New Study Shows Three Abrupt Pulses of CO2 during Last Deglaciation

KC_SLIDE_Examining-core-for-NSF

Breakthrough after field project collects richly detailed ice core records from Antarctica

 

A new multi-institutional study including Scripps Institution of Oceanography, UC San Diego, 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 CO2 rose abruptly.

Scientists are not sure what caused these abrupt increases, during which levels of carbon dioxide, a greenhouse gas, rose about 10-15 parts per million (ppm) – or about five percent per episode – over a period of one to two centuries. It likely was a combination of factors, they say, including ocean circulation, changing wind patterns, and terrestrial processes. Scripps geoscientist Jeff Severinghaus said the three episodes, which took place 16,100 years ago, 14,700 years ago, and 11,700 years ago are strongly linked to abrupt climate change events that took place in the Northern Hemisphere.

“Abrupt climate change has its own small but significant impacts on atmospheric CO2 and no one knew that before now,” said Severinghaus, a study co-author.

Results of the National Science Foundation-funded study appear today in the journal Nature.

“We used to think that naturally occurring changes in carbon dioxide 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 postdoctoral researcher at Oregon State University. “This abrupt, centennial-scale variability of CO2 appears to be a fundamental part of the global carbon cycle.”

Some previous research has hinted at the possibility that spikes in atmospheric carbon 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 a detailed enough record to be able to see changes on fine time scales. The core was retrieved ­– with difficulty – from a region in which snow accumulated and compacted at a rate of 25 centimeters per year. That meant the ice core preserved a more detailed record from the gas bubbles trapped in the ice than did other cores from Antarctic regions where only 2 centimeters of ice represent a year.

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.

Severinghaus said the new cores, collected during the recently concluded multi-year WAIS Divide field project, came from a part of Antarctica so snowy that researchers’ camps were frequently buried in snowdrifts.

Coring in that location is “not an easy thing to do, so that’s why it wasn’t done before,” Severinghaus said.

The new core from West Antarctica, drilled to a depth of 3,405 meters (11,170 feet) 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.

“It is a remarkable ice core 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 carbon cycle 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 rate of change during these events is still significantly less than present-day changes in atmospheric CO2 concentrations. The Keeling Curve record of atmospheric carbon dioxide, launched by the late Scripps geochemist Charles David Keeling, recorded levels of 315 ppm when it began in 1958. In 2014, monthly average concentrations reached 401 ppm, an increase of more than 85 parts per million in less than 60 years.

The overall rise of atmospheric carbon dioxide during the last deglaciation was thought to have been triggered by the release of CO2 from the deep ocean – especially the Southern Ocean. But the century-scale events must involve a different mechanism that can act faster, said Severinghaus. One possibility is a major increase in the winds that blow around Antarctica, which are known to bring up CO2 from mid-depths and cause it to outgas into the atmosphere.

 

12 thoughts on “New Study Shows Three Abrupt Pulses of CO2 during Last Deglaciation”

  1. “… from a part of Antarctica so snowy that researchers’ camps were frequently buried in snowdrifts. …” Does that not speak for these ice cores being much younger than you deem them to be? There has been quite some controversy about whether these cores actually date back that far or what the correct time scales are. Give a few hundred or a few thousand years and the question whether CO2 increase predates warming or is an after-effect gain is in limbo …

    1. Dear CrisisMaven,

      The dating of the ice core is not in question – we can identify annual layers and have counted them, much as tree rings are counted. Furthermore, the atmospheric methane record from our ice core clearly shows the abrupt fluctuations of tropical rainfall, where most methane was produced during pre-industrial time. These methane fluctuations can be confidently matched to the cave records from the tropics, which have the unique property that they can be radiometrically dated using uranium and thorium radioactive decay. These precise clocks agree well with our annual layer counting. Hence, our dating of the ice core is highly robust and not in doubt.

      Regarding the question you raise of whether the temperature or the CO2 rose first, it is clear from our record that the temperature rose first. This is consistent with many, many other studies done on Antarctic ice cores over the past three decades, and is not in any doubt.

      For the significance of this finding, please see my commentary on http://www.realclimate.org/index.php/archives/2004/12/co2-in-ice-cores/

      Sincerely,
      Jeff Severinghaus
      Professor of Geosciences
      Scripps Institution of Oceanography

  2. According to Henrys Law there is a connection between ocean temperature and the CO2-level (in balance).
    From several comments on Internet I have noted that 1 degree(C)
    seems to correspond with app. 15 ppm increase of CO2.
    From this I have assumed that the quick increases in CO2 just after a temperature rise might be caused by a rise of ocean temperature.
    30-45 ppm corresponds to 2-3 degrees ocean temperature increase.
    Is this a possible explanation?

    (Sorry for a mistake in my first comment)

    1. Dear Knut,
      You are right, ocean surface warming should cause a rise of about 10 ppm per degree in atmospheric CO2. Indeed, immediately prior to and coincident with the latter two of these three “steps” in CO2, there were large abrupt warmings of the northern hemisphere. So your explanation is probably the most likely one for these two events. But it cannot explain the first. At that time the ocean surface did not warm.

  3. What is known about the retreat of ice for this time?
    Biological processes following thawing should be abruptly contributing CO2 especially if large areas change from (sub)arctic to our present conditions.

    1. Dear Energetic,
      Ice retreated rapidly in the few hundred years after these two abrupt events. We know this because sea level rose rapidly in so-called “melt water pulse” 1A and 1B, corresponding to the event at 14.7 ka and 11.7 ka, respectively. However, biological CO2 does not appear to the cause of these two rapid CO2 increases, because the carbon-13 isotope of atmospheric CO2 does not show the tell-tale fingerprint of biological CO2 (depletion in C-13). Although a substantial amount of CO2 was no doubt released from warming soils, a large amount of new vegetation also probably grew at the same time on the land newly exposed by retreating ice. So the biological effects (respiration and photosynthesis) probably canceled each other out.

      Sincerely,
      Jeff Severinghaus
      Professor of Geosciences

  4. Can you elaborate on whether or not the ice core data after 1958 compliments Mauna Loa data. If so, have these findings been published?

  5. It doesn’t really matter which goes up first in this climate system, as temperature, CO2 and methane are coupled. Whatever happens to one, happens to all. Sometimes temp goes up first and triggers the releases of CO2 and methane, other times CO2 or methane go up first and trigger the temperature rise.

  6. I am an amateur student of historical global and climate change corresponding with fluctuations of temperature(temp) change up and down.

    The three temp fluctuations showing large upward Co2 spikes in the last roughly 14-15,000 yrs. , 12,000 yrs., and 10,000 yrs. respectively were shown by analysis of Antarctic ice cores are fascinating. These Co2 fluctuations seem to have a causal relationship with mid to deep oceanic ‘flip flops.’

    I am 75 yrs. old and remember the headlines of the 1970’s believing a ‘new ice age approaching. Now 40 yrs. later we are in global warming. Aside from pollution caused by humans, is it safe to say that ‘mother earth’ may be the true decider of her global climate change?

  7. @ harry

    hi harry; you have 21 years on me; I was in high school in the 70’s,and don’t remember any of the “headlines” about global cooling or the next ice age coming

    but i’d suggest that it is quite obviously up to us whether we want “mother earth” to remain as a viable lifeboat for her , supposedly, most intelligent species.

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