'Anonymous' current may keep Europe warm

Thursday 28th Apr 2011 by theWeather Club

The North Atlantic Drift, the Gulf Stream, the Thermohaline current - three different names for the ocean current that transfers heat northwards from the equatorial regions, famously keeping us from having the same climate as Moscow. It is just as famously under threat of slowing down or even stopping as freshwater from melting polar ice disrupts its driving mechanism. However before we rush out to stock up on extra-strength thermals and ice grips for our shoes, help may be at hand.

Nothing environmental happens in isolation, and while the Gulf Stream has been under the spotlight, another lesser known ocean current has also been changing. The Agulhas Current flows southwards down the eastern coast of Africa. When it reaches the southern tip - Cape Agulhas - most of the water swings eastward and back into the Indian Ocean. But some of it forms giant eddies and rings, up to 300km across, that push water in the other direction - rounding the cape and into the Atlantic. This flow is known as the Agulhas Leakage. Once in the Atlantic, the warm and salty Agulhas water acts to strengthen the main current system, the Atlantic Meridional Overturning Circulation (AMOC), of which the Gulf Stream is a part.

Exactly how much water is involved is not yet known, but it is thought to vary greatly from year to year. However a team of scientists drawn from the US and Europe say wind shifts further south make it likely that the volume of water is increasing. "The leakage itself is very difficult to measure because it happens over a wide corridor of ocean and because of its eddying nature," said assistant professor Dr Lisa Beal from the Rosen School of Marine and Atmospheric Science in the US. She told reporters that research on the current had been sparse because it is remote from western research centres, making studies expensive and difficult.

Last year, Dr Beal's group put an array of underwater remote sensors into the Agulhas Current to try and collect more raw data to help provide some answers. At present oceanic models cannot replicate the circular eddies typical of the Agulhas system, as they do not have the necessary data sets.

The long term aim of the research is to gain a much better understanding of how the whole AMOC behaves, particularly whether it can shut down for long periods, and what that would mean for European weather. The researchers suggest that the Agulhas Leakage could potentially compensate for any decline in the Gulf Stream. "This could mean that current IPCC (International Panel on Climate Change) model predictions for the next century are wrong and there will be no cooling in the North Atlantic," said Dr Beal. "Instead, increasing Agulhas Leakage could stabilise the oceanic heat transport carried by the Atlantic overturning circulation."