Lugworm’s turn to feel effects of ocean acidity

Lugworm’s turn to feel effects of ocean acidity

Researchers in the UK have found evidence that a marine worm is being damaged by the increasing ocean acidification that was widely thought to imperil mainly shellfish and coral.

LONDON, 27 October, 2014 − A common marine worm has alerted scientists to the likelihood that the effects of ocean acidification may be more widespread and severe than they had realised.

The lugworm (Arenicola marina) − common on the coasts of Europe and North America, where it can grow to 30 cms in length and is a bait popular with anglers − is being affected by rising levels of acid in the coastal seas. The acid is reported also to be affecting sea urchins.

This is further confirmation that ocean acidification is affecting species other than those that scientists call calcifying organisms − creatures that rely on calcium carbonate to form shells and similar structures.

The pH (a measure of acidity – the lower the pH, the more acidic the water) of the planet’s oceans is dropping rapidly, largely because the carbon dioxide levels in the atmosphere are increasing. Since carbon dioxide dissolves in water to form carbonic acid, the seas are responding to global change.

Highest rate

Scientists say the oceans are now 30% more acidic than they were at the beginning of the industrial revolution about 250 years ago. The current rate of acidification is thought to be the highest for 65 million years.

Among the sea species most vulnerable to acidification are shellfish, coral and other creatures − including some species of plankton − which suffer because the build-up of acid prevents them from developing their calcium shells. Animals further up the marine food chain are also at risk when their prey feels the acidity’s effects.

Researchers at the University of Exeter’s College of Life and Environmental Sciences in the UK have now found that other creatures are also being affected because the growing acidity is increasing their vulnerability to coastal pollutants such as copper.

Writing in the journal Environmental Science and Technology, they explain how they found that the extra copper harms lugworms’ sperm, meaning that their young fail to develop properly. They say: “Larval survival was reduced by 24% when exposed to both OA [ocean acidification] and copper combined, compared to single OA or copper exposures.”

Toxic effects

Sperm motility − the ability of the sperm to swim strongly − was damaged by both OA and copper alone, but with added toxic effects when both factors were combined. Individually, both OA and copper also reduced the lugworms’ fertilisation success.

One of the report’s authors, Dr Ceri Lewis, a marine biologist at Exeter, told BBC News: “It’s a bit of a shock, frankly. It means the effects of ocean acidification may be even more serious than we previously thought. We need to look with new eyes at things that we thought were not vulnerable.

“Our work means we are underestimating effects of acidification for coastal invertebrates. We are now realising there are many indirect impacts of ocean acidification on other processes. It could be that we are facing a lot more surprises ahead.”

Dr Lewis told the Climate News Network: “Lugworms do as important a job as gardeners of our beaches as earthworms do on land, and they bring oxygen down to the underwater sediments. The discovery that they too are affected means there’s a whole new area of concern now, looking at the indirect effect of pollutants and at other species that may be harmed as the acidification increases.”

She has also found more evidence that copper pollution is damaging another marine species − sea urchins. They are already affected by the seawater’s increasing acidity, which means they have to spend more energy on making their shells and spines. − Climate News Network

Ice loss sends Alaskan temperatures soaring

Ice loss sends Alaskan temperatures soaring

Scientists analysing more than three decades of weather data for the northern Alaska outpost of Barrow have linked an astonishing 7°C temperature rise to the decline in Arctic sea ice.

LONDON, 17 October, 2014 − If you doubt that parts of the planet really are warming, talk to residents of Barrow, the Alaskan town that is the most northerly settlement in the US.

In the last 34 years, the average October temperature in Barrow has risen by more than 7°C − an increase that, on its own, makes a mockery of international efforts to prevent global temperatures from rising more than 2°C above their pre-industrial level.

A study by scientists at the University of Alaska Fairbanks analysed several decades of weather information. These show that temperature trends are closely linked to sea ice concentrations, which have been recorded since 1979, when accurate satellite measurements began.

The study, published in the Open Atmospheric Science Journal, traces what has happened to average annual and monthly temperatures in Barrow from 1979 to 2012.

