Tracing Circumpolar Climate Change 8'800 Years Back

10:51, February 8, 2021

Ural team of scientists went to Yamal peninsula (Russia) and came back with the longest chronology for the circumpolar regions on Earth

Scientists have built a continuous tree-ring chronology with a duration of 8768 years (from 6748 BC to 2019) on trees, the remains of which were found in the river and peat deposits of the Yamal Peninsula. This chronology is the longest for the circumpolar regions of the Earth and is one of the longest chronologies in the world.

"Unfortunately, we could not round up the number to 10'000 years back. Probably before 7500 BCE, there were so few trees on Yamal that their remains have not survived. But it is quite possible to construct a chronology with a duration of 9500 years soon," explains Rashit Khantemirov, co-author of the study, leading researcher of the laboratories of dendrochronology of the Ural Branch of the Russian Academy of Sciences, natural science methods in humanitarian research, Ural Federal University.

Each annual ring of trees keeps the memory of what the year was like and what happened around. In the permafrost of Yamal, there are the remains of trees that grew centuries and millennia ago. The information in the growth rings of these trees, in contrast to the areas more favorable for tree growth, is unambiguous. In extreme conditions, trees are very sensitive to annual changes. Therefore, Yamal is almost an ideal place for creating a long and very informative tree-ring chronology.

"The further back the centuries, the less we know about those times and the more valuable the information of tree rings. In the world, there are only a few continuous series of observations of tree rings that go back thousands of years. There are even fewer rows whose information we can decipher," says the scientist.

To determine the exact year of tree ring formation, dendrochronologists use a method similar to fingerprinting: climate variability affects the formation of a unique tree ring pattern.

“Each sufficiently long time in a specific place is 'imprinted' with a well-defined pattern of rings of different widths. Consequently, if the lifetime of a dead tree partially coincided with the lifetime of a living tree, then by superimposing the pattern of the annual rings of one tree on the pattern of another, one can find the place - that is, the time - of their complete coincidence and determine the exact years of ring formation in the dead tree, "- describes the process Rashit Khantemirov.

Ultra-long chronology data helps to decipher climatic signals and reconstruct various indicators of the air temperature of the summer seasons. By studying other parameters of tree rings, such as anatomical anomalies or the isotopic composition of carbon, researchers identify events such as large volcanic eruptions or powerful solar flares.

“With the help of chronology, one can carry out massive and very accurate dating of the lifetime of ancient trees. Such datings make it possible to find out in which direction and at what speed the forest border moved in the past, how the density of forest stands changed, what types of trees grew. Besides, with the help of chronology, it is possible to very accurately and quickly date the archaeological sites of Yamal, in which the remains of wood have been preserved. No other currently known method can provide such a massive and accurate dating of wood remains,” says the researcher.

Note that the study was supported by the Russian Foundation for Basic Research (project No. 18-05-00575). For many decades, employees of the laboratory of dendrochronology of the UB RAS have been working on the creation of an ultra-long chronology. In recent years, the project has received an additional impetus thanks to cooperation with the Laboratory of Natural Science Methods in Humanitarian Research of the Ural Federal University, the  Swiss Federal Institute for Forest, Snow and Landscape Research (Birmensdorf, Switzerland), and the ion beam physics laboratory of the Swiss Higher Technical School of Zurich.