Caltech Awards Innovators of Carbon-Reducing Technologies

On the Caltech campus, a number of initiatives are under way to help achieve the Institute's goal of reducing its ecological footprint, including water conservation efforts and infrastructure upgrades to increase energy efficiency. Caltech's Resnick Sustainability Institute takes a broader view, encouraging and supporting science and engineering breakthroughs that can positively alter sustainability worldwide.

To that end, last year the Resnick Institute inaugurated the Resonate Awards as a way to draw attention to important work by early-career researchers and emerging leaders in green innovation—work that is often overlooked among other advances in technology. In line with the Resnick Institute's aim to advance research in sustainability science, this year's awards honored five innovators with creative solutions for reducing large sources of carbon dioxide—a greenhouse gas and contributor to climate change.

In their work, the honorees addressed several key areas in which innovations in technology can have a significant impact on reducing energy-related carbon dioxide emissions that contribute to climate change, such as improving the efficiency of energy systems and electronic devices, advancing clean-energy technologies, and pioneering methods to turn waste CO2 into a useful industrial product.

The 2015 Resonate Awards went to

  • Stanford University's Yi Cui for his work in the design of nanomaterials for energy conversion and storage.
  • Joel L. Dawson from Eta Devices for his contributions to solving power challenges in the cellular communications industry.
  • Tsutomu Ioroi from the Research Institute of Electrochemical Energy/National Institute of Advanced Industrial Science and Technology in Japan for his work in advancing materials for the next generation of fuel cells.
  • Mika Järvinen from Aalto University in Finland for inventing a CO2 sequestration process that converts a steel-manufacturing by-product into a valuable industrial resource.
  • Delia J. Milliron from the University of Texas at Austin for using nanomaterials to improve the carbon-reduction capabilities of smart windows.

The winners participated in a panel discussion on July 3rd at the Aspen Ideas Festival in Aspen, Colorado focused on how technological innovations can make an impact on global challenges.

"These talented scientists are producing innovations that make a tremendous positive impact on the environment. The goal of the Resonate Awards is to focus attention on creative people tackling these very tough problems," says Harry Atwater, Howard Hughes Professor of Applied Physics and Materials Science and director of the Joint Center for Artificial Photosynthesis at Caltech, as well as the founder of the Resonate Awards program.

In addition to honoring the rigorous scientific achievements of these individuals, the awards are also meant to celebrate the use of creativity to solve some of the world's biggest energy and environmental problems—an important part of the Resnick Institute's mission to change the balance of the world's sustainability.

"Challenges in sustainability are becoming increasingly visible on many fronts—from the Vatican to new government agreements and plans in the lead up to the upcoming Paris Cop21 climate talks," said Neil Fromer, executive director of the Resnick Sustainability Institute. "These awards shine a light on a wide range of new technology solutions designed to meet these challenges."

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Understanding Monsoons

Studies of the global environment are complex, involving interactions between oceans, solid earth, biological systems, and the atmosphere, over time scales ranging from nanoseconds to millions of years. Investigating and understanding these complicated and interconnected systems is the goal of Caltech's Ronald and Maxine Linde Center for Global Environmental Science. To that end, the center hosts workshops that bring together scientists from a range of disciplines to discuss current research and collaborate on solutions to pressing issues facing the global environment.

"The Linde Center workshops aim to provide a venue for a small group of scientists and engineers to discuss and put forward cutting edge, 'future-looking' plans for global environmental science," says Paul Wennberg, the R. Stanton Avery Professor of Atmospheric Chemistry and Environmental Science and Engineering and director of the Linde Center.

The topic of the center's latest workshop, held May 18–22, was monsoons, circulation patterns that develop over subtropical continents (up to around latitude 30 degree north and south of the equator) in response to seasonal variations in the amount of solar radiation received in these regions. Monsoons are characterized by seasonally reversing winds and summertime rainfall. Although monsoons occur across the globe, they are more often studied in Southeast Asian countries—where warm, moist air from the Indian Ocean brings humidity and rainfall during the summer, while winds from the northeast produce dry winters—and in West Africa. Because of their effects on the water supply, monsoons have a large impact on society, especially in densely populated countries and rapidly growing economies. And, as noted by the workshop organizers, "with projected increases in population and pressure for food and water security, understanding how anthropogenic climate change will affect monsoons is both a priority and a major challenge in climate science."

