Thermohaline turbulence may increase West European warming

Two weeks ago scientists from NOAA reported in Nature they had discovered unexpected behaviour of an ocean current in the Indian Ocean, known as the Agulhas Current.

The current was found to be leaking tropical warm water around the South African cape into the Atlantic. Over time such masses of warm water may reach the Atlantic Gulf Stream and influence West European weather, increasing the likelihood of warm summers and mild and wet winters.

Normally the current, that flows in a column from the water surface to the ocean bottom, curves back eastwards from Cape Agulhas into the Indian Ocean. Some of the water though is presently observed to form giant (up to 300km) eddies, that round the cape and transport warm water masses westwards into the Atlantic.

Wind climate feedback

Precise water amounts and trends have not yet been determined. Variations from year to year may be large, but overall the leakage seems to be increasing, possibly due to changing wind patterns, the researchers state:

The Southern Hemisphere Westerlies, that blow over the oceans bordering Antarctica, have shown to be moving towards the South Pole over recent decades, allowing occasional easterlies further north.

The NOAA researchers think this ‘Agulhas Leakage’ may compensate should the ‘normal’ Atlantic Gulf Stream weaken as a result of climate change [and the influx of fresh Greenland melting water - or as a result of weakening Atlantic trade winds].

The importance of variations in the thermohaline circulation has been stressed by other recent research that shows a temporary decline in Gulf Stream velocities may be the main culprit behind the Little Ice Age.

© Rolf Schuttenhelm | www.bitsofscience.org

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