Radioactive traces in tree rings reveal Earth’s history of unexplained ‘radiation storms’

Hexbyte Glen Cove

In searching for planets and studying their stars, I’ve had the privilege to use some of the world’s great telescopes. However, our team has recently turned to an even larger system to study the cosmos: Earth’s forests.

We analyzed radioactive signatures left in around the world to study mysterious “radiation storms” that have swept over Earth half a dozen times in the past 10,000 years or so.

Our results, published today in Proceedings of the Royal Society A, rule out “solar superflares” as the culprit—but the true cause remains unknown.

A history written in tree rings

When high-energy radiation strikes the it turns into radioactive carbon-14, or radiocarbon. The radiocarbon then filters through the air and the oceans, into sediments and bogs, into you and me, into animals and plants—including hardwoods with their yearly tree rings.

To archaeologists, radiocarbon is a godsend. After it is created, carbon-14 slowly and steadily decays back into nitrogen—which means it can be used as a clock to measure the age of organic samples, in what is called radiocarbon dating.

To astronomers, this is equally valuable. Tree rings give a year-by-year record of high-energy particles called “cosmic rays” going back millennia.

The magnetic fields of Earth and the sun shield us from cosmic rays shooting through the Galaxy. More cosmic rays reach Earth when these magnetic fields are weaker, and fewer when the fields are stronger.

This means the rise and fall of carbon-14 levels in tree rings encodes a history of the 11-year cycle of the solar dynamo (which creates the sun’s magnetic field) and the reversals of Earth’s magnetic field.

Miyake events

But tree rings also record events we cannot presently explain. In 2012, Japanese physicist Fusa Miyake discovered a spike in the radiocarbon content of tree rings from 774 AD. It was so big that several ordinary years’ worth of must have arrived all at once.

As more teams have joined the search, tree ring evidence has been uncovered of further “Miyake events”: from 993 AD and 663 BC, and prehistoric events in 5259 BC, 5410 BC, and 7176 BC.

These have already led to a revolution in archaeology. Finding one of these short, sharp spikes in an ancient sample pins its date down to a single year, instead of the decades or centuries of uncertainty from ordinary radiocarbon dating.

Among other things, our colleagues have used the 993 AD event to reveal the exact year of the first European settlement in the Americas, the Viking village at L’Anse aux Meadows in Newfoundland: 1021 AD.

Could huge radiation pulses happen again?

In physics and astronomy, these Miyake events remain a mystery.

How do you get such a huge pulse of radiation? A flurry of papers have blamed supernovae, gamma-ray bursts, explosions from magnetized neutron stars, and even comets.

However, the most widely accepted explanation is that Miyake events are “solar superflares.” These hypothetical eruptions from the sun would be perhaps 50–100 times more energetic than the biggest recorded in the modern era, the Carrington Event of 1859.

If an event like this occurred today, it would devastate power grids, telecommunications and satellites. If these occur randomly, around once every thousand years, that is a 1% chance per decade—a serious risk.

Noisy data

Our team at UQ set out to sift through all the available tree ring data and pull out the intensity, timing, and duration of Miyake events.

To do this we had to develop software to solve a system of equations that model how radiocarbon filters through the entire global carbon cycle, to work out what fraction ends up in trees in what years, as opposed to the oceans, bogs, or you and me.

Working with archaeologists, we have just released the first reproducible, systematic study of all 98 trees of published data on Miyake events. We have also released open source modeling software as a platform for future work.

Storms of solar flares

Our results confirm each event delivers between one and four ordinary years’ worth of radiation in one go. Earlier research suggested trees closer to Earth’s poles recorded a bigger spike—which is what we would expect if solar superflares are responsible—but our work, looking at a larger sample of trees, shows this is not the case.

We also found these events can arrive at any point in the sun’s 11-year activity cycle. Solar flares, on the other hand, tend to happen around the peak of the cycle.

Most puzzling, a couple of the spikes seem to take longer than can be explained by the slow creep of new radiocarbon through the carbon cycle. This suggests that either the events can sometimes take longer than a year, which is not expected for a giant solar flare, or the growing seasons of the trees are not as even as previously thought.

For my money, the sun is still the most likely culprit for Miyake events. However, our results suggest we’re seeing something more like a storm of rather than one huge superflare.

To pin down what exactly happens in these events, we will need more data to give us a better picture of the events we already know about. To obtain this data, we will need more tree rings—and also other sources such as ice cores from the Arctic and Antarctic.

