text | "China Science Daily" Intern Reporter Wang Min
Science Expedition Team drilled the ice core in the Qiangtang Glacier on the Qinghai-Tibet Plateau. Photo provided by Polar Future
Qinghai-Tibet Plateau What kind of sparks will a 109-meter ice core drilled at an altitude of 5,900 meters, encountering a new dating method based on quantum precision measurement?
Recently, the single atom detection team led by Professor of the University of Science and Technology of China (hereinafter referred to as of the University of Science and Technology of China) and the single atom detection team led by Jiang Wei and the glacier science team led by Tian Lide, a researcher at of the Yunnan University (hereinafter referred to as of the Yunnan University ), jointly published research results in the Proceedings of the National Academy of Sciences in the United States. The team conducted an argon-39 isotope dating measurement of the ice core for the first time in the world, establishing a precision chronological scale for the Qiangtang Glacier ice core on the Qinghai-Tibet Plateau for thousands of years.
"unique archive" of the atmospheric environment
The so-called ice core is the core obtained from the inside of the glacier by drilling. Generally speaking, the more the ice core goes upward, the newer it is.
"These ice cores record a variety of climate and environmental change indicators, which are usually divided into three categories: the first category is ice itself, and the ratio of hydrogen and oxygen isotopes in water molecules can reflect temperature changes; the second category is the atmospheric components and content in the ice core, such as carbon dioxide , methane and other greenhouse gas , which can reveal the process of changes in atmospheric components." Tian Lide introduced that the third category is the various impurities contained in the ice core, such as dust visible to the naked eye, which can infer that sandstorm was more active at that time; and various chemical components detected by laboratory instruments can provide relevant information on natural activities and human activities.
Therefore, ice core can be regarded as a "unique archive" for preserving the atmospheric environment. Mastering the accurate era information of ice core is the first step in decoding the "archive". The Qinghai-Tibet Plateau in my country is known as the third pole in the world and is a treasure house for research on paleoclimates at medium and low latitudes.
"Unlike the Antarctic and Arctic, the Qinghai-Tibet Plateau has a large amount of snow accumulation and the ice core resolution is higher. Its latitude is located in human settlements and has many activity trajectories. The history of the ice core record is closely related to the human living environment." Tian Lide said that this makes the ice core research on the Qinghai-Tibet Plateau particularly important. It is precisely because of this that the Qinghai-Tibet Plateau has attracted scientists from all over the world and has become a "competition field" for international ice core research.
In May 2014, Tian Lide and his colleagues worked hard on the top of the "Qiantang No. 1" glacier on the Qinghai-Tibet Plateau at an altitude of 5,900 meters (the temperature was high during the day, and the melted ice chips could easily get the drilling rig stuck), and successfully drilled two 109 meters of ice cores and kept them in the Yunda Cold Storage at -17℃ all year round. What era are the two ice cores from
, what information does it contain, and how to decode this hard-won "archive" are the topics faced by Tian Lide's team. The team of Lu Zhengtian of the University of Science and Technology of China happens to have the "key" to open this "file".
Grab argon-39 into the atom "well"
There are three rare radiogas isotopes in the atmosphere, namely kr-85, argon-39, and krypton-81. As early as 1969, Swiss geoscientists Hans Oeschger and Hugo Loosli proposed that argon-39 and other are ideal dating isotopes for mountain glaciers.
However, detecting them is extremely difficult. "The abundance of argon-39 isotopes is extremely low, as low as one billionth of a billion. And these atoms are mixed in argon atoms 17 orders of magnitude more than it." Lu Zhengtian said that this detection difficulty is like finding a special grain of sand on a beach. Therefore, the quantitative analysis of argon-39 in ice cores has been a difficult problem for the past half century.
In this study, Lu Zhengtian’s team adopted the “atomic well trace analysis (ATTA)” method. This method was invented by Lu Zhengtian when he was working at the Argonne National Laboratory in the United States in his early years. The principle is to use precisely controlled lasers to manipulate argon-39 atoms and capture them into a "atomic well" composed of six laser beams. The atoms fluoresce in the well, and individual argon-39 atoms are detected with a sensitive EMCCD camera and “count” them one by one.
ar-39 has a half-life of 268 years, and it can date environmental samples from 1,800 to 50 years ago.
