Sunlight has more powerful influence on ocean circulation and climate than North American ice sheets

From A study reported in today’s issue of Nature disputes a longstanding picture of how ice sheets influence ocean circulation during glacial periods.

The distribution of sunlight, rather than the size of North American ice sheets, is the key variable in changes in the North Atlantic deep-water formation during the last four glacial cycles, according to the article. The new study goes back 425,000 years, according to Lorraine Lisiecki, first author and assistant professor in the Department of Earth Science at the University of California, Santa Barbara.

Lisiecki and her co-authors studied 24 separate locations in the Atlantic by analyzing information from ocean sediment cores. By observing the properties of the shells of tiny marine organisms, called foraminifera, found in these cores, they were able to deduce information about the North Atlantic deep water formation. Scientists can discern historical ocean temperature and circulation patterns through the analysis of the chemical composition of these marine animals.

Previously, scientists relied on a study called “Specmap,” performed in 1992, to find out how different parts of the climate system interacted with one another during glacial cycles. Specmap analyzed ocean circulation at only one place in the Atlantic.

“What I found was that the one site that the Specmap study used actually didn’t match most of the other sites in the Atlantic,” said Lisiecki. “They just happened to have a strange site that didn’t behave like most of the other sites. The other sites show that the circulation is not responding to the ice volume, but that it is responding to changes in the distribution of sunlight.”

Previously, scientists believed that deep ocean circulation –– the amount of water formed in the North Atlantic that goes into the deep ocean –– varied or responded according to the amount of ice volume in the Northern Hemisphere. The prevailing idea was that when ice ages occur, with large sheets of ice over North America, the amount of North Atlantic deep water is reduced.

“That’s an important part of circulation,” said Lisiecki. “The Gulf Stream brings up warm water from the tropics and that water is turned into this North Atlantic deep water that then sinks and moves southward at depth so you have a cycle. Warm water moves northward and then cools and sinks. That’s the North Atlantic deep water formation process.”

When warm water in the Gulf Stream comes north, it brings heat to the North Atlantic and Europe and then sinks in the North Atlantic and flows back southward at a depth of 3,000 meters.

“This is fairly important for the climate because it brings this heat northward,” said Lisiecki. “The Specmap study in 1992 found that circulation is reduced when you have large ice sheets –– presumably because you have less of this North Atlantic deep water forming. Our results show that this is not always true.”

She explained that the new data changes our understanding about how the different parts of the climate system are interacting with one another and in particular the influence of the ice sheets on climate.

“Because the ice sheets are so large, it was a nice simple story to say that they were having the predominant influence on all the parts of the climate system,” said Lisiecki. “But our study showed that this wasn’t the only important part of the changes in climate. The distribution of sunlight is the controlling factor for North Atlantic deep water formation.

“Our study tells us a lot about how the ocean circulation is affected by changes in climate,” she adds. “The ocean does not always follow the climate; it exerts its own impact on climate processes. In other words, the ocean circulation doesn’t just follow along with the rest of the climate, it actually changes in different ways than the ice sheets during glacial cycles.”

Source: University of California – Santa Barbara

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November 9, 2008 6:22 pm

I haven’t been able to figure out how the ‘distribution of sunlight’ works its wonders.

November 9, 2008 6:32 pm

EGAD! It can’t be the sun, can it?
Thank you to Lisiecki and her co-authors for doing science and not politics.

November 9, 2008 6:32 pm

Surely they can’t be serious. Where’s the mention of CO2? They can’t be climate scientists. Fancy ascribing causation to the sun!

November 9, 2008 6:57 pm

Leif! It’s your sun. Comments?

Mike C
November 9, 2008 7:04 pm

This is a good case study where all of the factors of the climate system are not being considered.
When the snows of Kilimanjaro melted, they found it had nothing to do with temperature, instead, deforestation caused changes in cloud formation.
When arctic ice melted they learned the cause was wind and not temperature.
When I look at this study and other general circulation studies related to the glacial period, I never see consideration of the fact that sea level was 300 plus feet lower at the time… and how that would affect ocean circulation… which in turn affects global temperature.

November 9, 2008 7:22 pm

Kim…. That would be Milankovic cycles…. The shifting of the area north or south that the highest intensity of sunlight falls, due to the wobble of the Earth as it spins about its axis.
over ten thousand years ago the intensity was further north. At that time the Atlantic monsoon was also further north, which in turn caused the Sahara desert to be a green swampy area with grasslands and higher rainfall etc…. It also caused the Mediterranean to be less saline which in turn caused it’s deep water to become anoxic below 250 meters… a 150 in the Adriatic.
….. Anyway. That’s what I think they mean.

