An underwater navigation system powered by sound

GPS isn’t waterproof. The navigation system depends on radio waves, which break down rapidly in liquids, including seawater. To track undersea objects like drones or whales, researchers rely on acoustic signaling. But devices that generate and send sound usually require batteries — bulky, short-lived batteries that need regular changing. Could we do without them?

MIT researchers think so. They’ve built a battery-free pinpointing system dubbed Underwater Backscatter Localization (UBL). Rather than emitting its own acoustic signals, UBL reflects modulated signals from its environment. That provides researchers with positioning information, at net-zero energy. Though the technology is still developing, UBL could someday become a key tool for marine conservationists, climate scientists, and the U.S. Navy.

These advances are described in a paper being presented this week at the Association for Computing Machinery’s Hot Topics in Networks workshop, by members of the Media Lab’s Signal Kinetics group. Research Scientist Reza Ghaffarivardavagh led the paper, along with co-authors Sayed Saad Afzal, Osvy Rodriguez, and Fadel Adib, who leads the group and is the Doherty Chair of Ocean Utilization as well as an associate professor in the MIT Media Lab and the MIT Department of Electrical Engineering and Computer Science.

“Power-hungry”

It’s nearly impossible to escape GPS’ grasp on modern life. The technology, which relies on satellite-transmitted radio signals, is used in shipping, navigation, targeted advertising, and more. Since its introduction in the 1970s and ’80s, GPS has changed the world. But it hasn’t changed the ocean. If you had to hide from GPS, your best bet would be underwater.

Because radio waves quickly deteriorate as they move through water, subsea communications often depend on acoustic signals instead. Sound waves travel faster and further underwater than through air, making them an efficient way to send data. But there’s a drawback.

“Sound is power-hungry,” says Adib. For tracking devices that produce acoustic signals, “their batteries can drain very quickly.” That makes it hard to precisely track objects or animals for a long time-span — changing a battery is no simple task when it’s attached to a migrating whale. So, the team sought a battery-free way to use sound.

Good vibrations

Adib’s group turned to a unique resource they’d previously used for low-power acoustic signaling: piezoelectric materials. These materials generate their own electric charge in response to mechanical stress, like getting pinged by vibrating soundwaves. Piezoelectric sensors can then use that charge to selectively reflect some soundwaves back into their environment. A receiver translates that sequence of reflections, called backscatter, into a pattern of 1s (for soundwaves reflected) and 0s (for soundwaves not reflected). The resulting binary code can carry information about ocean temperature or salinity.

In principle, the same technology could provide location information. An observation unit could emit a soundwave, then clock how long it takes that soundwave to reflect off the piezoelectric sensor and return to the observation unit. The elapsed time could be used to calculate the distance between the observer and the piezoelectric sensor. But in practice, timing such backscatter is complicated, because the ocean can be an echo chamber.

The sound waves don’t just travel directly between the observation unit and sensor. They also careen between the surface and seabed, returning to the unit at different times. “You start running into all of these reflections,” says Adib. “That makes it complicated to compute the location.” Accounting for reflections is an even greater challenge in shallow water — the short distance between seabed and surface means the confounding rebound signals are stronger.

The researchers overcame the reflection issue with “frequency hopping.” Rather than sending acoustic signals at a single frequency, the observation unit sends a sequence of signals across a range of frequencies. Each frequency has a different wavelength, so the reflected sound waves return to the observation unit at different phases. By combining information about timing and phase, the observer can pinpoint the distance to the tracking device. Frequency hopping was successful in the researchers’ deep-water simulations, but they needed an additional safeguard to cut through the reverberating noise of shallow water.

Where echoes run rampant between the surface and seabed, the researchers had to slow the flow of information. They reduced the bitrate, essentially waiting longer between each signal sent out by the observation unit. That allowed the echoes of each bit to die down before potentially interfering with the next bit. Whereas a bitrate of 2,000 bits/second sufficed in simulations of deep water, the researchers had to dial it down to 100 bits/second in shallow water to obtain a clear signal reflection from the tracker. But a slow bitrate didn’t solve everything.

To track moving objects, the researchers actually had to boost the bitrate. One thousand bits/second was too slow to pinpoint a simulated object moving through deep water at 30 centimeters/second. “By the time you get enough information to localize the object, it has already moved from its position,” explains Afzal. At a speedy 10,000 bits/second, they were able to track the object through deep water.

Efficient exploration

Adib’s team is working to improve the UBL technology, in part by solving challenges like the conflict between low bitrate required in shallow water and the high bitrate needed to track movement. They’re working out the kinks through tests in the Charles River. “We did most of the experiments last winter,” says Rodriguez. That included some days with ice on the river. “It was not very pleasant.”

Conditions aside, the tests provided a proof-of-concept in a challenging shallow-water environment. UBL estimated the distance between a transmitter and backscatter node at various distances up to nearly half a meter. The team is working to increase UBL’s range in the field, and they hope to test the system with their collaborators at the Wood Hole Oceanographic Institution on Cape Cod.

They hope UBL can help fuel a boom in ocean exploration. Ghaffarivardavagh notes that scientists have better maps of the moon’s surface than of the ocean floor. “Why can’t we send out unmanned underwater vehicles on a mission to explore the ocean? The answer is: We will lose them,” he says.

UBL could one day help autonomous vehicles stay found underwater, without spending precious battery power. The technology could also help subsea robots work more precisely, and provide information about climate change impacts in the ocean. “There are so many applications,” says Adib. “We’re hoping to understand the ocean at scale. It’s a long-term vision, but that’s what we’re working toward and what we’re excited about.”

This work was supported, in part, by the Office of Naval Research.

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National Science Foundation Convergence Accelerator awards two grants to MIT

Two grants have been awarded to MIT researchers on the themes of socio-resilient infrastructure, and on the future of oceans. The grants are part of the U.S. National Science Foundation Convergence Accelerator program, designed to foster global cross-disciplinary and cross-sector workshops on emerging areas of critical societal importance. The NSF Convergence Accelerator program further aims to accelerate use-inspired, convergence research via partnerships between academic and non-academic stakeholders.

Socio-resilient infrastructures

The Socioresilient Infrastructure: Precision Materials, Assemblages, and Systems project is co-led by Christine Ortiz, the Morris Cohen Professor of Materials Science and Engineering, and Ellan Spero, a historian of science and technology and instructor in the Department of Materials Science and Engineering. This project will engage leading researchers from around the world to advance an intellectual framework for socio-resilient infrastructure, where social resilience is considered to be the ability of human communities to cope with and adapt to stresses and shocks such as social, political, environmental, or economic change.

This workshop will integrate exciting advances across length scales from materials (i.e., materials science and engineering, chemistry, and mechanical engineering) to assemblages (i.e., civil, structural, and environmental engineering; architecture; art and design) to systems (i.e., engineering systems, computer science and engineering, urban studies and planning including civic design and engagement). It will incorporate and center cross-cutting humanistic and socially-focused research in material culture, social justice, equity-based, community and participatory co-design, environmental and social life cycle assessment, socio-technical and sociological analysis (i.e., social sciences, STS, history).

Broad topic areas will include emerging approaches to socio-resilient and circular materials design, structural engineering, and intelligent infrastructure systems. The merging of ideas, new computational and manufacturing technologies, and research methods across disparate disciplines is expected to lead to the development of equitable, inclusive, and sustainable innovation and commercialization of socio-resilient infrastructure.

The future of oceans

In addition, the Signal Kinetics Group at the MIT Media Lab has joined forces with the Woods Hole Oceanographic Institution (WHOI) to spearhead Smart Oceans 2020, a series of cross-cutting, multidisciplinary virtual plenaries and workshops to be held the week of Oct. 5-9. Under the leadership of Media Lab associate professor and Doherty Chair Fadel Adib and WHOI’s assistant scientist Seth Zippel, this conference will “blue sky” the future of the ocean, aiming to accelerate the field of ocean science.

The conference will feature a mix of invited plenary speakers, lightning talks, and brainstorming sessions, all with the purpose of accelerating use-inspired convergence research. The goal of the conference organizers is to foster a wealth of synergy, connections, and cooperation, which will lead to partnerships between academia, industry, non-governmental organizations, government, philanthropy, and venture capital across sectors such as climate and environmental sustainability, computing, marine biology and ecology, geopolitics, and defense.

“This workshop is a tremendously exciting opportunity to bring together communities in the ocean sciences who don’t necessarily cross paths,” comments Lara Campbell, program director for the NSF Convergence Accelerator Program in the Office of Integrative Activities at the U.S. National Science Foundation. “More valuable still, it’s a chance to think together about what the greatest opportunities are for accelerating research into near-term impacts that allow us to sustainably engage with the tremendous resources of the oceans.”

The organizers of Smart Oceans 2020 are hopeful that by identifying convergent approaches for ocean innovation, exploration, and utilization, this series of workshops will have a direct impact on issues of sustainability, national security, and national industries. “The series of workshops will cover a variety of exciting topics, ranging from designing and building an ocean internet-of-things to identifying convergent approaches to address climate challenges,” notes Adib. “The NSF convergence accelerator is uniquely positioned to propel this field forward, as it has done for other topics through investments of over $50 million.” 

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MIT research on seawater surface tension becomes international guideline

The property of water that enables a bug to skim the surface of a pond or keeps a carefully placed paperclip floating on the top of a cup of water is known as surface tension. Understanding the surface tension of water is important in a wide range of applications including heat transfer, desalination, and oceanography. Although much is known about the surface tension of fresh water, very little has been known about the surface tension of seawater — until recently.

