Oxygen-starved oceans held back life’s recovery after the ‘Great Dying’

Stanford scientists have found that chronically low levels of oxygen throughout the oceans hampered the recovery of life after the Permian-Triassic extinction, the most catastrophic die-off in our planet’s history. Also known as the “Great Dying,” global ecosystems collapsed as some 90 percent of species perished in this extinction event 250 million years ago.

The new findings, published this week in the journal for the Proceedings of the National Academy of Sciences, for the first time convincingly show that ocean anoxia, or oxygen deficiency, was a global rather than an isolated phenomenon. The study paints a dire portrait of how anoxic conditions reduced seawater oxygen levels by 100-fold at the onset of the mass extinction. Oxygen levels then slowly rose, only returning to pre-extinction levels after 5 million years, corresponding to when the climate became more stable and life regained its former diversity.

“Explaining the 5 million year delay in the Earth system’s recovery to pre-extinction conditions after the Permian extinction has been a challenge,” said Kimberly Lau, a PhD candidate in Geological Sciences at Stanford’s School of Earth, Energy & Environmental Sciences. “Our results suggest a unified explanation for biological and biogeochemical observations stemming from the most severe biotic crisis in Earth’s history.”

A devastating confluence of geological events is thought to have triggered the Great Dying a quarter billion years ago, including a massive eruption of climate-changing carbon dioxide from volcanoes associated with the Siberian Traps. Numerous studies have pointed to ocean anoxia playing a role both in the actual extinction event as well as its prolonged recovery phase. But until now these studies could not reliably testify beyond local conditions to the world’s waters as a whole…

Many researchers are now taking a greater interest in the resurrection of flora and fauna worldwide following calamities, and not just how life was sent reeling in the first place.

“We tend to focus so much on the extinction event, not so much the recovery,” Maher said, “but the recovery is also a really important piece that sets the stage for what happens in the next interval of life.”

The new findings also have implications for our modern world, Payne said.

“These findings highlight the fact that ocean deoxygenation during the 21st century and beyond may lead not only to the loss of marine animal populations and species but also to unexpected feedbacks in the Earth system,” he added. “The timescales of these feedbacks are long, meaning that the consequences of profound and extensive deoxygenation today could reverberate for many centuries, millennia, or longer.”

See the complete article at Science Daily or the journal reference:  Kimberly V. Lau, Kate Maher, Demir Altiner, Brian M. Kelley, Lee R. Kump, Daniel J. Lehrmann, Juan Carlos Silva-Tamayo, Karrie L. Weaver, Meiyi Yu, Jonathan L. Payne. Marine anoxia and delayed Earth system recovery after the end-Permian extinction. Proceedings of the National Academy of Sciences, 2016; 201515080 DOI: 10.1073/pnas.1515080113