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Rising temperatures could boost mercury levels in fish by up to seven times the current rates, say Swedish researchers.

They've discovered a new way in which warming increases levels of the toxin in sea creatures.

In experiments, they found that extra rainfall drives up the amount of organic material flowing into the seas.

This alters the food chain, adding another layer of complex organisms which boosts the concentrations of mercury up the line.

The study has been published in the journal, Science Advances.

Toxic form

Mercury is one of the world's most toxic metals, and according to the World Health Organization, is one of the top ten threats to public health. The substance at high levels has been linked to damage to the nervous system, paralysis and mental impairment in children.

The most common form of exposure to mercury is by eating fish containing methylmercury, an organic form of the chemical which forms when bacteria react with mercury in water, soil or plants.

Levels of mercury in the world's ecosystems have increased by between 200 and 500%, since the industrial revolution say experts, driven up by the use of fossil fuels such as coal.

In recent years there are have been concentrated efforts to limit the amount of mercury entering the environment, with an international treaty, called the Minamata Convention, signed by 136 countries in place since 2013.

But this new study suggests that climate change could be driving up levels of methylmercury in a manner not previously recognised.

In a large laboratory, Swedish researchers recreated the conditions found in the Bothnian sea estuary. They discovered that as temperatures increase, there is an increased run-off of organic matter into the world's oceans and lakes. This encourages the growth of bacteria at the expense of phytoplankton.

"When bacteria become abundant in the water there is also a growth of a new type of predators that feed on bacteria," lead author Dr Erik Bjorn from Umea University in Sweden told BBC News.

"You basically get one extra step in the food chain and methylmercury is enriched by about a factor of ten in each such step in the food web."

Under the warmest climate scenario suggested by the Intergovernmental Panel on Climate Change, there would be an increase in organic matter run-off of 15-20% by the end of this century. This in turn would see levels of methylmercury in zooplankton, the bottom link in the food chain, grow by between two and seven fold.

Different parts of the world will suffer different impacts say the researchers, with lakes and coastal waters in the northern hemisphere being the most likely to have significant increases in methylmercury levels in fish, while the Mediterranean, the central US and Southern Africa will likely see reductions.

Researchers hope that the Minamata treaty will be successful and countries reduce the amount of mercury that is being produced. Otherwise this discovery of a previously unknown source could have impacts for human health.

"If we reduce mercury emissions, then we need to know how fast will ecosystems recover," said Dr Bjorn.

"If we don't do anything and mercury doesn't decrease, and we add this on top then the implications would be severe."

Other researchers in the field say that the new study highlights important issues that have previously been little known.

"This work experimentally proves that climate change will have a significant effect of methylmercury budgets in coastal waters and its concentrations in fish," said Milena Horvat from the Jozef Stefan Institute in Slovenia.

"This work will also have an important impact on future scenario simulations on the presence of mercury in fish in response to global mercury reductions from emission sources (primarily industrial)."

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Rising temperatures could boost mercury levels in fish by up to seven times the current rates, say Swedish researchers. They've discovered a new way in which warming increases levels of the toxin in sea creatures. In experiments, they found that extra rainfall drives up the amount of organic material flowing into the seas.

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The first pictures of a huge coral reef system discovered in the Amazon last year have been released by environmental campaigners.

The Amazon Reef is a 9,500 sq km (3,600 sq miles) system of corals, sponges and rhodoliths, Greenpeace says.

The reef is almost 1,000 km (620 miles) long, and is located where the Amazon River meets the Atlantic Ocean.

Oil drilling could start in the area if companies obtain permits from the Brazilian government, the group warns.

"This reef system is important for many reasons, including the fact that it has unique characteristics regarding use and availability of light, and physicochemical water conditions," researcher Nils Asp, from the Federal University of Para, said in a statement.

"It has a huge potential for new species, and it is also important for the economic well-being of fishing communities along the Amazonian coastal zone."

Scientists were surprised by the discovery, in April 2016, as they thought it was unlikely that reefs would be found it the area given unfavourable conditions," they said in a paper in the scientific journal Science Advances.

The reef ranges from about 25-120m deep (82-393ft)

Mr Asp now says that his team wants to gradually map the system. At the moment, only 5% of it has been mapped.

"Our team wants to have a better understanding of how this ecosystem works, including important questions like its photosynthesis mechanisms with very limited light."

But Greenpeace says drilling in the area means a "constant risk of an oil spill".

