Worm droppings can obviously be a treasure for research: By analyzing so-called calcite grains in ancient earthworm excretions, scientists have gained insights into temperatures and precipitation in today's Germany during the Ice Age. Accordingly, the summers in Central Europe were at times warmer than previously known. The scientists say that the potential of the earthworm method for paleoclimate research should now be systematically exploited.
What was the weather like in certain regions during past warm and cold periods in Earth's history? Insights into this question can help to better understand climate events on our planet - also with a view to the currently critical developments. In addition, paleoclimatological information can provide anthropology with clues: They shed light on the living conditions that people once found in certain regions. From a climatic and anthropological point of view, the last ice age in Europe, which reached its peak about 25,000 years ago, is particularly interesting. In order to reconstruct the climate of the past, an international team of researchers has now explored the potential of a new and surprising method as part of the "TerraClime" project.
"Until now, the Ice Age climate has essentially been reconstructed by analyzing microorganisms in deep-sea deposits," says co-author Peter Fischer from Johannes Gutenberg University Mainz. For the mainland, however, climate data are largely missing. To show a way to change this, the scientists used climate archives thanks to Ice Age earthworms. "This new method was discovered at the Université Paris 1 Panthéon-Sorbonne and further developed at the Max Planck Institute for Chemistry," says Fischer. Now the method was put to practical use: "We used it to reconstruct the climate on Schwalbenberg near Remagen and in Nußloch near Heidelberg."
Palaeoclimate research with worm
As the researchers explain, terrestrial sediments from the Ice Age can be found at both sites. In the so-called loess there are sequences from the period from 45,000 to 22,000 years before today. The earthworms of this era have also immortalized themselves in these deposits in the form of 2.5 millimeter large calcite grains - "Earthworm Calcite Granules" (ECGs). These structures, which mainly consist of lime, are excreted daily by earthworms with the droppings. This also happened once in the non-glaciated grasslands that stretched at the two sites in the Ice Age.
The scientists explain that modern analysis methods can be used to obtain key data for paleoclimate research from these earthworm calcite grains: First, the radiocarbon method, which is based on the decay of the naturally occurring radioactive carbon isotope 14C, can be used to precisely determine the age of the structures. Analyzes of the ratios of stable oxygen isotopes and stable carbon isotopes in the grains can then also provide conclusions about two important weather parameters: It is known from earlier investigations of calcite deposits that temperatures and precipitation conditions are reflected in certain patterns of the isotope ratios. In other words, the analysis results can show how warm and how humid it was at the time the worm excrement was formed, the researchers explain.
Warmer summers than previously thought
As they report, the results now confirm the potential of the method: "The analysis of the data obtained using the ECGs shows that 45,000 to 22,000 years ago it was much drier in Central Europe than it is today, with up to 70 percent less moisture," says First -Author Charlotte Prud'homme from the University of Lausanne. This confirms and expands previous knowledge about the Ice Age climate. The researchers emphasize that the testing of the method was also able to provide a new insight: The results of the investigation show that the summer temperatures at that time were significantly higher than previously assumed. "Although the summers at the peak of the last ice age were about four to eleven degrees colder than today, they were only one to four degrees below the values of short, milder climate phases that occurred in the last ice age," says Fischer.
This result is also interesting from an anthropological point of view, emphasizes co-author Olaf Jöris from the Roman-Germanic Central Museum in Mainz: "Perhaps, given these summer temperatures, it was also possible for people in Central Europe to make a living during the cold maximum - at a time for which up to now it is assumed that humans could not survive here,” says the expert in Pleistocene and early Holocene archaeology.
As Fischer finally emphasizes, there is now potential for the earthworm method in paleoclimate research: "Since ECGs can be found in many loess sequences, temperatures and precipitation patterns of the past can now be determined on land over a large area. In this way, a database could be set up with the help of which past climate changes on the mainland could be precisely documented," says the scientist. According to him, this could also be of current importance: "By taking land-based climate data into account, past climate models will be able to access more comprehensive data and cause-effect chains will also be better understood with regard to future climate fluctuations," says Fischer.
Source: Johannes Gutenberg University Mainz, specialist article: Communications Earth & Environment, doi: 10.1038/s43247-022-00595-3