Indeed, the workshop—entitled "Monsoons: Past, Present, and Future" and co-led by monsoon researcher Simona Bordoni, assistant professor of environmental science and engineering at Caltech—was focused on understanding how monsoons have changed and how they will change in the future, across a variety of time scales, in response to different forcing agents—perturbations of Earth's energy balance caused by changing environmental parameters such as solar variability or human-induced greenhouse gas emissions.

"One of the central themes of the discussion," Bordoni says, "was how modern theories of the fundamental dynamics of monsoons can be used to better constrain future monsoon projections and past monsoon changes and shifts recorded by paleo-proxies"—media such as tree rings and ice cores that preserve information about past climates—"and how these paleo-reconstructions can provide support to emerging hypotheses and guide modeling studies. The implications of these modern theories are only now beginning to be explored."

Each section of the invitation-only workshop covered a particular subject area within monsoon research, including paleoclimate, aerosols, the intertropical convergence zone (the band of clouds encircling the equator), and thermal contrasts between land and sea. Speakers from institutions around the country gave talks on past and potential future changes in the monsoon cycle, the role of aerosols on monsoon circulation, and monsoon modeling, among other topics.

In a talk entitled "Monsoons on Idealized Continents," for example, Bordoni discussed how she uses models of "idealized" continental geometry to study how monsoons would develop on hypothetical planets—for example, a planet with land everywhere above 10 degrees north of the equator, and ocean everywhere south of that. Recently, Bordoni and her group also created simulations of an "aquaplanet"—a planet entirely covered with ocean. With the aquaplanet simulations, the team demonstrated that the rapid onset of large-scale monsoons, such as the Asian monsoon, results not from temperature differences between oceans and land, as previously believed. Instead, they found, the rapid appearance of this monsoon is controlled by the interaction between large swirling regions of turbulent air called eddies and the tropical circulation. These eddies, which are generated in mid-latitudes, propagate to lower latitudes towards the subtropics and interact with the tropical circulation, causing it to reverse rapidly, initiating the onset of the monsoon. Bordoni's group also studies the North American monsoon, which usually occurs during the summer over southwestern North America, when warm and moist air moving northwest from the Gulf of California meets similar air moving northwest from the Gulf of Mexico; the dynamics of the East Asian monsoon and its response to climate changes; the year-to-year variability of the Indian monsoon; and how mountain ranges such as those in Africa and Asia influence the larger-scale circulation of this monsoon.

The workshop was co-led by Timothy Merlis (Ph.D. '11), an assistant professor in atmospheric and oceanic sciences at McGill University. He gave a talk on tropical circulation changes influenced by various forcing agents. Other speakers from Caltech included Jess Adkins, professor of geochemistry and global environmental science, who gave a talk on historical precipitation variability over Borneo as measured in stalagmites; Salvatore Pascale, a NOAA Climate and Global Change postdoctoral scholar in environmental science and engineering; and Ho Hsuan Wei, a graduate student in environmental science and engineering. Hui Su, a JPL atmospheric scientist, gave a talk on the tropical Hadley cell (a pattern of atmospheric circulation in which warm air rises near the equator, cools as it travels at high altitude toward the poles, then sinks as cold air and warms as it travels toward the equator) and feedback from clouds. In addition, JPL scientist Christian Frankenberg—who will join the Caltech faculty in September as an associate professor of environmental science and engineering—discussed remote sensing of water isotopes.

The previous Linde Center workshop was held February 2–5 and focused on physical, chemical, and biological processes crucial to the circulation and ecosystems of the Southern Ocean around Antarctica.

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JCAP Receives a 5-Year, $75M Funding Renewal

On Monday, April 27, the Department of Energy (DOE) announced a five-year, $75 million renewal of the Joint Center for Artificial Photosynthesis (JCAP). JCAP's mission is to explore the science and technology of artificial photosynthesis to harness solar energy for the production of fuel.

