Who were the people of the Nordic Bronze Age?

Ancient DNA has revealed that large scale migrations and population replacements have often accompanied major cultural changes in prehistoric Europe. But, for now, my opinion is that the formation of the archeologically ostentatious Nordic Bronze Age wasn’t associated with any significant foreign gene flow into Scandinavia. I’ve tested this as best as I could with the few relevant ancient samples that are currently available.

For instance, below are among the most successful qpAdm mixture models that I was able find for various ancient Scandinavian groups dating back to the local Middle Neolithic (MN) period. The Nordic Bronze Age population is represented by three individuals labeled Nordic_BA. Unfortunately, the guy pictured above, from the famous Borum Eshøj barrow burial in what is now Denmark, didn’t make the cut. For more details about my sampling and labeling strategies refer to the text file here.

Nordic_MN_B
CWC_CZE 0.822±0.059
POL_Globular_Amphora 0.178±0.059
chisq 14.478
tail prob 0.341086
Full output
SWE_Battle_Axe
CWC_Baltic_early 0.662±0.028
POL_Globular_Amphora 0.338±0.028
chisq 11.234
tail prob 0.591189
Full output
Nordic_LN
Nordic_MN_B 0.928±0.069
SWE_TRB 0.072±0.069
chisq 12.139
tail prob 0.516307
Full output
Nordic_BA
Nordic_LN 0.851±0.061
SWE_TRB 0.149±0.061
chisq 10.897
tail prob 0.619475
Full output

It’s impossible to successfully model the ancestries of Nordic_MN_B and SWE_Battle_Axe simply with the populations that were living in Scandinavia before them. Therefore, it’s likely that they were migrants or the recent descendants of migrants to Scandinavia. But there’s nothing surprising about that, because they’re archeologically associated with the Corded Ware culture (CWC), which has always been seen as intrusive to Scandinavia from the south and east.
Conversely, it’s easy to produce statistically sound mixture models for both Nordic_LN and Nordic_BA exclusively with earlier Scandinavian populations. Indeed, based on the outgroups or right pops that I’m using, Nordic_LN is almost indistinguishable from Nordic_MN_B, and the same can be said of Nordic_BA in regards to Nordic_LN.
Of course, if I mixed and matched reference populations from across prehistoric Europe, I could probably come up with some spectacular statistical fits even without the need for any Scandinavians. Essentially that’s because Nordic_LN and Nordic_BA are closely related to many earlier and contemporaneous peoples living all the way from the Atlantic facade to the Ural Mountains. My point, however, is that this isn’t crucial, despite the dearth of ancient samples from Scandinavia.
This is how things look in a Principal Component Analysis (PCA) of Northern European genetic variation based on my Global25 test. Strikingly, Nordic_MN_B, SWE_Battle_Axe, Nordic_LN and Nordic_BA more or less recapitulate the cluster made up of present-day Swedish samples. The relevant datasheet is available here.

Granted, two of the Nordic_BA samples sit just south of the Swedes, no doubt due to their slightly higher ratios of Neolithic farmer (SWE_TRB-related) ancestry, but this is also an area of the plot that many present-day Danes call home (not shown, because I don’t have any suitable academic Danish samples to run).
I’ll eat my hat if it turns out that Scandinavia experienced a major population shift (say, more than a collateral ~10%) during the LN and/or BA periods. And I’ll post a clip of it online too.
See also…
The Trundholm sun chariot was found in a peat bog on the island of Zealand, Denmark, in 1902. It’s thought to be an Indo-European religious artifact dating back to the Nordic Bronze Age; a representation of a horse pulling the sun and perhaps also the moon in a spoked wheel chariot. So one way or another it appears to be a reference to the Divine Twins mythos. Click on the image for more…

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Global 5G wireless networks threaten weather forecasts

Global Telecommunications Network logo.

May 19, 2019

Next-generation mobile technology could interfere with crucial satellite-based Earth observations.

Image above: Water vapour over the continental United States is shown in this false-colour satellite image from the National Oceanic and Atmospheric Administration. Image Credits: NOAA/GOES.

