New Satellite Data Reveals Dramatic Shrinkage of Arctic Ice Cap
An ice cap in the high Arctic has lost what British scientists say is a significant amount of ice in an unusually short time.
Photo credit: Woodwalker via Wikimedia Commons
It has thinned by more than 50 metres since 2012—about one sixth of its original thickness—and the ice flow is now 25 times faster, accelerating to speeds of several kilometers per year.
Over the last two decades, thinning of the Austfonna ice cap in the Svalbard archipelago—roughly half way between Norway and the North Pole—has spread more than 50km inland, to within 10km of the summit.
A team led by the scientists from the UK Centre for Polar Observation and Modelling (CPOM) at the University of Leeds combined observations from eight satellite missions, including Sentinel-1A and CryoSat, with results from regional climate models, to understand what was happening.
Sea level rise
The study’s lead author, geophysicist Dr. Mal McMillan, a member of the CPOM team, said: “These results provide a clear example of just how quickly ice caps can evolve, and highlight the challenges associated with making projections of their future contribution to sea level rise.”
The study, published in Geophysical Research Letters, is the first to make use of measurements from the European Space Agency’s latest Earth observation satellite, Sentinel-1A.
Dr. McMillan said: “New satellites, such as the Sentinel-1A and CryoSat missions, are essential for enabling us to systematically monitor ice caps and ice sheets, and to better understand these remote polar environments.”
Melting ice caps and glaciers account for about a third of recent global sea level rise. Although scientists predict that they will continue to lose ice in the future, determining the exact amount is difficult, because of a lack of observations and the complex nature of how they interact with the climate around them.
The 20 years of satellite data that the scientists have amassed show some fairly small changes at the start of the study period, but these have since increased.
“Glacier surges, similar to what we have observed, are a well-known phenomenon,” said Professor Andrew Shepherd, the director of CPOM. “What we see here is unusual because it has developed over such a long period of time, and appears to have started when ice began to thin and accelerate at the coast.”
There is evidence that the surrounding ocean temperature has increased in recent years, which may have been the original trigger for the ice cap thinning.
Prof. Shepherd said: “Whether or not the warmer ocean water and ice cap behaviour are directly linked remains an unanswered question. Feeding the results into existing ice flow models may help us to shed light on the cause, and also improve predictions of global ice loss and sea level rise in the future.”
The team says long-term observations by satellites are the key to monitoring such climate-related phenomena.
Dr. McMillan told Climate News Network he did not think what was happening in Austfonna suggested any sort of tipping point in the Arctic, which scientists say is warming more than twice as fast as anywhere else on Earth.
He said: “What I take from this work is that we don’t understand well enough what’s caused this sort of behavior—natural variability, ocean temperatures or atmospheric temperatures. It reinforces the complexities and the challenges of the future.”
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The ghoulishly named ogre-faced spider can "hear" with its legs and use that ability to catch insects flying behind it, the study published in Current Biology Thursday concluded.
"Spiders are sensitive to airborne sound," Cornell professor emeritus Dr. Charles Walcott, who was not involved with the study, told the Cornell Chronicle. "That's the big message really."
The net-casting, ogre-faced spider (Deinopis spinosa) has a unique hunting strategy, as study coauthor Cornell University postdoctoral researcher Jay Stafstrom explained in a video.
They hunt only at night using a special kind of web: an A-shaped frame made from non-sticky silk that supports a fuzzy rectangle that they hold with their front forelegs and use to trap prey.
They do this in two ways. In a maneuver called a "forward strike," they pounce down on prey moving beneath them on the ground. This is enabled by their large eyes — the biggest of any spider. These eyes give them 2,000 times the night vision that we have, Science explained.
But the spiders can also perform a move called the "backward strike," Stafstrom explained, in which they reach their legs behind them and catch insects flying through the air.
"So here comes a flying bug and somehow the spider gets information on the sound direction and its distance. The spiders time the 200-millisecond leap if the fly is within its capture zone – much like an over-the-shoulder catch. The spider gets its prey. They're accurate," coauthor Ronald Hoy, the D & D Joslovitz Merksamer Professor in the Department of Neurobiology and Behavior in the College of Arts and Sciences, told the Cornell Chronicle.
What the researchers wanted to understand was how the spiders could tell what was moving behind them when they have no ears.
It isn't a question of peripheral vision. In a 2016 study, the same team blindfolded the spiders and sent them out to hunt, Science explained. This prevented the spiders from making their forward strikes, but they were still able to catch prey using the backwards strike. The researchers thought the spiders were "hearing" their prey with the sensors on the tips of their legs. All spiders have these sensors, but scientists had previously thought they were only able to detect vibrations through surfaces, not sounds in the air.
To test how well the ogre-faced spiders could actually hear, the researchers conducted a two-part experiment.
First, they inserted electrodes into removed spider legs and into the brains of intact spiders. They put the spiders and the legs into a vibration-proof booth and played sounds from two meters (approximately 6.5 feet) away. The spiders and the legs responded to sounds from 100 hertz to 10,000 hertz.
Next, they played the five sounds that had triggered the biggest response to 25 spiders in the wild and 51 spiders in the lab. More than half the spiders did the "backward strike" move when they heard sounds that have a lower frequency similar to insect wing beats. When the higher frequency sounds were played, the spiders did not move. This suggests the higher frequencies may mimic the sounds of predators like birds.
University of Cincinnati spider behavioral ecologist George Uetz told Science that the results were a "surprise" that indicated science has much to learn about spiders as a whole. Because all spiders have these receptors on their legs, it is possible that all spiders can hear. This theory was first put forward by Walcott 60 years ago, but was dismissed at the time, according to the Cornell Chronicle. But studies of other spiders have turned up further evidence since. A 2016 study found that a kind of jumping spider can pick up sonic vibrations in the air.
"We don't know diddly about spiders," Uetz told Science. "They are much more complex than people ever thought they were."
Learning more provides scientists with an opportunity to study their sensory abilities in order to improve technology like bio-sensors, directional microphones and visual processing algorithms, Stafstrom told CNN.
"The point is any understudied, underappreciated group has fascinating lives, even a yucky spider, and we can learn something from it," he told CNN.
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