Ancient flood shut down Gulf Stream 8200 years ago
London, Dec 7: A massive release of fresh water from a huge glacial lake in Canada triggered the most dramatic spell of chill in Europe and North America some 8200 years ago, according to a new study.
The burst in Lake Agassiz, which was a giant water body that formed at the end of the last ice age as the huge Laurentide ice sheet melted, led to an estimated 100,000 cubic kilometres of fresh water rushing into the North Atlantic.
Now, researchers from the University of Bergen in Norway say they are convinced that this cataclysmic event shut down the Gulf Stream and cooled parts of the northern hemisphere by several degrees for more than a hundred years.
They say the findings prove that modelling studies are right to propose that something similar could happen with equal abruptness as the planet warms under human influence.
Previously, climate historians have found that the lake burst suddenly, clearing down the Hudson Strait and into the Labrador Sea west of Greenland, reports NewScientist.com.
Researchers have speculated that the huge slug of water from the emptying lake could have refreshed the ocean water so much that this sinking stopped, shutting down the circulation, including the Gulf Stream, which keeps countries around the North Atlantic warm, which would clarify why Greenland ice centres show temperatures in the area dropping by up to 8 °C.
Now Helga Kleiven at the University of Bergen in Norway and colleagues claim to have found evidence behind the theory.
The team drilled the core off the southern tip of Greenland, where sediment-rich deep waters slow down and deposit their loads, and found obvious signs of major changes precisely when the lake emptied and the temperatures dropped.
The changes include a flood of fine sediment from the land, coinciding with a sharp slump in the amount of particles of magnetite usually carried to the area by deep ocean currents.
The study also demonstrated that the changes were sudden, happening within a decade or so, in warm climate conditions not unlike those of today.
The main concern nowadays arises because melting ice, especially on Greenland and in Siberia, is making the North Atlantic less saline.
Oceanographers fear that this might ultimately be adequate to shut down the ocean circulation, says Kleiven, just as happened 8000 years ago, "particularly given the concerns about the impact of future warming on the Greenland ice sheet. "
Kleiven said that the next step would be to use the findings to work out exactly how much freshwater may be needed to shut down the circulation.
The findings are published in Science Express. (ANI)