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ASU grad student leads study estimating oxygen loss in ancient ocean

August 9, 2017

Oceanic extinction event 94 million years ago may be able to tell us about the future of today's seas, researchers say

A loss of oxygen in global ocean seawater 94 million years ago led to a mass extinction of marine life that lasted for roughly half a million years.

Scientists have found several potential explanations for how the loss of oxygen happened. These could include enhanced volcanic activity, increased nutrients reaching the ocean, rising sea levels, and warming sea and surface temperatures. But to point a finger at any one cause (or several of them) requires knowing how fast the oxygen loss happened.

A new technique, developed by Arizona State University graduate student Chad Ostrander (pictured above, right) with colleagues at Wood Hole Oceanographic Institution (WHOI) and Florida State University (FSU), has put a timetable on the oxygen loss associated with this major ocean extinction event, which is known to science as Oceanic Anoxic Event 2.

Their research was published today in the journal Science Advances.

"The project began when I was an undergraduate Summer School Fellow at Woods Hole," said Ostrander, a doctoral student at ASU's School of Earth and Space Exploration. His co-authors on the paper are Jeremy Owens at Florida State and Sune Nielsen at Woods Hole.

"We were able to track changes to the oxygen content of ancient seawater by measuring isotopes of thallium in ancient seafloor sediments," Ostrander explained. "Since the oxygen in the rocks we measure wouldn't really give any valuable information, we use thallium and other elements as stand-ins, or proxies."

This exposure of sediments in Italy includes a record in the black shales (dark diagonal layers) of the 94-million-year-old Oceanic Anoxic Event 2. Although these shales were analyzed by the team, the ocean-oxygen study focused primarily on core samples taken at sea because they preserved better the chemical evidence for ancient oxygen loss. Photo by Jeremy Owens/Florida State University

Sediments preserve the thallium isotope composition of seawater, which changes depending on the amount of oxygen in the deep ocean at the time they were deposited. The sediments pile up over time, with deeper levels corresponding to times further in the past.     

The sediments the team studied were organic-rich black shales collected as core samples by deep ocean drilling in 2003. The site was the Demerara Rise, a submarine plateau in the Atlantic Ocean off the coasts of Suriname and French Guiana.

"We dissolved the rocks in our lab," explained Ostrander, "and then chemically separated everything but thallium, the element we needed for analysis."

Then using mass spectrometry, the team measured variations in thallium within sedimentary rocks as a proxy for changes in oxygen levels over tens of thousands of years.

Based on the analysis, the researchers suspect that up to half of the deep ocean had become oxygen-depleted during Oceanic Anoxic Event 2, and remained so for about half a million years before it recovered.

"The loss of oxygen took 43,000 years to occur, plus or minus about 11,000," Ostrander said. "Call it 50,000 years or less."

The primary cause of Oceanic Anoxic Event 2 may have been increased nutrient delivery to the oceans, the researchers said. An increase in nutrients fuels the production of organic matter, and subsequent remineralization by bacteria feeding on it.

"It's this remineralization that is specifically responsible for the oxygen loss, because these bacteria consume oxygen in order to oxidize the organic, or carbon-bearing, matter," Ostrander said. "We see a similar scenario in the modern ocean, again due to increased nutrient delivery, but largely driven by fertilizers used in farming."

In fact, he said, "the largest 'dead zone' observed in the Gulf of Mexico is occurring right now for this very reason."

Adding nutrients to the ocean causes increased production of organic matter such as phytoplankton. When these die, they sink to the bottom as "marine snow" and decompose, consuming oxygen in the process. This is thought to be primarily responsible for large-scale oxygen loss in ancient oceans, leading to mass extinctions in the marine environment. The modern ocean exhibits similar symptoms. Image by Natalie Renier/WHOI

The researchers draw a distinct parallel between the rate of deoxygenation back then and modern trends in oceanic oxygen loss.

Said co-author Nielsen, "Our results show that marine deoxygenation rates prior to the ancient event were likely occurring over tens of thousands of years, and are surprisingly similar to the 2 percent oxygen depletion trend we're seeing induced by human-related activity over the last 50 years."

He added, "We don’t know if the ocean is headed toward another global anoxic event, but the trend is, of course, worrying."

Ostrander said, "At this point, we are only just beginning to understand how oxygen levels in the ocean have changed in the past. But with our new tool, we’ve already learned that one of the most extreme climate events in the sedimentary record provides an uncomfortably reasonable analog for possible future ocean oxygen loss and subsequent ecological shifts."

He added, "We hope to use this information to gain a better look into the short-, medium- and long-term future for oxygen content in today's oceans."


Top photo: Co-authors Sune Nielsen (left) of Woods Hole Oceanographic Institution and Chad Ostrander from Arizona State University working in the lab. Photo by Matt Barton/WHOI

Robert Burnham

Science writer , School of Earth and Space Exploration


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ASU Regents' Professor and diamond expert examines scientific uses for gemstone.
August 10, 2017

ASU professor exploring ways to use diamonds in electronics, cancer, space

Diamonds are among the most coveted objects in the world. As gemstones, they are brilliant, rare and symbolic. As a raw material, they are a physicist’s best friend.

If you think about certain characteristics of a material — hardness, for example, or ability to conduct heat — diamonds are usually at one extreme end of the spectrum.

