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      A coral pollution study unexpectedly helped explain Hurricane Maria’s fury

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      Hurricane Maria struck the island of Puerto Rico early on September 20, 2017, with 250-kilometer-per-hour winds, torrential rains and a storm surge up to three meters high. In its wake: nearly 3,000 people dead, an almost yearlong power outage and over $90 billion in damages to homes, businesses and essential infrastructure, including roads and bridges.

      Geologist and diver Milton Carlo took shelter at his house in Cabo Rojo on the southwest corner of the island with his wife, daughter and infant grandson. He watched the raging winds of the Category 4 hurricane lift his neighbor’s SUV into the air, and remembers those hours as some of the worst of his life.

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      For weeks, the rest of the world was in the dark about the full extent of the devastation, because Maria had destroyed the island’s main weather radar and almost all cell phone towers.

      Far away on the U.S. West Coast, in Santa Cruz, Calif., oceanographer Olivia Cheriton watched satellite radar images of Maria passing over the instruments she and her U.S. Geological Survey team had anchored a few kilometers southwest of Puerto Rico. The instruments, placed offshore from the seaside town of La Parguera, were there to track pollution circulating around some of the island’s endangered corals.

      More than half a year went by before she learned the improbable fate of those instruments: They had survived and had captured data revealing hurricane-related ocean dynamics that no scientist had ever recorded.

      The wind-driven coastal currents interacted with the seafloor in a way that prevented Maria from drawing cold water from the depths of the sea up to the surface. The sea surface stayed as warm as bathwater. Heat is a hurricane’s fuel source, so a warmer sea surface leads to a more intense storm. As Cheriton figured out later, the phenomenon she stumbled upon likely played a role in maintaining Maria’s Category 4 status as it raked Puerto Rico for eight hours.

      “There was absolutely no plan to capture the impact of a storm like Maria,” Cheriton says. “In fact, if we somehow could’ve known that a storm like that was going to occur, we wouldn’t have put hundreds of thousands of dollars’ worth of scientific instrumentation in the water.”

      A storm’s path is guided by readily observable, large-scale atmospheric features such as trade winds and high-pressure zones. Its intensity, on the other hand, is driven by weather events inside the hurricane and wave action deep below the ocean’s surface. The findings by Cheriton and colleagues, published May 2021 in Science Advances, help explain why hurricanes often get stronger before making landfall and can therefore help forecasters make more accurate predictions.

      Reef pollution

      Cheriton’s original research objective was to figure out how sea currents transport polluted sediments from Guánica Bay — where the Lajas Valley drains into the Caribbean Sea — to the pristine marine ecosystems 10 kilometers west in La Parguera Natural Reserve, famous for its bioluminescent waters.

      Endangered elkhorn and mountainous star corals, called “the poster children of Caribbean reef decline” by marine geologist Clark Sherman, live near shore in some of the world’s highest recorded concentrations of now-banned industrial chemicals. Those polychlorinated biphenyls, or PCBs, hinder coral reproduction, growth, feeding and defensive responses, says Sherman, of the University of Puerto Rico–Mayagüez.

      Elkhorn coral (left) and mountainous star coral (right) were once ubiquitous in the Caribbean. Their numbers have dropped greatly due to bleaching and disease. Pollution is partly to blame.  FROM LEFT: NICK HOBGOOD/WIKIMEDIA COMMONS (CC BY-SA 3.0); NOAA FISHERIES

      Half of corals in the Caribbean have died since monitoring began in the 1970s, and pollution is a major cause, according to an April 2020 study in Science Advances. Of particular interest to Cheriton, Sherman and their colleagues was whether the pollution had reached deepwater, or mesophotic, reefs farther offshore, which could be a refuge for coral species that were known to be dying in shallower areas.

      The main artery for this pollution is the Rio Loco — which translates to “Crazy River.” It spews a toxic runoff of eroded sediments from the Lajas Valley’s dirt roads and coffee plantations into Guánica Bay, which supports a vibrant fishing community. Other possible contributors to the pollution — oil spills, a fertilizer plant, sewage and now-defunct sugar mills — are the subject of investigations by public health researchers and the U.S. Environmental Protection Agency.

      In June 2017, the team convened in La Parguera to install underwater sensors to measure and track the currents in this threatened marine environment. From Sherman’s lab on a tiny islet overrun with iguanas the size of house cats, he and Cheriton, along with team leader and USGS research geologist Curt Storlazzi and USGS physical scientist Joshua Logan, launched a boat into choppy seas.

      Marine geologist Clark Sherman dives amid colonies of healthy great star corals, black corals, a large sea fan and a variety of sponges along the steep island shelf of southwest Puerto Rico. Sherman helped investigate whether pollution was reaching these deepwater reefs.E. TUOHY/UNIV. OF PUERTO RICO–MAYAGÜEZ

      At six sites near shore, Storlazzi, Sherman and Logan dove to the seafloor and used epoxy to anchor pressure gauges and batonlike current meters. Together the instruments measured hourly temperature, wave height and current speed. The team then moved farther offshore where the steep island shelf drops off at a 45-degree angle to a depth of 60 meters, but the heavy ocean chop scuttled their efforts to install instruments there.

