"The Arctic sea ice responded very rapidly to past climate changes. During the coldest periods of the past 90,000 years the sea ice edge spread relatively quickly to the Greenland-Scotland Ridge, and probably far into the Atlantic Ocean." says first author Ulrike Hoff, a researcher at Centre for Arctic Gas Hydrate, Environment and Climate (CAGE). Sea ice amplifies the climate changes that are occurring at any given time. Its growth and melting has profound effects on climate, the marine environment and ocean circulation. 

Tiny pieces that complete the big picture

Hoff and colleagues studied the past distribution of sea ice, in the so far longest existing sea ice record in a marine sediment core. The core was retrieved from 1200m water depth from the ocean floor of the Nordic Seas, just off the Faroe Islands. The core represents 90,000 years of sediment layers, and it is by studying those layers that scientist can reveal the changes in sea ice and past climate. 

It was the tiniest of evidence in these layers that brought this strong confirmation of sea ice behavior to light. They are a type of phytoplankton, called diatoms, and they are everywhere around you. Diatoms are single celled algae with a cell wall made up of silica. 

"They are the golden brown coating in the glass of a street lamp, and shiny stuff in your make-up. They are even used in tooth paste as a cleaning agent.," says Hoff. 

"Diatoms are truly amazing, and can be preserved in marine and lake sediments for millions of years. I have personally examined diatom fossils that are 65 million of years old, and they look much the same as the diatoms that we find living today."