“It’s surprising that a material so simple, just carbon atoms arranged in this cubic crystal system, has such unusual properties in so many ways,” said Robert Nemanich, a Regents’ Professor of physicsThe Department of Physics is a unit of the College of Liberal Arts and Sciences. at Arizona State University.

As one of the world’s foremost experts on diamonds, Nemanich knows what they are capable of. And he has a different sort of proposal for how to use them.

Doping diamonds for better electronics

Diamonds are the overachievers of the materials world. They can sustain incredibly high temperatures and electric fields. They also conduct heat better than any other material. These properties make them ideal for very specific applications.

Currently, silicon dominates the electronics market. It’s used to make everything from your cellphone computer chip and laptop processor to microwave ovens. But as versatile as silicon is, there are certain areas where it falls flat.

“When it comes to high-temperature, high-power, radiation-hard devices, silicon doesn’t work as well. In fact, it doesn’t work at all,” said Manpuneet Kaur Benipal, a postdoctoral researcher in Nemanich’s lab.

Benipal and her colleague Brianna Eller both received their doctorates from ASU. With Nemanich as an adviser, they are now starting a company, ADVENT Diamond, to make electronic devices out of diamond.

But we’re not talking about using recycled wedding rings. Eller and Benipal are working with doped diamond layers grown on small diamond plates. The ASU team even has a patent in the works for part of the growth process, called doping.

Take a tour of Robert Nemanich's lab and learn more about doping diamonds.

The term “doping” may conjure images of athletes illegally growing their muscles, but in the materials field, doping allows scientists to grow diamonds specifically for electronic purposes. Here’s how it works: You take a diamond substrate, or a small sample of diamond, and immerse it in a plasma composed of a mixture of chemicals. The atoms from the added chemicals organize themselves on the surface of the diamond, replicating the crystal structure of the substrate.

The lab-grown diamond layers that result include impurities that change the material’s electrical properties. Benipal and Eller use microfabrication processing of the doped diamond layers so that they behave precisely in the way they want. The process works so well that a small diamond can do the same work as materials that are much larger in size.

Does this mean we can expect to see tiny diamonds in our smartphones soon? Not exactly. Silicon continues to be more cost-effective for low-temperature applications, like cellphones and laptops. But diamond is a good choice for anything with a high-powered engine, such as an electric vehicle or an aircraft. Because diamond is excellent at conducting away heat, it would completely replace the need for a cooling system. Diamond also works well at very high pressures, which makes it perfect for deep-earth drilling.

More precise cancer treatment

We know diamonds’ ability to withstand extreme heat and pressure makes them superheroes in the world of electronic devices. But they have another power that scientists are harnessing to improve an entirely different field — cancer treatment.

Diamond is radiation-hard, meaning it takes much longer than most other materials to degrade under X-rays, gamma rays and fast charged particles. This property makes diamonds an ideal material to build radiation detectors for a variety of applications, including proton beam technology. This is a form of radiation therapy that precisely targets and destroys tumors with highly charged subatomic particles called protons.

Researchers at Nemanich’s lab, along with proton beam experts at Mayo Clinic Arizona, are working together to see if the use of diamond detectors can further enhance proton beam’s benefits to patients. Mayo Clinic is currently the only site in the Southwest to offer the technology.

Mayo Clinic’s intensity-modulated proton beam therapy features pencil beam scanning, which deposits streams of protons back and forth through a tumor. The beam closely targets the tumor, while largely sparing surrounding healthy tissue and organs from its radiation.

The researchers are studying to see if diamonds can be used as a detector for the pencil beam to go through. This could possibly help radiation oncologists further fine-tune the path of the protons, which could be particularly beneficial for pediatric patients.

“It’s most important in children to spare healthy tissues because those tissues are still growing, so we have to be very careful to treat as little of the healthy tissue as possible,” said Martin Bues, a proton beam physicist and researcher at Mayo Clinic’s Phoenix campus who is working with Nemanich and the ASU team on this project.

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“It’s surprising that a material so simple, just carbon atoms arranged in this cubic crystal system, has such unusual properties in so many ways,” said Robert Nemanich, a Regents’ Professor of physics at Arizona State University. Photo by Charlie Leight/ASU Now

A diamond in the sky

If diamond is a material superhero, perhaps it’s only fitting that scientists want to send it into space. Nemanich was recently awarded a grant from NASA to build diamond electronics for a rover that will explore the surface of Venus.

“Venus is 450 degrees centigrade,” Nemanich said, “So it’s very, very hot.”

How hot, exactly? To give you an idea, 450 degrees centigrade is about 842 degrees Fahrenheit. In comparison, the hottest weather ever recorded on Earth was a mere 129 degrees F, in Death Valley, California, in 2013.

Through the NASA grant, Nemanich and his team are building an amplifier, a device that increases the power of an electrical signal. But Eller said that diamond could be useful for other parts of the rover as well, since very few other materials can function in such extreme heat.

As demand for high-powered electronics increases, diamonds will have an even larger role to play. Space exploration, electronic vehicles and deep-earth drilling only scratch the surface of potential applications.

Just as silicon brought about a new era of electronics, novel materials often drive the progress of new systems and devices. Perhaps the most exciting applications for diamonds are those that haven’t been thought of yet, since diamond would enable them to be built.

“There is always a need for something bigger, something better, something more efficient, something that works at higher temperature or higher voltage, which we think diamond can do,” Eller said.

Allie Nicodemo

Communications specialist , Office of Knowledge Enterprise Development