Arctic seas without salt
The blanket shows Diamond Beach and Jokulsarlon Glacier Lagoon in Iceland. It is believed that much of the Arctic Ocean was once covered by an ice shelf, but clear evidence of this has proved elusive. In this week’s issue, Walter Geibert and colleagues reveal results that suggest that in recent glacial periods the Arctic Ocean and adjacent northern seas have been largely filled with fresh water and covered by a thick ice shelf. The researchers looked at marine sediment cores for thorium-230, which is produced from the degradation of uranium in salt water. They found that thorium-230 was missing from several layers in the Arctic Ocean and northern seas, which they interpreted as meaning that there was no salt water. The team suggests that the ice shelf effectively created a dam, separating these bodies of water from the Atlantic Ocean and filling the region with fresh water for two periods, 70,000–62,000 and 150,000–131,000 years ago.
Cover image: Aleksandar Tomic / Alamy.