Researchers have found traces of an enormous freshwater flood in the Arctic region said to have triggered abrupt climate change thousands of years ago.
In a five-year study that culminated this year, scientists have found that freshwater from a melting glacier coursed through what is now Canada's Mackenzie River.
The freshwater disrupted the North Atlantic's deep-water current system, creating changes in weather patterns that triggered the Younger Dryas, a mini Ice Age that took place in the northern hemisphere following the last glacial period of the Quaternary Ice Age.
The Younger Dryas
Forty-five thousand years ago, the last major glacial period came to an end when the Earth's climate began to shift to a warmer interglacial state. However, a thousand years into the transition, the northern hemisphere returned to glacial conditions in a period called the Younger Dryas.
Named after the Dryas octopetala flower that thrived in the harsh environments of Europe at the time, the Younger Dryas came after a gradual global warming that took place over 1,000 years. This is according to oceanographer Lloyd Keigwin, lead author of the new study published in the journal Natural Geoscience.
For years, experts have debated the cause of the Younger Dryas. The popular theory is it was triggered by a sudden influx of fresh water coming from the melting glaciers and ice sheets of North America.
As the fresh water merged with the North Atlantic, it disrupted the deep-water current system called the Atlantic Meridional Overturning Circulation. The AMOC carries heat from the tropics to the North Atlantic, where it is released into the atmosphere.
Source Of Freshwater Flood
In 2013, Keigwin's team from WHOI, along with geologists and geophysicists at the University of California San Diego's Scripps Institution of Oceanography and the Oregon State University, sailed for the Beaufort Sea north of Alaska, Yukon, and the Northwestern Territories onboard the US Coast Guard Cutter Healy.
The goal was to look for proof of a freshwater flood at the place where the Mackenzie River empties into the Arctic Ocean. To accomplish this, the researchers collected cylindrical samples of sediments found on the eastern slopes of the Mackenzie River.
They then analyzed fossil planktons embedded in shells in the sediments, leading them to conclude that an abundance of glacial meltwater gushed through the Mackenzie River into the North Atlantic.
"The signature of oxygen isotopes recorded in foraminifera shells preserved in the sediment allowed us to fingerprint the source of the glacial lake discharge down the Mackenzie River 13,000 years ago," says co-principal investigator Neal Driscoll of Scripps Oceanography.
Implications For Current Climate Change Studies
The researchers plan to examine how much freshwater flowing to the North Atlantic was needed to set off an abrupt change in climate. They would also like to know how long it took for the freshwater flood to cause the Younger Dryas.
The insights that can be gleaned from a future study could help experts looking into the melting ice caps in Greenland and the warming of the Arctic region.
"In the long run, I think the findings from this paper will stimulate more research on how much fresh water is really necessary to cause a change in the system and weakening of the AMOC," Keigwin says.
In earlier research done by WHOI experts, they found that the AMOC has been weakening since the middle of the 19th century. It is currently at its weakest point in 1,600 years. If conditions persist, the researchers say it could cause major weather disruptions across the United States, Europe, and the Sahel region in Africa.
Photo: Rachel Hobday | Flickr