By: Editorial Team Reading time: 3 Minutes
◤ GEOLOGY
Stalagmite isotopes refine the climate model
What can climate research learn from dripstone caves? What did 10th-century warrior-horsemen eat? The distribution of certain isotopes provides deep insights into history – and prognoses for the future. The systems that analyze them use high-purity gases.
"Fifteen years ago, climate models predicted a probable temperature increase of from 1 to 1.5 degrees Celsius. With a possible deviation of plus-or-minus 5 degrees, it was clearly not a reliable prognosis. Today, thanks to climate history research, the deviation tolerance might be reduced to a half a degree,” says Attila Demény. He is the Director of the Institute for Geological and Geochemical Research in Budapest: “Using data collected throughout the world, now we can derive fairly precise pictures of the climate.”
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Comparison with earlier warming periods shows that over the longer term the weather may become much more humid.
Attila Demény, Director of the Institute for Geological and Geochemical Research in Budapest
500,000 years of climate history
The contribution of his institute consists in the analysis of stalagmite and flowstone samples from the world over. They give us a glimpse of a half million years of climate history. The typical stalagmite columns form from rainwater seeping through limestone formations. They consist mainly of calcium carbonate (CaCO₃) and contain trace elements such as phosphorous, magnesium and strontium.
“In general, the warmer and wetter the climate, the greater the biological activity on the ground over the cave and the greater the phosphorous content of the stalagmite,” explains the geoscientist. “Based on the distribution of the different oxygen isotopes, we can determine whether the rain clouds came primarily from the Atlantic or from the Mediterranean Sea. That gives us more information about the climatic conditions.”
Comparison of warm phases
Using those data – along with data from many other sources – scientists have developed maps of historic climate conditions. In the meantime, they are enabling detailed prognoses for further development – in the Carpathian basin, for example: increased warming may first create a Mediterranean climate in the coming decades there, with long dry spells and very irregular precipitation. “But the comparison with earlier warming periods also shows that over the longer term the weather may become much more humid,” predicts Attila Demény. “For our region, long-term global warming may not be necessarily a bad thing – but for the Netherlands or Venice, however, it’s rather menacing.” The accuracy of today’s climate models is based not least on the precision of laboratory analyses. Carbon dioxide from the carbonate samples, and water from their fluid inclusions are extracted from the stalagmites and flowstones, then the stable isotopic compositions of the molecules are subsequently determined using a mass spectrometer, or a laser spectroscope. Both methods use high-purity gases such as helium as a carrier gas. The institute obtains them from Messer.
Millet for warriors
The same methods are also used at the Institute for Geological and Geochemical Research to research the dietary habits of Hungarians shortly after they first arrived in the Carpathian basin. For her dissertation, Ariana Gugora is studying bones and teeth from 10th century cemeteries. The surprising result of her investigation: “Based on carbon and nitrogen isotopes, it is possible to determine how much animal protein people consumed during their lifetime. Amazingly, military leaders – in other words, the topmost elite – did not eat more meat than the rest of the population. Their main source of food was apparently millet – probably because it is non-perishable, highly nutritious, and easily transported by horse during military campaigns.”