The US government has begun auctioning off blocks of wireless radio frequencies to be used for the next-generation mobile communications network known as 5G. But some of these frequencies lie close to those that satellites use for crucial Earth observations — and meteorologists are worried that 5G transmissions from cellphones and other equipment could interfere with their data collection.

Unless regulators or telecommunications companies take steps to reduce the risk of interference, Earth-observing satellites flying over areas of the United States with 5G wireless coverage won’t be able to detect concentrations of water vapour in the atmosphere accurately. Meteorologists in the United States and other countries rely on those data to feed into their models; without that information, weather forecasts worldwide are likely to suffer.

“This is a global problem,” says Jordan Gerth, a meteorologist at the University of Wisconsin–Madison.

The US National Oceanic and Atmospheric Administration (NOAA) and NASA are currently locked in a high-stakes negotiation with the Federal Communications Commission (FCC), which oversees US wireless networks. NOAA and NASA have asked the FCC to work with them to protect frequencies used for Earth observations from interference as 5G rolls out. But the FCC auctioned off the first chunk of the 5G spectrum with minimal protection. The sale ended on 17 April and reaped nearly US$2 billion.

Sharing the sky

Because the United States is such a large communications market, the decisions the government makes about how to deploy 5G are likely to influence global discussions on how to regulate the technology. Regulators from around the world will gather starting on 28 October in Sharm el-Sheikh, Egypt, to hammer out international agreements for which frequencies companies will be able to use for 5G transmissions, and what level of interference with Earth-observation frequencies is acceptable.

Astronomers, meteorologists and other scientists have long worked to share the spectrum with other users, sometimes shifting to different frequencies to prevent conflicts. But “this is the first time we’ve seen a threat to what I’d call the crown jewels of our frequencies — the ones that we absolutely must defend come what may”, says Stephen English, a meteorologist at the European Centre for Medium-Range Weather Forecasts in Reading, UK.

Image above: Weather Satellites, an artist’s rendering of NASA’s new Global Precipitation Monitoring Core Observatory and partner satellites orbiting the Earth. Image Credit: NASA.

They include the 23.8-gigahertz frequency, at which water vapour in the atmosphere emits a faint signal. Satellites, such as the European MetOp probes, monitor energy radiating from Earth at this frequency to assess humidity in the atmosphere below — measurements that can be taken during the day or at night, even if clouds are present. Forecasters feed these data into models to predict how storms and other weather systems will develop in the coming hours and days.

But a 5G station transmitting at nearly the same frequency will produce a signal that looks much like that of water vapour. “We wouldn’t know that that signal is not completely natural,” says Gerth. Forecasts would become less accurate if meteorologists incorporated those bad data into their models.

Noisy neighbours

The recent FCC auction involved 2 groups of frequencies: one between 24.25 and 24.45 gigahertz and the other between 24.75 and 25.25 gigahertz. Wireless equipment transmitting near the lower end of that range could interfere with the 23.8-gigahertz water-vapour measurement. The FCC did not respond to Nature’s request for comment on the matter.

The situation is akin to having a noisy neighbour next door, Gerth says. If that person blasts music, a lot of the noise will probably bleed through the wall into your apartment. But if you can persuade the person to turn their music down, you’ll be able to sleep more peacefully.

Source: ITU

Radio-frequency engineers measure noise in units of decibel watts. Regulators set controls that limit the noise allowed; more-negative numbers indicate increasingly stringent controls. The FCC auction set a noise limit on the US 5G network of –20 decibel watts, which is much noisier than the thresholds under consideration by almost every other nation for their systems. The European Commission, for instance, has settled on –42 decibel watts for 5G base stations, and the World Meteorological Organization (WMO) is recommending –55 decibel watts.

Many hope that the WMO numbers will influence regulators to adopt strict global noise standards at the meeting in Egypt. Because of how the scale is devised, the US proposal would allow over 150 times more noise than the European proposal — and more than 3,000 times more than the WMO plan, says Eric Allaix, a meteorologist at Météo-France in Toulouse who heads a WMO steering group on radio-frequency coordination.

