The Azolla Event
A freshwater fern blankets the Arctic Ocean for 800,000 years and helps pull the world out of its greenhouse.
- When
- —
- Duration
- 1.2 million years
- Known to
- ± 300 thousand years
- Era
- Eocene, Cenozoic
Around 49 million years ago the Arctic Ocean is nearly enclosed and receives enough river runoff to float a freshwater lid on top of the salt water. The floating fern Azolla, which fixes nitrogen with symbiotic cyanobacteria and can double its mass in days, blooms across the entire basin. Its remains accumulate in the anoxic depths as a sediment layer up to eight metres thick. Estimates of the carbon dioxide drawn down run into the trillions of tonnes, and the event sits at the start of the long cooling that ends in the ice ages. How much of the cooling it caused is still argued.