A continental trigger may wipe-out deep ocean life, study says

It is impossible to imagine a life without oxygen. It is just as crucial for life in the sea as it is for life on land. However, according to a recent study, continental movements could bring a mass extinction to marine life.

The "unrecognized role" of continents could bring irremediable results, according to a study published by Nature journal on Wednesday.

Scientists led by Alexandre Pohl, a paleoclimate researcher at the Université Bourgogne Franche-Comté, have enucleated that circulating oxygen is pretty efficient for marine species.

“Continental drift seems so slow, like nothing drastic could come from it, but when the ocean is primed, even a seemingly tiny event could trigger the widespread death of marine life,” said Andy Ridgwell, the co-author of the study.

But how is that possible?

When the water on the ocean surface approaches the north and south poles, it cools, condenses, and then sinks. As the water sinks, the atmosphere pulled from Earth's surroundings is carried to the ocean floor, reported Eurekalert.

A return flow brings nutrients released from sunken organic matter back to the ocean’s surface, where it fuels the growth of plankton and this causes a great amount of marine animal diversity.

However, new findings indicate that oxygen circulation and nutrients can end all of a sudden. The researchers investigated whether the locations of continental plates affect how the ocean moves oxygen around by using complex computer models.

“Many millions of years ago, not so long after animal life in the ocean got started, the entire global ocean circulation seemed to periodically shut down,” said Ridgwell. “We were not expecting to find that the movement of continents could cause surface waters and oxygen to stop sinking, and possibly dramatically affecting the way life evolved on Earth.”

Ocean anoxia is now detectable

Models examining 540 million years of marine life were relatively simple and were not based on circulation in the ocean. This problem has been resolved with the new models used in the study, which can detect ocean anoxia - times when oceanic oxygen disappeared.

For the first time, this study also used a model in which the ocean was represented in three dimensions and in which ocean currents were accounted for. Results show that collapse in global water circulation leads to a stark separation between oxygen levels in the upper and lower depths.

“Circulation collapse would have been a death sentence for anything that could not swim closer to the surface and the life-giving oxygen still present in the atmosphere,” Ridgwell said.

Summarizing the research theoretically, Andrew Ridgwell said that all marine life would be destroyed as a result of an unexpected hot summer or any erosion.

Study abstract:

The early evolutionary and much of the extinction history of marine animals is thought to be driven by changes in dissolved oxygen concentrations ([O2]) in the ocean1. In turn, [O2] is widely assumed to be dominated by the geological history of atmospheric oxygen (pO2). Here, by contrast, we show by means of a series of Earth system model experiments how continental rearrangement during the Phanerozoic Eon drives profound variations in ocean oxygenation and induces a fundamental decoupling in time between upper-ocean and benthic [O2]. We further identify the presence of state transitions in the global ocean circulation, which lead to extensive deep-ocean anoxia developing in the early Phanerozoic even under modern pO2. Our finding that ocean oxygenation oscillates over stable thousand-year (kyr) periods also provides a causal mechanism that might explain elevated rates of metazoan radiation and extinction during the early Palaeozoic Era. The absence, in our modelling, of any simple correlation between global climate and ocean ventilation, and the occurrence of profound variations in ocean oxygenation independent of atmospheric pO2, presents a challenge to the interpretation of marine redox proxies, but also points to a hitherto unrecognized role for continental configuration in the evolution of the biosphere.