"The Gulf Stream's climate dominance over Europe relies on events some 30 millions years ago, when Antarctica started to freeze following the final break-up of Gondwana, the great southern continent, according to Dr Matthew England, whose research with PhD student Willem Sijp was published in the Journal of Physical Oceanography.

"The loss of a 'land bridge' between Australia and Antarctica effectively isolated Antarctica and depressed its temperature by up to 9 degrees C," says Dr England. "Once it was cut adrift in the Southern Ocean, a powerful circumpolar current was established that separated Antarctica from warm subtropical waters to the north."

The Antarctic circumpolar current is a massive force. It flows at the rate of over 100 million cubic metres of water a second and takes eight years to circumnavigate the frozen continent. As a result, the icy waters of the polar reaches of the Southern Ocean don't dominate global ocean currents and climate as they did 30 million years ago.

The Gulf Stream is a super warm Atlantic current that moves tropical waters north towards Europe. As it does so it releases heat into the atmosphere that gives adjacent countries a warmer climate than they would otherwise have.

"This means that Portugal and other Mediterranean countries have a much warmer climate than places on the same latitude, such as New York," says England, who is co-director of the UNSW Centre for Environmental Modelling and Prediction.

"After the Gulf Stream waters release their heat, they cool, sink deep into the ocean, and flow south to eventually resurface in the southern hemisphere oceans.

The waters then make their way northward via various ocean routes, being rewarmed in the tropics before returning to the North Atlantic. But the driver for these ocean currents is in the North Atlantic, not the Antarctic, because of the isolating effect of the circumpolar current in the far Southern Ocean.

"Having Antarctica cut-off from the subtropics because of the Southern Ocean reduces the icy continent's impact on the global climate system", says Dr England. "We've shown that the isolation of Antarctica is necessary for the Gulf Stream's warming of Europe to be so pronounced".

So if it weren't for Antarctica's breakaway 30 million years ago, lazing by the Mediterranean today would be a much chillier affair.

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