Future fears

There’s relatively little research on exactly how bad weather forecasts could get as interference increases at 23.8 gigahertz and other frequencies crucial for Earth observations, says Gerth. “But the more we lose, the greater the impact will be,” he says.

NOAA and NASA have reportedly finished a study on the effects of differing levels of noise interference, but it has not been made public, despite at least one formal request from Congress. A 2010 report from the National Academies of Sciences, Engineering and Medicine concluded that losing scientific access to the 23.8-gigahertz signal would eliminate 30% of all useful data in microwave frequencies, which contribute significantly to global weather forecasts.

Weather Satellites around the world. Image Credit: CEOS

And not having atmospheric data from the United States can dramatically hurt forecasts for Europe, whose weather patterns are often steered by conditions over the United States 3–4 days earlier, says English.

The Department of Commerce, which oversees NOAA, said that it «strongly supports the administration’s policy to promote US leadership in secure 5G networks, while at the same time sustaining and improving critical government and scientific missions.» NASA administrator Jim Bridenstine declined to comment, but spoke at length about his concerns over 5G at an agency meeting earlier this month. «This is a big deal,» Bridenstine said.

The FCC plans to begin its next 5G auction, which will be the country’s largest ever, in December. It will involve three more frequency bands — some of which are used for satellite observations of precipitation, sea ice and clouds.

Related article on Nature:

https://www.nature.com/articles/d41586-019-01305-4?utm_source=Nature+Briefing&utm_campaign=ecff27402a-briefing-dy-20190429&utm_medium=email&utm_term=0_c9dfd39373-ecff27402a-42550087

Nature: https://www.nature.com/

Related link:

European Centre for Medium-Range Weather Forecasts: https://www.ecmwf.int/

Images (mentioned), Text, Credit: Nature.

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Seasonal Monsoon Rains Block Key Ocean Current

NASA — Soil Moisture Active Passive (SMAP) patch.

May 19, 2019

Our oceans and the complex «conveyer belt» system of currents that connects them play an important role in regulating global climate. The oceans store heat from the Sun, and ocean currents transport that heat from the tropics to the poles. They release the heat and moisture into the air, which moderates climate nearby. But what happens if part of that conveyer belt jams?

Animation above: This animation shows a time lapse of sea surface salinity and soil moisture from NASA’s Soil Moisture Active Passive (SMAP) satellite from April 2015 through February 2019. Image Credits: NASA/JPL-Caltech/GSFC.

It’s not a theoretical question. Scientists have observed that a major ocean current called the Indonesia Throughflow, which provides the only tropical connection between the Pacific and Indian oceans, slows dramatically near the surface during the Northwest Asia monsoon season — usually December through March. And a team of scientists, led by Tong Lee of NASA’s Jet Propulsion Laboratory in Pasadena, California, has figured out why.

«We have found that this current, which is a very important element of the global ocean current system, is significantly affected by local precipitation,» Lee said. «It is fairly common knowledge that winds drive ocean currents. In this case, however, the precipitation is actually a dominant factor during the monsoon season.»

It’s a discovery that will improve our understanding of complex Earth processes. During this season, about 10 feet (3 meters) of rain fall over the maritime continent, a region of Southeast Asia between the Indian and Pacific oceans through which the Indonesia Throughflow current travels. This influx of local rain reduces the pressure force that drives the current through the region.

How does that work?

Gravity causes water to travel «downhill» from areas of relatively higher sea level toward areas of lower sea level unless opposed by another force. In the tropical Pacific, trade winds also influence the flow of water. They blow from east to west, causing ocean currents to transport large amounts of water from the U.S. westward toward Asia. This raises the sea level on the Asian side of the Pacific Ocean and provides enough force to keep the Indonesia Throughflow moving, connecting the two oceans.

However, the influx of rain during monsoon season temporarily but significantly raises the local sea level in the Indonesian seas that sit between the Pacific and Indian oceans enough to essentially eliminate the downhill flow. Think of it like a ball rolling freely downhill versus a ball on a flat surface, which has little momentum to move forward.

Although the slowing of this current is primarily seasonal, it still affects the amount of heat transported from the Pacific Ocean to the Indian Ocean, which can change regional climate in Southeast Asia.