JCAP is the nation's largest research program dedicated to the development of an artificial solar-fuel generation technology. Established in 2010 as a DOE Energy Innovation Hub, JCAP aims to create a low-cost generator to make fuel from sunlight 10 times more efficiently than plants. Such a breakthrough would have the potential to reduce our country's dependence on oil and enhance energy security.

The Hub is directed by Caltech, but it has its primary sites both at Lawrence Berkeley National Laboratory (LBNL) and at Caltech. JCAP brings together more than 150 scientists and engineers from Caltech and LBNL, and also draws on the expertise and capabilities of key partners at UC Irvine, UC San Diego, and the SLAC National Accelerator Laboratory at Stanford.

The funding renewal announcement was made at LBNL by Franklin Orr, under secretary for science and energy at DOE.

"JCAP's work to produce fuels from sunlight and carbon dioxide holds the promise of a potentially revolutionary technology that would put America on the path to a low-carbon economy," said Orr in a DOE press release. "While the scientific challenges of producing such fuels are considerable," the released noted, "JCAP will capitalize on state-of-the-art capabilities developed during its initial five years of research, including sophisticated characterization tools and unique automated high-throughput experimentation that can quickly make and screen large libraries of materials to identify components for artificial photosynthesis systems."   

"We are honored and delighted to receive renewed support from the Department of Energy for JCAP," says JCAP director Harry A. Atwater, Howard Hughes Professor of Applied Physics and Materials Science at Caltech. "Thanks to this renewal, JCAP will continue to push the scientific frontiers of artificial photosynthesis, with an emphasis on selective carbon dioxide reduction under mild temperature and pressure conditions. Carbon dioxide reduction is at the core of natural photosynthesis, and understanding the science and technology of this reaction is also central to society's efforts to mitigate carbon dioxide emission. It is an enormous challenge, but just the sort of problem that is worthy of sustained scientific investment. We are excited for the work ahead."

In its first five years of research, JCAP has made significant advances in a number of areas, including the automated and rapid discovery and characterization of new catalysts and light absorbers, the development of techniques for protecting the light-absorbing components in solar-fuels generators, and the creation of experimental protocols for objective evaluations of the activity and stability of materials. All of these technologies are critical to the development of solar-driven water splitting and the reduction of carbon dioxide to produce fuel.

For more information about JCAP, please visit http://solarfuelshub.org/.

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Space-Based Solar Power Project Funded

A sponsored research agreement with Northrop Grumman Corporation will provide Caltech up to $17.5 million over three years for the development of the Space Solar Power Initiative (SSPI). The SSPI will develop the scientific and technological innovations necessary to enable a space-based solar power system—consisting of ultralight, high-efficiency photovoltaics, a phased-array system to produce and distribute power dynamically, and ultralight deployable space structures—that ultimately will be capable of generating electric power at a cost comparable to that from fossil-fuel power plants.

The project was conceived and will be led jointly by three professors in Caltech's Division of Engineering and Applied Science (EAS): Harry A. Atwater, Howard Hughes Professor of Applied Physics and Materials Science and director of the Resnick Sustainability Institute; Ali Hajimiri, Thomas G. Myers Professor of Electrical Engineering; and Sergio Pellegrino, Joyce and Kent Kresa Professor of Aeronautics, professor of civil engineering, and a senior research scientist at Caltech's Jet Propulsion Laboratory.

Atwater's group will design and demonstrate ultralight, high-efficiency photovoltaics optimized for space conditions and compatible with an integrated, modular power conversion/transmission system.

Hajimiri's team will develop the integrated circuits and the antenna design for the system's large-scale phased array, timing control, and conversion of direct current to radio frequency power. "The three groups are working closely to take a holistic approach to the design of the entire system," he says.

Through a modular approach power will be generated, converted, and radiated locally at the same place in space using a distributed power conversion and transmission solution created with modern integrated electronics that eliminates inter- and intramodule power wiring in the system. "This significantly reduces the system mass, and thereby its cost," he adds.

"This space-based, highly adaptive power generator will enable versatile on-demand power anywhere on the planet and will be able to almost instantly distribute the power to different locations," Hajimiri says. "This is enabled through an agile phased-array system that can dynamically direct the power to the desired locations on Earth and simultaneously provide power to multiple destinations on demand. This can substantially reduce the need and the cost associated with the power distribution network across the globe."