      In June 2017, research geologist Curt Storlazzi (left) and physical scientist Joshua Logan (right) prepare to dive near Puerto Rico’s Guánica Bay to install instruments for monitoring currents suspected of delivering pollution to coral reefs.USGS

      For help working in the difficult conditions, Sherman enlisted two expert divers for a second attempt: Carlo, the geologist and diving safety officer, and marine scientist Evan Tuohy, both of the University of Puerto Rico–­Mayagüez. The two were able to install the most important and largest piece, a hydroacoustic instrument comprising several drums fastened to a metal grid, which tracked the direction and speed of currents every minute using pulsating sound waves. A canister containing temperature and salinity sensors took readings every two minutes. Above this equipment, an electric thermometer extended to within 12 meters of the surface, registering temperature every five meters vertically every few seconds.

      The instruments installed by Storlazzi, Logan and others collected unexpected underwater ocean observations during Hurricane Maria. An acoustic Doppler current profiler (left) used pulsating sound waves to measure the direction and speed of currents at the shelf break and slope site about 12 kilometers offshore of La Parguera. A Marotte current meter (right) measured wave height, current speed and temperature at six spots close to shore.USGS

      Working in concert, the instruments gave a high-resolution, seafloor-to-surface snapshot of the ocean’s hydrodynamics on a near-continuous basis. The equipment had to sit level on the sloping seafloor so as not to skew the measurements and remain firmly in place. Little did the researchers know that the instruments would soon be battered by one of the most destructive storms in history.

      Becoming Maria

      The word hurricane derives from the Caribbean Taino people’s Huricán, god of evil. Some of the strongest of these Atlantic tropical cyclones begin where scorching winds from the Sahara clash with moist subtropical air over the island nation of Cape Verde off western Africa. The worst of these atmospheric disturbances create severe thunderstorms with giant cumulonimbus clouds that flatten out against the stratosphere. Propelled by the Earth’s rotation, they begin to circle counterclockwise around each other — a phenomenon known as the Coriolis effect.

      Weather conditions that summer had already spawned two monster hurricanes: Harvey and Irma. By late September, the extremely warm sea surface — 29º Celsius or hotter in some places — gave up its heat energy by way of evaporation into Maria’s rushing winds. All hurricanes begin as an area of low pressure, which in turn sucks in more wind, accelerating the rise of hot air, or convection. Countervailing winds known as shear can sometimes topple the cone of moist air spiraling upward. But that didn’t happen, so Maria continued to grow in size and intensity.

      Meteorologists hoped that Maria would lose force as it moved across the Caribbean, weakened by the wake of cooler water Irma had churned up two weeks earlier. Instead, Maria tracked south, steaming toward the eastern Caribbean island of Dominica. Within 15 hours of making landfall, its maximum sustained wind speed doubled, reaching a house-leveling 260 kilometers per hour. That doubling intensified the storm from a milder (still dangerous) Category 1 to a strong Category 5.

      NOAA’s computer forecasting models did not anticipate such rapid intensification. Irma had also raged with unforeseen intensity.

      After striking Dominica hard, Maria’s eyewall broke down, replaced by an outer band of whipping thunderstorms. This slightly weakened Maria to 250 kilometers per hour before it hit Puerto Rico, while expanding the diameter of the storm’s eyewall — the area of strong winds and heaviest precipitation — to 52 kilometers. That’s close to the width of the island.

      Hurricane Maria made landfall on Puerto Rico early in the morning on September 20, 2017, and cut across the island diagonally toward the northwest. Its eyewall generated maximum sustained winds of  250 kilometers per hour and spanned almost the width of the island.CIRA/NOAA

      It’s still not fully understood why Maria had suddenly gone berserk. Various theories point to the influence of hot towers — convective bursts of heat energy from thunderclouds that punch up into the stratosphere — or deep warm pools, buoyant freshwater eddies spilling out of the Amazon and Orinoco rivers into the Atlantic, where currents carry these pockets of hurricane-fueling heat to the Gulf of Mexico and the Caribbean Sea.

      But even though these smaller-scale events may have a big impact on intensity, they aren’t fully accounted for in weather models, says Hua Leighton, a scientist at the National Oceanic and Atmospheric Administration’s hurricane research division and the University of Miami’s Cooperative Institute for Marine and Atmospheric Studies. Leighton develops forecasting models and investigates rapid intensification of hurricanes.

      “We cannot measure everything in the atmosphere,” Leighton says.

      Without accurate data on all the factors that drive hurricane intensity, computer models can’t easily predict when the catalyzing events will occur, she says. Nor can models account for everything that happens inside the ocean during a hurricane. They don’t have the data.

      Positioning instruments just before a hurricane hits is a major challenge. But NOAA is making progress. It has launched a new generation of hurricane weather buoys in the western North Atlantic and remote control surface sensors called Saildrones that examine the air-sea interface between hurricanes and the ocean (SN: 6/8/19, p. 24).

      Underwater, NOAA uses other drones, or gliders, to profile the vast areas regularly traversed by tropical storms. These gliders collected 13,200 temperature and salinity readings in 2020. By contrast, the instruments that the team set in Puerto Rico’s waters in 2017 collected over 250 million data points, including current velocity and direction — a rare and especially valuable glimpse of hurricane-induced ocean dynamics at a single location.

      A different view

      After the storm passed, Storlazzi was sure the hurricane had destroyed his instruments. They weren’t designed to take that kind of punishment. The devices generally work in much calmer conditions, not the massive swells generated by Maria, which could increase water pressure to a level that would almost certainly crush instrument sensors.

      But remarkably, the instruments were battered but not lost. Sherman, Carlo and Touhy retrieved them after Maria passed and put them in crates awaiting the research group’s return.

