The photo is sourced from freep.com
The bottom of the northern seas is covered with a large number of gouges, which formed due to the movement of large icebergs that used to plow the underlying surface with their lower edges (keels). When oil-and-gas production and pipeline infrastructure gets built on the seabed, the continued drifting of ice creates the risk of oil spills and gas leaks. To assess this risk, scientists study the age and structure of ice gouges to find out whether gouges are still forming and whether the icebergs that create them could pose a threat to mining.
In most cases, sea shelf changes are monitored through geophysical surveys, which are carried out onboard ships. On a periodic basis, scientists compare the condition of the bottom relief in the same places with the results of the previous survey, after which the differences get compared. However, this approach does not make it possible to determine the origins and age of gouges dating back from before the monitoring. This gap has been filled by the scientists from the Geological Institute of the RAS, the Murmansk Marine Biological Institute of the RAS and the Shirshov Institute of Oceanology of the RAS, who have proposed to determine the age of gouges on the seabed by measuring the radioactivity of lead-210 that found its way into the bottom sediments from the atmosphere due to the decaying of the natural radionuclide uranium-238. Once in the sediments, atmospheric lead-210 begins to decay itself. Knowing the half-life of this element, experts can determine the age of the sediments in which it is located.
The new method was tested in several stages. Using a corer, the authors of the study took samples from the bottom of a large ice gouge near the coast of the Kara Sea at a depth of 28 to 32 metres. The corer allowed the scientists to obtain samples of sediments from different depths (from young surface sediments to older, deeper ones). This made it possible to examine the accumulation of sediment layers in the gouge.
The researchers then analysed the radioactivity of the lead-210 isotope at different depths by measuring the X-ray and gamma radiation from the samples, and performed mathematical calculations to determine the age of each layer. They found out that the sediments lying at a depth of 15 centimetres under the modern layer of the gouge were formed in the 2000s, and those at the depth of 43 metres date back to the early 20th century.
The scientists also used the cesium-137 isotope to determine if the time intervals were correct, as its high levels indicate that the sediments were formed during the periods of nuclear weapons testing. The highest level of cesium-137 radioactivity was found in a layer of 30–32 centimeters and was linked to the testing of nuclear weapons in 1963. The oldest layers, from which sedimentation began immediately after the formation of the gouge, were a little over 200 years old. The scientists thus came to the conclusion that the gouge was formed around 1810, i.e., during the Little Ice Age, which ended in the Arctic at the turn of the 20th century.
“The proposed approach has made it possible to determine the age of the largest ice gouge among those known on the Kara Sea shelf in the Baidarata Bay area. It can be used to survey bottom sections where it is planned to lay pipelines and install oil-and-gas production facilities. In view of the active destruction of glaciers and the drifting of individual icebergs increasingly observed in the northern seas due to climate warming, this method will give us additional information to assess the safety of economic activities in various areas of the Arctic,” Osip Kokin, candidate of geographical sciences and junior researcher at the Geological Institute of the RAS, is quoted as saying by the Russian Science Foundation.