Any such system must first be able to collect the solar energy that is then converted and distributed. "One of the key barriers to the realization of cost-competitive space-based solar power systems is the deployment in space of large surface area structures to collect solar power, at low cost," says Pellegrino. "The cost and complexity of launching and deploying conventional deployable structures would be unacceptable for many applications." To circumvent this barrier, his team is developing novel architectures for multifunctional deployable space structures with an overall areal density on the order of 100 grams per square meter, equivalent to one or two sheets of paper. "The concepts that we are investigating build on over 10 years of research on deployable thin-shell structures, which most recently had resulted in the development of low-cost fiber-composite booms and reflectors in which elastic hinges are created simply by making small cuts in the wall of a shell structure," he says.

To achieve all of these goals, Atwater, Hajimiri, and Pellegrino already have assembled a team of students, postdoctoral scholars, and senior researchers that will eventually exceed 50 members. In addition, the EAS division is in the process of building specialized laboratory facilities to support the team. Meanwhile, Northrop Grumman engineers and scientists will collaborate with the Caltech researchers to develop solutions, build prototypes, and obtain experimental and numerical validation of concepts that will allow for the eventual implementation of the system.

"This initiative is a great example of how Caltech engineers are working at the leading edges of fundamental science to invent the technologies of the future," says Ares Rosakis, Otis Booth Leadership Chair of the EAS division and the Theodore von Kármán Professor of Aeronautics and Mechanical Engineering. "The Space Solar Power Initiative brings together electrical engineers, applied physicists, and aerospace engineers in the type of profound interdisciplinary collaboration that is seamlessly enhanced at a small place like Caltech. I believe it also demonstrates the value of industry and academic partnerships. We are working on extremely difficult problems that could eventually provide the world with new, and very cost-competitive technology for sustainable energy."

"By working together with Caltech, Northrop Grumman extends its long heritage of innovation in space-based technologies and mission solutions," said Joseph Ensor, vice president and general manager, Space Intelligence, Surveillance and Reconnaissance (ISR) Systems, Northrop Grumman, in a press release. "The potential breakthroughs from this research could have extensive applications across a number of related power use challenges."

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Tracking Photosynthesis from Space

Watching plants perform photosynthesis from space sounds like a futuristic proposal, but a new application of data from NASA's Orbiting Carbon Observatory-2 (OCO-2) satellite may enable scientists to do just that. The new technique, which allows researchers to analyze plant productivity from far above Earth, will provide a clearer picture of the global carbon cycle and may one day help researchers determine the best regional farming practices and even spot early signs of drought.

When plants are alive and healthy, they engage in photosynthesis, absorbing sunlight and carbon dioxide to produce food for the plant, and generating oxygen as a by-product. But photosynthesis does more than keep plants alive. On a global scale, the process takes up some of the man-made emissions of atmospheric carbon dioxide—a greenhouse gas that traps the sun's heat down on Earth—meaning that plants also have an important role in mitigating climate change.

To perform photosynthesis, the chlorophyll in leaves absorbs sunlight—most of which is used to create food for the plants or is lost as heat. However, a small fraction of that absorbed light is reemitted as near-infrared light. We cannot see in the near-infrared portion of the spectrum with the naked eye, but if we could, this reemitted light would make the plants appear to glow—a property called solar induced fluorescence (SIF). Because this reemitted light is only produced when the chlorophyll in plants is also absorbing sunlight for photosynthesis, SIF can be used as a way to determine a plant's photosynthetic activity and productivity.

"The intensity of the SIF appears to be very correlated with the total productivity of the plant," says JPL scientist Christian Frankenberg, who is lead for the SIF product and will join the Caltech faculty in September as an associate professor of environmental science and engineering in the Division of Geological and Planetary Sciences.

Usually, when researchers try to estimate photosynthetic activity from satellites, they utilize a measure called the greenness index, which uses reflections in the near-infrared spectrum of light to determine the amount of chlorophyll in the plant. However, this is not a direct measurement of plant productivity; a plant that contains chlorophyll is not necessarily undergoing photosynthesis. "For example," Frankenberg says, "evergreen trees are green in the winter even when they are dormant."