Most striking

In that period, the average annual temperature rose by 2.7°C. But the November increase was far higher − more than six degrees. And October was the most striking of all, with the month’s average temperature 7.2°C higher in 2012 than in 1979.

Gerd Wendler, the lead author of the study and a professor emeritus at the university’s International Arctic Research Center, said he was “astonished”. He told the Alaska Dispatch News: “I think I have never, anywhere, seen such a large increase in temperature over such a short period.”

The study shows that October is the month when sea ice loss in the Beaufort and Chukchi Seas, which border northern Alaska, has been highest. The authors say these falling ice levels over the Arctic Ocean after the maximum annual melt are the reason for the temperature rise. “You cannot explain it by anything else,” Wendler said.

They have ruled out the effects of sunlight because, by October, the sun is low in the sky over Barrow and, by late November, does not appear above the horizon.

Instead, they say, the north wind picks up stored heat from water that is no longer ice-covered in late autumn and releases it into the atmosphere.

At first sight, the team’s findings are remarkable, as Barrow’s 7.2°C rise in 34 years compares with a global average temperature increase over the past century of up to about 0.8°C. But what’s happening may be a little more complex.

Warming faster

The fact that temperatures in and around Barrow are rising fast is no surprise, as the Arctic itself is known to be warming faster than most of the rest of the world.

The Intergovernmental Panel on Climate Change says observed warming in parts of northern Alaska was up to 3°C from the early 1980s to the mid-2000s. It also concludes that about two-thirds of the last century’s global temperature increase has occurred since 1980.

But Barrow’s long-term temperature rise has not been uniform, the Fairbanks study says. Its analysis of weather records between 1921 and 2012 shows a much more modest average annual rise, of 1.51°C. In 2014, the city experienced the coolest summer day recorded − 14.5°C.

So one conclusion is to remember just how complex a system the climate is − and how even 34 years may be too short a time to allow for any certainty. − Climate News Network

Oceans’ greater heat explains warming ‘pause’

Oceans' greater heat explains warming 'pause'

New technology is helping scientists to re-assess how much heat is being absorbed by the world’s oceans – much more in some regions than realised, they say.

LONDON, 7 October 2014 – One of the most hotly-argued questions in climate research – whether global warming has slowed or even stopped – appears to have been definitively answered. And the scientists’ conclusion is unambiguous: the Earth continues to warm at a dangerous pace.

All that’s happening, they say, is that the extra heat being produced – mainly by the burning of fossil fuels – is concentrating not in the skies but in the seas. They have found new evidence that backs them up.

Instead of driving up the temperature of the atmosphere quite as fast as predicted, the evidence shows that the heat from greenhouse gas emissions is warming the oceans much more rapidly than had been realised.

In some regions the water appears to have been warming, for over 40 years, more than twice as quickly as thought, for instance in the upper 2,300 feet (700 metres) of the southern hemisphere’s oceans.

Paul Durack from the Lawrence Livermore National Laboratory in California and colleagues compared direct and inferred sea temperature measurements with the results of climate models. Together the three sets of measurements suggest estimates of northern hemisphere ocean warming are about right.

Serious under-estimate

But the team report in Nature Climate Change their estimate that warming in the southern seas since 1970 could be far higher than scientists have been able to deduce from the limited direct measurements from this under-researched region. Globally, they conclude the oceans are absorbing between 24 and 58% more energy than thought.

The researchers were able to use data from satellites and from a new source – Argo floats, a fleet of more than 3,000 free-floating monitors which drift through the water and measure the temperature and salinity of the upper 6,500 feet (2,000 m) of the ocean.

A year ago, the Intergovernmental Panel on Climate Change published its Fifth Assessment Report. Professor Chris Rapley, a former director of both the British Antarctic Survey and  the Science Museum in London, told the Climate News Network then of his alarm at what the IPCC said about the oceans.

He said the Earth’s energy imbalance, and evidence that the 93% of the energy build-up absorbed by the oceans continued to accumulate, meant the slow-down in the rise of surface temperatures appeared “a minor and temporary fluctuation”.

