Who has drawn the bottom of the Caspian Sea with cross lines? That was the question that Norman Curing posed when he first saw a satellite image of the shallow waters around the Seal Islands.
Curing, a NASA oceanographer, frequently studies photographs taken by the Landsat 8 satellite, which is 700 km above the Earth. However, the scientist had never seen before what the underwater "scars" look like, stretching for many kilometers along the green-blue bottom.
“I had no idea what they were,” says Curing. "I thought they were trawler tracks that sometimes disturb the bottom."
Curing and his colleagues tweeted the unusual photo and asked for help. However, other scientists were also confused. Some have suggested that the "scars" are marks from a motor boat engine. But after a few tweets, a more likely suspect emerged - ice.
The ice in the north of the Caspian Sea is thin, only about 40 cm, but the water depth near the islands is also small, only about three meters.
The theory suggests that large chunks of ice were blown across the sea by the wind. Then the layers of ice piled on top of each other, like ice cubes in a jug. The piled ice could well have gouged the seabed. The winds blew, and the ice moved along the bottom, plowing through the sea grass and seaweed.
With a new guess, Curing returned to the photographs from the Landsat-8 satellite and drew attention to the January images, when winter was still shackling the region. The photos showed that the region was covered with ice in the same places where the tracks were found.
“At that point, it became absolutely clear that most of the markings were from ice floes,” said Curing. "It looks like a big rake that was taken along the bottom."
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The hypothesis of Kuring and his colleagues was confirmed by Stanislav Ogorodov, a researcher at Moscow State University. Lomonosov, who had previously observed sea "scars" known as erosion.
