(CN) – Staggering drops in oceanic oxygen, a devastating consequence of greenhouse gas emissions that leads to mass extinctions of sea life, come to an end naturally. It just takes a million years to happen.
In a study published Friday in the journal Nature Communications, a team of researchers presents a timeline for this gradual buildup following such a reduction in oxygen, a phenomenon known as anoxia.
The scientists studied how periods of anoxia end and found that the decrease in oxygen causes more organic carbon to be buried in sediment on the ocean floor. Eventually, this stockpile of carbon raises oxygen in the atmosphere, which in turn oxygenates the ocean.
This finding is especially critical today, as experts believe the modern ocean is rapidly approaching anoxia. The team says it is “critical” to reduce carbon emissions before the point of no return.
“Once you get into a major event like anoxia, it takes a long time for the Earth’s system to rebalance,” said lead author Sarah Baker, a geographer at the University of Exeter.
Among the scenarios the team reviewed was the Toarcian Oceanic Anoxic Event, which took place 183 million years ago and led to a major disturbance in the global carbon cycle and mass extinction of marine life.
“This shows the vital importance of limiting disruption to the carbon cycle to regulate the Earth system and keep it within habitable bounds,” Baker said.
For the Toarcian Oceanic Anoxic Event, statistical models projected that increased organic carbon – stemming from less decomposition and additional marine and plant productivity in the warmer, carbon-rich environment – would raise atmospheric oxygen and end an anoxic event after a million years.
The scientists tested this theory by reviewing fossil charcoal samples for evidence of wildfires, which are more common in oxygen-rich times. The team found a period of increased wildfire activity that began a million years after the onset of the event. This phase of elevated wildfire activity lasted for about 800,000 years.
“We argue that this major increase in fire activity was primarily driven by increased atmospheric oxygen,” Baker said.
“Our study provides the first fossil-based evidence that such a change in atmospheric oxygen could occur in a period of one million years.”