In 2012, John Lienhard, the Abdul Latif Jameel Professor of Water and Mechanical Engineering, and then-graduate student Kishor Nayar SM ’14, PhD ’19 embarked on a research project to understand how the surface tension of seawater changes with temperature and salinity. Two years later, they published their findings in the Journal of Physical and Chemical Reference Data. This spring, the International Association for the Properties of Water and Steam (IAPWS) announced that they had deemed Lienhard and Nayar’s work an international guideline.

According to the IAPWS, Lienhard and Nayar’s research “presents a correlation for the surface tension of seawater as a function of temperature and salinity.” The announcement of the guideline marked the completion of eight years of work with dozens of collaborators from MIT and across the globe.

“This project grew out of my work in desalination. In desalination, you need to know about the surface tension of water because that affects how water travels through pores in a membrane,” explains Lienhard, a world leading expert in desalination — the process by which salt water is treated to become potable freshwater.

Lienhard suggested Nayar take measurements of seawater’s surface tension and compare the results to the surface tension of pure water. As they would soon find out, getting reliable data from salt water would prove to be incredibly difficult. 

“We had thought originally that these experiments would be pretty simple to do, that we'd be done in a month or two. But as we started looking into it, we realized it was a much harder problem to tackle,” says Lienhard.

From the outset, Nayar hoped to get enough accurate data to inform a property standard. Doing so would require the uncertainty in the measurements to be less than 1 percent.

“When you talk about property measurements, you need to be as accurate as possible,” explains Nayar. The first hurdle he had to surmount to achieve this level of accuracy was finding the appropriate instrumentation to make reliable measurements — something that turned out to be no easy feat.

Measuring surface tension

To measure the surface tension of water, Lienhard and Nayar teamed up with Gareth McKinley, professor of mechanical engineering, and then-graduate student Divya Panchanathan SM '15, PhD '18. They began with a device known as a Wilhelmy plate, which finds the surface tension by lowering a small platinum plate into a beaker of water then measuring the force the water exerts as the plate is raised.

Nayar and Panchanathan struggled to measure the surface tension of salt water at higher temperatures. “The issue we kept finding was once the temperature was above 50 degrees Celsius, the water on the beaker evaporated faster than we could take the measurements,” Nayar says. 

No instrument would allow them to get the data they needed — so Nayar turned to the MIT Hobby Shop. Using a lathe, he built a special lid for the beaker to keep vapor in.

“The little lid Kishor built had accurately cut doors that allowed him to put a surface tension probe through the lid without letting water vapor get out,” explains Lienhard.

After making progress on obtaining data, the team suffered a massive setback. They found that barely visible salt scales, which formed on their test beaker over time, had introduced errors to their measurements. To get the most accurate values, they decided to use fresh new beakers for every single test. As a result, Nayar had to repeat nine months of work just prior to his master’s thesis being due. Fortunately, since the main problem was identified and solved, experiments could be repeated much faster.

Nayar was able to redo the experiments on time. The team measured surface tension in seawater ranging from room temperature to 90 degrees Celsius and salinity levels ranging from pure water to four times the salinity of ocean water. They found that surface tension decreases by roughly 20 percent as water goes from room temperature toward boiling. Meanwhile, as salinity increases, surface tension increases as well. The team had unlocked the mystery of seawater surface tension.

“It was literally the most technically challenging thing I had ever done,” Nayar recalls.

Their data had an average deviation of 0.19 percent, with a maximum deviation of just 0.6 percent — well within the 1 percent bound needed for a guideline.

From master’s thesis to international guideline

Three years after completing his master’s thesis, Nayar, by then a PhD student, attended an IAPWS meeting in Kyoto, Japan. The IAPWS is a nonprofit international organization responsible for releasing standards on the properties of water and steam. There, Nayar met with leaders in the field of water surface tension who had been struggling with the same issues Nayar had faced. These contacts introduced him to the long, rigorous process of declaring something an international guideline.

The IAPWS had previously published standards on the properties of steam developed by the late Joseph Henry Keenan, professor and one-time department head of mechanical engineering at MIT. To join Keenan as authors of an IAPWS standard, the team’s data needed to be verified by measurements conducted by other researchers. After three years of working with the IAPWS, the team’s work was finally adopted as an international guideline.

For Nayar, who graduated with his PhD last year and is now a senior industrial water/wastewater engineer at engineering consulting firm GHD, the guideline announcement made the long months collecting data well worth it. “It felt like something getting completed,” he recalls. 

The findings that Nayar, Panchanathan, McKinley, and Lienhard reported back in 2014 are broadly applicable to a number of industries, according to Lienhard. “It’s certainly relevant for desalination work, but also for oceanographic problems such as capillary wave dynamics,” he explains.

It also helps explain how small things — like a bug or a paperclip — can float on seawater.

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Machine learning helps map global ocean communities

On land, it’s fairly obvious where one ecological region ends and another begins, for instance at the boundary between a desert and savanna. In the ocean, much of life is microscopic and far more mobile, making it challenging for scientists to map the boundaries between ecologically distinct marine regions.

One way scientists delineate marine communities is through satellite images of chlorophyll, the green pigment produced by phytoplankton. Chlorophyll concentrations can indicate how rich or productive the underlying ecosystem might be in one region versus another. But chlorophyll maps can only give an idea of the total amount of life that might be present in a given region. Two regions with the same concentration of chlorophyll may in fact host very different combinations of plant and animal life.

“It’s like if you were to look at all the regions on land that don’t have a lot of biomass, that would include Antarctica and the Sahara, even though they have completely different ecological assemblages,” says Maike Sonnewald, a former postdoc in MIT’s Department of Earth, Atmospheric and Planetary Sciences.

Now Sonnewald and her colleagues at MIT have developed an unsupervised machine-learning technique that automatically combs through a highly complicated set of global ocean data to find commonalities between marine locations, based on their ratios and interactions between multiple phytoplankton species. With their technique, the researchers found that the ocean can be split into over 100 types of “provinces” that are distinct in their ecological makeup. Any given location in the ocean would conceivably fit into one of these 100 ecological  provinces.

The researchers then looked for similarities between these 100 provinces, ultimately grouping them into 12 more general categories. From these “megaprovinces,” they were able to see that, while some had the same total amount of life within a region, they had very different community structures, or balances of animal and plant species. Sonnewald says capturing these ecological subtleties is essential to tracking the ocean’s health and productivity.

“Ecosystems are changing with climate change, and the community structure needs to be monitored to understand knock on effects on fisheries and the ocean’s capacity to draw down carbon dioxide,” Sonnewald says. “We can't fully understand these vital dynamics with conventional methods, that to date don’t include the ecology that’s there. But our method, combined with satellite data and other tools, could offer important progress.”

Sonnewald, who is now an associate research scholar at Princeton University and a visitor at the University of Washington, has reported the results today in the journal Science Advances. Her coauthors at MIT are Senior Research Scientist Stephanie Dutkiewitz, Principal Research Engineer Christopher Hill, and Research Scientist Gael Forget.

Rolling out a data ball

The team’s new machine learning technique, which they’ve named SAGE, for the Systematic AGgregated Eco-province method, is designed to take large, complicated datasets, and probabilistically project that data down to a simpler, lower-dimensional dataset.

“It’s like making cookies,” Sonnewald says. “You take this horrifically complicated ball of data and roll it out to reveal its elements.”

In particular, the researchers used a clustering algorithm that Sonnewald says is designed to “crawl along a dataset” and hone in on regions with a large density of points — a sign that these points share something in common. 

Sonnewald and her colleagues set this algorithm loose on ocean data from MIT’s Darwin Project, a three-dimensional model of the global ocean that combines a model of the ocean’s climate, including wind, current, and temperature patterns, with an ocean ecology model. That model includes 51 species of phytoplankton and the ways in which each species grows and interacts with each other as well as with the surrounding climate and available nutrients.

If one were to try and look through this very complicated, 51-layered space of data, for every available point in the ocean, to see which points share common traits, Sonnewald says the task would be “humanly intractable.” With the team’s unsupervised machine learning algorithm, such commonalities “begin to crystallize out a bit.”

This first “data cleaning” step in the team’s SAGE method was able to parse the global ocean into about 100 different ecological provinces, each with a distinct balance of species.

The researchers assigned each available location in the ocean model to one of the 100 provinces, and assigned a color to each province. They then generated a map of the global ocean, colorized by province type.  

“In the Southern Ocean around Antarctica, there’s burgundy and orange colors that are shaped how we expect them, in these zonal streaks that encircle Antarctica,” Sonnewald says. “Together with other features, this gives us a lot of confidence that our method works and makes sense, at least in the model.”

Ecologies unified

The team then looked for ways to further simplify the more than 100 provinces they identified, to see whether they could pick out commonalities even among these ecologically distinct regions.

“We started thinking about things like, how are groups of people distinguished from each other? How do we see how connected to each other we are? And we used this type of intuition to see if we could quantify how ecologically similar different provinces are,” Sonnewald says.

To do this, the team applied techniques from graph theory to represent all 100 provinces in a single graph, according to biomass — a measure that’s analogous to the amount of chlorophyll produced in a region. They chose to group the 100 provinces into 12 general categories, or “megaprovinces.” When they compared these megaprovinces, they found that those that had a similar biomass were composed of very different biological species.

