West Antarctic volcanic eruptions coincided exactly with the onset of the period of most rapid, widespread climate change in the Southern Hemisphere during the end of the last ice age, as well as the start of increasing global greenhouse gas concentrations.
These eruptions were identified using geochemical fingerprinting to Mt. Takahe, a shield volcano located about 350 km north of the WAIS Divide drilling site.
Rather than a highly improbable coincidence, the researchers postulate that these halogen-rich eruptions created a stratospheric ozone hole over Antarctica that, analogous to the modern human-caused ozone hole, led to large-scale changes in atmospheric circulation and hydroclimate throughout the Southern Hemisphere triggering the onset of the shift from a largely glacial to a largely interglacial climate state.
The study was lead by Professor Joe McConnell at the Desert Research Institute (DRI) – an expert in ice core research. Associate Professor John F. Burkhart at the Department of Geosciences, University of Oslo has expertise in ice core analysis and atmospheric transport modeling and provided information to quantify the possible extent of the eruptions.
Additional analyses and modeling studies critical to support the authors’ findings were made by collaborating institutions throughout the U.S. and around the world.
Ice cores keep evidences for climate changes
The ice core samples taken from Antarctica give evidences for a sudden poleward shift in westerly winds encircling Antarctica with corresponding changes in sea ice extent, ocean circulation, and ventilation of the deep ocean.
Evidence of these changes are found in many parts of the Southern Hemisphere and in different paleoclimate archives, but what prompted these changes has remained largely unexplained.
"We know that rapid climate change at this time was primed by changes in solar insolation and the Northern Hemisphere ice sheets”, explains McConnell, who is the leader of the study. “Glacial and interglacial cycles are driven by the sun and Earth orbital parameters that impact solar insolation (intensity of the sun’s rays) as well as by changes in the continental ice sheets and greenhouse gas concentrations”.
"We postulate that these halogen-rich eruptions created a stratospheric ozone hole over Antarctica that, analogous to the modern ozone hole, led to large-scale changes in atmospheric circulation and hydroclimate throughout the Southern Hemisphere”, he added. “Although the climate system already was primed for the switch, we argue that these changes initiated the shift from a largely glacial to a largely interglacial climate state. The probability that this was just a coincidence is negligible.”
Furthermore, the fallout from these eruptions – containing elevated levels of hydrofluoric acid and toxic heavy metals – extended at least 2,800 kilometers from Mt. Takahe and likely reached southern South America.
How can the ice cores explain climate changes?
The ice core laboratory at DRI enabled high-resolution measurements of ice cores extracted from remote regions of the Earth, such as Greenland and Antarctica. One such ice core - the West Antarctic Ice Sheet Divide (WAIS Divide) core was drilled to a depth of more than two miles (3,405 meters), and much of it was analyzed in the Ultra-Trace Laboratory at DRI for more than 30 different elements and chemical species.
The precise, high-resolution records illustrate that the chemical anomaly observed in the WAIS Divide ice core was the result of a series of eruptions of Mt. Takahe located 350 kilometers to the north. Mass spectrometers enable measurement of these elements to as low as parts per quadrillion (the equivalent of 1 gram in 1,000,000,000,000,000 grams).
– No other such long-lasting record was found in the 68,000-year WAIS Divide record”, notes Michael Sigl, a Ph.D. who first observed the anomaly during chemical analysis of the core. “Imagine the environmental, societal, and economic impacts if a series of modern explosive eruptions persisted for four or five generations in the lower latitudes or in the Northern Hemisphere where most of us live!”
Volcano eruptions from the Mt. Takahe
Discovery of this unique event of eruptions in the WAIS Divide record was not the first indication of a chemical anomaly occurring ~17,700 years ago.
"The anomaly was detected in much more limited measurements of the Byrd ice core in the 1990s”, according to McConnell, “but exactly what it was or what created it, wasn’t clear. Most previous Antarctic ice core records have not included many of the elements and chemical species that we study, such as heavy metals and rare earth elements, that characterize the anomaly – so in many ways these other studies were blind to the Mt. Takahe event.”
The initial findings from the DRI laboratory were confirmed by analysis of replicate samples from WAIS Divide, producing nearly identical results, as from preserved samples of the Byrd Core available from the University of Copenhagen and ice from Taylor Glacier in the Antarctic Dry Valleys.
The WAIS Divide ice core sample holds data about the past 30,000 years of snowfall in individual layers of ice, thus enabling detailed examination of conditions during deglaciation.
About the study
This study was recently published in the leading American scientific journal Proceedings of the National Academy of Sciences of the United States of America (PNAS). The study has been carried out with contributions from several researchers from different institutions and countries, and lead by Professor Joe McConnell at the Desert Research Institute (DRI), US. From University of Oslo Associate Professor John Faulkner Burkhart has contributed.
Joseph R. McConnella,J.R. et al. 2017. Synchronous volcanic eruptions and abrupt climate change ∼17.7 ka plausibly linked by stratospheric ozone depletion, PNAS, Vol. 114 no. 38; pp 10035–10040, doi: 10.1073/pnas.1705595114