Frontiers of Geochemistry: Jaime Barnes Breaks New Ground in Use of Chlorine Isotopes

Jaime Barnes
Jaime Barnes

Jaime Barnes is happy to be back home. A San Antonio native who received her bachelor’s degree from The University of Texas at Austin, Barnes left the Lone Star State to pursue her graduate education. Now, the assistant professor at the Jackson School of Geosciences returns to Austin having built an impressive standing in the field of geochemistry for her groundbreaking work with chlorine isotopes.

Barnes studies high-temperature fluid-rock interactions. The research she began as a doctoral student at the University of New Mexico focuses on serpentinites, hydrated pieces of the ocean crust. Serpentinites have recently come into vogue among geoscientists as indicators of volcanic and earthquake activity related to subduction zones. The rock contains a great deal of water and when it dehydrates–as a result of sinking to certain depths through the subduction of ocean slabs, for instance–it releases a lot of fluids that can include chlorine and other highly saline yet soluble elements.

Using ocean drill cores obtained through the Integrated Ocean Drilling Program, Barnes has analyzed samples for chlorine isotopes and then tracked the origin and concentration of serpentinites, and whether they are feeding into (or off of) volcanoes, or triggering earthquakes. She has also taken a more direct approach, collecting samples from Poás Volcano in Costa Rica.

Within the field of geochemistry, chlorine isotopes have rarely been used for this purpose, compared with oxygen or hydrogen isotopes, “probably because they’re a pain in the butt,” Barnes jokes. Scientists first measured chlorine isotope ratios in the 1960s, but the method to extract chlorine from rock and turn it into a gas to analyze in a mass spectrometer is complex.

“There’s a lot of chemistry involved and it’s not easy,” Barnes says, “and the gas that they were sticking into the mass spectrometer was hydrochloric acid, which is not the best thing to stick into an analytical instrument. You produce this nasty gas and then the precision wasn’t very good and didn’t look like it was going to tell you all that much.”

In the 1990s, geochemists figured out a way to measure chlorine isotopes without creating hydrochloric acid while improving the precision, but few researchers jumped at the advances. So when Barnes came along in search of a tracer for serpentinites, she practically had the discipline to herself.

Barnes spent two years learning extraction and purification methods for the chlorine isotopes, until she was able to accurately analyze the trace amounts present in rocks and minerals. Part of her doctoral research, in collaboration with advisers and colleagues, contributed to a better understanding of the cycling of chlorine and its isotope composition among the planet’s mantle, crust, and meteorites.

“I’ve been very busy with it, and people seem to be very interested now partly because there’s a lot of interest in serpentinites and subduction zones, and also the chemistry of saline fluids,” Barnes says. “There’s not that much that’s been done on it, so it’s kind of a wide-open field.”

Her pursuits into a less-explored corner of the geosciences have rightfully earned Barnes recognition from her peers. She won the L’Oreal USA for Women in Science Fellowship as she was completing her doctorate degree. In 2009, the Geological Society of America presented her the Outstanding Woman in Science Award, an annual honor bestowed to women whose doctoral research has a profound impact in the field of geosciences.

Barnes says the awards have led to exciting collaborations with other researchers from around the world, particularly those who want to tap into her experience with chlorine isotopes. At the Jackson School, the mass spectrometer that Barnes uses in her lab is one of just a few in the world configured for chlorine isotopes. She also recognizes that she is among a few women working in a field traditionally dominated by men, and she hopes to encourage Texas students to strike off on their own pioneering paths in the geosciences.

Among her ongoing projects, Barnes is studying the chlorine composition of lunar rocks, which have very a different isotope value than terrestrial samples, which puzzles geoscientists.

“The moon was created from a large impact, smacking into the Earth, and then the material coalesced to form the moon, so why is the chlorine composition so different?” Barnes says. “What does that tell us about the formation of the moon?”

She also plans to investigate whether she can use chlorine, which often bonds with metals, to trace the original sources of economic ore deposits.

“I end up doing a lot of chlorine work primarily because there’s not a whole lot of labs that do it,” Barnes says. “It has started out with this little trail, and it’s become bigger and bigger.”

Of course, back home in Texas, everything is bigger, as they say, and Barnes is poised for grand opportunities at the Jackson School.

By Joshua Zaffos

For more information about the Jackson School contact J.B. Bird at, 512-232-9623.