80-meter-thick sedimentary succession in Charyn Canyon, Kazakhstan, records interactions between land, atmosphere and ocean – sciencedaily


Paleo researcher Charlotte Prud’homme, who until recently worked at the Max Planck Institute of Chemistry and is now a researcher at the University of Lausanne, explains: “The 80-meter-thick sedimentary sequence that we found at Charyn Canyon in southeastern Kazakhstan provides us with a virtually continuous record of five million years of climate change. This is a very rare event on earth! “The 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 five years. Eurasia’s land surfaces appear to have contributed more actively to the land-atmosphere-ocean water cycle over the past million years than previously thought. The preserved sediments at Charyn Canyon served as a litmus test for the influx of fresh water into the Arctic Ocean, stimulating the transport of moist air masses from the North Atlantic to the mainland via airflows. from the west, ”explains the corresponding author Prud’homme. The research results have been published in the scientific journal Earth and Environment Communications.

The researchers focused their investigation on the Pliocene and Pleistocene periods. The Pliocene, five to 2.6 million years ago, represents the best analogue for the climatic conditions of the Anthropocene: this geological 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 information on the sediments of Charyn Canyon is so essential to understand the future climate,” said Prud’homme.

Until now, little was known about the role that Central Asia plays in shaping the global climate past and present. The evolution of Earth’s climate over the past five million years has been understood primarily from the perspective of marine mechanisms. In contrast, the importance of climate feedbacks that originated on land – rather than in oceans, lakes or ice cores – has remained largely unexplored. The international research team filled this gap with their field research at Charyn Canyon.

Interactions between climate systems in mid and high latitudes

The geographical location of the study site in the middle of Central Asia was of utmost importance to the team: “We had to find a place inland and as far from the ocean as possible”, Kathryn Fitzsimmons, group leader of the Terrestrial Paleoclimatic Reconstruction Research Group at the Max Planck Institute of Chemistry, explains. “We could hardly find a more continental situation than in Charyn Canyon in southeast Kazakhstan.” The canyon’s semi-arid climate and landscape have been shaped by the interplay between mid-latitude westerly winds and high-latitude polar fronts, and by sediment transported from the nearby Tien Shan mountains. Charyn Canyon is ideal, according to Kathryn Fitzsimmons, for studying long-term earth-climate feedback mechanisms.

The researchers examined the 80-meter-thick sedimentary succession and recalled to ensure continuous coverage of the record. By measuring the relative concentrations of isotopes in soil carbonates, they reconstructed the changing availability of moisture in the soil over time. A combination of paleomagnetic analyzes and absolute uranium and lead dating of soil carbonates allowed the age and accumulation rates of sedimentary data to be established. Soil samples revealed a region characterized by ever-increasing aridity over the past five million years. At the start of the Pliocene, the soil was significantly wetter than in later times or than the current climate. This process of aridification was not, however, linear; it was interrupted by short-term climatic fluctuations which provide insight into the interaction between mid-latitude westerlies and the Siberian high pressure system.

Interaction between the Siberian high pressure and rain-bearing westerly winds

Research at Charyn Canyon has allowed scientists to study the long-term interaction of the Siberian high pressure with rain-bearing westerly winds. Kathryn Fitzsimmons said: “We are convinced that the changes in soil moisture that we found at our site can also be used as an indicator of the activity of the Siberian river further north.” Charyn Canyon’s hydroclimate mirrors that of the steppe to the north, where a number of large Siberian rivers flow, such as the Irtysh and Ob, she says. These are similarly influenced by the dynamics of high altitude and western Siberian air masses. One particular phase where this connection is important stands out: an extended period of wet conditions in Charyn Canyon just before the world’s first great glaciation about 3.3 million years ago. These wet conditions are likely to have spread to the Siberian rivers to the north, whose freshwater outlet to the Arctic Ocean may have passed a tipping point for widespread sea ice formation.

The information from this most comprehensive terrestrial climate archive of the past five million years provides a very valuable basis for future climate models. Charlotte Prud’homme literally says: “We have opened a door.

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