Humans are fascinated by the distant past of our planet. Since recorded human history dates back only a few thousand years, we probe Earth’s “memory” in various ways to uncover its secrets. One such method is to search for traces of the past, also known as “proxies”, which help scientists understand what the Earth was like long ago.
A recent study published in PNAS describes the planet’s history by extracting previously unavailable information from ice cores from the far western Kunlun Mountains.
Ice cores are columns of ice drilled through glaciers located in extreme environments such as the Arctic, Antarctica and the Third Pole, centered on the Tibetan Plateau.
Ice cores are amazing because they record everything in the atmosphere and freeze it in time. They are windows that unlock the mysteries of the past as they not only record indicators of climate events, such as temperature and precipitation, but they also record evidence of events that influence climate, such as tephra and sulphates. from volcanic eruptions; the cosmic nuclei chlorine 36 and beryllium 10 which indicate changes in the energy production of the sun; and the chemistry of air trapped in bubbles in the ice that show the past composition of Earth’s atmosphere. Ice cores also give us histories of temperature changes as recorded by the chemistry of snow that falls on glaciers and later compresses into ice.
According to the authors of the recent PNAS article, since 1950, the ratios of heavy oxygen to light oxygen in the ice (oxygen isotopes) were the highest in the last 12,000 years, suggesting recent dramatic changes in the climate of this region, which is experiencing rapid population growth and agricultural development.
While it is very difficult to drill ice cores at high altitudes, extracting information from them can be even more difficult. According to Lonnie Thompson, the study’s lead author and a professor at the Byrd Polar and Climate Research Center and The Ohio State University School of Earth Sciences, understanding climate records from ice cores from the third pole is less straightforward. than that of polar ice cores, because they form under lower air pressure and contain more microorganisms and melt layers, which can complicate the interpretation of ice chemistry.
Co-author Jeffrey Severinghaus of the Scripps Institution of Oceanography and the University of California, San Diego successfully adapted a method – previously used almost exclusively in dating polar ice cores – to ice cores from the third pole in adding new fixes.
“The air isotopes trapped in the bubbles of the ice and the atmospheric history of the last 15,000 years have been corroborated by other indirect records,” said study co-author and professor Yao Tandong. at the Tibetan Plateau Research Institute. , Chinese Academy of Sciences.
The ice cores used in this study were drilled from the Guliya Ice Sheet in 1992 and 2015 by an expedition team led by the professors. Yao and Thompson, co-chairs of Third Pole Environment, an international science program designed to better understand changes in the third pole environment and their ramifications.
More information:
Thompson, Lonnie G. et al, Use of δ18Oatm in dating a Tibetan ice core record of Holocene/late glacial climate, Proceedings of the National Academy of Sciences (2022). DOI: 10.1073/pnas.2205545119. doi.org/10.1073/pnas.2205545119
Provided by Chinese Academy of Sciences
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