Study: Gulf Stream slower than ever before

POTSDAM, Germany, March 23 (UPI) -- The Gulf Stream is the weakest it's been in the last 1,000 years. And as glacier melt in the Arctic continues to accelerate, the foot of the Atlantic's most powerful ocean current keeps pressing harder and harder on the brake pedal.

A team of researchers recently analyzed an exhaustive catalog of geologic samples -- including ice cores, tree rings and coral, as well as ocean and lake sediments -- dating back to the year 900. Using sea-surface and atmospheric temperature data derived from the samples, scientists were able to plot a history of ocean current behavior.

The findings suggest the current slowdown is not only the most dramatic in recorded history, but also well outside the norm -- enough to suggest it is not part of natural fluctuation.

"There is more than a 99 per cent probability that this slowdown is unique over the period we looked at since 900 AD," Stefan Rahmstorf, study author and researcher at Germany's Potsdam Institute for Climate Impact Research, told The Independent. "We conclude that the slowdown many have described is in fact already underway and it is outside of any natural variation."

Researchers believe the Gulf Stream is being influenced by changes in water densities brought on by the influx of fresh water from melting glaciers. Differences in density and temperature, as well as the surface winds and weather patterns, drive the powerful flow of water known as the Gulf Stream, which pushes warm surface water northward and pulls deep cold water southward.

Among other climatic conditions, the Gulf Stream is credited with moderating Europe's temperatures and weather systems.

"Now freshwater coming off the Greenland ice sheet is likely disturbing the circulation," said co-author Jason Box, a researcher with the Geological Survey of Denmark and Greenland. "So the human-caused mass loss of the Greenland ice sheet appears to be slowing down the Atlantic overturning, and this effect might increase if temperatures are allowed to rise further."

The Gulf Stream is just one component -- albeit the largest and most powerful -- of the system of ocean water flows known as the Atlantic Meridional Overturning Circulation. Similar overturning systems happen in all of the world's oceans. The latest research supports previous studies that suggest overturning has slowed abruptly over the last several decades.

"If the slowdown of the Atlantic overturning continues, the impacts might be substantial," Rahmstorf said in a statement. "Disturbing the circulation will likely have a negative effect on the ocean ecosystem, and thereby fisheries and the associated livelihoods of many people in coastal areas. A slowdown also adds to the regional sea-level rise affecting cities like New York and Boston."

The latest research was published this week in the journal Nature Climate Change.