MADRID, 7 Jun. (EUROPA PRESS) –
An unusual sedimentary succession 80 meters thick on a wall of the Charyn Canyon, Kazakhstan, it holds a virtually continuous record of five million years of climate change.
Alternating layers of dust and soil provide the first reliable evidence, in one place, of Long-term interactions between the major climate systems of the Eurasian continent.
“Over the past five million years, Eurasia’s land surfaces appear to have contributed more actively to the land-atmosphere-ocean water cycle than previously recognized. The sediments preserved in Charyn Canyon acted as a litmus test for the inflow of fresh water in the Arctic Ocean, stimulating the transport of masses of humid air from the North Atlantic towards the earth through the air flows of the west “, explains it’s a statement researcher at the Max Planck Institute for Chemistry Charlotte Prud’homme, whose findings are published in Communications Earth and Environment.
The researchers focused their research on the Pliocene and Pleistocene periods. The Pliocene, five to 2.6 million years ago, represents the best analogue of the climatic conditions of the Anthropocene: this geological time period was the last time that the concentration of carbon dioxide in the atmosphere was comparable to today, around 400 parts per million (ppm). “This is why our knowledge of the Charyn Canyon sediments is so essential to understanding future climate,” says Prud’homme.
Until now, little was known about the role Central Asia plays in the evolution of global climate in the past and present. The evolution of the Earth’s climate over the past five million years has been understood primarily from the perspective of marine mechanisms. Rather, the importance of climate feedback that originated on land, rather than oceans, lakes, or ice cores, has remained largely unexplored. The international research team has filled this gap with their field research.
The geographic location of the study site in central Central Asia was of key importance to the team: “We needed to find a place that was inland and as far from the ocean as possible,” Kathryn Fitzsimmons, leader of the Paleoclimate Reconstruction Research Group at the Max Planck Institute for Chemistry, explains. “We could hardly find a more continental situation than in Charyn, in southeastern Kazakhstan.” The canyon’s semi-arid climate, and landscape, was shaped by the interaction between the mid-latitude westerly winds and the high-latitude polar fronts, and by sediments carried from the nearby Tien Shan Mountains. Charyn is ideal, according to Kathryn Fitzsimmons, to study long-term soil-climate feedback mechanisms.
The researchers examined the 80-meter-thick sedimentary succession and rappelled samples to ensure continuous coverage of the record. By measuring the relative concentrations of isotopes within the carbonates in the soil, they reconstructed the changing availability of moisture in the soil over time.
A combination of paleomagnetic analysis and absolute uranium-lead dating of the soil carbonates established the age and accumulation rates of the sediment record. Soil samples revealed a region characterized by increasing aridity over the past five million years. In the early Pliocene, the soil was significantly more humid than in later times or the current climate. However, this aridification process was not linear; it was interrupted by short-term climatic fluctuations that provide information on the interaction between the mid-latitude westerly winds and the Siberian high-pressure system.
The research at Charyn allowed scientists to investigate the long-term interaction of the Upper Siberian with the westerly winds that bring rain. Kathryn Fitzsimmons says: “We are confident that the changes in soil moisture that we find at our site they can also be used as an indicator of the activity of the northernmost Siberian rivers“.
The hydroclimate in Charyn mirrors that of the steppe to the north, from where several large Siberian rivers flow, such as the Irtysh and the Obi, he says. These are equally influenced by the dynamics of the upper and western air masses of Siberia. One particular phase in which this link is important stands out: a sustained period of wet conditions in Charyn just before the first great global ice age about 3.3 million years ago. These humid conditions likely extended to the northern Siberian rivers, whose freshwater outflow into the Arctic Ocean may have passed a tipping point for the widespread increase in sea ice formation.
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