“For instance, provinces D and K have almost the same amount of biomass, but when we look deeper, K has diatoms and hardly any prokaryotes, while D has hardly any diatoms, and a lot of prokaryotes. But from a satellite, they could look the same,” Sonnewald says. “So our method could start the process of adding the ecological information to bulk chlorophyll measures, and ultimately aid observations.”

The team has developed an online widget that researchers can use to find other similarities among the 100 provinces. In their paper, Sonnewald’s colleagues chose to group the provinces into 12 categories. But others may want to divide the provinces into more groups, and drill down into the data to see what traits are shared among these groups.

Sonnewald is sharing the tool with oceanographers who want to identify precisely where regions of a particular ecological makeup are located, so they could, for example, send ships to sample in those regions, and not in others where the balance of species might be slightly different.

“Instead of guiding sampling with tools based on bulk chlorophyll, and guessing where the interesting ecology could be found with this method, you can surgically go in and say, ‘this is what the model says you might find here,’” Sonnewald says. “Knowing what species assemblages are where, for things like ocean science and global fisheries, is really powerful.”

This research was funded, in part, by NASA and the Jet Propulsion Laboratory.

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Search-and-rescue algorithm identifies hidden “traps” in ocean waters

The ocean is a messy and turbulent space, where winds and weather kick up waves in all directions. When an object or person goes missing at sea, the complex, constantly changing conditions of the ocean can confound and delay critical search-and-rescue operations.

Now researchers at MIT, the Swiss Federal Institute of Technology (ETH), the Woods Hole Oceanographic Institution (WHOI), and Virginia Tech have developed a technique that they hope will help first responders quickly zero in on regions of the sea where missing objects or people are likely to be.

The technique is a new algorithm that analyzes ocean conditions such as the strength and direction of ocean currents, surface winds, and waves , and identifies in real-time the most attracting regions of the ocean where floating objects are likely to converge.

The team demonstrated the technique in several field experiments in which they deployed drifters and human-shaped manikins in various locations in the ocean. They found that over the course of a few hours, the objects migrated to the regions that the algorithm predicted would be strongly attracting, based on the present ocean conditions.

The algorithm can be applied to existing models of ocean conditions in a way that allows rescue teams to quickly uncover hidden “traps” where the ocean may be steering missing people at a given time.

“This new tool we’ve provided can be run on various models to see where these traps are predicted to be, and thus the most likely locations for a stranded vessel or missing person,” says Thomas Peacock, professor of mechanical engineering at MIT. “This method uses data in a way that it hasn’t been used before, so it provides first responders with a new perspective.”

Peacock and Pierre Lermusiaux, also a professor of mechanical engineering at MIT, who oversaw the project, and their colleagues report their results in a study published today in the journal Nature Communications. Their coauthors are lead author Mattia Serra and corresponding author George Haller of ETH Zurich, Irina Rypina and Anthony Kirincich of WHOI, Shane Ross of Virginia Tech, Arthur Allen of the U.S. Coast Guard, and Pratik Sathe of the University of California at Los Angeles.

Hidden traps

Today’s search-and-rescue operations combine weather forecasts with models of both ocean dynamics and the ways in which objects can drift through the ocean, to map out a search plan, or regions where teams should concentrate their search.

But the ocean is a complicated space of unsteady, ever-changing flow patterns. Coupled with the fact that a missing person has likely been continuously floating through this unsteady flow field for some time, Peacock and his colleagues say that significant errors can accumulate in predicting where to look first, when using a simple approach that directly predicts the trajectories of a few drifting objects.

Instead, the team developed a method to interpret the ocean’s complex flows using advanced, data-driven ocean modeling and prediction systems. They used a novel “Eulerian” approach, in contrast to more commonly used “Lagrangian” approaches — mathematical techniques that involve integrating snapshots of the ocean velocity due to waves and currents to slowly generate an uncertain trajectory for where a missing person or object may have been carried.

The new Eulerian approach uses the most reliable velocity forecast snapshots, close to the point where a missing person or object was last seen, and quickly uncovers the most attracting regions of the ocean at a given time. These Eulerian predictions are then continuously updated when the next batch of updated velocity information becomes available.

The team has named their approach TRAPS, for its goal of identifying TRansient Attracting Profiles, or short-lived regions where water may converge and be likely to pull objects or people. The method is based on a recent mathematical theory,

developed by Serra and Haller at ETH Zurich, to uncover hidden attracting structures in highly unsteady flow data.

“We were a bit skeptical whether a mathematical theory like this would work out on a ship, in real time,” Haller says. “We were all pleasantly surprised to see how well it repeatedly did.”

“We can think of these ‘traps’ as moving magnets, attracting a set of coins thrown on a table. The Lagrangian trajectories of coins are very uncertain, yet the strongest Eulerian magnets predict the coin positions over short times,” Serra says.

“The key thing is, the traps may not have any signature in the ocean current field,” Peacock adds. “If you do this processing for the traps, they might pop up in very different places from where you’re seeing the ocean current projecting where you might go. So you have to do this other level of processing to pull out these structures. They’re not immediately visible.”

Out at sea

Led by WHOI sea-going experts, the researchers tested the TRAPS approach in several experiments out at sea. “As with any new theoretical technique, it is important to test how well it works in the real ocean,” Rypina says.

In 2017 and 2018, the team sailed a small research vessel several hours out off the coast of Martha’s Vineyard, where they deployed at various locations, an array of small round buoys, and manikins.

“These objects tend to travel differently relative to the ocean because different shapes feel the wind and currents differently,” Peacock says. “Even so, the traps are so strongly attracting and robust to uncertainties that they should overcome these differences and pull everything onto them.”

The team ran their modeling and prediction systems, forecasting the ocean’s behavior and currents, and used the TRAPS algorithm to map out strongly attracting regions over the course of the experiment. The researchers let the objects drift freely with the currents for a few hours, and recorded their positions via GPS trackers, before retrieving the objects at the end of the day.

“With the GPS trackers, we could see where everything was going, in real-time,” Peacock says. “So we laid out this initial, widespread pattern of the drifters, and saw that, in the end, they converged on these traps.”

The researchers are planning to share the TRAPS method with first responders such as the U.S. Coast Guard, as a way to speed up search-and-rescue algorithms, and potentially save many more people lost at sea.

“People like Coast Guard are constantly running simulations and models of what the ocean currents are doing at any particular time and they’re updating them with the best data that inform that model,” Peacock says. “Using this method, they can have knowledge right now of where the traps currently are, with the data they have available. So if there’s an accident in the last hour, they can immediately look and see where the sea traps are. That’s important for when there’s a limited time window in which they have to respond, in hopes of a successful outcome.”

This research was primarily funded by the National Science Foundation’s Hazards SEES program, with additional support from the Office of Naval Research and the German National Science Foundation.

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Towable sensor free-falls to measure vertical slices of ocean conditions

The motion of the ocean is often thought of in horizontal terms, for instance in the powerful currents that sweep around the planet, or the waves that ride in and out along a coastline. But there is also plenty of vertical motion, particularly in the open seas, where water from the deep can rise up, bringing nutrients to the upper ocean, while surface waters sink, sending dead organisms, along with oxygen and carbon, to the deep interior.

Oceanographers use instruments to characterize the vertical mixing of the ocean’s waters and the biological communities that live there. But these tools are limited in their ability to capture small-scale features, such as the up- and down-welling of water and organisms over a small, kilometer-wide ocean region. Such features are essential for understanding the makeup of marine life that exists in a given volume of the ocean (such as in a fishery), as well as the amount of carbon that the ocean can absorb and sequester away.

Now researchers at MIT and the Woods Hole Oceanographic Institution (WHOI) have engineered a lightweight instrument that measures both physical and biological features of the vertical ocean over small, kilometer-wide patches. The “ocean profiler,” named EcoCTD, is about the size of a waist-high model rocket and can be dropped off the back of a moving ship. As it free-falls through the water, its sensors measure physical features, such as temperature and salinity, as well as biological properties, such as the optical scattering of chlorophyll, the green pigment of phytoplankton.

“With EcoCTD, we can see small-scale areas of fast vertical motion, where nutrients could be supplied to the surface, and where chlorophyll is carried downward, which tells you this could also be a carbon pathway. That’s something you would otherwise miss with existing technology,” says Mara Freilich, a graduate student in MIT’s Department of Earth, Atmospheric, and Planetary Sciences and the MIT-WHOI Joint Program in Oceanography/Applied Ocean Sciences and Engineering.

Freilich and her colleagues have published their results today in the Journal of Atmospheric and Oceanic Technology. The paper’s co-authors are J. Thomas Farrar, Benjamin Hodges, Tom Lanagan, and Amala Mahadevan of WHOI, and Andrew Baron of Dynamic System Analysis, in Nova Scotia. The lead author is Mathieu Dever of WHOI and RBR, a developer of ocean sensors based in Ottawa.

Ocean synergy

Oceanographers use a number of methods to measure the physical properties of the ocean. Some of the more powerful, high-resolution instruments used are known as CTDs, for their ability to measure the ocean’s conductivity, temperature, and depth. CTDs are typically bulky, as they contain multiple sensors as well as components that collect water and biological samples. Conventional CTDs require a ship to stop as scientists lower the instrument into the water, sometimes via a crane system. The ship has to stay put as the instrument collects measurements and water samples, and can only get back underway after the instrument is hauled back onboard.