He adds, "When a plant starts to undergo stress situations, like in California during a summer day when it's getting very hot and dry, the plants still have chlorophyll"—chlorophyll that would still appear to be active in the greenness index—"but they usually close the tiny pores in their leaves to reduce water loss, and that time of stress is also when SIF is reduced. So photosynthesis is being very strongly reduced at the same time that the fluorescence signal is also getting weaker, albeit at a smaller rate."

The Caltech and JPL team, as well as colleagues from NASA Goddard, discovered that they could measure SIF from orbit using spectrometers—standard instruments that can detect light intensity—that are already on board satellites like Japan's Greenhouse Gases Observing Satellite (GOSAT) and NASA's OCO-2.

In 2014, using this new technique with data from GOSAT and the European Global Ozone Monitoring Experiment–2 satellite, the researchers scoured the globe for the most productive plants and determined that the U.S. "Corn Belt"—the farming region stretching from Ohio to Nebraska—is the most photosynthetically active place on the planet. Although it stands to reason that a cornfield during growing season would be actively undergoing photosynthesis, the high-resolution measurements from a satellite enabled global comparison to other plant-heavy regions—such as tropical rainforests.

"Before, when people used the greenness index to represent active photosynthesis, they had trouble determining the productivity of very dense plant areas, such as forests or cornfields. With enough green plant material in the field of view, these greenness indexes can saturate; they reach a maximum value they can't exceed," Frankenberg says. Because of the sensitivity of the SIF measurements, researchers can now compare the true productivity of fields from different regions without this saturation—information that could potentially be used to compare the efficiency of farming practices around the world.

Now that OCO-2 is online and producing data, Frankenberg says that it is capable of achieving higher resolution than the preliminary experiments with GOSAT. Therefore, OCO-2 will be able to provide an even clearer picture of plant productivity worldwide. However, to get more specific information about how plants influence the global carbon cycle, an evenly distributed ground-based network of spectrometers will be needed. Such a network—located down among the plants rather than miles above—will provide more information about regional uptake of carbon dioxide via photosynthesis and the mechanistic link between SIF and actual carbon exchange.

One existing network, called FLUXNET, uses ground-based towers to measure the exchange of carbon dioxide, or carbon flux, between the land and the atmosphere from towers at more than 600 locations worldwide. However, the towers only measure the exchange of carbon dioxide and are unable to directly observe the activities of the biosphere that drive this exchange.

The new ground-based measurements will ideally take place at existing FLUXNET sites, but they will be performed with a small set of high-resolution spectrometers—similar to the kind that OCO-2 uses—to allow the researchers to use the same measurement principles they developed for space. The revamped ground network was initially proposed in a 2012 workshop at the Keck Institute for Space Studies and is expected to go online sometime in the next two years.

In the future, a clear picture of global plant productivity could influence a range of decisions relevant to farmers, commodity traders, and policymakers. "Right now, the SIF data we can gather from space is too coarse of a picture to be really helpful for these conversations, but, in principle, with the satellite and ground-based measurements you could track the fluorescence in fields at different times of day," he says. This hourly tracking would not only allow researchers to detect the productivity of the plants, but it could also spot the first signs of plant stress—a factor that impacts crop prices and food security around the world.

"The measurements of SIF from OCO-2 greatly extend the science of this mission", says Paul Wennberg, R. Stanton Avery Professor of Atmospheric Chemistry and Environmental Science and Engineering, director of the Ronald and Maxine Linde Center for Global Environmental Science, and a member of the OCO-2 science team. "OCO-2 was designed to map carbon dioxide, and scientists plan to use these measurements to determine the underlying sources and sinks of this important gas. The new SIF measurements will allow us to diagnose the efficiency of the plants—a key component of the sinks of carbon dioxide."

By using OCO-2 to diagnose plant activity around the globe, this new research could also contribute to understanding the variability in crop primary productivity and also, eventually, the development of technologies that can improve crop efficiency—a goal that could greatly benefit humankind, Frankenberg says.

