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Viewings: 4349If you have been hard to pronounce the name of the Icelandic volcano Eyjafjallajoekull, get ready for a new trial. On Chukotka there is a lake Elgygytgyn, and many scientists call it simply "e".
The reservoir depth of over 150 m formed 3.6 million years ago on the place of the impact crater. Since then the lake obediently collect sediment carried by him in the surrounding rivers. Glaciers passed this place, not disturbing the accumulated sediments.
The lake, not too rich in nutrients, the greater part of the year covered with ice; the water is clean and oxygenated. But the conditions are changing with climate and the terrestrial became a wealth of information for fans of paleoclimatic studies. Above sea level so long climatic chronicle look very hard. The ice cores from Greenland to look into the past only 125 thousand years, and the longest Antarctic Kern covers only 800 thousand years.
An international group of researchers, with a Herculean effort, was able to extract core samples from the bottom of lake Elgygytgyn, including 517-meter sample that pulled up to the crater. For the first time scientists have got the information about 2.8 million years of history of the Siberian Arctic.
On the results of the preliminary analysis, the experts reported two years ago at a conference, and here came the time of publication in the journal Science.
Many methods were used to study the cores. For example, a change of magnetic properties helps to determine the age of the layers (due to frequent fluctuations of the magnetic field of the Earth), and find out the level of oxygen in the water. When the lake remains stratified throughout the year, not mixing in spring and autumn, or when organic material doesn't hurt to be on the bottom and corrupting oxygen at a great depth is depleted and magnetite (iron oxide) is dissolved. Another way to measure the oxygenation provides the attitude of manganese to the iron.
The researchers also measured the concentration of organic carbon that "monitor" conservation and decomposition of organic matter, and the ratio of the amounts of silicon and titanium shows the performance of photosynthesis diatoms. In addition, we have isolated pollen, indicating changes in ecosystems around the lake.
Experts have identified in the sediment three facies. The first includes a thin gray and black layers of rocks that were deposited in the cold period when ice covers the lake all year round. Without mixing caused by wind, bottom water was wasting oxygen. Grey sludge indicates restored iron, and black points to the accumulation of organic material, degree not fully decomposed.
Second facies contains brownish residue. It is less clearly separated layers, but is most common. This sludge meets the conditions similar to modern: ice melts in the summer, opening the way for photosynthesis and oxygen therapy.
Third facies has rusty-red due to the large amount of oxidized iron that, apparently, is connected with a particularly warm episodes interglacial periods. Photosynthetic activity in such moments was the most high.
These periods are dated on the isotopic composition of bottom sediments of the oceans and called Marine Isotope Stages (MIS). Stage MIS 5e (about 130 thousand years ago) was at the peak summer solar radiation in the Arctic. The sea level was several meters higher than today. The period MIS 11c (a little more than 400 thousand years ago) was unusually long, though not so warm.
Ironically, during MIS 11c in the area of Terrestrial was much warmer than in the era of MIS 5e. And this is despite the less intensive summer solar radiation and similar concentration of greenhouse gases. Probably played a role of some other factors.
The Arctic is one of the most sensitive to climate changes of the Earth (due to the loss of snow and ice, for example), and ongoing impact on the rest of the planet. The explanation for high temperatures during MIS 11c would bring us many benefits.
Prepared according to Ars Technica.
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