During the past 2.8 million years extreme warm periods occurred in the Arctic at irregular intervals. Analytical results from the longest sediment core that has ever been drilled in the terrestrial areas of the Arctic have shown temperatures that were previously considered impossible for the Arctic Circle. In addition, a notable correlation of the warm periods in the Arctic with large melting events in Antarctica points to previously unknown interactions between the Polar Regions.

These are the findings of an international research team led by Professor Martin Melles of the University of Cologne in the latest issue of the journal "Science".

The results come from a sediment core that was drilled in 2009 from the lake El'gygytgyn in the extreme northeastern of Siberia as part of an elaborate winter expedition. The lake was formed 3.6 million years ago when a meteorite impact created a crater 18 kilometers in diameter.

Since then it is continuously collecting sediment, year by year. In addition, of all places the meteorite crashed into one of the few regions in the Arctic, which were not reached by glaciation during the ice ages. As a consequence, the sedimentary sequence is gapless and almost completely undisturbed.

"The uniqueness of the climate archive becomes clear when you keep in mind that with these core samples we advanced about 30 times further into Earth's history, as it is the case with the longest ice cores off the Greenland ice cap," says Martin Melles.

To do so, the age of each sediment layer of Lake El'gygytgyn had to be determined precisely. This was the task of the participating scientists from the GFZ German Research Centre for Geosciences (Helmholtz Association).

The researcher Eeva Haltia-Hovi (GFZ, now University of Lund, Sweden) used the magnetic properties of the minerals in the sediments: the Earth's magnetic field has reversed many times in the past million years, these reversals are reflected in the sediments.

The prerequisite for precise age determination is the detection of the color spectrum, millimeter by millimeter, and the magnetic susceptibility of the drilled sediments across the entire length of the core profile of 318 m. For this, GFZ scientist Norbert Nowaczyk especially developed a core scanner.

He also designed a software package that allows the processing of the extensive data records of all the partners. The diverse sedimentological, geochemical, magneto-and biostratigraphic records could thus be correlated with the known climate cycles of the last 3.6 million years in high resolution. Overall, the resulting age model created for the sediments from Lake El'gygytgyn includes more than 600 nodes.

The "El'gygytgyn Drilling Project" was part of the International Continental Scientific Drilling Program ICDP, the coordination of which is held at the GFZ.

The GFZ's Operational Support Group of the ICDP provided valuable data on various in-situ parameters (temperature, natural gamma radiation, etc.) via geophysical measurements in two wells.

The comparison of downhole measurements with measurements carried out on site on the drill cores allowed the correlation of depths and the filling of gaps in the core, an important prerequisite for further investigations.