North Atlantic overturning – back with a vengeance?NaturePosted on 12/03/2008 12:06:48 AM PST by neverdem
Convective mixing resumes after a decade due to massive loss of Arctic ice.
North Atlantic overturning – back with a vengeance?NatureScientists have found evidence that convective mixing in the North Atlantic, a mechanism that fuels ocean circulation and affects Earth's climate, has returned after a decade of near stagnation – thanks, perhaps, to a dramatic loss of sea-ice in the Arctic during the summer of 2007.
Convective mixing, or 'overturning', of ocean waters at high latitudes helps to drive the Atlantic 'heat conveyor belt' that carries warm water northwards and cooler deep-water back south. The phenomenon also helps to remove carbon dioxide from the atmosphere – as cold water sinks, it carries dissolved CO2 with it, locking it away in the depths of the ocean for centuries.
But cold winters are one of the prerequisites for convection in the deep-water formation regions around Greenland, such as the Labrador and Irminger Seas, and a warming climate would be expected to slow or stop the process.
There's been very little convection in the North Atlantic over the past decade, prompting concerns that the impact of global warming was already being felt.
Now two teams of scientists have independently found evidence that overturning has resumed in the North Atlantic.
A team led by Kjetil VÃ¥ge of the Woods Hole Oceanographic Institution in Massachusetts has found that convection returned to the region last winter (2007-2008) with a vengeance1. And Igor Yashayaev and John Loder of the Bedford Institute of Oceanography in Nova Scotia, Canada, separately report that the convection last winter in the Labrador Sea was the deepest since 19942.
VÃ¥ge and his colleagues suspect that weather peculiarities alone cannot explain the unexpected return of convection.
Temperatures last winter were 5-6 °C colder in the North Atlantic than in the previous seven years. But the location of high and low pressure systems over the region means that weather patterns did not favour overturning.
They suggest that a cap of cooler fresh water – massive sea-ice export from the Arctic basin along both sides of Greenland during the previous summer – has facilitated freezing of parts of the Labrador and Irminger Seas. As a result, cold continental-origin air blowing over the region had not been warmed by the relatively warm ocean when it reached the convection areas. The temperature difference between air and open water led to a massive transfer of heat from the ocean to the atmosphere, thus fuelling convection.
Whether the convection is back to stay, however, is not known. "There is a lot of natural fluctuation at play," says Detlef Quadfasel, an oceanographer and climate scientist at the University of Hamburg in Germany. "One nice day of ocean weather doesn't really tell you a lot about what you might have to expect in the future."
But there is little doubt that, in the long-term, ocean convection will decrease if northern latitudes continue to warm at the current rate. "As the water column gets ever more stable, it will get increasingly difficult in a warming environment to produce deep convection in the North Atlantic," says Jürgen Fischer, an oceanographer at the IFM-Geomar Leibniz Institute of Marine Sciences in Kiel, Germany. "You'll probably need very exceptional conditions, such as those of last winter, to mix the oceans."
Reduced convection should in theory weaken the entire Atlantic meridional overturning circulation (MOC) – responsible for carrying warm tropical water northwards – with far-reaching consequences for Earth's climate. But so far at least, scientists have not observed any significant changes to that large-scale circulation. Findings published in 2005 that seemed to indicate a big slowing of the MOC were later found to be in the range of natural fluctuations (see 'Ocean circulation noisy, not stalling').
One reason, says Fischer, is that the observational basis is still thin. The Argo programme, a global array of 3,000 robots that measure temperature, salinity and water pressure, has only last year become fully operational, for example.
But already it's clear that the response of the Atlantic Ocean circulation to high-latitude changes is much more complex than has been assumed. According to VÃ¥ge and his colleagues, the "myriad of factors" that favoured the return of overturning last winter make it "difficult to predict when deep mixing is likely to occur".
So, what we’re saying here is that the Earth knows more about itself than Al Gore does. Who knew??
Just wait and give Albore a chance to sound off on this — I’m sure that if he blows enough hot air all over the subject he can get millions of Envirowhackos to continue to follow the Goreacle.
btw, has anyone ever seen the Goreacle and the Obamessiah in the same room? How do such monstrous egos co-exist?
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north atlantic cooling ping
Their goal is always the same, self-appointed intellectual priest class controlling behaviors of human race.
I guess all that polar ice that is deeper and reaches farther than it has in many years is not to be accounted for in the calculations, huh?
It’s almost like ... things go in cycles ... or something.
When has it ever broken? Odd statement.
Typical Leftist bilge that the Earth is broken and WE Leftist know how to fix it! I have such deep hatred for these Enviro Morons and their drones.
I would expect all of this to correlate with the global warming/global cooling caused by the Sun. The global warming on the Earth, Venus, Mars, Jupiter was caused by the natural variation of the heat output of the Sun. Climate change is caused today by the Sun as it has been for billions of years.
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It’s great we take all of this data. The more accurate data we have, the better. What I get from this is basically, they/we really don’t understand what is going on or why it happens. Thus, any attempt to screw around with the climate based on this knowledge is nothing more than a scam. It’s like taking a one minute sample of your day and predicting your future decades from now based on that one minute. How much will you pay me to do that for you?
God’s never ending battle is watching over his creation and protecting it from LIBERALS set to “fix” it.
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More items to be ignored by the left.
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