Campaigner Thiago Almeida said environmental licensing processes for oil exploration there are already under way.

"The Cape Orange National Park, the northernmost point of the Brazilian state of Amapa, is home to the world's largest continuous mangrove ecosystem and there is no technology capable of cleaning up oil in a place of its characteristics," the group said.

"In addition, the risks in this area are increased due to the strong currents and sediment that the Amazon River carries."

The group said that, so far, 95 wells have been drilled in the region, and 27 of them were abandoned as a result of mechanical incidents - the rest due to the absence of economically or technically viable gas and oil.

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The first pictures of a huge coral reef system discovered in the Amazon last year have been released by environmental campaigners. The Amazon Reef is a 9,500 sq km (3,600 sq miles) system of corals, sponges and rhodoliths, Greenpeace says. The reef is almost 1,000 km (620 miles) long, and is located where the Amazon River meets the Atlantic Ocean.

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Taming Nature's Fury - Looking at Natural Hazards

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Taming Nature's Fury - Looking at Natural Hazards

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​Tornadoes sweep through central Kansas. Mudslides bury a neighborhood in Guatemala. A tsunami triggers a nuclear meltdown at a power station in Japan. Every day, the news brings fresh reminders of the great dangers our planet can unleash with little warning. The dangers remain, even as researchers slowly unpack the secrets behind volcanic eruptions, earthquakes, tropical storms, and other natural hazards. That knowledge can reveal new threats, such as the planet-changing possibility of volcanic supereruptions or collisions with mountain-sized bodies from space. However, this information also leads to better tools for studying natural hazards and estimating where, how often, and how fiercely they are likely to strike.

Our increasingly sophisticated toolbox is helping us understand the physical processes driving hazards such as large and damaging earthquakes; track tropical cyclones to project how increasing temperatures might change these powerful storms; provide much-needed warnings of volcanoes, landslides, and tsunamis; and recover from catastrophic events when they occur. These tools now allow researchers to analyze data collected as disasters occur, including the recent collapse of the Bárdarbunga caldera in Iceland.

The ways in which communities prepare and respond to potential disasters are also becoming more sophisticated. Social media allows for rapid dissemination of information before and during a disaster. Although social scientists sometimes face challenges in interpreting the digital record of these events, they may provide a valuable insight into an effective response. Communities that face risks from natural hazards benefit from investing time and effort into preparing for unlikely yet unavoidable events.

This special package explores some of the ways people are learning to assess risks, lessen dangers, and repair the damage from disasters that elude or breach our defenses. We will continue to highlight important research and news on our Natural Hazards topic page. Natural hazards will never go away, but we can always become better prepared for the inevitable.
Additional articles in our Natural Hazards feature package: Video images: Twisting tornado looms over central Kansas; Chile's Calbuco volcano spews ash and lava in 2015; Meteor Crater, in Arizona, marks the site of a 50,000-year-old asteroid crash; storm chasers study an approaching tornado; aftermath of landslide triggered by 2008 Tangjiashan earthquake in southwest China; lava from Sicily's Piano del Lago volcano outshines the lights of Catania below.

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Taming nature's fury: An in-depth look at natural hazards

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​Tornadoes sweep through central Kansas. Mudslides bury a neighborhood in Guatemala. A tsunami triggers a nuclear meltdown at a power station in Japan. Every day, the news brings fresh reminders of the great dangers our planet can unleash with little warning.

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A Series of Current Articles on Natural Hazards

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A Series of Current Articles on Natural Hazards

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In the not-too-distant future, our fields could be tilled, sown, tended and harvested entirely by fleets of co-operating autonomous machines by land and air.

And they'll be working both day and night.

Driverless tractors that can follow pre-programmed routes are already being deployed at large farms around the world.

Drones are buzzing over fields assessing crop health and soil conditions. Ground sensors are monitoring the amount of water and nutrients in the soil, triggering irrigation and fertiliser applications.

And in Japan, the world's first entirely automated lettuce farm is due for launch next year.

The future of farming is automated.

Food shortages, big business

The World Bank says we'll need to produce 50% more food by 2050 if the global population continues to rise at its current pace.

But the effects of climate change could see crop yields falling by more than a quarter.

So autonomous tractors, ground-based sensors, flying drones and enclosed hydroponic farms could all help farmers produce more food, more sustainably at lower cost.

No wonder the agricultural robotics sector is growing so fast.

One report, by US firm WinterGreen Research, forecasts that the market will grow from $817m (£655m) in 2013 to $16.3bn (£13bn) by 2020.

