More than 8,000 years ago, as the planet thawed following the end of the last ice age, Northern Europe abruptly cooled. New research reveals that Arctic ice melt weakened a critical ocean current, leaving Europe in the cold, a finding with important implications for future climate change.
For a roughly 200-year stretch, scientists believe, temperatures in Europe and the North Atlantic fell by as much as 9 degrees F (5 degrees C), spurring more rainfall in Europe and drought in parts of Africa. The cause of this cooling was a slowdown in the conveyor-belt-like current that carries warm, tropical water north across the surface of the Atlantic, and cold, Arctic water south across the seafloor.
This process is driven by the freezing of Arctic water. As seawater turns to ice, it expels its salt, leaving surrounding waters more saline. That dense, salty water then sinks to the seafloor, propelling the ocean conveyor belt. But 8,000 years ago, a sudden influx of fresh water disrupted this process.
Scientists previously believed the fresh water came from a massive lake in northern Canada, which drained into the ocean after an ice dam broke. But the new study finds much of the freshwater came from the melting of an ice sheet. For the study, scientists gathered samples of sediment along the Scottish coast, analyzing the fossilized remains of sea creatures to infer past sea level rise. They found that water levels rose by around 6 feet (2 meters) over 200 years, too much to be explained by the lake outburst alone.
“We have shown, that although huge, the lake was not large enough to account for all that water going into the ocean and causing the sea-level rise that we observed,” lead author Graham Rush, of the University of Leeds, said in a statement. A large volume of water, he said, must have come from melting ice. The study was published in the journal Quaternary Science Advances.
The future of the North Atlantic remains the subject of intense scientific debate. One recent study found that, as temperatures rise and the Greenland ice sheet melts, the Atlantic current could shut down this century, though those findings were met with skepticism. The new study offers additional evidence that present-day melting could lead to a slowdown in ocean currents.
Of the new study, Rush said, “We have shown that rapid ice-sheet retreat, which may occur in Greenland depending on the path of future fossil fuel emissions, can cause a range of significant climatic effects that would have very worrying consequences.”