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Monday, May 21, 2018

An Extraterrestrial Empanada, A Space Ravioli, and A Planetary Baguette: Simulating Saturn’s Moons

       An extraterrestrial empanada. . . A space ravioli. . . A planetary baguette.  Some of Saturn’s moons have shapes that are strangely reminiscent of culinary creations.

      In the image below, simulated collisions between two moonlets can lead to oddly shaped moons (bottom row) that closely resemble some of Saturn’s moons (top row; from left to right: Pan, Atlas and Prometheus).

     Images of the oddly-shaped moons, mostly from now-defunct Cassini spacecraft, got planetary scientists wondering how these satellites ended up with such strange shapes. Now, researchers suggest that collisions between moonlets could account for these shapes according to a study published online today, May 21, 2018, in Nature Astronomy. {The original Nature article includes some of these space culinary terms.}

     Dr. Adrien Leleu , a planetary scientist at the University of Bern in Switzerland, and colleagues developed computer simulations that let the scientists virtually smack together similar-sized moonlets at various speeds and angles. The team found that, at low angles and relative speeds of tens of meters per second (roughly equal to a car traveling on country roads), impacts can create offbeat shapes that look like the misfits around Saturn.

      Head-on collisions result in a flattened moon like Pan, which resembles an extraterrestrial empanada. An impact angle of just a few degrees leads to an elongated satellite such as Prometheus, which looks like a French baguette.

      Not all run-ins create a weird-looking moon. At higher angles, for example, moonlets might "hit and run." Or they could form highly elongated rotating moons that subsequently break apart.

     Dr. Leleu and collaborators focused on the smaller moons of Saturn that orbit within the planet’s rings. But the team also found that a similar collision between two larger moonlets could also account for the odd shape of Iapetus, a more distant walnut-shaped moon with a pronounced ridge along its equator that has puzzled scientists since the belt’s discovery. Other speculative origins for the ridge include volcanoes, plate tectonics or ring debris that rained down on the moon.

     I will admit that I was drawn to the odd shapes of possible moonlets because they reminded me of images of fossils like fusulinids (see below). Nature likes reusing cool shapes, I suppose.

Enjoy this planetary patisserie!

Wednesday, April 25, 2018

What Doesn't Krill Us Makes Us Stronger: Ocean Water Mixing By Tiny Organisms

        Swarms of tiny oceanic organisms known as zooplankton may have an outsized influence on their environment. New research at Stanford shows that clusters of centimeter-long individuals, each beating tiny feathered legs, can, in aggregate, create powerful currents that may mix water over hundreds of meters in depth.

     Although the work was carried out in the lab, the finding is the first to show that migrating zooplankton – or indeed any organism – can create turbulence at a scale large enough to mix the ocean’s waters. The work could alter the way ocean scientists think about global nutrient cycles like carbon, phosphate and oxygen, or even ocean currents themselves.

      A brine shrimp (below) tethered in place generates flow with its swimming motion, made visible with an overlaid time lapse of particles suspended in the water. Photo credit: Isabel Houghton.

      “Ocean dynamics are directly connected to global climate through interactions with the atmosphere,” said Dr. John Dabiri. “The fact that swimming animals could play a significant role in ocean mixing – an idea that has been almost heretical in oceanography – could therefore have consequences far beyond the immediate waters where the animals reside.”

        Dr. Dabiri, who was the senior author on the work published April 18, 2018, in Nature, added that the findings could also help scientists understand how the ocean sequesters carbon dioxide from the atmosphere and lead to updates in ocean climate models.

      “Right now a lot of our ocean climate models don’t include the effect of animals or if they do it’s as passive participants in the process,” Dabiri said.

      One of the most common zooplankton, krill are among the most abundant marine organisms and migrate daily in giant swarms, heading hundreds of meters deep by day and up to the ocean’s surface by night to feed.

      Dr. Dabiri knew that in terms of forces that drive the mixing of oceans, wind and tidal currents are thought to play the largest role. But he wondered if giant zooplankton migrations could also be involved – an idea first proposed by oceanographer Walter Munk in 1966, and since then debated but never systematically explored. {Dr. Munk, at 100 years of age, is still quite current (pun definitely intended!)}.

      Dr. Dabiri and graduate student Isabel Houghton tried to answer that question not in the ocean but in the relatively controlled environment of large water tanks in the lab. The pair worked to create flow environments that mimic the ocean with saltier water on the bottom of the tank and less salty water on the top. The resulting gradient mirrors ocean conditions that any organism would need to disrupt in order to cycle nutrients between the ocean’s surface and water deep below.

