Scientists have reported on another devastating biological disaster, caused by a patch of abnormally warm water in the Pacific Ocean known as ‘the Blob’.
This concentrated marine heatwave lingered in the northeast Pacific between 2013 and 2016, and researchers now think it was largely responsible for the death of almost a million common murres (Uria aalge), amongst other wildlife. This makes it the largest seabird die-off in recorded history.
The estimate is based on some 62,000 murres that washed ashore on the west coast of the US during 2015 and 2016, covering an area stretching from California to Alaska. Only a fraction of birds that die at sea typically wash ashore, indicating the scale of the mass dying was much larger than the number of bodies we’ve found.
The emaciated birds were left starved by a lack of food, caused by increased competition in the warmer waters, according to the scientists – and numerous other species may have been hit by the same confluence of factors.
“Think of it as a run on the grocery stores at the same time that the delivery trucks to the stores stopped coming so often,” says biologist Julia Parrish, from the University of Washington.
“We believe that the smoking gun for common murres – beyond the marine heat wave itself – was an ecosystem squeeze: fewer forage fish and smaller prey in general, at the same time that competition from big fish predators like walleye, pollock and Pacific cod greatly increased.”
The team reviewed studies of fish and plankton collected by fisheries during the time the blob was at its peak, as well as other field studies and reports, and concluded that the warmer temperatures in the water had increased the metabolism of these cold-blooded ocean dwellers.
That meant predatory fish would have been eating more than usual, and that’s likely to have caused pressure on the top of the food chain. In the end, the schools of forage fish that murres rely on would’ve become very hard to find.
While the common murre is one of the most resilient birds around – feeding on small ‘forage fish’ like herring, sardines, anchovies and young salmon – it was unable to cope with the effects of the blob.
“Food demands of large commercial ground fish like cod, pollock, halibut and hake were predicted to increase dramatically with the level of warming observed with the blob,” says biologist John Piatt, from the US Geological Survey’s Alaska Science Center.
“Since they eat many of the same prey as murres, this competition likely compounded the food supply problem for murres, leading to mass mortality events from starvation.”
Mass die-offs seen in Cassin’s auklets and puffins can most probably be attributed to warming events as well, the scientists say. They describe seabirds like the murres as “bellwethers” of warming oceans and the ecological change they bring.
Localised ocean heatwave blobs have become more common over the last century, and are expected to further increase in frequency as the planet warms up. This particular one was exacerbated with warming winds from El Niño during 2015 and 2016.
Similar blobs of heated ocean water are now forming across the globe, threatening to impact marine wildlife further. As far as the researchers behind this latest study are concerned, the toll taken on the murre population is a warning of what’s to come as climate change takes hold – in other words, the next die-off could be even worse.
“The magnitude and scale of this failure has no precedent,” says Piatt. “It was astonishing and alarming, and a red-flag warning about the tremendous impact sustained ocean warming can have on the ecosystem.”
The research has been published in PLOS One.
400 Marsquakes detected by UK sensors in one year – Famagusta Gazette
The seismicity of Mars – Phys.org
On 26 November 2018, the NASA InSight lander successfully set down on Mars in the Elysium Planitia region. Seventy Martian days later, the mission’s seismometer SEIS began recording the planet’s vibrations. A team of researchers and engineers at ETH Zurich, led by ETH Professor Domenico Giardini, had delivered the SEIS control electronics and is responsible for the Marsquake Service. The latter is in charge of the daily interpretation of the data transmitted from Mars, in collaboration with the Swiss Seismological Service at ETH Zurich. Now, the journal Nature Geoscience published a series of articles on the results of the mission in the first months of operation on Mars.
As reported in these articles, InSight recorded 174 events until the end of September 2019. Since then, the measurements have continued leading to more than 450 observed marsquakes as of today, which have not yet been analysed in detail. This accounts for one event a day on average.
The data allows researchers observing how seismic waves travel through the planet and unveiling its internal characteristics—similar to how x-rays are used in medical tomography. Before InSight landed, researchers had developed a wide range of possible models to represent the internal structure of the red planet. The recorded marsquakes, already after few months, enable refining the understanding of the structure of the planet and to reduce the uncertainties.
