Ocean circulation implicated in past abrupt climate changes

Ocean circulation implicated in past abrupt climate changes
A new study using sea floor sediment from the North Atlantic connects a series of abrupt climate changes during the last ice age with changes in the ocean overturning circulation. Credit: Margie Turrin/Lamont-Doherty Earth Observatory

There was a period during the last ice age when temperatures in the Northern Hemisphere went on a rollercoaster ride, plummeting and then rising again every 1,500 years or so. Those abrupt climate changes wreaked havoc on ecosystems, but their cause has been something of a mystery. New evidence published this week in the leading journal Science shows for the first time that the ocean's overturning circulation slowed during every one of those temperature plunges - at times almost stopping.

"People have long supposed this link between overturning circulation and these abrupt climate events. This evidence implicates the ocean," said L. Gene Henry, the lead author of the study and a graduate student at Columbia University's Lamont-Doherty Earth Observatory.

The impact of changes in the ocean overturning circulation on climate has become a hot topic today as global temperatures rise and melting sea ice and glaciers add freshwater to the North Atlantic. A 2015 study suggested that cooling in the North Atlantic may be due to a reduction in the overturning circulation, while a 2016 study suggested there had not been enough freshwater to have an effect.

The new study explores what happened to when the earth went through a series of abrupt climate changes in the past during a time when ice covered part of North America and temperatures were much colder than today. It looks at the Atlantic meridional overturning circulation, which distributes heat as it moves warmer surface water from the tropics toward Greenland and the high northern latitudes and carries colder, deeper water from the North Atlantic southward.

Using chemical tracers in sediment that builds up on the sea floor over time, Henry and his coauthors were able to document the relative speed of the Atlantic meridional overturning circulation during each abrupt climate change during the last ice age.

The chemical tracers show that the speed of the ocean overturning circulation changed first, and that sea surface temperature changed a while later. That suggests that cooling may start with changes in the ocean circulation, influencing the northern sea surface and atmosphere, said co-author Jerry McManus, a professor at Lamont-Doherty Earth Observatory. Evidence from ice cores and deep-sea sediment has shown that the northern climate also cooled before the southern climate during these abrupt changes, creating a "bipolar seesaw," with the north cool while the south was warm, and the south cooling as the north warmed.

The scientists stress that more work is needed to determine whether changes in ocean circulation initiated the abrupt climate changes or were an intermediary effect initially triggered by something else. "Our study supports the view that changes in ocean circulation were at least in part responsible for causing abrupt climate changes. However, what in turn caused those changes in circulation remains a mystery," Henry said.

Ocean circulation implicated in past abrupt climate changes
The global ocean overturning circulation, shown here in a simplified illustration, distributes heat through the oceans. In the Atlantic Ocean, the circulation carries warm water (red arrows) northward near the surface and cold deep water (blue arrows) southward. Credit: NASA/JPL

Also unclear is why these abrupt climate shifts, also seen in previous ice ages, haven't happened in the past 10,000 years. The instability appears to occur only in certain temperature ranges, and when there is a large amount of land ice that could contribute freshwater.

"We would all like to understand better how the earth's climate operates," McManus said. "This demonstrates the crucial role that global circulation can play. The dynamics of the deep ocean directly influence the earth's climate."

The series of abrupt climate changes studied here occurred between 60,000 and 25,000 years ago, ending as the last ice age peaked. Each followed a general pattern in the Northern Hemisphere: The cooling happening over hundreds to 1,000 years, then the frigid temperatures persisted for a few hundred years in what is known as a stadial, McManus said. Once warming started, it happened very rapidly, with a rise of 3 to 6 degrees Celsius in average sea surface temperature and larger changes over Greenland within a span of decades.

During every cold northern stadial, the overturning circulation had slowed, so it wasn't bringing as much heat northward from the tropics and Southern Hemisphere, the study shows. The chemical tracers also suggest that circulation slowed almost to a halt during certain stadials known as Heinrich events, when massive amounts of icebergs broke off and drifted away from the Laurentide ice sheet, which covered a large part of North America at the time. Icebergs carry freshwater that can affect ocean circulation, and computer models have suggested that adding that much freshwater to the Atlantic could shut down circulation. Exactly what influence the icebergs had during these periods will be the target of future research.

To determine how ocean circulation changed, the scientists measured three types of chemical tracers. By comparing the ratio of protactinium-231 to thorium-230, two daughter isotopes of uranium decay that remain in seawater for relatively short but consistently different periods of time before drifting into the seafloor, they could determine when circulation was strongest. Another isotope, carbon-13, captured in tiny shells, is more common in North Atlantic waters than in southern waters. When circulation was strong, protactinium was low and carbon 13 was high, because more protactinium was carried away by the current and more northern waters formed.

