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Uranium isotopes may point to fresh water reserves in Pre-Volga region, scientists say

Since 2020, FECIAR experts have been working on a project to study the permafrost melting in the Russian Arctic zone

ARKHANGELSK, July 29. /TASS/. Scientific studies into the permafrost thawing will be used to find fresh water in the Pre-Volga region. Specialists from the Laverov Federal Center for Integrated Arctic Research (FECIAR, Arkhangelsk) and the St. Petersburg State University have discovered a connection between the rate of uranium isotopes in water and the share of salt in it, FECIAR’s press service told TASS.

"The isotopic composition analysis will show which sources are involved in formation of groundwater and which direction we must take in order to explore further the water reserves. Later on, it will be possible to conduct industrial exploration," the press service said.

Since 2020, FECIAR experts have been working on a project to study the permafrost melting in the Russian Arctic zone. They study the isotopic composition of water in regions with frozen soils, for example, in Komi and Nenets regions. Radiologists measure the content of deuterium and oxygen-18 — those are the isotopes that are parts of the water molecule and the ratio of uranium-234 to uranium-238. "The project is supported by the Russian Science Foundation. The participants intend to develop new approaches, in particular, to offer methods to use natural uranium isotopes — uranium-234 and uranium-238. Their ratio, according to our proposed interpretation, marks the "revived" waters formed during the melting of the underground ice," Yevgeny Yakovlev, head of FECIAR’s environmental radiology laboratory, told TASS.

For comparison purposes, the experts wanted to have data from an area where the permafrost used to be but has already melted. They chose the Pre-Volga region, where the permafrost existed for dozens of thousands of years. During the studies, the scientists have found that uranium isotopes are in balance in "modern" water, and this water is fresh and suitable for drinking. As for salt waters, they are characterized by a significant excess of uranium-234 over uranium-238. This result could be used to search for fresh water, so that to skip unnecessary well drilling.

Permafrost’s salty "traces"

The Pre-Volga region is the right bank of the Volga River near the Kuibyshev reservoir: Chuvashia’s south, Tatarstan’s south-west and the Ulyanovsk region’s north. These regions experience big problems with fresh water. Only one city — Tetyushi — has a centralized water supply from the Volga. The underground water is mainly very saline. Until recently, the proven reserves of groundwater in the Pre-Volga region, which can be used for centralized drinking water supply, have been insignificant.

The water is salty even at relatively small depths of 50-70 meters. "To blame" for this is the melted permafrost. 12-100 thousand years ago, the Pre-Volga’s climate was very harsh. The cold snap peak was about 18 thousand years ago. At that time, mammoths lived in the Pre-Volga region. They wandered the dry Arctic steppe. The air temperature at that time was comparable to the current temperature in approximately Labytanga, though the precipitation was much less.

There were no glaciers in the Pre-Volga region, but the permafrost reached the depths of 200-300 meters due to severe frosts throughout the year. It began to melt 10 thousand years ago, and salts began to dissolve in the water. "The salts, formed in the dissolution of gypsum, have an abnormally high solubility at temperatures near zero degrees. Therefore, in the Pre-Volga region, both the former permafrost zone and the zone of residual solutions contain water with increased salinity," the expert said.

The water, formed from the permafrost melting, contains much more uranium-234 than uranium-238. During cold weather periods, uranium-234 gets accumulated in rocks. "When the permafrost melts, it is washed out faster than uranium-238, as it is more water-soluble and mobile," he added.

At the same time, the soils in the region have always contained a lot of clay, which kept that salt water close to the surface. The project participants believe that at bigger depths there could be areas containing low salinity water and even fresh water. During the studies, the scientists found both salty and fresh water.

Why study permafrost

Studies of the permafrost’s conditions are very important for the Russian Arctic zone, the scientist continued. The climate changes and the warming in the Arctic mean that practically in every region continue growing the areas, which thaw in summer. At the same time, it is unclear what happens inside the frozen soils, especially at a great depth. "These changes are manifested in destruction of sea shores, in methane emissions - the Yamal funnel, in the loss of soil strength under residential buildings and industrial structures, and in other similar negative phenomena," Yakovlev explained.

The currently growing human economic activity in the Arctic leads to the risk of accidents, including due to the permafrost degradation. Additionally, the permafrost keeps almost twice as much carbon as there is in the atmosphere. The melting can lead to the release of such amounts of methane and carbon dioxide, that they may cause yet further climate warming. The thawing permafrost changes the chemical composition of water, increases the content of heavy metals and organic compounds, since they are released during melting.

In order to explore what is stored in the depth, experts have to drill wells. "Studies of permafrost areas at big depths mean big material and financial expenses. Therefore, it is logical to search for such natural labels that could reveal the history of the climate change in the past and could be useful for studying modern natural processes," the researcher said. According to the scientist, studying "traces" of thawed perennially frozen soils may be helpful in studying the modern Arctic zone. The isotope methods are much less expensive than drilling, and they are effective in assessing conditions of frozen soils over significant areas. Presently, the scientists have been practicing the methods in the laboratory and collecting new data, in particular, in the Barents Sea.

FECIAR continues studying the permafrost degradation jointly with the St. Petersburg State University. The project is supported by the Russian Science Foundation.