Wednesday, February 28, 2018
Modern volcanism tied to events occurring soon after Earth's birth
Plumes of hot magma from the volcanic hotspot that formed Réunion Island in the Indian Ocean rise from an unusually primitive source deep beneath Earth's surface, according to new work in Nature from Carnegie's Bradley Peters, Richard Carlson, and Mary Horan along with James Day of the Scripps Institution of Oceanography.
Réunion marks the present-day location of the hotspot that 66 million years ago erupted the Deccan Traps flood basalts, which cover most of India and may have contributed to the extinction of the dinosaurs. Flood basalts and other hotspot lavas are thought to originate from different portions of Earth's deep interior than most volcanoes at Earth's surface and studying this material may help scientists understand our home planet's evolution.
The heat from Earth's formation process caused extensive melting of the planet, leading Earth to separate into two layers when the denser iron metal sank inward toward the center, creating the core and leaving the silicate-rich mantle floating above.
Over the subsequent 4.5 billion years of Earth's evolution, deep portions of the mantle would rise upwards, melt, and then separate once again by density, creating Earth's crust and changing the chemical composition of Earth's interior in the process. As crust sinks back into Earth's interior -- a phenomenon that's occurring today along the boundary of the Pacific Ocean -- the slow motion of Earth's mantle works to stir these materials, along with their distinct chemistry, back into the deep Earth.
But not all of the mantle is as well-blended as this process would indicate. Some older patches still exist -- like powdery pockets in a poorly mixed bowl of cake batter. Analysis of the chemical compositions of Réunion Island volcanic rocks indicate that their source material is different from other, better-mixed parts of the modern mantle.
Using new isotope data, the research team revealed that Réunion lavas originate from regions of the mantle that were isolated from the broader, well-blended mantle. These isolated pockets were formed within the first ten percent of Earth's history.
Isotopes are elements that have the same number of protons, but a different number of neutrons. Sometimes, the number of neutrons present in the nucleus make an isotope unstable; to gain stability, the isotope will release energetic particles in the process of radioactive decay. This process alters its number of protons and neutrons and transforms it into a different element. This new study harnesses this process to provide a fingerprint for the age and history of distinct mantle pockets.
Samarium-146 is one such unstable, or radioactive, isotope with a half-life of only 103 million years. It decays to the isotope neodymium-142. Although samarium-146 was present when Earth formed, it became extinct very early in Earth's infancy, meaning neodymium-142 provides a good record of Earth's earliest history, but no record of Earth from the period after all the samarium-146 transformed into neodymium-142. Differences in the abundances of neodymium-142 in comparison to other isotopes of neodymium could only have been generated by changes in the chemical composition of the mantle that occurred in the first 500 million years of Earth's 4.5 billion-year history.
The ratio of neodymium-142 to neodymium-144 in Réunion volcanic rocks, together with the results of lab-based mimicry and modeling studies, indicate that despite billions of years of mantle mixing, Réunion plume magma likely originates from a preserved pocket of the mantle that experienced a compositional change caused by large-scale melting of Earth's earliest mantle.
The team's findings could also help explain the origin of dense regions right at the boundary of the core and mantle called large low shear velocity provinces (LLSVPs) and ultralow velocity zones (ULVZs), reflecting the unusually slow speed of seismic waves as they travel through these regions of the deep mantle. Such regions may be relics of early melting events.
"The mantle differentiation event preserved in these hotspot plumes can both teach us about early Earth geochemical processes and explain the mysterious seismic signatures created by these dense deep-mantle zones," said lead author Peters.
Funding for fieldwork for this study was provided by the National Geographic Society (NGS 8330-07), the Geological Society of America (GSA 10539-14), and by a generous personal donation from Dr. R. Rex. Support for laboratory work was provided by Carnegie Institution for Science.
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Mangroves making way for fish farms
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Quinnipiac group restoring mangrove forest in Puerto Rico wrecked by Hurricane Maria
Mangroves are coming our way
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Tuesday, February 27, 2018
Scientists discover key gene for producing marine molecule with huge environmental impacts
Researchers at the University of East Anglia have discovered a key gene for the synthesis of one of the world's most abundant sulfur molecules.
Dimethylsulfoniopropionate (DMSP) is an important nutrient in marine environments with more than one billion tonnes produced annually by marine phytoplankton (microscopic plant-like cells), seaweed and bacteria.
When marine microorganisms break down DMSP, they release a climate-cooling gas called dimethylsulfide (DMS), which also gives the seaside its characteristic smell.
The discovery of a gene (named DSYB) responsible for synthesising DMSP, published today in Nature Microbiology, represents a huge step forward in the field of sulfur cycling in marine environments. It could also allow scientists to better predict the impact of climate change on DMSP production.
The team discovered that this gene, and therefore DMSP synthesis itself, likely originated in marine bacteria and was later passed onto phytoplankton, which have evolved to be marine factories for this molecule.
Lead researcher Dr Jonathan Todd, from UEA's School of Biological Sciences, said: "DMS is a very important gas. Across the world's oceans, seas and coasts, tens of millions of tonnes of it are released by microbes that live near plankton and marine plants, including seaweeds and some salt-marsh grasses.
"DMS is thought to affect climate by increasing cloud droplets that in turn reduce the amount of sunlight reaching the ocean's surface. These same clouds are vital in the movement of large amounts of sulfur from the oceans to land, making the production of DMSP and DMS a critical step in the global sulfur cycle.
"Marine phytoplankton produce the majority of global DMSP. Until now, we didn't know any of the phytoplankton genes responsible for the synthesis of this highly abundant marine nutrient."
The discovery of genes involved in the production of DMSP in phytoplankton, as well as bacteria, will allow scientists to better evaluate which organisms make DMSP in the marine environment and predict how the production of this influential molecule might be affected by future environmental changes, such as the warming of the oceans due to climate change.
Dr Todd said: "The identification of the DMSP synthesis genes in marine bacteria and phytoplankton allows us to evaluate for the first time which organisms produce DMSP in the environment. This discovery represents a huge step forward in the field of sulfur cycling in marine environments."
Dr Andrew Curson, also from UEA's School of Biological Sciences and one of the lead researchers on the paper, said: "The DSYB gene is found in all the major phytoplankton groups that produce this environmentally important molecule. Also, because it is involved in such a critical step in the synthesis pathway, the regulation of the DSYB gene by environmental conditions is of great significance in determining how much DMSP is ultimately produced."
PhD student Beth Williams, who was also a major contributor to the research, added: "The discovery of the evolutionary link between bacterial and phytoplankton DSYB was both surprising and interesting, as it indicated that the ability to synthesise DMSP through this pathway originated in bacteria. This suggests that bacteria may play an even more important role in global DMSP synthesis, both historically and in the present day."