      “There’s no appreciable deep mixing of oxygen or carbon dioxide in the ocean if you can’t overcome the stabilizing influence of salinity and temperature gradients,” Dr. Koseff said.

      In the lab, the group was looking to see whether the tiny organisms they studied – mostly brine shrimp (also known as sea monkeys) as a stand-in for less lab-hardy krill – are simply churning water locally, leaving the gradient intact, or redistributing salt into a more uniform mixture. If they can mix layers in the lab, chances are they can do the same in the ocean, the group argued.

      To carry out the study, Houghton placed brine shrimp in the tank and activated laser or LED lights from either above or below, because brine shrimp are attracted to light, so they migrated toward the source. When she reversed the lights the tiny creatures scurried to the other end in a migration that lasted about 10 minutes.

      With cameras closely recording the animals’ movements, the group has been able to measure the individual water eddies surrounding each brine shrimp and the larger currents in the tank. From these, they’ve shown that turbulence from individual organisms aggregates into a much larger turbulent jet in the wake of the migration.

     What’s more, those flows were powerful enough to mix the tank’s salt gradient. “They weren’t just displacing fluid that then returned to its original location,” Houghton said. “Everything mixed irreversibly.”

     Before this work, scientists had thought that krill and other zooplankton could only create turbulence in their own size range – on the order of centimeters. That’s hardly enough to move nutrients on a meaningful scale. Now it appears that zooplankton have the capacity to mix ocean waters, at least regionally. Furthermore, Dr. Dabiri said their findings might not just apply to organisms like krill in the upper kilometer of the ocean, but also to jellyfish, squid, fish and mammals that swim even deeper, potentially churning the entire water column.

     Dr.Dabiri said his lab members need to verify their findings in the ocean, which will involve finding and following swarms of krill in locations as diverse as the California coast and frigid Antarctic waters. But if they continue to see mixing at the scales the lab work suggests, the findings could change the way ocean scientists think about the role of animals in influencing their watery environment – and potentially our climate on land.

     These ocean mixers are vastly different from the mixers we had at Smith College (or are they?)

     Did you ever order sea monkeys?

Saturday, March 24, 2018

Zeptonewtons: Tiny Units of Measure of FORCE

     A single atom can gauge tiny electromagnetic forces.
The unit of measure of force, a zeptonewton, is equal to one billionth of a trillionth of a newton.    

      Scientists detected a tiny force using a charged atom (illustrated as a red sphere above), which moved (orange) when pelted with laser light (purple). A lens focused light emitted from the atom into a moving image (black arrow).

     Scientists used an atom of the element ytterbium (above) to sense an electromagnetic force smaller than 100 zeptonewtons, researchers report March 23, 2018,  in Science Advances. That’s less than 0.0000000000000000001 newtons (with 18 zeroes after the decimal.) At about the same strength as the gravitational pull between a person in Dallas and another in Washington, D.C., that’s downright feeble.

     After removing one of the atom’s electrons, researchers trapped the atom using electric fields and cooled it to less than a thousandth of a degree above absolute zero (–273.15° Celsius) by hitting it with laser light. 

      That light, counterintuitively, can cause an atom to chill out. The laser also makes the atom glow, and scientists focused that light into an image with a miniature Fresnel lens (as pictured above), a segmented lens like those used to focus lighthouse beams.

     Monitoring the motion of the atom’s image allowed the researchers to study how the atom responded to electric fields, and to measure the minuscule force caused by particles of light scattering off the atom, a mere 95 zeptonewtons.

I'm a little early for May, but, May the Fo(u)rth be with you,

Thursday, March 8, 2018

Ice-VII: Deep Ice, Tectonic Slabs, and Diamond Inclusions

      Ice is found deep within the hot interior of the earth. Let that statement sink in. In research published today, a form of super-compact ice, found embedded in diamonds, offers the first direct clue that there is abundant water more than 610 kilometers deep in the mantle.

      This ice, identified by its crystal structure and called ice-VII, doesn’t exist at Earth’s surface. It forms only at pressures greater than about 24 gigapascals — corresponding to depths between 610 and 800 kilometers, researchers report today in Science. The structure of ice-VII comprises a hydrogen bond framework in the form of two interpenetrating (but non-bonded) sublattices. Hydrogen bonds pass through the center of the water hexamers (as shown above, and, to some degree below) and thus do not connect the two lattices. 


