Studying stalagmites – cave deposits that grow from the floor, and can sometimes reach the ceiling – can reveal more data about what our planet's climate looked like in the distant past. Experts are now using data contained within these structures to study instances of past climate change.
Scientists from the California Institute of Technology (Caltech), in Pasadena, say that cave systems are very likely to respond to changes occurring in the environment outside, especially to variations in atmospheric carbon dioxide levels.
Since the start of the Industrial Age, these concentrations have been growing at an ever-accelerating pace, and experts believe that this change is reflected in the composition of cave stalagmites. At this point, most historical climate records are extracted from polar ice cores.
This means that the datasets contain a bias towards high latitudes, and sediments collected from the depths of the North Atlantic Ocean. It may soon be possible to augment this information with data collected from caves around the world.
According to geologists, a coupled ocean-atmosphere phenomenon called El Niño is one of the main factors influencing climate variability today. Its point of origin lies in the equatorial Pacific, an area not covered by ice cores samples.
“Stalagmites are the ice cores of the tropics,” explains Caltech professor of geochemistry and global environmental science, Jess Adkins. He led the team that recently collected stalagmite data from caves in northern Bornea.
Together with Caltech colleague and geochemist Kim Cobb, the expert analyzed oxygen isotope levels in these samples. This allowed the team to reconstruct a history of the climate over the tropical West Pacific during the late Pleistocene Era, which ranged from 570,000 to 210,000 years ago.
Details of their research were published in the May 3 issue of the top journal Science Express. Nele Meckler, who conducted the work as a Caltech postdoctoral scholar, was the lead author of the paper.
Interestingly, the samples revealed no traces of the Mid-Brunhes Event (MBE), a period that occurred around 430,000 years ago, when atmospheric CO2 levels spiked in the Arctic by about a third. This led to significant temperature increase in the area, and experts wanted to know whether the Equator suffered similar effects.
No signs of elevated temperatures or CO2 concentrations were discovered in the stalagmite records. This suggests that climate interactions were significantly more complex at that time than researchers were first led to believe.