Aurelia Butler

MIT students Spencer Compton, Karna Morey, Tara Venkatadri, and Lily Zhang have been selected to receive a Barry Goldwater Scholarship for the 2021-22 academic year. Over 5,000 college students from across the United States were nominated for the scholarships, from which only 410 recipients were selected based on academic merit. 

The Goldwater scholarships have been conferred since 1989 by the Barry Goldwater Scholarship and Excellence in Education Foundation. These scholarships have supported undergraduates who go on to become leading scientists, engineers, and mathematicians in their respective fields. All of the 2021-22 Goldwater Scholars intend to obtain a doctorate in their area of research, including the four MIT recipients. 

Spencer Compton

A junior majoring in computer science and engineering, Compton is set to graduate next year with both his undergraduate and master’s degrees. For Compton, solving advanced problems is as fun as it is challenging — he’s been involved in algorithm competitions since high school, where, on the U.S. team for the 2018 International Olympiad in Informatics, Compton won gold. “I still participate — there’s a college equivalent, the Intercollegiate Programming Contest or ICPC, and I’m on last year’s MIT team that won first in North America,” reports Compton. “We were supposed to represent MIT in the World Finals in Russia last summer, but it’s been postponed due to Covid.” Compton brings his competitive and enthusiastic mindset to his areas of research, including his collaboration on causal inference with the MIT-IBM Watson AI Lab, and his work on approximation algorithms and scheduling with professor of electrical engineering and computer science Ronitt Rubinfeld and postdoc Slobodan Mitrović​.

In her recommendation letter, Rubinfeld, a member of the Computer Science and Artificial Intelligence Laboratory, spoke at length about Compton’s aptitude as a student but she also left a glowing review as to Compton’s character. “Spencer is extraordinarily pleasant to work with. He is kind and caring when he interacts with younger students. I once had a high school student follow me for a day on which I happened to have a meeting with Spencer ­­— she was so impressed with him that he became a role model for her,” wrote Rubinfeld. Following the completion of his current degrees at MIT, Compton plans to obtain his PhD in computer science, continue his research in algorithms, and teach at the university level.

Karna Morey

Morey is a third-year majoring in physics with a minor in Spanish. He got interested in physics while reading Albert Einstein’s biography in the seventh grade, and performed research for two years in high school on gravitational wave physics of a body falling into a black hole. On campus, he has been involved in physics research in theoretical and observational astrophysics, as well as in condensed matter experiments. He recently authored an accepted paper on measuring the lifetime of high-redshift quasars to better understand the ways that supermassive black holes grow. Currently, he is working in the Gedik group, exploring quantum materials using second harmonic generation. Morey plans on pursuing a PhD in physics and one day conduct research at the university level.

“It was a great experience working with Karna. He was the first student I worked with and he set the bar very high for any future students,” said Christina Eilers, a Pappalardo Fellow in the MIT Department of Physics; Eilers supervised Morey’s research estimating the timescales of supermassive black holes in the early universe and was extremely impressed by his coding skills and confidence as a researcher. Morey is also heavily involved in diversity, equity, and inclusion efforts in the physics department and in the broader field, where he serves as one of the co-chairs of the cross-constituency Physics Values Committee, which seeks to work with department leadership and stakeholders to improve the climate and culture of the physics department. He hopes to make meaningful contributions not only to further scientific discoveries, but also to making science more inclusive.

Tara Venkatadri

A fourth-generation engineer and junior at MIT, Venkatadri is following her passion for space exploration, majoring in aeronautical and astronautical engineering with a minor in Earth, atmospheric, and planetary sciences. During her time at MIT, Venkatadri became interested in aerospace structures, pointing out that the unforgiving space environment places unique spacecraft constraints, especially for crewed missions. “As we go deeper into outer space and send humans to other planets, we need to design new methods and materials to ensure the safety of astronauts when pursuing increasingly ambitious space exploration,” she said.