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Largest Chinook salmon disappearing from West Coast
The largest and oldest Chinook salmon -- fish also known as "kings" and prized for their exceptional size -- have mostly disappeared along the West Coast.
That's the main finding of a new University of Washington-led study published Feb. 27 in the journal Fish and Fisheries. The researchers analyzed nearly 40 years of data from hatchery and wild Chinook populations from California to Alaska, looking broadly at patterns that emerged over the course of four decades and across thousands of miles of coastline. In general, Chinook salmon populations from Alaska showed the biggest reductions in age and size, with Washington salmon a close second.
"Chinook are known for being the largest Pacific salmon and they are highly valued because they are so large," said lead author Jan Ohlberger, a research scientist in the UW's School of Aquatic and Fishery Sciences. "The largest fish are disappearing, and that affects subsistence and recreational fisheries that target these individuals."
Chinook salmon are born in freshwater rivers and streams, then migrate to the ocean where they spend most of their lives feeding and growing to their spectacular body size. Each population's lifestyle in the ocean varies, mainly depending on where they can find food. California Chinook salmon tend to stay in the marine waters off the coast, while Oregon and Washington fish often migrate thousands of miles northward along the west coast to the Gulf of Alaska where they feed. Western Alaska populations tend to travel to the Bering Sea.
After one to five years in the ocean, the fish return to their home streams, where they spawn and then die.
Despite these differences in life history, most populations analyzed saw a clear reduction in the average size of the returning fish over the last four decades -- up to 10 percent shorter in length, in the most extreme cases.
These broad similarities point to a cause that transcends regional fishing practices, ecosystems, or animal behaviors, the authors said.
"This suggests that there is something about the larger ocean environment that is driving these patterns," Ohlberger said. "I think fishing is part of the story, but it's definitely not sufficient to explain all of the patterns we see. Many populations are exploited at lower rates than they were 20 to 30 years ago."
It used to be common to find Chinook salmon 40 inches or more in length, particularly in the Columbia River or Alaska's Kenai Peninsula and Copper River regions. The reductions in size could have a long-term impact on the abundance of Chinook salmon, because smaller females carry fewer eggs, so over time the number of fish that hatch and survive to adulthood may decrease.
There are likely many reasons for the changes in size and age, and the researchers say there is no "smoking gun." Their analysis, however, points to fishing pressure and marine mammal predation as two of the bigger drivers.
Commercial and sport fishing have for years targeted larger Chinook. But fishing pressure has relaxed in the last 30 years due to regulations to promote sustainable fishing rates, while the reductions in Chinook size have been most rapid over the past 15 years. Resident killer whales, which are known Chinook salmon specialists, as well as other marine mammals that feed on salmon are probably contributing to the overall changes, the researchers found.
"We know that resident killer whales have a very strong preference for eating the largest fish, and this selectivity is far greater than fisheries ever were," said senior author Daniel Schindler, a UW professor of aquatic and fishery sciences.
While southern resident killer whales that inhabit Puget Sound are in apparent decline, populations of northern resident killer whales, and those that reside in the Gulf of Alaska and along the Aleutian Islands, appear to be growing at extremely fast rates. The paper's authors propose that these burgeoning northern populations are possibly a critical, but poorly understood, cause of the observed declines in Chinook salmon sizes.
Scientists are still trying to understand the impacts of orcas and other marine mammals on Chinook salmon, and the ways in which their relationships may have ebbed and flowed in the past. It may not be possible, for example, for marine mammals and Chinook salmon populations to be robust at the same time, given their predator-prey relationship.
"When you have predators and prey interacting in a real ecosystem, everything can't flourish all the time," Schindler said. "These observations challenge our thinking about what we expect the structure and composition of our ecosystems to be."
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City to build new trails at estuary, Whiskey Ridge
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KELT returns the tide to a salt marsh in Georgetown
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Feng shui by the estuary
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Woman who jumped from Estuary Bridge in Mandurah escapes with minor injuries
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Amazing images of Tokyo before it became a city
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Monday, February 26, 2018
Could cleaning up beaches make Americans better off?
Cleaning up beaches could boost local economies in addition to preserving natural treasures and animal habitats.
In southern California's Orange County alone, the economic benefits of beach cleanup could range from $13 per resident in a three-month period if debris were reduced by 25 percent to $42 per resident with a 75 percent drop in plastics and other trash along the oceanfront, according to a new study. That could mean up to a $46 million boost to the county's economy in just one summer.
This is the first study to compare the amount of ocean debris with the behavior of beachgoers and to calculate an economic benefit to cleaning up those beaches, said Tim Haab, a professor of agricultural, environmental and development economics at The Ohio State University.
To come up with an estimated benefit, Haab and his co-authors embarked on a two-part study, which appears online in the journal Marine Resource Economics. The work was done in collaboration with the National Oceanic and Atmospheric Administration's marine debris program.
The researchers evaluated the amount of ocean debris on 31 California beaches and found that some were much dirtier than others. Debris includes plastics that wash in from ships, trash that finds its way to shore from rivers and the litter that beach visitors leave behind.
The research team also mailed surveys to 4,000 randomly selected Orange County residents to learn about which beaches they frequent and what they look for in a good sun-and-surf spot. They heard back from 36 percent of those households and analyzed their 1,436 completed surveys. Some people visited the beach often, others less frequently. Information from thousands of beach trips went into the analysis.
Overall, the Californians ranked absence of marine debris and good water quality as key characteristics when deciding on a beach to visit -- 66 percent of those surveyed called those factors "very important." Those qualities ranked above scenic beauty, convenient parking and sandiness.
The researchers were able to take information about the participants' beach-use patterns -- and how far they travel to get to a desirable beach -- to calculate a travel cost linked to skipping nearby dirty beaches in favor of longer jaunts to cleaner coastline. They took other influences on beachgoer behavior, such as availability of trash cans and beach congestion, into account when analyzing the data.
"A lot of work has been done to quantify the physical costs of ocean debris, but until now we haven't been able to quantify the economic benefit of cleaning up the beaches and preventing the problem in the first place," Haab said.
"We were able to correlate ocean debris with trip patterns and arrive at potential cost savings if people went to closer beaches."
Estimated savings ranged from $29.5 million ($12.91 per Orange County resident) to $46.5 million ($42.30 per Orange County resident) in a three-month period. The lower-end estimate was based on a 25 percent reduction in debris; the higher-end estimate on a 75 percent reduction.
"Given the magnitude of these benefits, a variety of marine debris abatement activities is likely to prove cost effective," the researchers wrote.
"In 2016, outdoor recreation accounted for $374 billion, or 2 percent, of the gross domestic product in the United States. This shows that improving environmental quality can benefit the economy," Haab said.
He said the savings could be even greater than outlined in the study. It did not take into account travelers from outside Orange County, for instance, nor did it consider benefits beyond those afforded to beach visitors, such as a healthier habitat for marine life.