Lu Zhengtian takes 1 kg of modern ice as an example. "There are about 10,000 argon-39 atoms in it. After an half-life , the number of argon-39 atoms will be reduced by half to 5,000; after another half-life, it will be reduced by half to 2,500. Over time, the number of argon-39 atoms will become smaller and smaller. Therefore, the abundance of argon-39 in the ice core can tell us the time when the ice is formed, that is, its age."
So, the question is. How to transport the 109-meter-long ice core stored in Yunda Cold Storage to the laboratory of the University of Science and Technology of China for research?
"At that time, my colleague Dr. Florian Ritterbusch went to the laboratory of Mr. Lide in Yundatian with a device like a pressure cooker, took out the gas from the ice core and brought it back to the University of Science and Technology of China." Jiang Wei said that this was the first step in the ice core dating.
Why do you call it a "pressure cooker"? "Because it has good sealing performance, we really ignite under the pot, melt the ice, and remove the gas." Jiang Wei said with a smile, "Don't underestimate this 'pressure cooker'. For sampling, it has been to the Qinghai-Tibet Plateau, Shanghai, Paris, France and Seoul, South Korea."
The second step is purification. Jiang Wei explained: "Because the retrieved gas contains various chemical components, other gases need to be reacted first, leaving only argon."
Finally, the separated argon gas was placed in the atomic well trace analysis instrument to measure the abundance of the argon-39 isotope and calculate the sample age.
In this study, the team of China University of Science and Technology and the Yun University used the argon-39 dating method to finally obtain the age distribution of the entire ice core, with the age at the bottom reaching 1300 years.
"The latest cooperation results confirm for the first time the huge potential of argon-39 in the research on absolute dating of millennium ice cores." Tian Lide said that the argon-39 dating technology can also be used for dating other ice cores on the Qinghai-Tibet Plateau, solving the problem of absolute dating of ice cores that geoscientists have not been able to overcome for many years.
plans to establish a global isotope detection center
In the laser trace detection and precision measurement laboratory of the University of Science and Technology of China, the optical platform of the atomic well trace analysis instrument is filled with various optical components, which is dazzling.
Jiang Wei introduced: "These optical components have fixed positions and are not placed casually. Students spent several months installing and debugging, so that the complex optical paths produce specific frequency lasers used to capture and detect argon-39 atoms."
Moreover, the efficiency of the latest instruments has also been greatly improved. "In 2010, we conducted an experiment with argon with natural abundance in the United States. At that time, we could see 1 argon-39 atom in 5 hours." Lu Zhengtian said that at the University of Science and Technology of China, we can use the latest instruments to measure argon with the same abundance, and 10 argon-39 atoms can be detected every hour, and the counting rate is about 50 times higher than that time.
In this study, the researchers also compared the argon-39 dating results with the ice core aging scale constructed based on the several-year layer method, corrected it, constrained the glacier flow model, and finally established a new ice core annual standard based on the argon-39 result.
"This article will arouse widespread interest among ice core scientists, paleoclimatologists, and radioisotope dating experts." Another reviewer said.
Lu Zhengtian and Jiang Wei's team have long been committed to developing ultra-sensitive detection technology for rare gas isotopes such as Krypton-81 and Argon-39, so that it can be truly applied to cutting-edge geoscience research. The cutting-edge measurement technology has attracted domestic and foreign scientists to cooperate, and has made a series of progress in research fields such as groundwater, glaciers and oceans, showing the role of new technologies in promoting innovative research.
Lu Zhengtian said: "In the next step, the team will continue to develop atomic well trace analysis instruments to improve the performance of various indicators, and make it an indispensable tool in the field of earth science. On the other hand, the team plans to establish an international isotope detection center in Hefei and cooperate with research groups from all over the world. It hopes to help our earth scientists achieve major original results and play a leading role in international cooperation."
Related paper information:
https://doi.org/10.1073/pnas.2200835119
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