But investment bank Goldman Sachs is far more bullish, predicting a $240bn market over the next five years. Manufacturers including John Deere, CNH Industrial and AGCO are all fighting to corner the market in driverless tractors.

As well as big kit, small kit is giving farmers up-to-the-second data on the state of their fields and produce - what Dr Roland Leidenfrost of Deepfield Robotics calls the "internet of plants and fields".

Bosch start-up Deepfield, based in Germany, is working to automate the growing and testing of seed crops, tracking the susceptibility to weeds and drought of different genetic varieties.

Meanwhile, engineers in Shropshire, England, are trying to show it is now possible to farm a field without a human setting foot in it at all.

The Hands Free Hectare project will use flying drones and automated tractors in the coming year to grow and harvest a cereal crop.

Engineers from Harper Adams University - together with a North Yorkshire farming technology company called Precision Decisions - are testing prototype machines now, and aim to plant their crop in March for harvest in September.

Precision pruning

It's hard to imagine the most traditional of agricultural sectors - wine making - as needing more than natural sunshine and soil. But even here automation is encroaching.

Wine makers have used drones to inspect their vineyards for several years, with high-definition cameras and sensors assessing crop and soil health.

But in France's Burgundy region, a shortage of farm labour has led inventor Christophe Millot to develop a vine-pruning robot called Wall-Ye.

The latest generation of this trundling four-wheeled robot can make a cut every five seconds. It has six cameras - some with infrared sensors - and two arms, and is controlled by a tablet computer inside.

The machine learns as it goes and can trim the grass around each vine. An onboard solar-powered battery gives 10-12 hours of charge, so with a change of battery, it can work day and night.

Visual recognition is the biggest challenge, says Mr Millot - knowing where to make the cut. This is actually easier at night, because the robot's lights can illuminate the plant, but not its background.

Next year, he plans to go to California - another major wine-producing area - to market his range of winery robots there.

Robo lettuce

But some people think farming land is old hat.

Japanese firm Spread's automated vegetable factory in Kyoto, due to launch next year, could produce 30,000 lettuces a day, the company says.

It stretches up, instead of across undulating fields, because "in countries like Japan, where land is actually a very scarce resource, it makes more sense to stack your production, just like a skyscraper," says JJ Price, Spread's global marketing manager.

Everything after seeding will be done by machines - watering, trimming, harvesting - on shelves stacked from floor to ceiling. It's a bit like the solitary drone farmers in the 1972 film Silent Running.

Automation has reduced labour costs by 50%, says Mr Price. And LED lighting developed specifically for plant cultivation reduces energy costs by 30%.

"It doesn't matter what the weather or climate is outside," he says.

And growing vegetables in vertical farms means you can recycle 98% of the water, says Mr Price, and produce food much closer to where people consume it, cutting down on transport costs and emissions.

Drone monitors

Back outside, drones are monitoring crop growth rates, spotting disease, and even spraying crops with pesticides and herbicides.

Now researchers are also trying to make them co-operate and work in swarms.

If they are mapping weeds in a field, say, "the drones will recruit each other to converge on those areas where the weed presence is higher," says Dr Vito Trianni of the Institute of Cognitive Sciences and Technologies in Rome.

Although GPS signals are generally strong in agricultural areas, one challenge for drones and other farmland robots is coping with patchy internet and mobile connectivity.

So Dr Trianni's team is using ultra-wideband radio for his drones to communicate without relying on rural 3G or 4G mobile connections.

Of course, automation might promise more efficient food production, but it also threatens agricultural jobs.

From 1950 to 2010, according to the International Labour Organization (ILO), agricultural labourers as a percentage of the workforce declined from 81% to 48.2% in developing countries, and from 35% to 4.2% in developed ones.

Robots will surely accelerate this decline.
Follow Technology of Business editor Matthew Wall on Twitter Click here for more Technology of Business features

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In the future, will farming be fully automated?

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In the not-too-distant future, our fields could be tilled, sown, tended and harvested entirely by fleets of co-operating autonomous machines by land and air. And they'll be working both day and night. Driverless tractors that can follow pre-programmed routes are already being deployed at large farms around the world.

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Antarctica

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The melting Antarctic glacier that now contributes more to sea-level rise than any other ice stream on the planet began its big decline in the 1940s.

This is when warm ocean water likely first got under Pine Island Glacier (PIG) to loosen the secure footing it had enjoyed up until that point.

