Sleeping giant puts an end to deep-sea life

Credit By Ocean Wise

In this study, the ocean was represented in three dimensions for the first time, and a model that considers ocean currents was used. The results revealed that the oxygen concentrations in the upper and lower layers differ markedly due to the disruption of the global water cycle.

This separation means that the entire seafloor, except for shallow areas near the coast, was completely devoid of oxygen for tens of millions of years, until the beginning of the Silurian period about 440 million years ago.

Ridgewell says, “The breakdown of circulation would have been a death sentence for anything that could not swim near the surface of the ocean and lacked the life-sustaining oxygen still present in the atmosphere.” Deep-sea creatures include oddly shaped fish, giant worms, crustaceans, squids, and sponges.

The paper does not address whether and when the Earth might experience a similar event in the future, making it difficult to determine when the collapse might occur and what might trigger it. Existing climate models, however, confirm that global warming will weaken ocean circulation, and some models predict the eventual collapse of a branch of circulation that begins in the North Atlantic.

Said Ridgewell, “We need higher-resolution climate models to predict mass extinctions.” That said, we are already concerned today about the North Atlantic water cycle, and there is evidence that water flow to depth is decreasing.”

In theory, Ridgewell said, unusually warm summers and cliff erosion could trigger a cascade of processes that would upend life today.

He said, “You would think that on the surface of the ocean, where you surf and sail, all the activity is going on. But at the bottom of the ocean, it’s working ceaselessly, providing vital oxygen to animals in the dark depths,” Ridgewell said.

The ocean allows life to flourish but can also take that life away. There is nothing to deny that as long as the continental plates continue to move.”

The hitherto overlooked location of the continents fills the Earth’s oceans with the oxygen necessary to sustain life. However, continental drift could conversely be killing marine life.

Andy Ridgewell, a geologist at the University of California, Riverside, and co-author of a new study on forces affecting ocean oxygen, said, “Continental drift is so slow that nothing dramatic seems to happen, but when the ocean is primed, even seemingly small events may cause widespread death of organisms,” she said.

Ocean waters become colder, denser, and sink as they approach the North and South Poles. As the water sinks, oxygen from the atmosphere flows into the ocean floor.

Eventually, nutrients released from the sinking organic matter return to the ocean surface and are used for plankton growth, a cycle that occurs. Thus, the supply of oxygen to the deep sea and the production of organic matter on the seafloor are responsible for the diversity of fish and animals that inhabit the ocean today.

Researchers at the University of California, Riverside, have discovered that this circulation of oxygen and nutrients may suddenly come to a halt. Using a complex computer model, the researchers examined whether the position of the continental plates affects the movement of oxygen in the oceans. Surprisingly, the results showed that the position of continental plates affects the movement of oxygen.

The findings are detailed in today’s issue of the journal Nature.

Professor Ridgewell said, “Millions of years ago, shortly after the birth of marine animals, the global ocean circulation seems to have been in a cyclical standstill.” We never expected to discover that continental drift would cause surface water and oxygen to cease to sink and perhaps dramatically affect how life on Earth has evolved.”

Until now, models used to study the evolution of ocean oxygen over the past 540 million years have been relatively simple and have not taken into account ocean circulation. In such models, “ocean anoxia,” the disappearance of ocean oxygen, means a decrease in atmospheric oxygen concentrations.

Alexandre Paul, a lead author of the study and former UCR paleoclimate modeler, now with the University of Burgundy-Franche-Comté, France, said, “Scientists had assumed that changes in oxygen concentrations in the ocean mostly reflected similar variations in the atmosphere.”

In this study, the ocean was represented in three dimensions for the first time, and a model that considers ocean currents was used. The results revealed that the oxygen concentrations in the upper and lower layers differ markedly due to the disruption of the global water cycle.

This separation means that the entire seafloor, except for shallow areas near the coast, was completely devoid of oxygen for tens of millions of years, until the beginning of the Silurian period about 440 million years ago.

Ridgewell says, “The breakdown of circulation would have been a death sentence for anything that could not swim near the surface of the ocean and lacked the life-sustaining oxygen still present in the atmosphere.” Deep-sea creatures include oddly shaped fish, giant worms, crustaceans, squids, and sponges.

The paper does not address whether and when the Earth might experience a similar event in the future, making it difficult to determine when the collapse might occur and what might trigger it. Existing climate models, however, confirm that global warming will weaken ocean circulation, and some models predict the eventual collapse of a branch of circulation that begins in the North Atlantic.

Said Ridgewell, “We need higher-resolution climate models to predict mass extinctions.” That said, we are already concerned today about the North Atlantic water cycle, and there is evidence that water flow to depth is decreasing.”

In theory, Ridgewell said, unusually warm summers and cliff erosion could trigger a cascade of processes that would upend life today.

He said, “You would think that on the surface of the ocean, where you surf and sail, all the activity is going on. But at the bottom of the ocean, it’s working ceaselessly, providing vital oxygen to animals in the dark depths,” Ridgewell said.

The ocean allows life to flourish but can also take that life away. There is nothing to deny that as long as the continental plates continue to move.”

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