      Milton Carlo (left) and Evan Tuohy (right), shown in an earlier deepwater dive, helped  place the current-monitoring instruments at the hard-to-reach sites where hurricane data were collected.MIKE ECHEVARRIA

      When Storlazzi and USGS oceanographer Kurt Rosenberger pried open the instrument casings in January 2018, no water gushed out. Good sign. The electronics appeared intact. And the lithium batteries had powered the rapid-fire sampling enterprise for the entire six-month duration. The researchers quickly downloaded a flood of data, backed it up and started transmitting it to Cheriton, who began sending back plots and graphs of what the readings showed.

      Floodwaters from the massive rains brought by Maria had pushed a whole lot of polluted sediment to the reefs outside Guánica Bay, spiking PCB concentrations and threatening coral health. As of a few months after the storm, the pollution hadn’t reached the deeper reefs.

      Then the researchers realized that their data told another story: what happens underwater during a massive hurricane. They presumed that other researchers had previously captured a profile of the churning ocean depths beneath a hurricane at the edge of a tropical island.

      Remarkably, that was not the case.

      “Nobody’s even measured this, let alone reported it in any published literature,” Cheriton says. The team began to explore the hurricane data not knowing where it might lead.

      “What am I looking at here?” Cheriton kept asking herself as she plotted and analyzed temperature, current velocity and salinity values using computer algorithms. The temperature gradient that showed the ocean’s internal or underwater waves was different than anything she’d seen before.

      Oceanographer Olivia Cheriton realized that data on ocean currents told a new story about Hurricane Maria.O.M. CHERITON

      During the hurricane, the top 20 meters of the Caribbean Sea had consistently remained at or above 26º C, a few degrees warmer than the layers beneath. But the surface waters should have been cooled if, as expected, Maria’s winds had acted like a big spoon, mixing the warm surface with cold water stirred up from the seafloor 50 to 80 meters below. Normally, the cooler surface temperature restricts the heat supply, weakening the hurricane. But the cold water wasn’t reaching the surface.

      To try to make sense of what she was seeing, Cheriton imagined herself inside the data, in a protective bubble on the seafloor with the instruments as Maria swept over. Storlazzi worked alongside her analyzing the data, but focused on the sediments circulating around the coral reefs.

      Cheriton was listening to “An Awesome Wave” by indie-pop band Alt-J and getting goosebumps while the data swirled before them. Drawing on instincts from her undergraduate astronomy training, she focused her mind’s eye on a constellation of data overhead and told Storlazzi to do the same.

      “Look up Curt!” she said.

      Up at the crest of the island shelf, where the seafloor drops off, the current velocity data revealed a broad stream of water gushing from the shore at almost 1 meter per second, as if from a fire hose. Several hours before Maria arrived, the wind-driven current had reversed direction and was now moving an order of magnitude faster. The rushing surface water thus became a barrier, trapping the cold water beneath it.

      As a result, the surface stayed warm, increasing the force of the hurricane. The cooler layers below then started to pile up vertically into distinct layers, one on top of the other, beneath the gushing waters above.

      Cheriton calculated that with the fire hose phenomenon the contribution from coastal waters in this area to Maria’s intensity was, on average, 65 percent greater, compared with what it would have been otherwise.

      Oceanographer Travis Miles of Rutgers University in New Brunswick, N.J., who was not involved in the research, calls Cheriton and the team’s work a “frontier study” that draws researchers’ attention to near-shore processes. Miles can relate to Cheriton and her team’s accidental hurricane discovery from personal experience: When his water quality–sampling gliders wandered into Hurricane Irene’s path in 2011, they revealed that the ocean off the Jersey Shore had cooled in front of the storm. Irene’s onshore winds had induced seawater mixing across the broad continental shelf and lowered sea surface temperatures.

      The Puerto Rico data show that offshore winds over a steep island shelf produced the opposite effect and should help researchers better understand storm-induced mixing of coastal areas, says NOAA senior scientist Hyun-Sook Kim, who was not involved in the research. It can help with identifying deficiencies in the computer models she relies on when providing guidance to storm-tracking meteorologists at the National Hurricane Center in Miami and the Joint Typhoon Warning Center in Hawaii.

      And the unexpected findings also could help scientists get a better handle on coral reefs and the role they play in protecting coastlines. “The more we study the ocean, especially close to the coast,” Carlo says, “the more we can improve conditions for the coral and the people living on the island.” More

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      The Tonga eruption may have spawned a tsunami as tall as the Statue of Liberty

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      The massive Tonga eruption generated a set of planet-circling tsunamis that may have started out as a single mound of water roughly the height of the Statue of Liberty.

      What’s more, the explosive eruption triggered an immense atmospheric shock wave that spawned a second set of especially fast-moving tsunamis, a rare phenomenon that can complicate early warnings for these oft-destructive waves, researchers report in the October Ocean Engineering.

      As the Hunga Tonga–Hunga Ha’apai undersea volcano erupted in the South Pacific in January, it displaced a large volume of water upward, says Mohammad Heidarzadeh, a civil engineer at the University of Bath in England (SN: 1/21/22). The water in that colossal mound later “ran downhill,” as fluids tend to do, to generate the initial set of tsunamis.

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      To estimate the original size of the mound, Heidarzadeh and his team used computer simulations, as well as data from deep-ocean instruments and coastal tide gauges within about 1,500 kilometers of the eruption, many of them in or near New Zealand. The arrival times of tsunami waves, as well as their sizes, at those locations were key pieces of data, Heidarzadeh says.

