Jurassic drop in ocean oxygen lasted a million years

The depletion of oxygen in the oceans is known as “anoxia,” and scientists from the University of Exeter have been studying how periods of anoxia end.

They found that the drop in oxygen causes more organic carbon to be buried in sediment on the ocean floor, eventually leading to rising oxygen in the atmosphere which ultimately re-oxygenates the ocean.

Scientists believe the modern ocean is “on the edge of anoxia” — and the Exeter researchers say it is “critical” to limit carbon emissions to prevent this.

“Once you get into a major event like anoxia, it takes a long time for the Earth’s system to rebalance,” said lead researcher Sarah Baker, a geographer at the University of Exeter.

“This shows the vital importance of limiting disruption to the carbon cycle to regulate the Earth system and keep it within habitable bounds.”

The researchers, who also include Professor Stephen Hesselbo from the Camborne School of Mines, studied the Toarcian Oceanic Anoxic Event, which took place 183 million years ago and was characterized by a major disturbance to the global carbon cycle, depleted oxygen in Earth’s oceans and mass extinction of marine life.

Numerical models predicted that increased burial of organic carbon — due to less decomposition and more plant and marine productivity in the warmer, carbon-rich environment — should drive a rise in atmospheric oxygen, causing the end of an anoxic event after one million years.

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