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

Nov 06, 2008

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

Explore further: Questions of continental crust

add to favorites email to friend print save as pdf

Related Stories

Climate capers of the past 600,000 years

Nov 17, 2014

If you want to see into the future, you have to understand the past. An international consortium of researchers under the auspices of the University of Bonn has drilled deposits on the bed of Lake Van (Eastern ...

New satellite movie shows US pre-winter wintry outbreak

Nov 14, 2014

(Phys.org) —Three days of satellite imagery from NOAA's GOES-East satellite were compiled into an animation that showed the progression of the storm system that dropped snow and brought gusty winds to the ...

New global maps detail human-caused ocean acidification

Nov 10, 2014

A team of scientists has published the most comprehensive picture yet of how acidity levels vary across the world's oceans, providing a benchmark for years to come as enormous amounts of human-caused carbon ...

Recommended for you

Questions of continental crust

54 minutes ago

Geological processes shape the planet Earth and are in many ways essential to our planet's habitability for life. One important geological process is plate tectonics – the drifting, colliding and general ...

Better forecasts for sea ice under climate change

Nov 25, 2014

University of Adelaide-led research will help pinpoint the impact of waves on sea ice, which is vulnerable to climate change, particularly in the Arctic where it is rapidly retreating.

User comments : 11

Adjust slider to filter visible comments by rank

Display comments: newest first

GrayMouser
3.4 / 5 (13) Nov 06, 2008
Another nail in the coffin of AGW?
MikPetter
2.5 / 5 (11) Nov 06, 2008
"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."
Given we are not in the peak of a glacial cycle the study doesn't directly relate to our current situation.
Perhaps those who are unconcerned or in denial about global warming would like to buy some nice beachfront properties in bangladesh or elsewhere?
jeffsaunders
4.6 / 5 (7) Nov 06, 2008
Beachfront properties may be good - but not for a long term investment by me.

I think that the naysayers (on the whole) are not saying there is no Global Warming. My reading of the comments lends me to believe that what I am reading is that most naysayers are disputing the interpretation of the facts.

The interpretation does include some conclusions that many are just not prepared to go along with.

Some do go further and say there is no Global Warming but the majority are willing to accept that perhaps there is Global Warming but that the exact cause cannot yet be determined and that wider vision is needed.
jeffsaunders
2.3 / 5 (3) Nov 06, 2008
"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."


WOW was that bad luck or what?
out7x
3.3 / 5 (10) Nov 07, 2008
Global warming is due to the earths rotational wobble. Ever hear of milankovich cycles? Amount of sunlight is also due to wobble.
GrayMouser
5 / 5 (3) Nov 07, 2008
"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."


WOW was that bad luck or what?


Bad luck happens. You should design your experiment to account for it (as much as it possible.)
rubberman
5 / 5 (2) Nov 09, 2008
you should also design your lottery numbers around the "bad luck", it seems to happen occasionally there too
denijane
3.5 / 5 (2) Nov 10, 2008
But the light distribution depends on the type of the surface it's falling on and thus, from the area that is covered with ice.
Anyway,I'm more interested in that specific site that goes against the other.I wonder why they didn't say where that is. It's very very curious...

http://tothefutur...spot.com
Velanarris
5 / 5 (3) Nov 12, 2008
"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."
Given we are not in the peak of a glacial cycle the study doesn't directly relate to our current situation.
Perhaps those who are unconcerned or in denial about global warming would like to buy some nice beachfront properties in bangladesh or elsewhere?


I'll take all the beachfront property I can. It's a win win.

If AGW is wrong then I have cheap property. If AGW is right, I own the beach. Either way there is profit to be made.
GrayMouser
5 / 5 (3) Nov 12, 2008
"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."


Isn't this a horse and cart issue? The ocean may be driving the climate. In fact, given the relative masses involved I'd say that the ocean is the predominant factor in climate (next to the Sun.)
dachpyarvile
not rated yet Aug 05, 2009
The Sun is the main driver behind climate. This, combined with Earth's rotation makes the winds and then this is combined with the gravitational pull of both Sun and Moon. The ocean certainly drives climate but it is the Sun which drives the mechanisms in the ocean, along with Earth's rotation and so forth.

And, as observed above, I have no problem with the idea that warming occurs on Earth. It has done so for millions and millions of years. I do, however, take issue with the hypothesis that man is responsible for global warming. AGW = Anthropogenic Global Warming = unproven hypothesis!

That we pollute the atmosphere and oceans I have no doubt. That CO2 is a pollutant I disbelieve. All we do is release into the atmosphere what was once already there. The amounts of CO2 we release is quite small compared to the overall picture.

At one time the CO2 in the atmosphere was over 7000 ppm and life flourished just fine. Plants can photosynthesize at levels up to or below 0.9% of atmosphere.

Our current levels of atmospheric CO2 are at a point between 0.03% and 0.04%. We will never be able to get the levels as high as the maximum, even if we burned everything organic on the planet at once.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.