The weird world of quantum mechanics is going for a swim. A team of Chinese researchers has, for the first time, transmitted quantum entangled particles of light through water – the first step in using lasers to send underwater messages that are impossible to intercept.

“People have talked about the idea of underwater quantum communication before, but I’m not aware of anyone who has done an experiment like this,” says at the University of Waterloo in Canada. “An obvious application would be a submarine which wants to remain submerged but communicate in a secure fashion.”

Entanglement starts with a beam of light shot into a crystal. This prism splits the light into pairs of photons with strangely linked behaviour. Manipulate one particle in a pair, and its partner will instantly react. Measure the first one’s polarisation, for example, and entanglement could ensure that its twin will have the opposite polarisation when measured.

These entangled photons can theoretically be used to set up a secure communication line between two people, with privacy guaranteed by the laws of physics.

But this fragile quantum state can easily be disturbed by the surrounding environment. So far, entanglement has been maintained between particles separated by long distances after traveling through air, space and optical fibres.

To test entanglement in water, which is less forgiving toward light, and his colleagues at Shanghai Jiao Tong University in China gathered saltwater from the Yellow Sea and placed it in a 3-metre-long container. They were able to transmit entangled photons through the water without disturbing their quantum link.

As the first experiment of its kind, it’s not clear whether this will be enough to build a communications system. Three meters may not seem that impressive compared with the 1200 kilometres that a Chinese satellite recently sent entangled particles down to Earth’s surface. “It’s not very surprising to me that if I send light through 10 feet of water it doesn’t get depolarised,” says at the University of Illinois at Urbana-Champaign.

But Jin says this is only the beginning. His team’s calculations suggest that it should be possible to communicate over nearly 900 metres in water. set a more conservative limit of just over 120 metres.

“Because ocean water absorbs light, extending this is going to difficult,” says at the University of Missouri in Columbia. “One option would be to use relays, but right now this is very far removed from anything that would be practical.”

Read more: Reality check: The hidden connections behind quantum weirdness

Objects: tiger stripes of Enceladus
Origins: ripped open by a jealous ruler

Here is the story of how Saturn’s geyser moon got its stripes. Once upon a time, in the blackness of space, there lived a giant gas ball known for his vanity. Unlike most of the other denizens of the solar system, mighty Saturn wore great big rings of ice that glittered for all to see.

Presently Saturn laid eyes on a small moon called Enceladus, who danced around him in an elongated path. Enceladus wore a bright coat of ice that covered her body and dazzled all who beheld her. Saturn grew jealous of the shining moon, and decided to remind Enceladus who was boss. The great big planet reached out and squeezed her.

Enceladus bulged and grew hot inside with anger but could not escape Saturn’s mighty grip. Her smooth white coat cracked and dark fissures appeared in her flanks, like tiger stripes. Then icy geysers erupted from them. To Saturn’s great delight, the ejected ice threw itself into orbit around him. From that day to this, cruel Saturn has pumped Enceladus for ever more of her ice so that he can gather the sparkling water around himself and make a new ring to wear.

Here on Earth people have told this tale for years, but no one could say for sure if it was just a myth – until now. Images taken by NASA’s Cassini probe support the idea that Saturn’s gravitational squeezing of the moon causes its fissures to widen and contract, controlling how much icy material erupts from the cracks.

Tiger, tiger, burning bright

As Enceladus orbits Saturn, changes in the strength of the giant planet’s tug create tidal stresses that squeeze and heat the moon’s interior. The ice geysers erupt from features on the moon’s south pole known as tiger stripes. These geysers sandblast other nearby moons and are probably the source of Saturn’s faint E ring. It is thought that a briny subsurface ocean is what feeds the plumes.

Previous calculations had suggested that tidal stress could also be why the amount of material ejected in the plumes varies. To test the idea, of Cornell University in Ithaca, New York, and his colleagues analysed seven years’ worth of Cassini data.

Looking at the brightness of the plumes and adjusting for the viewing angle, the team found that geyser activity peaks when Enceladus is at its most distant point from Saturn. That is when the moon experiences the strongest tensile stress, which probably widens the fissures and lets more material escape, says Hedman.