Physical oceanographers who do not study ocean biology, and therefore do not need to collect water samples, can sometimes use “UCTDs” — underway versions of CTDs, without the bulky water sampling components, that can be towed as a ship is underway. These instruments can sample quickly since they do not require a crane or a ship to stop as they are dropped.

Freilich and her team looked to design a version of a UCTD that could also incorporate biological sensors, all in a small, lightweight, towable package, that would also keep the ship moving on course as it gathered its vertical measurements.

“It seemed there could be straightforward synergy between these existing instruments, to design an instrument that captures physical and biological information, and could do this underway as well,” Freilich says.

“Reaching the dark ocean”

The core of the EcoCTD is the RBR Concerto Logger, a sensor that measures the temperature of the water, as well as the conductivity, which is a proxy for the ocean’s salinity. The profiler also includes a lead collar that provides enough weight to enable the instrument to free-fall through the water at about 3 meters per second — a rate that takes the instrument down to about 500 meters below the surface in about two minutes.

“At 500 meters, we’re reaching the upper twilight zone,” Freilich says. “The euphotic zone is where there’s enough light in the ocean for photosynthesis, and that’s at about 100 to 200 meters in most places. So we’re reaching the dark ocean.”

Another sensor, the EcoPuck, is unique to other UCTDs in that it measures the ocean’s biological properties. Specifically, it is a small, puck-shaped bio-optical sensor that emits two wavelengths of light — red and blue. The sensor captures any change in these lights as they scatter back and as chlorophyll-containing phytoplankton fluoresce in response to the light. If the red light received resembles a certain wavelength characteristic of chlorophyll, scientists can deduce the presence of phytoplankton at a given depth. Variations in red and blue light scattered back to the sensor can indicate other matter in the water, such as sediments or dead cells — a measure of the amount of carbon at various depths.

The EcoCTD includes another sensor unique to UCTDs — the Rinko III Do, which measures the oxygen concentration in water, which can give scientists an estimate of how much oxygen is being taken up by any microbial communities living at a given depth and parcel of water.

Finally, the entire instrument is encased in a tube of aluminum and designed to attach via a long line to a winch at the back of a ship. As the ship is moving, a team can drop the instrument overboard and use the winch to pay the line out at a rate that the instrument drops straight down, even as the ship moves away. After about two minutes, once it has reached a depth of about 500 meters, the team cranks the winch to pull the instrument back up, at a rate that the  instrument catches up to the ship within 12 minutes. The crew can then drop the instrument again, this time at some distance from their last dropoff point.

“The nice thing is, by the time we go to the next cast, we’re 500 meters away from where we were the first time, so we’re exactly where we want to sample next,” Freilich says.

They tested the EcoCTD on two cruises in 2018 and 2019, one to the Mediterranean and the other in the Atlantic, and in both cases were able to collect both physical and biological data at a higher resolution than existing CTDs.

“The ecoCTD is capturing these ocean characteristics at a gold-standard quality with much more convenience and versatility,” Freilich says.

The team will further refine their design, and hopes that their high-resolution, easily-deployable, and more efficient alternative may be adapted by both scientists to monitor the ocean’s small-scale responses to climate change, as well as fisheries that want to keep track of a certain region’s biological productivity.  

This research was funded in part by the U.S. Office of Naval Research.

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Melting glaciers cool the Southern Ocean

Tucked away at the very bottom of the globe surrounding Antarctica, the Southern Ocean has never been easy to study. Its challenging conditions have placed it out of reach to all but the most intrepid explorers. For climate modelers, however, the surface waters of the Southern Ocean provide a different kind of challenge: It doesn’t behave the way they predict it would. “It is colder and fresher than the models expected,” says Craig Rye, a postdoc in the group of Cecil and Ida Green Professor of Oceanography John Marshall within MIT’s Department of Earth, Atmospheric and Planetary Sciences (EAPS).

In recent decades, as the world warms, the Southern Ocean’s surface temperature has cooled, allowing the amount of ice that crystallizes on the surface each winter to grow. This is not what climate models anticipated, and a recent study accepted in Geophysical Research Letters attempts to disentangle that discrepancy. “This paper is motivated by a disagreement between what should be happening according to simulations and what we observe,” says Rye, the lead author of the paper who is currently working remotely from NASA’s Goddard Institute for Space Studies, or GISS, in New York City.

“This is a big conundrum in the climate community,” says Marshall, a co-author on the paper along with Maxwell Kelley, Gary Russell, Gavin A. Schmidt, and Larissa S. Nazarenko of GISS; James Hansen of Columbia University’s Earth Institute; and Yavor Kostov of the University of Exeter. There are 30 or so climate models used to foresee what the world might look like as the climate changes. According to Marshall, models don’t match the recent observations of surface temperature in the Southern Ocean, leaving scientists with a question that Rye, Marshall, and their colleagues intend to answer: how can the Southern Ocean cool when the rest of the Earth is warming?

This isn’t the first time Marshall has investigated the Southern Ocean and its climate trends. In 2016, Marshall and Yavor Kostov PhD ’16 published a paper exploring two possible influences driving the observed ocean trends: greenhouse gas emissions, and westerly winds — strengthened by expansion of the Antarctic ozone hole — blowing cold water northward from the continent. Both explained some of the cooling in the Southern Ocean, but not all of it. “We ended that paper saying there must be something else,” says Marshall.

That something else could be meltwater released from thawing glaciers. Rye has probed the influence of glacial melt in the Southern Ocean before, looking at its effect on sea surface height during his PhD at the University of Southampton in the UK. “Since then, I’ve been interested in the potential for glacial melt playing a role in Southern Ocean climate trends,” says Rye.

The group’s recent paper uses a series of “perturbation” experiments carried out with the GISS global climate model where they abruptly introduce a fixed increase in melt water around Antarctica and then record how the model responds. The researchers then apply the model’s response to a previous climate state to estimate how the climate should react to the observed forcing. The results are then compared to the observational record, to see if a factor is missing. This method is called hindcasting.

Marshall likens perturbation experiments to walking into a room and being confronted with an object you don’t recognize. “You might give it a gentle whack to see what it’s made of,” says Marshall. Perturbation experiments, he explains, are like whacking the model with inputs, such as glacial melt, greenhouse gas emissions, and wind, to uncover the relative importance of these factors on observed climate trends.

In their hindcasting, they estimate what would have happened to a pre-industrial Southern Ocean (before anthropogenic climate change) if up to 750 gigatons of meltwater were added each year. That quantity of 750 gigatons of meltwater is estimated from observations of both floating ice shelves and the ice sheet that lies over land above sea level. A single gigaton of water is very large — it can fill 400,000 Olympic swimming pools, meaning 750 gigatons of meltwater is equivalent to pouring water from 300 million Olympic swimming pools into the ocean every year.

When this increase in glacial melt was added to the model, it led to sea surface cooling, decreases in salinity, and expansion of sea ice coverage that are consistent with observed trends in the Southern Ocean during the last few decades. Their model results suggest that meltwater may account for the majority of previously misunderstood Southern Ocean cooling.

The model shows that a warming climate may be driving, in a counterintuitive way, more sea ice by increasing the rate of melting of Antarctica’s glaciers. According to Marshall, the paper may solve the disconnect between what was expected and what was observed in the Southern Ocean, and answers the conundrum he and Kostov pointed to in 2016. “The missing process could be glacial melt.”

Research like Rye’s and Marshall’s help project the future state of Earth’s climate and guide society’s decisions on how to prepare for that future. By hindcasting the Southern Ocean’s climate trends, they and their colleagues have identified another process, which must be incorporated into climate models. “What we’ve tried to do is ground this model in the historical record,” says Marshall. Now the group can probe the GISS model response with further “what if?” glacial melt scenarios to explore what might be in store for the Southern Ocean.

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Protecting seafarers and the global supply chain during Covid-19

The offshore and shipping industries are grappling with unique challenges in the face of the Covid-19 pandemic. The virus’ rapid spread on ships like the Diamond Princess and USS Theodore Roosevelt highlighted the health risks that the 1.2 million workers currently at sea face. Travel restrictions and closed borders offer an additional challenge by not only disrupting the global supply chain, but preventing scheduled crew changeovers from taking place.

To address these issues, the UN Global Compact Action Platform for Sustainable Ocean Business recently released recommendations developed by their Covid-19 Task Force. Thomas Peacock, professor of mechanical engineering, is a member of the task force, along with representatives from professional societies, international agencies, industry, nonprofits, and academia.

According to the UN, 90 percent of traded goods are transported via shipping. On a typical day, there are 50,000 vessels at sea, making a total of 4 million ports of call annually. Meanwhile, offshore platforms supply one third of the world’s oil and gas.

“The shipping and offshore industries are the heart of the global supply chains,” explains Peacock. “Governments need to take a unified approach to not only avoid disruptions to the international supply chain, but to protect the health of seafarers.”

Peacock has conducted research at sea for 15 years on global-class research vessels and aboard local coastal vessels all over the world — from the South China Sea to the Arctic. Peacock was originally connected to the UN Global Compact through the MIT Policy Lab at the Center for International Studies for his extensive work in deep-sea mining.

As Covid-19 began its global spread, the UN Global Compact focused on the associated challenges. They drafted a plan to operate in phases, or “short sprints.” “The goal of this first ‘short sprint’ has been to identify the most pressing issues and try and deal with them first,” adds Peacock.