Soil Moisture Active Passive (SMAP) satellite. Image Credit: NASA

«The increase in local sea level due to the seasonal freshening of seawater pushes against the normally higher sea level from the Pacific Ocean,» said Lee. «It restricts the surface flow of this current during the monsoon season, which prevents a lot of the heat normally carried by the current from making its way to the Indian Ocean.»

Furthermore, since all of these currents are connected globally, less warm water is transported into the Indian Ocean, and in turn, less warm water is transported from the Indian Ocean to the Atlantic Ocean over the long term. So the Indonesia Throughflow — one element of a much larger system — can have a significant effect thousands of miles away from where it flows.

The results of this study will help to improve climate models by enabling scientists to factor in these effects and changes. Titled «Maritime Continent water cycle regulates low-latitude chokepoint of global ocean circulation,» the study was recently published in Nature.

NASA satellite data, particularly ocean salinity measurements from the Soil Moisture Active Passive (SMAP) satellite, were instrumental in these findings. Although SMAP was designed primarily to measure soil moisture, its radiometer is also able to measure sea surface salinity. The results of this paper demonstrate the utility of SMAP salinity data in exploring changes in the water cycle, sea level, ocean circulation and climate.

More information on SMAP is available here: https://smap.jpl.nasa.gov/

Animation (mentioned), Image (mentioned), Text, Credits: NASA/JPL/Esprit Smith.

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2019 May 19 A Circumhorizontal Arc Over Ohio Image Credit &…

2019 May 19

A Circumhorizontal Arc Over Ohio
Image Credit & Copyright: Todd Sladoje

Explanation: Why would clouds appear to be different colors? The reason here is that ice crystals in distant cirrus clouds are acting like little floating prisms. Sometimes known as a fire rainbow for its flame-like appearance, a circumhorizon arc lies parallel to the horizon. For a circumhorizontal arc to be visible, the Sun must be at least 58 degrees high in a sky where cirrus clouds are present. Furthermore, the numerous, flat, hexagonal ice-crystals that compose the cirrus cloud must be aligned horizontally to properly refract sunlight in a collectively similar manner. Therefore, circumhorizontal arcs are quite unusual to see. This circumhorizon display was photographed through a polarized lens above Dublin, Ohio in 2009.

∞ Source: apod.nasa.gov/apod/ap190519.html

I’m sori I’m rusty! Image of the Week — May 20, 2019CIL:38946 -…

I’m sori I’m rusty! Image of the Week — May 20, 2019

CIL:38946 — http://cellimagelibrary.org/images/38946

Description: Light micrograph of a transverse section through wheat stem showing uredosori of wheat rust (Puccinia graminis). These sori appear as rust-coloured streaks on the wheat. The released uredospores will infect other wheat plants.

Authors: Spike Walker

Licensing: Attribution-NonCommercial-NoDerivs 2.0 UK: England & Wales (CC BY-NC-ND 2.0 UK)

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Calcite with Sphalerite and Fluorite | #Geology #GeologyPage…

Calcite with Sphalerite and Fluorite | #Geology #GeologyPage #Mineral

Locality: Millclose Mine, South Darley, Matlock, Derbyshire, England, Europe

Dimensions: 6.0 × 3.9 × 2.6 cm

Photo Copyright © Crystal Classics

Geology Page

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https://www.instagram.com/p/BxnaZ-ijXYe/?igshid=1qkz52b4vyy79

Fluorite | #Geology #GeologyPage #Mineral Locality: De’an…

Fluorite | #Geology #GeologyPage #Mineral

Locality: De’an fluorite mine, Wushan, De’an Co., Jiujiang Prefecture, Jiangxi Province, China

Size: 10.8 x 6.3 x 3.4 cm

Photo Copyright © Anton Watzl Minerals

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ALMA discovers aluminum around young star

Researchers using ALMA data discovered an aluminum-bearing molecule for the first time around a young star. Aluminum rich inclusions found in meteorites are some of the oldest solid objects formed in the Solar System, but their formation process and stage is still poorly linked to star and planet formation. The discovery of aluminum oxide around a young star provides a crucial chance to study the early formation process of meteorites and planets like the Earth.