Sideways action

“The correlation is very striking and very convincing,” says of the Southwest Research Institute in Boulder, Colorado. “It gives us a really solid handle on how Enceladus works.”

But this just-so story has not yet reached its conclusion. “We still don’t know whether there’s a liquid ocean below the surface or not,” says of the California Institute of Technology in Pasadena, a member of the team that first discovered the moon’s plumes in 2005.

Saturn could be pumping water from an underground body of water by widening the moon’s fissures, as Hedman’s team suggests, says Ingersoll. But it is also possible that ice on the surface is simply evaporating around the cracks, he says, which might grind against each other in a sideways motion and be heated by friction.

Journal reference: Nature, DOI: 10.1038/nature12371

Though scientists tend to agree that summer ice at the North Pole will eventually disappear, they haven’t settled on a date. And one group now claims to have evidence that Santa may have to start swimming much sooner than we thought.

US researchers claim to have found evidence that accelerated melting has crossed a “tipping point” from which there is no going back.

The amount of summer ice at the North Pole has steadily declined since 1979, according to satellite images. Computer models predict that this trend will continue, leaving the Arctic completely ice-free during the summers as early as 2030.

In 2007, though, the ice surprised everyone by contracting far more rapidly than the models predicted. A particularly warm summer left only 4.28 million square kilometres by September – a record 23% below the previous minimum.

Accelerated ice loss

At the time, researchers including of National Snow and Ice Data Center in Boulder, Colorado claimed that the Arctic had reached a “tipping point” – a dramatic and irreversible slide towards ice-free conditions.

As the summer melting season finished up this year, they waited with bated breath to see how much, if any, ice would survive.

4.67 million square kilometres remained at the end of September. A positive interpretation says that the Arctic defied the apocalyptic prophecies by recovering slightly, thanks to a pattern of colder and windier weather.

But Serreze is sticking to the idea that we have reached a point of no return.

“If you look over the past five years, you see an acceleration of ice loss,” says Serreze. Though 2008 did not beat the record set by 2007, it is still the second-lowest amount on record, below the record lows of 2002 and 2005.

He and his colleagues, speaking at the this week, presented new evidence for a mechanism driving this acceleration.

Dramatic changes

During the summer, as ice melts, it is replaced by dark ocean waters that absorb heat. When the cooler winter weather arrives, the oceans release this warmth, creating a pocket of higher temperatures above the Arctic that slows down the regrowth of sea ice during the winter.

By measuring the air temperature directly over the Arctic after the end of the summer melt, Serreze found a large amount of released heat. Temperatures in areas losing ice were as much as 5 °C higher over the last four years as compared to the historic average.

The computer models predict this “Arctic acceleration,” says Serreze but 20 years into the future. “The models are giving us the big picture of what is going on, but it’s all happening much faster than expected,” he says.

This change may already be irreversible, as the extra heat creates a runaway thinning of ice that will soon be unable to survive in the summer Sun. If it disappears entirely during the summers, the ramifications would be global.

“The Arctic is the heat sink of the Northern hemisphere; the circulation patterns of the oceans could change dramatically,” says Serreze.

What’s more, the effects from this rush of heat seem to already be bleeding out into neighbouring Alaska and Siberia.

Balmy spell?

of the University of Alaska, Fairbanks, presented data at the AGU suggesting that lakes and permafrost are thawing in these regions. These changes release methane – a greenhouse gas with 21 times the warming power of carbon dioxide.

of the University of Washington in Seattle, who helped to create one of the more widely accepted climate models, agrees that an ice-free Arctic ocean is inevitable at this point.

She suspects, though, that the rapid sea-ice loss of recent years may simply be a fluke of the weather that will soon return to the longer trend. “I can’t predict the short-term weather, but I do have a good idea about the long-term climate,” says Bitz.

Her latest simulations, also presented at the AGU meeting, offer a message of tentative hope for recovery. At constant greenhouse gas emissions fixed to projected 2020 levels, sea ice retreats slowly, not precipitously. And when greenhouse gases are removed entirely from the model, sea ice regrows, even in future scenarios in which global warming has stripped the Arctic of ice year-round.

“A tipping point suggests falling of a cliff, with no way to climb back up – I can’t see the evidence for this,” says Bitz.