      Ice-VII's presence in diamonds suggests that there is water-rich fluid in the transition zone between the upper and lower mantle, and even into the top of the lower mantle.

     “This is really the first time that we see water at such depths,” says Dr. Oded Navon, a mantle petrologist at the Hebrew University of Jerusalem.

      When slabs of earth’s crust sink into the mantle layer below, they drag ocean water with them. How deep the slabs sink has been a long-standing question. Researchers have suspected that abundant aqueous fluid exists in the deep mantle, carried there by slabs bearing water-rich minerals that shed their water when they reach the transition zone. But scientists have not previously found direct evidence of that water.

     That is where diamonds come in. Diamonds form at high temperatures and pressures, crystallizing in pockets rich in the mineral carbonate before being carried to the surface with erupting magma. As the diamond crystals form, they can enclose tiny amounts of fluid or rock from their surroundings. These impurities represent tiny capsules of mantle. Diamond inclusions are the only direct window scientists have into the fabric of earth more than a kilometer beneath the surface.

     Dr. Oliver Tschauner, a mineralogist at the University of Nevada, Las Vegas, and his colleagues set out to study diamond inclusions, but they weren’t looking for ice. They were hunting for signs of a molecular form of carbon dioxide that might help reveal clues to the cycling of carbon from slabs into the mantle. The researchers used a variety of techniques, including X-ray diffraction, infrared spectroscopy and X-ray fluorescence, to try to identify the composition of the inclusions within three diamonds, one from China and two from southern Africa.

      Instead of carbon dioxide, the team saw a telltale pattern in how some of the X-rays scattered as they passed through the diamond. That pattern pointed to ice-VII. The presence of that extremely high-pressure form of ice was a powerful clue to the depth at which the diamond must have formed. The diamonds also contained separate inclusions of fluids rich in certain salts, such as magnesium calcite and halite, and of carbon-rich fluids. 

     Water-rich fluids deep in the mantle could be important for driving the circulation that fuels the movements of tectonic plates and the eruptions of volcanoes. The presence of water can make it easier for rocks to melt, Dr.  Navon says, by lowering the melting point of hot rock under pressure. Additionally, fluids can help redistribute heat within the mantle.

     In addition, some large, heat-producing radioactive elements such as potassium, thorium and uranium don’t fit easily into the rigid crystalline structures of minerals, so scientists prefer melted rock when it’s available. “You just need a little bit of fluid, and they are moving into the melt,” Dr. Navon adds.

     The study also raised another mystery. Fluid inclusions within diamonds originating at shallower depths, perhaps 150 to 200 kilometers below the surface, contain a mélange of water, salt, and carbonates. But Dr. Tschauner and his colleagues found that in their deep diamonds, the inclusions are sequestered individually: ice in one inclusion, carbonates in another, salts in yet a third. “We were surprised that they were all separate rather than occurring together,” Dr. Tschauner said.  

Any ideas about this mysterious separation in the materials in inclusions? 

And, how cool to have remnants of tectonic slabs as inclusions in your jewelry!

Wednesday, February 7, 2018

Extensive Mid-Oceanic Magma Eruption at the Cretaceous-Paleogene Time Boundary

     The asteroid that hit earth 66 million years ago appears to have caused large amounts of magma to spew out of the bottom of the ocean, a new study of seafloor data finds.

      The discovery, described today in the journal Science Advances, adds to the picture of an extinction event that was as complex as it was deadly.

      For decades, researchers have pointed to a cataclysmic asteroid crashing into the planet as the reason the dinosaurs, and many other species of life on Earth, were wiped out during the Cretaceous-Paleogene (K-Pg) extinction event. That impact, which scientists think left the roughly 110-mile-wide Chicxulub crater in the Gulf of Mexico, would have vaporized living things nearby and sent choking clouds of debris into the air, obscuring the sun.

      But scientists have also pointed to another culprit: the Deccan Traps in present-day India, one of the largest volcanic provinces in the world, which just happened to be very active at the time of the extinction event. The ash and noxious gases from the Deccan Traps are really what killed the dinosaurs, some scientists say, downplaying the asteroid's role.

     "People still argue about which one was actually the primary driver of environmental changes that resulted in the death of dinosaurs," said senior author Dr. Leif Karlstrom, an earth scientist at the U. of Oregon.