November 9, 2008 7:29 pm

Mike C, I have often wanted to be able to take a map of the earth and reduce the sea level by 300-400 feet and see what it looked like. There seem to be lots of maps where you can increase the sea level, but not many where you can reduce it.
The area around Florida is quite shallow. Lowering sea levels 300-400 feet could drastically change how the gulf stream behaves.
Anyone know of a map where you can adjust sea level down?

November 9, 2008 7:46 pm

evanjones (18:57:29) :
Leif! It’s your sun. Comments?
They are talking about solar insolation rather than solar irradiance. Insolation depends on orbital/tilt parameters and has nothing to do with solar actitivity. For example, the 23 degree tilt of the Earth’s axis determines the seasons. If there was no tilt we would not have seasons, no summer, no winter. A change of the tilt [which does happen due to planetary perturbations] results in a change of the polar-equator temperature difference and hence of atmospheric circulation, and hence of climate. This should also [partly] address kim’s question.

November 9, 2008 7:58 pm

Thanks. Obliquity, then.
Here is my “postcard” on the Milankovitch (Milankovic) Cycles (the standard 3 plus Inclination). There are a couple of blanks and the explanations may be incomplete or in error.
Milankovitch Cycles
Eccentricity (Fluctuating ellipticity)
95,000 years – 120,000 (Jup/Sat throw it off)
Larger 400,000 yr cycle
0.5% to 5.8% from circular, mean 2.8% (perihelion to aphelion)
20%-30% TSI variation from perihelion to aphelion at max ellipticity
???% TSI variation from perihelion to aphelion at min ellipticity
Cooler at max, warmer at min
Current State:
Ellipticity: 1.7% (near minimum)
6% more TSI in January (perihelion) than July (aphelion)
Non-glaciation phase
Inclination (“up/down” orbital position – not studied by Milankovitch)
+/-???° from orbital plane
70,000 yrs
100,000 yr-variation due to pull of other planets
Drift in/out of dust plane (Jan & July) may affect meteor activity
Seems to correspond with ice ages
Current State:
Obliquity (Axial Tilt)
41,000 years
22.1° – 24.5°
Less Tilt:
More even TSI distribution betw. Summer/winter
Less even TSI distr. Betw. Polar/Equatorial
Warmer winter (more precip), cooler summer (less melt)
Greater Tilt: Opposite of above
Current State:
23.5° (decreasing; min. in 8.000 yrs??? Graph shows opposite)
Position not favorable to Glaciation
Precession (Wobble)
21-26,000 years
[ ~ circle, varying circumference defined by current degree of tilt ]
??? [ min/max circumference ]
North Star varies from Polaris to Vega
Reversals of hemispheric seasons re. aphelion/perihelion
When axis aligned towards Sun during perihelion
Northern hemisphere – warmer summers, cooler winters (extreme)
Southern Hemisphere – cooler winters, warmer summers (mild)
Current State:
Polaris is N. Star
NH summer at aphelion, SH summer at perihelion
Position favorable to Glaciation
Combined effects of all Milankovitch cycles
Even if all favor glaciation, albedo feedback loops still required to trigger ice age.

little ice
November 9, 2008 8:04 pm

Off Topic, but interesting for some readers. I posted this on a prev thred, but I thought I would post it here as well
I am not sure if you are aware of this, but the following web site has summaries and citations of several hundred studies which show the global reach of MWP and LIA.
Pls patronize the site. They do a weekly update of a new peeer reviewed article which demonstrates the existence of MWP and LIA

November 9, 2008 9:01 pm

…the first refuge of scoundrels
‘Aliens Cause Global Warming’ (Michael Crichton Lecture, Caltech, Jan. 17, 2003)

Julian in Wales
November 9, 2008 9:53 pm

I think I read that there are estimated to be about 700,000 deep sea volcanos, how about the heat added from this volcanic activity on the ocean beds? Is it variable and is it sufficient to alter the behavior of the ocean currents?

Leon Brozyna
November 10, 2008 12:17 am

Specmap analyzed ocean circulation at only one place in the Atlantic.
It’s no wonder science has so many critics. An understanding of ocean circulation was built up on the findings from a single site. Last I looked, the oceans are rather large things. It’s like creating a computer model based on an assumption that only greenhouse gases can explain climatic changes when there are so many other factors at play that are barely understood. Even such a commonly talked about subject such as the PDO, wasn’t even officially known to exist until a bit more than a decade ago. There’s still a lot of work to be done before science can claim to begin to understand the how and why of climate changes.