The study could serve to inform policy decisions by showing that there are economic reasons -- in addition to the environmental ones -- to look for ways to prevent ocean debris and clean up the plastics and other litter on beaches.
"We put a dollar value on beach cleanup efforts. This is important because it helps government agencies quantify the benefits of efforts to keep marine debris out of our waterways and off of our beaches," said study co-author Christopher Leggett of Bedrock Statistics.
Haab would like to work on a larger-scale evaluation of the economic impact of ocean debris to better understand differences in coastal communities around the U.S. and abroad, he said.
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King penguins may be on the move very soon
"The main issue is that there is only a handful of islands in the Southern Ocean and not all of them are suitable to sustain large breeding colonies" says Robin Cristofari, first author of the study, from the Institut Pluridisciplinaire Hubert Curien (IPHC/CNRS/University of Strasbourg) and the Centre Scientifique de Monaco (CSM).
King penguins are in fact picky animals: in order to form a colony where they can mate, lay eggs and rear chicks over a year, they need tolerable temperature all year round, no winter sea ice around the island, and smooth beach of sand or pebbles. But, above all, they need an abundant and reliable source of food close by to feed their chicks. For millennia, this seabird has relied on the Antarctic Polar Front, an upwelling front in the Southern Ocean concentrating enormous amounts of fish on a relatively small area. Yet, due to climate change, this area is drifting south, away from the islands where most King penguins currently live. Parents are then forced to swim farther to find food, while their progeny is waiting, fasting longer and longer on the shore. This study predicts that, for most colonies, the length of the parents' trips to get food will soon exceed the resistance to starvation of their offspring, leading to massive King penguin crashes in population size, or, hopefully, relocation.
Using the information hidden away in the penguin's genome, the research team has reconstructed the changes in the worldwide King penguin population throughout the last 50,000 years, and discovered that past climatic changes, causing shifts in marine currents, sea-ice distribution and Antarctic Polar Front location, have always been linked to critical episodes for the King penguins. However, hope is not lost yet: King penguins have already survived such crises several times (the last time was 20 thousand years ago), and they may be particularly good at it. "Extremely low values in indices of genetic differentiation told us that all colonies are connected by a continuous exchange of individuals," says Emiliano Trucchi formerly at the University of Vienna and now at the University of Ferrara, one of the coordinator of the study. "In other words, King penguins seem to be able to move around quite a lot to find the safest breeding locations when things turn grim."
But there is a major difference this time: for the first time in the history of penguins, human activities are leading to rapid and/or irreversible changes in the Earth system, and remote areas are no exception. In addition to the strongest impact of climate change in Polar Regions, Southern Ocean is now subject to industrial fishing, and penguins may soon have a very hard time fighting for their food. "There are still some islands further south where King penguins may retreat," notes Céline Le Bohec (IPHC/CNRS/University of Strasbourg and CSM), leader of the programme 137 of the French Polar Institut Paul-Emile Victor within which the study was initiated, "but the competition for breeding sites and for food will be harsh, especially with the other penguin species like the Chinstrap, Gentoo or Adélie penguins, even without the fisheries. It is difficult to predict the outcome, but there will surely be losses on the way. If we want to save anything, proactive and efficient conservation efforts but, above all, coordinated global action against global warming should start now."
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Tracking data reveal the secret lives of marine animals
The movements of marine mammals and other large animals that spend their lives in the ocean were largely unknown prior to the development of sophisticated tracking devices researchers could deploy on animals in the wild. Insights gained from this technology have revealed unexpected behaviors and migratory patterns in marine animals ranging from sharks and seals to turtles and albatrosses.
Researchers from around the world have now pooled their data on the movements of a wide array of marine animals, enabling them to look for common features in how animals move throughout the world's oceans. The results, published February 26 in Proceedings of the National Academy of Sciences, show remarkable convergence in the movement patterns of different species, even those widely separated by geography, phylogeny (evolutionary history), or mode of travel.
The biggest differences were between different habitats rather than between different species. In coastal areas, tracking tags revealed complex movement patterns dominated by search behavior, while in the open ocean they showed simpler, more predictable movements over longer distances.
"It makes sense, because the coast is a much more complicated environment, whereas the open ocean is more homogeneous and the features are more spread out in space and time," said coauthor Daniel Costa, a distinguished professor of ecology and evolutionary biology at UC Santa Cruz. "Regardless of what species it is, the movement patterns match the oceanographic features of their environment."
These insights can be useful, he said, for understanding how marine life will respond to climate change and for predicting the movements of species for which tracking data are lacking. "Many of these species are endangered and we have no tracking data, but we can extrapolate from other species to understand how they are likely to interact with fisheries, shipping, or other human activities," Costa said.
Costa has been at the forefront of developing high-tech tracking devices and using them to study marine animals. UCSC's Long Marine Laboratory is known as a leading center for research on marine vertebrates, including seals, sea lions, sea otters, dolphins, and whales. The coauthors of the PNAS paper include six other UC Santa Cruz researchers in addition to Costa.
"This paper is the result of a big international effort. We realized that if we all share our data and work together in a concerted manner, we can learn a lot more about these animals," he said.
Costa and other UCSC researchers deployed the first satellite tracking tags on elephant seals at the Año Nuevo rookery north of Santa Cruz in the 1990s. The initial results were astonishing.
"Before we put tags on elephant seals, all the books said they were limited to the California Current. We had no idea they were traveling these incredible distances and using the entire North Pacific Ocean," Costa said. "We went from studying them where we could watch them to having the animals tell us where they were going."
In 2000, Costa joined forces with Barbara Block at Stanford University and others to launch the Tagging of Pacific Predators (TOPP) program, a decade-long effort to track the movements of top marine predators in the Pacific Ocean. Costa oversaw the tracking of marine mammals, birds, and turtles for TOPP, which also included tracking of sharks and tunas.
Costa's lab has carried out groundbreaking tracking studies of a wide range of species around the world, including albatrosses, sooty shearwaters, California sea lions, Galapagos sea lions, crabeater seals, Weddell seals, and southern elephant seals. Meanwhile, his team has continued to learn new things about elephant seal biology from ongoing studies of the northern elephant seals at UC's Año Nuevo Natural Reserve.
One recent study, published February 14 in Biology Letters, revealed the effects of pregnancy on the diving behavior of female elephant seals. Led by postdoctoral researcher Luis Huckstadt, the researchers found that the dives of pregnant seals became shorter, probably due to an increasing demand for oxygen for the fetus.
"The only way we could do that is because we now have over 500 tracks of female elephant seals, and a small number of them didn't have a pup or lost it at sea, so we could compare and see the effects of pregnancy. It's not surprising, but nobody had been able to document it," Costa said.
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Series of storms more than 150 years ago caused extensive erosion of the Carpinteria Salt Marsh
Flooding isn't new to the Santa Barbara coastline. However, the inundation doesn't always come from the mountains as it did last month in Montecito.
