Clues on ancient climate change

The sudden cold snap in the northern hemisphere between 12,700 and 11,600 years ago has been found in climate records from Greenland ice cores and Central European lake sediments. It was named after the mountain avens (Latin: Dryas octopetala) – an Arctic plant species that predominantly spreads during cold conditions. The discovery of fossil pines in a French river valley near Avignon now close an important knowledge gap, as they shows how the climate in the Mediterranean changed in this period. With accurate radiocarbon dating, the scientists were able to prove that the buried pines had started their growth in the warm days of the Allerød just before the Younger Dryas and had survived the sudden cold snap for several decades. They were thus witnesses of this extreme climate change.

In their analyzes, the researchers found signs of increased air mass transport from the North Atlantic. “We were surprised that about sixty years before the actual climate change, a significant alteration in the precipitation source was recognized,” says first author Maren Pauly of the GFZ. According to the results, humid air masses arriving from the Atlantic side enhanced, while rainfall originating from the Mediterranean side diminished, evidenced by a steadily increasing variability of the oxygen isotopes of the soil water. Isotopes are atoms with a different number of neutrons in the nucleus. From the ratios of light and heavy isotopes conclusions can be drawn on the origin of air masses and thus of precipitation. “Especially striking is the increase of extreme polar air surges, winter precipitation and winter storms at the beginning of the Younger Dryas,” adds Achim Brauer, Head of GFZ’s section Climate Dynamics and Landscape Evolution and Director of Department 5 at GFZ. Maren Pauly works as a PhD student in his group.

Source: Searching for clues on extreme climate change