The abnormally cold weather this winter is a result of a change in wind patterns. Typically, the westerly winds warmed by Atlantic surface ocean currents maintain temperatures in Europe but this year, cold northerly Arctic winds are creating a colder winter.
Scientists have suspected that more severe and longer-lasting cold intervals have been cause by changes to the circulation of the warm Atlantic ocean currents themselves. Now, a new study, published on January 14 in the journal Science, shows that these ocean circulation changes may be more dramatic than previously thought. The research was led by Cardiff University, with scientists from the UK and US.
The findings show that as the last ice age came to an end 10,000 to 20,000 years ago, the formation of deep water in the North-East Atlantic repeatedly switched on and off, causing the climate to warm and cool for centuries at a time.
Ocean circulation helps regulate global climate through the transport of heat carried by vast ocean currents which form the ‘great ocean conveyor belt.’ Part of this conveyor belt involves the sinking of water in the North-East Atlantic, a process that causes warm tropical waters to flow northwards in order to replace the sinking water. Europe is kept warmer by this process. A reduction in the rate at which deep water forms could cause widespread cooling of up to 10 degrees Celcius.
Lead author Dr David Thornalley, Cardiff School of Earth and Ocean Sciences, explains how the scientists studied changes in ocean circulation: “We retrieved ocean sediment cores from the seafloor of the Northeast Atlantic which contained the shells of small organisms. 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.”
The team found that every time deep water formation turned off, the Northeast Atlantic did not fill with water that sank locally. Instead it became inundated with water that originated from Antarctica and spread rapidly northwards. These results show that the Atlantic ocean is capable of radical changes in circulation on a timescale as short as only a few decades.
“These insights highlight just how dynamic and sensitive ocean circulation can be,” Thornalley said. “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.”
Copyright © 2011 by Marine Science Today, a publication of OceanLines LLC.