ALMA image of the distributions of AlO molecules (color) and warm dust particles (contours).
The molecular outflow (not shown in this image) extends from the center to the top-left
and bottom-right [Credit: ALMA(ESO/NAOJ/NRAO), Tachibana et al. 2019]

Young stars are surrounded by disks of gas. Some of the gas condenses into dust grains which then stick together to form larger objects, building up to form meteors, planetesimals, and eventually planets. Understanding the formation of these first solid objects is important for understanding everything which follows.

Shogo Tachibana, a professor at the University of Tokyo/Japan Aerospace Exploration Agency (JAXA), and his team analyzed the ALMA (Atacama Large Millimeter/submillimeter Array) data for Orion KL Source I, a young massive protostar, and found distinctive radio emissions from aluminum oxide (AlO) molecules. This is the first unambiguous detection of AlO around a young star.

«Aluminum oxide played a very important role in the formation of the oldest material in the Solar System,» says Tachibana «Our discovery will contribute to the understanding of material evolution in the early Solar System.»

Interestingly, the radio emissions from the AlO molecules are concentrated in the launching points of the outflows from the rotating disk around the protostar. In contrast, other molecules such as silicon monoxide (SiO) have been detected in a wider area in the outflow. Normally, the temperature is higher at the base of the outflows and lower in the downstream gas. «Non-detection of gas-phase AlO downstream indicates that the molecules have condensed into solid dust particles in the colder regions,» explains Tachibana. «Molecules can emit their distinctive radio signals in gas-phase, but not in solid-phase.»

ALMA’s detection of AlO in the hot base of the outflow suggests that the molecules are formed in hot regions close to the protostar. Once moved to colder regions, AlO would be captured in dust particles which can become aluminum-rich dust, like the oldest solid in the Solar System, and further the building blocks for planets.

The team will now observe other protostars looking for AlO. Combining the new results with data from meteorites and sample return missions like JAXA’s Hayabusa2 will provide important insights into the formation and evolution of our Solar System and other planetary systems.

The study is published in The Astrophysical Journal.

Source: National Institutes of Natural Sciences [May 16, 2019]

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Galaxy blazes with new stars born from close encounter

The irregular galaxy NGC 4485 shows all the signs of having been involved in a hit-and-run accident with a bypassing galaxy. Rather than destroying the galaxy, the chance encounter is spawning a new generation of stars, and presumably planets.

Irregular galaxy NGC 4485, captured by Hubble’s Wide Field Camera 3 (WFC3) [Credit: NASA, ESA;
acknowledgment: T. Roberts (Durham University, UK), D. Calzetti (University of Massachusetts)
and the LEGUS Team, R. Tully (University of Hawaii) and R. Chandar (University of Toledo)]

The right side of the galaxy is ablaze with star formation, shown in the plethora of young blue stars and star-incubating pinkish nebulas. The left side, however, looks intact. It contains hints of the galaxy’s previous spiral structure, which, at one time, was undergoing normal galactic evolution.
The larger culprit galaxy, NGC 4490, is off the bottom of the frame. The two galaxies sideswiped each other millions of years ago and are now 24,000 light-years apart. The gravitational tug-of-war between them created rippling patches of higher-density gas and dust within both galaxies. This activity triggered a flurry of star formation.

This galaxy is a nearby example of the kind of cosmic bumper-car activity that was more common billions of years ago when the universe was smaller and galaxies were closer together.
NGC 4485 lies 25 million light-years away in the northern constellation Canes Venatici (the Hunting Dogs).

This new image, captured by Hubble’s Wide Field Camera 3 (WFC3), provides further insight into the complexities of galaxy evolution.

Source: ESA/Hubble Information Centre [May 16, 2019]

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New Horizons team publishes first Kuiper Belt flyby science results

NASA’s New Horizons mission team has published the first profile of the farthest world ever explored, a planetary building block and Kuiper Belt object called 2014 MU69.

