Antarctic ice sheet is result of CO2 decrease, not continental breakup

Jul 30, 2014

Climate modelers from the University of New Hampshire have shown that the most likely explanation for the initiation of Antarctic glaciation during a major climate shift 34 million years ago was decreased carbon dioxide (CO2) levels. The finding counters a 40-year-old theory suggesting massive rearrangements of Earth's continents caused global cooling and the abrupt formation of the Antarctic ice sheet. It will provide scientists insight into the climate change implications of current rising global CO2 levels.

In a paper published today in Nature, Matthew Huber of the UNH Institute for the Study of Earth, Oceans, and Space and department of Earth sciences provides evidence that the long-held, prevailing theory known as "Southern Ocean gateway opening" is not the best explanation for the climate shift that occurred during the Eocene-Oligocene transition when Earth's polar regions were ice-free.

"The Eocene-Oligocene transition was a major event in the history of the planet and our results really flip the whole story on its head," says Huber. "The textbook version has been that gateway opening, in which Australia pulled away from Antarctica, isolated the polar continent from warm tropical currents, and changed temperature gradients and circulation patterns in the ocean around Antarctica, which in turn began to generate the ice sheet. We've shown that, instead, CO2-driven cooling initiated the ice sheet and that this altered ."

Huber adds that the gateway theory has been supported by a specific, unique piece of evidence—a "fingerprint" gleaned from oxygen isotope records derived from deep-sea sediments. These sedimentary records have been used to map out gradient changes associated with ocean circulation shifts that were thought to bear the imprint of changes in ocean gateways.

Although declining atmospheric levels of CO2 has been the other main hypothesis used to explain the Eocene-Oligocene transition, previous modeling efforts were unsuccessful at bearing this out because the CO2 drawdown does not by itself match the isotopic fingerprint. It occurred to Huber's team that the fingerprint might not be so unique and that it might also have been caused indirectly from CO2 drawdown through feedbacks between the growing Antarctic ice sheet and the ocean.

Says Huber, "One of the things we were always missing with our CO2 studies, and it had been missing in everybody's work, is if conditions are such to make an ice sheet form, perhaps the ice sheet itself is affecting ocean currents and the climate system—that once you start getting an ice sheet to form, maybe it becomes a really active part of the climate system and not just a passive player."

For their study, Huber and colleagues used brute force to generate results: they simply modeled the Eocene-Oligocene world as if it contained an Antarctic of near-modern size and shape and explored the results within the same kind of coupled ocean-atmosphere model used to project future and across a range of CO2 values that are likely to occur in the next 100 years (560 to 1200 parts per million).

"It should be clear that resolving these two very different conceptual models for what caused this huge transformation of the Earth's surface is really important because today as a global society we are, as I refer to it, dialing up the big red knob of but we're not moving continents around."

Just what caused the sharp drawdown of CO2 is unknown, but Huber points out that having now resolved whether gateway opening or CO2 decline initiated glaciation, more pointed scientific inquiry can be focused on answering that question.

Huber notes that despite his team's finding, the gateway opening theory won't now be shelved, for that massive continental reorganization may have contributed to the CO2 drawdown by changing that created huge upwellings of nutrient-rich waters containing plankton that, upon dying and sinking, took vast loads of carbon with them to the bottom of the sea.

Explore further: West Antarctic ice sheet formed earlier than thought

More information: Nature 511, 574–577 (31 July 2014) DOI: 10.1038/nature13597

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User comments : 17

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Dr_toad
Jul 30, 2014
This comment has been removed by a moderator.
antigoracle
1.6 / 5 (13) Jul 30, 2014
Well, we did not have to wait for stupid above.
Dr_toad
Jul 30, 2014
This comment has been removed by a moderator.
TegiriNenashi
1.2 / 5 (10) Jul 30, 2014
Well, if CO2 levels explain everything in nature
http://www.number...list.htm
then why not Antarctic ice shelf formation?
skills4u
1 / 5 (2) Jul 30, 2014
Retracted my statement as I just woke op from a nap and misread article, head still groggy !
antigoracle
1.8 / 5 (10) Jul 30, 2014
Careful there toadstool, you don't want to burn out that lone neuron you share with the rest of the peanut gallery.
Protoplasmix
4.4 / 5 (7) Jul 30, 2014
Well, if CO2 levels explain everything in nature
http://www.number...list.htm
then why not Antarctic ice shelf formation?

