Two short warm periods in transition between last interglacial and glacial epochs

In a new study, German and Russian climate researchers have found that there were at least two short warming periods in the transition between the last interglacial and glacial epochs, around 115,000 years ago.

The researchers, who evaluated geochemical and pollen analyses of lake sediments in Saxony-Anhalt, Brandenburg and Russia, determined that in Central and Eastern Europe, the slow transition from the Eemian Interglacial to the Weichselian Glacial was marked by a growing instability in vegetation trends with possibly at least two warming events.

Scientists from the Helmholtz Centre for Environmental Research (UFZ), the Saxon Academy of Sciences (SAW) in Leipzig and the Russian Academy of Sciences say that a short warming event at the very end of the last interglacial period marked the final transition to the ice age.

The Eemian Interglacial was the last interglacial epoch before the current one, the Holocene.

It began around 126,000 years ago, ended around 115,000 years ago and is named after the river Eem in the Netherlands.

The followed Weichselian Glacial ended around 15,000 years ago is the most recent glacial epoch named after the Polish river Weichsel.

At its peak around 21,000 years ago, the glaciers stretched as far as the south of Berlin.

The researchers studied lake sediments to reconstruct the climate history of the Eemian Interglacial, since deposits on river and lake beds can build up a climate archive over the years.

As well as pollen concentrations, the researchers analyzed the level and ratios of stable carbon (13C/12C) and oxygen isotopes (18O/16O) in carbonates and organic matter from sediment layers, since these provide information about the vegetation development and an indication of the climate.

The results show a relatively stable climate over most of the time, but with instabilities at the beginning and end of the Eemian Interglacial.

"The observed instability with the proven occurrence of short warming events during the transition from the last interglacial to the last glacial epoch could be, when viewed carefully, a general, naturally occurring characteristic of such transition phases," said Dr Tatjana Boettger of the UFZ, who analyzed the sediment profiles at the UFZ's isotope laboratory in Halle.

"Detailed studies of these phenomena are important for understanding the current controversial discussed climate trend so that we can assess the human contribution to climate change with more certainty," explained Dr Frank W. Junge of the SAW.