      The team analyzed nine possibilities for the initial wave, each of which was shaped like a baseball pitcher’s mound and had a distinct height and diameter. The best fit to the real-world data came from a mound of water a whopping 90 meters tall and 12 kilometers in diameter, the researchers report.

      That initial wave would have contained an estimated 6.6 cubic kilometers of water. “This was a really large tsunami,” Heidarzadeh says.

      Despite starting out about nine times as tall as the tsunami that devastated the Tohoku region of Japan in 2011, the Tongan tsunamis killed only five people and caused about $90 million in damage, largely because of their remote source (SN: 2/10/12).

      Another unusual aspect of the Tongan eruption is the second set of tsunamis generated by a strong atmospheric pressure wave.

      That pressure pulse resulted from a steam explosion that occurred when a large volume of seawater infiltrated the hot magma chamber beneath the erupting volcano. As the pressure wave raced across the ocean’s surface at speeds exceeding 300 meters per second, it pushed water ahead of it, creating tsunamis, Heidarzadeh explains.

      The eruption of the Hunga Tonga-Hunga Ha’apai volcano also triggered an atmospheric pressure wave that in turn generated tsunamis that traveled quicker than expected.NASA Earth Observatory

      Along many coastlines, including some in the Indian Ocean and Mediterranean Sea, these pressure wave–generated tsunamis arrived hours ahead of the gravity-driven waves spreading from the 90-meter-tall mound of water. Gravity-driven tsunami waves typically travel across the deepest parts of the ocean, far from continents, at speeds between 100 and 220 meters per second. When the waves reach shallow waters near shore, the waves slow, water stacks up and then strikes shore, where destruction occurs.

      Pressure wave–generated tsunamis have been reported for only one other volcanic eruption: the 1883 eruption of Krakatau in Indonesia (SN: 8/27/83).

      Those quicker-than-expected arrival times — plus the fact that the pressure-wave tsunamis for the Tongan eruption were comparable in size with the gravity-driven ones — could complicate early warnings for these tsunamis. That’s concerning, Heiderzadeh says.

      One way to address the issue would be to install instruments that measure atmospheric pressure with the deep-sea equipment already in place to detect tsunamis, says Hermann Fritz, a tsunami scientist at Georgia Tech in Atlanta.

      With that setup, scientists would be able to discern if a passing tsunami is associated with a pressure pulse, thus providing a clue in real time about how fast the tsunami wave might be traveling. More

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      Extreme climate shifts long ago may have helped drive reptile evolution

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      There’s nothing like a big mass extinction to open up ecological niches and clear out the competition, accelerating evolution for some lucky survivors. Or is there? A new study suggests that the rate of climate change may play just as large a role in speeding up evolution.

      The study focuses on reptile evolution across 57 million years — before, during and after the mass extinction at the end of the Permian Period (SN: 12/6/18). That extinction event, triggered by carbon dioxide pumped into the atmosphere and oceans through increased volcanic activity about 252 million years ago, knocked out a whopping 86 percent of Earth’s species. Yet reptiles recovered from the chaos relatively well. Their exploding diversity of species around that time has been widely regarded as a result of their slithering into newly available niches.

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      But rapid climate fluctuations were already taking place much earlier in the Permian, and so were surges of reptile diversification, researchers say. Analyzing fossils from 125 reptile species shows that bursts of evolutionary diversity in reptiles were tightly correlated with relatively rapid fluctuations in climate throughout the Permian and millions of years into the next geologic period, the Triassic, researchers report August 19 in Science Advances.

      Scientists’ understanding of evolution is expanding as they become more tuned into the connection between it and environmental change, says Jessica Whiteside, a geologist at the University of Southampton in England who works on mass extinctions but was not involved in the new work. “This study is bound to become an important part of that conversation.”

      To investigate reptile evolution, evolutionary paleobiologist Tiago Simões of Harvard University and colleagues precisely measured and scanned reptile fossils ranging from 294 million to 237 million years old. In all, the researchers examined 1,000 specimens at 50 research institutions in 20 countries.  For climate data, the team used an existing large database of sea surface temperatures based on oxygen isotope data, extending back 450 million years, published in 2021.

      By closely tracking changes in body and head size and shape in so many species, paired with that climate data, the researchers found that the faster the rate of climate change, the faster reptiles evolved. The fastest rate of reptile diversification did not occur at the end-Permian extinction, the team found, but several million years later in the Triassic, when climate change was at its most rapid and global temperatures witheringly hot. Ocean surface temperatures during this time soared to 40° Celsius, or 104⁰ Fahrenheit — about the temperature of a hot tub, says Simões.

      A few species did evolve less rapidly than their kin, Simões says. The difference? Size. For instance, reptiles with smaller body sizes are already preadapted to live in rapidly warming climates, he says. Due to their greater surface area to body ratio, “small-bodied reptiles can better exchange heat with their surrounding environment,” so stay relatively cooler than larger animals.

      “The smaller reptiles were basically being forced by natural selection to stay the same, while during that same period of time, the large reptiles were being told by natural selection ‘You need to change right away or you’re going to go extinct,’” Simões says.

      This phenomenon, called the Lilliput effect, is not a new proposal, Simões says, adding that it’s been well established in marine organisms. “But it’s the first time it’s been quantified in limbed vertebrates across this critical period in Earth’s history.”

      Simões and colleagues’ detailed work has refined the complex evolutionary tree for reptiles and their ancestors. But, for now, it’s unclear which played a bigger role in reptile evolution long ago — all those open ecological niches after the end-Permian mass extinction, or the dramatic climate fluctuations outside of the extinction event.

