In search of the oldest ice on earth

For some reason, we, people, have a craving for all kinds of antiquities. We like to learn about which of the cities on Earth is the oldest; When and by whom the first mechanical clock was created, the first brewery was built, the first cockory pattern was made; How old is the old tree and the oldest stone. Sometimes behind these issues is not only idle curiosity, but also scientific interest. We will talk about the most ancient ice on our planet - where it can be found, what is its age and why we need it.

Interest in the past is due to the fact that without the knowledge and understanding of the driving forces of any process in the previous stages of its development, it is difficult to adequately assess the current situation and predict future changes. A striking example is a climate. Instrumental observations of weather and climate began about 150 years ago (somewhere earlier, somewhere later), and these one and a half centuries are characterized by a rather intense change in climatic characteristics, including a significant increase in air temperature. But in order to understand the mechanisms and causes of these changes, we need to know what the climate in the pre -industrial era was hundreds and thousands of years ago, when the influence of a person on the environment was relatively weak. The study of what was the geographical shell of our planet in the past (before the start of instrumental measurements) is engaged in paleogeography, which includes paleoclimatology.

There are a great many methods and objects of the study of paleogeography, but in general, the data about the past are recorded in the “natural archives” - objects in which the continuous accumulation of the material occurs, and the properties of this material carry information about what conditions it was formed. The most striking examples of such “archives” are the annual layers of trees and corals, bottom precipitation of lakes and seas, stalactites of caves, loss deposits of deserts, layers of snow and ice in glaciers.

An analysis of the climatic series over the past 2000 years obtained on the basis of these data, in particular, has shown that modern warming is unprecedented in speed and size and does not fit into the framework of natural variability [ 1 ].

A special place among the methods of paleogeography is the drilling of polar ice shields and the study of extracted ice cores. Ice layers accumulate continuously for a long time, can be easily dated and allow the climatic conditions under which they were formed with great resolution. So, the isotopic composition of ice (the ratio of heavy and light isotopes of hydrogen and oxygen) depends on the air temperature at the time of precipitation; The content of chemical impurities and dust can tell about the nature of atmospheric circulation, volcanic activity, sea ice area, biological productivity and other environmental parameters. Finally, ice cores are the only source of direct data on the gas composition of the atmosphere in the past, including the concentration of greenhouse gases. The fact is that in the central parts of the polar glands, the temperature is so low that even in the summer they do not rise above 0 ° C - respectively, there is no question of melting and the ice is formed by a dry way due to slow compression of snow grains. At the same time, the air contained in the pores of snow is captured by ice and remains unchanged for millennia.

The first deep wells in the ice of Greenland and Antarctica were drilled in the early 1960s, and since then several dozen drilling projects were completed there. In the 1990s, the Russian-Franco-American project of deep drilling of ice was successfully implemented at the Russian station of Vostok (Fig. 1), thanks to which a climatic series was obtained with a length of 420 thousand years [ 2 ]. For the first time, the most important climate -forming role of greenhouse gases was reliably confirmed, and it was also shown that their modern concentration greatly exceeds natural variability over the past half a million years. In 2020, the concentration of CO2 reached 413 PPM (parts per million), and in antiquity it was from 180 PPM to cold eras to 280 PPM in warm (Fig. 2).

From the very beginning, the data of ice cores were widely used in the reports of the international group of climate experts [ 3 ] as the natural background on which anthropogenic changes in the climate and the environment are imposed in the modern era.

To date, the longest climatic row on ice core (800 thousand years) was obtained as a result of ice drilling as part of the European Epica project in the central part of Eastern Antarctica [ 4 ].

The study of ice cores made it possible to establish the general laws of natural changes in the climate of the planet over the past 0.8 million years. In the first approximation of temperature changes were quasi -pieridical and asymmetric. Approximately every 100 thousand years there were short warm interglacials, replaced by long cold glacial periods, and the transition from warm eras to cold was gradual, and the transition from cold eras to warm - sharp and intense. Golucen - the modern interglacial in which we live - began 11,700 years ago. It is interesting that the warmest stage of the holocene, its thermal optimum, we passed 6-8 thousand years ago and since then slowly moved to the next ice age, but modern anthropogenic warming turned this process back.

