On the trail of prehistoric climate change

Prolonged drought and major water problems are increasingly turning the Iberian Peninsula into a climate hotspot. At the Collaborative Research Centre Scales of Transformation and the Cluster of Excellence ROOTS, Dr Mara Weinelt is investigating how people encountered the climate stress of that time around 4,000 years ago.

Drill cores with labels
© Artur Ribeiro, UFG Kiel

Older individual segments of the 19-metre-long drill core that was extracted at a station northwest of Seville. Researchers at Kiel University hope to gain climatic insights from it from Roman times back to the Neolithic.

Water has always been a rare commodity on the Iberian Peninsula in summer. Nonetheless, the precious commodity is used in generous quantities for vegetable cultivation in Spain and Portugal as well as for tourism in the region. But for some years now, the all-important winter rains have increasingly failed. At the same time, summer heat waves are causing the groundwater level to drop, reservoirs to dry up, and the landscape to wither.

Layer by layer and millimetre by millimetre, the drill core takes us from Roman times back to the Neolithic.

Mara Weinelt

"Above-average temperatures with long-lasting, intense periods of drought and a fall in precipitation as predicted by model scenarios: it's already impossible to overlook the development into a climate hotspot," fears Dr Mara Weinelt, private lecturer at Kiel University. "And it's all down to man-made climate change." In order to investigate and understand similarly dangerous conditions such as those of today and in the future, we need to look far into the past, says the scientific coordinator of the Cluster of Excellence ROOTS and head of a subproject in Collaborative Research Centre (CRC) 1266 "Scales of Transformation". In cooperation with researchers from Spain and Portugal, Kiel scientists from the fields of archaeology and environmental science are currently investigating how societies and the environment on the Iberian Peninsula changed under climate stress between 2,000 and 6,000 years ago.


Nineteen metres down into the past

In today's Spain and Portugal, it is possible to "read" underground what the prevailing climatic conditions were in the transition from the Copper to the Bronze Age. Organic compounds – micro-smallest plant remains – are found in the various layers of sediments there that testify to the temperature and precipitation of that time. "As the climate changes, so too does the vegetation. The plants that grow in arid regions are different from those that grow in humid forests," explained Dr Weinelt.

The ROOTS team uses drill samples to investigate the climatic findings revealed by the subsurface in Spain. More specifically, a 19-meter-long drill core taken from a former lagoon northwest of Seville. On its coast was what was then the biggest Copper Age settlement in Andalusia, a hub of lively trade and cultural exchange. The team is hoping for very good results. "With its clear, fine stratification, the drill core is something very special," reported the expert on the discovery of this "high-resolution climate archive". "This is possibly the first climate archive on the Iberian Peninsula where we can read changes in temperature, precipitation and plant growth per year and at the same time gain information on human intervention in the environment at that time. Layer by layer and millimetre by millimetre, the drill core takes us from Roman times back to the Neolithic."

Dr Weinelt is particularly excited about the results that the drill core will reveal from about 4,200 years ago. "At the time there was a drastic change in climate, which led to a cooling down and an unusual drought in the northern hemisphere." This resulted in large refugee movements in Mesopotamia as well as in India. The ROOTS team's archaeological cooperation partners from the German Archaeological Institute Madrid and the University of Seville were also able to identify changes in settlement structures for the region in question around Seville. "The large settlement on the lagoon was gradually abandoned step by step after centuries of thriving activity about 4,200 years ago – presumably as the result of abrupt climate changes in combination with social changes," said Dr Weinelt. Among other things, the change in funeral rites, which became less and less elaborate over time, bears witness to the crisis at that time. As does the decrease in the quality of clay vessels, which was revealed by the study of shards in large contemporary Portuguese settlements. "It is possible that because of the increase in climate stress and the simultaneous increase in population numbers, people were no longer able to maintain their previously well-regulated economy and cultural activities."

"The burning question for us researchers is: to what extent were people in the Copper and Bronze Ages economically and socially able to adapt to changing climate conditions? And what made them more resilient to abrupt climate change?" Because these reconstructions of the processes of social and environmental changes could also help us to overcome our current challenges.

Author: Jennifer Ruske