Back in 1861-2, a series of large storms washed beach sand more than a quarter mile inland into what today is the Carpinteria Salt Marsh. Although historical accounts document the inland flooding, little has been known about how those storms impacted a now heavily developed California coast.
In a new paper in the journal Marine Geology, UC Santa Barbara geologists provide the first physical evidence of coastal erosion and inundation produced by these storms. In the upper meter of marsh sediments, they found a unique deposit -- in fact the only such deposit to have happened over the past 300 or so years.
"The deposit is comparable in scale to those caused by moderate hurricanes or even small tsunamis," explained co-author Alex Simms, an associate professor in UCSB's Department of Earth Science. "The deposit suggests that the 1861-62 storm season was erosive enough to remove coastal barriers, allowing extensive coastal flooding in areas currently developed today."
The team conducted its work at the Carpinteria Salt Marsh Reserve, part of UCSB's Natural Reserve System.
Lead author Laura Reynolds, a graduate student in Simms' lab, and co-authors mapped the sand deposit within the Carpinteria marsh using 40 sediment cores, tubes of sediment up to 4 meters long. They confirmed the deposit's age using the presence of European crop pollen as well as tiny grains known as spheroidal carbonaceous particles, which are created by the burning of fossil fuels.
The researchers compared the candidate storm deposit to sand from modern stream, beach and dune environments. They determined that the sediments from the candidate storm deposit were most similar to modern beach sand in terms of mineral content and the size of the sand grains. This suggests the sand was brought into the marsh from the beach, not from streams.
The storms of 1861-62 are hypothesized to have resulted from atmospheric rivers, concentrated zones of water vapor high up in the atmosphere that produce intense precipitation and river flooding along coastlines on which they occur. Although ocean flooding from tsunamis and other large storms has happened throughout the past 200 years in Southern California, no other event is known to have washed beach sand into the Carpinteria Salt Marsh.
This suggests that the storm season was unusually destructive to the sandy barrier that separates the marsh from the ocean. Therefore, efforts to prepare for a recurrence of storms like those that occurred during that time need to address potential coastal impacts.
"This is particularly troubling considering coastal systems that once took the brunt of storm events -- dunes, beaches and estuaries -- are today some of the most degraded and developed environments in coastal regions around the world," Reynolds said. "Consequently, mitigation efforts for prolonged stormy periods should consider the effects of coastal erosion and inundation in addition to the effects of excess precipitation."
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New understanding of ocean turbulence could improve climate models
Brown University researchers have made a key insight into how high-resolution ocean models simulate the dissipation of turbulence in the global ocean. Their research, published in Physical Review Letters, could be helpful in developing new climate models that better capture ocean dynamics.
The study was focused on a form of turbulence known as mesoscale eddies, ocean swirls on the scale of tens to hundreds of kilometers across that last anywhere from a month to a year. These kinds of eddies can pinch off from strong boundary currents like the Gulf Stream, or form where water flows of different temperatures and densities come into contact.
"You can think of these as the weather of the ocean," said Baylor Fox-Kemper, co-author of the study and an associate professor in Brown's Department of Earth, Environmental and Planetary Sciences. "Like storms in the atmosphere, these eddies help to distribute energy, warmth, salinity and other things around the ocean. So understanding how they dissipate their energy gives us a more accurate picture of ocean circulation."
The traditional theory for how small-scale turbulence dissipates energy states that as an eddy dies out, it transmits its energy to smaller and smaller scales. In other words, large eddies decay into smaller and smaller eddies until all the energy is dissipated. It's a well-established theory that makes useful predictions that are widely used in fluid dynamics. The problem is that it doesn't apply to mesoscale eddies.
"That theory only applies to eddies in three-dimensional systems," Fox-Kemper said. "Mesoscale eddies are on the scale of hundreds of kilometers across, yet the ocean is only four kilometers deep, which makes them essentially two-dimensional. And we know that dissipation works differently in two dimensions than it does in three."
Rather than breaking up into smaller and smaller eddies, Fox-Kemper says, two-dimensional eddies tend to merge into larger and larger ones.
"You can see it if you drag your finger very gently across a soap bubble," he said. "You leave behind this swirly streak that gets bigger and bigger over time. Mesoscale eddies in the global ocean work the same way."
This upscale energy transfer is not as well understood mathematically as the downscale dissipation. That's what Fox-Kemper and Brodie Pearson, a research scientist at Brown, wanted to do with this study.
They used a high-resolution ocean model that has been shown to do a good job of matching direct satellite observations of the global ocean system. The model's high resolution means it's able to simulate eddies on the order of 100 kilometers across. Pearson and Fox-Kemper wanted to look in detail at how the model dealt with eddy dissipation in statistical terms.
"We ran five years of ocean circulation in the model, and we measured the damping of energy at every grid point to see what the statistics are," Fox-Kemper said. They found that dissipation followed what's known as a lognormal distribution -- one in which one tail of the distribution dominates the average.
"There's the old joke that if you have 10 regular people in a room and Bill Gates walks in, everybody gets a billion dollars richer on average -- that's a lognormal distribution," Fox-Kemper said. "What it tells us in terms of turbulence is that 90 percent of the dissipation takes place in 10 percent of the ocean."
Fox-Kemper noted that the downscale dissipation of 3-D eddies follows a lognormal distribution as well. So despite the inverse dynamics, "there's an equivalent transformation that lets you predict lognormality in both 2-D and 3-D systems."
The researchers say this new statistical insight will be helpful in developing coarser-grained ocean simulations that aren't as computationally expensive as the one used in this study. Using this model, it took the researchers two months using 1,000 processors to simulate just five years of ocean circulation.
"If you want to simulate hundreds or thousands or years, or if you want something you can incorporate within a climate model that combines ocean and atmospheric dynamics, you need a coarser-grained model or it's just computationally intractable," Fox-Kemper said. "If we understand the statistics of how mesoscale eddies dissipate, we might be able to bake those into our coarser-grained models. In other words, we can capture the effects of mesoscale eddies without actually simulating them directly."
The results could also provide a check on future high-resolution models.
"Knowing this makes us much more capable of figuring out if our models are doing the right thing and how to make them better," Fox-Kemper said. "If a model isn't producing this lognormality, then it's probably doing something wrong."
The research was supported by the National Science Foundation (OCE-1350795), Office of Naval Research (N00014-17-1-2963) and the National Key Research Program of China (2017YFA0604100.