Her interest in aerospace structures eventually landed her in the lab of Professor Tal Cohen, the Robert N. Noyce Career Development Professor and assistant professor of civil and environmental engineering and mechanical engineering. Venkatadri is trying to understand how adhesive materials deform under torsion in order to use them safely and efficiently in real-world structures, such as spacecraft. There has been increasing interest in adhesives across many industries because they can bond dissimilar materials together without welding and do not concentrate stress on the materials the way mechanical fastenings like bolts and rivets do. In his letter of recommendation, Olivier de Weck, a professor of aeronautics and astronautics and of engineering systems at MIT, cited Venkatadri’s research rigor, academic scholarship, and significant acts of service to the department, noting “without hesitation that Tara is the most impressive undergraduate student I have seen in our department over the last decade.”

Lily Zhang

Zhang is a junior double-majoring in Earth, atmospheric, and planetary sciences as well as physics, with minors in public policy and math. Zhang has a passion for climate science, something she’s known since she first viewed Al Gore’s “An Inconvenient Truth” as a child. That passion was encouraged by her father, a professor of meteorology. “He was really passionate about his research and loved his job, which helped me develop my own appreciation for science and academia,” says Zhang. Though her father passed away in 2019, Zhang says he remains a major inspiration on her life.

At MIT, Zhang is now in the finishing stages of two of her own research projects, including using satellite observations to fill in the historic Halley ozone record with Professor Susan Solomon, the Lee and Geraldine Martin Professor of Environmental Studies in the Department of Earth, Atmospheric and Planetary Sciences. “Lily never ceases to astonish me with her ability to tackle research questions and come up with clever solutions. The Goldwater scholarship is fitting recognition of her enormous potential,” said Solomon. Zhang is thankful to all of her mentors, both past and present, and says that the opportunity to work alongside them and observe their research approaches first-hand has been a dream. After finishing her undergraduate degree, Zhang aims to obtain her PhD and bring her zest for education and research as a professor in climate science.

The Barry Goldwater Scholarship and Excellence in Education Program was established by Congress in 1986 to honor Senator Barry Goldwater, a soldier and national leader who served the country for 56 years. Awardees receive scholarships of up to $7,500 a year to cover costs related to tuition, room and board, fees, and books. More

Since its invention several millennia ago, concrete has become instrumental to the advancement of civilization, finding use in countless construction applications — from bridges to buildings. And yet, despite centuries of innovation, its function has remained primarily structural.

A multiyear effort by MIT Concrete Sustainability Hub (CSHub) researchers, in collaboration with the French National Center for Scientific Research (CNRS), has aimed to change that. Their collaboration promises to make concrete more sustainable by adding novel functionalities — namely, electron conductivity. Electron conductivity would permit the use of concrete for a variety of new applications, ranging from self-heating to energy storage.

Their approach relies on the controlled introduction of highly conductive nanocarbon materials into the cement mixture. In a paper in Physical Review Materials, they validate this approach while presenting the parameters that dictate the conductivity of the material. 

Nancy Soliman, the paper’s lead author and a postdoc at the MIT CSHub, believes that this research has the potential to add an entirely new dimension to what is already a popular construction material.

“This is a first-order model of the conductive cement,” she explains. “And it will bring [the knowledge] needed to encourage the scale-up of these kinds of [multifunctional] materials.” 

From the nanoscale to the state-of-the-art

Over the past several decades, nanocarbon materials have proliferated due to their unique combination of properties, chief among them conductivity. Scientists and engineers have previously proposed the development of materials that can impart conductivity to cement and concrete if incorporated within.

For this new work, Soliman wanted to ensure the nanocarbon material they selected was affordable enough to be produced at scale. She and her colleagues settled on nanocarbon black — a cheap carbon material with excellent conductivity. They found that their predictions of conductivity were borne out.

“Concrete is naturally an insulative material,” says Soliman, “But when we add nanocarbon black particles, it moves from being an insulator to a conductive material.”

By incorporating nanocarbon black at just a 4 percent volume of their mixtures, Soliman and her colleagues found that they could reach the percolation threshold, the point at which their samples could carry a current.

They noticed that this current also had an interesting upshot: It could generate heat. This is due to what’s known as the Joule effect.

“Joule heating (or resistive heating) is caused by interactions between the moving electrons and atoms in the conductor, explains Nicolas Chanut, a co-author on the paper and a postdoc at MIT CSHub. “The accelerated electrons in the electric field exchange kinetic energy each time they collide with an atom, inducing vibration of the atoms in the lattice, which manifests as heat and a rise of temperature in the material.”