     Researchers have also suggested that perhaps the two were connected — perhaps the asteroid triggered Deccan Trap volcanism, producing a brutal one-two punch that ultimately knocked out roughly three-quarters of the earth's plant and animal species. But recent work has shown that the traps started spewing roughly a quarter-million years before the asteroid hit, Dr. Karlstrom said.

     Yet, scientists have wondered if there might indeed be some kind of connection between the two. And lead author Dr. Joseph Byrnes, a geophysicist at the U. of Minnesota, realized something: If the asteroid impact had had a major impact on volcanism at the time, that effect should have shown up in the activity along the Earth's mid-ocean ridges. So he and Dr. Karlstrom went looking for it.

     As we've discussed here at Partial Ellipsis of the Sun before, the mid-ocean ridges are long cracks in the Earth's crust at the bottom of the ocean floor where tectonic plates meet. As the plates pull apart, hot magma rises up between them, flowing out on either side of the crack before cooling, creating new seafloor in the process. With more than 40,000 miles of ridges, this network of cracks forms the longest mountain chain on earth.

     Scientists used magnetic data compiled by other researchers and combined it with another data set showing the gravitational field of the surface beneath the ocean. The stronger the gravitational field in a given spot, the more mass there is. 

    "We have a topographic map of the Earth's surface and we have topographic maps of Mars and Venus, but we don't have that for the ocean floor," Dr. Byrnes said. "We have it for places where people have taken ships, but it would take something like 900 years to survey the whole ocean floor. It's just too resource-intensive — so we have to use the gravitational anomalies as a proxy."

     The graph below shows a spike in the creation of new seafloor about 66 million years ago. That's when the Chicxulub asteroid struck the Earth, wiping out the dinosaurs. The impact also instigated the release of massive amounts of magma.

     Sure enough, the scientists found that at the time the asteroid hit the Earth, there was a sudden surge in the magma pouring out of these mid-ocean ridges, which put out on the order of a hundred thousand to a million cubic kilometers of volcanic material. That's not too far behind the estimated several million cubic kilometers or so of magma produced by the Deccan Traps.

     It's possible that the powerful seismic waves produced by the impact triggered the release of reservoirs of magma beneath the surface, Dr. Karlstrom said. And if it affected the mid-ocean ridges this way, it could have played a similar role in the Deccan Traps, triggering even more volcanism than before.

     The mid-ocean ridges, then, could be a bellwether for a similar phenomenon occurring in the already-active Deccan Traps.

       But did that marine magma release do any damage of its own? While it's unclear whether this extra load of ocean floor magma worsened the extinction event, it could potentially have played a role by further acidifying the oceans. Previous work indicates that marine species that were more sensitive to ocean acidification were worse hit by the extinction event. But probing that possibility will take more research, the scientists added.

      "That's what we need to work on next, I would say: trying to tease out what the effects on the environment were of the volcanic activity," Dr. Byrnes said.

Thoughts on this new data? Have you been to the Deccan Traps?

Speaking of stitches, here's the full quilt my friend made:


Wednesday, January 17, 2018

Bee Bedevilments: Colony Collapse Disorder and More

      Colony Collapse Disorder (CCD) was one of the most striking mysteries in the news 11-12 years ago; honeybee workers were vanishing fast for no clear reason. To this day, that puzzle has never been entirely solved, researchers say.

     And perhaps it never will be. Colony collapse disorder has faded in recent years as mysteriously as it began. It’s possible the disappearances could start up again, but meanwhile bees are facing other problems.

     CCD probably peaked around 2007 and has faded since, says Dr. Jeff Pettis, who during the height of national curiosity was running the Beltsville, MD, honeybee lab for the U.S. Department of Agriculture. Five years have passed since Dennis vanEngelsdorp, who studies bee health at the University of Maryland  has seen a “credible case” of colony collapse (see below in the lower part of the image.)

     Beekeepers still report some cases, but Dr. Pettis and Dr. vanEngelsdorp aren’t convinced such cases really are colony collapse disorder, a term that now gets used for a myriad of things that are bad for bees. To specialists, colony collapse is a specific phenomenon. An apparently healthy colony over the course of days or a few weeks loses much of its workforce, while eggs and larvae, and often the queen herself, remain alive. Also food stores in collapsing colonies don’t get raided by other bees as a failing colony’s treasures usually do.

      “I think I know what happened,” says Dr. Pettis, now in Salisbury, MD, consulting on pollinator health. His proposed scenario for CCD, like those of some other veterans of the furor, is complex and doesn’t rest on a single exotic killer. But so far, no experiment has nailed a proof.

