A fascinating piece of research by Beth Fox of Waikato University and Tammo Reichgelta and William J. D'Andrea of the Columbia University, USA has been able to analyse soft tissue from 23 million years ago and discover more about CO2 levels of the Oligocene/Miocene period.
On Radio NZ Nine to Noon Kathryn Ryan,
On Radio NZ Nine to Noon Kathryn Ryan,
The problem with obtaining knowledge of this type from 23 million years ago is that most samples are rock and obtaining soft tissue from that period, which can be dated accurately, is a real challenge. Beth Fox had the idea (and knew the place in New Zealand) of a cone shaped volcano caldera where there was no input from rivers to contaminate the scene and where the debris that fell to the bottom of the cone was preserved close to its natural state, over millions of years.
The research involved drilling a 180 metre core sample in the bottom of the volcano caldera and this revealed a perfect, layered record, going back more than 23 million years and examination of the contents revealed leaves that were perfectly preserved and could be analysed for the CO2 levels of that period.
The research involved drilling a 180 metre core sample in the bottom of the volcano caldera and this revealed a perfect, layered record, going back more than 23 million years and examination of the contents revealed leaves that were perfectly preserved and could be analysed for the CO2 levels of that period.
What they revealed was that changes in the stomatal cells and carbon isotope ratios in the leaves indicated a major increase in the levels of CO2, rising from about 500 parts per million (ppm) to between 750 and 1550 ppm over a span of less than 10,000 years.
“What surprised us was how such large CO2 fluctuations happened over geologically, relatively short time scales,” says Dr Fox.
“We found that atmospheric CO2 levels began to rapidly increase around the same time as the ice-sheet began to decline, and more importantly, even when the CO2 levels dropped back to previous levels, the ice kept on melting. Once the process of destabilisation of the ice-sheet was kick-started, it could keep going by itself.”
The ice goes from about 125% of the present day Antarctic ice sheet to about 50% of the present day Antarctic ice sheet over that period of time. It’s a massive loss of ice, but the carbon dioxide levels do not stay high for the whole time, they actually go down and the ice appears to be able to keep on melting by itself presumably after it has been kick started by that carbon dioxide increase.”
“What surprised us was how such large CO2 fluctuations happened over geologically, relatively short time scales,” says Dr Fox.
“We found that atmospheric CO2 levels began to rapidly increase around the same time as the ice-sheet began to decline, and more importantly, even when the CO2 levels dropped back to previous levels, the ice kept on melting. Once the process of destabilisation of the ice-sheet was kick-started, it could keep going by itself.”
The ice goes from about 125% of the present day Antarctic ice sheet to about 50% of the present day Antarctic ice sheet over that period of time. It’s a massive loss of ice, but the carbon dioxide levels do not stay high for the whole time, they actually go down and the ice appears to be able to keep on melting by itself presumably after it has been kick started by that carbon dioxide increase.”
This important research gives us an insight into what happens to the planet as the CO2 levels rise and will help to identify a point when the climate will reach a tipping point and change from one stage to another. By implication the tipping point would move us from the climate we have today to one with higher temperatures and much higher sea levels due to the melting of the ice caps. Having tipped the climate to a new state it did not recover even when CO2 levels returned to the original levels again.
The cause of the increase in CO2 is not known but it could be a comet impact, indicated by spherule layers at the Oligocene Miocene boundary or volcanos (La Garita Caldera of Colorado), or possibly both.
The cause of the increase in CO2 is not known but it could be a comet impact, indicated by spherule layers at the Oligocene Miocene boundary or volcanos (La Garita Caldera of Colorado), or possibly both.
Another surprise was the relatively quick reduction in the levels of CO2 which possibly could have been the result of the opening up of the Drake passage between South America and West Antarctica which allowed the Southern Ocean to circulate and absorb or consume CO2 from the atmosphere.
There is still a lot of uncertainty about the timeline but Beth Fox and colleagues have added some important parts to the jigsaw and with a really neat piece of research.
There is still a lot of uncertainty about the timeline but Beth Fox and colleagues have added some important parts to the jigsaw and with a really neat piece of research.
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