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Mumbai's Mangrove Warriors: Meet the citizens who're working to reclaim city's lost mangroves
Botched Mangroves Bill draws large public opposition
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Outdoor Program to host spring break trip to Florida mangrove
Naigaon mangrove plot converted into banana plantation and vegetable field
Sunday, February 25, 2018
Nervous night for Havelock man as ex-Cyclone Gita fills estuary
Saturday, February 24, 2018
Mangroves free of 500 tonne plastic
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A Bird-Lover's Paradise in the Mangroves Outside of Cartagena, Colombia
Birding paradise in Mexico's Riviera Nayarit
Exploring Cayman's magical mangroves
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Local Focus: 'District Councils lack expertise for mangrove management' - Forest and Bird
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Friday, February 23, 2018
When every fish counts: Genetic tools can ensure accuracy of identification of endangered fish
Guest Commentary: Kayaking in the Nauset Estuary
Lagoon report shows a waterway in peril
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Edgartown Great Pond Comeback Is Communal Effort
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Thursday, February 22, 2018
Stagnation in the South Pacific
A team led by geochemist Dr. Katharina Pahnke from Oldenburg has discovered important evidence that the rise in atmospheric carbon dioxide levels at the end of the last ice age was triggered by changes in the Antarctic Ocean. The researchers from the University of Oldenburg's Institute for Chemistry and Biology of the Marine Environment (ICBM), the Max Planck Institute for Marine Microbiology in Bremen and the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) were able to demonstrate that the deep South Pacific was strongly stratified during the last ice age, and could thus have facilitated long-term, deep-sea storage of the greenhouse gas carbon dioxide (CO2). The study, which has now been published in the academic journal Science, also indicates that in the course of the warming following the end of the last ice age the mixing of the deep water masses increased, releasing stored CO2 and enhancing global warming.
The Southern Ocean plays an important role in climate events because CO2 can be absorbed from the atmosphere into the ocean. When increased amounts of dust are deposited in the seawater, microscopic algae multiply because the iron contained in the dust acts as a fertilizer. When these single celled algae die, they sink to the ocean floor, taking the sequestered carbon dioxide with them. To ensure long-term removal of the CO2 from the atmosphere, however, it must be stored in stable conditions in deep water over long periods of time.
In order to find out how water masses in the deep South Pacific have developed over the last 30,000 years, the team recovered sediment cores from water depths of between 3,000 and more than 4,000 metres during an expedition of the research vessel "Polarstern" to the South Pacific. The geochemists Dr. Chandranath Basak and Dr. Henning Fröllje of the ICBM -- the two main authors of the study -- extracted tiny teeth and other skeletal debris of fossil fish from the sediment to analyse their content of isotopes of the rare earth metal neodymium.
"Neodymium is particularly useful for identifying water masses of different origin," said Pahnke, the head of the Max Planck Research Group for Marine Isotope Geochemistry based at the ICBM and the Max Planck Institute for Marine Microbiology in Bremen, explaining that each layer of water has its own characteristic neodymium signature. The isotope ratios of this element vary depending on which ocean basin the water comes from. For instance, the coldest and therefore deepest water mass in the Southern Pacific forms on the continental shelf of Antarctica and carries a distinct neodymium signature. Overlying this mass is a layer that combines water from the North Atlantic, the South Pacific and the North Pacific and hence is marked by a different signature.
Using fish debris in deep-sea sediments, the researchers were able to trace the variations in neodymium concentrations at different depths over the course of time. The result: at the peak of the last ice age approximately 20,000 years ago, the neodymium signature of samples taken from depths below 4,000 metres was significantly lower than at lower depths. "The only explanation for such a pronounced difference is that there was no mixing of the water masses at that time," said Fröllje, who currently works at the University of Bremen. He and his colleagues concluded from this that the deep waters were strongly stratified during the glacial period.
As the climate in the southern hemisphere grew warmer towards the end of the last ice age around 18,000 years ago, the stratification of the water masses was broken up and neodymium values at different depths converged. "There was probably more mixing because the density of the water decreased as a result of the warming," Pahnke explained. This then led to the release of the carbon dioxide stored in deep waters.
For some time now climate researchers have been speculating on why fluctuations in atmospheric CO2 levels followed the same pattern as temperature in the southern hemisphere whereas the temperature in the north at times ran counter to these fluctuations. One theory is that certain processes in the Southern Ocean played an important role.
"With our analyses we have for the first time provided concrete evidence supporting the theory that there is a connection between the CO2 fluctuations and stratification in the Southern Ocean," said co-author of the study Dr. Frank Lamy of the AWI in Bremerhaven. The current study supports the hypothesis that the warming of the southern hemisphere broke up stable stratification in the Antarctic Ocean, resulting in the release of the carbon dioxide that was stored in these waters.
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Wednesday, February 21, 2018
Solar radiation mineralizes terrestrial dissolved organic carbon in the ocean
Organic carbon dissolved in water plays a vital role in the Earth's carbon cycle. Understanding carbon cycling is central to understanding climate change and how aquatic communities are structured and supported. Senior Lecturer Anssi Vähätalo and his research group from Department of Biological and Environmental Science at the University of Jyväskylä has found out that solar radiation mineralizes more terrestrial dissolved organic carbon in the ocean than in the inland waters.
Rivers discharge annually 248 teragrams (248,000,000,000,000 grams) of terrestrial dissolved organic carbon from the continents to the ocean. The majority of terrestrial dissolved organic carbon is recalcitrant against microbial mineralization in the ocean, but solar radiation can photochemically mineralize part of it into carbon dioxide.
An article published in the Global Biogeochemical Cycles on 20th of February 2018 estimates that solar radiation mineralizes 45 teragrams of terrestrial dissolved organic carbon in the ocean. The amount is larger than the corresponding photochemical mineralization in the lakes and the reservoirs. Thus, solar radiation mineralizes terrestrial dissolved organic carbon more in the ocean than in the inland waters concludes Anssi Vähätalo, the leader of the research group.
"The export of terrestrial dissolved organic carbon from inland water to the ocean is faster than its photochemical mineralization in the inland waters. When terrestrial dissolved carbon enters to the ocean, it will quickly spread into river plumes. ," says Anssi Vähätalo. "The area of these river plumes, where the photochemical mineralization takes place, is 34 million squarekilometers, for example about three times the area of Europe.," he continues,
For this project, water samples were collected from the ten largest rivers in the world. Water samples were taken, e.g. from the Amazon, the Mississippi, the Congo and the Yangtze Rivers.
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First evidence of surprising ocean warming around Galápagos corals
The ocean around the Galápagos Islands has been warming since the 1970s, according to a new analysis of the natural temperature archives stored in coral reefs.
The finding surprised the University of Arizona-led research team, because the sparse instrumental records for sea surface temperature for that part of the eastern tropical Pacific Ocean did not show warming.
"People didn't know that the Galápagos or eastern Pacific was warming. People theorized or suggested it was cooling," said lead author Gloria Jimenez, a UA doctoral candidate in geosciences.
Scientists thought strong upwelling of colder deep waters spared the region from the warming seen in other parts of the Pacific, she said.