In their experiments, they found that even a small voltage — as low as 5 volts — could increase the surface temperatures of their samples (approximately 5 cm3 in size) up to 41 degrees Celsius (around 100 degrees Fahrenheit). While a standard water heater might reach comparable temperatures, it’s important to consider how this material would be implemented when compared to conventional heating strategies.

“This technology could be ideal for radiant indoor floor heating,” explains Chanut. “Usually, indoor radiant heating is done by circulating heated water in pipes that run below the floor. But this system can be challenging to construct and maintain. When the cement itself becomes a heating element, however, the heating system becomes simpler to install and more reliable. Additionally, the cement offers more homogenous heat distribution due to the very good dispersion of the nanoparticles in the material.”

Nanocarbon cement could have various applications outdoors, as well. Chanut and Soliman believe that if implemented in concrete pavements, nanocarbon cement could mitigate durability, sustainability, and safety concerns. Much of those concerns stem from the use of salt for de-icing.

“In North America, we see lots of snow. To remove this snow from our roads requires the use of de-icing salts, which can damage the concrete, and contaminate groundwater,” notes Soliman. The heavy-duty trucks used to salt roads are also both heavy emitters and expensive to run.

By enabling radiant heating in pavements, nanocarbon cement could be used to de-ice pavements without road salt, potentially saving millions of dollars in repair and operations costs while remedying safety and environmental concerns. In certain applications where maintaining exceptional pavement conditions is paramount — such as airport runways — this technology could prove particularly advantageous.       

Tangled wires

While this state-of-the-art cement offers elegant solutions to an array of problems, achieving multifunctionality posed a variety of technical challenges. For instance, without a way to align the nanoparticles into a functioning circuit — known as the volumetric wiring — within the cement, their conductivity would be impossible to exploit. To ensure an ideal volumetric wiring, researchers investigated a property known as tortuosity.

“Tortuosity is a concept we introduced by analogy from the field of diffusion,” explains Franz-Josef Ulm, a leader and co-author on the paper, a professor in the MIT Department of Civil and Environmental Engineering, and the faculty advisor at CSHub. “In the past, it has described how ions flow. In this work, we use it to describe the flow of electrons through the volumetric wire.”

Ulm explains tortuosity with the example of a car traveling between two points in a city. While the distance between those two points as the crow flies might be two miles, the actual distance driven could be greater due to the circuity of the streets.

The same is true for the electrons traveling through cement. The path they must take within the sample is always longer than the length of the sample itself. The degree to which that path is longer is the tortuosity.

Achieving the optimal tortuosity means balancing the quantity and dispersion of carbon. If the carbon is too heavily dispersed, the volumetric wiring will become sparse, leading to high tortuosity. Similarly, without enough carbon in the sample, the tortuosity will be too great to form a direct, efficient wiring with high conductivity.

Even adding large amounts of carbon could prove counterproductive. At a certain point conductivity will cease to improve and, in theory, would only increase costs if implemented at scale. As a result of these intricacies, they sought to optimize their mixes.

“We found that by fine-tuning the volume of carbon we can reach a tortuosity value of 2,” says Ulm. “This means the path the electrons take is only twice the length of the sample.”

Quantifying such properties was vital to Ulm and his colleagues. The goal of their recent paper was not just to prove that multifunctional cement was possible, but that it was also viable for mass production.

“The key point is that in order for an engineer to pick up things, they need a quantitative model,” explains Ulm. “Before you mix materials together, you want to be able to expect certain repeatable properties. That’s exactly what this paper outlines; it separates what is due to boundary conditions — [extraneous] environmental conditions — from really what is due to the fundamental mechanisms within the material.”

By isolating and quantifying these mechanisms, Soliman, Chanut, and Ulm hope to provide engineers with exactly what they need to implement multifunctional cement on a broader scale. The path they’ve charted is a promising one — and, thanks to their work, shouldn’t prove too tortuous.

The research was supported through the Concrete Sustainability Hub by the Portland Cement Association and the Ready Mixed Concrete Research and Education Foundation. More

Kiara Wahnschafft started her first company at age 16. After her classmate passed away from a drunk driving accident, Wahnschafft couldn’t stop thinking about ways technology could have saved a life. With two other students, she built a prototype for a car key that works only after the driver passes a breathalyzer test. Wahnschafft went on to create a company called SafeStart Technologies, ultimately patenting the product and winning several competitions.