This project is funded by the Keck Institute for Space Studies and JPL. Wennberg is also an executive officer for the Environmental Science and Engineering (ESE) program. ESE is a joint program of the Division of Engineering and Applied Science, the division of Chemistry and Chemical Engineering, and the Division of Geological and Planetary Sciences.

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Caltech’s Linde Center Helps Navigate the Southern Ocean

At Caltech's Ronald and Maxine Linde Center for Global Environmental Science, researchers from diverse disciplines work together to investigate Earth's climate and its atmosphere, oceans, and biosphere; their evolution; and how they may change in the future.

In early February, the center hosted a three-day workshop focused on the Southern Ocean around Antarctica. Scientists from around the world working at the intersection of fluid dynamics and biochemistry gathered to summarize our current knowledge of the physical, chemical, and biological processes that are critical to the Southern Ocean's circulation and marine ecosystems. The researchers set out to identify areas where collaboration across disciplines is needed to push that understanding forward. Here are a few of the topics they covered.

The Use of Autonomous Underwater Vehicles for Observation 


Credit: Sunke Schmidtko

The Southern Ocean is one of the most inhospitable places on Earth. Despite the area's importance to the global climate, measurements and data are hard to come by because it is difficult to deploy research vessels in the region, especially in winter. Little, if any, data have been collected in some areas, especially in the deep ocean and underneath ice shelves.

But many new tools now exist to improve data collection and measurement in these remote regions. Autonomous gliders (shown above) have gathered information on currents, water density, and temperature at many depths, helping researchers like workshop participants Nicole Couto (Rutgers University), Mike Meredith (British Antarctic Survey), as well as Caltech's Andrew Thompson, assistant professor of environmental science and engineering, understand how warm waters are causing ice sheets to melt. Meanwhile, an extensive system of autonomous floats monitors temperature, salinity, dissolved gases and currents in the earth's oceans; moored instruments track what is happening beneath ice shelves; and even Antarctic seals outfitted with sensors provide scientists access to, and information about, some of the ocean's coldest and most inaccessible waters.

Iron Limitation on Phytoplankton Growth


Credit: NASA/Suomi NPP/Norman Kuring

Phytoplankton, microscopic algae that perform photosynthesis, the base of the Southern Ocean food web. These organisms require both nutrients and sunlight to survive. The Southern Ocean is a region where nutrients and sunlight (at least in summer) are plentiful, yet many parts of the Southern Ocean have extremely low phytoplankton concentrations. This is because not all nutrients are treated equally. Take iron, for example. Although iron is needed only in small amounts by phytoplankton, it is scarce throughout most of the Southern Ocean. Iron enters ocean waters by way of dust falling out of the atmosphere, from melting icebergs or glaciers, and from the ocean floor. Meeting participants Phil Boyd (University of Tasmania) and Nicolas Cassar (Duke University) are working to understand how sources of iron will respond to changing atmospheric and oceanic conditions, as well as how Southern Ocean ecosystems will adapt, are important research questions.

Phytoplankton distributions are largely observed by measuring ocean color from space. This image shows data from NASA's MODIS (MODerate resolution Imaging Spectroradiometer) satellite, which measures light coming off the ocean, NASA scientists use this information to determine the concentration of phytoplankton in the water. Here, yellow and orange colors indicate the presence of more phytoplankton.

The Importance of High Spatial Resolution in Ocean Models


Credit: Jeff Schmalz/NASA

The ocean is similar to the atmosphere in that much of the variability is contained in "weather systems," or high- and low-pressure areas. These weather systems create swirling currents, called eddies, that are the ocean equivalent of atmospheric storms. While storms in the atmosphere span hundreds of kilometers, eddies in the ocean only cover a few tens of kilometers. When numerical models, such as those run by meeting participant Andy Hogg (Australia National University), capture these smaller scales, the simulations explode with previously unseen dynamics and produce an energetic circulation that is more vigorous than seen in models that only simulate larger scales.

This image of Chatham Island, off the coast of New Zealand, was taken by MODIS. The blue wispy pattern (upper right) is a phytoplankton bloom that is being stretched and stirred by ocean eddies. Images like this one verify that high-resolution numerical models accurately reproduce oceanic motions and provide insight into how these small-scale currents influence Southern Ocean ecosystems.

