An international research expedition is currently drilling in the depths of the Antarctic ice, with the aim of finding out why the ice ages significantly lengthened over a million years ago. Their findings may also help in understanding the rise in global temperatures that we are experiencing today
By Eleanor Ben Yehuda, Angle - news agency for science and the environment
About 1.2 million years ago, the earth's climate underwent a dramatic change: the length of the ice ages more than doubled. If before that, each ice age lasted approximately 41 years, after this change, which was called the "Mid-Pleistocene Transition", the Earth was frozen for approximately 120 years at a time. Yet, The reason This significant lengthening is unknown even today. In recent years, researchers have begun to examine more deeply (literally) what caused the phenomenon, in an interesting way: geological drilling on ice of the continent of Antarctica. Beyond the information that will be revealed about the past, the findings of the drilling may shed light on the temperature changes that are occurring even today, as part of the climate crisis.
The drillings that are being carried out today are conducted by an international research expedition named Beyond EPICA, which recently started its activities on the frozen continent. The scientists will drill to the depth of 1.5 million year old ice layers, analyze the composition of the gases in the air bubbles trapped in them and compare these samples to 800 thousand year old samples collected in the past. Thus, they will be able to get an idea of the state of the earth's overall atmosphere in the different periods. The drillings were intended to be the starting point in testing the assumption that changes in the composition of the atmosphere - and in particular, changes in the levels of carbon dioxide in it - played a role in the extension of the ice ages and the change in the ancient climate.
These drillings join several studies conducted in the Antarctic ice in recent years. In 2012, a Chinese expedition began drilling at one of the highest points in Antarctica, and in the coming years, Japanese and Russian expeditions are also planned to reach the continent. The United States also decided to finance a research expedition worth 25 million dollars, in order to establish its own drilling site. The various delegations Hope to reach ancient ice layers very, formed in warmer periods, with the aim of investigating not only what is the reason for the Pleistocene transition period - but also how the Earth might react following the current global temperature increase due to the climate crisis.
"For the past 40-30 years, drilling has been conducted both in Greenland and in Antarctica," says Prof. Yossi Ashkenazi, a lecturer in the Department of Solar Energy and Environmental Physics at Ben Gurion University. "Antarctica is basically a desert, the amount of precipitation there is very low and amounts to a few tens of centimeters a year. This means that the ice layers that accumulate in Antarctica are thin, so when you drill 3 kilometers in, you can reach quite ancient layers.'
Historical weather signature
Why do air bubbles form in the deep ice of Antarctica? "Snow is an airy deposit, so there are many voids in the piled ice," explains Ashkenazi. "As the ice piles up on top and tightens in depth, the air is reduced - and air bubbles are formed that separate from each other. These bubbles create a kind of signature of the climate of that time.'
The origin of the air in the bubbles in the ice is indeed in the atmosphere of Antarctica - but it can also testify to the climate in the rest of the earth at that time. "Carbon dioxide is a gas that is well mixed in the atmosphere, so if you find measures of it in one place - you can project it on the whole globe, more or less," explains Ashkenazi.
"What is special about drilling in Antarctica, at least those of Beyond EPICA, is that the layers are very continuous in terms of dating," adds Ashkenazi. According to him, in other drillings conducted in Greenland, young layers were found hiding under older layers. No such situations were discovered in the drilling of Beyond EPICA, although there is a fear that this will occur in the deeper core.
The ice ages are changing again
The ice ages on Earth began to occur about 2.7 million years ago. An ice age comes when there is a gradual cooling in the climate, as a result of an increase in the amount of solar radiation that is emitted out of the earth instead of warming the planet. The rest of the period is characterized by low temperatures, due to which large areas are covered with ice surfaces.
The increase in radiation emissions has several factors, one of which is a change in the composition of the greenhouse gases in the atmosphere. When their direction is reversed, such changes may cause the opposite phenomenon - an increase in global temperature, such as the one currently caused by the climate crisis. "The more triatomic or pentaatomic molecules there are in the atmosphere, such as water vapor, carbon dioxide or methane, they capture more long-wave radiation that comes out of the earth, and return it to the surface - which causes the climate to heat up," explains Ashkenazi.
Admittedly, in the new research in the Antarctic ice, the researchers are trying to understand the changes that took place in the length of the ice age cycle over a million years ago - but it is possible that these cycles are changing again even today. "In the last 800 thousand years, the melting after the ice age takes about 10-20 thousand years," says Ashkenazi. "The peak of the previous ice age was about 20 years ago, and since then the climate has warmed for about 10 years. However, at the moment, we see that what happened in the previous ice ages is not repeating itself - and we are not starting another ice age." The reasons for this They are the differences between the periodicity of the earth's orbit around the sun and the periodicity of the angle of its axis - and The significant increase in the concentration of greenhouse gases in the atmosphere, which leads to the increase in global temperature that is currently occurring as part of the climate crisis. "It seems that our interglacial period is not similar to the interglacial periods of the Earth's past," concludes Ashkenazi.
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