The experience was Wahnschafft’s introduction to a unique way in which she could improve the lives of those around her. “I was always looking for an artistic outlet as a kid,” she says. “When I discovered programming, it was like I finally had this blank canvas on which to freely create potentially meaningful solutions.”

Wahnschafft arrived at MIT with the desire to continue pursuing product engineering for social entrepreneurship. She experimented with mechanical engineering classes through MIT D-Lab, a program focused on equitable design and development, and soon found herself surrounded by startups working to alleviate poverty and improve living standards around the world. One company, called Sanergy, stood out to her for its innovative approach toward improving sanitation in urban settlements. Through a PKG Center fellowship, she traveled to Nairobi, Kenya, and interned at Sanergy during Independent Activities Period (IAP) in January, 2020.

On her first day, Wahnschafft went with co-workers to the settlements where the company’s sanitation units were being built. Seeing the systems and meeting those operating them in person, as well as speaking with new co-workers and friends who had grown up in Nairobi, gave her a much deeper understanding of the challenge. While her engineering work focused on improving sanitation conditions, she learned more about the systemic reasons why settlements were expansive in the first place.

One of these such issues was job instability. Upon returning to MIT, Wahnschafft dove into an economics research opportunity focused on evaluating a program that teaches Kenyan workers skills needed for digital work. The findings revealed that the program helped to improve wages, employment, and life satisfaction. Wahnschafft then shared her findings with the program’s managers, providing them quantitative reasons to expand their work. The experience introduced her to an evidence-based method for tackling societal challenges.

Today, Wahnschafft is a junior studying both mechanical engineering and economics. In her career, she aims to help solve what she deems the greatest global challenge of our time: the climate crisis. In learning about and working on the energy transition, Wahnschafft often finds herself leveraging her two disciplines together. For example, she notes, “if we’re proposing the installation of heat pumps, it’s helpful to understand both the technical justification for their energy efficiency and the economic policies required for their widescale adoption.”

As a researcher in the MIT Environmental Solutions Initiative Rapid Response Group and the MIT Sloan Climate Pathways Project, Wahnschafft has written multiple briefs to inform Massachusetts and federal policymakers, often utilizing MIT climate research to do so. Both now and in the future, her goal is to ensure climate policy is backed by scientific evidence.

Wahnschafft has also collaborated with the student body and leaders in the administration to improve MIT. As the chief of staff of the Undergraduate Association (UA), the undergraduate student government, she has focused on pulling the student voice into Institute decisions in this unique year, particularly in the area of climate change. She worked with a large group of students, interviewing faculty and other stakeholders in the process, to develop recommendations for climate action at MIT, and is now working with the Institute’s administration to incorporate some of these ideas into MIT’s Plan for Action on Climate Change.

At a forum about MIT’s Climate Action Plan, Wahnschafft spoke on a panel focused on MIT’s role in the energy transition, and proposed ideas on ways to coordinate the wealth of climate research on campus. After working for a few different MIT climate-focused research centers, she has seen how “MIT has all this amazing research, but it’s often in silos.” After conversations with many faculty and students, she believes that MIT can “exponentially increase its impact” by connecting researchers with each other and with opportunities to influence climate policy.

Effective communication is also the theme of Wahnschafft’s favorite class, 11.011 (The Art and Science of Negotiation), for which she has served as a teaching assistant. She believes that the course should be an essential part of any MIT student’s curriculum. “I used to think negotiating meant sitting down at the bargaining table to haggle over prices,” she says. “Through the class, you learn that negotiation is so much more: It is practicing empathy and finding common ground. Especially in our polarized country, and especially on issues like climate that are so cross-cutting, we need to open up conversations to reach some mutual understanding.”

Wahnschafft plans on putting her negotiation skills to the test this summer, when she will be interning in Washington through the MIT Washington Summer Internship Program. She hopes to continue working on climate issues that sit at the intersection of evidence and policy. She feels “It’s going to take time to solve the climate crisis. But my everyday focus will be thinking about if the decisions I’m making are always socially and ethically responsible,” says Wahnschafft.

