September 20, 2021

I, Science

The science magazine of Imperial College

If rising sea levels, ocean acidification, extreme weather, drought, food shortages and wars over water didn’t have you convinced, here’s one more reason why pumping large quantities of carbon dioxide into the atmosphere is a really bad idea.

One hundred and twenty million years ago, during the Cretaceous period when dinosaurs like iguanodon roamed the land, oxygen suddenly disappeared from the deep oceans.  Until recently no one knew why.  Now it seems carbon dioxide was to blame.

Loss of oxygen from deep sea water – ocean anoxia – is disastrous for marine life.  250 million years ago it was responsible for the greatest mass extinction of all time, the Permian-Triassic event, when 96% of all marine species were wiped out.

Though less devastating, the Cretaceous event is much better preserved in the fossil record, providing scientists with vital insights into these catastrophic phenomena.

Another consequence of carbon emissions?

Researchers led by German geologist, Wolfgang Kuhnt, analysed carbon in Cretaceous rocks from a disused quarry.  Their results, published in this month’s Geology journal, show evidence of a huge increase in atmospheric CO2 just before the oxygen departed.   The rise came in pulses over a 100,000 year period, leading the team to believe that either a volcano or big, intermittent releases of methane into the atmosphere were responsible.

According to Kuhnt’s team, global warming from the high CO2 melted the polar ice caps, causing sea levels to rise.  It’s thought that the associated changes in ocean currents brought less oxygenated water to the deep ocean.

The consequences were far-reaching, with plankton bearing the brunt.  Some, like the nannoconids, were wiped out completely, while other groups took a hit in diversity.  Those that did survive were often malformed or stunted in size and it took 350,000 years for things to get back to normal.


By James Pope