"My colleagues and I show that the ocean around the northern Galápagos Islands is warming and has been since the 1970s," Jimenez said. The research is part of her doctoral work.
Jimenez studied cores taken from coral heads in the uninhabited northern part of Galápagos National Park. The cores represented the years 1940 to 2010. Corals lay down seasonal growth layers that serve as a natural archive of ocean temperatures.
Her analysis revealed that from 1979 to 2010, regional ocean temperatures increased almost 0.4 degrees F (0.2 degrees C) per decade -- about 1.1 degrees F (0.6 degrees C) overall.
The very strong El Niño of 1982-83 temporarily warmed the surrounding ocean so much that most of the corals in the southern part of the Galápagos died, said co-author Julia Cole, who collected the coral cores while she was a faculty member at the UA.
She is concerned about ocean warming around the northern Galápagos and parts of the eastern tropical Pacific.
"Warming in this area is particularly disturbing, because it's the only place that reefs have persisted in the Galápagos. This suggests those reefs are more vulnerable than we thought," said Cole, who is now a professor of earth and environmental sciences at the University of Michigan.
The research paper, "Northern Galápagos corals reveal twentieth century warming in the eastern tropical Pacific," by Jimenez, Cole and their co-authors, Diane M. Thompson of Boston University in Massachusetts and Alexander W. Tudhope of the University of Edinburgh in the UK, is scheduled to be published in Geophysical Research Letters on Feb. 21.
The National Science Foundation, the UK Natural Environment Research Council and the Philanthropic Education Organization Fellowship funded the research.
For 30 years, Cole, a paleoclimatologist, has been studying climate change and the El Niño/ La Niña climate cycle.
In 1989 she went to the Galápagos hoping to use the natural climate archives stored in corals to develop a long-term record of El Niño, but found that none of the large, old corals others reported had survived the intense warming of the 1982-83 El Niño.
"We went from site to site -- and they were all gone," Cole said. "One of my co-workers said, 'There used to be corals here, and now all I see is sand.'"
Years later, she heard large corals were still alive near Wolf Island in the remote northern part of the Galápagos archipelago, so in 2010 she followed up on the tip with a team that included co-authors Tudhope and Thompson, then a UA graduate student.
The team members dove to the reef and took several cores from large, blobby dome-shaped Porites lobata corals using an underwater hydraulic drill powered by vegetable oil. The three-and-a-half-inch (8.9 cm) diameter cores ranged from two to three feet long and had annual bands 0.4 to 0.8 inches (1-2 cm) wide. Each core showed damage from when the coral stopped growing during the 1982-83 El Niño and then started growing again.
Jimenez used chemical analysis to tease temperature information out of two of those coral cores.
Coral skeletons are made mostly of calcium carbonate. However, corals sometimes substitute the element strontium for the calcium. Corals substitute more strontium when the water is cold and less when the water is warm, so the strontium/calcium ratio of a bit of skeleton can reveal what the water temperature was when that piece of skeleton formed.
Jimenez used a little drill bit to take a tiny sample every millimeter for the length of each core. She took 10 to 20 samples from each annual band of each core and analyzed the samples for the strontium/calcium ratio using atomic emission spectrometry.
She then used that information to create a continuous record of the region's ocean temperature from 1940 to 2010.
Because the El Niño/ La Niña climate cycle generates large fluctuations in ocean temperatures around the Galápagos and in the eastern tropical Pacific, long-term changes can be hard to spot.
Jimenez wanted to determine whether the region's ocean temperature changed significantly from 1940 to 2010. Therefore she analyzed her Galápagos coral temperature chronologies alongside published coral temperature chronologies from islands farther north and west and instrumental sea surface temperature records from the southern Galápagos town of Puerto Ayora and the Peruvian coastal town of Puerto Chicama.
Jimenez said her research convinces her that the ocean around the Galápagos and much of the eastern tropical Pacific is warming. She's concerned about the effect of warming seas.
"The Galápagos National Park has been designated a World Heritage Site because it's a special and unique place," Jimenez said. "Losing the corals would be an enormous blow to the underwater biodiversity."
Jimenez's next project involves analyzing an eight-foot-long Galápagos coral core she collected in 2015 that goes back to about 1850.
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Sea urchins erode rock reefs, excavate pits for themselves
Through their grazing activity, sea urchins excavate rock and form the pits they occupy. This activity may cause significant bioerosion of temperate reefs, according to a study published February 21, 2018 in the open-access journal PLOS ONE by Michael Russell from Villanova University, U.S., and colleagues.
Sea urchins live in high densities on rocky temperate reefs, and are often so snugly nestled into cavities that researchers have long wondered if they excavate these pits themselves. However, there was no experimental data to support this hypothesis or to assess its environmental consequences. The authors of the present study investigated this question by monitoring purple sea urchins, Strongylocentrotus purpuratus, on flattened rock surfaces in the lab. They used fine- and medium-grain sandstone, mudstone and granite rocks from three Californian reef sites naturally occupied by sea urchins, where the researchers also conducted field measurements.
The researchers found that sea urchins did indeed visibly sculpt the rock, removing material from all the rock surfaces during the laboratory experiment. Rates of excavation varied greatly by rock type in the lab: while each urchin excavated around 32g of medium-grain sandstone over a year, meaning that an average-sized pit could be sculpted in under five years, granite excavation was 37 times slower, so arduous that it would take more than a century to form a pit. Field measurements reflected this difference, with granite pits being shallower, and sea urchins flatter, than their sandstone counterparts.
The authors combined the laboratory rates with urchin density measurements, estimating that on medium-grain sandstone reefs, urchins might produce almost 200 tonnes of sediment per hectare per year. However, excavation rates in the field might differ significantly from laboratory rates. Nonetheless, the authors note that urchin-mediated bioerosion is a potentially important factor in temperate reef coastal erosion, and deserves further investigation.
"What shocked us was the rate of bioerosion -- particularly on sandstone," says Russel. "In the course of feeding, sea urchins scrape the rock surface using their self-sharpening, regenerating teeth, which act as 'rock picks' and this process results in the excavation of pits."
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'Chameleon' ocean bacteria can shift their colors
Cyanobacteria -- which propel the ocean engine and help sustain marine life -- can shift their colour like chameleons to match different coloured light across the world's seas, according to research by an international collaboration including the University of Warwick.
The researchers have shown that Synechococcus cyanobacteria -- which use light to capture carbon dioxide from the air and produce energy for the marine food chain -- contain specific genes which alters their pigmentation depending on the type of light in which they float, allowing them to adapt and thrive in any part of the world's oceans.
"Blue light is most prevalent in the open oceans, as it penetrates into deep waters -- whereas in warm equatorial and coastal waters there is more green light, and in estuaries the light is often red," explains David Scanlan, who is Professor in Marine Microbiology in the University of Warwick's School of Life Sciences.
