Oceans Great Dying 2.0: Mass extinction haunts oceans

Justin Penn and Curtis Deutsch, scientists from Stanford University, had simulated during 2016-2018 how Earth’s climate changed some 250 million years ago to know what triggered the Permian extinction.

The planet’s biggest mass extinction of species had wiped out most newly evolved lives in the oceans.

Penn and Deutsch were curious to know what triggered this climate change. For, it held clues to how the current climate crisis would impact the oceans.

The Permian era, a period spanning 298.9 million-252.2 million years ago, was a time before the dinosaurs ruled the planet. Global ocean temperatures were 10 degrees higher than today. Oxygen levels were 80 per cent lower.

During this period, land masses collided to form the supercontinent Pangaea. The supercontinent was arid; only a few parts received rainfall round the year.

However, the large Panthalassic Ocean, which covered much of Earth, was home to many sponge and coral species, ammonites (tiny shelled organisms), brachiopods (invertebrate animals closely related to starfish) and fusulinid foraminifera (single-celled organisms closely associated with modern amoebas). Reptiles began to flourish. Sharks and bony fishes also thrived.

Towards the end of the era, a series of volcanic eruptions occurred in central Siberia, injecting massive amounts of greenhouse gases (GHG) into the atmosphere. Then, as now, the uncontrolled GHG emissions triggered climatic changes.

What Penn and Deutsch found in the simulated scenario was astonishing. The change in climate after the volcanic eruptions was a death knell for the flourishing and diverse life forms.

Many long-lived lineages vanished. Roughly 96 per cent of marine species and 70 per cent of land species went extinct. Thus, scientists refer to this period as the ‘Great Dying’.   

Next, the team did another simulation called the Ecophysiological model. The supercomputer analyses species’ traits to map out how species were distributed - from surface to deep sea, from the equatorial waters to the poles.

“The traits capture information on whether a species can tolerate warm waters or low oxygen levels,” Deutsch said.

Read DTE’s special series on the Sixth Mass Extinction

The team shortlisted 61 living species types based on their traits. The last part of the job was to get the earth system to talk to the Ecophysiological model.

The interaction gave them an output, which according to Curtis, is a map describing how many different species could inhabit a particular location's environmental conditions.

The duo then warmed up the climate by 2-10 degrees Celsius to see how species responded. “Some species will have to leave because it got too hot or the oxygen got too low. Some species from the tropics can move into polar waters because it is more welcoming,” he notes.

The scientists had an affirmative answer to their query: Whether low oxygen and warm conditions drove the extinction of marine organisms 250 million years ago.

With this, they also got a clue to what must be happening to the life in oceans currently.

“This is important because climate change that happened at the end of the Permian era is similar to the one that is unfolding now,” Deutsch told Down To Earth. To sum up, oceans are in a churn in the current era fuelled by human-induced global warming.

Life has bounced back since the Permian extinction. Oceans are the planet’s largest ecosystem accounting for 95 per cent of all spaces available for life and hosting 90 per cent of the planet’s total species. 

But, how climate change would be impacting or is already impacting the oceans usually draws a long and uncertain reaction.

David S Schoeman, Professor at the University of the Sunshine Coast, said the simulations provide a broad picture of what may happen in the future, but:

We are still woefully short on data for most marine species.

This is because we don’t know much of the impacts for the simple reason that we actually have not explored the oceans to begin with.

The average depth of the oceans is 12, 100 feet; and 80 per cent of the areas have not been explored at all. After 1,000 metres from the surface, the most diverse and unique world of oceans starts, thriving in primordial darkness.

The exact number of species inhabiting the ocean world is not known yet; 91 per cent of the species are yet to be described or classified. As it is popularly said we know more about the moon and Mars surfaces than our sea surface.

Deep oceans are warming up. Scientists look at ocean heat content as an indicator of climate change. Ocean heat content is the energy accumulated by the ocean.

Continuous GHG emissions are preventing heat from going back into space. But the atmosphere has a low heat capacity compared to the ocean water, which can accommodate 1000 times more heat. So, most of it is moving into the ocean.

Ocean heat content reached a record high in 2021. The upper 2,000 metres of the ocean absorbed 235 zettajoules (ZJ) heat in 2021 relative to the 1981-2010 average. The sum of the energy used by humans across the world in a single year is about half a ZJ (one ZJ is equal to 10^21 joules.)

“There is an energy imbalance from the build-up of carbon dioxide and other greenhouse gases,” Kevin Trenberth, a distinguished scholar at the National Center for Atmospheric Research in Colorado, told Down To Earth.

Back to Justin Penn and Curtis Deutsch’s seminal work on the oceans and climate change simulation experiment. In 2018, they initiated another related study: what does climate change mean for the future?

This time, they used a dozen Earth system models to make their simulations more accurate. They cranked up temperatures to see how the species distributions changed.

What they found was alarming: if emissions continue to climb and temperatures reach around 4.9 degrees Celsius by the end of this century, close to about 40 per cent of marine genera could perish by 2300 and 8 per cent by 2100. They published their findings in Science in 2022.

The global average temperature in the current Anthropocene era is already up by 1.1 degrees Celsius since pre-industrial times. It is predicted to increase by 5 degrees Celsius by 2100 if the world takes the high GHGs emission trajectory.

The oceans, too, are accumulating heat and losing oxygen rapidly - events that are reminiscent of the Permian era. According to the IPCC’s “Climate Change 2022: Impacts, Adaptation and Vulnerability”, due to warming of the seas, species have travelled poleward at the rate of 59 km per decade on average.

You can read the next parts of the series here and here. Click for the accompanying factsheet.

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