Researchers figured out the timing by dating the sediments beneath the PIG.

It puts the glacier's current changes in their proper historical context, the scientists tell Nature magazine.

These changes can now be regarded as unprecedented in thousands of years.

Not only is the glacier going backwards, it is also thinning fast - losing more than 2m in elevation every year.

Other field studies and computer models suggest a runaway collapse might even be possible. The PIG on its own could add up to 10mm to sea levels over the next couple of decades.

"This glacier used to be pinned to a ridge and once it moved away from that ridge, it started to retreat rapidly; and without other pinning points it could continue to retreat rapidly inland, contributing significantly to global sea level," Dr James Smith from the British Antarctic Survey told BBC News.

The PIG is a colossal feature that drains a region of the West Antarctic Ice Sheet some two-thirds the size of the UK.

It is a marine-terminating glacier, which means its front flows off the land and pushes out into the ocean along the seafloor until its mass begins to lift up and float. Eventually, the buoyant section breaks up to form icebergs.

Currently, the PIG is dumping many billions of tonnes of ice into the ocean every year.

Submersible surveys under its floating front - its "ice shelf" - had revealed the contact point with the seabed once draped over a large ridge.

Having a "grounding line" in such a position would have helped anchor and constrain the whole glacier.

Some of the earliest satellite imagery indicated the PIG must have broken free completely of this pinning bump in the 1970s, but when exactly it started to disengage was far less certain.

It could have been many decades previously; several centuries or even millennia ago.

Now, Dr Smith and colleagues look to have solved this problem.

They drilled through the ice shelf to sample, analyse and date the muddy sediments that cover the ridge. And their investigation reveals that warm water is likely to have started to melt a cavity in the grounded glacier behind the pinch point in about the mid-1940s.

One of the reasons they can be sure of the timing is because of where plutonium traces start to appear in the sediment layers.

This radioisotope is a tell-tale signature for the atomic bomb tests that began in earnest after WWII and which peaked in the 1960s.

It leaves open the question of why the unpinning of the PIG occurred when it did, but the team point to the strong warming the region would have experienced following a big El Nino event between 1939 and 1942.

El Ninos are associated with the development of particular wind patterns and warm water movements in the Central Pacific, but the impacts affect weather globally.

"It's an amazing teleconnection that far-field changes can really have a profound impact on the Antarctic ice sheet," said Dr Smith.

Significantly, however, El Nino conditions have waxed and waned over the decades since, but the PIG now continues its relentless retreat.

Dr Anna Hogg from Leeds University, UK, monitors Pine Island Glacier on a daily basis using Europe's Cryosat and Sentinel satellites.

These spacecraft can measure from orbit the velocity and thickness of the ice stream.

She commented: "We know from satellite observations that the PIG has sped up and retreated episodically since the late 1970s, so it's interesting to see that the sediments beneath the glacier record similar periods of variability dating back to the 1940s.

"This erratic past behaviour suggests that we should not expect these colossal glaciers to respond in a steady way in the future, making continuous monitoring increasingly important."

Jonathan.Amos-INTERNET@bbc.co.uk and follow me on Twitter: @BBCAmos

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The melting Antarctic glacier that now contributes more to sea-level rise than any other ice stream on the planet began its big decline in the 1940s. This is when warm ocean water likely first got under Pine Island Glacier (PIG) to loosen the secure footing it had enjoyed up until that point.

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Japan

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Japan's government estimates the cost of cleaning up radioactive contamination and compensating victims of the 2011 Fukushima nuclear disaster has more than doubled, reports say.

The latest estimate from the trade ministry put the expected cost at some 20 trillion yen ($180bn, £142bn).

The original estimate was for $50bn, which was increased to $100bn three years later.

The nuclear meltdown at Fukushima was triggered by an earthquake and tsunami.

The powerful quake and waves that followed left more than 18,000 people dead, tens of thousands more displaced and well over a million buildings destroyed or damaged.

Almost 4,000 roads, 78 bridges and 29 railways were also affected.

Aftershock

The majority of the money will go towards compensation, with decontamination taking the next biggest slice.

Storing the contaminated soil and decommissioning are the two next greatest costs.

The compensation pot has been increased by about 50% and decontamination estimates have been almost doubled.

The BBC's Japan correspondent, Rupert Wingfield-Hayes, says it is still unclear who is going to pay for the clean up.

Japan's government has long promised that Tokyo Electric Power, the company that owns the plant, will eventually pay the money back.