The result is a list of 14 recommendations that help “ensure the continuing safe and efficient function of ocean-related supply chains during the Covid-19 pandemic.” One main theme that emerges from these recommendations is that in order to protect both seafarers and the global supply chain, a unified international response will be vital.

Ensuring the health and safety of seafarers

After the plight of cruise ships and news broke about the Covid-19 cases aboard the USS Roosevelt, concerns about the impact the pandemic may have on seafarers increased. “The USS Roosevelt will have world-class medical capabilities on board,” explains Peacock. “If that level of offshore vessel faced challenges coping with a Covid outbreak, you can appreciate the challenges facing a commercial shipping fleet.”

The most pressing issue the shipping industry will face in the next few weeks relates to the changeover of crew onboard that typically takes places each month. The crew on shipping vessels rotate over a certain period of time — usually a few months. Each month, roughly 100,000 seafarers change over, with crew members who have been at sea relieved by a new set of crew members once they arrive in port. At present, new data from the International Chamber of Shipping suggest the current number is at 150,000.

As travel bans and restrictions were put in place across the world in March and April, the typical crew changeover that would have occurred in mid-April was put on hold. Crew members currently at sea had their contracts extended. Additionally, repair work and inspections have been delayed. With many of the travel restrictions still in place, a solution for May is urgently needed.

“There comes a point when you have to switch people out from the ship, get new people on board, and make any necessary repairs to vessels and offshore platforms,” says Peacock. “And so, unless appropriate action is taken, there could be major challenges pending regarding the May crew changeovers.” He adds, “It is also important to recognize the selfless contribution that many  seafarers have made in dealing with the situation throughout April by remaining at sea.”

One of the solutions the UN Global Compact Task Force recommends is classifying seafarers as “key workers” and deeming shipping and offshore activities an “essential service.” Doing so would help ensure the freedom of movement necessary to protect seafarers’ health and minimize impact to the global supply chain.

An international approach

Response to the spread of Covid-19 has varied widely across different countries. From quarantine measures to contact tracing and travel bans, government intervention has differed at the national, state, and local level. But when it comes to ocean supply chains, according to the UN Global Compact recommendations, a unified international approach is essential.

“If there are different rules and protocols in one country compared to another, this inevitably brings challenges,” explains Peacock. “As much as possible, there needs to be a unified approach and leading agencies such as the IMO, the ILO, the WHO, and many others have been working incredibly hard to develop protocols and recommendations.”

To help shape this international approach, the UN Global Compact Task Force has recommended the establishment of an Ocean Supply Chain Task Force in pursuit of “holistic and harmonized global cooperation and coordination to ensure the safety and integrity of ocean-related global supply chains.”

Another element that will need to be consistent across borders according to the UN Global Compact Task Force includes the certification and classification procedures

“Shipping relies on certification and classification programs that everyone has to abide by to be able operate,” adds Peacock. “Those take time to reassess, but there must be pragmatism in making certain allowances in light of this global pandemic.”

The recommendations outlined by the UN Global Compact Task Force serve as a first step toward addressing the threats Covid-19 brings to both the safety of those at sea and the integrity of the global supply chains. The task force will continue meeting to draft additional recommendations in the hopes that governments will work together and take an international approach.

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3 Questions: Harnessing wave power to rebuild islands

Many island nations, including the Maldives in the Indian Ocean, are facing an existential threat as a result of a rising sea level induced by global climate change. A group of MIT researchers led by Skylar Tibbits, an associate professor of design research in the Department of Architecture, is testing ways of harnessing nature’s own forces to help maintain and rebuild threatened islands and coastlines.

Some 40 percent of the world’s population lives in coastal areas that are threated by sea level rise over the coming decades, yet there are few proven measures for countering the threat. Some suggest building barrier walls, dredging coastlines to rebuild beaches, or building floating cities to escape the inevitable, but the search for better approaches continues.

The MIT group was invited by Invena, a group in the Maldives who had seen the researchers’ work on self-assembly and self-organization and wanted to collaborate on solutions to address sea-level rise. The resulting project has now shown promising initial results, with a foot and a half of localized sand accumulation deposited in just four months. MIT News asked Tibbits to describe the new approach and its potential.

Q: People have been trying to modify and control the movement of sand for centuries. What was the inspiration for this new and different approach to rebuilding beaches and shorelines?

A: When we first visited the Maldives, we were taken to a local sandbar that had just formed. It was incredible to see the size of the sandbar, about 100 meters long and 20 meters wide, and the quantity of sand, over 1 meter deep, that was built completely on its own, in just a matter of months. We came to understand that these sandbars appear and disappear at different times of the year based on the forces of the ocean and underwater bathymetry. Local historians told us about how they would collaborate with the ocean, growing vegetation to expand their islands or morph their shape. These natural and collaborative approaches to growing land mass through sand self-organization came in stark contrast to the human dredging of sand from the deep ocean, which is also used for island reclamation. In the same amount of time that it takes to dredge an island, which takes months, we watched three different sandbars form themselves, through satellite imagery.

We started to realize that the amount of energy, time, money, labor, and destruction of the marine environment that is caused by dredging could likely be stopped if we could understand why sandbars form naturally and tap into this natural phenomenon of self-organization. The goal of our lab and field experiments is to test hypotheses on why sandbars form, and translate those into mechanisms for promoting their accumulation in strategic locations.

By collaborating with the natural forces of the ocean we believe we can promote the self-organization of sand structures to grow islands and rebuild beaches. We believe this is a sustainable approach to the problem that can eventually be scaled to many coastal areas around the world, just as forest management is used to help strengthen and protect forests from uncontrolled fires or overgrowth.

Q: Can you describe how this system works, and how it harnesses the energy of the waves to build up the sand in the places where it's needed?

A: Together with our collaborators in the Maldives, we are designing, testing, building, and deploying submersible devices that, based simply on their geometry in relationship to the ocean waves and currents, promote sand accumulation in specific areas. In our first field experiment we built bladders out of heavy-duty canvas, sewn together into the precise ramp geometries. With our second field experiment, we took the best designs from hundreds of lab experiments and had them fabricated from a geotextile membrane. In both experiments we filled the bladders with sand to weigh them down and then submerged them underwater. For our next field experiment we are building bladders that have internal chambers that act like a ballast in a submarine, allowing the bladder to sink or float and to be quickly moved or deployed. Each experiment is attempting to make the fabrication and installation process as simple and scalable as possible.

The simplest mechanism that we are testing is a ramp-like geometry that sits on the ocean floor and rises vertically to the surface of the water. To the best of our understanding, what we are seeing is that as the water flows over the top of the ramp it creates turbulence on the other side, mixing the sand and water and then creating sediment transport. The sand begins to accumulate on the backside of the ramp, continually piling on top of itself. We have tested many other geometries that attempt to minimize wrap-around effects, or focus the accumulation in specific areas, and we are continuing to search for optimal geometries. In many ways, these behave like natural depth variations, reef structures, or volcanic formations and may function similarly in promoting sand accumulation. Our goal is to create adaptable versions of these geometries which can be easily moved, reoriented, or deployed whenever seasons change or storms are increasing.

Since 2018 we have been conducting experiments in our lab at MIT in collaboration with Taylor Perron in [the Department of] Earth, Atmospheric and Planetary Sciences. We have built two wave tanks where we are testing a variety of wave conditions, sand behaviors, and geometries to promote accumulation. The goal is to align our lab experiments and models with real-world conditions specific to the two predominant seasons in the Maldives. We have done hundreds of tank experiments so far and are using these studies to gain intuition and insight into what mechanisms result in the greatest sand accumulation. The best of these lab experiments is then translated to field experiments twice a year.

Q: How were you able to detect and quantify the effects of your experiment, and what are your plans for continuing and expanding this project?

A: We have collected satellite imagery, drone footage, and physical measurements ever since installing our first field experiment in February 2019 and our second field experiment in October / November 2019. The satellite images and drone footage give us a visual indication of sand accumulation; however, it is challenging to quantify the amount of sand from those images. So we rely heavily on physical depth measurements. We have a series of coordinates that we send to our collaborators in the Maldives who then take a boat or jet ski out to those coordinates and take depth measurements. We then compare these measurements with our previous measurements, considering the day/time and relationship to the tide height.

With our latest field experiment, we have been collecting imagery and physical measurements to analyze the sand accumulation. We are now seeing roughly a half meter (about 20 inches) of new sand accumulation over an area of approximately 20 meters by 30 meters, since November. That is about 300 cubic meters of sand accumulation, in roughly four months. We see these as promising early results that are part of a much longer-term initiative where we aim to continue to test these approaches in the Maldives and various other locations around the world.

We have recently been awarded a National Geographic Exploration grant and plan to go back to the Maldives for two more field installations later this year and in 2021. Our long-term goal is to create a system of submersible structures that can adapt to the dynamic weather conditions to naturally grow and rebuild coastlines. We aim to scale this approach and tailor it to many locations around the world to help rebuild and stabilize heavily populated coastlines and vulnerable island nations.

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Researchers explore ocean microbes’ role in climate effects

A new study shows that “hotspots” of nutrients surrounding phytoplankton — which are tiny marine algae producing approximately half of the oxygen we breathe every day — play an outsized role in the release of a gas involved in cloud formation and climate regulation.

The new research quantifies the way specific marine bacteria process a key chemical called dimethylsulfoniopropionate (DMSP), which is produced in enormous amounts by phytoplankton. This chemical plays a pivotal role in the way sulfur and carbon get consumed by microorganisms in the ocean and released into the atmosphere.