     Looking back, Pettis realizes he had heard about what might have been early cases of CCD, described as colonies “just falling apart,” for several years before the phenomenon made headlines. Then in November 2006, Pennsylvania beekeeper David Hackenberg, as usual, sent his colonies to Florida for the winter. They arrived in fine shape. Soon after, however, many buzzing colonies had shrunk to stragglers. Yet there were no dire parasite infestations and no dead bee bodies in sight.

      “It was, ‘OK, something weird just happened,’ ” remembers Dr. Jay Evans of the USDA’s honeybee lab in Beltsville. “It looked like a ‘flu,’ something that kind of swept through miraculously fast.”

      No single menace, however, could be tightly linked to every sick colony, or only to sick colonies. Varroa mites, small hive beetles, Nosema fungi, deformed wing virus, unusual signs of pesticide exposure, for instance —screening techniques at the time just weren’t picking up a clear pattern in any of these bee bedevilments.

     Entomologists were hounded by the press, not to mention leaned on by politicians and pursued by would-be entrepreneurs. “For me, what made it rewarding,” Dr. Pettis says, “was that people were learning about the value of pollination.”

      A Columbia University researcher who had identified pathogens in mysterious human disease outbreaks looked at the problem. Dr. Ian Lipkin had never worked with bees, but he and his lab collaborated with entomologists and other bee specialists to search for any genetic signature of a pathogen appearing only in collapsing colonies. The approach of searching through mass samples, with their messy traces of gut microbes and random parasites, is now familiar as metagenomics. At the time, this way of searching for pathogens was groundbreaking, says collaborator Diana Cox-Foster, then at Penn State U. The resulting paper, in Science, pointed to several viruses, especially the previously obscure Israeli Acute Paralysis Virus, or IAPVThat emphasis on IAPV, which got a lot of attention at the time, hasn’t held up well. “It’s not 100 percent ruled out,” Evans says. But the explanation’s main problem is shared by other threats proposed as a single cause of CCD. After finding IAPV or another presumed single menace in sick bees in one place, he says, “you could go to other apiaries that were collapsing and not find it, or you could find it in healthier colonies.”

      As an apiary inspector for Pennsylvania at the time, vanEngelsdorp monitored for signs of collapse in over 200 hives. “We tried to watch it happen but we couldn’t,” he says. None collapsed. Even finding the sickest bees in collapsing colonies was a challenge. Doomed bees presumably flew off in multiple directions, and birds or other scavengers usually found the bees before scientists could.

     Dr. Pettis now sees the disaster as a two-step process. Various stressors such as poor nutrition and pesticide exposure weakened bees so much that a virus, maybe IAPV, could quickly kill them in droves. Evans, too, sees various stressors mixing and matching. When pressed for his best guess, he says “all of the above.”

       Dr. Cox-Foster has managed to re-create part of the process, the vanishing effect that marked the end for stressed bees. When she infected honeybee colonies in a greenhouse with a virus, the sick bees left the hive but were trapped by the greenhouse walls before dispersing too far to be found. (Of course, this experiment doesn’t demonstrate how colonies with no sign of a virus died.

     That tendency for sick bees to leave hives, Dr. vanEngelsdorp proposes, could have developed as a hygiene benefit. “Altruistic suicide,” as social-insect biologists call it. Flying away from the colony could minimize a sick bee’s tendency to pass disease to the rest of the hive.

     Colony losses each year are still running higher than beekeepers say would be acceptable (gray bar in the image below). Even though hives can be split so numbers eventually build up again, the slowdown and expense raise the costs of pollination.

      Today, hive losses remain high even with CCD waning or gone, according to national surveys by the Bee Informed Partnership, a nonprofit bee health collaboration. Beekeepers typically note that they either expect or can tolerate annual losses between 15 and 20 percent of their total number of colonies. Yet from April 2016 until March 2017, losses across the United States ran at about a third of hives. And that was a so-called good year, the second-lowest loss in the seven years with data on annual losses.

      Classic CCD may not be as much of a threat these days, but the “four p’s” — poor nutrition, pesticides, pathogens and parasites — are, says Dr. Cox-Foster, now at a USDA lab for pollinating insects in Logan, Utah. Coping with the four p’s may not fire the imaginations of armchair entomologists. But it’s more than enough of a challenge for the bees.

       Answer? Choose B (but it's still a confounding mystery.)

Bee well,