changes to the global climate at an unprecedented time resolution. Professor Laura Robinson said: "The data show that deep ocean circulation can change surprisingly rapidly, and that this can rapidly release CO2 to the atmosphere."
Scientists have suspected the Southern Ocean had a big part to play in ending the last ice age for some time.
Co-author Dr Tao Li, also of Nanjing University, said: "There is no doubt that Southern Ocean processes must have played a critical role in these rapid climate shifts and the fossil corals provide the only possible way to examine Southern Ocean processes on these timescales."
Another theory, that the CO2 was released from deep sea sediments at the end of the last ice age, was ruled out by the scientists in another study published in the journal Nature Geoscience this week.
Co-author Andrea Burke, also of the University of St Andrews, said: "There have been some suggestions that reservoirs of carbon deep in marine mud might bubble up and add CO2 to the ocean and the atmosphere, but we found no evidence of this in our coral samples."
Dr R ae said: "Although the rise in CO2 at the end of the ice age was dramatic in geological terms, the recent rise in CO 2 due to human activity is much bigger and faster. What the climate system will do in response is pretty scary."