Using soil samples from a test field, Erik Thomsen and Rasmus Andreasen from the Department of Geoscience, have demonstrated that strontium runs off from the top layer of soil along with the agricultural lime used to enrich the soil.

They have presented their findings in two new articles in the scientific journal Frontiers in Ecology and Evolution, in a special edition on the use of the strontium method in archaeology and palaeo-ecology. One of the articles was written in collaboration with Tine Rasmussen from the Arctic University of Norway.

In the articles, they refute a hypothesis that researchers from the University of Copenhagen and the National Museum of Denmark came up with in 2019. The hypothesis suggested that strontium from agricultural lime is effectively retained in the upper soil layers and thus does not affect strontium analyses of remnants of prehistoric humans and animals. This hypothesis was suggested after Erik Thomsen and Rasmus Andreasen had shown earlier that year that the origins of the Egtved girl and the Skrydstrup woman could not be determined based on strontium.

Over-limed test field

In the new articles by the two geologists, the term "test field" is crucial. In the field in question, located south of Ikast in Voulund, the geologists could calculate the run-off very accurately because they knew how much agricultural lime had been applied and when.

De Nationale Geologiske Undersøgelser for Danmarks og Grønland (GEUS) benyttede fra 2010 til 2014 From 2010 to 2014, the Geological Survey of Denmark and Greenland (GEUS) used the field for an experiment into test whether large amounts of lime could improve the soil’s ability to bind CO₂. The field was divided into sections on which different amounts of lime were spread. One of the sections was given approx. 48-times more lime than a farmer would normally use.

Erik Thomsen and Rasmus Andreasen took new samples from this section and its neighbouring sections five years after the experiment ended: and the samples showed that 80 to 100 per cent of the strontium storied in the lime had been washed out.

The geologists were able to compare their samples with samples taken from the same section by researchers from the National Museum of Denmark in 2014. These were the samples referred to by the researchers from the National Museum of Denmark and the University of Copenhagen in their 2019 article in which they concluded that strontium from agricultural lime is effectively retained in the upper soil layers, and thus they rejected that agricultural lime affects the strontium signatures in the environment.

Indigenous Vikings

Erik Thomsen, Rasmus Andreasen and Tine Rasmussen have also expanded their studies of strontium isotope values in Danish soil to include several new areas in which they again identified large variations in strontium isotope values in areas not affected by modern agriculture, just as they did in the areas around Egtved and Skrydstrup.

Among other things, they identified similar high values in the moraines on the coast of Southwest Zealand. The results are interesting as they show that the majority of the individuals buried at the Viking burial site at Trelleborg were most likely indigenous to the area and elsewhere in Denmark, for example the area around Jelling, and that most of them did not necessarily come from abroad as previously believed on the basis of the 2010 studies.

This new basis for comparison means that in all probability only three of the 48 individuals were not indigenous to Denmark.

Additionally, these new studies show high and variable strontium isotope values in areas with a low natural lime content in the soil. This phenomenon is not unique to Denmark; it also applies for large areas in the northern hemisphere located close to edge of the ice sheet during the last Ice Age.  The three researchers also point out that if the effect of agricultural lime on strontium levels in the surface environment is not taken into account, then other researchers may well overestimate the mobility of prehistoric individuals.

Further information

The scientific articles from Frontiers in Ecology and Evolution:

Strontium Is Released Rapidly From Agricultural Lime–Implications for Provenance and Migration Studies

Homogeneous Glacial Landscapes Can Have High Local Variability of Strontium Isotope Signatures: Implications for Prehistoric Migration Studies

Contact

Associate Professor emeritus Erik Thomsen
Department of Geoscience
Aarhus University
Mail: erik.thomsen@geo.au.dk
Mobile: +45 2911 2961

Academic employee Rasmus Andreasen
Department of Geoscience
Aarhus University
Mail: rasmus.andreasen@geo.au.dk
Mobile: +45 9350 8497