The first link I clicked on, "Black Hawk down," gives error 404, page not found. If you were trying to make a point, your bias precluded it.
TegiriNenashi
1.4 / 5 (8) Jul 30, 2014
Well, nothing is perfect. For that matter I thoroughly enjoyed "extinction of logic(!)" which is technically a link to Cato publication. Unfair? Sure. Still entertaining.
Dr_toad
Jul 30, 2014
This comment has been removed by a moderator.
antigoracle
1.5 / 5 (8) Jul 30, 2014
Oh toadstool, the rest of the peanut gallery are going to be very cross when you burn out that lone neuron you share.
Dr_toad
Jul 30, 2014
This comment has been removed by a moderator.
antigoracle
1.9 / 5 (9) Jul 30, 2014
Hey toadstool when did you use that lone neuron to come up with one neuron?
Protoplasmix
4.2 / 5 (6) Jul 30, 2014
Says Huber, "One of the things we were always missing with our CO2 studies, and it had been missing in everybody's work, is if conditions are such to make an ice sheet form, perhaps the ice sheet itself is affecting ocean currents and the climate system—that once you start getting an ice sheet to form, maybe it becomes a really active part of the climate system and not just a passive player."

Pretty good observation, I think. An ice circle illustrates it quite dynamically on a short term, small scale: http://www.youtub...NLpYLNGs
Dr_toad
Jul 30, 2014
This comment has been removed by a moderator.
runrig
5 / 5 (8) Jul 31, 2014
Well, if CO2 levels explain everything in nature


It doesn't.
Protoplasmix
4.3 / 5 (3) Jul 31, 2014
Proto, I gave you a better vote than I should have

Cheers, Doc, I didn't mean to conflate weather with climate or suggest that polar ice caps are spinning or rotating or anything like that, although here's a video of a rolling iceberg: http://www.youtub...pDEsTg4g

And there are 16' swells in the Arctic. Because no ice sheet: http://www.dailyk...Warming#

I think the ice circle and these are all examples of ice (or lack of it) having a dramatic effect on currents, in support of the assertion that, 'maybe it becomes a really active part of the climate system and not just a passive player.'
antigoracle
1 / 5 (6) Aug 01, 2014
CO2 decline initiated glaciation

Perhaps one of the "geniuses" in the AGW Cult, who boasts that they know the "science", would be so kind to inform us what CO2 level would initiate glaciation.
runrig
5 / 5 (6) Aug 01, 2014
CO2 decline initiated glaciation

Perhaps one of the "geniuses" in the AGW Cult, who boasts that they know the "science", would be so kind to inform us what CO2 level would initiate glaciation.


The one that was applicable to the orbital characteristics and albedo of Earth at the time my friend, such that if high then a larger amount would be needed to balance the climate, and if albedo was low viki verki.
You see, there is no "one size fits all", contrary to the scientifically (read ideologically ) challenged.
antigoracle
1 / 5 (5) Aug 01, 2014
Okay runrig, so what level of CO2 would initiate glaciation now.
runrig
5 / 5 (7) Aug 01, 2014
Okay runrig, so what level of CO2 would initiate glaciation now.

I don't know - but if the level that was consistent with a balance at onset of the Industrial revolution is anything to go by (280ppm) - then something less than that.
BUT, CO2 does NOT initiate an IA - orbital forcing does and CO2 follows from the biosphere.
To initiate an IA, man would have to extract CO2 to a level below 280ppm. Not going happen.
The driver is the Earth's orbit and CO2 (normally and without pesky humans buggering it up) follows.
Now we've reversed the normal process.
Well done humankind.
F***ng great. But, wait we have a thinking brain, unique among creatures inhabiting this planet.....but
Still we have the Neandertals denying.
jackofshadows
not rated yet Aug 02, 2014
It's nice to see an examination of feedback loops in climate modeling. You know that Man, the Tinkerer, will try to engineer the Earth's climate so any analysis of past cycles would be great to on have on tap.
Landrew
not rated yet Aug 03, 2014
Is there not a big problem with ignoring the data which shows that follows a change in CO2 levels, and does not follow it?
Dr_toad
Aug 03, 2014
This comment has been removed by a moderator.