So how do scientists measure sea level, anyway?

Gary Griggs, University of California, Santa Cruz

There are about 330 million cubic miles of water in the world oceans today, 97% of all the water on the planet. Early in our planet’s 4.5 billion year history, water from the atmosphere and from the interior of the Earth gradually collected in the low areas on the planet’s surface to form the ocean basins, accumulating salts along the way.

Sea level change between 1993 and 2008 NASA/JPL

The level of the ocean around the Earth, and therefore the location of the shoreline, are directly related to the total amount of water in the oceans, and also closely tied to climate. As climate changes, so does sea level.

Throughout the history of the oceans, which goes back about 3.5 billion years, give or take a few million, climate has constantly changed and, in response, sea level has gone up and down. As seawater warms, it expands and sea level rises. As the Earth warms, ice sheets and glaciers melt and retreat, adding more water to the oceans, which raises sea level.

Installing a tide gauge in Alaska. NOAA Photo Library, CC BY

People have been keeping track of sea level, or the elevation of the oceans, for about 200 years. Until fairly recently, this was done with tide gauges, which are water-level recorders anchored to some structure along the coastline. It might be a wharf, a concrete breakwater or some other solid structure that is stable over long periods of time.

The oldest tide gauge in the world is on the coast of Poland and was installed in 1808. In the United States, there are two tide gauges that have been in operation since 1856, one in New York and one in San Francisco. There are many others as well, but most of them are much newer; many were set up over the past 50-75 years.

A tidal gauge, ready to be installed. David Monniaux, CC BY-SA

A tide gauge is essentially a large pipe inserted into the ocean, which has a float inside that moves up and down as the water level changes. As the tide rises and falls each day, these gauges record those changes in water level, day after day, year after year.

These instruments were first set up to provide accurate information on water depths so ships could enter and leave ports safely. As time went on, however, it became clear that sea level recorded on these instruments was rising globally.

NOAA tide gauge data for Grand Isle, Louisiana (near New Orleans), where sea level is rising relative to the land at 9.03 mm/yr (36 inches/century) due to subsidence of the Mississippi delta area. NOAA

Each of these official tide gauges keeps track of sea level at a particular coastal location. Many coastal areas are not stable, however. Some are sinking (such as New Orleans or Venice), and some are rising (Alaska and Scandinavia, for example). Each tide gauge keeps track of how sea level is changing relative to the land on which it is anchored.

NOAA tide gage record for Juneau, Alaska, where local sea level is dropping relative to the land at 13.16 mm/year (4.3 feet/century) due to uplift of the coastline. NOAA

Even though sea level rose around the world at a rate of about 1.7 millimeters per year over the last century (nearly seven inches per century), because some gauges are on coasts that are rising and some on coasts that are sinking, these local sea-level rise rates will vary. In parts of Alaska, the land is rising faster than sea level, so the tide gauge actually records a drop in sea level relative to the land.

Global mean sea level as measured by satellite. University of Colorado/NASA

These geographic variations were resolved in 1993 when two satellites were launched that use radar to measure the level of the ocean very precisely from space. This high-tech approach eliminates the problems of land motion on Earth and has given us a new global sea-level rise rate over the past 22 years of 3.2 millimeters per year, the equivalent of 12 inches per century.

Wind and currents can affect a sea’s level. NASA Goddard Space Flight Center, CC BY

Elevations on land, contour lines on maps and depths on nautical charts are based on the long-term average of sea level. This is complicated by the fact that sea level around the world at any instant is not the same, due to local variations resulting from differences in water temperatures, currents, atmospheric pressure and wind.

In order to bring some order to all of these geographical variations, and to provide a constant point of reference, a datum or base level was established based on averaging out the elevation of sea level from many tide gauges over an extended period of time. This datum is now called the North American Vertical Datum (or NAVD) and is the elevation (close to mean sea level) on which all map elevations are based. So if a wharf, highway or building is “20 feet above sea level,” it is 20 feet above this official North American Vertical Datum.

The Conversation

Gary Griggs is Director, Institute of Marine Sciences and Distinguished Professor of Earth & Planetary Sciences at University of California, Santa Cruz.

This article was originally published on The Conversation. Read the original article.

A star nicknamed 'Nasty' gives hints to evolution of extremely massive stars

Astronomers using NASA's Hubble Space Telescope have uncovered surprising new clues about a hefty, rapidly ageing star whose behaviour has never been seen before in our Milky Way galaxy. [Credit: NASA/Hubble]


A giant, rapidly ageing star has given astronomers using NASA's Hubble Space Telescope clues to how stars evolve.