The work is reported today in the journal Nature Communications, in a paper by MIT graduate student Cherry Gao, former MIT professor of civil and environmental engineering Roman Stocker (now a professor at ETH Zurich, in Switzerland), in collaboration with Jean-Baptiste Raina and Professor Justin Seymour of University of Technology Sydney in Australia, and four others.

More than a billion tons of DMSP is produced annually by microorganisms in the oceans, accounting for 10 percent of the carbon that gets taken up by phytoplankton — a major “sink” for carbon dioxide, without which the greenhouse gas would be building up even faster in the atmosphere. But exactly how this compound gets processed and how its different chemical pathways figure into global carbon and sulfur cycles had not been well-understood until now, Gao says.

“DMSP is a major nutrient source for bacteria,” she says. “It satisfies up to 95 percent of bacterial sulfur demand and up to 15 percent of bacterial carbon demand in the ocean. So given the ubiquity and the abundance of DMSP, we expect that these microbial processes would have a significant role in the global sulfur cycle.”

Gao and her co-workers genetically modified a marine bacterium called Ruegeria pomeroyi, causing it to fluoresce when one of two different pathways for processing DMSP was activated, allowing the relative expression of the processes to be analyzed under a variety of conditions.

One of the two pathways, called demethylation, produces carbon and sulfur based nutrients that the microbes can use to sustain their growth. The other pathway, called cleavage, produces a gas called dimethylsulfide (DMS), which Gao explains “is the compound that’s responsible for the smell of the sea. I actually smelled the ocean a lot in the lab when I was experimenting.”

DMS is the gas responsible for most of the biologically derived sulfur that enters the atmosphere from the oceans. Once in the atmosphere, sulfur compounds are a key source of condensation for water molecules, so their concentration in the air affects both rainfall patterns and the overall reflectivity of the atmosphere through cloud generation. Understanding the process responsible for much of that production could be important in multiple ways for refining climate models.

Those climate implications are “why we're interested in knowing when bacteria decide to use the cleavage pathway versus the demethylation pathway,” in order to better understand how much of the important DMS gets produced under what conditions, Gao says. “This has been an open question for at least two decades.”

The new study found that the concentration of DMSP in the vicinity regulates which pathway the bacteria use. Below a certain concentration, demethylation was dominant, but above a level of about 10 micromoles, the cleavage process dominated.

“What was really surprising to us was, upon experimentation with the engineered bacteria, we found that the concentrations of DMSP in which the cleavage pathway dominates is higher than expected — orders of magnitude higher than the average concentration in the ocean,” she says.

That suggests that this process hardly takes place under typical ocean conditions, the researchers concluded. Rather, microscale “hotspots” of elevated DMSP concentration are probably responsible for a highly disproportionate amount of global DMS production. These microscale “hotspots” are areas surrounding certain phytoplankton cells where extremely high amounts of DMSP are present at about a thousand times greater than average oceanic concentration.

“We actually did a co-incubation experiment between the engineered bacteria and a DMSP-producing phytoplankton,” Gao says. The experiment showed “that indeed, bacteria increased their expression of the DMS-producing pathway, closer to the phytoplankton.”

The new analysis should help researchers understand key details of how these microscopic marine organisms, through their collective behavior, are affecting global-scale biogeochemical and climatic processes, the researchers say.

The research team included MIT and ETH Zurich postdocs Vicente Fernandez and Kang Soo Lee, graduate student Simona Fenizia, and Professor Georg Pohnert at Friedrich Schiller University in Germany. The work was supported by the Gordon and Betty Moore Foundation, the Simons Foundation, the National Science Foundation, and the Australian Research Council.

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3 Questions: Greg Britten on how marine life can recover by 2050

As the largest ecosystem on the planet, the ocean provides incredible resources and benefits to humanity — including contributing 2.5 percent of global GDP and 1.5 percent of global employment, as well as regulating our climate, providing clean energy, and producing much of the oxygen we breathe. But exploitation and human pressures — like pollution, overfishing, and climate change — have stressed its life-support systems, depleting biodiversity, reducing habitats, and undermining ocean productivity.

Study and public awareness of the of these problems, as well as the beauty of these ecosystems, has led to conservation efforts beginning in the 1980s. By that time, however, significant damage had been done and some losses were permanent. Years of increased management and international policy since then have made measurable gains. At the same time, growing human populations are leaning harder on ocean resources. Understanding the critical need to rebuild these habitats and species populations has reached the level of the United Nations, which instated the Sustainable Development Goal 14 to “conserve and sustainably use the oceans, seas and marine resources for sustainable development.” The effort sets benchmarks and indicators of environmental successes in the area but threats, both local and international, persist and in some cases are worsening.

In a new Nature Review paper, Greg Britten, a postdoc in the MIT Department of Earth, Atmospheric and Planetary Sciences, and his colleagues examine different aspects of marine life and argue that aggressive interventions could lead to recovery of marine life by 2050. Here, he elucidates some of the findings from this work, which was supported, in part, by the Simons Collaboration on Computational Biogeochemical Modeling of Marine Ecosystems/CBIOMES.

Q: What is the current state of the world’s marine life and what recovery efforts have been attempted in the past?

A: While marine populations have been exploited throughout all of human history, the rate and magnitude of exploitation expanded exponentially between the 1950s and 1990s, largely due to the advent of industrial-scale fishing technology and large-scale habitat destruction via development of coastal areas. By the year 2000, it was estimated that the oceans’ “big fish” (tunas, large sharks, and billfish) were depleted by 90 percent relative to pre-exploitation levels. Further, approximately 60 percent of the world’s fisheries were considered “collapsed,” meaning that catches were at, or below, 10 percent of their historical maximum. At the same time, habitat destruction reached unprecedented levels — particularly in coastal areas.

These findings caused a tremendous response when revealed to the public that led to widespread calls for conservation intervention. Since then, marine exploitation has been significantly curtailed in much of the developed world, to a point where levels of exploitation are widely considered “sustainable”. Major global policy initiatives, like the Convention on the Trade of Endangered Species (CITES) and improvements to the Clean Water Act, also significantly reduced conservation threats like pollution, as well as the implementation of the International Convention for the Prevention of Pollution from Ships.

But this does not mean that populations immediately rebounded — indeed, they did not. It can take many years and decades for populations to fully rebuild to previous levels after the rate of exploitation has been reduced, and the impact of historical pollution and habitat destruction can linger for decades or longer. Furthermore, rates of exploitation and habitat destruction in the rest of the developing world have not been reduced as quickly, or remain unknown, while agreements to limit pollution and habitat destruction are generally also much weaker in developing countries.

Q: Tell us about your assessment of various interventions and potential future outcomes. What efforts have been successful so far, and where is there room for improvement?

A: We used a very large synthesis of available data to calculate historical and future trajectories of depleted marine populations under various levels of exploitation globally. We also documented the rates of recovery of habitats and ecosystems after pollution reductions and remediations were implemented.

We found that conservation and pollution reduction efforts, along with global environmental policy initiatives, have had a strong net positive influence on the recovery of marine populations, habitats, and ecosystems. We documented many cases of coral reef and mangrove recovery after local pollution remediation efforts. These occurred on a similar time scale as fish stocks, ranging from one to two decades for saltmarshes, to 30 years to a century for deep-sea corals and sponges that grow more slowly and are facing climate change, trawling, and oil spills. Globally, our research showed that the number of species listed as endangered by the International Union for the Conversation of Nature decreased from 18 percent in 2000 to 11.4 percent in the 2019, while the area of Marine Protected Areas (MPAs) increased from 0.13 million square kilometers to 27.4 million over the same period. These MPAs help protect multiple layers of the ecosystem, from coastal habitats to fish and megafauna species. The switch to unleaded gasoline in the 1980s reduced marine lead concentrations to those comparable to the time before leaded gasoline was introduced, due to the relatively low residence time of lead in marine surface waters.

Going forward, we found the vast majority of populations and habitats (with available data) could be rebuilt based on documented recovery rates by the year 2050, if exploitation is not increased beyond current levels. However, large-scale environmental agreements were most successful in developed countries, whereas enforcement and financial commitment was generally poorer in developing countries. Marine environmental “success stories” were generally of smaller scale in the developing world and often involved the intervention of international, non-governmental organizations.

Our analysis of recovery times showed that there are reasons for hope. Assuming that there’s a 2.95 percent annual recovery rate across ecosystems, and provided conditions aren’t depleted to less than 50 percent of their original level, we estimate that, on average, 90 percent of the original ecosystem could be regained in about 21 years — what we would consider a “substantial recovery.” However, since pressures like climate change and plastic pollution are increasing, and species and habitats are on the decline, more time is needed for recovery. Taking into account uncertainties associated with poor data coverage and varied national commitments, we believe it is possible to rebuild the vast majority of depleted marine populations and ecosystems by some 50 to 90 percent by 2050 — a goal we have labeled a “Grand Challenge for humanity.”

Q: What are barriers to recovery and why is it critical to act now to find a way around them for humanity and the planet?

A: Lack of consistency in national marine commitments, funding, and regulations around the globe is perhaps the largest barrier to marine population and habitat recovery. For example, many nations differ in their fishing policies, in and around MPAs, which means that migratory populations like bluefin tuna and large sharks may be protected across much of their habitat while also encountering areas where fishing policies are less stringent, which can significantly slow rebuilding efforts.