Heat Input


Credit: Courtesy of Whit Anderson/The Geophysical Fluid Dynamics Lab in Princeton, NJ

Increasing carbon dioxide concentrations in the atmosphere warm the planet, with roughly 90 percent of the extra energy going into the oceans. The ocean warming that results is not uniform around the globe. Numerical models from the group of meeting participant John Marshall (MIT) suggest that the warming of the Southern Ocean will occur later than that of other oceans. The reason? The Southern Ocean provides a gateway where cold, dense waters, stored in the deep ocean, are brought up to the surface by the ocean circulation and are exposed to the atmosphere. These cold waters have the potential to store a large amount of heat. Understanding when this reservoir will be exhausted is critical to predicting future Southern Ocean temperature changes.

In this sea-surface temperature map created by a NOAA Geophysical Fluid Dynamics Laboratory model, Southern Ocean waters (green and blue) represent regions where cold water rises up to the surface, warms, and moves northward.

The Distribution of Sea Ice


Credit: Hannah Joy-Warren, Stanford graduate student, taken during the Phantastic II cruise to the west Antarctic Peninsula (October/November 2014).

The distribution of sea ice in the Southern Ocean is important for many reasons. For instance, sea ice can act as a cap on the ocean, limiting atmospheric interactions with the ocean surface that may trap carbon in the deep ocean. Recently, Caltech researchers including Thompson and Jess Adkins, professor of geochemistry and global environmental science, discovered a link between the distribution of sea ice in the Southern Ocean and differences in the ocean circulation in our present climate and at the Last Glacial Maximum.

As sea ice retreats, additional melting can be a source of iron to the ocean, influencing phytoplankton growth. The capacity for plankton and other organisms to survive the Antarctic winter is only just beginning to be understood, as explained in a recent review article on sea ice ecosystems by meeting participant Kevin Arrigo (Stanford University). Future under-ice observations are needed to improve our ability to estimate ecosystem changes in polar regions.

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JPL News: California Tuolumne Snowpack 40 Percent of Worst Year

New NASA data find the snowpack in the Tuolumne River Basin in California's Sierra Nevada—a major source of water for millions of Californians—currently contains just 40 percent as much water as it did near this time at its highest level of 2014, one of the two driest years in California's recorded history. The data were acquired through a partnership with the California Department of Water Resources, the San Francisco Public Utilities Commission and the Turlock and Modesto irrigation districts.

Read the full story from JPL News

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Friday, April 17, 2015
Sherman Fairchild Library 328 (Multimedia Conference Room) – Sherman Fairchild Library of Engineering and Applied Science

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Friction Means Antarctic Glaciers More Sensitive to Climate Change Than We Thought

One of the biggest unknowns in understanding the effects of climate change today is the melting rate of glacial ice in Antarctica. Scientists agree rising atmospheric and ocean temperatures could destabilize these ice sheets, but there is uncertainty about how fast they will lose ice.

The West Antarctic Ice Sheet is of particular concern to scientists because it contains enough ice to raise global sea level by up to 16 feet, and its physical configuration makes it susceptible to melting by warm ocean water. Recent studies have suggested that the collapse of certain parts of the ice sheet is inevitable. But will that process take several decades or centuries?

Research by Caltech scientists now suggests that estimates of future rates of melt for the West Antarctic Ice Sheet—and, by extension, of future sea-level rise—have been too conservative. In a new study, published online on March 9 in the Journal of Glaciology, a team led by Victor Tsai, an assistant professor of geophysics, found that properly accounting for Coulomb friction—a type of friction generated by solid surfaces sliding against one another—in computer models significantly increases estimates of how sensitive the ice sheet is to temperature perturbations driven by climate change.

Unlike other ice sheets that are moored to land above the ocean, most of West Antarctica's ice sheet is grounded on a sloping rock bed that lies below sea level. In the past decade or so, scientists have focused on the coastal part of the ice sheet where the land ice meets the ocean, called the "grounding line," as vital for accurately determining the melting rate of ice in the southern continent.

"Our results show that the stability of the whole ice sheet and our ability to predict its future melting is extremely sensitive to what happens in a very small region right at the grounding line. It is crucial to accurately represent the physics here in numerical models," says study coauthor Andrew Thompson, an assistant professor of environmental science and engineering at Caltech.

