Low-Oxygen Ocean Dead Zones Could Make Marine Life Extinct, Study Shows

In a new study, a group of researchers used an ancient mass extinction event as an analog to demonstrate how the current course of global climate change could prove devastating for marine life in the future.

Some 182 to 174 million years ago, during the early Jurassic era, a mass extinction event referred to as Toarcian Oceanic Anoxic Event or T-OAE occurred. The event, triggered by the decline in oxygen levels prevailing in the oceans around the globe, marked the end of many sea organisms living during that time.

It is well known today that rising global temperatures are one of the biggest reasons behind the declining levels of oxygen in oceans around the globe. As the amount of carbon dioxide increases in the atmosphere, the problem of climate change is fueled, which in turn drains the oceans of oxygen. Due to this, the so-called oxygen minimum zones or dead-zones have been expanding at an alarming rate in the world’s oceans.

Though nobody knows where this will exactly lead, researchers from Florida State University looked for some answers by studying Earth’s response to a similar situation in the past.​

The group looked into the T-OAE and analyzed the chemical makeup of rocks from that time, found in Europe and North America. Their findings revealed the amount of oxygen in the oceans around the globe started declining much before the extinction event began.

This, the researchers noted, was a consequence of intense volcanic activity which started hundred thousand years before the T-OAE. The eruption increased the amount of carbon dioxide in the atmosphere and triggered a chain of events that skyrocketed temperature levels and led to a series of biological, hydrological, and chemical changes that drained the oceans of oxygen.

“We want to understand how volcanism, which can be related to modern anthropogenic carbon dioxide release, manifests itself in ocean chemistry and extinction events,” study co-author Jeremy Owens said in a statement. “Could this be a precursor to what we’re seeing today with oxygen loss in our oceans? Will we experience something as catastrophic as this mass extinction event?”

As the researchers' findings suggested, the event marked the end of widespread marine life and was not much different from human-induced CO2 emission.

“Over the past 50 years, we’ve seen that a significant amount of oxygen has been lost from our modern oceans,” Theodore Them, the lead author behind the study, said in the statement. “While the timescales are different, past volcanism and carbon dioxide increases could very well be an analog for present events.”

Scientists have theorized a connection between volcanism, ocean deoxygenation, and mass extinctions, but this study is the first one to provide conclusive data. More importantly, it paints a bleak picture of how things could pan out if the pressing concern of climate change isn’t handled in time.

“If you’re an oxygen-consuming organism, you don’t want to see major changes in marine oxygen levels,” Them added. “You either adapt or go extinct.”

The study titled, "Thallium isotopes reveal protracted anoxia during the Toarcian (Early Jurassic) associated with volcanism, carbon burial, and mass extinction," was published June 11 in the journal PNAS.