The ice core is known as the “wordless environmental cryptographic archive”. Recently, Chinese researchers used the self-designed ice core thermal drill system and lake core gravity drill system, the first time to obtain the Karakoram Mountains outside the deep ice core and lake core samples. These ice and lake core samples can be used to reconstruct the history of climate change in the Pan-Third Pole region. So, how exactly are the ice cores and lake cores generated? What are the indicators for documenting environmental change? What is the practical significance of the data measured by the ice core and the lake core?
Samples of ice cores drilled by the scientific team
The wordless “archive” of the climate environment
In fact, the so-called ice core is a cylindrical ice body that is made inside the glacier with drilling equipment. In the high cold of the plateau, the snow accumulates year after year, and the snow at a certain altitude or polar region softens, and gradually forms glaciers. Over thousands of years or even millions of years, layers of snow accumulate, and year after year, different layers of ice form from the bottom up, which are getting new from the bottom to the next.
In general, the researchers told reporters, winter temperatures are low, the formation of snow particles are characterized by thin and tight, while the summer temperature is high, the formation of snow particles show a coarse and loose state. Therefore, there will be obvious layer structure differences between the ice formed by the snow in winter and summer.
As a result, the “ice stick” taken from the glacier carried the “historical data” left over from thousands or even millions of years of climate change. It not only records information on natural changes in the climate environment in the past, but also records the effects of past human activities on the climate environment. “The year of snow in the ice core records the environmental information of the year, so studying the ice core is like reading a history book, from the bottom to the top, from the old to the new, and we can restore the whole history of climate change.” Xu Baiqing, a researcher at the Qinghai-Tibet Plateau Research Institute of the Chinese Academy of Sciences, told science and technology daily.
Similar to the ice core, the lake core is also a cylinder drilled by the researchers, except that the lake core comes from lake sediments, which naturally settle into the lake floor from gases or water bodies and accumulate from layers of sediment of various ages, some of which reflect the sedimentary environment and climatic conditions of the time. “Compared to the ice cores of large-scale environmental change recorders, the lake core is a loyal recorder of regional climate change and the history of human activity. Xu said.
Drilling and saving are different
Drilling ice cores is not an easy task. To obtain ice cores in glaciers, a special drilling system, such as mechanical or hot drills, is required. Before drilling, the team will generally examine the target glaciers, including geological features, ice thickness, sub-ice terrain and so on. Drilling ice cores in the middle or lower part of the glacier may encounter melting zones or flowing glaciers, subject to more interference factors. “Drilling is generally done at the top of the glacier, in a relatively flat area, to ensure the integrity and continuity of ice information. Xu said.
In addition, the researchers said, in order to ensure that the ice core does not melt, so the ice core to hit at night. According to the actual terrain conditions, researchers also have to choose different drills, such as hot drills by the thermal ring melt down, easy to drill deep, but to electe, steep glaciers can not bring generators up, and cold drills are divided into mechanical drills and hammer drills, etc. , when used to choose according to the hardness and thickness of the ice and other factors.
The process of drilling the lake core is more testing experience and patience. After the team touched the sampling tube to the bottom of the lake, the sediment samples were lifted into the tube by gravity, and then lifted. If the angle of the sampler deviates when it touches the surface of the sediment, the resulting sediment does not truly reflect the chronological climate. At the same time, the sample amount should be just right, if the sampling tube sinks too shallow, it may not take the sample, if the sinking is too deep, the sample in the sampling tube may be severely squeezed to cause deformation.
After the ice core and the lake core are drilled out, in order to ensure that the order and hierarchy are not disorderly, it is necessary to number, indicate the upper and lower order of each ice core and lake core, and strictly package to prevent contamination.
There are also significant differences between ice core and lake core preservation. “The ice core must be kept in a frozen environment, the temperature of the cold storage is generally minus 25 degrees C, but the lake core is not frozen, once the lake core is frozen, its structure will change, will generally be drilled in the lake core in the environment of 4 c-7 degrees C to save.” Xu said.
The indicators for documenting environmental changes vary
In Xu’s view, the index of ice core recording environmental change can be divided into three categories.
“The first type is the information that the ice itself carries, which is to write about ‘water molecules’. Xu said that water molecules are composed of hydrogen and oxygen two elements, measuring the ratio of hydrogen and oxygen isotopes in the ice core can be calculated in the past environmental temperature, the ice core accumulation rate can show the size of precipitation changes.
Ice on the plateau comes from precipitation, in the process of precipitation, the phenomenon of isotope shunt, relatively heavy isotopes easily fall with precipitation, and relatively light isotopes are more likely to form gases. “This diversion process has a lot to do with temperature, and we can analyze the temperature of the atmosphere at that time by the determination of isotopes. Xu said.
In addition, the structure of the ice itself, the size of the crystals and its arrangement are all very related to the environment in which it was formed, and can reflect the dynamic characteristics and processes of the formation of the glacier.
The second type of indicator is the various substances contained in the ice core. By analyzing the composition of the ice core, such as water and the minerals contained, some important environmental events of the historical period can be restored. For example, the intensity of dust storm activity can be inferred from the amount of dust in the ice. Dr. Yu Chao of the Qinghai-Tibet Plateau Research Institute of the Chinese Academy of Sciences has found that, based on the changes in the content of l-goofic glucan detected in the ice core, it can be inferred that biomass combustion in subtropical Asia has increased since 1990.
In addition, because the ice on the plateau is gradually accumulated by the snow, when the snow lands, there is a gap between the particles, in the process of snow compacting into ice, also the gap bubbles sealed up. These bubbles are the Earth’s atmosphere when ice first formed, containing endless information about the past. By studying the gas composition and content of ice core bubbles, we can reveal the evolutionary history of atmospheric composition, such as carbon dioxide, methane and other greenhouse gas changes.
“Compared to the ice core, the index of lake core recording environmental change is relatively single. Xu said the main detection object of the lake core is the various substances it contains, the composition of the sediments is different, reflecting different information on environmental changes. For example, through the increase in sulfur content in the core of the lake in the southern part of Mount Everest, researchers have revealed that the changes in sulfur isotopes are mainly due to increased aerosols from dust sources and increased erosion of the surface associated with climate change, which has played a significant role in understanding the environmental change characteristics of high-altitude climates and ecologically sensitive areas of the Himalayan high mountains. (Reporter Lu Chengguang)