The study offers a new perspective on a series of severe environmental crises known as oceanic anoxic events, which occurred between 185 and 85 million years ago when the oceans were critically low on dissolved oxygen.
Researchers from the University of Southampton, who led the study, explained that these events led to major biological upheavals, including mass extinctions of marine species.
The findings were published on Thursday, August 29, in 'Nature Geoscience'.
"Oceanic anoxic events were like hitting the reset button on the planet's ecosystems," said Professor Tom Gernon, the lead author and a Professor of Earth Science at Southampton. "The challenge was understanding which geological forces hit the button."
The research, conducted in collaboration with universities in the UK, Australia, the Netherlands, Canada, and the US, explored the impact of plate tectonics on ocean chemistry during the Jurassic and Cretaceous Periods, part of the Mesozoic era.
This era, known as the age of the dinosaurs, is prominently displayed along the Jurassic Coast in southern England and other locations like Whitby and Eastbourne.
The team utilized statistical analyses and advanced computer models to examine how oceanic chemical cycles could have been influenced by the breakup of the supercontinent Gondwana, a landmass once inhabited by dinosaurs.
"The Mesozoic era saw the breakup of this massive landmass, leading to widespread volcanic activity," explained Prof. Gernon. "As tectonic plates moved and new seafloors formed, large amounts of phosphorus, an essential nutrient for life, were released from weathering volcanic rocks into the oceans."
The study identified multiple pulses of chemical weathering on both the seafloor and continents, which alternately disrupted the oceans. "It's like a geological tag-team," said Prof. Gernon.
The researchers found that the timing of these weathering pulses aligned with most oceanic anoxic events in the geological record. They suggest that the influx of phosphorus acted like a natural fertilizer, increasing the growth of marine organisms. However, this surge in biological activity led to significant amounts of organic matter sinking to the ocean floor, consuming large quantities of oxygen.
"This process eventually caused vast areas of the oceans to become anoxic, or oxygen-depleted, creating 'dead zones' where most marine life perished," said co-author Professor Benjamin Mills from the University of Leeds. He noted that these anoxic events typically lasted around one to two million years, profoundly impacting marine ecosystems.
The study also highlights how nutrient overloading, similar to that caused by human activities today, can severely damage marine environments. The researchers explained that current human activities have already reduced mean oceanic oxygen levels by about two percent, significantly expanding anoxic water masses.
"Studying geological events offers valuable insights that can help us grasp how the Earth may respond to future climatic and environmental stresses," added Prof. Gernon.
The findings demonstrate a stronger connection than previously understood between the Earth's internal geological processes and surface environmental changes, particularly during periods of tectonic and climatic upheaval. "It's remarkable how a chain of events within the Earth can impact the surface, often with devastating effects," Prof. Gernon added. "Tearing continents apart can have profound repercussions for the course of evolution."
Research Report:Solid Earth forcing of Mesozoic oceanic anoxic events
Related Links
University of Southampton
Explore The Early Earth at TerraDaily.com
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