“I think that as MIT students, we need to be very thoughtful with where we choose to dedicate our minds. I know so many of my peers will go on to become incredible leaders in all types of important organizations,” she says. “We so often have such incredible opportunities at our fingertips during and after our time at MIT, and that’s amazing. So, we can and should be intentional with which of these we pursue and in the decisions we make as leaders, always considering the implications for our diverse local and global communities.”

Wahnschafft applies the same principles when looking the the future. “I’ve had the most incredible education and am very often thinking about where I can best apply it to make this world a little better. Applying my education to help combat climate change, one of the greatest global challenges in history, is the way in which I hope to make a difference.” More

Ambitious goals are often called moonshots, but the challenge of addressing climate change will be even more monumental. This “Earthshot,” as MIT President L. Rafael Reif calls it in an op-ed published today in The Boston Globe, is an enormously complex problem with no single right answer, no clear finish line, multiple stakeholders with conflicting priorities, and no central authority empowered to solve it.

The “super wicked problem” of bringing the global economy to net-zero carbon and adapting to aspects of climate change we can’t prevent will require sustained contributions from every corner of industry, government, academia, philanthropy, and every individual, Reif writes.

To get there, he argues for pursuing two tracks at once. “On path one, we must go as far as we can, as fast as we can, with the tools we have now. And by tools, I mean not only science and technology, but also policy, infrastructure, behavioral and cultural changes, and more,” he writes.

“But the fact is,” he adds, “current technology alone will not get us to the 2050 target.”

Reif thus proposes a path two, involving the creation and deployment of new tools, including science and technology breakthroughs, to approach the many parts of the climate change problem, including aviation, supply chains, agriculture, environmental justice, jobs, and much more.

To meet this path two challenge, he writes, research universities have a special role: “to spawn ideas that meet the needs of different sectors, and to optimize a system for speeding the mind-to-lab-to-market flow of technological answers, while helping to shape policies and processes to support adoption at scale.”

For instance, MIT has launched the MIT Climate Grand Challenges, which has led to novel proposals, from capturing carbon dioxide by domesticating fast-growing microbes to developing plasma-assisted technologies as enablers of green aviation.

Universities can help “tough tech” ideas like these reach the market by creating specialized accelerators. In the MIT ecosystem, The Engine identifies entrepreneurs with bold new-science answers to deep societal problems and connects them with impact investors.

The Institute is also working to create an innovation marketplace based on collaboration, not competition. For example, the member companies of the new MIT Climate and Sustainability Consortium are working with MIT researchers and with each other to speed the creation, testing, and deployment of practical climate solutions within their production processes, supply chains, and service models.

“With a super wicked problem, nobody has all the answers. But if individuals and institutions in every part of the economy and society tackle the pieces of the problem within their reach and collaborate with each other, we have a real shot — an Earthshot ­— at preserving a habitable world,” Reif writes. More

Found in jewelry, car parts, pigments, and industrial chemical reactions, the metal chromium and its compounds are often employed for their color, finish, and anti-corrosive and catalytic properties. Currently, geoscientists and paleoceanographers from MIT and the Woods Hole Oceanographic Institution (WHOI) are looking to add another use to that list: as a way to examine chemical shifts in ancient Earth’s oceans and atmosphere that are preserved in the seafloor’s paleorecord. More specifically, they want to reconstruct rising atmospheric oxygen levels, which began around 2.4 billion years ago, and their effect on the seas. Since biology and the environment are intimately intertwined, this information could help illuminate how the Earth’s life and climate evolved.

While researchers have widely applied chromium as a tool to understand the rock record around this global transition, they’re still working out what different chemical signals mean. This is especially true for evaluating ocean sediments, which could reveal where and when oxygen began penetrating and was being formed in the oceans. However, paleoscientists have largely lacked an understanding of how trace amounts of chromium mechanistically interact and cycle in modern, oxygenated seas, let alone the early oceans — a key component needed for any interpretation — until now.

Research recently published in the Proceedings of the National Academy of Sciences and led by MIT-Woods Hole Oceanographic Institution Joint Program graduate student Tianyi Huang investigated the trace metal’s promise as a paleoproxy for oxygen. For this, the team tracked how oxygen-sensitive chromium isotopes circulated and how they were chemically oxidized or reduced within an oxygen-deficient patch of water in the tropical Pacific Ocean, an analog for early, anaerobic seas. Their findings help validate chromium tracking as a reliable instrument in geology toolbox.