But on Monday it admitted that electricity consumers would be forced to pay a portion of the clean up costs through higher electricity bills.

Critics say this is effectively a tax on the public to pay the debt of a private electricity utility.

The fault that caused the earthquake and tsunami is still causing trouble.

Last week, a magnitude 7.4 earthquake hit Fukushima and Miyagi prefectures. Japan's scientists said this was a strong aftershock of the massive 2011 quake.

This time, Japan escaped with only a few reports of minor injuries, and tsunami waves of over 1m.

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Japan's government estimates the cost of cleaning up radioactive contamination and compensating victims of the 2011 Fukushima nuclear disaster has more than doubled, reports say. The latest estimate from the trade ministry put the expected cost at some 20 trillion yen ($180bn, £142bn). The original estimate was for $50bn, which was increased to $100bn three years later.

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Great Barrier Reef

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Higher water temperatures in 2016 caused the worst destruction of corals ever recorded on Australia's Great Barrier Reef, a study has found.

Some 67% of corals died in the reef's worst-hit northern section, the ARC Centre of Excellence for Coral Reef Studies report said.

The situation was better in the central section, where 6% perished, while the southern reef is in good health.

But scientists warn recovery could be difficult if climate change continues.

Coral bleaching happens when water temperatures rise for a sustained period of time.

In February, March and April, sea surface temperatures across the Great Barrier Reef were the hottest on record, at least 1C higher than the monthly average.

"Some of the initial mortality was down to heat stress," said study leader Professor Terry Hughes.

"The coral was cooked."

How bleaching occurs

Far more has been lost through gradual starvation, after the coral expelled the colourful algae zooxanthella, which turns sunlight into food.

This is what leads to the white, skeletal appearance of the coral, which is left without its main source of energy.

The study also found that the coral which survived the bleaching have now come under greater threat from predators such as snails and crown of thorns starfish.

This year's mass bleaching was the worst-ever recorded on the Great Barrier Reef, following two previous events in 1998 and 2002.

Professor Hughes is certain that the increased water temperature is the result of carbon emissions, and warns that climate change could bring annual bleaching within 20 years.

"Most of the losses in 2016 have occurred in the northern, most pristine part of the Great Barrier Reef," he said.

"This region escaped with minor damage in two earlier bleaching events in 1998 and 2002, but this time around it has been badly affected."

Where is the damage?

One of the worst-hit areas is around Lizard Island in Far North Queensland, where around 90% of the coral has died.

Dr Andrew Hoey, whose team charted the area, said the impact was far worse than feared after an initial survey in April.

"It's devastating to get in the water somewhere you've been coming for almost 20 years, and it's just knocked it on its head," he said.

"There's very little coral cover left there. It was dominated by the acropora - the branching corals - but we lost most of them."

Lizard Island is home to a research station, where scientists from across the world have come for decades to study marine life

One of its directors, Dr Anne Hogget, said this was by far the worst event to hit the Great Barrier Reef since she started working there in 1990.

"We had bleaching here in 2002," she said. "We thought this was bad at the time, but this has blown it completely out of the water."

She is hopeful that the reef is capable of recovery, but fears it may not be give an opportunity, as sea temperatures continue to rise.

"The trajectory is not good," Dr Hogget explained.

"We keep pumping carbon dioxide into the atmosphere, and this happened absolutely because of that."

What happens next?

On the central and southern parts of the Great Barrier Reef, where bleaching was not as prevalent, there is concern that it has been misreported, with one magazine even publishing an obituary of the reef earlier this year.

Tourism operators like Michael Healey from the Quicksilver Group are keen to point out that many sites were unaffected, but there is concern for the reef's long term health.

"Without the Great Barrier Reef, we wouldn't survive," he said.

"So it is absolutely of the utmost importance that we ensure that our politicians and everyone else in our community and around the world are doing what they can."

The Australian Government has published a long-term sustainability plan for the reef, and pledged financial support for research into coral bleaching.

The 2050 plan identifies the need to help make the reef more resilient to climate change in the future, while trying to lower carbon emissions.

Mr Healy argued even those not financially involved had a stake in the reef.

"I'd say every human on the planet does," he said.

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Barrier Reef coral bleaching 'worst ever'

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Higher water temperatures in 2016 caused the worst destruction of corals ever recorded on Australia's Great Barrier Reef, a study has found. Some 67% of corals died in the reef's worst-hit northern section, the ARC Centre of Excellence for Coral Reef Studies report said.