Open the secret of volcanic eruptions in the past

A US and French research team has just developed a method that is able to determine the impact of volcanic eruptions in the past on the climate and chemistry of the upper atmosphere and can significantly reduce errors in models that predict future climate change.

In the ' Science ' issue of January 5, scientists at the University of California, San Diego, CNRS National Center for Scientific Research and the University of Grenoble in France have said that traces of chemistry Learning of radioactive dust from previous volcanoes can indicate how much volcanic substances that erupt reach and what chemical reactions take place when those substances are in the atmosphere.

This work is particularly significant because of the effects of atmospheric particles or aerosols, which is unknown in the climate prediction model, Mark Thiemens, professor of biochemistry. and chemistry, head of the Department of Physical Sciences at the University of California, San Diego.

Mr. Joel Savarino is collecting snow samples in Doem C area (Photo: Joel Savarino, CNRS)

'In the predictions of global warming, most of the errors in the predictions are due to aerosols,' explains Thiemens (his laboratory is a development of measurement-based methods. sulfur isotopes) 'Now we have been able to explain all the chemical reactions that require sulfate and this will help eliminate the uncertainties about how these particles are made and transported. how. It is a very important method of addressing climate change. '

Determining the height of the previous volcanic eruption can bring important information about its impact on the climate. If volcanic substances only reach lower altitudes in the lower atmosphere, then the effects are quite local and persist for quite a short time because they will be washed away by rain. But if the eruption reaches a higher altitude, up to the stratosphere it will have a huge effect on the climate.

'In the stratosphere, sulfur dioxide originates from magma, oxidizes and forms sulfuric acid droplets,' said Joël Savarino, a scientist at the CNRS Center and Grenoble University, who led the study. . 'This acid layer may exist for many years in the stratosphere because there is no water in this atmosphere. This acid layer will therefore act as a blanket, reflecting the sun and thus reducing the ground temperature significantly and for many years. '

To distinguish volcanic eruptions that reach the elevation of the stratosphere with the eruptions that do not reach this height, scientists examined sulfur isotopes in radioactive dust stored in Antarctic ice. . The substances erupted from volcanoes are brought there by air currents. Mr. Thiemens, Mr. Savarino and his two students went to Antarctica and restored models by digging snow pits near the Antarctic and Dome area C.

Sulfur reaches a height to the stratosphere, on the oxone layer, will be exposed to short wavelength ultraviolet light. This UV exposure creates a significant proportion of sulfur isotopes. Therefore, the characteristic characteristics of sulfur isotopes in radioactive dust can indicate whether a volcanic eruption reaches the altitude of the stratosphere.

To develop this method, the team focused on two volcanic eruptions. And according to isotope measurements, both these eruptions, the 1963 Agung eruption in Bali and the Pinatubo eruption in 1991 in the Philippines, all reached elevations in the stratosphere.

'Young volcanoes have the advantage of having modern equipment, such as satellites or airplanes, record information about them,' said Savarino, who started his research in measurements. Sulfur isotope when he was a doctor of science working with Mr. Thiemens, said. 'We can therefore compare our measurement results with radioactive dust stored in the snow with atmospheric observations.'

As a result, their isotope measurements are not only consistent with atmospheric observations, but they can also distinguish between the volcanic eruption of Pinatubo and the Cerro Hudson volcanic eruption that same year . The Cerro Hudson volcanic eruption does not " send " the substances it spews to the stratosphere and fallout from the Cerro Hudson eruption leaving traces of sulfur isotopes different from fallout from the Pinatubo eruption.

Substances erupting from volcanoes of eruptions a long time ago are stored in Antarctica, but snow layers change seasonally, deeper and perennial are extremely thin due to the pressure of the snow layer. So, now it is impossible to get enough radioactive dust from the snow to apply isotope methods to all the volcanic eruptions in the past. However, Data from eruptions over the years has shown which sulfur chemical reactions take place in the high atmosphere.

Some scientists suggest that if global warming becomes severe, sulfur can be ' injected ' into the stratosphere to prevent some solar radiation and reduce the temperature. Mr. Thiemens explained that understanding sulfur chemical reactions in the stratosphere is extremely important in determining whether this method is effective or not.

'Sulfur can cause warming or coldness depending on how they are made,' he said. 'They are usually white particles, which tend to reflect light, but if they are made on black particles like soot, they can absorb heat and make the condition worse.'

Thanh Van