The short span of observation data of modern weather stations (mostly less than 100 years) restricts people's understanding of the earth's climate. For more than 100 years, geologists have used various geological biological carriers on the earth, such as ice cores, ocean sediments, tree rings, corals, lakes, marshes, stalagmites, etc., to obtain a large amount of data on the past climate change of the earth.
However, the current time resolution of paleoclimatic research carriers is low, usually from decades to months. Such a time resolution can study the earth's past climate change, but it cannot be used to study weather changes that occur on day-hours or even shorter time scales.
Under the guidance of An Zhisheng, an academician of the Chinese Academy of Sciences, researchers at the Institute of Earth Environment of the Chinese Academy of Sciences and other units have worked hard for more than five years to discover that ancient weather information with day-hour resolution can be obtained from the fossils in the South China Sea. Related papers were published in the Proceedings of the National Academy of Sciences recently. The first author of our special paper, Yan Hong, a researcher at the Institute of Earth Environment of the Chinese Academy of Sciences, does relevant scientific interpretation for readers.
Why is there only paleoclimatology and no paleoclimatology?
Climate is the long-term average state or change of atmospheric physical characteristics, with time scales ranging from months, seasons, years, years to hundreds of years. The climate is measured by the characteristics of cold, warm, dry and wet, and is usually characterized by the average value and dispersion value of a certain period. Weather is an instantaneous state of atmospheric physical characteristics, with time scales of days, hours, minutes, and even seconds, such as a heavy rain, a typhoon, and a cold wave.
Since the birth of human civilization, cognition of climate and weather changes has become one of the most important tasks. For example, in ancient Chinese historical documents, a lot of information on climate and weather changes has been recorded. The Spring and Autumn and Warring States Period was born as a great Twenty-four solar terms are still in use today. In Europe, the ancient Greek philosopher Aristotle had written "Meteorological Theory" more than 300 BC, which is also the earliest meteorological book in the world.
After the mid-16th century, the development of European industry promoted the development of science and technology. Various meteorological observation instruments were invented. For example, the Italian scholar Galileo invented the thermometer in 1593, and the Italian scholar Tori Deli invented the barometer in 1643. Hur invented the hygrometer and so on. These instruments provide the necessary conditions for the establishment of meteorological stations. Ground meteorological observation stations and stations have been established one after another, forming a ground meteorological observation network.
Although humans have invented meteorological observation instruments such as thermometers and barometers for nearly 400 years, the early observation data either have no uniform standards or have been lost, and the geographical distribution is relatively sparse and uneven. Observation data of high-quality meteorological stations is no longer than 100 years, and most meteorological stations are less than 100 years old.
Meteorological data of less than a century is not enough to accurately understand the changes in the earth's climate and weather and predict the future. In order to make up for the shortage of modern instrumental data, since the mid-19th century, geologists have begun to use various geological biological carriers on the earth, such as ice cores, marine sediments, tree rings, corals, lake marsh sediments, stalagmites, etc., to reconstruct The past climate change of the earth has created a discipline such as paleoclimatology.
For example, the width of the tree ring is used to reconstruct the temperature or precipitation changes of a certain area in the past thousands of years; the oxygen isotope and element ratio of the coral annual layer is used to reconstruct the temperature change of the ocean surface; the granularity of the loess deposit is used to indicate East Asia in the past millions The intensity of the winter monsoon and so on.
After more than a hundred years of hard work, geologists have successfully constructed a framework for Earth ’s climate change over the past 65 million years or more. This knowledge has greatly enriched our understanding of the history of the Earth ’s climate, letting us know that there have been super-glacial and super-warm periods in the history of the earth, as well as severe glacial-interglacial cycles, and also helped us understand the current The role of global warming in the history of the earth ’s climate.
Although the study of paleoclimatology has achieved a lot of results and provided important help for us to understand the climate change of the earth, we seem to rarely hear the term paleoclimatology. Is paleoweather research not important? of course not.
Although geologists have developed many carriers of paleoclimatic research, such as ice cores, marine sediments, tree rings, corals, ponds, stalagmites, etc., the time resolution of the information they can provide is too low, usually tens of Years to hundreds of years, the highest resolution carriers such as tree rings and corals can only reach the year or month. In other words, the climate information we obtain through these geological biological carriers is an average of hundreds of years and an average of up to several months. This information can be used to understand changes in the Earth's climate (monthly and above), but it cannot be used to study weather changes that occur on a day-hour or even shorter time scale.
