In a paper published in the journal Nature Geoscience, scientists offer a new explanation for a string of severe environmental crises, called oceanic anoxic events, which happened between 185 and 85 million years ago (Mesozoic era); these occurred when the seas became critically depleted of dissolved oxygen.
“Oceanic anoxic events were like hitting the reset button on the planet’s ecosystems,” said University of Southampton’s Professor Tom Gernon.
“The challenge was understanding which geological forces hit the button.”
The researchers examined the impact of plate tectonic forces on ocean chemistry during the Jurassic and Cretaceous periods, collectively known as the Mesozoic era.
“This chapter of Earth’s history is often dubbed the age of the dinosaurs and is famously exposed along the Jurassic Coast on the UK’s south coast as well as along the cliffs of Whitby in Yorkshire and Eastbourne in East Sussex,” Professor Gernon said.
The scientists combined statistical analyses and sophisticated computer models to explore how chemical cycles in the ocean could have feasibly responded to the breakup of the supercontinent Gondwana, the great landmass once roamed by the dinosaurs.
“The Mesozoic era witnessed the breakup of this landmass, in turn bringing intense volcanic activity worldwide,” Professor Gernon said.
“As tectonic plates shifted and new seafloors formed, large amounts of phosphorus, a nutrient essential for life, were released from weathering volcanic rocks into the oceans.”
“Crucially, we found evidence of multiple pulses of chemical weathering on both the seafloor and continents, which alternately disrupted the oceans. It’s like a geological tag-team.”
The authors found the timing of these weathering pulses matched up with most oceanic anoxic events in the rock record.
They propose that the weathering-related influx of phosphorus to the ocean acted like a natural fertilizer, boosting the growth of marine…
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