These specific 'chromatic adaptor' genes are abundant in ocean dwelling Synechococcus -- enabling these colour-shifting microorganisms to change their pigment content in order to survive and photosynthesise in ocean waters, especially when the light quality changes from blue to green.
Professor Scanlan commented on the significance of the research:
"Finding Synechococcus cells capable of dynamically changing their pigment content in accordance with the ambient light colour -- abundant in ocean ecosystems, making them planktonic 'chameleons' -- gives us a much deeper understanding of those processes essential to keep the ocean 'engine' running.
"This will help improve how we look after our waters -- and will allow us to better predict how oceans will react in the future to a changing climate with increasing levels of carbon dioxide in the atmosphere."
The researchers made their discovery using data from the Tara Oceans expedition -- which took seawater samples from ocean waters all over the world.
From this data, Professor Scanlan and colleagues analysed specific gene sequences from Synechococcus in the different samples, identifying particular 'chromatic adaptor' genes in bacteria living thousands of miles apart.
This discovery represents a major breakthrough in our understanding of these organisms, which are key primary producers and potentially excellent bio-indicators of climate change.
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Beluga whales dive deeper, longer to find food in Arctic
Reductions in sea ice in the Arctic have a clear impact on animals such as polar bears that rely on frozen surfaces for feeding, mating and migrating. But sea ice loss is changing Arctic habitat and affecting other species in more indirect ways, new research finds.
Beluga whales that spend summers feeding in the Arctic are diving deeper and longer to find food than in earlier years, when sea ice covered more of the ocean for longer periods, according to a new analysis led by University of Washington researchers. The study, published this month in the journal Diversity and Distributions, is one of the first to consider the indirect effects of sea ice loss on Arctic species that dwell near the ice, but don't necessarily depend on it for survival.
"I think this paper is novel in that we're presenting some of the first indirect effects of sea ice loss for an Arctic whale species," said lead author Donna Hauser, a postdoctoral researcher at the UW's Polar Science Center and former doctoral student at the School of Aquatic and Fishery Sciences. "As changes in sea ice affect oceanographic properties, that could be affecting the distribution, abundance or species composition of prey for belugas."
Two genetically distinct beluga populations spend winters in the Bering Sea, then swim north in the early summer as sea ice melts and open water allows them passage into the Beaufort and Chukchi seas. There they feast all summer on fish and invertebrates before traveling back south in the fall. Both populations are considered healthy.
The researchers analyzed migration data collected intermittently from two different periods -- referred to in the paper as "early" and "late" -- for two beluga populations, covering the years 1993-2002 and 2004-2012. Satellite-linked tags attached to the whales tracked their movements around and away from the high Arctic feeding grounds. Dive-depth data were collected for only one population, the Chukchi belugas, because the other population's tags did not have those capabilities.
Researchers also tracked sea ice cover in the Arctic over these two periods and found that the ice declined substantially from the first to the second period.
"We have documented loss of sea ice and reductions of habitat for Arctic marine mammals across most of the circumpolar Arctic, so this area is not unique," said co-author Kristin Laidre, a UW associate professor in the School of Aquatic and Fishery Sciences and the Polar Science Center. "We're seeing this ice loss broadly in all areas where belugas occur."
Sea ice loss appears to affect how the Chukchi belugas dove for their food. During the later period, when there was less sea ice, the whales dove significantly longer and deeper than in the earlier period -- presumably in search of prey as the animals, in turn, changed their habits because of different ocean conditions brought on by sea ice loss.
Specifically, during the earlier period belugas dove for 20 minutes or longer only once per day, compared to nearly three times a day during the later period. Similarly, their average daily dive depth increased from about 50 meters (164 feet) to 64 meters (210 feet) between the two periods.
The belugas might be diving longer and deeper to follow prey that has dispersed or been driven deeper itself from changing ocean conditions. It's also possible that feeding opportunities are actually better for belugas in an ocean with less sea ice.
"Reduced sea ice cover over a longer period of time over the summer could mean improved foraging for belugas," said Hauser, who is also a researcher at the University of Alaska Fairbanks. "But it's also important to recognize these changes in diving behavior are energetically costly."
It's unclear whether diving changes are positive or negative for belugas, and studies on body condition and health are needed to understand the implications of these changes, she added.
Aside from changes in how belugas dove for food, the nearly two decades of data show that the whales were able to thrive in their summer and fall ocean habitats, despite less ice cover. This adaptability to changes in Arctic conditions speaks to the whales' resiliency, the researchers said.
"Belugas feed on a lot of different prey and use many different habitats, across open water and dense sea ice and everything in between," Hauser said. "Because they are such generalists, that could buffer them under climate change."
Other co-authors are Harry Stern of the UW; Robert Suydam of North Slope Borough in Utqia?vik, Alaska; and Pierre Richard of Fisheries and Oceans Canada.
This analysis was funded by the National Science Foundation's UW IGERT Program on Ocean Change, NASA and the UW School of Aquatic and Fishery Sciences. Many individuals and organizations supported beluga whale tagging, including the Alaska Beluga Whale Committee, North Slope Borough, Village of Point Lay, the Inuvialuit Hunter and Trapper Committees, Fisheries and Oceans Canada, National Marine Fisheries Service, Alaska Department of Fish and Game, National Fish and Wildlife Foundation and the Minerals Management Service.
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Sea-level legacy: 20 cm more rise by 2300 for each 5-year delay in peaking emissions
Their central projections indicate global sea-level rise between 0.7m and 1.2m until 2300 with Paris put fully into practice. As emissions in the second half of this century are already outlined by the Paris goals, the variations in greenhouse-gas emissions before 2050 will be the major leverage for future sea levels. The researchers find that each five year delay in peaking global CO2 emissions will likely increase median sea-level rise estimates for 2300 by 20 centimeters.
"Man-made climate change has already pre-programmed a certain amount of sea-level rise for the coming centuries, so for some it might seem that our present actions might not make such a big difference -- but our study illustrates how wrong this perception is," explains lead author Matthias Mengel from the Potsdam Institute for Climate Impact Research (PIK). "Every delay in peaking emissions by five years between 2020 and 2035 could mean additional 20 cm of sea-level rise in the end -- which is the same amount the world's coasts have experienced since the beginning of the pre-industrial era."
Global sea-level rise is driven by warming and expanding ocean water, as well as the melting of mountain glaciers, ice caps, and the vast Greenland and Antarctic ice sheets. These contributors respond in different ways and within different timescales to a warmer climate, ranging from centuries to millennia -- a delayed response to today's atmospheric warming. To analyze the sea-level rise under the Paris Agreement and the legacy of delayed mitigation, the scientists used a combined climate-sea-level model. They fed it with a set of scenarios of emission reductions in line with the Paris goals that span different reduction rates and emission peak years.