Axel Timmermann, a professor of oceanography at the University of Hawaii who studies abrupt climate changes and was not involved in this study, called it a "breakthrough analysis."

"Large changes in the North Atlantic meridional are thought to have played a major role in generating millennial-scale global variability, known as Dansgaard-Oechger events, during the last glacial period. The paper by Henry, McManus and colleagues finally provides supporting evidence for this fundamental scientific hypothesis," Timmermann said.


Explore further

Wind-blown Antarctic sea ice helps drive ocean circulation

More information: "North Atlantic ocean circulation and abrupt climate change during the last glaciation," by L.G. Henry et al. DOI: 10.1126/science.aaf5529
Journal information: Science

Citation: Ocean circulation implicated in past abrupt climate changes (2016, June 30) retrieved 18 July 2019 from https://phys.org/news/2016-06-ocean-circulation-implicated-abrupt-climate.html
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Jun 30, 2016
Indeed the oceans control climate not the other way around and they do this via 'plankton cooling.' We can restore green plants equivalent to 10 Amazon Rainforests in just 5 years time. That regenerated ocean plant life we have destroyed will as it is revived manage the lions share of the world's CO2 immediately at the cost of mere millions as opposed to the trillions in new carbon taxes. http://russgeorge...5-years/

Jun 30, 2016
Could 'up & down' sea-levels due extensive glaciation have pinched the warm flow near Borneo ??

Jul 01, 2016
think... the answer you seek is easy to find

Jul 01, 2016
This comment has been removed by a moderator.

Jul 02, 2016
An Interesting piece in that they are studying sediment laid down during the ice ages when the global currents slowed and even stopped, there were 1500 yr periods of building cold, a few hundred years of solid freeze, and then rather fast warming, and they are dating these events by the levels of protactinium and thorium, which are products of uranium decay...which to me sounds like tech rise every 1500 years, with increased tech and quick global warming, then nuke war and global ice age again, for cycles every 1500 years, so it is no wonder the Norse talked about the Gods and the Frost Giants, they were very real and very much at war, tearing the world apart, time and time again in their struggles for domination. We KNOW there have been nuclear wars on this planet before, that is HOW they know about Nuclear Winters. Consider all the different legendary lost lands, many we are finding not far offshore or in shallower waters. Will we, our Generations, be different? I hope so.

Jul 02, 2016
And as far as knowing that there had been atomic blasts on this planet before, the Green Glass found in the Sahara, in circular areas, is almost exactly like that from the testing site at Alamagordo. J. Oppenheimer himself had studied the Ancient Indian Vedas, and they actually contain some rather detailed tech, enough for him to be able to take Einstein's basic idea and be able to expand upon it using information from those very ancient texts that actually talk about the launching and then detonation of a nuclear tipped missile, in very clear terms, and gave details as to the radiation sickness that occurred later. The Vedas were accurate in their descriptions, very much so. There are also the blasted cities in India like in Rajahsthan, the Mahabharata Vedas (6-12K yrs old) are vividly clear, and that is what Oppenheimer quoted when he saw the first detonation, he KNEW that we were not the first High Civilization on this planet, and this was proof, to his lasting regret.

Jul 02, 2016
Indeed the oceans control climate not the other way around and they do this via 'plankton cooling.' We can restore green plants equivalent to 10 Amazon Rainforests in just 5 years time. That regenerated ocean plant life we have destroyed will as it is revived manage the lions share of the world's CO2 immediately at the cost of mere millions as opposed to the trillions in new carbon taxes. http://russgeorge...5-years/


How long did it take you to come up with this dumb analogy ?

Jul 02, 2016
The AMOC starts throughout the Arctic Ocean basin. It does NOT start next to Greenland and there is no fresh water flow off of Greenland that has any meaningful impact on the ocean salinity there.

There are way too many myths in climate science that just seem to persist and persist despite reality.

Jul 02, 2016
Earth is heating up, but so is Mars, Pluto and other planets in the solar system. Is hot gas from the Earth globalists warming Mars?

Jul 02, 2016
The AMOC starts throughout the Arctic Ocean basin. It does NOT start next to Greenland and there is no fresh water flow off of Greenland that has any meaningful impact on the ocean salinity there.

There are way too many myths in climate science that just seem to persist and persist despite reality.
So, where does the cold spot southeast of the southern tip of Greenland come from? You know, this one: http://www.realcl..._1rc.jpg That's from Rahmstorf et al. 2015. Obviously, warm water from the equator isn't making it there. How hard is that to figure out?

Meanwhile, Greenland is melting and the Arctic already has. Where do you suppose all that water goes? We're talking 239 cubic kilometers per year from Greenland alone. Are you seriously claiming that much fresh water won't make a difference to the salinity?

