Toxic Ocean Conditions During Mass Extinction Reveals Insight into Today's Climate

Tuesday, October 29, 2013

Toxic Ocean Conditions During Mass Extinction Reveals Insight into Today's Climate

First Posted: Oct 29, 2013 10:56 AM EDT

It turns out that it doesn't take much to turn our planet's ocean waters into something that's toxic to life. Scientists have taken a closer look at a massive extinction event that occurred 93.9 million years ago and have found that it didn't take as much sulfide as previously thought in the ocean waters to cause this major climatic perturbation.
In order to examine this particular extinction, the scientists examined the chemistry of rocks deposited during that time period. This revealed that oxygen-free and hydrogen sulfide-rich waters extended across roughly five percent of the global ocean. That's far more than today modern ocean's at .1 percent, but far less than previously thought.
"These conditions must have impacted nutrient availability in the ocean and ultimately the spatial and temporal distribution of marine life," said Jeremy Owens, one of the researchers, in a news release. "Under low-oxygen environments, many biologically important metals and other nutrients are removed from seawater and deposited in the sediments on the seafloor, making them less available for life to flourish."

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The Daily Galaxy

EcoAlert --Toxic Hydrogen Sulfide-Rich Oceans Led to Major Extinction 93.9 Million Years Ago

“Today, we are facing rising carbon dioxide contents in the atmosphere through human activities, and the amount of oxygen in the ocean may drop correspondingly in the face of rising seawater temperatures,” said said Timothy W. Lyons, a professor of biogeochemistry at University of California (Riverside). “Oxygen is less soluble in warmer water, and there are already suggestions of such decreases. In the face of these concerns, our findings from the warm, oxygen-poor ancient ocean may be a warning shot about yet another possible perturbation to marine ecology in the future.”

Oxygen in the atmosphere and ocean rose dramatically about 600 million years ago, coinciding with the first proliferation of animal life. Since then, numerous short-lived biotic events — typically marked by significant climatic perturbations — took place when oxygen concentrations in the ocean dipped episodically. The most studied and extensive of these events occurred 93.9 million years ago. By looking at the chemistry of rocks deposited during that time period, specifically coupled carbon and sulfur isotope data, a research team led by UCR biogeochemists reports that oxygen-free and hydrogen sulfide-rich waters extended across roughly five percent of the global ocean during this major climatic perturbation — far more than the modern ocean’s 0.1 percent but much less than previous estimates for this event.
The research suggests that previous estimates of oxygen-free and hydrogen sulfide-rich conditions, or “euxinia,” were too high. Nevertheless, the limited and localized euxinia were still sufficiently widespread to have dramatic effect on the entire ocean’s chemistry and thus biological activity.

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