“People have seen the that chromium isotopes in the geological records kind of track the atmospheric oxygen levels. But, because you’re using something that is buried in the sediments to interpret what is happening in the atmosphere, there’s a missing link in between, and that is the ocean,” says Huang. Further, “how that chromium cycles might change our interpretations of geological records.”

“The evolution of oxygen on Earth is only known in a coarse fashion, but it is crucial to the development and survival of complex multicellular life,” says Ed Boyle, professor of ocean geochemistry of MIT’s Department of Earth, Atmospheric and Planetary Sciences (EAPS); MIT-WHOI Joint Program director; and study co-author, along with Simone Moos PhD ’18 of the Elementar Corporation. “In addition, there is ongoing concern about the past few decades of decreasing oceanic oxygen levels in the ocean, and we need tools to better understand the ocean’s oxygen dynamics.” 

Bridging a gap

Billions of years ago, when Earth and its atmosphere were essentially devoid of molecular oxygen (O2), chemical reactions and biological metabolisms would have occurred in a chemically reduced, anaerobic environment. During the Great Oxidation Event, which occurred over the course of millions of years, oxygen levels rose planet-wide, and life transitioned accordingly. Further, the environment largely became an oxidized one that grappled with stress processes like rusting and free radicals.

Some evidence has shown that chemical reactions involving chromium track this process, through effects on its isotopes, chromium-52 and chromium-53, and their oxidation states, primarily the trivalent, reduced form Cr (III) and a hexavalent, oxidized one Cr (VI). The latter is more likely to be found in oxygenated, surface seawater and is considered a health and environmental hazard. Previous studies have shown that the upper ocean tends to have more of the heavier isotope than the lighter one, suggesting some preferential uptake by marine microorganisms. The problem, Huang notes, is that after chromium enters the oceans from rivers, scientists don’t really know the mechanisms behind these observations and if the trends are consistent. In today’s oxygen-deficient waters, she says, “chromium could potentially be reduced, and we want to know the isotope signal of that and other chromium processes that might leave an isotope fingerprint.”

To investigate these phenomena, Huang joined two research cruises to the eastern tropical North Pacific Ocean’s oxygen-deficient zone (ODZ) and gathered vertical profiles of seawater samples down to 3,500 meters from across a transect of sea. Some of these seawater samples were frozen to be analyzed for concentrations of trivalent and hexavalent chromium. After being shipped back to the lab, these samples were thawed and purified. The team analyzed the isotope composition of the Cr (III) samples. They then acidified the Cr (VI) samples to convert them to Cr (III) before performing the same isotope analysis as before. The researchers also measured the total chromium in the samples to be able to account for any chemical transformations or migration within the ODZ. With the addition of data from another cruise, Boyle, Moos, and Huang examined the fraction of each isotope over the depth range, compared to an average partitioning, to see if there was any enrichment in a particular area of the ODZ and which oxidation state it existed in. They charted this against the samples’ oxygen levels and put the results in context of known ocean features to help explain how chromium is cycling.

A ground truth for chromium cycling

The oceanographers found a pattern. In surface, oxygenated ocean, hexavalent chromium was consumed, likely by microbial life, and transported deeper, into the ODZ. Around the 200-meter mark, the metal began to accumulate in the seawater, and the lighter isotope, chromium-52, was preferentially reduced. This depth happens to coincide with anaerobic, denitrifying microbes that produce nitrite. Huang says that this could be a sign that nitrogen and chromium cycling are entangled, but that doesn’t rule out other biotic or abiotic mechanisms, like reduction by iron, that could be affecting ocean sediment records.

Chromium doesn’t linger here forever, though. While data showed that most of it remained in oxygen-deficient zone, which extends from 90 to 800 meters, for about 20-50 years, a small portion of it attached to sinking particles, sank into the deep ocean where there is more dissolved oxygen, and later oxidized back to hexavalent chromium. Here, it could begin incorporating and interacting with sediments.

“I think it is exciting that we could determine the chromium [oxidation] species, and from that, we could calculate its isotope fractionation,” says Huang. “Nobody has done that in this way before.”