Nicknamed it "Nasty 1" – a play on its catalogue name of NaSt1 – star may represent a brief transitory stage in the evolution of extremely massive stars as they rapidly shed their hydrogen-filled outer layers, exposing their super-hot and extremely bright helium-burning cores.

Nasty 1 was first observed decades ago and identified as a Wolf-Rayet star – a rapidly evolving star more than 20 times as massive as our sun that spews out ionised helium and nitrogen or carbon. But recent observations show Nasty 1 is not behaving like one.

Instead of twin lobes of gas flowing from opposite sides of the star, Hubble revealed a pancake-shaped disc of gas, some three trillion kilometres wide, encircling the star. Astronomers believe it may have formed from an unseen companion star that snacked on the outer envelope of Nasty 1.

Based on current estimates, the nebula surrounding the stars is just a few thousand years old, and as close as 3,000 light-years from Earth.

"We were excited to see this disc-like structure because it may be evidence for a Wolf-Rayet star forming from a binary interaction," said study leader Jon Mauerhan of the University of California, Berkeley. "There are very few examples in the galaxy of this process in action because this phase is short-lived, perhaps lasting only 100,000 years, while the timescale over which a resulting disc is visible could be only 10,000 years or less."

In the team's proposed scenario, a massive star evolves very quickly, and as it begins to run out of hydrogen, it swells up. Its outer hydrogen envelope becomes more loosely bound and vulnerable to gravitational stripping, or a type of stellar cannibalism, by a nearby companion star. In that process, the more compact companion star winds up gaining mass, and the original massive star loses its hydrogen envelope, exposing its helium core to become a Wolf-Rayet star.

Another way Wolf-Rayet stars are said to form is when a massive star ejects its own hydrogen envelope in a strong stellar wind streaming with charged particles. The binary interaction model where a companion star is present is gaining traction because astronomers realise that at least 70% of massive stars are members of double-star systems. Direct mass loss alone also cannot account for the number of Wolf-Rayet stars relative to other less-evolved massive stars in the galaxy.

"We're finding that it is hard to form all the Wolf-Rayet stars we observe by the traditional wind mechanism, because mass loss isn't as strong as we used to think," said Nathan Smith of the University of Arizona in Tucson, who is a co-author on the new NaSt1 paper.

"Mass exchange in binary systems seems to be vital to account for Wolf-Rayet stars and the supernovae they make, and catching binary stars in this short-lived phase will help us understand this process."

The disc is thought to form from stripped matter from the star that spills out during the mass transfer process due to competing gravitational fields.

"That's what we think is happening in Nasty 1," Mauerhan said. "We think there is a Wolf-Rayet star buried inside the nebula, and we think the nebula is being created by this mass-transfer process. So this type of sloppy stellar cannibalism actually makes Nasty 1 a rather fitting nickname."

For images and more information about Nasty 1 and the Hubble Space Telescope, visit:

Liquid crystal lens configuration works like an insects eye

The micro-lenses self-assemble around a central pillar. [Credit: University of Pennsylvania]

The micro-lenses self-assemble around a central pillar. [Credit: University of Pennsylvania]

Engineers and physicists at the University of Pennsylvania have developed a way to use liquid crystals to grow compound lenses that work like insects.

Insects use thousands of individual lenses that work together to provide a wealth of input.

The lenses could be used for three-dimensional imaging, as they produce sets of images with different focal lengths, ranging from a few micrometres to a few tens of micrometres. The lenses are reconfigurable with temperature and sensitive to light polarisation – the latter thought to be one of the ways bees navigate..

The research was published in Advanced Optical Materials.

Futurity has the details.

Previous work by the group had shown how smectic liquid crystal, a transparent, soap-like class of the material, naturally self-assembled into flower-like structures when placed around a central silica bead. Each “petal” of these flowers is a “focal conic domain,” a structure that other researchers had shown could be used as a simple lens.
“Given the liquid crystal flower’s outward similarity to a compound lens, we were curious about its optical properties,” says study co-leader Mohamed Amine Gharbi, a postdoctoral researcher in the physics and astronomy department

The researchers made the lenses using photolithography to create a sheet of micropillars, then spread the liquid crystal on the sheet.

At room temperature, the liquid crystal adheres to the top edges of the posts, transmitting an elastic energy cue that causes the crystal’s focal conic domains to line up in concentric circles around the posts

The rise of wearable health tech could mean the end of the sickie

Data from wearable tech such as Fitbit could be used to prove how well, or unwell, you are – such as when phoning in sick.

Data from wearable tech such as Fitbit could be used to prove how well, or unwell, you are – such as when phoning in sick.

