The Antarctic Half of the Global Thermohaline Circulation Is Faltering

Shocking news: "the southern branch of the global thermohaline circulation has slowed dramatically." This is already begun to affect global climate, including Arctic ice melt, increased droughts in the US and storminess in the North Atlantic. Climate models hadn't predicted this behavior.

The cold dense brine that forms at the margin of freezing Antarctic sea ice normally sinks to the ocean bottom to drive the thermohaline circulation. Now it's is being deflected instead of sinking. That cold water stays near the top, changing the equator to pole heat gradient, which speeds wind currents.

The global oceans' coldest water, Antarctic bottom water forms in several key spots around Antarctica. The water is so cold and dense that it spreads out along the bottom all of the major ocean basins except the north Atlantic and Arctic. Multiple recent reports provide strong evidence that the formation of Antarctic bottom water has slowed dramatically in response to massive subsurface melting of ice shelves and glaciers. The meltwater is freshening a layer of water found between depths of 50 and 150 meters. This lightened layer is impeding the formation of Antarctic bottom water, causing the Antarctic half of the global thermohaline circulation to falter.

This post is based on a synthesis of very recent research reports. The key report, that found the layer of fresh water between 50 and 150 meters deep, was just published.

That lens of (relatively) fresh water that is forming around Antarctica is challenging, and changing, almost everything in global circulation patterns.  It freezes sooner (and at a higher temperature).  That shields the water from the wind, and reduces wind-driven mixing.  It reduces, perhaps to the point of stopping altogether, the present global ocean circulation patterns.  That in turn will change global atmospheric weather.

Nobody knows exactly what comes next.  We've never seen it happen ...
... intensifying winds are speeding up below surface currents bringing more above freezing water in contact with deep ice around Antarctica. Twenty of the ice shelves and many of the glaciers that feed them are melting from below.

The melting from below is creating a layer of relatively fresh water 50 to 150 meters below the surface around Antarctica. This layer of light fresh water is floating above a  salty layer below. When ice forms at the surface in the Antarctic winter it creates cold dense salty water that tends to sink to the bottom, forming bottom water. However, this layer of light melt water is tending to block the water in the top 50 meters from sinking. The area of Antarctic sea ice has expanded because the layer of cold water has stayed on top and expanded outwards instead of sinking.

Brine ... isn't sinking because it is ponding above a freshening layer located at depths between 50 and 150 meters.

Analysis of potential temperatures, which are temperatures adjusted for the effects of increasing pressure with depth, shows the surface water in the top hundred meters is cooling over a vast area from 40°S to 80°S while the water in that vast area below 150 meters is warming.
The decline in Antarctic bottom water formation, combined with the southward expansion of warm subtropical water in the south Pacific and south Indian oceans has led to the rapid heating of intermediate and deep ocean water in the southern hemisphere.

As the earth has warmed in response to the effects of increasing levels of greenhouse gases the southern subtropical belt in the oceans and atmosphere has expanded, tightening the rings of winds and ocean currents around Antarctica. Enormous volumes of warm subtropical water have been added to the southern ocean at depths greater than 300 meters (greater than approximately 1000 feet).

Another recent detailed study of the water properties of the southern ocean has independently determined that the southern branch of the global thermohaline circulation has slowed dramatically, contributing to a large uptake of heat by the deep southern ocean.

The slowdown of the southern branch of the thermohaline circulation and the cooling of the surface waters close to Antarctica are enhancing the thermal gradient from the tropics to the pole, speeding up the winds in the southern hemisphere. These increases in wind speeds are likely increasing the flow of water from the Pacific to the Atlantic ocean, enhancing the northward flow of water, salt and heat from the south to the north Atlantic.

Thus, increased melting of Arctic sea ice may be related to declines in Antarctic bottom water formation. Likewise, the cool Pacific, warm Atlantic pattern causing increased U.S. droughts and storminess in the north Atlantic may be tied to these changes in ocean circulation patterns. Paleoclimate studies have consistently shown oscillations between Antarctic and north Atlantic bottom water formation and between relative coolness around Antarctica and north Atlantic warmth.

The Arctic melt down that is far exceeding model predictions is connected to the slow down in Antarctic bottom water formation. Climate modelers will be challenged to model the connections and the details. The cooling waters around Antarctica, while apparently good news, are not. The rapid melting of the Arctic will be enhanced.

The red layer at the top (the surface) is the salty cold water that should be sinking. The blue layer is fresher warmer water coming from bottom of melting Antarctic Ice Shelves, which deflects the salty cold water.

Given the importance of the Global Conveyor Belt (thermohaline circulation) I recommend reading the article yourself with a critical eye. This is a major climate tipping point.

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Replies to This Discussion

No! I don't "like" this. However, there have been those warning us for years. I first learned of the potential problem in 1959 on a flight to Alaska with a glaciologist seat mate who told an incredible story of ice changes taking place. Who would listen to him then? I just thought it was an interesting job. 

Hubris! Human beings think Earth is here to serve humans, and to use water, soils and air as sewers. Well, the chickens have come home and it isn't a pretty sight. We clearly are not going to be able to stop this process taking place now. Because we can't stop it, scapegoating has already begun in earnest. Not being in control of our lives, not being able to predict what will happen ... the formula for depression and anxiety as well as inducing crazy thinking. 

So, we can be afraid, angry, helpless, hopeless and worry. What good will that do anyone? 

It seems to me the first thing to do is be flexible, go with the flow type of thinking, marshall resources and prepare for a ride of an eon. 

In the meantime, I'm off to see the wizard tomorrow. You schedule a mammogram, please. 

Yes, Joan.

We clearly are not going to be able to stop this process taking place now.

Not being in control of our lives, not being able to predict what will happen ...

But there's good news too. Since the right wing got in bed with climate deniers, as it becomes undeniable in 2013 that we've destabilized our planet's climate, the political penduluum will have to swing. Demand for sustainability will sweep the crazies out of power. In another sense we will gain some control of our lives by toppling insane policies that prevented us from saving ourselves.

Oh yes! A clean sweep. That would make a good political slogan! Even if it has been used before. Ruth, you have done a wonderful job of providing basic research information and help explain it to us. Your projects exist as genuine treasures. You need a wider audience. 

Oh Oh, I should explain I was responding to the Thermohlaine Circulation faltering in Southern Hemisphere!!!
That and Boston's tragic bombing.

Thanks Ruth! A rather difficult text for me to read in English but I understand the outline well enough. Some years ago there were documentaries here about what would happen if/when the Global Conveyor Beld stopped. Europe would become very cold.. I remember that they told us that the Global Conveyor Belt had stopped in one of the last Ice Ages (and started again later). But now that it is happening - I'm glad that I kept to my resolution never to have children.

I don't share your hope that the political pendulum will have to swing, I haven't got that much confidence in politics. Here we have got a rightwing prime minister who attacks the problems with a grin and nothing else, and the people are distracted with a new king, sports and soaps. I'm sure that all will be 'business as usual'.  

I'm not all that confident that a political swing will happen, until it's far far too late, Chris.

I'm depressed about the thermohaline circulation decline, like the drone of a distant bagpipe dirge at the back of my mental landscape.

I know how you feel Ruth - one clear voice more in the warning concert, but nobody listens. I hate the thought that occurs to me now and then, that I will be able to live out my life in a rather normal way, as concerns climate, but the next generation will have to face the trouble. I always tried to make things a little better.  


Who is this, Joan? Three pics of a kind looking man and my name - perhaps the rest of the message disappeared.  

Thank you, Joan. A real pleasure to hear him talk!

Interesting, thanks.


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