Warm Gulf Stream Kept Flowing Even During the Last Ice Age

It turns out that the Gulf Stream, the warm North Atlantic current that flows into the Nordic seas, wasn't all that affected by the last Ice Age. Scientists have found that this current continued to flow, despite previous theories that it actually ceased to function.

"It is widely thought that during cold periods of the last Ice Age the warm Atlantic water had stopped its flow into the Nordic Seas," said Mohamed Ezat, one of the researchers, in a news release. "The results of our recent study suggest that the Atlantic water never ceased to flow into the Nordic Seas during the glacial period."

In order to learn a bit more about this glacial period, the researchers examined the shells of single celled organisms, called benthic foraminifera. When these creatures die, they become part of the ocean sediment; yet the conditions in which they lived, including ocean temperatures, are recorded in the chemistry of their shells.

"The amount of magnesium in the shells of specific species of foraminifera depends primarily on temperature," said Ezat. "By measuring the ratio of magnesium to calcium we can estimate changes in temperature. We were lucky to find a continuous record of well-preserved benthic species for the analyses."

It turns out that while air temperatures became colder, the deep ocean water became warmer.  The ice sheets across Scandinavia and North America produced a large amount of melt water from icebergs. This meant that the surface water couldn't sink, which formed an icy "seal" over the Atlantic water beneath.

"Warm water was there, but deep under the cold icy surface," said Ezat. "So the climate experience was colder, as the atmospheric records from Greenland ice cores show. But what eventually happened, is that the warm water reached a critical point, surged upwards to the surface, and contributed to the abrupt warming of the surface water and atmosphere."

The findings aren't just relevant to the past climate, though. It also helps scientists understand what may happen to our oceans if Greenland and Antarctica melt in the future-something that may very well happen with rising temperatures.

The findings are published in the journal Geology.