The collaborative study saw the participation of experts from Germany, Austria, and Switzerland. The research team probed the geological past using stalagmites found in the European Alps, demonstrating that periods of warmth during ice ages typically coincided with peak summer insolation in the Northern Hemisphere.

Ice ages in the Northern Hemisphere have historically been punctuated by sudden transitions from cold to warm phases, each lasting several millennia. These transitions remain a puzzle for scientists, although evidence hints that the size of the continental ice sheets could be a factor.

Past records derived from the ice sheets in Greenland register 25 warm-cold cycles over a period spanning 115,400 to 14,700 years ago. This recent study takes a deeper dive into the enigma, examining 16 similar fluctuations that occurred during the penultimate glacial period, from 185,000 to 130,000 years ago, by analyzing stalagmites from the Melchsee-Frutt cave system in the Swiss Alps.

Stalagmites in caves serve as significant records for climate research, yielding insights into shifts in temperature, precipitation, and vegetation cover. "By precisely determining their age, we can scrutinize the chronological progression of abrupt ice age climate fluctuations identified through oxygen isotope values," clarifies Prof. Dr Norbert Frank from the Institute of Environmental Physics at Heidelberg University.

Dr. Jens Fohlmeister, the study's head, further elaborates on the research objective. "We aimed to find out if changes in the global distribution of insolation, driven by orbital variations, could have influenced these abrupt climate changes, along with the ice volumes in the Northern Hemisphere," he says.

To investigate this, researchers analyzed the age and oxygen isotope composition of stalagmites from the Melchsee-Frutt cave system, focusing on the transitions between warm-cold cycles during the penultimate ice age. Dr. Fohlmeister explains their findings, stating, "Our newly acquired data shows that warm phases often coincided with the peak phase of summer insolation in the Northern Hemisphere, even when the sea level - indicative of the volume of continental ice sheets - remained near its minimum during peak glacial periods." Model simulations substantiate these observations, predicting the frequency and duration of warm phases matching the corresponding sea level and existing insolation.

The research involved contributions from scientists at the Potsdam Institute for Climate Impact Research, the GFZ German Research Centre for Geosciences Potsdam, Heidelberg University, the University of Innsbruck, the Swiss Institute for Speleology and Karst Studies, and the Karst and Caves Natural Heritage Foundation Obwalden. The German Research Foundation funded the study, the results of which were recently published in the journal "Communications Earth and Environment".

Research Report:The role of Northern Hemisphere summer insolation for millennial-scale climate variability during the penultimate glacial

Related Links
Heidelberg University
Beyond the Ice Age