Their work, Huang says, helps validate chromium as an indicator of different redox environments. “We’re seeing this signal and it’s not vanishing.” Further, it seems consistent over the seasons. However, the team isn’t convinced yet. They plan to test this in other oxygen-deficient zones around the world to see if a similar chromium signature pops up, as well as investigate the composition of the sinking particles carrying the trivalent chromium and the surface of ocean sediments, in order to get a more complete picture of the ocean’s involvement.

For now, they advise against drawing conclusions, but are guardedly optimistic about its potential. “I think people need to interpret this proxy with more caution,” says Huang. “It might not be purely the atmospheric oxygen that is determining the measurement, but there could be other [biotic or abiotic] processes in the ocean that could alter their paleorecords.” So, they suggest not to read into the chromium signals in the paleorecord too much, yet.

This research was supported, in part, by the National Science Foundation. More

The ocean’s “biological pump” describes the many marine processes that work to take up carbon dioxide from the atmosphere and transport it deep into the ocean, where it can remain sequestered for centuries. This ocean pump is a powerful regulator of atmospheric carbon dioxide and an essential ingredient in any global climate forecast.

But a new MIT study points to a significant uncertainty in the way the biological pump is represented in climate models today. Researchers found that the “gold standard” equation used to calculate the pump’s strength has a larger margin of error than previously thought, and that predictions of how much atmospheric carbon the ocean will pump down to various depths could be off by 10 to 15 parts per million.

Given that the world is currently emitting carbon dioxide into the atmosphere at an annual rate of about 2.5 parts per million, the team estimates that the new uncertainty translates to about a five-year error in climate target projections.

“This larger error bar might be critical if we want to stay within 1.5 degrees of warming targeted by the Paris Agreement,” says Jonathan Lauderdale, a research scientist in MIT’s Department of Earth, Atmospheric and Planetary Sciences. “If current models predict we have until 2040 to cut carbon emissions, we’re expanding the uncertainty around that, to say maybe we now have until 2035, which could be quite a big deal.”

Lauderdale and former MIT graduate student B.B. Cael, now at the National Oceanography Center in Southampton, U.K., have published their study today in the journal Geophysical Research Letters.

Snow curve

The marine processes that contribute to the ocean’s biological pump begin with phytoplankton, microscopic organisms that soak up carbon dioxide from the atmosphere as they grow. When they die, phytoplankton collectively sink through the water column as “marine snow,” carrying that carbon with them.

“These particles rain down like white flaky snow that is all this dead stuff falling out of the surface ocean,” Lauderdale says.

At various depths the particles are consumed by microbes, which convert the particles’ organic carbon and respire it into the deep ocean in an inorganic, mineral form, in a process known as remineralization.

In the 1980s, researchers collected marine snow at locations and depths throughout the tropical Pacific. From these observations they generated a simple power law  mathematical relationship — the Martin curve, named after team member John Martin — to describe the strength of the biological pump, and how much carbon the ocean can remineralize and sequester at various depths.

“The Martin curve is ubiquitous, and it’s really the gold standard [used in many climate models today],” Lauderdale says.

But in 2018, Cael and co-author Kelsey Bisson showed that the power law derived to explain the Martin curve was not the only equation that could fit the observations. The power law is a simple mathematical relationship that assumes that particles fall faster with depth. But Cael found that several other mathematical relationships, each based on different mechanisms for how marine snow sinks and is remineralized, could also explain the data.

For instance, one alternative assumes that particles fall at the same rate no matter the depth, while another assumes that particles with heavy, less-consumable phytoplankton shells fall faster than those without.

“He found that you can’t tell which curve is the right one, which is a bit troubling, because each curve has different mechanisms behind it,” Lauderdale says. “In other words, researchers might be using the ‘wrong’ function to predict the strength of the biological pump. These discrepancies could snowball and impact climate projections.”

A curve, reconsidered

In the new study, Lauderdale and Cael looked at how much difference it would make to estimates of carbon stored deep in the ocean if they changed the mathematical description of the biological pump.

They started with the same six alternative equations, or remineralization curves, that Cael had previously studied. The team looked at how climate models’ predictions of atmospheric carbon dioxide would change if they were based on any of the six alternatives, versus the Martin curve’s power law.