The root cause of these 100-thousandth climatic fluctuations were the so-called Milankovich cycles-changes in the parameters of the Earth’s orbit, such as the inclination of the rotation axis, the precession of the equinoxes and eccentricity (for more details for this, see [ 5 ]). During the cycles of Milankovich, the arrival of solar heat to the high latitudes of the northern hemisphere in the summer is slightly changed - this affects the balance of the mass of the integumentary glaciers and triggers a complex cascade of feedback in the climate system of the Earth, which initially strengthen the faint signal of “solar force”.

It would seem that this story can be finished. Indeed, 800 thousand years are a colossal period compared to the history of human civilization, which has a little more than 5 thousand years (if we count from the invention of writing). But on the other hand, 0.8 million years is a brief moment not only in comparison with the geological history of the Earth (4.5 billion years), but even compared to Cenozoa - the era of mammals, which began 65 million years ago with the death of dinosaurs.

We know much less about these past eras than about the last hundreds of thousands of years - simply because we have at our disposal much less “climatic archives”, from where you can draw information about the so distant past. If we talk about the Cenozoic era, then the main source of information is sea bottom precipitation. The limestone shells of microscopic marine animals, foraminifer, are deposited at the bottom of the oceans for millions of years, and the isotopic composition of these sedimentary rocks allows you to reconstruct the temperature of the planet throughout the entire cinosa [ 6 ]. And these data say that only two million years ago the climatic variability of the planet was different from the one that we know from the ice cores: the vibration period was significantly shorter (40 thousand years instead of 100 thousand years), and the amplitude of the oscillations was about half as much.

The transition from a 40-thousand-thousandth regime to a 100-thousand-thousandth ("Middle Playystocene climatic transition", or, in English, MPT-MID-printocene Transition) began about 1.2 million years ago and ended 0.85 million years ago (Fig. 3). The reason for MPT is still a mystery. Indeed, after all, Milankovich’s cycles were the same that now, two million years ago. But the climatic response of the earth has changed.

There are several hypotheses that are trying to explain the causes of MPT, but all of them in one way or another imply the key role of greenhouse gases [ 7 ]. In the era to the MPT, the concentration of CO2 was generally higher, its variability between cold and warm eras is lower, and this led to a decrease in the period and amplitude of climate vibrations. Accordingly, in order to confirm this hypothesis, scientists need ice for at least 1.5 million years, because, as we already know, only the ice of polar glaciers contain samples of an ancient atmosphere. Studies of such ice could not only shed light on the causes of MPT, but also give an idea of ​​how our planet will look in the near future (in the XXII century) if humanity cannot be radically reduced by CO2 emissions in the next decades.

So is there such an ancient ice on Earth or not? Until recently, this could only be discussed about this theoretically, operating on the results of computer modeling of ice dynamics.

First of all, it is necessary to distinguish between the age of the glacier itself as a geographical object and the age of the ice that is compassing it. Antarctica covering glazing exists, either by contracting, then expanding, at least the last 34 million years [ 6 ]. But the ice luring it is much younger, since it is in constant movement: the older layers of ice go down and compressed, spreading to the sides, and eventually ending their way on the edge of the glacier, failing in the form of icebergs. And fresh snow falls from above, which is gradually compacted and forms new layers of ice.

About the conditions that favors the preservation of ancient ice in the basal (tribute) horizons of the glacier, I already told a note dedicated to our expedition to the ice precision in Antarctica [ 8 ]: the small speed of snow -beaming, not too large and not too low the thickness of the ice (about 2500 m), the small value of the geothermal flow of heat. In addition, it is necessary that the ice layers lie evenly, not be mixed and not formed at the folds - that is, the desired ice should lie in the area of ​​ice domes or ice sheets, where the horizontal movement of ice is minimal. Modeling the age of ice suggests that a million -year -old ice must really exist in the central parts of East Antarctica [ 9 ].

And recently, we know for sure that such ice actually exists.