By Emmanuel Tsekleves, Lancaster University

Now that the sun is shining and the temperature is rising, it’s officially sickie season: go to work, or get struck down with “flu”, a “24-hour virus”, or that faithful stand-by, the dodgy prawn takeaway.

Figures show that over a third of employees in the UK admit to pulling a sickie at some point or other. But things may be changing soon – wearable tech such as the Apple Watch, Microsoft Band, Fitbit, or Jawbone Up may become mainstream within a few years, bringing health monitoring capabilities that reveal how your body is performing. It’s not inconceivable that in time this same data could be used to prove how well, or unwell, you are – such as when phoning in sick.

Wearable health tech is still in its early days. These devices come with sensors that can record how many steps and how much exercise you’ve taken, how well and long you‘ve slept, stress levels, blood pressure, sun exposure, even what you’ve have eaten. Added together, all this could easily demonstrate that you’re not so sick after all.

Since some wearables are aimed at being fashionable accessories, employers might be minded to tap into the trend. So next time you’re pulling a sickie, you might need the data to back up your story. With GPS-equipped devices there’ll be no opportunity to escape your sickbed to a barbeque or trip to the beach, while ultraviolet sensors will detect the increase in sunshine and motion sensors detect movement not typically associated with bed rest.

Using your data against you

What if employers and health insurance companies move in the direction that the car insurance industry has taken, where every health transgression (a boozy night out, a Christmas feast, or too many lazy days on the sofa) could increase your health premium rates? Such a scenario isn’t so far away, and this should concern us. Apple is clearly making a beeline for the health and fitness industry with Watch and its integrated HealthKit software, now integrated with its iOS mobile operating system, and it is the only firm to do so.

Typically, health insurers use body mass index (a calculation of body fat that takes into account your age, weight and height) to set premiums, and some insurers set rates based on basic data from wearables, such as the number of steps we take link?. Fitbit and Jawbone Up are both already playing a bigger role in how health insurance is calculated, with more employers opting to monitor data generated by such wearable trackers. And here’s the catch: employers are holding their insured staff to account with penalties and rewards as part of an increasing number of so-called “corporate-wellness programmes”.

For example, at BP staff are given Fitbits for free as long as the company has access to their data. The more physically active an employee is (as measured by the device) the more points they’re awarded. Higher points lower the company’s insurance premium. Other companies are adopting similar wellbeing employee health insurance programmes too.

Consent, for now

Wearable tech is still far from perfect, and that means inventive workarounds will be found. A few acquaintances of mine who shall remain nameless have found creative ways of racking up a few more miles, while actually continuing their usual, less-than-active habits. These include holding and shaking the device for a few minutes at a time, or attaching it to their cat or dog, or offering pocket money to other, younger and fitter family members to wear. Obviously insurers and developers are aware of these, so it won’t be long until such loopholes are closed.

For now, we can consent to share our health data from wearables with employers or insurers in exchange or lower premiums or cheaper travel. But how long before the company wearable is a mandatory part of the uniform?

The Conversation

Emmanuel Tsekleves is Senior Lecturer in Design Interactions at Lancaster University.

This article was originally published on The Conversation. Read the original article.

A new history of ancient snakes

An artist's impression of an ancient snake, with tiny hind limbs. [Credit: Julius T. Csotonyi]

An artist's impression of an ancient snake, with tiny hind limbs. [Credit: Julius T. Csotonyi]

Early snakes had hind legs, according to Yale palaeontologists who have analysed snake genomes and new fossil records.

"We generated the first comprehensive reconstruction of what the ancestral snake was like," said Allison Hsiang, lead author the study published in the journal BMC Evolutionary Biology

"We infer that the most recent common ancestor of all snakes was a nocturnal, stealth-hunting predator targeting relatively large prey, and most likely would have lived in forested ecosystems in the Southern Hemisphere," she said.

The scientists concluded that the most recent common ancestor of all 3,400 species of living snakes would have already lost its forelimbs, but would still have had tiny hind limbs, with complete ankles and toes.

"It would have first evolved on land, instead of in the sea," said co-author Daniel Field. "Both of those insights resolve longstanding debates on the origin of snakes."

The ancestral snakes originated about 128.5 million years ago, during the middle Early Cretaceous period, the study suggests. They were non-constricting, wide-ranging foragers that seized their prey with needle-like hooked teeth and swallowed them whole.

"Primate brains, including those of humans, are hard-wired to attend to serpents, and with good reason," said Jacques Gauthier, senior author of the study.

