Regarding public awareness, floods, heat waves, and drought episodes are among the most apparent indicators of a changing climate. However, forecasting the magnitude of extreme events at local and regional scales has been a significant challenge. Developing reliable small-scale climate models requires testing against past climate records, but these are usually incomplete and cover only partial aspects of environmental parameters.
Role of Stalagmites in Keeping Climate Records
Scientists have used several studies' tree-ring records and independent measurements to analyze short-term climate fluctuations over centuries. The size of tree rings, varying by a few millimeters, offers information on the dynamics of seasonal precipitation. In turn, it points to climatic conditions in a particular growth period.
Compared to tree rings, stalagmites have only been used in exceptional cases to measure climate data and their annual differences systematically. Recently, these mineral deposits have gained the attention of experts due to their potential to reveal natural climate fluctuations. Since the growth zones of stalagmites are a hundred times thinner than a tree ring, just a few centimeters can offer data on the climatic conditions over a thousand years.
In assessing climate extremes, the decisive factor is the rainwater that infiltrates a cave, whose dissolved lime forms the stalagmites. This water originates from local precipitation in the cold and warm seasons, each characterized by a particular isotopic oxygen composition. From these deposits, analyses can be derived to indicate whether and in which years winter or summer precipitation dominated.
Decoding the Secrets of "Kleine Teufelshöhle"
In collaboration with researchers from the Heidelberg Graduate School of Fundamental Physics (HGSFP), experts from KIT studied a stalagmite from the "Kleine Teufelshöhle" found in Franconian Switzerland. The result of their study is described in the paper "Assessment of climate extremes at the regional scale during the last millennium using an annually resolved stalagmite record."
The research team measured the composition of oxygen isotopes using the ion probe at the Institute of Earth Sciences of Heidelberg University. Only this large-scale research device can carry out precise measurements required to analyze annual growth zones of just a few micrometers.
As reported by researchers, the climate data acquired from the "Kleine Teufelshöhle" stalagmite revealed regional and global environmental events. This particular stalagmite under study grew much more slowly than comparable ones since its growth rate is only 0.39 - 1.6 inches (1 - 4 centimeters) per millennium. This annual growth rate is about the width of a single hair strand.
Geoscientist Dr. Tobias Kluge from Karlsruhe Institute of Technology (KIT) states that summers with heavy rainfall are expected in cold years, while very wet winters are expected in warm years. In 1816, the world experienced a frigid climate in a historical event known as the Year Without a Summer. This phenomenon was caused by the eruption of the Tambora volcano in Indonesia in April 1815, possibly exacerbated by an unknown volcanic eruption six years prior.
The collected data from the stalagmite measurements indicate that summers were cold and winters were very wet during this period. Combined with year-round flooding, the event has led to poor harvests and famine.
The information stored in the "Kleine Teufelshöhle" stalagmite also offered evidence of long-term climate fluctuations like the Little Ice Age, whose main period began at the end of the 16th century and continued until the late 17th century.
Researchers noted that this period was marked by frequent flooding, an event documented in Nuremberg near Teufelshöhle. The climate data from the cave was verified using a tree-ring archive taken from the vicinity. The data highlights the cold, dry winter, which delayed the annual ice and snow melts and led to major short-term floods with catastrophic consequences.
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