Part of the seafloor on which the West Antarctic Ice Sheet rests slopes upward toward the ocean in what scientists call a "reverse slope gradient." The end of the ice sheet also floats on the ocean surface so that ocean currents can deliver warm water to its base and melt the ice from below. Scientists think this "basal melting" could cause the grounding line to retreat inland, where the ice sheet is thicker. Because ice thickness is a key factor in controlling ice discharge near the coast, scientists worry that the retreat of the grounding line could accelerate the rate of interior ice flow into the oceans. Grounding line recession also contributes to the thinning and melting away of the region's ice shelves—thick, floating extensions of the ice sheet that help reduce the flow of ice into the sea.

According to Tsai, many earlier models of ice sheet dynamics tried to simplify calculations by assuming that ice loss is controlled solely by viscous stresses, that is, forces that apply to "sticky fluids" such as honey—or in this case, flowing ice. The conventional models thus accounted for the flow of ice around obstacles but ignored friction. "Accounting for frictional stresses at the ice sheet bottom in addition to the viscous stresses changes the physical picture dramatically," Tsai says.

In their new study, Tsai's team used computer simulations to show that even though Coulomb friction affects only a relatively small zone on an ice sheet, it can have a big impact on ice stream flow and overall ice sheet stability.

In most previous models, the ice sheet sits firmly on the bed and generates a downward stress that helps keep it attached it to the seafloor. Furthermore, the models assumed that this stress remains constant up to the grounding line, where the ice sheet floats, at which point the stress disappears.

Tsai and his team argue that their model provides a more realistic representation—in which the stress on the bottom of the ice sheet gradually weakens as one approaches the coasts and grounding line, because the weight of the ice sheet is increasingly counteracted by water pressure at the glacier base. "Because a strong basal shear stress cannot occur in the Coulomb model, it completely changes how the forces balance at the grounding line," Thompson says.

Tsai says the idea of investigating the effects of Coulomb friction on ice sheet dynamics came to him after rereading a classic study on the topic by American metallurgist and glaciologist Johannes Weertman from Northwestern University. "I wondered how might the behavior of the ice sheet differ if one factored in this water-pressure effect from the ocean, which Weertman didn't know would be important when he published his paper in 1974," Tsai says.

Tsai thought about how this could be achieved and realized the answer might lie in another field in which he is actively involved: earthquake research. "In seismology, Coulomb friction is very important because earthquakes are thought to be the result of the edge of one tectonic plate sliding against the edge of another plate frictionally," Tsai said. "This ice sheet research came about partly because I'm working on both glaciology and earthquakes."

If the team's Coulomb model is correct, it could have important implications for predictions of ice loss in Antarctica as a result of climate change. Indeed, for any given increase in temperature, the model predicts a bigger change in the rate of ice loss than is forecasted in previous models. "We predict that the ice sheets are more sensitive to perturbations such as temperature," Tsai says.

Hilmar Gudmundsson, a glaciologist with the British Antarctic Survey in Cambridge, UK, called the team's results "highly significant." "Their work gives further weight to the idea that a marine ice sheet, such as the West Antarctic Ice Sheet, is indeed, or at least has the potential to become, unstable," says Gudmundsson, who was not involved in the study.

Glaciologist Richard Alley, of Pennsylvania State University, noted that historical studies have shown that ice sheets can remain stable for centuries or millennia and then switch to a different configuration suddenly.

"If another sudden switch happens in West Antarctica, sea level could rise a lot, so understanding what is going on at the grounding lines is essential," says Alley, who also did not participate in the research.

"Tsai and coauthors have taken another important step in solving this difficult problem," he says.

Along with Tsai and Thompson, Andrew Stewart, an assistant professor of atmospheric and oceanic sciences at UCLA, was also a coauthor on the paper, "Marine ice sheet profiles and stability under Coulomb basal conditions." Funding support for the study was provided by Caltech's President's and Director's Fund program and the Stanback Discovery Fund for Global Environmental Science.

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Ice Sheets Melting Faster than Expected?
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Ice Sheets Melting Faster than Expected?
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