This is truly interdisciplinary science. Normally I think about beautifully clean, precise telescopes: it is much harder to understand the complex, interconnected Earth.



More information:
Qingyuan Zhang et al, Modelling cosmic radiation events in the tree-ring radiocarbon record, Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences (2022). DOI: 10.1098/rspa.2022.0497

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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Hexbyte Glen Cove Turkey and neighbours pledge to clean up Mediterranean

Hexbyte Glen Cove

Vast patches of ‘sea snot’ mucilage on Turkey’s coastline this summer put the spotlight on caring for the Mediterranean.

Turkey and its neighbours pledged Friday to do a better job addressing the threats posed by pollution to people’s health and the natural habitats of the Mediterranean Sea.

From to slimy mucilage forming on their coasts, the ring of tourism-dependant Mediterranean countries have battled a steady stream of environmental problems, raising the issue’s importance in voters’ eyes.

Responding to the tide of public unease, envoys from 21 regional states agreed at a four-day gathering ending Friday on Turkey’s southern coast to slash the use of sulphur in fuel for ships.

Their decision to reduce the sulphur content of the fuel to 0.1 percent from 0.5 percent in the Mediterranean will be submitted to the International Maritime Organisation.

Once approved, the cap will come into force in January 2025.

“We expect that through the implementation of this decision, there will be an important reduction of pollution coming from ships,” said Tatjana Hema, coordinator of the Mediterranean Action Plan at the United Nations Environment Programme.

‘Breakthrough’

Mediterranean countries and the European Union hope the limit on sulphur use—the culmination of five years of talks that could provide a template for other deals—will ultimately save lives.

Besides hurting the sea, air pollution caused by smoke-chugging ships can be linked to 60,000 premature deaths a year globally, according to some expert estimates.

Hema told AFP any cut in sulphur would have positive “socioeconomic and health” effects by reducing hazardous emissions.

The EU led the effort to reduce sulphur content in fuel, said Patrick Child, deputy director general for the environment at the European Commission.

“It’s one of the seas with the most challenging environmental biodiversity threats,” he said, calling the agreement on sulphur oxides a “breakthrough”.

But the list of increasingly urgent problems is long, putting pressure on regional governments.

The Mediterranean is “a hotspot for “, said Carlos Bravo, an ocean policy expert who works for the Swiss-based OceanCare advocacy group.

Other issues include ships colliding with marine mammals, Bravo said, since the sea is one of the most dense for shipping traffic.

Action was also needed to eliminate “bycatch”, where turtles and sharks get trapped in commercial fishing nets, and to reduce noise pollution from ships that affects more than 150 species, Bravo said.

Cleaning ‘sea snot’

Turkey, which this year became the last G20 country to ratify the Paris climate agreement, has come under particularly heavy criticism for how it treats its water.

The issue gained international attention when a thick layer of slime dubbed “sea snot” covered Istanbul’s southern shores on the Sea of Marmara last summer.

Scientists blamed the mucus on Turkey’s failure to properly treat agricultural and before it flows down rivers into the sea, whose unusual warmth creates ripe conditions for algae to grow out of control.

The sea snot has all been cleaned up, said Soner Olgun, laboratory, measurement and monitoring department chief at Turkey’s environment ministry, adding he did not “expect it to return this year or next year”.

Turkish officials now stress the imperative of eliminating all forms of waste—particularly plastics—to save the sea.

“It’s not just related to marine litter, but also related to waste water treatment, as we saw in Istanbul with the mucilage,” Mehmet Emin Birpinar, Turkey’s deputy environment minister, told AFP.

Eighty percent of sea waste arrives from land, Birpinar said.

Turtles eating plastic

A Greek study in October said 3,760 tons of plastic waste were floating in the Mediterranean, whose littoral states stretch from North Africa to the Middle East and southwestern Europe.

One of the most poignant examples of the plastics’ harm comes from the famous but endangered loggerhead turtles, whose babies hatch on Turkey’s southern coast before crawling into the sea when they are ready.

They are carnivores but tend to confuse jellyfish for plastic bags, explained Yakup Kaska, head of the Sea Turtle Research, Rescue and Rehabilitation Centre based in Mugla, southwestern Turkey.

Kaska said rising sea temperatures also led to an increase in female turtles because heat determines the creatures’ sex.

“We are getting nearly 90 percent of the hatchlings who are females. We need males,” Kaska said.

“If one degree Celsius is the best scenario for the temperature increase, we may have all female hatchlings in 50 or 100 years.”



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