Robert Bateman
November 10, 2008 3:43 am

We might have a chance if some of those Aliens visited and handed us a billion years worth of sensor readings or some fortunate archaeologist happens to dig up a prehistoric lost civilization complete with all the data we need.

November 10, 2008 5:12 am

What if much of the AGW brouhaha were basically a game of Chinese whispers, with the original “interesting perhaps” notion at the scientific beginning, slowly but steadily distorted into an “alarming for sure” cry at the political end ?

November 10, 2008 6:41 am

Leon Brozyna-
This is a case of the article mis-representing the purpose of SPECMAP which wasn’t just about ocean currents.
The project had several parts, but the initial one was to develop a better chronology for deep-sea sediments by tuning the dO18 signal to the Milankovich cycles described above by evanjones. The problem with these records is that they don’t have precise dating at different depth (unlike tree rings) so the few radiometrically-determined dates have to be interpolated. SPECMAP assembled a few higher resolution cores from around the world and “stacked” them (ie, matched the wiggles) using a couple of methods for cross-checking and came up with the best chronology to that point (it’s gotten better with more data). Once the chronology was pinned down with sufficient accuracy (a couple of percent over 300,000+ year time series), then the investigators had a powerful tool for explaining the paleoclimate. However, at that time (1980s) there wasn’t a lot data available so explanations were somewhat speculative and tenuous.
Find the web page of Lorraine Lisiecki at the UCSB Department of Earth Sciences and see how much more information is available now. She’s stacked many dozens of cores and extended the chronology back over 5,000,000 years. The coverage is improved so the conclusions she draws have more reliability than the pioneering work.

Steve Keohane
November 10, 2008 7:50 am

crosspatch, for ancient shorelines check out this site:
It’s called the Paleo Map Project, you can’t adjust sea levels, but you can look at the shorelines in different eras.

Bill P
November 10, 2008 9:25 am

JAXA should really update its home page. Their “latest” press release:
Total area of sea ice in Arctic Ocean smallest since observations started – Much faster pace of ice melting than forecasted – [August 16, 2007 (JST)]
Their graph, carried as a thumbnail on this site, is up-to-date, and for a few days, it has shown the November, 2008 Arctic sea ice extent exceeds same-period readings from the last five years. Seems to me like quite a recovery!
Jaxa’s e-mail is a non-working link.
Denver Post carried an article on Barack Obama’s transition plans: a list of 100 Bush policies to quickly reverse. Climate change features prominently.

Some related reforms embraced by Obama’s transition advisers would alter procedures for decision-making on climate issues. A book titled “Change for America,” being published next week by the Center for American Progress, an influential liberal think tank, will recommend, for example, that Obama rapidly create a National Energy Council to coordinate all policymaking related to global climate change.

One must wonder who these advisers are.

November 10, 2008 9:49 am

“Steve Keohane: for ancient shorelines check out …”
Thanks but things have drifted somewhat and continents have different shapes, etc. Basically what I would want to do is pull the shoreline down to the 100 meter sea floor contour line and have a look. I am guessing that a lot would change. A lot of land area in the Caribbean would become exposed. How would that change the path of the Gulf Stream? Would the stream get “split” somewhere? It certainly would change tropical storm behavior in the region with much more land area storms would behave differently.
What I would be most interested in is if the stream gets pushed considerably farther East before heading into the Atlantic and if it might become split by some landmass in its path. Or does the amount of water available for the current become reduced greatly because of considerable shallowing of the path? Basically I just want to see what that region looks like with the ocean level 100 meters lower.

November 10, 2008 11:00 am

And I will tell the underlying reason(s) for my curiosity. Looking at the current ice age that probably started around 2 million years ago, glaciation is the “normal” state and the interglacial is the “odd” period. Some 100K years of glacial and 10K years, roughly, of interglacial. These periods seem to flip state dramatically and in a very short period of time.
Orbital changes happen gradually over long periods of time. Changes from glaciation to interglacial happen practically instantly on a geological timescale. I wonder why. Could a general cooling slowly lower ocean levels until the gulf stream changes in some significant way and causes less heat to be transported Northward and suddenly the entire North Atlantic climate changes? During ice ages, what is the delta in temperatures in North Atlantic climates vs North Pacific climates? Does the Atlantic make an extreme change and the Pacific not change much at all? Why do things suddenly warm up out of glaciation for about 10K years and then go back to the “normal” glaciation state?
I am curious what I might find if I am able to gradually drop sea levels. How does the Gulf Stream react and is there a certain point where things succenly change.

