MIL-OSI Russia: NSU scientists using accelerator mass spectrometry have established the age of methane in the seeps of the middle Ob region

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MIL OSI Translation. Region: Russian Federation –

Source: Novosibirsk State University – Novosibirsk State University –

An unusual study was carried out at the Center for Collective Use “Accelerator Mass Spectrometry of NSU-NNSC” – for the first time, an accelerator mass spectrometer was used to carry out radiocarbon analysis of methane isolated from samples of swamp gas, which were taken by researchers of the Yugra State University from seeps in the swamps of the Khanty-Mansiysk Autonomous Okrug . It was important for them to find out the age and origin of methane.

Three origin hypotheses

Researchers from Southern State University were faced with the task of determining the origin of methane in seeps – recently discovered active sources of swamp gas in the floodplains of the middle Ob region, and also to study the biogeochemical processes associated with the production and transport of this gas to seeps.

Barn owls were first found in the early 2000s near the Mukhrino international field station, 25 km from Khanty-Mansiysk. They were pools in a stream, from which bubbles saturated with methane were actively rising. It quickly became clear that there are many similar sources throughout the entire Khanty-Mansi Autonomous Okrug-Yugra. Subsequently, SSU scientists estimated the area of their distribution from satellite images using convolutional neural networks. Seeps can look different: like craters, puddles, craters, defects in the beds of rivers and streams. These objects have two common properties – they are all located in floodplains of rivers or streams and extremely intensively emit methane, the second most important greenhouse gas for the Earth’s climate after carbon dioxide. The latter aroused the initial interest of researchers in these objects.

“To determine the future fate of seeps as a source of methane, it was necessary to understand the origin and migration routes of this gas. We had three hypotheses about this. The first – “petroleum” – suggested that methane in seeps is produced during the thermal decomposition of organic compounds (oil or kerogen) in hydrocarbon-rich Jurassic and Cretaceous sediments located at a depth of more than 1 km, and rises to the surface along breaks and cracks in the earth’s crust. This hypothesis was quite natural, because about half of all Russian oil is produced in the Khanty-Mansi Autonomous Okrug-Yugra, and hydrocarbon-rich formations are ubiquitous in the region. The second hypothesis – “permafrost” – assumed that methane is released from degrading relict permafrost in Oligocene deposits at a depth of 150-200 m. It was supported by the fact that the southern border of the layer of relict permafrost is located in exactly the same part of the Khanty-Mansi Autonomous Okrug-Yugra , where the barn owls were found. High concentrations of methane are often found in permafrost, which also makes this hypothesis quite logical. The third hypothesis, the “swamp” hypothesis, suggested that methane enters the seeps from the raised bogs that cover about half of the region, from where it migrates with groundwater. Swamps are the main natural source of methane in Western Siberia. Methane from the upper layers of swamps escapes into the atmosphere through plant roots. They are absent in the deep layers of swamps, but methane can enter the groundwater from the mineral horizons underlying the swamp, explained Alexander Sabrekov, a researcher at the Research Center “Environmental Dynamics and Global Climate Change” at Ugra State University.   

If the first, “oil” hypothesis is correct, then the emission of methane from seeps will begin to decline as oil and gas are produced, since the pressure in the formations, due to which they come to the surface, will decrease. If the second, “permafrost” hypothesis is confirmed, one can expect an explosive increase in emissions from seeps due to the accelerating degradation of relict permafrost associated with global warming, followed by a subsequent decrease due to the absence of a source of methane in Oligocene sediments. Establishing the truth of the third, “swamp” hypothesis, suggests that methane will be released from seeps as long as a significant part of the region’s territory is covered with swamps.

Non-trivial task

It was possible to determine which of the three hypotheses was correct by, among other things, determining the age of the methane released from these seeps. This can be done using the accelerator mass spectrometry method.

— This study was special for us and we actually carried it out on our own initiative – the request of our colleagues from Southern State University was very interesting for us. We usually study solids – establishing the radiocarbon age of archaeological finds, works of art, carbonates and humic acids. We already had experience working with gases – 10 years ago we analyzed exhaled air to diagnose the stomach for the presence of the bacterium Helicobacter pylori, which is the causative agent of a number of diseases of the stomach and duodenum. Our graphitizer is adapted to work with carbon dioxide, and for us this was a familiar job, but we had not previously carried out the extraction of methane from a certain mixture, its further graphitization and dating. It was very interesting to do this work and see its results,” said Ekaterina Parkhomchuk, director of the accelerator mass spectrometry unit of NSU-NNSC.