Why does 磗 磲 have the potential to become a carrier of ancient weather research?
First let's understand what is 磗 磲.
Clamshell is the world's largest bivalve shell, and has been an important part of the tropical Pacific-Indian Ocean coral reef since the Eocene (about 50 million years ago). The life span of the clam can reach even more than 100 years, and the growth rate of its carbonate shell is very fast, which can grow to more than 1 meter in decades. The clam shell usually has an annual growth pattern or even a daily growth pattern. It is an ideal high-resolution global weather change historical research carrier.
As we all know, our common small shells usually open downwards and can move through muscles. However, the clams are generally fixed upwards on the coral reef tray, and will not move for a lifetime. This fixed feature is very important for us to do paleoclimate and paleoweather research. If the clams move continuously, the recorded climate and environment information will be disturbed as the location changes. Fortunately, Chong Ting does not move for a lifetime, just like a marine weather station, it keeps recording the surrounding ocean, weather, and climate information at the same location. It is simply a natural "geological meteorological station".
There are a lot of zooxanthellae on the coat membrane on the surface of the giant clam. The photosynthesis of the zooxanthellae can directly provide energy to the giant clam. Therefore, the giant clam is actually living on photosynthesis. She has hardly eaten all her life. The characteristics of Chongqin living by photosynthesis are also very important for us to use Chongqin for ancient weather reconstruction. As the weather changes, the photosynthetic efficiency of zooxanthellae will change, and the biogeochemical characteristics such as Chongqin growth rate will change. Therefore, by testing the growth rate of fossil clams, it is possible to extract information on changes in ancient climate and weather.
The longevity of the clam can reach 100 years, most of which are around 50 years. In other words, a single clam can provide 50-100 years of climate or weather records. Although it is not long, we have many fossil clams, some lived a few decades ago, some thousands or even tens of thousands of years ago, many fossil clams together, can provide a lot of past climate and Weather change information.
First of all, let's take a look at the ridge layer of 磗 磲. We can clearly see the grain layer on the cross section of the giant clam that was collected from Xisha of the South China Sea. This layer is the annual layer of the giant clam. Because of the different growth rates in winter and summer, carbonates exhibit different optical characteristics. The width of the striae varies from year to year, about 1-20 mm. It grows faster in childhood and grows slower in old age. But it will not grow as old as a person.
Using the micro-drilling equipment developed by our laboratory, more than 12 samples can be taken from each grain layer of the clam year, and samples with monthly resolution can be obtained. By testing these samples, we can obtain records of oxygen isotopes and element ratios with monthly resolution. These data are mainly controlled by temperature. There is a quantitative relationship between them and temperature, and a conversion equation can be established to calculate the current temperature.
This is the basic principle of using 磗 磲 to conduct paleoclimatic research. Usually, after collecting a fossil clam, we will use radiocarbon dating to determine the approximate age in which it lives, and then take more than 12 samples in each year, then test the oxygen isotope and element ratio of the sample, and then use Conversion equation, calculate the temperature at that time, and discuss the corresponding climate system changes.
So far, what we have done with Chongqi is still paleoclimate research, with a resolution of months, and we still can't go deep into the day-hour scale of weather changes.
The next important point is that we used the naked eye to observe the annual striae of the 磗 磲, and then we upgraded it, using the laser confocal microscope commonly used in biological research. Under the microscope, we saw a clear and continuous day. Growing lines. The width of the sunburst layer is 10-60 microns. In other words, clams actually grow a small layer every day, but we can't see it with the naked eye, but we can see it with a microscope.
This sunburst layer is important because it can be used to establish a chronological framework for daily resolution, which is also the basis for our research on ancient weather with daily resolution.
If the clam has a clear and continuous layer of sun grains, then we can separate the time experienced during the life of the clam. It is then possible to establish the growth rate change of the daily resolution of the clams at least according to the daily growth width. As we mentioned earlier, the growth of clams depends on photosynthesis and will be affected by weather changes. Therefore, the speed of the daily growth rate may reflect the weather changes at that time.
With an accurate chronological framework of daily resolution, we can further make a fuss in each Japanese grain layer to further improve the resolution. For example, using nano-secondary ion mass spectrometry to test the distribution of elements in the sun grain layer.