Since developing nations lack conservation capacity and financial resources, we argue that enhancing the regulatory power of international bodies such as CITES and the United National Environment Program has the potential to solve these issues. But, it will require concerted effort among all countries, along with significant financial commitments, to improve and enforce these agreements internationally. However, achieving the desired results may be problematic if groups are failing to meet commitments to existing problems, like the Paris Agreement with climate change — an issue that affects whole ecosystems, causing species displacement and mass mortalities, and dictates rebuilding efforts.

If international, regional, and local communities prioritize “blue infrastructure” and marine life, the societal benefits and economic return by 2050 would be numerous. For every dollar invested, yields would be 10 dollars and over a million jobs. Revitalized fish populations, supported by policies and incentives, would see a huge jump in profits while improving overall health and sustainability of life in the area. Worldwide, the seafood profits would increase $53 billion. Further, $52 billion would be saved by restoring wetlands, which control storm surge, flooding, subsistence, and assist with climate change. Multi-tiered, complementary strategies, accountability, and buy-in can make this an achievable goal.

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Understanding the impact of climate change on the ocean

When deciding on a major, one thing was clear for Michelle Kornberg — she didn’t want to be stuck inside for four years. “I like the environment of working on something in the lab, but I grew up in a very outdoorsy family,” she says. “I definitely knew I didn’t want to be inside all the time.”

During MIT’s First-Year Pre-Orientation Program, Kornberg got a sense of which major would help her achieve this goal. One of her orientation counselors presented on their summer aboard the research vessel Nautilus Explorer. The counselor was studying Course 2-OE (Mechanical and Ocean Engineering). Later that year, Kornberg declared 2-OE.

“I think ocean engineering as a field is really interesting because it marries the holistic side of living on planet Earth with solving all the technical challenges mechanical engineers face,” explains Kornberg, now a senior.

This balance of using fundamental theories in areas like fluid dynamics, controls, and acoustics to solve problems in underwater environments has been a driving force throughout her academic career.

“I am interested in how we can apply specific ocean engineering solutions to larger global problems, particularly climate change,” Kornberg adds.

Throughout her time in Course 2-OE, Kornberg has tackled problems stemming from climate change through an ocean engineer’s lens in a number of ocean environments, including Boston Harbor and the Great Barrier Reef.

Measuring ocean acidification in Boston Harbor

By the middle of her first year, Kornberg started working with the MIT Sea Grant College Program as an undergraduate researcher working alongside Thomas Consi, research education specialist. In addition to building a model tugboat through her work with Consi, Kornberg worked on a project to track ocean acidification in Boston Harbor.

During coastal ocean acidification, higher levels of carbon in the water cause algae blooms that negatively impact organisms in the ecosystems. In Boston Harbor, shellfish suffer in particular. To understand the impact coastal ocean acidification has in Boston, Kornberg worked with Consi on developing a suite of sensors to take measurements below the water.

“Being able to track different elements of the coastal ocean environment is important to understanding the chain of events that leads to things like coastal ocean acidification,” she says.

In addition to mapping the topography of the ocean floor — known as bathymetry — the team measured variables such as water current speed. Their goal was to identify the best place to situate a measurement station that could track coastal ocean acidification in Boston Harbor.

Kornberg would have more opportunities to work on one of Boston’s waterways throughout her 2-OE classes. In the capstone classes 2.013/2.014 (Engineering Systems Design and Development) during her junior year, she worked with a team on designing and building a working prototype of an autonomous vehicle.

“The class was the first time I had the experience of working on a team with people with very different backgrounds,” Kornberg adds. “It was such a good experience — you had some people who focused on electronics and others who had a background in materials science.”

The student team built a prototype for an MIT Lincoln Laboratory project called the Ionobot. An autonomous surface vessel, the Ionobot measures changes in the ionosphere to help identify and prevent interference with GPS signals. 

On the day of the final project presentation, Kornberg and her team assembled on the docks of the MIT Sailing Pavilion, nervously awaiting the moment of truth. Would their prototype work as they planned?

An angry storm offered the team one additional challenge — windy conditions made for a choppy day on the Charles River. The team launched the Ionobot prototype and took a sigh of relief. It performed as they expected.

“It was objectively the worst weather day that semester, but it was still somehow the greatest day,” recalls Kornberg.

Several weeks later, Kornberg would be working in very different conditions along the northeast coast of Australia.

Tracking coral bleaching in the Great Barrier Reef

Last summer, Kornberg worked at the Australian Institute of Marine Science (AIMS) in Townsville, Australia through the MIT International Science and Technology Initiatives. Alongside Nicholas Fritzinger-Pittman, a senior studying mechanical engineering, Kornberg worked on developing a rail system that would enable a hyperspectral scanner to collect accurate data on thousands of coral samples in the AIMS Sea Simulator.

“In a regular camera, each pixel has a specific color. A hyperspectral camera, on the other hand, assigns a frequency distribution to each pixel, allowing you to track more than just physical light,” explains Kornberg.

This technology is particularly useful in predicting whether or not a coral is experiencing the early stages of bleaching — a condition often caused by climate change that has destroyed of large swaths of coral reefs globally.

“Coral depend on algae to stay alive. The algae can tell when conditions are suboptimal for photosynthesis before the coral can so they ‘get out of Dodge’ and leave the coral. This is the first sign of coral bleaching,” Kornberg adds.

Since researchers are unable to see algae leave the coral using the visual spectrum, they rely on a linear hyperspectral scanner to capture this process.

Before Kornberg and Fritzinger-Pittman arrived at AIMS, coral samples would have to be transported from one tank to the tank with the hyperspectral scanner on it. Since removing the coral from their environment could compromise the experiment, Kornberg and Fritzinger-Pittman worked with researchers at AIMS to develop a portable rail system that would bring the hyperspectral scanner to the coral — not the other way around.

As part of their time at AIMS, Kornberg and Fritzinger-Pittman joined a research cruise on the RV Cape Ferguson. Over the course of six days, the team visited Keeper Reef and John Brewer Reef. During breaks in research, they were able to snorkel explore the reef.

“Snorkeling along the reef was just an incredibly humbling and magical experience,” says Kornberg.

Later in the summer, the pair also took a scuba diving trip to Cairns, Australia. While they got to see colorful reefs and animals like clownfish, giant clams, and sea turtles, they also saw the effects of coral bleaching on some parts of the reef off the coast of Cairns.

“Seeing some coral bleaching in the reef itself was a really sad, sobering sight,” she adds.

Wave energy conversion in Spain

As Kornberg prepares for life after graduation this May, she is shifting her focus to renewable energy.

“I personally am most interested in looking at how we can build platforms that harness energy from the ocean environment,” she says.

Kornberg plans to work for several months this fall at Seaplace in Madrid, Spain. Her focus will be on designing and building marine turbines for wave energy conversion.

“Waves offer so much potential in terms of renewable energy. We’ve known this for a long time, but haven’t been able to figure out how to best harness this energy,” she explains. “I’m really interested in working on technologies that can help us utilize wave energy at scale.”

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Staring into the vortex

Imagine a massive mug of cold, dense cream with hot coffee poured on top. Now place it on a rotating table. Over time, the fluids will slowly mix into each other, and heat from the coffee will eventually reach the bottom of the mug. But as most of us impatient coffee drinkers know, stirring the layers together is a more efficient way to distribute the heat and enjoy a beverage that’s not scalding hot or ice cold. The key is the swirls, or vortices, that formed in the turbulent liquid.

“If you just waited to see whether molecular diffusion did it, it would take forever and you'll never get your coffee and milk together,” says Raffaele Ferrari, Cecil and Ida Green Professor of Oceanography in MIT’s Department of Earth, Atmospheric and Planetary Sciences (EAPS).

This analogy helps explain a new theory on the intricacies the climate system on Earth — and other rotating planets with atmospheres and/or oceans — outlined in a recent PNAS paper by Ferrari and Basile Gallet, an EAPS visiting researcher from Service de Physique de l'Etat Condensé, CEA Saclay, France.

It may seem intuitive that Earth’s sun-baked equator is hot while the relatively sun-deprived poles are cold, with a gradient of temperatures in between. However, the actual span of that temperature gradient is relatively small compared to what it might otherwise be because of the way the Earth system physically transports heat around the globe to cooler regions, moderating the extremes.

Otherwise, “you would have unbearably hot temperatures at the equator and [the temperate latitudes] would be frozen,” says Ferrari. “So, the fact that the planet is habitable, as we know it, has to do with heat transport from the equator to the poles.”

Yet, despite the importance of global heat flux for maintaining the contemporary climate of Earth, the mechanisms that drive the process are not completely understood. That’s where Ferrari and Gallet’s recent work comes in: their research lays out a mathematical description of the physics underpinning the role that marine and atmospheric vortices play in redistributing that heat in the global system.

Ferrari and Gallet’s work builds on that of another MIT professor, the late meteorologist Norman Phillips, who, in 1956, proposed a set of equations, the “Phillips model,” to describe global heat transport. Phillips’ model represents the atmopshere and ocean as two layers of different density on top of each other. While these equations capture the development of turbulence and predict the distribution of temperature on Earth with relative accuracy, they are still very complex and need to be solved with computers. The new theory from Ferrari and Gallet provides analytical solutions to the equations and quantitatively predicts local heat flux, energy powering the eddies, and large-scale flow characteristics. And their theoretical framework is scalable, meaning it works for eddies, which are smaller and denser in the ocean, as well as cyclones in the atmosphere that are larger.

