The Azimuth Project
Azolla event

Idea

The dinosaurs were wiped out by an asteroid about 65 million years ago. Then came the Cenozoic Era: first the Paleocene, then the Eocene, and so on. At this time the Earth was very warm compared to now:

Paleontologists call the peak of high temperatures the Eocene optimum?. It was about 12 °C warmer then. There were crocodiles and palm trees in Antarctica.

Why did it get colder? This is a fascinating and important puzzle. And some scientists argue that one cause was the Azolla event — a huge bloom of freshwater plants in the Arctic ocean, which removed lots of carbon from the biosphere as they rotted and fell to the sea floor.

Details

In the early Eocene, the Arctic Ocean was almost entirely surrounded by land:

Early Eocene Arctic basin

A surface layer of less salty water formed from inflowing rivers, and around 49 million years ago, vast blooms of freshwater fern Azolla began to grow in the Arctic Ocean. And as bits of it died, it sank to the sea floor. This went on for about 800,000 years, and formed a layer 8 up to meters thick. And some scientists speculate that this process sucked up enough carbon dioxide to significantly chill the planet! In fact, some claim that CO2 concentrations fell from 3500 ppm in the early Eocene to 650 ppm at around the time of this event.

References

Start here:

For a well-written blog article on this topic, try:

For a more detailed review article, see:

  • Eveline N. Speelman et al., The Eocene Arctic Azolla bloom: environmental conditions, productivity and carbon drawdown, Geobiology 7 (2009), 155–170.

For a discussion of the DARWIN Azolla Project based at Utrecht University, see:

The figure of 3500 ppm for peak Cenozoic CO2 concentrations is on the high side; it was inferred from boron isotope studies:

For more, see Paleoclimate. The graph of Cenozoic temperatures was produced by Global Warming Art and was taken from Wikimedia Commons. The picture of the early Eocene Earth comes from

  • H. Brinkhuis et al., Episodic fresh surface waters in the Eocene Arctic Ocean, Nature 441 (2006), 7093.

and was taken from Wikipedia.

category: climate