Credit: Christian R. Rohleder

According to their study, even during periods of extreme cold, the Arctic retained areas of open water with seasonal sea ice, providing conditions for life.

The team studied sediment cores from the Arctic Ocean floor and the Yermak Plateau. These samples contained chemical signatures of ancient algae, specifically a molecule called IP25, which is produced by algae that live in seasonal sea ice that forms and melts throughout the year.

The presence of this molecule in sediment layers suggests that the ice cover was not continuous and permanent.

To support their findings, the scientists used a high-resolution computer model, the Earth System Model, that simulated Arctic conditions during two key periods: the Last Glacial Maximum about 21,000 years ago and an earlier period about 140,000 years ago, when ice sheets covered large areas of the Arctic.

The modeling showed that even during these periods, warm Atlantic waters penetrated the Arctic, preventing the ocean from freezing completely and maintaining seasonal melting of the ice.

The results of the study cast doubt on the theory that a single massive ice shelf covered the entire Arctic Ocean for thousands of years.

Although local and temporary glacial formations may have occurred, there is no evidence of their persistent existence on an Arctic-wide scale. There was only a short-term decrease in biological activity about 650,000 years ago, which scientists believe was temporary.

Understanding the dynamics of sea ice and ocean currents in the past helps to better predict changes in ice cover and marine ecosystems in the context of today’s warming climate, says Gerrit Lohmann of the Helmholtz Centre for Polar and Marine Research.