Taking gas samples in swampy areas required researchers to be careful and careful.

— To determine the age of methane using UMS, the gas sample must be quite voluminous – at least 100 ml, and preferably more. At the same time, from the point of view of gas extraction, seeps are extremely unpleasant objects: water-saturated soil sucks in an approaching researcher no worse than quicksand, and any careless movement displaces this soil, blocking the channel through which gas rises from the depths, after which it is no longer possible to extract it. Gas bubbles come to the surface unevenly: sometimes, in order to gain the required volume, one had to stand motionless next to the seep for more than an hour, while the temperature of groundwater in the region is close to zero at any time of the year. Most hopper seeps are very shallow, so a modification of the inverted hopper method had to be developed to extract gas from them. Before sampling, water was filled into the funnel, which was displaced by the gas escaping in bubbles. This gas was pumped into a syringe attached to the funnel to refill the funnel with water. On the same day, the gas was pumped from the syringe into a 300 ml plastic bottle, pre-filled with a saturated solution of table salt, but so that some water still remained in the bottle. In this form, the gas could be stored for years, and this is how we sent it for analysis to Novosibirsk,” explained Alexander Sabrekov.

Correct hypothesis

Scientists from the Center for Collective Use “Accelerator Mass Spectrometry of NSU-NSC” successfully extracted swamp gas, fed it to a graphitizer and obtained graphite targets. Work on its analysis continued throughout the year. During the first series of studies to determine the radiocarbon content in methane, they did not pay attention to the existing isotope shift for another carbon isotope – C-13, but later, reading the preliminary text of the article with the results obtained, they saw an unusually large value of the isotopic shift and processed the results with taking it into account, obtaining reliable results. According to which, the third, “swamp” hypothesis of the origin and transportation of methane in seeps was unambiguously confirmed to be correct.

— All measured geochemical indicators either confirmed it or did not contradict it. In swamps and groundwater, we found methane with exactly the same composition of stable isotopes as in seeps, in the same concentration range. However, the lower the methane concentration in seeps, the more the composition of stable methane isotopes in them deviated from the swamp. Most likely, this is due to the fact that methane is synthesized not only in swamps, but also during transport to seeps in groundwater from dissolved organic matter, which also enters groundwater from swamps, said Alexander Sabrekov.

The researcher noted that the use of the UMS method was of decisive importance in determining the origin of methane: based on its results, it was possible to unequivocally say that the methane is modern, that is, Holocene, and is no older than the deepest (and therefore the oldest) peat in modern swamps covering the region. This fact immediately clearly excludes both the “oil” and “permafrost” hypotheses.

The significance of the study by scientists from SSU directly depended on which of the hypotheses was confirmed. If the first is “oil”, then the locations of the seeps could be used in the exploration of new fields. It is known that seeps are a very good marker of fields where it is commercially profitable to extract oil. In addition, if this hypothesis were correct, it would mean that groundwater, which is actively used for drinking water supply in much of Western Siberia, could be contaminated with carcinogenic heavy metals and organic compounds, which are abundant in oil-bearing formations. The correctness of the second, “permafrost” hypothesis, would indicate that the layer of relict permafrost that protects drinking groundwater from pollution from the surface is thinning, and the potential danger of such pollution is increasing.

Confirmation of the validity of the third, “swamp” hypothesis, indicates the presence in Western Siberia of a powerful source of methane, which will exist until the swamps disappear. Scientists have a clearer understanding of how closely landscapes are interconnected, which is very important for predicting the consequences of their changes due to global warming or anthropogenic impact (for example, pollution from oil production).

“This fact means that the described mechanism of methane transport can also take place in other regions with a similar structural landscape, where they need to be searched and studied,” the scientist concluded.

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Please note; This information is raw content directly from the information source. It is accurate to what the source is stating and does not reflect the position of MIL-OSI or its clients.

EDITOR’S NOTE: This article is a translation. Apologies should the grammar and or sentence structure not be perfect.

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