The strange ice rings of Lake Baikal in Siberia appear to form as a result of warm clockwise currents of water under the surface, scientists have said. The discovery goes some way to explaining the annual phenomenon that has perplexed researchers for decades.
Lake Baikal is the world's deepest known lake and, at an estimated 25 million years old, is also one of the oldest. It formed from a rift valley and, because of its isolation, is "one of the world's richest and most unusual freshwater faunas," UNESCO notes.
The ice rings were first spotted via satellite images in the early 2000s. The rings were found to have darker, thinner ice at the edge, with thicker ice in the center. They normally measure between 3 and 4.3 miles wide and appear in different places across the lake in an "unpredictable manner," scientists wrote in the journal Limnology and Oceanography.
To better understand the rings, a team, led by Alexei Kouraev, from the University of Toulouse, France, carried out field surveys at the lake over 2016 and 2017. Their findings, published last October, were recently the subject of NASA Earth Observatory's Image of the Day.
The researchers deployed field sensors at the lake to measure the temperature and salinity of the water below the surface of the ice. Previously, scientists had suggested the ice rings may be related to methane escaping from the bottom of the lake. The latest findings suggest this is not the case. They found the water at the edge of the ice circle was 1 to 2 C warmer than at the center of the circle, or outside of it. The circular current, or eddy, appears to be driving the formation.
"[The] results of our field surveys show that before and during ice ring manifestation, there are warm eddies that circulate in a clockwise direction under the ice cover," Kouraev told NASA. "In the eddy center, the ice does not melt—even though the water is warm—because the currents are weak. But on the eddy boundary, the currents are stronger and warmer water leads to rapid melting."
Exactly how and why these currents form is unknown, but it appears to be related to wind patterns and water flowing into the lake, NASA said. Kouraev says they appear to form as a result of the wind moving the water from the bay into the lake, while the flow of water is blocked by the Svyatoy Nos peninsula.
The team say their research suggests that ice rings have been appearing on Lake Baikal for over 50 years, with 56 detected in total. They are found in two other lakes besides Baikal—Teletskoye Lake, also in Russia, and Hovsgol Lake in Mongolia—suggesting the phenomenon is more common than once thought.
The researchers also say all three of these lakes are long and narrow, with steep slopes, "but there is no specific reason that lens‐like eddies and associated ice rings should exist only for lakes with such a shape."
Concluding, they said Lake Baikal presents a "unique opportunity" for continuous monitoring of the ice ring phenomenon. Further studies, through satellite images and field observations, and laboratory work should help "bring new insights to help understand and monitor complex dynamical processes taking place in wintertime," they wrote.
"This includes the generation and evolution of lens‐like eddies and giant ice rings (as their surface manifestations) not only in lakes Baikal, Hovsgol and Teletskoye, but possibly in other lakes of the world."
Regular updates about the ice rings are posted to a website run by the team. Kouraev told Newsweek they are planning to return to Lake Bakail this month to carry out more surveys. They hope to find more eddies and monitor known ice rings.
Kouraev also said understanding why and where the ice rings form will help protect people living in the region, who often drive over the lake when it is frozen during winter months. The rings are so large they cannot be seen from land. During the study period, two vans sank into the lake after driving over one of these formations.
He told NASA: "People often drive a direct line between Nizhneye Izgolovye Cape and Khoboy Cape, but we strongly advise that they take a more southerly route to avoid the frequent ice rings in this dangerous region."
This article has been updated to include more information about the ice rings from Alexei Kouraev. More information on the formation of eddies has also been included.
Correction 2/4/20, 11:26 a.m. ET: The original article said 51 ice rings have been discovered, when the total is now 56.