This composite image of the primordial contact binary Kuiper Belt Object 2014 MU69 (nicknamed Ultima Thule) – featured
on the cover of the May 17 issue of the journal Science – was compiled from data obtained by NASA’s New Horizons
spacecraft as it flew by the object on Jan. 1, 2019. The image combines enhanced color data (close to what
the human eye would see) with detailed high-resolution panchromatic pictures [Credit: NASA/Johns
Hopkins University Applied Physics Laboratory/Southwest Research Institute/Roman Tkachenko]

Analyzing just the first sets of data gathered during the New Horizons spacecraft’s New Year’s 2019 flyby of MU69 (nicknamed Ultima Thule) the mission team quickly discovered an object far more complex than expected. The team publishes the first peer-reviewed scientific results and interpretations – just four months after the flyby – in the journal Science.

In addition to being the farthest exploration of an object in history – four billion miles from Earth – the flyby of Ultima Thule was also the first investigation by any space mission of a well-preserved planetesimal, an ancient relic from the era of planet formation.

The initial data summarized in Science reveal much about the object’s development, geology and composition. It’s a contact binary, with two distinctly differently shaped lobes. At about 22 miles (36 kilometers) long, Ultima Thule consists of a large, strangely flat lobe (nicknamed «Ultima») connected to a smaller, somewhat rounder lobe (nicknamed «Thule»), at a juncture nicknamed «the neck.» How the two lobes got their unusual shape is an unanticipated mystery that likely relates to how they formed billions of years ago.

The lobes likely once orbited each other, like many so-called binary worlds in the Kuiper Belt, until some process brought them together in what scientists have shown to be a «gentle» merger. For that to happen, much of the binary’s orbital momentum must have dissipated for the objects to come together, but scientists don’t yet know whether that was due to aerodynamic forces from gas in the ancient solar nebula, or if Ultima and Thule ejected other lobes that formed with them to dissipate energy and shrink their orbit. The alignment of the axes of Ultima and Thule indicates that before the merger the two lobes must have become tidally locked, meaning that the same sides always faced each other as they orbited around the same point.

«We’re looking into the well-preserved remnants of the ancient past,» said New Horizons Principal Investigator Alan Stern, of the Southwest Research Institute, Boulder, Colorado. «There is no doubt that the discoveries made about Ultima Thule are going to advance theories of solar system formation.»

As the Science paper reports, New Horizons researchers are also investigating a range of surface features on Ultima Thule, such as bright spots and patches, hills and troughs, and craters and pits on Ultima Thule. The largest depression is a 5-mile-wide (8-kilometer-wide) feature the team has nicknamed Maryland crater – which likely formed from an impact. Some smaller pits on the Kuiper Belt object, however, may have been created by material falling into underground spaces, or due to exotic ices going from a solid to a gas (called sublimation) and leaving pits in its place.

In color and composition, Ultima Thule resembles many other objects found in its area of the Kuiper Belt. It’s very red – redder even than much larger, 1,500-mile (2,400-kilometer) wide Pluto, which New Horizons explored at the inner edge of the Kuiper Belt in 2015 – and is in fact the reddest outer solar system object ever visited by spacecraft; its reddish hue is believed to be caused by modification of the organic materials on its surface New Horizons scientists found evidence for methanol, water ice, and organic molecules on Ultima Thule’s surface – a mixture very different from most icy objects explored previously by spacecraft.

Data transmission from the flyby continues, and will go on until the late summer 2020. In the meantime, New Horizons continues to carry out new observations of additional Kuiper Belt objects it passes in the distance. These additional KBOs are too distant to reveal discoveries like those on MU69, but the team can measure aspects such as the object’s brightness. New Horizons also continues to map the charged-particle radiation and dust environment in the Kuiper Belt.

The New Horizons spacecraft is now 4.1 billion miles (6.6 billion kilometers) from Earth, operating normally and speeding deeper into the Kuiper Belt at nearly 33,000 miles (53,000 kilometers) per hour.

Source: NASA [May 16, 2019]

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24% of West Antarctic ice is now unstable

By combining 25 years of European Space Agency satellite altimeter measurements and a model of the regional climate, the UK Centre for Polar Observation and Modelling (CPOM) have tracked changes in snow and ice cover across the continent.

