New study shows three abrupt pulse of carbon dioxide during last deglaciation

October 29, 2014
A composite image of the Western hemisphere of the Earth. Credit: NASA

A new study shows that the rise of atmospheric carbon dioxide that contributed to the end of the last ice age more than 10,000 years ago did not occur gradually, but was characterized by three "pulses" in which C02 rose abruptly.

Scientists are not sure what caused these abrupt increases, during which C02 levels rose about 10-15 parts per million – or about 5 percent per episode – over a period of 1-2 centuries. It likely was a combination of factors, they say, including ocean circulation, changing wind patterns, and terrestrial processes.

The finding is important, however, because it casts new light on the mechanisms that take the Earth in and out of ice age regimes. Results of the study, which was funded by the National Science Foundation, appear this week in the journal Nature.

"We used to think that naturally occurring changes in took place relatively slowly over the 10,000 years it took to move out of the last ice age," said Shaun Marcott, lead author on the article who conducted his study as a post-doctoral researcher at Oregon State University. "This abrupt, centennial-scale variability of CO2 appears to be a fundamental part of the ."

Some previous research has hinted at the possibility that spikes in dioxide may have accelerated the last deglaciation, but that hypothesis had not been resolved, the researchers say. The key to the new finding is the analysis of an ice core from the West Antarctic that provided the scientists with an unprecedented glimpse into the past.

Scientists studying past climate have been hampered by the limitations of previous ice cores. Cores from Greenland, for example, provide unique records of rapid climate events going back 120,000 years – but high concentrations of impurities don't allow researchers to accurately determine atmospheric carbon dioxide records. Antarctic ice cores have fewer impurities, but generally have had lower "temporal resolution," providing less detailed information about atmospheric CO2.

However, a new core from West Antarctica, drilled to a depth of 3,405 meters in 2011 and spanning the last 68,000 years, has "extraordinary detail," said Oregon State paleoclimatologist Edward Brook, a co-author on the Nature study and an internationally recognized ice core expert. Because the area where the core was taken gets high annual snowfall, he said, the new ice core provides one of the most detailed records of atmospheric CO2.

"It is a remarkable and it clearly shows distinct pulses of carbon dioxide increase that can be very reliably dated," Brook said. "These are some of the fastest natural changes in CO2 we have observed, and were probably big enough on their own to impact the Earth's climate.

"The abrupt events did not end the ice age by themselves," Brook added. "That might be jumping the gun a bit. But it is fair to say that the natural can change a lot faster than was previously thought – and we don't know all of the mechanisms that caused that rapid change."

The researchers say that the increase in atmospheric CO2 from the peak of the last ice age to complete deglaciation was about 80 parts per million, taking place over 10,000 years. Thus, the finding that 30-45 ppm of the increase happened in just a few centuries was significant.

The overall rise of during the last deglaciation was thought to have been triggered by the release of CO2 from the deep ocean – especially the Southern Ocean. However, the researchers say that no obvious ocean mechanism is known that would trigger rises of 10-15 ppm over a time span as short as one to two centuries.

"The oceans are simply not thought to respond that fast," Brook said. "Either the cause of these pulses is at least part terrestrial, or there is some mechanism in the ocean system we don't yet know about."

One reason the researchers are reluctant to pin the end of the last solely on CO2 increases is that other processes were taking place, according to Marcott, who recently joined the faculty of the University of Wisconsin-Madison.

"At the same time CO2 was increasing, the rate of methane in the atmosphere was also increasing at the same or a slightly higher rate," Marcott said. "We also know that during at least two of these pulses, the Atlantic Meridional Overturning Circulation changed as well. Changes in the would have affected CO2 – and indirectly methane, by impacting global rainfall patterns."

"The Earth is a big coupled system," he added, "and there are many pieces to the puzzle. The discovery of these strong, rapid pulses of CO2 is an important piece."

Explore further: The last ice age

More information: Centennial-scale changes in the global carbon cycle during the last deglaciation, Nature, DOI: 10.1038/nature13799

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9 comments

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Captain Stumpy
4.3 / 5 (6) Oct 29, 2014
study is paywalled

does anyone have a link to the entire thing?

I would like to read it

If you don't, then you can PM me at http://saposjoint.net/Forum/ (my login name there is: Truck Captain Stumpy) or at http://www.sciforums.com/ (TruckCaptainStumpy) and send me your e-mail address

i will be willing to swap a science magazine full study for the above full study
(for anyone who has access to this but doesn't have access to AAAS or Science Mag)
Da Schneib
5 / 5 (5) Oct 29, 2014
This news release from UW has a few more details you may find helpful: http://www.washin...ciation/

I wasn't able to find a copy of the study anywhere.
gkam
4.4 / 5 (7) Oct 29, 2014
This is the closest I got:
http://www.nature...799.html
dustywells
1 / 5 (1) Oct 30, 2014
Why do they only mention the amount of change and not the total ppm?
Scroofinator
1 / 5 (2) Oct 30, 2014
Either the cause of these pulses is at least part terrestrial, or there is some mechanism in the ocean system we don't yet know about.


It is likely both. Take for instance the current eruption in Iceland, we know it releases copious amounts of GHGs.
http://www.thenew...missions
A series of similiar eruptions over decades could theoretically lead to this CO2 increase.
Da Schneib
5 / 5 (1) Oct 30, 2014
This greatly increases the likelihood that blooms of zooplankton generated the CO₂; this is just what we'd expect if that were the case.
Scroofinator
1 / 5 (1) Oct 30, 2014
I think you got it backwards Schneib, an increase in oceanic CO2 concentrations leads to more plankton.
http://phys.org/n...co2.html
gkam
3.7 / 5 (3) Oct 30, 2014
There are phytoplankton, which use photosynthesis to make Oxygen, and zooplankton, which respires Oxygen.
Scroofinator
1 / 5 (1) Oct 30, 2014
Understood gkam, but if you read the linked article you would see why it's backwards.

The main result was that the smallest plankton, the pico- and nanoplankton, grow more rapidly and produce more organic carbon when CO2 levels are high. But, as these tiny plankton proliferate, they consume mineral salts, like nitrates, which would otherwise be available for larger species. The growth of these tiny plankton, which are at the bottom of the food chain, therefore deprives the diatoms, larger phytoplankton belonging to the microplankton. This experiment was too short to determine whether the phenomonon would have an impact on the nutrition of zooplankton, which feed on phytoplankton.


So the only way there can be large numbers of zooplankton is if there already a large bloom of phytoplankton. One converts CO2 to oxygen, the other takes oxygen and makes CO2. The question is, which converts more? That would be a nice model to create.

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