Fools’ Gold Found to Regulate Global Oxygen

The sulfur-based chemistry of iron pyrite may play a major role in atmospheric oxygen concentrations

From The Weizmann Institute of Environmental Science:

Pyrite (iron disulfide)
Pyrite (iron disulfide) (Photo credit: Wikipedia)

As sulfur cycles through Earth’s atmosphere, oceans and land, it undergoes chemical changes that are often coupled to changes in other such elements as carbon and oxygen. Although this affects the concentration of free oxygen, sulfur has traditionally been portrayed as a secondary factor in regulating atmospheric oxygen, with most of the heavy lifting done by carbon. However, new findings that appeared this week in Science suggest that sulfur’s role may have been underestimated.

Drs. Itay Halevy of the Weizmann Institute’s Environmental Science and Energy Research Department (Faculty of Chemistry), Shanan Peters of the University of Wisconsin and Woodward Fischer of the California Institute of Technology, were interested in better understanding the global sulfur cycle over the last 550 million years – roughly the period in which oxygen has been at its present atmospheric level of around 20%. They used a database developed and maintained by Peters at the University of Wisconsin, called Macrostrat, which contains detailed information on thousands of rock units in North America and beyond.

The researchers used the database to trace one of the ways in which sulfur exits ocean water into the underlying sediments – the formation of so-called sulfate evaporite minerals. These sulfur-bearing minerals, such as gypsum, settle to the bottom of shallow seas as seawater evaporates. The team found that the formation and burial of sulfate evaporites were highly variable over the last 550 million years, due to changes in shallow sea area, the latitude of ancient continents and sea level. More surprising to Halevy and colleagues was the discovery that only a relatively small fraction of the sulfur cycling through the oceans has exited seawater in this way. Their research showed that the formation and burial of a second sulfur-bearing mineral – pyrite – has apparently been much more important.

Pyrite is an iron-sulfur mineral (also known as fools’ gold), which forms when microbes in seafloor sediments use the sulfur dissolved in seawater to digest organic matter. The microbes take up sulfur in the form of sulfate (bound to four oxygen atoms) and release it as sulfide (with no oxygen). Oxygen is released during this process, thus making it a source of oxygen in the air. But because this part of the sulfur cycle was thought be minor in comparison to sulfate evaporite burial (which does not release oxygen), its effect on oxygen levels was also thought to be unimportant.

In testing various theoretical models of the sulfur cycle against the Macrostrat data, the team realized that the production and burial of pyrite has been much more significant than previously thought, accounting for more than 80% of all sulfur removed from the ocean (rather than the 30-40% in prior estimates). As opposed to the variability they saw for sulfate evaporite burial, pyrite burial has been relatively stable throughout the period. The analysis also revealed that most of the sulfur entering the ocean washed in from the weathering of pyrite exposed on land. In other words, there is a balance between pyrite formation and burial, which releases oxygen, and the weathering of pyrite on land, which consumes it. The implication of these findings is that the sulfur cycle regulates the atmospheric concentration of oxygen more strongly than previously appreciated.

“This is the first use of Macrostrat to quantify chemical fluxes in the Earth system,” said Peters. “I met my coauthors at a lecture I gave at Caltech, and we immediately began discussing how we might apply Macrostrat to understanding biogeochemical cycling. I think this study will open the door to many more uses of Macrostrat for constraining biogeochemical cycles.”

“For me, the truly surprising result is that pyrite weathering and burial appear to be such important processes in the sulfur cycle throughout all of Earth’s history. The carbon cycle is recognized as the central hub controlling redox processes on Earth, but our work suggests that nearly as many electrons are shuttled through the sulfur cycle,” said Fischer.

Halevy: “These findings, in addition to shedding new light on the role of sulfur in regulating oxygen levels in the atmosphere, represent an important step forward in developing a quantitative, mechanistic understanding of the processes governing the global sulfur cycle.”

Dr. Itay Halevy’s research is supported by the Sir Charles Clore Research Prize; and the estate of Olga Klein Astrachan.

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July 23, 2012 7:45 am

Geologists have known about this for a long time. It seems that scientists are re-discovering what geologists have known for decades. You are unlikely to find many geologists who believe in CAGW simply because there is absolutely nothing unprecedented about variations in our climate today.

July 23, 2012 7:45 am

Our ignorance of our complex world is not surprising but the hubris of the AGW crowd, pretending to understand everything about the environment and the various cycles that contribute to changes in any aspect of this complex system is amazing.
Thanks to our host for educating us on the complexity of our world. I wish the decision makers in our increasingly disfunctional governments flailing while trying to control outcomes of systems they obviously don’t understand would read these articles and develop a little humility.