      “We cannot say which one was more important,” Simões says. “Without either one, the course of evolution in the Triassic and the rise of reptiles to global dominance in terrestrial ecosystems would have been quite different.”  More

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      Common, cheap ingredients can break down some ‘forever chemicals’

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      There’s a new way to rip apart harmful “forever chemicals,” scientists say.

      Perfluoroalkyl and polyfluoroalkyl substances, also known as PFAS, are found in nonstick pans, water-repellent fabrics and food packaging and they are pervasive throughout the environment. They’re nicknamed forever chemicals for their ability to stick around and not break down. In part, that’s because PFAS have a super strong bond between their carbon and fluorine atoms (SN: 6/4/19). Now, using a bit of heat and two relatively common compounds, researchers have degraded one major type of forever chemical in the lab, the team reports in the Aug. 19 Science. The work could help pave the way for a process for breaking down certain forever chemicals commercially, for instance by treating wastewater.

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      “The fundamental knowledge of how the materials degrade is the single most important thing coming out of this study,” organic chemist William Dichtel said in an August 16 news conference.

      While some scientists have found relatively simple ways of breaking down select PFAS, most degradation methods require harsh, energy-intensive processes using intense pressure — in some cases over 22 megapascals — or extremely high temperatures — sometimes upwards of 1000⁰ Celsius — to break the chemical bonds (SN: 6/3/22).

      Dichtel, of Northwestern University in Evanston, Ill., and his team experimented with two substances found in nearly every chemistry lab cabinet: sodium hydroxide, also known as lye, and a solvent called dimethyl sulfoxide, or DMSO. The team worked specifically with a group of forever chemicals called PFCAs, which contain carboxylic acid and constitute a large percentage of all PFAS. Some of these kinds of forever chemicals are found in water-resistant clothes.

      When the team combined PFCAs with the lye and DMSO at 120⁰ C and with no extra pressure needed, the carboxylic acid fell off the chemical and became carbon dioxide in a process called decarboxylation. What happened next was unexpected, Dichtel said. Loss of the acid led to a process causing “the entire molecule to fall apart in a cascade of complex reactions.” This cascade involved steps that degraded the rest of the chemical into fluoride ions and smaller carbon-containing products, leaving behind virtually no harmful by-products.     .

      “It’s a neat method, it’s different from other ones that have been tried,” says Chris Sales, an environmental engineer at Drexel University in Philadelphia who was not involved in the study. “The biggest question is, how could this be adapted and scaled up?” Northwestern has filed a provisional patent on behalf of the researchers.

      Understanding this mechanism is just one step in undoing forever chemicals, Dichtel’s team said. And more research is needed: There are other classes of PFAS that require their own solutions. This process wouldn’t work to tackle PFAS out in the environment, because it requires a concentrated amount of the chemicals. But it could one day be used in wastewater treatment plants, where the pollutants could be filtered out of the water, concentrated and then broken down. More

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      The Arctic is warming even faster than scientists realized

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      The Arctic is heating up at a breakneck speed compared with the rest of Earth. And new analyses show that the region is warming even faster than scientists thought. Over the last four decades, the average Arctic temperature increased nearly four times as fast as the global average, researchers report August 11 in Communications Earth & Environment.

      And that’s just on average. Some parts of the Arctic Ocean, such as the Barents Sea between Russia and Norway’s Svalbard archipelago, are warming as much as seven times as fast, meteorologist Mika Rantanen of the Finnish Meteorological Institute in Helsinki and colleagues found. Previous studies have tended to say that the Arctic’s average temperature is increasing two to three times as fast as elsewhere, as humans continue causing the climate to change.

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      To calculate the true pace of the accelerated warming, a phenomenon called Arctic amplification, the researchers averaged four sets of satellite data from 1979 to 2021 (SN: 7/1/20). Globally, the average temperature increase over that time was about 0.2 degrees Celsius per decade. But the Arctic was warming by about 0.75 degrees C per decade.

      Even the best climate models are not doing a great job of reproducing that warming, Rantanen and colleagues say. The inability of the models to realistically simulate past Arctic amplification calls into question how well the models can project future changes there.

      It’s not clear where the problem lies. One issue may be that the models are struggling with correctly simulating the sensitivity of Arctic temperatures to the loss of sea ice. Vanishing snow and ice, particularly sea ice, are one big reason why Arctic warming is on hyperspeed. The bright white snow and ice create a reflective shield that bounces incoming radiation from the sun back into space. But open ocean waters or bare rocks absorb that heat, raising the temperature. More

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      Sea sponges launch slow-motion snot rockets to clean their pores

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      The next time you spot a sea sponge, say “gesundheit!” Some sponges regularly “sneeze” to clear debris from their porous bodies.

      As filter feeders, sponges draw in water through inlet pores — called ostia — and strain it through an internal canal system for nutrients. But there are also inedible bits in the water, like sediment. To prevent the undesirable junk from clogging up their outer pores, a Caribbean tube sponge (Aplysina archeri) uses mucus to trap and sneeze out unwanted particles, Niklas Kornder, a marine biologist at the University of Amsterdam, and colleagues report online August 10 in Current Biology. To the team’s surprise, it found that the sponge expels its snot from the same pores through which it absorbs water.

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      It’s “like someone with a runny nose,” says team member Sally Leys, an evolutionary biologist at the University of Alberta in Edmonton, Canada. “It’s constantly streaming, but it’s going counterflow to the in-current.”

