Warming event that took place 56 million years ago led to significant ecological disruption and could shed light on modern climate change

a, Black line, global mean surface ocean pH values across the PETM, from experiment R07sm_Corg (these are our main pH estimates, obtained using the inorganic borate ion calibration and the RH07 age model, and including an assumption of organic carbon burial after the peak PETM). Red circles represent the annual mean pH values at Site 401 (location shown in b) in the model, taken at times in the model simulation that have corresponding δ11B-derived pH data points; note that we do not use all of the observed data points). b, Model-projected spatial pattern of annual mean surface ocean pH at time zero (that is, PETM onset). The star shows the location of Site 401. c–f, Model-projected spatial patterns of the annual mean surface ocean pH anomaly compared with time 0, for the highlighted time points from a (5.0, 31.6, 58.2 and 71.5 kyr after onset). g, Model-projected spatial pattern of annual mean surface ocean pH in the modern ocean under pre-industrial (year 1765) atmospheric CO2 levels (278 p.p.m.). The model is configured as described in ref. 74 and driven with a CO2 emissions scenario that is consistent with RCP 6.0. h, i, Model-projected spatial pattern of the annual mean surface ocean pH anomaly compared with that for 1765, at years 2010 and 2050. The scale is as for c–f. Graphic: Gutjahr, et al., 2017 / Nature

By Sarah Nightingale
30 August 2017

RIVERSIDE, California (UCR Today) – A natural global warming event that took place 56 million years ago was triggered almost entirely by volcanic eruptions that occurred as Greenland separated from Europe during the opening of the North Atlantic Ocean, according to an international team of researchers that includes Andy Ridgwell, a University of California, Riverside professor of earth sciences.

The findings, published today in Nature, refute the more commonly favored explanation that the event, called the Palaeocene-Eocene Thermal Maximum (PETM), was caused by the release of carbon from sedimentary reservoirs such as frozen methane.

“While it has long been suggested that the PETM was caused by injection of carbon into the atmosphere and ocean, the mechanism has remained elusive until now,” Ridgwell said. “By combining geochemical measurements and a global climate model that my group has been developing for over a decade, we have shown that this event was caused almost entirely by carbon emissions from the Earth’s interior.”

Scientists are interested in studying ancient warming events to understand how the Earth behaves when the climate system is dramatically perturbed. During the PETM, atmospheric carbon dioxide more than doubled and global temperatures rose by 5 degrees Celsius, an increase that is comparable with the change that may occur by later next century on modern Earth. While there was significant ecological disruption during the PETM, most species were able to avoid extinction via adaptation or migration. However, the rate of carbon addition during the onset of the PETM lasted for several thousand years, as described in a related Nature Communications paper by Sandra Kirtland Turner, an assistant professor of earth sciences at UCR, whereas current climate change is occurring on a century time-scale.

To identify the source of carbon during the PETM, the researchers studied the remains of tiny marine creatures called foraminifera, the shells of which shed light on the environmental conditions when they lived millions of years ago. By separating the different atomic masses (‘isotopes’) of the element boron in the foraminifera shells, they tracked how the pH of seawater changed during the PETM.

By combining this data with Ridgwell’s global climate model, the team deduced the amount of carbon added to the ocean and atmosphere and concluded that volcanic activity during the opening of the North Atlantic was the dominant force behind the PETM.

“The amount of carbon released during this time was vast—more than 30 times larger than all the fossil fuels burned to date and equivalent to all the current conventional and unconventional fossil fuel reserves we could feasibly ever extract.” Ridgwell said.

An unexpected finding was that enhanced organic matter burial was important in ultimately sequestering the released carbon and accelerating the recovery of the Earth’s ecosystem without massive extinctions.

“Studying the PETM helps us understand the mechanisms that aid recovery from global warming, thereby helping researchers reduce the uncertainties surrounding the Earth’s response to global climate change,” Ridgwell said. “While it is encouraging that most ecosystems were able to adapt during the PETM, today’s global temperature could be increasing at a rate that is too fast for plants and animals to adjust.”

The title of the paper is “Very Large Release of Mostly Volcanic Carbon during the Palaeocene-Eocene Thermal Maximum.” The lead author is Marcus Gutjahr, who completed the project as a post-doctoral researcher at the University of Southampton and is now at the GEOMAR Helmholtz Centre for Ocean Research in Kiel Germany. Other collaborators are from: Open University in Milton Keynes, UK; University of Bristol, UK; Cardiff University, UK; University of Bremen, Germany; University of California, San Diego, and Yale University.

The title of Turner’s paper is “A Probabilistic Assessment of the Rapidity of PETM Onset.” Previous estimates of the speed of carbon released during the PETM onset have varied greatly, from a few decades to around 20,000 years. This paper demonstrates that the PETM onset occurred over less than 5,000 thousand years. Ridgwell is a co-author.

Both studies were partly funded by the Heising–Simons Foundation.


Sarah Nightingale
Tel: (951) 827-4580
E-mail: sarah.nightingale@ucr.edu
Twitter: snightingale

Volcanic Eruptions Drove Ancient Global Warming Event

ABSTRACT: The Palaeocene–Eocene Thermal Maximum1, 2 (PETM) was a global warming event that occurred about 56 million years ago, and is commonly thought to have been driven primarily by the destabilization of carbon from surface sedimentary reservoirs such as methane hydrates3. However, it remains controversial whether such reservoirs were indeed the source of the carbon that drove the warming1, 3, 4, 5. Resolving this issue is key to understanding the proximal cause of the warming, and to quantifying the roles of triggers versus feedbacks. Here we present boron isotope data—a proxy for seawater pH—that show that the ocean surface pH was persistently low during the PETM. We combine our pH data with a paired carbon isotope record in an Earth system model in order to reconstruct the unfolding carbon-cycle dynamics during the event6, 7. We find strong evidence for a much larger (more than 10,000 petagrams)—and, on average, isotopically heavier—carbon source than considered previously8, 9. This leads us to identify volcanism associated with the North Atlantic Igneous Province10, 11, rather than carbon from a surface reservoir, as the main driver of the PETM. This finding implies that climate-driven amplification of organic carbon feedbacks probably played only a minor part in driving the event. However, we find that enhanced burial of organic matter seems to have been important in eventually sequestering the released carbon and accelerating the recovery of the Earth system12.

Very large release of mostly volcanic carbon during the Palaeocene–Eocene Thermal Maximum


  1. Dennis Mitchell said...

    I hope this is true. Methane from the permafrost scares me. My trust in science has wavered. Cross my fingers and hope, but I doubt it will apply.  

  2. Anonymous said...

    Any validity to this experiment?



  3. Jim said...

    The experiment certainly can be improved (see the comment by Martin Hertzberg on 26 August 2017), but this in no way weakens the case for anthropogenic global warming or suggests that the science of radiative thermodynamics is wrong.  


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