Interpreting marsquake data is challenging
Marsquakes are similar to the seismic events we see on Earth, although they are generally of smaller magnitude. The 174 registered marsquakes can be categorized in two families: One includes 24 low-frequency events with magnitudes between 3 and 4, as documented in the papers, with waves propagating through the Martian mantle. A second family of marsquakes comprises 150 events with smaller magnitudes, shallower hypocentral depth and high frequency waves trapped in the Martian crust.
“Marsquakes have characteristics already observed on the Moon during the Apollo era, with a long signal duration (10 to 20 minutes) due to the scattering properties of the Martian crust,” explains ETH Professor Giardini. In general, however, he says, interpreting marsquake data is very challenging and in most cases, it is only possible to identify the distance but not the direction from which the waves are arriving.
InSight landed on a thin, sandy layer
InSight opens a new era for planetary seismology. The SEIS performance exceeded so far expectations, considering the harsh conditions on Mars, characterized by temperatures ranging from minus 80 to 0 degrees Celsius every day and by strong wind oscillations. Indeed wind shakes the InSight lander and its instrumentation during the day leading to a high level of ambient noise. However, at sunset, the winds calm down allowing recording the quietest seismic data ever collected in the solar system. As a result, most seismic events detected on Mars by SEIS occurred in the quiet night hours. The challenging environment also requires to carefully distinguishing between seismic events and signals originating from movements of the lander, other instruments or atmospheric-induced perturbances.
The hammering by the HP3 instrument (another InSight experiment) and the close passage of whirlwinds (dust devils), recorded by SEIS, allow to map the physical properties of the shallow soil layers just below the station. We now know that SEIS landed on a thin, sandy layer reaching a few meters deep, in the middle of a 20 meter-wide ancient impact crater. At greater depths, the Martian crust has properties comparable to Earth’s crystalline massifs but appears to be more fractured. The propagation of the seismic waves suggest that the upper mantle has a stronger attenuation compared to the lower mantle.
Seismic activity also induced by tectonic stress
InSight landed in a rather quiet region of Mars, as no events near the station have been recorded up to now. The three biggest events were located in the Cerberus Fossae region about 1’500 km away. It is a tectonic graben system, caused by the weight of the Elysium Mons, the biggest volcano in the Elysium Planitia area. This provides strong evidence that seismic activity on Mars is not only a consequence of the cooling and therewith the shrinking of the planet but also induced by tectonic stress. The total seismic energy released on Mars lies between the one of Earth and of the Moon.
SEIS, complementary to other InSight measurements, also meaningfully contributed data to better understand the meteorological processes on Mars. The instrument’s sensitivity to both wind and atmospheric pressure allowed identifying meteorological phenomena characteristic of Mars, including the many dust devils that pass by the spacecraft every afternoon.
W. Bruce Banerdt et al. Initial results from the InSight mission on Mars, Nature Geoscience (2020). DOI: 10.1038/s41561-020-0544-y
D. Giardini et al. The seismicity of Mars, Nature Geoscience (2020). DOI: 10.1038/s41561-020-0539-8
P. Lognonné et al. Constraints on the shallow elastic and anelastic structure of Mars from InSight seismic data, Nature Geoscience (2020). DOI: 10.1038/s41561-020-0536-y
The seismicity of Mars (2020, February 24)
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Mars InSight Lander Yields a Year of Surprising Discoveries Above
A batch of new papers summarizes the lander’s findings.
A new understanding of Mars is beginning to emerge, thanks to the first year of NASA’s InSight lander mission. Findings described in a set of six papers published today reveal a planet alive with quakes, dust devils and strange magnetic pulses.
Five of the papers were published in Nature. An additional paper in Nature Geoscience details the InSight spacecraft’s landing site, a shallow crater nicknamed “Homestead hollow” in a region called Elysium Planitia.
InSight is the first mission dedicated to looking deep beneath the Martian surface. Among its science tools are a seismometer for detecting quakes, sensors for gauging wind and air pressure, a magnetometer, and a heat flow probe designed to take the planet’s temperature.