      Researchers knew that sponges used contractions dubbed “sneezing” to move water through their bodies in a one-way flow. Typically, water comes in through numerous ostia and leaves through the osculum, a hole near the sponges’ top.

      But when the team captured time-lapse video of A. archeri, it saw tiny specks of mucus exiting from the ostia, moving against the flow of incoming water. Sneezelike contractions appeared to expel and move the specks along a “mucus highway” across the surface of the sponge to points where they collected in stringy, gooey clumps. Unlike an explosive human sneeze, the sponges slowly and continuously secreted debris-laden mucus from their ostia, with one contraction taking between 20 and 50 minutes, the study finds.

      [embedded content]
      The Caribbean tube sponge (Aplysina archeri) uses contractions — called “sneezes” — to help eject mucus from its pores, or ostia. As the time-lapse video zooms in closer, it’s possible to see tiny specks of debris floating out of these pores and traveling along a “mucus highway” where they collect into stringy clumps of goo floating above the surface of the sponge. In real time, this sponge takes between 20 and 50 minutes to complete a sneeze.

      Other sea critters feast on these ocean boogers, like brittle stars and small crustaceans. Scientists view sponges primarily as habitat builders, but the mucus buffet shows they also perform an important function as food providers, says Amanda Kahn, a marine biologist at Moss Landing Marine Labs in California who was not involved with this work.

      “There’s so much to be said for a study that really spends time and watches,” Kahn says. “They let the animals show for themselves what was happening.”

      Most sponges appear to sneeze, so it’s likely not just A. archeri that uses the counterflow technique, Leys says. The team also noted a similar behavior in an Indo-Pacific sponge (Chelonaplysilla sp). But biologists need to dig deeper to figure out how widespread the mechanism is. It’s also unclear exactly what the mucus is or how it’s moving backward through pores. More

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      Relocated beavers helped mitigate some effects of climate change

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      In the upper reaches of the Skykomish River in Washington state, a pioneering team of civil engineers is keeping things cool. Relocated beavers boosted water storage and lowered stream temperatures, indicating such schemes could be an effective tool to mitigate some of the effects of climate change.

      In just one year after their arrival, the new recruits brought average water temperatures down by about 2 degrees Celsius and raised water tables as much as about 30 centimeters, researchers report in the July Ecosphere. While researchers have discussed beaver dams as a means to restore streams and bulk up groundwater, the effects following a large, targeted relocation had been relatively unknown (SN: 3/26/21).

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      “That water storage is so critical during the drier periods, because that’s what can keep the ecosystem resilient to droughts and fires,” says Emily Fairfax, an ecohydrologist at California State University Channel Islands in Camarillo who was not involved with the study.

      The Skykomish River flows down the west side of Washington’s Cascade Mountains. Climate change is already transforming the region’s hydrology: The snowpack is shrinking, and snowfall is turning to rain, which drains quickly. Waters are also warming, which is bad news for salmon populations that struggle to survive in hot water.

      Beavers are known to tinker with hydrology too (SN: 7/27/18). They build dams, ponds and wetlands, deepening streams for their burrows and lodges (complete with underwater entrances). The dams slow the water, storing it upstream for longer, and cool it as it flows through the ground underneath.

      From 2014 to 2016, aquatic ecologist Benjamin Dittbrenner and colleagues relocated 69 beavers (Castor canadensis) from lowland areas of the state to 13 upstream sites in the Skykomish River basin, some with relic beaver ponds and others untouched. As beavers are family-oriented, the team moved whole clans to increase the chances that they would stay put.

      The researchers also matched singletons up with potential mates, which seemed to work well: “They were not picky at all,” says Dittbrenner, of Northeastern University in Boston. Fresh logs and wood cuttings got the beavers started in their new neighborhoods.

      At the five sites that saw long-term construction, beavers built 14 dams. Thanks to those dams, the volume of surface water — streams, ponds, wetlands — increased to about 20 times that of streams with no new beaver activity. Meanwhile below ground, wells at three sites showed that after dam construction the amount of groundwater grew to more than twice that was stored on the surface in ponds. Stream temperatures downstream of the dams fell by 2.3 degrees C on average, while streams not subject to the beavers’ tinkering warmed by 0.8 degrees C. These changes all came within the first year after relocation.

      “We’re achieving restoration objectives almost instantly, which is really cool,” Dittbrenner says.

      Crucially, the dams lowered temperatures enough to almost completely take the streams out of the harmful range for salmon during a particularly hot summer. “These fish are also experiencing heat waves within the water system, and the beavers are protecting them from it,” Fairfax says. “That to me was huge.”

      The study also found that small, shallow abandoned beaver ponds were actually warming streams, perhaps because the cooling system had broken down over time. Targeting these ponds as potential relocation sites could be the most effective way to bring temperatures down, the researchers say.  When relocated populations establish and breed, young beavers leaving their homes could seek those abandoned spots out first, Dittbrenner says, as it uses less energy than starting from scratch. “If they find a relic pond, it’s game on.”      More

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      in Heart

      Electrical bacteria may help clean oil spills and curb methane emissions

      by

      The small motorboat anchors in the middle of the Chesapeake Bay. Shrieks of wintering birds assault the vessel’s five crew members, all clad in bright orange flotation suits. One of the crew slowly pulls a rope out of the water to retrieve a plastic tube, about the length of a person’s arm and filled with mud from the bottom of the bay. As the tube is hauled on board, the stench of rotten eggs fills the air.