Setting the process in motion

The physics behind vortices in your coffee cup differ from those in nature. Fluid media like the atmosphere and ocean are characterized by variations in temperature and density. On a rotating planet, these variations accelerate strong currents, while friction — on the bottom of the ocean and atmosphere — slows them down. This tug of war results in instabilities of the flow of large-scale currents and produces irregular turbulent flows that we experience as ever-changing weather in the atmosphere.

Vortices — closed circular flows of air or water — are born of this instability. In the atmosphere, they’re called cyclones and anticyclones (the weather patterns); in the ocean they’re called eddies. In both cases, they are transient, ordered formations, emerging somewhat erratically and dissipating over time. As they spin out of the underlying turbulence, they, too, are hindered by friction, causing their eventual dissipation, which completes the transfer of heat from the equator (the top of the hot coffee) to the poles (the bottom of the cream).

Zooming out to the bigger picture

While the Earth system is much more complex than two layers, analyzing heat transport in Phillips’ simplified model helps scientists resolve the fundamental physics at play. Ferrari and Gallet found that the heat transport due to vortices, though directionally chaotic, ends up moving heat to the poles faster than a more smooth-flowing system would. According to Ferrari, “vortices do the dog work of moving heat, not disorganized motion (turbulence).”

It would be impossible to mathematically account for every single eddy feature that forms and disappears, so the researchers developed simplified calculations to determine the overall effects of vortex behavior, based on latitude (temperature gradient) and friction parameters. Additionally, they considered each vortex as a single particle in a gas fluid. When they incorporated their calculations into the existing models, the resulting simulations predicted Earth’s actual temperature regimes fairly accurately, and revealed that both the formation and function of vortices in the climate system are much more sensitive to frictional drag than anticipated.

Ferrari emphasizes that all modeling endeavors require simplifications and aren’t perfect representations of natural systems — as in this instance, with the atmosphere and oceans represented as simple two-layer systems, and the sphericity of the Earth is not accounted for. Even with these drawbacks, Gallet and Ferrari’s theory has gotten the attention of other oceanographers.

“Since 1956, meteorologists and oceanographers have tried, and failed, to understand this Phillips model,” says Bill Young, professor of physical oceanography at Scripps Institution of Oceanography, “The paper by Gallet and Ferrari is the first successful deductive prediction of how the heat flux in the Phillips model varies with temperature gradient.”

Ferrari says that answering fundamental questions of how heat transport functions will allow scientists to more generally understand the Earth’s climate system. For instance, in Earth’s deep past, there were times when our planet was much warmer, when crocodiles swam in the arctic and palm trees stretched up into Canada, and also times when it was much colder and the mid-latitudes were covered in ice. “Clearly heat transfer can change across different climates, so you'd like to be able to predict it,” he says. “It's been a theoretical question on the minds of people for a long time.”

As the average global temperature has increased more than 1 degree Celsius in the past 100 years, and is on pace to far exceed that in the next century, the need to understand — and predict — Earth’s climate system has become crucial as communities, governments, and industry adapt to the current changing environment.

“I find it extremely rewarding to apply the fundamentals of turbulent flows to such a timely issue,” says Gallet, “In the long run, this physics-based approach will be key to reducing the uncertainty in climate modelling.”

Following in the footsteps of meteorology giants like Norman Phillips, Jule Charney, and Peter Stone, who developed seminal climate theories at MIT, this work too adheres to an admonition from Albert Einstein: "Out of clutter, find simplicity."

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Scientists quantify how wave power drives coastal erosion

Over millions of years, Hawaiian volcanoes have formed a chain of volcanic islands stretching across the Northern Pacific, where ocean waves from every direction, stirred up by distant storms or carried in on tradewinds, have battered and shaped the islands’ coastlines to varying degrees.

Now researchers at MIT and elsewhere have found that, in Hawaii, the amount of energy delivered by waves averaged over each year is a good predictor of how fast or slow a rocky coastline will erode. If waves are large and frequent, the coastline will erode faster, whereas smaller, less frequent waves will result in a slower-eroding coast.

Their study helps to explain the Hawaiian Islands’ meandering shorelines, where north-facing sea cliffs, experiencing larger waves produced by distant storms and persistent tradewinds, have eroded farther inland. In contrast, south-facing coasts typically enjoy calmer waters, smaller waves, and therefore less eroded coasts.

The results, published this month in the journal Geology, can also help scientists forecast how fast other rocky coasts around the world might erode, based on the power of the waves that a coast typically experiences.

“Over half of the world’s oceanic coastlines are rocky sea cliffs, so sea-cliff erosion affects a lot of coastal inhabitants and infrastructure,” says Kim Huppert ’11, PhD ’17, lead author of the study and a former graduate student in MIT’s Department of Earth, Atmospheric and Planetary Sciences. “If storminess increases with climate change, and waves get bigger, we need to understand specifically how waves affect erosion.”

Huppert, who is now a senior research scientist at the German Research Center for Geosciences, has co-authored the paper with Taylor Perron, professor of earth, atmospheric, and planetary sciences and associate department head at MIT, and Andrew Ashton of the Woods Hole Oceanographic Institution.

Sink and carve

Scientists have had some idea that the rate of coastal erosion depends on the power of the waves that act on that coast. But until now, there’s been no systematic study to confirm this relationship, mainly because there can be so many other factors contributing to coastal erosion that can get in the way.

The team found the Hawaiian Islands provide an ideal environment in which to study this relationship: The islands are all made from the same type of bedrock, meaning they wouldn’t have to account for multiple types of rock and sediment and their differences in erosion; and the islands inhabit a large oceanic basin that produces a wide range of wave “climates,” or waves of varying sizes and frequencies.

“As you go around the shoreline of different islands, you see very different wave climates, simply by turning a corner of the island,” Huppert notes. “And the rock type is all the same. So Hawaii is a nice natural laboratory.”

The researchers focused their study on 11 coastal locations around the islands of Hawaii, Maui, and Kaho‘olawe, each facing different regions of the Pacific that produce varying sizes and frequencies of waves.

Before considering the wave power at these various locations, they first worked to estimate the average rate at which the sea cliffs at each coastal location eroded over the last million years. The team sought to identify the erosion rates that produced the coastal profiles of Hawaiian Islands today, given the islands’ original profiles, which can be estimated from each island’s topography. To do this, they first had to account for changes in each island’s vertical motion and sea level change over time.

After a volcanic island forms, it inevitably starts to subside, or sink under its own weight. As an island sinks, the level at which the sea interacts with the island changes, just as if you were to lower yourself into a pool: The water’s surface may start at your ankles, and progressively lap at your knees, your waist, and eventually your shoulders and chin.

For an island, the more slowly it sinks, the more time the sea has to carve out the coastline at a particular elevation. In contrast, if an island sinks quickly, the sea has only fleeting time to cut into the coast before the island subsides further, exposing a new coastline for the sea to wear away. As a result, the rate at which an island sinks strongly affects how far the coast has retreated inland at any given elevation, over millions of years.

To calculate the speed of island sinking, the team used a model to estimate how much the lithosphere, the outermost layer of the Earth on which volcanic islands sit, sagged under the weight of each Hawaiian volcano formed in the past million years. Because the Hawaiian Islands are close together, the sinking of one island can also affect the sinking or rising of neighboring islands, similar to the way one child may bounce up as another child sinks into a trampoline.

The team used the model to simulate various possible histories of island sinking over the last million years, and the subsequent erosion of sea cliffs and coastlines. They looked for the scenario that best linked the islands’ original coastlines with today’s modern coastlines, and matched the various resulting erosion rates to the 11 locations that they focused on in their study.

“We found erosion rates that vary from 17 millimeters per year to 118 millimeters per year at the different sites,” Huppert says. “The upper end of that range is nearly half a foot per year, so some of those rates are pretty fast for rock.”

Waves of a size

They chose the 11 coastal locations in the study for their variability: Some sea cliffs face north, where they are battered by stronger waves produced by distant storms. Other north-facing coasts experience tradewinds that come from the northeast and produce waves that are smaller but more frequent. The coastal locations that face southward experience smaller, less-frequent waves in contrast.

The team compared erosion rates at each site with the typical wave power experienced at each site, which they calculated from wave height and frequency measurements derived from buoy data. They then compared the 11 locations’ wave power to their long-term rates of erosion.

What they found was a rather simple, linear relationship between wave power and the rate of coastal erosion. The stronger the waves that a coast experiences, the faster that coast erodes. Specifically, they found that waves of a size that occur every few days might be a better indicator of how fast a coast is eroding than larger but less frequent storm waves. That is, if  waves on normal, nonstormy days are large, a coast is likely eroding quickly; if the typical waves are smaller, a coast is retreating more slowly.

The researchers say carrying out this study in Hawaii allowed them to confirm this simple relationship, without confounding natural factors. As a result, scientists can use this relationship to help predict how rocky coasts in other parts of the world may change, with variations in sea level and wave activity as a result of climate change.

“Sea level is rising along much of the world’s coasts, and changes in winds and storminess with ongoing climate change could alter wave regimes, too,” Perron points out. “To be able to isolate the influence of wave climate on the rate of coastal erosion gets you one step closer to going to a particular place and calculating the change in erosion rate there.”

This research was supported, in part, by the NEC Corporation, and by NASA.

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