Thursday, December 2, 2021

Volcanic eruptions drove severe mass extinction, say scientists

Abrupt climate change ~450-440 million years ago caused the demise of the trilobite, Selenopeltis (pictured, in Oxford University Museum of Natural History).
Photograph: Dr Tom Gernon

Two intense periods of volcanism triggered a period of global cooling which caused one of the most severe mass extinctions in Earth history, according to new research.

The study, published in Nature Geoscience, was conducted by scientists at the University of Plymouth, the University of Oldenburg, the University of Southampton and the University of Leeds.

They examined the effects of volcanism on ocean chemistry during a period of extreme environmental change around 450 million years ago.

This period brought about intense planetary cooling, which culminated in a glaciation and the major ‘Late Ordovician Mass Extinction’. It led to the loss of about 85% of species dwelling in the oceans, reshaping the course of evolution of life on Earth.

Through their research, the team identified that two exceptionally large pulses of volcanic activity across the globe – occurring in parts of present-day North America and South China – coincided very closely with two peaks in glaciation and extinction separated by about 10 million years.

They also discovered that widespread blankets of volcanic material laid down on the seafloor during the Ordovician Period would have released sufficient phosphorus into the ocean to drive a chain of events including climatic cooling, glaciation, widespread low oxygen levels in the ocean, and mass extinction.

Dr Hayley Manners
Dr Hayley Manners, Lecturer in Organic Chemistry at the University of Plymouth, was involved in the sampling, sample preparation and analysis of the volcanic material that was analyzed for phosphorous content. She said:

“When volcanic material is deposited into the oceans a series of rapid chemical changes occur, which can include the release of phosphorus. This led our team to study volcanic ash layers in much younger marine sediments to compare their phosphorus contents before and after they were modified by interactions with seawater. The study of past climates can directly impact our understanding of how the earth will adapt to current climate change. Volcanic eruptions are typically considered as contributing to global warming via the release of greenhouse gases, but this study highlights the role of volcanism in global cooling over longer time periods.”

Dr Jack Longman, lead author of the study based at the University of Oldenburg, said:

“It’s been suggested that global cooling was driven by an increase in phosphorus to the oceans. Phosphorus is one of the key elements of life, determining the pace at which tiny aquatic organisms like algae are produced. Our study may prompt reinvestigations of other mass extinctions during Earth history.”

Dr Tom Gernon, Associate Professor at the University of Southampton and co-author of the study, added:

“The unresolved puzzle during our research was why glaciation and extinction occurred in two distinct phases at this time, separated by about 10 million years. That required some mechanism to pulse the supply of phosphorus, which is hard to explain. Intense bursts of volcanism are more typically linked to massive CO2 release, which should drive global warming, so another process must be responsible for sudden cooling events.”

Faced with such a conundrum, the researchers considered whether a secondary process – natural breakdown or ‘weathering’ of the volcanic material – may have provided the surge in phosphorus need to explain the glaciations.

They studied volcanic ash layers in much younger marine sediments to compare their phosphorus contents before and after they were modified by interactions with seawater.

This meant they were better placed to understand the potential geochemical impact of extensive volcanic layers from enormous eruptions during the Ordovician.

They were also able to develop a global biogeochemical model to understand the knock-on effects on the carbon cycle of rapidly adding a surge of phosphorus leached from volcanic deposits into the ocean.

However, while it might be tempting to think that seeding the oceans with phosphorus may help solve the current climate crisis, the scientists caution that this may have more damaging consequences.

They conclude that whilst on short timescales massive volcanic eruptions can warm the climate via CO2 emissions, equally they can drive global cooling on multimillion-year timescales.

Source/Credit: University of Plymouth