Scientists have long assumed that the long-lasting and severe cold spells in Europe that have taken place since the Last Glacial Maximum some 10,000 to 20,000 years ago have been the result of changes in the circulation of the Atlantic Ocean currents.
New research led by Cardiff University has now shown that ocean circulation changes may have been even more dramatic than previously assumed.
The new findings, which have been published in the latest edition of the journal Science, show that since the end of the Last Glacial Maximum the formation of deep water in the North-East Atlantic Ocean has repeatedly switched on and off, causing the climate to warm and cool for centuries at a time.
“We retrieved ocean sediment cores from the seafloor of the Northeast Atlantic which contained the shells of small organisms,” said lead author Dr David Thornalley, Cardiff School of Earth and Ocean Sciences, in explaining how the scientists studied changes in ocean circulation. “We used these shells to examine the past distribution of radiocarbon in the ocean. Radiocarbon is a radioactive form of carbon that acts like a natural stopwatch, timing how long it has been since water was last at the sea surface. This allows us to determine how quickly deep water was forming in the Northeast Atlantic at different times in the past.”
Deep water is the result of water cooling, increasing the density of the water and causing it to drop to deeper levels of the ocean. As part of the Great Conveyor Belt of the oceans, this sends cooler water down south and allows the warmer tropical waters to move north, affecting the atmospheric temperatures over Europe.
The team of scientists led by Thornalley found that each time deep water formation turned off, the North-East Atlantic did not fill with water that sank locally, but rather filled with water that had originally formed near Antarctica in the Southern Ocean which then spread rapidly northward.
These results show that the Atlantic Ocean is capable of radical changes in a very short amount of time, as small as a few decades.
“These insights highlight just how dynamic and sensitive ocean circulation can be,” said Dr Thornalley. “Whilst the circulation of the modern ocean is probably much more stable than it was at the end of the last Ice Age, and therefore much less likely to undergo such dramatic changes, it is important that we keep developing our understanding of the climate system and how it responds when given a push.”