From the point of view of scientists, arctic ice is of two types. Ice floating on the surface of the water for several years is old. It either freezes or thaws, but in general it remains very thick - about 2-5 meters. Ice that forms in one winter and then melts with the arrival of spring is seasonal. It is much thinner.
Today, 70% of Arctic people are seasonal ice. But just half a century ago, the ratio was different. During this time, the area of old Arctic ice has decreased by 2 million square meters. km.
Scientists, after analyzing data on the thickness of the Arctic ice over the past sixty years, have come to the conclusion that since 1958, the Arctic ice sheet has lost 2/3 of its thickness. For calculations, the ice thickness averaged over the entire Arctic as of the end of summer was taken. The findings are published in Environmental Research Letters.
Let's not forget that sea ice of any age is frozen ocean water. However, with each seasonal thaw, its properties change. Old ice, as a rule, has a lower salinity in addition to being thicker. In the 19th century, the then Arctic polar explorers used it to obtain drinking water. In addition, due to its greater power, it is less prone to wind movements.
In previous years, a certain amount of perennial ice floated from the Barents Sea to the outskirts of Greenland every summer and melted there. Now this is not the case - the ice melts earlier.