By Stephen Beech via SWNS
Ocean life was devastated by a deadly land-sea “tag team” 100 million years ago, reveals new research.
A string of catastrophic environmental events triggered “mass extinctions” of marine species, say scientists.
The study, published in the journal Nature Geoscience, shows how the “tag team” – made up of the oceans and continents – altered the course of evolution on Earth.
Researchers have unearthed a new explanation for a string of severe environmental crises – called “oceanic anoxic events” – which occurred between 185 and 85 million years ago when the seas became critically depleted of dissolved oxygen.
The international research team, led by University of Southampton scientists, say the events triggered “significant” biological upheavals – including mass extinctions of marine species.
Lead author Dr. Tom Gernon said: “Oceanic anoxic events were like hitting the reset button on the planet’s ecosystems.
“The challenge was understanding which geological forces hit the button.”
Southampton scientists conducted the study along with colleagues from Leeds University, Bristol University, Adelaide University in Australia, Utrecht University in the Netherlands, Waterloo University in Canada, and Yale University in the United States.
The team examined the impact of plate tectonic forces on ocean chemistry during the Jurassic and Cretaceous Periods, collectively known as the Mesozoic era.
Dr. Gernon explained that 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 North Yorkshire and Eastbourne, East Sussex.
The team combined statistical analyses and sophisticated computer models to explore how chemical cycles in the ocean could have feasibly responded to the break-up of the supercontinent Gondwana, the great landmass once roamed by the dinosaurs.
Dr. Gernon said: “The Mesozoic era witnessed the break-up of this landmass, in turn bringing intense volcanic activity worldwide.
“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 researchers found the timing of the weathering pulses matched up with most oceanic anoxic events in the rock record.
They believe that the weathering-related influx of phosphorus to the ocean acted like a natural fertilizer, boosting the growth of marine organisms.
But the team say the fertilization episodes came at a “major cost” for marine ecosystems.
Study co-author Dr. Benjamin Mills, of the University of Leeds, explained that the increase in biological activity led to “huge” amounts of organic matter sinking to the ocean floor, where it consumed large quantities of oxygen.
He said: “This process eventually caused swathes of the oceans to become anoxic, or oxygen-depleted, creating “dead zones” where most marine life perished.
“The anoxic events typically lasted around one to two million years and had profound impacts on marine ecosystems, the legacy of which are even felt today.
“The rocks rich in organic matter that accumulated during these events are by far the largest source of commercial oil and gas reserves globally.”
As well as explaining the cause of extreme biological turmoil in the Mesozoic, the team say their findings highlight the devastating effects that nutrient overloading can have on marine environments today.
They explained how present-day human activities have reduced mean oceanic oxygen levels by about two percent, leading to a significant expanse in anoxic water masses.
Dr. Gernon said: “Studying geological events offers valuable insights that can help us grasp how the Earth may respond to future climatic and environmental stresses.”
He says the findings, overall, reveal a stronger-than-expected connection between the Earth’s solid interior and its surface environment and biosphere, especially during periods of tectonic and climatic upheaval.
He added: “It’s remarkable how a chain of events within the Earth can impact the surface, often with devastating effects.
“Tearing continents apart can have profound repercussions for the course of evolution.”