November 10, 2008 11:21 am

The prevailing theory is that Milankovitch cycles come into congruence, reduce albedo, and at that point positive feedback loops take over and the change is rapid.
Not unlike IPCC tipping-point theory.
There is an argument over which is more of a primary driver, obliquity or eccentricity. (There are some inclination fans as well.) The reason for this is that at one point, ice ages were occurring every c. 50,000 years and before that ever 100,000. Others argue that it is not one driver but a conjunction which causes the feedback loops.

November 10, 2008 12:34 pm

Right, Evan, I am aware of that, but we seem to go from maximum cold to maximum warmth in a period of about 100 years. Those orbital changes would be insignificant over a period of only 100 years. In other words, things are pretty much the same now as they were 100 years ago … or even 200 years ago.
While orbital mechanics might be an “enabling” mechanism, something must act as a trigger (in both directions). I am simply wondering if that trigger might be a major change in tropical Atlantic (or maybe even somewhere else) currents when ocean levels reach a certain point. So do oceans rise until Florida is flooded causing the “Gulf Stream” not to be channeled around the end of Florida forming a stream? Do oceans drop until the stream is basically cut off? Is that the “trigger”? And even then I would think it would be a gradual change. Whatever happens seems to happen quite dramatically. In the space of one modern human’s lifetime we go from maximum cold and glaciation to the warmest period of the interglacial. The contrast in temperatures over only a couple of hundred years is simply amazing and something that is counter-intuitive to me if orbital changes are the cause of it.

November 10, 2008 12:44 pm

While orbital mechanics might be an “enabling” mechanism, something must act as a trigger (in both directions).
That is the prevailing theory.
I am simply wondering if that trigger might be a major change in tropical Atlantic (or maybe even somewhere else) currents when ocean levels reach a certain point.
Could be. Land configuration is a significant factor. The theory doesn’t exactly explain how the ice forms (then leads to albedo feedback), merely that it does.

November 10, 2008 12:58 pm

Some say the world will end in Eccentricity
Some say in Obliquity
But many in my generation
Tend to favor Inclination
So we are left to wonder when
Until our earth returns through dust
And will again
As so it must

November 10, 2008 3:35 pm

From New Scientist
“THE sun is nearly 150 million kilometres away, but it seems to have Earth’s rivers on a leash. The flow of a huge South American river – and thus the rainfall that feeds it – appears to rise and fall with the number of sunspots.”

November 10, 2008 6:46 pm

Richard (15:35:39) There is an older study linking Nile River levels, also with a very long span of documentation, with Aurorae Borealis.

Robert Bateman
November 10, 2008 7:30 pm

Ok, how about increased solar activity equals more energy to evaporate water off the oceans and the more moisture available plus energy to transport it and increase the precipitation.
Less solar activity equals less evaporation and less enegy to tranport and therefore less precipitation. It could get even more straightforward if extra energy results in the precipitation getting shifted elsewhere, like a jet stream too hot that overshoots in turn 3 and hits the wall or can’t slow down to make the turn into the pits.

Bill P
November 10, 2008 8:45 pm

A relief map of the Atlantic Ocean floor:
Don’t know if that’s what you were looking for.

Bill P
November 10, 2008 9:45 pm

A 2-D map of the main currents, side-by-side with the 3-Dimensional map above, can give a sense of what’s going on under the surface.

Steve Keohane
November 12, 2008 9:13 am

crosspatch, in case you didn’t look at the site I mentioned, this is a lion to a map at the last glacial maximum. The shore lines do not change that much, there is no land mass in the Atlantic to change current flow.

Arthur Glass
November 16, 2008 1:36 pm

‘“The ocean does not always follow the climate; it exerts its own impact on climate processes. In other words, the ocean circulation doesn’t just follow along with the rest of the climate, ***it actually changes in different ways than the ice sheets during glacial cycles.”
I thought that the ocean was a major part of climate, a factor but not a distinct actor.

Arthur Glass
November 16, 2008 2:46 pm

” Land configuration is a significant factor. ‘
Over what time period? The Isthmus of Panama, for example, developed some 40 million years ago; before there was a connection between the two Americas, the oceanic circulation must have been significantly different, with a concurrently different distribution of the heat budget.

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