The properties of sediments from the bottom of the Arctic Ocean have so far led to discrepancy about the processes taking place on the Arctic shelf during glacial periods. Isotope analysis of sediments from the bottom of the Arctic Ocean and adjacent seas, revealed that these basins were not only covered by an extensive ice shelf, but also completely filled with freshwater. Researchers from the Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research, published the results of analyzes of the content of the Thorium 230 (230Th) isotope in Arctic sediments. They concluded that a volume of fresh water of the order of 9 million km3 filled the Arctic basin under thick iceshelf, and it occured twice, 70,000 – 62,000 and 150,000 – 131,000 years ago. These results, given the possibility of a rapid release of such a mass of water into the World Ocean, provide new variables for oceanographic models based on 230Th content, describing sea level changes in the Pleistocene.