A team of researchers, including geoscientists from the University of Heidelberg and the Karlsruhe Institute of Technology, have demonstrated that stalagmites, when combined with tree ring data, can provide a unique archive for studying natural climate fluctuations over hundreds of years. By analyzing the isotopic composition of oxygen in a stalagmite formed from limestone water in a cave in southern Germany, the researchers were able to reconstruct short-term climate fluctuations over centuries and correlate them with historically documented environmental events.

The size of tree rings, which varies by a few millimeters, provides information about the dynamics of seasonal precipitation and climatic conditions during specific growth periods. Stalagmites, on the other hand, have only been used in exceptional cases to systematically measure climate data and annual variations. The decisive factor is the rainwater that infiltrates into a cave, forming the stalagmites. This water comes from local precipitation in the cold and warm seasons and is characterized by a unique isotopic composition of oxygen, allowing for analysis to determine which years were dominated by winter or summer precipitation.

The researchers studied a stalagmite from the «Kleine Teufelshöhle» in Franconian Switzerland, with a growth rate of one to four centimeters per millennium. The thin growth zones of stalagmites provide data on climatic conditions over a thousand years. Oxygen isotope composition was measured using the ion probe at the University of Heidelberg’s Earth Science Institute.

The data obtained from the stalagmite revealed regional and global environmental events, such as the unusually cold year of 1816, known as the Year Without a Summer, caused by the eruption of the Tambora volcano in Indonesia in 1815. The stalagmite measurements showed cold summers and very wet winters during this time, leading to poor harvests and famines.

The information stored in the stalagmite also provides evidence of long-term climate fluctuations, such as the Little Ice Age, which occurred from the late 16th century to the late 17th century, marked by frequent floods. The cave’s climate data were verified using tree ring archives from the surrounding area.

The research results were published in the journal «Letters on Planetary and Earth Sciences» and involved scientists from Heidelberg, Karlsruhe, Berlin, Hohenheim, and Mannheim.