Scientists uncover relationship between lavas erupting on sea floor and deep-carbon cycle
Scientists from the Smithsonian and the University of Rhode Island have found unsuspected linkages between the oxidation state of iron in volcanic rocks and variations in the chemistry of the deep Earth. Not only do the trends run counter to predictions from recent decades of study, they belie a role for carbon circulating in the deep Earth. The team's research was published May 2 in Science Express.
Elizabeth Cottrell, lead author and research geologist at the Smithsonian's National Museum of Natural History, and Katherine Kelley at the University of Rhode Island's Graduate School of Oceanography measured the oxidation state of iron, which is the amount of iron that has a 3+ versus a 2+ electronic charge, in bits of magma that froze to a glass when they hit the freezing waters and crushing pressures of the sea floor. Due to the high precision afforded by the spectroscopic technique they used, the researchers found very subtle variations in the iron-oxidation state that had been overlooked by previous investigations.
The variations correlate with what Cottrell described as the "fingerprints" of the deep Earth rocks that melted to produce the lavas -- but not in the way previous researchers had predicted. The erupted lavas that have lower concentrations of 3+ iron also have higher concentrations of elements such as barium, thorium, rubidium and lanthanum, that concentrate in the lavas, rather than staying in their deep Earth home. More importantly, the oxidation state of iron also correlates with elements that became enriched in lavas long ago, and now, after billions of years, show elevated ratios of radiogenic isotopes. Because radiogenic isotopic ratios cannot be modified during rock melting and eruption, Cottrell called this "a dead ringer for the source of the melt itself."
Carbon is one of the "geochemical goodies" that tends to become enriched in the lava when rocks melt. "Despite is importance to life on this planet, carbon is a really tricky element to get a handle on in melts from the deep Earth," said Cottrell. "That is because carbon also volatilizes and is lost to the ocean waters such that it can't easily be quantified in the lavas themselves. As humans we are very focused on what we see up here on the surface. Most people probably don't recognize that the vast majority of carbon -- the backbone of all life -- is located in the deep Earth, below the surface -- maybe even 90 percent of it."
The rocks that the team analyzed that were reduced also showed a greater influence of having melted in the presence of carbon than those that were oxidized. "And this makes sense because for every atom of carbon present at depth it has to steal oxygen away from iron as it ascends toward the surface," said Cottrell. This is because carbon is not associated with oxygen at depth, it exists on its own, like in the mineral diamond. But by the time carbon erupts in lava, it is surrounded by oxygen. In this way, concludes Cottrell, "carbon provides both a mechanism to reduce the iron and also a reasonable explanation for why these reduced lavas are enriched in ways we might expect from melting a carbon-bearing rock."
- Link between sea floor lavas and deep-carbon cyclefrom Science BlogFri, 3 May 2013, 9:00:20 EDT
- Lava erupting on sea floor linked to deep-carbon cyclefrom Science DailyThu, 2 May 2013, 20:30:27 EDT
- Scientists uncover relationship between lavas erupting on sea floor and deep-carbon cyclefrom PhysorgThu, 2 May 2013, 17:30:45 EDT
Latest Science NewsletterGet the latest and most popular science news articles of the week in your Inbox! It's free!
Check out our next project, Biology.Net
From other science news sites
Popular science news articles
- Caltech chemists solve major piece of cellular mystery
- Future climate models greatly affected by fungi and bacteria
- Researchers use DNA 'clews' to shuttle CRISPR-Cas9 gene-editing tool into cells
- Moffitt makes important steps toward developing a blood test to catch pancreatic cancer early
- Sir Elton John is the inspiration behind the name of a new coral reef crustacean species
- Rare nautilus sighted for the first time in 3 decades
- Want a better relationship and a better sex life?
- Unlike boys, girls lose friends for having sex, gain friends for making out
- Massive study reports challenges in reproducing published psychology findings
- Record-high pressure reveals secrets of matter
- Gravitational constant appears universally constant, pulsar study suggests
- Robotic insect mimics Nature's extreme moves
- California 'rain debt' equal to average full year of precipitation
- Special issue: Philae results shed light on the nature of comets
- Researchers find that Earth's magnetic shield is much older than previously thought