While the team continues to work on getting the probe into the Martian surface as intended, the ultra-sensitive seismometer, called the Seismic Experiment for Interior Structure (SEIS), has enabled scientists to “hear” multiple trembling events from hundreds to thousands of miles away.
Seismic waves are affected by the materials they move through, giving scientists a way to study the composition of the planet’s inner structure. Mars can help the team better understand how all rocky planets, including Earth, first formed.
Mars trembles more often — but also more mildly — than expected. SEIS has found more than 450 seismic signals to date, the vast majority of which are probably quakes (as opposed to data noise created by environmental factors, like wind). The largest quake was about magnitude 4.0 in size — not quite large enough to travel down below the crust into the planet’s lower mantle and core. Those are “the juiciest parts of the apple” when it comes to studying the planet’s inner structure, said Bruce Banerdt, InSight principal investigator at JPL.
Scientists are ready for more: It took months after InSight’s landing in November 2018 before they recorded the first seismic event. By the end of 2019, SEIS was detecting about two seismic signals a day, suggesting that InSight just happened to touch down at a particularly quiet time. Scientists still have their fingers crossed for “the Big One.”
Mars doesn’t have tectonic plates like Earth, but it does have volcanically active regions that can cause rumbles. A pair of quakes was strongly linked to one such region, Cerberus Fossae, where scientists see boulders that may have been shaken down cliffsides. Ancient floods there carved channels (see image below) nearly 800 miles (1,300 kilometers) long. Lava flows then seeped into those channels within the past 10 million years — the blink of an eye in geologic time.
Some of these young lava flows show signs of having been fractured by quakes less than 2 million years ago. “It’s just about the youngest tectonic feature on the planet,” said planetary geologist Matt Golombek of JPL. “The fact that we’re seeing evidence of shaking in this region isn’t a surprise, but it’s very cool.”
At the Surface
Billions of years ago, Mars had a magnetic field. It is no longer present, but it left ghosts behind, magnetizing ancient rocks that are now between 200 feet (61 meters) to several miles below ground. InSight is equipped with a magnetometer — the first on the surface of Mars to detect magnetic signals.
The magnetometer has found that the signals at Homestead hollow are 10 times stronger than what was predicted based on data from orbiting spacecraft that study the area. The measurements of these orbiters are averaged over a couple of hundred miles, whereas InSight’s measurements are more local.
Because most surface rocks at InSight’s location are too young to have been magnetized by the planet’s former field, “this magnetism must be coming from ancient rocks underground,” said Catherine Johnson, a planetary scientist at the University of British Columbia and the Planetary Science Institute. “We’re combining these data with what we know from seismology and geology to understand the magnetized layers below InSight. How strong or deep would they have to be for us to detect this field?”
In addition, scientists are intrigued by how these signals change over time. The measurements vary by day and night; they also tend to pulse around midnight. Theories are still being formed as to what causes such changes, but one possibility is that they’re related to the solar wind interacting with the Martian atmosphere.
In the Wind
InSight measures wind speed, direction and air pressure nearly continuously, offering more data than previous landed missions. The spacecraft’s weather sensors have detected thousands of passing whirlwinds, which are called dust devils when they pick up grit and become visible. “This site has more whirlwinds than any other place we’ve landed on Mars while carrying weather sensors,” said Aymeric Spiga, an atmospheric scientist at Sorbonne University in Paris.
Despite all that activity and frequent imaging, InSight’s cameras have yet to see dust devils. But SEIS can feel these whirlwinds pulling on the surface like a giant vacuum cleaner. “Whirlwinds are perfect for subsurface seismic exploration,” said Philippe Lognonné of Institut de Physique du Globe de Paris (IPGP), principal investigator of SEIS.
Still to Come: The Core
InSight has two radios: one for regularly sending and receiving data, and a more powerful radio designed to measure the “wobble” of Mars as it spins. This X-band radio, also known as the Rotation and Interior Structure Experiment (RISE), can eventually reveal whether the planet’s core is solid or liquid. A solid core would cause Mars to wobble less than a liquid one would.
This first year of data is just a start. Watching over a full Martian year (two Earth years) will give scientists a much better idea of the size and speed of the planet’s wobble.
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