      “Chesapeake Bay mud is stinky,” says Sairah Malkin, a biogeochemist at the University of Maryland Center for Environmental Science in Cambridge who is aboard the boat. The smell comes from sulfuric chemicals called sulfides within the mud. They’re quite toxic, Malkin explains.

      Malkin and her team venture out onto the bay every couple of months to sample the foul muck and track the abundance of squiggling mud dwellers called cable bacteria. The microbes are living wires: Their threadlike bodies — thinner than a human hair — can channel electricity.

      Sairah Malkin, of the University of Maryland Center for Environmental Science, cuts holes in a large sediment coring tube to sample mud collected from the bottom of the Chesapeake Bay.Clara Fuchsman

      Cable bacteria use that power to chemically rewire their surroundings. While some microbes in the area produce sulfides, the cable bacteria remove those chemicals and help prevent them from moving up into the water column. By managing sulfides, cable bacteria may protect fish, crustaceans and other aquatic organisms from a “toxic nightmare,” says Filip Meysman, a biogeochemist at the University of Antwerp in Belgium. “They’re kind of like guardian angels in these coastal ecosystems.”

      Now, scientists are studying how these living electrical filaments might do good in other ways. Laboratory experiments show that cable bacteria can support other microbes that consume crude oil, so researchers are investigating how to encourage the bacteria’s growth to help clean up oil spills. What’s more, researchers have shown that cable bacteria could help slash emissions of a potent greenhouse gas — methane — into the atmosphere.

      There’s plenty of evidence that cable bacteria exert a strong influence over their microbial neighbors, Meysman says. The next step, he says, is to figure out how to channel that influence for the greater good.

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      Electric life

      Under the microscope, cable bacteria resemble long sausage links. Their multicellular bodies can grow up to 5 centimeters long. Embedded in the envelope of each cell are parallel “wires” of conductive proteins, which the bacteria use to channel electrons. According to Meysman, the wires are more conductive than the semi­conductors found in electronics.

      About a decade ago, a team of scientists first discovered cable bacteria, in sediment collected from the bottom of Denmark’s Aarhus Bay. Since then, cable bacteria have been found on at least four continents, in streams, lakes, estuaries and coastal environments. “Name me a country, and I’ll show you where the cable bacteria are,” Meysman says.

      Most often, cable bacteria nestle shallow in the sediment, with one end positioned near the surface where there is oxygen and the other end plugged into deeper, sulfide-rich zones. Using their filamentous bodies as electrical conduits, cable bacteria snatch electrons from sulfides on one end and off-load them to oxygen — an eager electron acceptor — at the other, says Nicole Geerlings, a biogeochemist at Utrecht University in the Netherlands. Similar to how batteries charge and release energy by transferring electrons between an anode and cathode, cable bacteria power themselves by channeling electrons, she says. “The electron transport gives [cable bacteria] energy.”

      This unique lifestyle allows cable bacteria to survive in an environment that many organisms could not endure.

      A cable bacterium (right) has a multicellular, segmented body that can grow up to 5 centimeters. Electrically conductive, parallel fibers (visible in the close-up at left) encase the body.From left: N. Geerlings/Utrecht Univ.; Silvia Hidalgo Martinez/Univ. of Antwerp

      Toxic fire wall

      In 2015, Malkin, Meysman and colleagues reported that cable bacteria may help to counteract the onset of euxinia — a fatal buildup of sulfides in oxygen-starved bodies of water. Euxinia can trigger mass die-offs of fish, crustaceans and other aquatic life.

      The lethal phenomenon can occur after fertilizers or sewage are washed into the sea or lakes. That flow of nutrients can trigger algal blooms. When those nutrients are depleted, the blooms die, and large quantities of organic matter sink and accumulate on the sediment. Microbes then decompose the dead material, devouring much of the oxygen in the surrounding water in the process. When oxygen levels become critically low, sulfides may begin to leak from the sediment into the water, giving rise to euxinia.

      Sediments near the bottom of this core sample, taken from the Chesapeake Bay, are probably dark due to the presence of sulfides, while sediments near the top are lighter because cable bacteria have removed the sulfides.S. Malkin

      While studying cable bacteria in a brackish body of water in the Netherlands, Malkin and colleagues discovered a thin layer of rust coating the lake’s bottom. As the cable bacteria pulled electrons from sulfides, converting the noxious chemicals into less-harmful sulfates, the water within the sediment became more acidic, which dissolved some minerals containing iron. The now-mobile iron percolated upward in the sediment, until it interacted with oxygen to form rust.

      This layer of rust could capture sulfides that would otherwise flow into the water, acting as a “fire wall” that could delay euxinia for over a month, or even prevent it altogether, the researchers reported. Even when the cable bacteria’s population dropped, the rust layer persisted, protecting other aquatic creatures from sulfide exposure. The rust may explain why even though instances of nutrient pollution, algal blooms and oxygen depletion are relatively common, reports of euxinia are rare.

      Oil cleanup

      Some researchers are trying to harness the bacteria’s electrical abilities to tackle another devastating threat to coastal ecosystems — oil spills.

      When an oil spill happens in a body of water, booms, skimmers or sorbents are often deployed to limit the spread of hydrocarbons on the surface. But oil may also wash onto beaches, mix with sediments in shallow waters and aggregate onto sinking particles of organic debris, hitching a ride to the seafloor.