July 23, 2012 8:07 am

Wasn’t it Hugo Chavez who first smelled the sulfur?

Alan the Brit
July 23, 2012 8:50 am

Wagathon says:
July 23, 2012 at 8:07 am
Wasn’t it Hugo Chavez who first smelled the sulfur?
No, but he was among the first leaders of a developing nation to smell the $$$$ to be screwed out of the evil wicked Climate Change Causing capitalist western nations who have something called democracy (or at least used to), as he quaintly pointed out at Copenhagen 2009!!!!

Kelvin Vaughan
July 23, 2012 8:59 am

I used to break small glass ampoules full of sulphur dioxide when I was 6. Especially in crowded places!

John R
July 23, 2012 9:29 am

WOW. Again. Most days, this site either teaches me something new or reinforces what I already knew. Sometimes it just gives a different twist or emphasis. This site must be potentially one of the best teaching resources on the planet. The quality of the various contributors here collectively make this place probably the best university for scientific subjects. This layperson is immensely impressed. Thank you, Anthony for pulling together for the rest of us.

John R
July 23, 2012 9:32 am

Thank you, Anthony for pulling together for the rest of us.
Thank you, Anthony for pulling IT together for the rest of us.

Steve R
July 23, 2012 9:55 am

I don’t think this is a new idea.

July 23, 2012 10:12 am

JR, first construction works just fine, too.

kadaka (KD Knoebel)
July 23, 2012 10:42 am

Wagathon said on July 23, 2012 at 8:07 am:

Wasn’t it Hugo Chavez who first smelled the sulfur?

He who smelled it, dealt it.
(Usage note: “Smelt it” would be reserved for processing iron pyrite into iron by melting, not flatulence detection.)

George E. Smith;
July 23, 2012 11:56 am

So obviously life on earth started in Hell, around some sulphurous black smoker at the bottom of the ocean, and had nothing to do with the sun, or for that matter, earth’s climate.

Steve in SC
July 23, 2012 12:30 pm

Wagathon says:
July 23, 2012 at 8:07 am
Wasn’t it Hugo Chavez who first smelled the sulfur?

No brimstone yet but there is hope that the trip to Cuba will have a recurrence like the previous one.
There is hope yet and I have every confidence that is his ultimate destination.

July 23, 2012 2:05 pm

George E. Smith; says:
July 23, 2012 at 11:56 am
So obviously life on earth started in Hell, around some sulphurous black smoker at the bottom of the ocean, and had nothing to do with the sun, or for that matter, earth’s climate.

Quite likely. One of the “wows” of college biology and geology was the realization that the basic elemental ratios and concentrations in – say – a human cell are very similar to the estimated composition and chemistry of early oceans. In effect, our cells encapsulate a replica of the early Archaeozoic oceans. That could put a curious twist on the Gaea hypothesis.

Keith Pearson, formerly bikermailman, Anonymous no longer
July 23, 2012 7:05 pm

Some brilliant people here, whose knowledge reaches beyond matters climatic, makes me both laugh and hope for the future.
As someone who grew up revelling in found fool’s gold in the High Rockies, and was taught about matters geologic, this post takes me back to the 70s. I found much of it in high mountain streams, and was educated by my dad and older brother in different mineral finds, and it lead me to have an appreciation to the geologists of the world, including one who is a fellow mail carrier. Appreciation to you all!

michael hart
July 23, 2012 9:03 pm

It’s not just oceanic microbes that employ iron sulfide chemistry to affect oxygen chemistry in their environment: Radiative physicists on the surface use different oxidation states of sulfur to regulate their cellular metabolism. Iron-sulfide clusters are also common as both structural units of many proteins, and as obligate functional components of many enzymes involved in oxidation/reduction reactions.

G. Karst
July 24, 2012 6:31 am

Iron pyrites are scattered throughout coal seams. So many many tons have been brought to the surface and ground finer by industrial pulverizers. Does this mean that the coal industry is helping to oxygenate our atmosphere?? GK

July 24, 2012 8:44 am

mmmmm. Steady deposition since the Cambrian (when benthic forams first show up), balanced by weathering. Much headline about nothing.

July 24, 2012 8:48 am

Jeremy, you are quite correct. Bravo!
Also as a reminder, there are hundreds of miles of dense pyrite beds in the Appalachian range as massive sulfide deposition from ancient sea bed spreading centers–black smokers. The extent of these large scale sulfide beds in fold belts and other settings has never been mapped around the earth.

July 24, 2012 6:50 pm

Please don’t tell the feds. They will want to own and/or regulate iron pyrite for a thousand yet to be determined reasons, and for a hundred thousand yet to be determined catastrophic consequences.
They might even start minting coin from it.
Owe, they already do.

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