Iceberg at Marguerite Bay, Antarctic Peninsula 
[Credit: Andrew Shepherd]

A team of researchers, led by Professor Andy Shepherd from the University of Leeds, found that Antarctica’s ice sheet has thinned by up to 122 metres in places, with the most rapid changes occurring in West Antarctica where ocean melting has triggered glacier imbalance.

This means that the affected glaciers are unstable as they are losing more mass through melting and iceberg calving than they are gaining through snowfall.

The team found that the pattern of glacier thinning has not been static. Since 1992, the thinning has spread across 24% of West Antarctica and over the majority of its largest ice streams — the Pine Island and Thwaites Glaciers — which are now losing ice five times faster than they were at the start of the survey.

The study, published in Geophysical Research Letters, used over 800 million measurements of the Antarctic ice sheet height recorded by the ERS-1, ERS-2, Envisat, and CryoSat-2 satellite altimeter missions between 1992 and 2017 and simulations of snowfall over the same period produced by the RACMO regional climate model.

By combining 25 years of ESA satellite data, scientists have discovered that warming ocean waters have caused
 the ice to thin so rapidly that 24% of the glaciers in West Antarctica are now affected. A paper published
in Geophysical Research Letters describes how the UK Centre for Polar Observation and Modelling (CPOM)
 used over 800 million measurements of the height of the Antarctic ice sheet recorded by radar altimeter
 instruments on ESA’s ERS-1, ERS-2, Envisat, and CryoSat satellite missions between 1992 and 2017.
They used simulations of snowfall produced by the RACMO regional climate model to identify
changes that were due to glacier dynamics alone (green contours). In some places, the
glacier thinning has spread far inland during the survey period [Credit: CPOM]

Together, these measurements allow changes in the ice sheet height to be separated into those due to weather patterns, such as less snowfall, and those due to longer term changes in climate, such as increasing ocean temperatures that eat away ice.

Lead author and CPOM Director Professor Andy Shepherd explained: «In parts of Antarctica the ice sheet has thinned by extraordinary amounts, and so we set out to show how much was due to changes in climate and how much was due to weather.»

To do this, the team compared the measured surface height change to the simulated changes in snowfall, and where the discrepancy was greater they attributed its origin to glacier imbalance.

They found that fluctuations in snowfall tend to drive small changes in height over large areas for a few years at a time, but the most pronounced changes in ice thickness are signals of glacier imbalance that have persisted for decades.

Time sequence of Antarctic glacier ice thickness change (left) and associated contribution
to sea level rise (right) between 1992 and 2017 [Credit: CPOM]

Professor Shepherd added: «Knowing how much snow has fallen has really helped us to detect the underlying change in glacier ice within the satellite record. We can see clearly now that a wave of thinning has spread rapidly across some of Antarctica’s most vulnerable glaciers, and their losses are driving up sea levels around the planet.
«Altogether, ice losses from East and West Antarctica have contributed 4.6 mm to global sea level rise since 1992.»

Dr Marcus Engdahl of the European Space Agency, a co-author of the study, added: «This is an important demonstration of how satellite missions can help us to understand how our planet is changing. The polar regions are hostile environments and are extremely difficult to access from the ground. Because of this, the view from space is an essential tool for tracking the effects of climate change.»

Source: University of Leeds [May 16, 2019]

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Mapping the global distribution of phytoplankton

Researchers at ETH have charted the distribution of phytoplankton in the world’s oceans for the first time and investigated the environmental factors that explain this distribution. They concluded that plankton diversity is only partially congruent with previous theories of biodiversity for the seas between the equator and the poles.

Phytoplankton boasts an amazing variety of forms and species
[Credit: www.secchidisk.org]

With some 10,000 to 20,000 different species in the world’s oceans, the diversity of phytoplankton (phyto from the Greek for plant) species is extremely rich. These phytoplankton form a key element of ocean ecosystems and life on this planet, producing more oxygen than all the world’s rainforests combined. They also serve as the fundamental basis of the marine food chain.