The 'origami' drone that fits in your pocket

Researchers at the Swiss Federal Institute of Technology have developed a tiny folding quadcopter that can go from pocket to airborne within one second. The propeller arms are built with two vertical folds allowing them to wrap around the core, as well as a horizontal fold to provide stability during flight.

Momentum snaps the drone’s propellers out for take-off, while magnets keep them locked in place.

Have scientists finally put the nature vs nurture debate to rest?

No, seems to be the short answer, but the good news is that everyone is right.

University of Queensland scholar Dr Beben Benyamin. [Credit: University of Queensland]

University of Queensland scholar Dr Beben Benyamin. [Credit: University of Queensland]

A meta-analysis of data going back 50 years found that 49% of the variation for human traits and diseases could be blamed on genetics, while 51% were due to environmental factors.

University of Queensland research fellow Dr Beben Benyamin and a team from the VU University of Amsterdam analysed studies of more than 14.5 million twin pairs across 17,804 traits from 2,748 publications.

Benyamin said he was surprised by how similar an influence each aspect had.

"Most of the reviews have been for specific traits, like people are interested in studying one particular disease and review all the twin studies for one disease," he told the media. "But this is I think is the first one to review everything about all disease and all twin studies that are available at the moment."

He said the study showed that the influence of nature and nurture should be understood as a complex interplay rather than a simple either/or.

"The findings show that we need to look at ourselves outside of a view of nature versus nurture, and instead look at it as nature and nurture," he said.

His research was published in Nature.

Women scientists quick to show they like their toys, too

The Twittersphere has reacted rapidly to comments by California Institute of Technology astronomy and planetary science professor Shrinivas Kulkarni, who told NPR recently that many scientists "are what I call 'boys with toys".

In next to no time, female scientists took to Twitter to remind the world that they are doing crucial work – and like their toys just as much as the "boys" do.

In 48 hours, there were nearly 17,000 tweets under the hashtag #GirlsWithToys as female scientists from all over the world posted images of themselves with their scientific equipment.

Here's just some of them, via, starting with Cosmos contributor and astrophysicist Katie Mack @AstroKatie

It's back to square one in the search for the fountain of youth

Scientists have called into question previous research that suggested blood of a young mouse can reinvigorate an older one – in fact the opposite may be happening they say.

The technique, parabiosis, involves sewing a young mouse and an old mouse together so that they share a circulatory system. So promising have been the results that it has led to attempts to commercialise the procedure in humans.

Nature has the details.

In 2013, a team led by Amy Wagers, a stem-cell researcher at Harvard University in Cambridge, Massachusetts, seemed to offer an explanation for this blood-doping effect. The scientists found that levels of a protein called GDF11 decreased in the blood of mice as they grew older. When the researchers injected the protein into the heart muscle of old mice, it became 'younger' — thinner and better able to pump blood. Two subsequent studies by Wagers and her colleagues found that GDF11 boosted the growth of new blood vessels and neurons in the brain and spurred stem cells to regenerate skeletal muscle at the sites of injuries.

But another team of scientists has tested the results and found something different going on. They used a combination of chemicals to injure a mouse’s skeletal muscles, and then regularly injected the animal with GDF11. But rather than regenerating the muscle, the protein injections seemed to make the damage worse.

But Wagers stands by her work, believing that there could be multiple forms of GDF11.

“We look forward to addressing the differences in the studies with additional data very soon,” Wagers says.


Could viruses be our secret weapon against drug-resistant bacteria?

Scientists have found viruses that can increase E. Coli's sensitivity to antibiotics.

Scientists have found viruses that can increase E. Coli's sensitivity to antibiotics.

We may be able to enlist the help of viruses to fight antibiotic-resistant strains of bacteria, according to Israeli scientists.

They believe there is potential to use the viruses in hand sanitisers and on surfaces in hospitals, where the build up of bacteria can cause fatal diseases. (see Microbial gangs are organised killers).

The researchers at Tel Aviv University developed two kinds of bacteria-killing viruses known as bacteriophages – against E. coli.

One kind killed E. coli outrightbut the other kind injected the bacteria with DNA disrupted the antibiotic-resistance genes in the bacteria, making them sensitive to drugs that they might otherwise have developed a resistance against.

"We managed to construct a system that restores antibiotic sensitivity to drug-resistant bacteria," said study co-author, molecular biologist Udi Qimron.

While the research is promising, it does have its limitations. Most of the bacteriophages infect just one species of bacteria, and some are even limited to a few strains within a species. But the scientists are hopeful they can develop mutant strains with a wider target range of strains and species.

The research was published in the journal Proceedings of the National Academy of Sciences.