To make the comparison as statistically similar as possible, they first fit each alternative equation to the Martin curve. The Martin curve describes the how much marine snow reaches various depths through the ocean. The researchers entered the data points from the curve into each alternative equation. They then ran each equation through the MITgcm, a general circulation model that simulates, among other processes, the flux of carbon dioxide between the atmosphere and the ocean.

The team ran the climate model forward in time to see how each alternative equation for the biological pump changed the model’s estimates of carbon dioxide in the atmosphere, compared with the Martin curve’s power law. They found that the amount of carbon that the ocean is able to draw down and sequester from the atmosphere varies widely, depending on which mathematical description for the biological pump they used.

“The surprising part was that even small changes in the amount of remineralization or marine snow making it to different depths due to the different curves can lead to significant changes in atmospheric carbon dioxide,” Lauderdale says.

The results suggest that the ocean’s pumping strength, and the processes that govern how fast marine snow falls, are still an open question.  

“We definitely need to make many more measurements of marine snow to break down the mechanisms behind what’s going on,” Lauderdale adds. “Because probably all these processes are relevant, but we really want to know which are driving carbon sequestration.”

This research was supported, in part, by the National Science Foundation, the Simons Collaboration on Computational Biogeochemical Modeling of Marine Ecosystems, and the UK National Environmental Research Council. More

Gregory Norris is an expert on quantifying firms’ impacts on the environment over the life cycles of their products and processes. His analyses help decision-makers opt for more sustainable, Earth-friendly outputs.

He and others in this field of life-cycle assessment (LCA) have largely gone about their work by determining firms’ negative impacts on the environment, or footprints, a term most people are familiar with. But Norris felt something was missing. What about the positive impacts firms can have by, for example, changing behaviors or creating greener manufacturing processes that become available to competitors? Could they be added to the overall LCA tally?

Introducing handprints, the term Norris coined for those positive impacts and the focus of MIT’s Sustainability and Health Initiative for NetPositive Enterprise (SHINE). SHINE is co-led by Norris and Randolph Kirchain, who both have appointments through MIT’s Materials Research Laboratory (MRL).

Positive impacts

“If you ask LCA practitioners what they track to determine a product’s sustainability, 99 out of 100 will talk about footprints, these negative impacts,” Norris says. “We’re about expanding that to include handprints, or positive impacts.”

Says Kirchain, “we’re trying to make the [LCA] metrics more encompassing so firms are motivated to make positive changes as well.” And that could ultimately “increase the scope of activities that firms engage in for environmental benefits.”

In a February 2021 paper in the International Journal of Life Cycle Assessment, Norris, Kirchain, and colleagues lay out the methodology for not only estimating handprints but also combining them with footprints. Additional authors of the paper are Jasmina Burek, Elizabeth A. Moore, and Jeremy Gregory, who are also affiliated with the MRL.

“By giving handprints a defendable methodology, we get closer to the ideal place where everything that counts can be counted,” says Jeff Zeman, principal of TrueNorth Collective, a consulting firm for sustainability. Zeman was not involved in the work.

As a result, Zeman continues, “designers can see the positive impact of their work show up in an organization’s messaging, as progress toward its sustainability goals, and bridge their work with other good actors to create shared benefits. Handprints have been a powerful influence on me and my team — and continue to be.”

How it works

Handprints are measured with the same metrics used for quantifying different footprints. For example, a classic metric for determining a product’s water footprint is the liters of water used to create that product. The same product’s water handprint would be calculated by determining the liters of water saved through a positive change such as instituting a new manufacturing process involving recycled materials. Both footprints and handprints are measured using existing life-cycle inventory databases, software, and calculation methods.

The SHINE team has demonstrated the impact of adding handprints to LCA analyses through case studies with several companies. One such study described in the paper involved Interface, a manufacturer of flooring materials. The SHINE team calculated the company’s handprints associated with the use of “recycled” gas to help heat its manufacturing facility. Specifically, Interface captured and burned methane gas from a landfill. That gas would otherwise have been released to the atmosphere, contributing to climate change.

After calculating both the company’s handprints and footprints, the SHINE team found that Interface had a net positive impact. As the team wrote in their paper, “with the SHINE handprint framework, we can help actors to create handprints greater than, and commensurate with, their footprints.”

Concludes Norris: “With this paper, we hope that work on sustainability will get stronger by making these tools available to more people.”

This work was supported by the SHINE consortium. More