Melting of massive ice 'lid' resulted in huge release of CO2 at the end of the ice age

January 4, 2016
Credit: Jenny Roberts

A new study reconstructing conditions at the end of the last ice age suggests that as the Antarctic sea ice melted, massive amounts of carbon dioxide that had been trapped in the ocean were released into the atmosphere.

The study includes the first detailed reconstruction of the Southern Ocean density of the period and identified how it changed as the Earth warmed. It suggests a massive reorganisation of ocean temperature and salinity, but finds that this was not the driver of increased concentration of in the atmosphere. The study, led by researchers from the University of Cambridge, is published in the journal Proceedings of the National Academy of Sciences.

The ocean is made up of different layers of varying densities and chemical compositions. During the last , it was thought that the deepest part of the ocean was made up of very salty, dense water, which was capable of trapping a lot of CO2. Scientists believed that a decrease in the density of this deep water resulted in the release of CO2 from the to the atmosphere.

However, the new findings suggest that although a decrease in the density of the deep ocean did occur, it happened much later than the rise in atmospheric CO2, suggesting that other mechanisms must be responsible for the release of CO2 from the oceans at the end of the last ice age.

"We set out to test the idea that a decrease in ocean density resulted in a rise in CO2 by reconstructing how it changed across time periods when the Earth was warming," said the paper's lead author Jenny Roberts, a PhD student in Cambridge's Department of Earth Sciences who is also a member of the British Antarctic Survey. "However what we found was not what we were expecting to see."

In order to determine how the oceans have changed over time and to identify what might have caused the massive release of CO2, the researchers studied the chemical composition of microscopic shelled animals that have been buried deep in ocean sediment since the end of the ice age. Like layers of snow, the shells of these tiny animals, known as foraminifera, contain clues about what the ocean was like while they were alive, allowing the researchers to reconstruct how the ocean changed as the ice age was ending.

They found that during the cold glacial periods, the deepest water was significantly denser than it is today. However, what was unexpected was the timing of the reduction in the deep ocean density, which happened some 5,000 years after the initial increase in CO2, meaning that the density decrease couldn't be responsible for releasing CO2 to the atmosphere.

"Before this study there were these two observations, the first was that glacial deep water was really salty and dense, and the second that it also contained a lot of CO2, and the community put two and two together and said these two observations must be linked," said Roberts. "But it was only through doing our study, and looking at the change in both density and CO2 across the deglaciation, that we found they actually weren't linked. This surprised us all."

Through examination of the shells, the researchers found that changes in CO2 and density are not nearly as tightly linked as previously thought, suggesting something else must be causing CO2 to be released from the ocean.

Like a bottle of wine with a cork, sea ice can prevent CO2-rich water from releasing its CO2 to the atmosphere. The Southern Ocean is a key area of exchange of CO2 between the and atmosphere. The expansion of sea ice during the last ice age acted as a 'lid' on the Southern Ocean, preventing CO2 from escaping. The researchers suggest that the retreat of this sea ice lid at the end of the last ice age uncorked this vintage CO2, resulting in an increase in carbon dioxide in the .

"Although conditions at the end of the last ice age were very different to today, this study highlights the importance that dynamic features such as have on regulating the climate system, and emphasises the need for improved understanding and prediction as we head into our ever warming world," said Roberts.

Explore further: Researchers look to the Southern Ocean for an explanation of the 'Last Glacial Maximum'

More information: Evolution of South Atlantic density and chemical stratification across the last deglaciation, PNAS, www.pnas.org/cgi/doi/10.1073/pnas.1511252113

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9 comments

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Benni
2.3 / 5 (18) Jan 04, 2016
O my god, we've got to do something about this CO2 release before it's too late!
Mike_Massen
3.5 / 5 (16) Jan 04, 2016
Benni with sarcasm
O my god, we've got to do something about this CO2 release before it's too late!
Well it likely won't be too late for the planet as such as we are still some way from secondary thermal runaway but, it might be too late for many in coastal regions where the added effect of storm surges affects habitability...

Benni, what is your problem with CO2/AGW - didnt you study radiative heat transfer at uni ?

What then do you imagine is wrong with radiative transfer, radiative forcing and the particular properties of GHG's to absorb/emit infra red ?

Why can't you address the differential equation within radiative transfer and find out for yourself, you often jump in offhand and claim at the drop of a hat others can't do those equations implying you can, well prove it please ?

If not the above then, what precisely is the problem you seem to have with AGW ?

Why can't you be quantitative like a real Electrical Engineer *should* be able to function ?
Benni
2.3 / 5 (16) Jan 04, 2016
Muttering Mike where were you when the cave dwellers of the melting ice age needed a paper on radiative transfer?

Now it's too late by 15k years when the dawn of the Ice Ages reconstituted CO2 to make up 0.04% of Earth's atmosphere! We're just so darn lucky we're not all dead by now, and most of us would never have been born to begin with.
Mike_Massen
3.6 / 5 (14) Jan 04, 2016
Benni says
Muttering Mike where were you when the cave dwellers of the melting ice age needed a paper on radiative transfer?
Be pardon ?
You made a snipe at the definitive position on AGW & this is the best you can do ?

Do you get it crystal clear now - your claim to be an Electrical/Nuclear Engineer is proven overwhelmingly False at many levels !
Trained uni gradates aren't inarticulate as you on a straightforward issue of Physics !

Benni claims
Now it's too late by 15k years when the dawn of the Ice Ages reconstituted CO2 to make up 0.04% of Earth's atmosphere!
Beg Pardon, CO2 was at 280ppm last century, on what possible basis do you claim 400ppm results from "Ice Ages reconstituted" ?

Benni claims
.. and most of us would never have been born to begin with.
Really ?
Each time you blurt you do put your foot in it & so very solidly too, tah !

Learn Physics !

btw: Tell us why you claim or idly imagine natural gas is somehow not a fossil fuel ?
cjones1
1 / 5 (5) Jan 04, 2016
The article "suggests" that a large amount of CO2 may have been released. There is no time line, graph, or definite source identified. Hypothetically possible, but not convincing. I suspect a volcano is the actual source of the CO2 mentioned.
Vietvet
4.4 / 5 (9) Jan 04, 2016
The article "suggests" that a large amount of CO2 may have been released. There is no time line, graph, or definite source identified. Hypothetically possible, but not convincing. I suspect a volcano is the actual source of the CO2 mentioned.


Wouldn't they have found evidence of volcanic activity in the cores they studied?
ForFreeMinds
2.3 / 5 (6) Jan 04, 2016
Seems to me that if ice is preventing CO2 in the water to escape to the atmosphere, it will eventually disperse to that part of the ice shelf that ends, and then release into the atmosphere. I think the researchers lack evidence for their theory.

"They found that during the cold glacial periods, the deepest water was significantly denser than it is today. However, what was unexpected was the timing of the reduction in the deep ocean density, which happened some 5,000 years after the initial increase in CO2, meaning that the density decrease couldn't be responsible for releasing CO2 to the atmosphere."

This seems to contradict their theory. The initial increase in CO2 happened 5000 years after the reduction in ocean density; thus, happened 5000 years after the ice melted.
InterestedAmateur
3.8 / 5 (10) Jan 05, 2016
Benni... If Ignorance is bliss you must be one happy happy soul. Instead you are angst/attitude and IGNORANCE personified. Do they offer courses in stupidity under your name yet or are they waiting for the waiver.Seriously SHUT UP, adults are speaking.
Jayded
5 / 5 (2) Jan 11, 2016
cjones1 - not sure the volume of CO2 in large volcanic explosions also surely there would be some other signs that would indicate a volcanic driver?

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