[contd]

Jul 02, 2016
[contd]
So let's have a look at what actual measurement of the AMOC has to say:

http://www.aoml.n...2015.pdf

Looks like there is an array of sensors measuring it. But wait there's more, they not only measure water and heat transport, they also have salinity sensors. Says so right in that article I just linked.

Finally, the AMOC is where the warm salty water from the Gulf Stream gets turned colder and fresher by water from the Arctic- including Greenland, remember, 239 cubic kilometers- and drops to the ocean floor and turns back south. I have no idea what the AMOC "starting" means, but wherever that is, it certainly isn't the floor of the ocean.

Speaking of climate myths.

Jul 02, 2016
Could 'up & down' sea-levels due extensive glaciation have pinched the warm flow near Borneo ??

The channels between the Indonesian islands are quite deep and the currents not especially fast so my guess is that a fall in sea level would not change this overall pattern. For example, between Bali and Lombok, the channel is 1.1km deep.

Jul 02, 2016
Now thats some global warming

Jul 03, 2016
Earth is heating up, but so is Mars, Pluto and other planets in the solar system. Is hot gas from the Earth globalists warming Mars?


By that it sounds like your head is heating up by hot gasses failing to escape inside you, but that's normal for a antigoracle, aka antisciencegorilla sock so don't worry.... ;)

Jul 03, 2016
Now thats some global warming


You bet monkey goracle sock, we've been reading about your hot air all over the physics forum ;)

Jul 03, 2016
Hi, Lupus ! Googling for 'Indonesian Gateway' found this *free* article...
http://citeseerx....type=pdf
quote:
"The critical plates are those of SE Asia, India–Australia and the Philippine Sea, and the crucial region lies between Borneo and the Bird's Head of New Guinea, including the islands of Sulawesi and the Banda arc. The relevant time interval comprises the last 30 million years, when tectonic processes led to significant changes in the distribution of land and sea and in particular in the configuration of deep-water passages to the north of Australia."

My hasty reading suggests two deep passages stay open, but flow would have been impaired by seasonal changes and the Sundaland etc shelf...

Jul 03, 2016


Ocean circulation implicated in past abrupt climate changes


What, no humans to implicate?

Jul 04, 2016
This comment has been removed by a moderator.

Jul 06, 2016
What do you mean it's clear as day we know you are an antigoricle sock, so here have a banana ;)

Jul 06, 2016
This comment has been removed by a moderator.

Jul 06, 2016
The AMOC starts throughout the Arctic Ocean basin. It does NOT start next to Greenland and there is no fresh water flow off of Greenland that has any meaningful impact on the ocean salinity there.

There are way too many myths in climate science that just seem to persist and persist despite reality.

So, where does the cold spot southeast of the southern tip of Greenland come from? You know, this one: http://www.realcl..._1rc.jpg That's from Rahmstorf et al. 2015. Obviously, warm water from the equator isn't making it there. How hard is that to figure out?


When you're quoting lame talking points from Watts rather than actual science? Easy.

Jul 08, 2016
I think it funny that a horde of sock puppets AUTOMATICALLY vote me down for ANY of my posts, no matter how factual they are, no matter how sound the science behind them, no matter the subject, I am ALWAYS voted down by masses of obvious sock-bots.

And then I laugh myself silly when I find the very articles and facts that back up my own theories, and people still do not see it, or plain Refuse to See what is right there in front of them.

As far as the oceans, yes the entire Indonesia, Malaysia, the PI and Sumatra all slow the water currents and the ocean is shallower there, so it is allowed to heat, like going through an old style brick heat recycler for the pre-heat for old blast furnaces (look that one up) since it is a wide, and has been changing, area.

Jul 08, 2016
I think it funny that a horde of sock puppets AUTOMATICALLY vote me down for ANY of my posts, no matter how factual they are, no matter how sound the science behind them, no matter the subject, I am ALWAYS voted down by masses of obvious sock-bots.

And then I laugh myself silly when I find the very articles and facts that back up my own theories, and people still do not see it, or plain Refuse to See what is right there in front of them.

As far as the oceans, yes the entire Indonesia, Malaysia, the PI and Sumatra all slow the water currents and the ocean is shallower there, so it is allowed to heat, like going through an old style brick heat recycler for the pre-heat for old blast furnaces (look that one up) since it is a wide, and has been changing shallow, area perfect for heating seawater for millenia..

Jul 11, 2016
Out of curiosity I went back and read your posts, Steelwolf. I would not describe them as science. I think it would be more accurate to call them "rabid and deranged". Maybe that's the reason for the down posts?

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