Large ice loss from Antarctica seems possible even under modest warming
The model represents the sea-level contributors individually and can thus reflect their different responses to a warming world. The authors incorporate new scientific insights pointing to an Antarctic ice sheet very sensitive to atmospheric warming. "Indeed, the uncertainty of future sea-level rise is at present dominated by the response of Antarctica. With present knowledge on ice sheet instability, large ice loss from Antarctica seems possible even under modest warming in line with the Paris agreement," says Matthias Mengel. "Even a sea-level rise of up to three meters until 2300 cannot be ruled out completely, as we are not yet fully certain how the Antarctic ice sheet will respond to global warming."
"The Paris Agreement calls for emissions to peak as soon as possible," adds co-author Carl-Friedrich Schleussner from PIK and Climate Analytics, a non-profit research and policy institute in Berlin. "This might sound like a hollow phrase to some, but our results show that there are quantifiable consequences of delaying action. So even within the Paris Agreement range, swift climate mitigation is crucial to limit additional risks. For millions of people around the world living in coastal areas, every centimeter can make a huge difference -- to limit sea-level rise risks immediate CO2 reduction is key."
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Oil-eating microbes are challenged in the Arctic
New economic developments in the Arctic, such as trans-Arctic shipping and oil exploitation, will bring along unprecedented risks of marine oil spills. The world is therefore calling for a thorough understanding of the resilience and "self-cleaning" capacity of Arctic ecosystems to recover from oil spills.
Although numerous efforts are put into cleaning up large oil spills, only 15 to 25% of the oil can be effectively removed by mechanical methods. This was the case in major oil disasters such as the Exxon Valdez spill in Prince William Sound, Alaska, and the Deepwater Horizon in the Gulf of Mexico. Future spill will be no different. Oil-eating microbes played the major role in degrading the oil and reducing the impact of the spilled oil during these past oil disasters.
"We are now presenting a first assessment of the microbial degradation potential in seawaters off Greenland," postdoc Leendert Vergeynst, Arctic Research Centre at Aarhus University, explains.
The research group has identified six factors challenging the microbes in Arctic seas.
Low temperatures, sea ice and few nutrients
Low temperature changes the chemical properties of spilled oil and slows down biodegradation. For example, cold oil is more viscous, which hampers oil dispersion. The efficiency of microbial degradation is decreased when oil is not dispersed in small droplets.
Waves also plays an important role in breaking the oil into droplets. However, where there is sea ice, there are much less or no waves.
The Arctic is generally an environment with very low amounts of nutrients such as nitrogen and phosphorus. These nutrients are not present in the oil and oil-eating bacteria therefor need to find them in the water. Few nutrients result in reduced activity of the oil-eating bacteria.
Particle formation, sunlight and adaptation
Massive phytoplankton (algae) blooms and suspended mineral particles released by glaciers occur during the Arctic spring and summer. The concentrations of particles from glacier outlets and algae blooms in Arctic waters can be magnitudes higher than in the Gulf of Mexico, where phytoplankton, particles and oil droplets were sticking together and sank to the seafloor, forming a "dirty blizzard" during the Deepwater Horizon oil spills in 2010. Microbial degradation of oil on the seafloor is much slower than in the water column.
The 24-h sunlight during the Arctic summer may help the microbes to break up oil molecules into smaller pieces. However, it may also make the oil compounds more toxic for aquatic organisms. We still need a lot of knowledge to properly understand the effect of sunlight on oil spills in Arctic ecosystems.
Regular small oil spills in other marine waters have adapted ('learned') microbes to eat oil molecules. However, the Arctic is still a very pristine environment. The researchers are therefore currently investigating if the microbial populations present in the Arctic have adapted to degrading oil compounds.
"We are especially concerned that the most toxic molecules in the oil, such as polycyclic aromatic hydrocarbons, may be the most difficult to degrade" says Leendert Vergeynst.
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Mumbai can soon enjoy boat rides amid Dahisar mangroves
Mangroves to make way for new Brisbane River mooring
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Koh Kong probing filling in of mangrove forest
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Tuesday, February 20, 2018
Stable gas hydrates can trigger landslides
Like avalanches onshore, there are different processes that cause submarine landslides. One very widespread assumption is that they are associated with dissociating gas hydrates in the seafloor. However, scientists at GEOMAR Helmholtz Centre for Ocean Research Kiel have now found evidence that the context could be quite different. Their study has been published in Nature Communications.
In the mid-1990s, German scientists, among others, were able to prove that the continental slopes at ocean margins contain large amounts of gas hydrates. These solid, ice-like compounds of water and gas are often considered a kind of cement, which stabilizes the slopes. Since gas hydrates are only stable at high pressure and low temperature, rising water temperatures can cause gas hydrates to dissociate, or 'melt', in simple terms. It has been suggested previously that large-scale gas hydrate dissociation could cause submarine landslides that could in turn trigger tsunamis. The fact that many fossil landslides correlate spatially with sediments containing gas hydrates seems to strengthen this argument.
Now, researchers from GEOMAR Helmholtz Centre for Ocean Research Kiel, together with colleagues from Kiel University and the Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, have found evidence that gas hydrates and submarine landslides are indeed linked -- but in a quite different way than previously thought. "Our data show that stable gas hydrates can indirectly destabilize the sediment above," says Dr. Judith Elger from GEOMAR. She is the lead author of the study, which has been published in the international journal Nature Communications.
An inconsistency in the previous theory, which focused on melting gas hydrates as the cause of submarine landslides, was the starting point of the new research. "The water depths did not match. With rising water temperatures or decreasing sea levels, gas hydrate melting would be initiated around the upper parts of continental slopes. However, most known fossil submarine landslides were triggered in greater depths," explains Dr. Elger.
To resolve this contradiction, the geophysicist examined seismic data from the area of the Hinlopen Slide, which occurred about 30,000 years ago north of Svalbard in 750 to 2,200 meters water depth. The team used the seismic data to simulate new processes with a computer model.
It turned out that gas hydrates can form a solid, impermeable layer beneath the seafloor. Free gas and other fluids can accumulate below this layer. Over time they create overpressure. Eventually, gas hydrates and sediments no longer withstand this elevated pore pressure and hydro fractures form in the sediments. These fractures form conduits that transfer overpressure to shallower coarse-grained sediments and thereby trigger shallow slope failure. In the case of the Hinlopen Slide, these fluid conduits are still visible in the seismic data.
"We were able to show that this process is a realistic alternative to other triggering processes for the Hinlopen Slide, and it is completely independent of climatic changes. However, important information about the properties of gas hydrate-bearing sediments is still lacking to improve our models," says Dr. Elger.
In any case, the study shows a new causal process that has not been considered so far in the search for causes of submarine landslides. "Further studies that combine seismic data and geotechnical laboratory experiments must now show whether similar fractures can be detected beneath the seafloor on other historical landslides and whether this is a common phenomenon,§ Dr. Elger concludes.
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