In 2019, American scientists published the results of studying the samples of “blue ice” obtained in the Allan-Hills area near the Mc-Murdo station [ 10 ]. “Blue ice” is formed mainly in the coastal parts of Antarctica, in areas with a negative balance of mass (as a rule, fresh snow is blown away by a strong wind and sublimate), and ancient layers of ice come to the surface. Allan-Hills ice was dated according to the isotopic composition of the Argon in air bubbles inside this ice, and the age of the ancient sample was 2.7 million years old. Unfortunately, according to these samples, it is impossible to reconstruct the sequence of climatic events during MPT, they only give “pictures”, temporary sections of the isotopic composition of ice and the concentration of greenhouse gases in the atmosphere in certain points of time - but, in any case, these data do not contradict the hypothesis that the variability of the concentration of CO2 in the atmosphere was in the atmosphere. lower than for the past million years. And at the same time, we note that in general, the concentration of this gas in the air nearly 3 million years ago was significantly lower than now.

It is even more interesting that ancient ice was discovered in that very Kern from the Vostok station, which was in our hands for 20 years! The depth interval of 3310–3538 m “Eastern” Kern contains mixed and inverted layers of atmospheric (that is, formed from atmospheric precipitation) of ice. From the very beginning, it was clear that their age exceeds 420 thousand years, but it was not possible to determine it, since ordinary dating methods based on modeling ice dynamics are not applicable to such ice. But recently two new methods of absolute dating were proposed: one is based on measuring the size of air hydrates in ice (the diameter of which continuously increases with age), and the second - on measuring the concentration of the radioactive isotope of crypton 81KR. These methods have shown that in the lower layers of the specified interval, the age of ice reaches 1.2 million years [ 11 ].

Thus, ancient ice really exists - it remains only to find the place where the layers of this ice are characterized, as geologists say, “consonant in the first time” - they are not turned, not mixed and the climatic signal contained in them is not erased by molecular diffusion.

And for this ice, a real hunt turned! All leading Antarctic countries declared their plans for the search, drill and study of ancient ice. Japan will look for him near its station “Dome Fuji” [ 12 ], China in the Dome A region, where the Kunlun station is located [ 13 ]. The United States plans to search and drill ancient ice in the area between the South Pole and the dome and in the next 10 years [ 14 ]. Interest in ancient ice was expressed by Australia, South Korea and a number of other countries.

At the moment, Europeans have advanced the farthest in this race: their project “Beond Epica - Oldest Ice”, in which 14 scientific centers from 10 countries participate, officially began on June 1, 2019. They have already determined the place of future drilling - it is located on a small dome C 50 km from the Concordia station at a point with coordinates 75.30 ° s. Sh. and 122.45 ° c. the village, where in January 2020 a well was drove a depth of 240 m [ 15 ]. In the summer Antarctic season 2020/2021, work was not carried out there due to the pandemic of Covid, the continuation of the drilling was scheduled for December 2021.

Russia has a chance to be among the leaders of this competition. Firstly, ancient ice is already in our hands, although with a distorted climatic signal. Secondly, there is a great chance that even more ancient ice-and, moreover, with an unexplored sequence of layers-lies at the base of the glacier in the area of ​​ice breeding B (70.02 ° w. And 93.69 ° C) at a distance of 300 km from the Vostok station-that is, at the point where the glacier flows towards the east.

In January 2020, the first scientific campaign in this hitherto not investigated area took place [ 8 ]. The data obtained made it possible to simulate the temperature and age of ice at this point, which showed that the temperature on the glacier bed is about -13 ° C (that is, ice melting is unlikely), and the age of ice at a mark of 60 m above the bed is at least 1.2 million years. These results will soon be published in the first issue of the journal "Ice and Snow" for 2021 [ 16 ].

Of course, I would like to finish this note with the words that soon we will begin a deep drilling on the ice precision B. But alas, such projects are relatively expensive, a grant of the Russian Scientific Fund can not be bypassed here, we need targeted state funding.

Is Russia ready to support a similar project? I hope we find out the answer this year.

Alexey Ekaykin, Vedas. scientific. sore. laboratories
climate and environmental changes in the Arctic and Antarctic Research Institute

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