      Cleaning up oil at the bottom of the sea is a difficult job, says Ugo Marzocchi, a biogeochemist at Aarhus University in Denmark. “I am not aware of a very effective way to remove hydrocarbons from the seafloor,” he says. “In inland freshwater systems, what is generally done is to dig out the sediments,” he says, an expensive strategy that would be even more costly at sea.

      [embedded content]
      Electrical cable bacteria (white filaments) emerge from the seafloor sediment (at bottom) stretching their bodies to reach a zone of oxygen in the water. The stringy organisms use the oxygen to offload electrons they’ve harvested from harmful sulfides found in the sediment. As sulfide concentrations go down, the water becomes more habitable to microbes that can clean up oil spills.

      Some soil-dwelling microorganisms can use hydrocarbons to fuel their metabolism, and researchers have been studying how some of these oil burners might assist in the cleanup of contaminated sediments. But as they break down hydrocarbons, the microbes generate those concerning sulfides, which are detrimental to the microbes’ own survival, Marzocchi says. In other words, the microbes can help clean up the oil for only so long before they’re overwhelmed by their own toxic waste.

      Cable bacteria might be just the solution, Marzocchi thought. In 2016, researchers reported finding evidence of the electrical microbes in a tar oil-contaminated groundwater aquifer in Germany. Knowing that cable bacteria could occupy sediments contaminated with hydrocarbons, Marzocchi and colleagues reasoned that these bacteria might be able to assist oil-burning microbes and accelerate oil cleanup.

      The researchers filled several containers with oil-contaminated sediment from Aarhus Bay — which contained naturally occurring oil-eating bacteria. The group then injected a few containers with cable bacteria and monitored the degree of hydrocarbon degradation in all of the containers over seven weeks. By the end of the test, the concentration of alkanes — a type of hydrocarbon — in the sediment with cable bacteria had dropped from 0.125 milligrams per gram of sediment to 0.086 milligrams per gram — a 31 percent drop. That’s 23 percentage points more than the 9 percent decrease in the control samples. Cable bacteria helped accelerate the metabolic activity of their oil-eating neighbors by converting the toxic sulfides into sulfates. The sulfates didn’t harm the oil-eating microbes — in fact, they used the chemicals as fuel.

      The researchers are now trying to develop methods to promote cable bacteria growth in the field and see if it’s possible to enhance their effect on oil degradation. One catch is that in oil-contaminated sediment, oxygen is quickly used up by the microbes that break down hydrocarbons. That’s a problem since cable bacteria need access to oxygen. Salts that slowly release oxygen or nitrate — which cable bacteria can use in place of oxygen — might help spur the electrical organisms’ growth at oil spills. But more work is needed to identify the right chemical components and dosage, Marzocchi says.

      Meanwhile, scientists are investigating how cable bacteria might help reduce emission of another hydrocarbon — one that accumulates in the sky.

      Methane at the root

      Colorless, odorless methane is the simplest hydrocarbon (SN: 8/15/20, p. 8). It consists of a single carbon atom attached to a quartet of hydrogen atoms. And it’s a potent greenhouse gas — more than 25 times as effective at trapping heat in the atmosphere as carbon dioxide.

      One major source of methane is rice paddies (SN: 9/25/21, p. 16). During the growing season, rice farmers typically flood their fields to help stave off weeds and pests. Methane-producing microbes — aptly named methanogens — thrive in these waterlogged soils. Paddy-dwelling methanogens are so prolific that rice fields are estimated to generate about 11 percent of all human-induced methane emissions.

      But cable bacteria like paddies too. In 2019, Vincent Scholz, a microbiologist at Aarhus University, and colleagues reported that cable bacteria could flourish among the roots of rice plants and several other aquatic plant species.

      In an experiment, pots of rice plants grown in soils with cable bacteria (right) developed orange layers of rust and emitted less methane than pots without cable bacteria (left).V.V. Scholz/Aarhus Univ.

      That discovery inspired the researchers to investigate how the bacteria interact with methanogens in soils that grow rice. The team grew its own rice plants — some potted in soils with cable bacteria, and some without — and monitored methane emissions.

      To the researchers’ surprise, adding cable bacteria reduced rice soil methane emissions by 93 percent. In the process of removing electrons from sulfides, the bacteria generate sulfates, which other microbes can use as fuel. These sulfate-consuming microbes outcompeted methanogens for nutrients such as hydrogen and acetate in the rice soils, the researchers found. The results were “quite amazing,” Scholz says, though the effectiveness of the electrical microbes in real rice fields has yet to be tested.

      There are signs that cable bacteria are already plugged into real rice paddy soils. After analyzing genetic data collected from rice paddies in the United States, India, Vietnam and China, Scholz and colleagues reported in 2021 the presence of cable bacteria at sites in all four countries. Scholz is in Northern California this summer studying how cable bacteria live in rice fields and whether they’re already impacting methane emissions. He is also exploring ways to introduce cable bacteria to rice fields where they don’t yet exist or enhance the microbes’ numbers in fields where they do.

      There is still much to discover about how the wispy electrical conductors influence our world, Malkin says. Back in the Chesapeake Bay, she and colleagues have found that cable bacteria tend to flourish in the spring, a surge that has also been observed in the Netherlands. The findings add to a growing body of work that suggests cable bacteria are opportunistic organisms that interact with their environments in similar ways all around the world.

      If cable bacteria are already hard at work across the planet, then a bit of coaxing from researchers may be all it takes to turn the mud-dwelling creatures into the most helpful neighbors that a living thing could ask for. More