To date, however, very little has been known about the geographic and seasonal diversity of phytoplankton. Although many species of phytoplankton have been identified, the question of when and where they occur is largely unexplored; in light of the current biodiversity crisis, this represents a serious knowledge gap.

In early May, the Intergovernmental Platform on Biodiversity and Ecosystem Services stated in its latest report that a million of all known species on earth are under threat of extinction as a result of human activity and climate change. However, for many important species, especially species of the world’s smallest form of marine life, plankton, our knowledge of their distribution and diversity remains inadequate or non-existent to this day.

Now, a team of researchers from ETH Zurich and the Swiss Federal Institute for Forest, Snow and Landscape Research WSL have filled in some of this knowledge gap. In a study published recently in the Science Advances journal, they modelled the spatial and temporal distribution of over 530 different species of phytoplankton. As the basis for their distribution charts, they used around 700,000 water samples from across the world’s oceans.

Biodiversity in tropical seas

Their study reveals that tropical waters hold the richest diversity of species at all times of the year. Phytoplankton diversity is particularly high in the seas of the Indonesian-Australian archipelago, in parts of the Indian Ocean and in the equatorial Pacific Ocean. In the subtropics, biodiversity drops off markedly beyond 30 degrees latitude North and South, reaching its lowest values around a latitude of 55 degrees. Diversity then picks up again slightly towards the poles.

The global distribution of phytoplankton in January. Dark areas indicate a high biodiversity,
light areas a low one. The number of species was not determined for the white areas
[Credit: Righetti et al. 2019]

«We were surprised to find that on a monthly basis, the polar seas present greater diversity than the mid-latitudes,» says Damiano Righetti, the lead author of the study. He is a Ph.D. student with ETH professor Nicolas Gruber and senior scientist Meike Vogt. «It’s remarkable because global species distribution and diversity are normally closely linked to environmental temperature trends.»
Species diversity typically decreases continuously towards the poles, where it is normally at its lowest. Temperature could plausibly be the direct driver of this decline. According to metabolic theory, higher temperatures accelerate metabolism, mutations of genetic material and speciation. This explains why the tropics are richer in species than the mid-latitudes and the polar regions, as would be expected.

Biodiversity surprisingly low at mid-latitudes

The study reveals that phytoplankton does not always behave in line with this theory. «Evidently, there are factors other than temperature affecting plankton diversity,» Righetti says. Two of these might be the strong currents and turbulence, which are prevalent in the mid-latitudes, but less so in polar or tropical seas. «The seasonal fluctuations and ocean turbulence in these latitudes might suppress the development of biodiversity, even though the temperatures here are higher than in the polar oceans,» the ecologist says.

Righetti and colleagues also found that phytoplankton diversity in the mid-latitudes, unlike in the tropics, varies greatly from season to season. Righetti explains that although the number of species in the mid-latitudes is constant over time, the species composition changes over the course of the year: «In contrast to tropical seas, the diversity here is dynamic throughout the year, but hardly any research has been done on this.»

Samples collected on shipping routes

Working with ETH adjunct professor Niklaus Zimmermann and other colleagues from the WSL, Righetti developed a computer model to map the diversity distribution of phytoplankton. They fed this model with observational data and used it to project where each species occurs – with a temporal resolution of one month.

The observational data came from water samples collected during research trips as well as from normal shipping routes. Phytoplankton specialists subsequently studied the samples under the microscope to determine which species they contained. Over time, these research cruises amassed huge amounts of observational data on several thousand different species. Righetti and colleagues then gathered the data available into a database and analyzed it.

It must be noted, however, that sampling has not been evenly distributed across the oceans and, in many regions, has not spanned all seasons. Thanks to British researchers, the North Atlantic is very well represented, but very little data exist for large parts of the other oceans. The ETH researchers compensated for this distortion in their models.

Their work is significant in a number of respects. Not only are their distribution maps the first to chart phytoplankton; their models can also be used to predict how the diversity of phytoplankton could develop under changing temperature conditions. Warmer waters as a result of climate change could alter the distribution of phytoplankton. «In turn, this could have a serious impact on the entire marine food chain,» Righetti says.

Author: Peter Ruegg | Source: ETH Zurich [May 16, 2019]

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