Movement of continents capable of strangling marine oxygen

A previously overlooked factor – the placement of continents – helps fill Earth’s oceans with essential oxygen. The movement of the continents could ultimately have the opposite effect, killing off most deep ocean creatures.

“Continental drift seems so slow, as if nothing drastic could come of it, but when the ocean is primed, even a seemingly small event could trigger the widespread death of marine life,” said Andy Ridgwell, a UC Riverside geologist and co-author of a new study of forces affecting ocean oxygen.

Water at the surface of the ocean becomes colder and denser as it cools approaches the north or south pole, then sinks. As the water flows, it carries oxygen extracted from the Earth’s atmosphere to the bottom of the ocean.

Finally, a return flow nutrients released by sunken organic matter are brought back to the surface of the ocean, where they fuel the growth of plankton. The uninterrupted supply of oxygen at lower depths and the organic matter produced at the surface area support an incredible diversity of fish and other animals in today’s ocean.

New findings led by researchers based at UC Riverside have shown that this circulation of oxygen and nutrients can end quite suddenly. Using complex computer models, the researchers investigated whether the location of continental plates affects how the ocean moves oxygen. To their shock, it does.

This finding, published today, is detailed in the journal Character.

“Several million years ago, soon after animal life began in the ocean, all global ocean circulation seemed to periodically stop,” Ridgwell said. “We did not expect to find that the movement of continents could prevent ground water and oxygen from flowing, and possibly significantly affect the way life evolved on Earth.”

Up to now, the models used to study the evolution of marine oxygen over the 540 last million years were relatively simple and did not take ocean circulation into account. In these models, ocean anoxia – times when ocean oxygen disappeared – implied a drop in atmospheric oxygen concentrations.

“Scientists previously assumed that the changes in oxygen levels in the ocean mainly reflected similar fluctuations in the atmosphere,” said Alexandre Pohl, first author of the study and former UCR paleoclimate modeller, now at the Université Bourgogne Franche-Comté in France.

This study used, for the first time, a model in which the ocean was represented in three dimensions, and in which ocean currents were taken into account. The results show that the collapse of the global water circulation results in a sharp separation between oxygen levels at upper and lower depths.

This separation meant that the he entire seabed, except for shallow places near the coast, lost oxygen entirely for several tens of millions of years, until approximately 440 million years ago at the beginning of the Silurian period.

“The collapse of the circulation would have been a death sentence for all that could not not swim closer to the ground and the very important oxygen still present in the atmosphere,” Ridgwell said. Creatures of the deep include bizarre fish, giant worms and crustaceans, squid, sponges and more.

The doc does not specify if or when Earth might expect a similar event in the future, and it is difficult to identify when a collapse might occur, or what caused it. sets off. However, existing climate models confirm that increasing global warming will weaken the ocean circulation, and some models predict a possible collapse of the circulation branch that begins in the North Atlantic.

“We would need a higher resolution climate model to predict a mass extinction event,” Ridgwell said. “That said, we already have concerns about water circulation in the North Atlantic today, and there is evidence that the flow of water to depth is decreasing.”

In theory, Ridgwell said that an unusually hot summer or the erosion of a cliff could trigger a cascade of processes that disrupt life as it appears today.

“You would think that the ocean floor, the part you might surf or sail on, is where all the action takes place. But below, the ocean works tirelessly, providing critical oxygen to animals in the dark depths,” Ridgwell said. life to flourish, but he can take it back. Nothing excludes this as the continental plates continue to move.”

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