The global mass extinction that ended the Triassic – and ushered in the Jurassic - was marked by inhospitable, sulphurous seas all around the coast, according to a new study.
While life on land seems to have been recovering, repeated poisoning of shallow seas with hydrogen sulphide knocked back the recovery of marine life during the early Jurassic. And some experts say a build-up of noxious gas could happen again.
“These coastal seas were stinking fouling seas, very unpleasant to higher life forms,” said Bas van de Schootbrugge of Goethe University Frankfurt, an author of the study published in Nature Geoscience.
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Life in the Triassic world had already been decimated by catastrophic volcanic eruptions which swept in a period of high carbon dioxide levels and global warming. A fall in oxygen levels at sea and global warming led rising hydrogen sulphide levels in the shallow seas, a hotbed of marine biodiversity during this time.
“We have conclusively shown for the first time that bottom waters were strongly anoxic [low in oxygen] and rich in hydrogen sulphide directly after the mass-extinction event. Our data show that the environmental impact was of a much longer duration [than previously thought],” said van de Schootbrugge. And the lack of oxygen would have inhibited the recovery of life, prolonging the environmental misery at sea.
The scientists studied sediments from northern Germany and Luxemburg buried during at the Triassic-Jurassic boundary; they used geochemical analyses to fingerprint fossilised pigments used exclusively by green sulphur bacteria.
These bacteria live under conditions of zero oxygen but high concentrations of hydrogen sulphide. “Imagine a shallow sea where the bottom waters of up to about 20 metres under the surface are devoid of oxygen,” said Schootbrugge, describing this as bad news for corals and bivalves.
Link. Awaiting paper.
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