Arctic seas without salt
The cover shows Diamonds Beach and Jokulsarlon Glacier Lagoon in Iceland. Much of the Arctic Ocean is believed to have been covered by an ice shelf, but clear evidence of this has proven elusive. In this week’s issue, Walter Geibert and colleagues reveal results that suggest that in recent glacial periods the Arctic Ocean and adjacent Nordic seas were mostly filled with fresh water and covered with a thick ice platform. The researchers analyzed marine sediment nuclei for thorium-230, which occurs from the decay of uranium into salt water. They found that thorium-230 was missing in several layers of Arctic Ocean cores and the Nordic seas, which they interpret to mean that there was no salt water. The team suggests that the ice shelf actually created a dam, separating these bodies of water from the Atlantic Ocean and filling the freshwater region for two periods, 70,000–62,000 and 150,000–131,000 years ago.
Cover image: Aleksandar Tomic / Alamy.