New Scientist
Image: NASA: 2Explore
A warming world could slow the circulation of the Atlantic Ocean, potentially triggering African droughts and more rapid sea level rise around Europe. If it happens, it won’t be the first time the Atlantic has been disrupted during a warm period.
Water in the Atlantic is constantly on the move. In the icy north, cool and dense surface water sinks and flows south, forming the North Atlantic Deep Water. The NADW then encourages warm surface water in the south to flow north, creating the Gulf Stream.
In theory, this “conveyor belt” could weaken as a result of climate change. A hugely exaggerated version of this proposal was the premise for the film The Day After Tomorrow. But until now the evidence from warmer periods in Earth’s past suggested that temperature rises would not affect the circulation. A new study indicates otherwise.
Eirik Vinje Galaasen at the University of Bergen, Norway, and his colleagues looked at deep-sea sediments from a site off the southern tip of Greenland. Sediment builds up so rapidly there that 3.5 centimetres are deposited each century, meaning that important but short-lived climate shifts show up clearly.
The team focused on sediments from the last interglacial, a warm period between 130,000 and 115,000 years ago, before the last ice age. The ratio of carbon isotopes in fossilised microbes from this time showed several sudden shifts, each indicating an abrupt change in environmental conditions and probably in the NADW.
Some members of the team had seen a similar isotope ratio shift before, in marine sediments from 8200 years ago. In 2007 they showed that the shift occurred when a vast North American lake burst
, sending 100,000 cubic kilometres of fresh water into the North Atlantic, and briefly reducing formation of the NADW. Galaasen says NADW reductions were common in the last interglacial, when the North Atlantic was warmer. Read more on newscientist.com…