Just now we mentioned that the width of each sunburst layer is 10-60 microns, and the test resolution of nano secondary ion mass spectrometry can reach 1 micrometer or even higher. In theory, 10-60 can be obtained in each sunburst layer. A continuous element data (data resolution 0.4-2.4 hours), can establish the hour resolution geochemical sequence.
With the growth rate of daily resolution and the geochemical record of hour resolution, we can carry out paleo-weather research with day-hour resolution. For example, we found that the pulse-like mutations in the record of the growth rate and element ratio of the 砗 磲 day-hour resolution are almost all related to the extreme weather events in the northern South China Sea, such as the typhoon in summer and the cold wave in winter. For example, when the typhoon hits the northern part of the South China Sea, the daily growth rate of the clam will be reduced due to the worsening weather conditions; at the same time, the strong wind agitation caused by the typhoon can lead to the increase of nutrients such as Fe and Ba on the surface of the ocean and the increase of surface productivity , And is recorded in the geochemical parameters of 磗 磲.
This information indicates that the daily growth pattern of the giant clams has the potential to be used to study extreme weather events such as typhoons and cold waves that occurred in the past. That is to say, how many typhoons there are every year, how many rainstorms there are, how many cold waves there are in winter, etc., all of this information can be read in the fossils of 磗 磲.
For example, we obtained a fossil clam, using carbon dating method to get this clam was survived about 2000 years ago, that is, during the Han Dynasty in China. Then through the striae of the naked eye for several years, we know that the life span of this clam is 60 years, then we can establish a relative chronological framework for 60 consecutive years. We can calculate the average climate state at that time by testing the oxygen resolution and element ratio of the monthly resolution. If the calculation result shows that the temperature at that time was 1.2 ° C higher than it is now, then we can infer that the temperature in the South China Sea was higher High 1.2 ℃, is a typical warm period. Further using laser confocal microscopy and nano-secondary ion mass spectrometry, we can obtain biogeochemical records with a day-hour resolution in these 60 years. Then we can analyze the weather conditions at that time, such as how many typhoons there are each year, how many rainstorms there are, how many cold waves there are in winter, and so on.
Further reading
Sunburst layer unique to 磗 磲
As mentioned earlier, Chongqi has the potential to record ancient weather information, the key is that it has a sunburst layer. Then the question is coming, do other geologic biocarriers have sunburst? Such as tree wheels and corals.
The answer is that scientists have also made many attempts, and for the time being, there is no other carrier that has a clear and continuous sun grain layer.
Such as the tree round. Microscopic analysis shows that the trees basically grow some cell layers in a season, but not every day, the sun grain layer cannot be obtained. And trees usually stop growing or grow slowly in winter, and they do not provide continuous records.
Another example is coral. We also conducted microscopic analysis of coral samples from the South China Sea, and no sunburst was found. In theory, clams are a single living body, which secretes calcium fluid every day, and it is reasonable to grow a layer. Coral is formed by the aggregation of calcareous bones secreted by coral insects. In theory, it is difficult to have a clear and continuous layer of sun grains.
Other small shells are similar to Clams, theoretically there may be, but compared to Clams, their growth rate is too slow, and it may be difficult to obtain a clear and continuous sunburst layer from the prior art.
Some people have suggested, will there be any missing layers in the ridge layer? We have done some verification on this, and no obvious missing phenomenon has been found yet. For example, we collected a large clam in the South China Sea. The annual striation and isotopic annual cycle show that the life span is 23.5-24 years. We count the sunstroke layer, the total sunstroke layer is 8649 layers, the average is 360 to 368 floors, basically no obvious missing.
Scientific Interpretation
Does the carbon 14 dating error affect the research of Chongqi ancient weather?
Another question is that the carbon 14 dating error will be several decades. The dating of fossil clams can only be measured with carbon 14. Will it affect the research on the ancient weather of cicadas?
The answer is: no. The carbon 14 test just tells us the era in which Chongqi lived, which is enough. What we need most is accurate relative chronology, to ensure that the daily resolution records we get are continuous for decades during the life of the clam, so that we can analyze how the weather conditions are in these decades of.
For example, the above mentioned Han Dynasty fossil clam, what we finally got is that in the 60 years since 2000, the South China Sea temperature is about 1.2 ℃ higher than it is now, which is a typical warm period, and during these 60 years, typhoons How, how about heavy rain, how is the cold wave and so on. It is not very important whether these 60 years are from 2060-2000 or 2070-2010.
Yan Hong