Doubling the Level of Atmospheric CO2
Twenty thousand years of massive volcanic eruptions doubled the level of carbon dioxide (CO2) in
Earth's atmosphere 200 million years ago, according to research by Rutgers geologists published
recently in the journal Science.
Morgan Schaller, Jim Wright and Dennis Kent report that the level of atmospheric CO2 went from about
2,000 parts per million to 4,000 parts per million and then shrank back to pre-eruption levels over
the next 300,000 years. This implies that events of this scale have the potential to rapidly double
the concentration of CO2 in earth's atmosphere.
Their work, funded by a grant from the National Science
Foundation, was based on measurements on cores taken from sites in northeastern New Jersey. Schaller is a
PhD student, Wright an associate professor and Kent a professor of earth and planetary sciences in Rutgers'
School of Arts and Sciences.
Rifting and the Break-up of Pangea
Two-hundred million years ago, the super-continent called Pangea began to break apart, forming a rift
stretching from what is now Nova Scotia to Brazil. A series of exceptionally massive volcanic eruptions,
called the Central Atlantic Magmatic Province (CAMP), ensued and are now preserved in volcanic rocks spread
over four continents.
Estimating CO2 in the Ancient Atmosphere
This rifting formed lake basins, like the Newark Basin in New Jersey, and rock cores
through these ancient lake sediments preserve the lavas from the CAMP eruptions. Schaller was able to estimate
the carbon dioxide content of the atmosphere using ancient soils from the Newark Rift basin - soils that formed
before and after each of the eruptions. Using a mass spectrometer, he measured the carbon isotopic composition
of carbonate nodules formed in these soils, which are sensitive to the concentration of CO2 in earth's atmosphere,
and reconstructed ancient atmospheric composition.
"You see these big eruptions throughout Earth's history," says Schaller. "But it's always been unclear what
they can do to the atmosphere. It turns out, they may do a lot."
A Scale Unknown in Modern Times
To a non-geologist, it might seem that any volcanic eruption might affect the atmosphere, but it's important to
understand even the largest eruptions of individual volcanoes seem puny beside the events Schaller studies - a
million cubic kilometers of lava pouring out of fissures in the earth's surface in less than 20,000 years.
"Mt. St. Helens in 1980, Mt. Pinatubo in 1991 - those were big eruptions," Kent says. "Lots of ash and aerosols,
but hardly a ripple in atmospheric CO2."
Kent added that the famous Krakatoa eruption in 1883 occurred before regular measurements of atmospheric CO2,
which began in 1958. But ice core data from that time show no detectable perturbation of atmospheric carbon dioxide.
The Rate of Volcanism is the Key
"Where CAMP really packs a punch on the atmosphere is in the rate of volcanism," Wright adds. "The rate of
volcanism there was roughly 1,000 times the rate of volcanism that formed the Big Island of Hawaii - and keep
in mind that most of Hawaii's volume is below sea level, so it's really higher than Mt. Everest. The key point
of Morgan's research is that the CO2 increase requires a high rate of volcanism."
Support and Cooperation
Schaller used cores taken by the U.S. Army Corps of Engineers, who took hundreds of cores in the Newark Basin
as part of a plan to construct a tunnel for diversion of Passaic River flood waters in the 1980s. Schaller and
his co-authors focused on these cores, along with those taken as part of the Newark Basin Coring Project with
National Science Foundation funding in the 1990's. Without the stratigraphic context of the Newark basin, and
the cores archived at the Rutgers Core Repository, the discoveries of this study would not have been possible.
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| Two-hundred million years ago rifting was breaking up the supercontinent of Pangea. This rifting was accompanied by intense volcanic activity with high levels of carbon dioxide emissions. Over a period of just 20,000 years, carbon dioxide levels in the atmosphere had doubled. Images by USGS.
| Core samples from Essex County, New Jersey, used by Schaller, Wright and Kent to measure ancient atmospheric carbon dioxide. Image by Rutgers University.