Speaking of the latest research, Profesor Rapley told the Network: “The newly reported results of a combination of satellite altimetry measurements of globally mapped sea level rise combined with ocean heat modelling, and a further analysis of the in situ measurements from the Argo buoys, add to the evidence that the so-called ‘pause’ in global warming is confined to surface temperature data, whilst the planet’s energy imbalance continues unabated.

Cold depths

“Once more we need to assess our appetite for risk, and consider seriously what measures we should take to minimise the threats to food and water supplies, the impacts of extreme weather, and the consequences of these to the world economic system and human wellbeing.”

A second study, also published in Nature Climate Change, by scientists at NASA’s Jet Propulsion Laboratory in Pasadena, California, concluded tentatively that all ocean warming from 2005 to 2013 had occurred above depths of 6,500 feet, and that it was not possible to detect any contribution by the deep oceans to sea level rise or energy absorption.

Josh Willis, a co-author of this study (which like that by Dr Durack and his colleagues results from the work of NASA’s newly-formed Sea Level Change Team)  said the findings did not throw suspicion on climate change itself. He said: “The sea level is still rising. We’re just trying to understand the nitty-gritty details.”

This study therefore leaves several questions still unanswered. Will more research find evidence that deep water is in fact warming, for instance? Why are the oceans now apparently absorbing more heat than they once did? And if the southern oceans are heating up faster, then may that help to speed up Antarctic ice melt?

One urgent question that needs answering is how much longer the water near the surface can continue to absorb the extra heat which human activities are producing. Another is what will happen when the oceans no longer absorb heat but start to release it. The answers could be disturbing. – Climate News Network

Surfers fear climate will wipe out big waves

Surfers fear climate will wipe out big waves

Dedicated surfers, deeply involved with monitoring the natural coastal environment around the world, warn that climate change now poses a major threat to this booming leisure industry.

LONDON, 5 October, 2014 − The world’s oceans are alive with surfers enjoying one of the fastest growing leisure activities. It is estimated there are now at least 35 million people around the globe who regularly ride the waves, and many thousands of people are employed in what has grown into a multi-billion dollar industry.

A warming world should be good news for all those artists of the waves. Warming oceans mean more storms, and the theory goes that more storms will lead to ever bigger waves. So why then are surfing websites – the internet is waterlogged with them – full of concern about changes in the climate?

Two studies appearing in the journal Nature Climate Change have made surfers stand up on their boards and reconsider the situation.

A study led by Dr Andrew Dowdy, a researcher at the Centre for Australian Weather and Climate Research (CAWCR) predicts that rising temperatures will in fact reduce the number of storms causing big waves by the end of the century on the central east coast of Australia.

Potentially destructive

The storms that do occur could be more intense and potentially destructive – but the consistency of wave patterns will be reduced.

That’s bad news for surfers of the future in that area – one of the world’s surfing hotspots. They’ll just have to move elsewhere. Dowdy told the Climate News Network that his projections only relate to that particular region, and they are not necessarily applicable to other coastal regions.

But another study, led by Mark Hemer, a senior research scientist at CAWCR, indicates that surfers might be having to ride smaller waves in future in other parts of the world as well.

Using ocean modelling techniques, Hemer and his colleagues predict a decrease in annual wave height over more than 25% of the global ocean area by the end of the century. The North Atlantic is likely to see a decrease in wave heights during all seasons, and waves are likely to be smaller in the winter months in the North Pacific and Indian Ocean.

But all is not lost. The study predicts that some regions − including  the waters off the south coast of Australia and New Zealand − will see bigger waves of between 5% and 10% above present size averages during winter months.

Surfers are worried about other climate change related threats to their activities. There are fears that rising sea levels could threaten key surfing areas.

Surfers regularly monitor water conditions – everything from acidity levels to rubbish content and sewage levels in the seas.

Surf zone

The Save the Waves Coalition − a US-based group that lobbies to protect the coastal environment, with a particular focus on what it calls the surf zone − monitors development activities in surfing areas worldwide.

Its “endangered waves” campaign lists projects that threaten key surfing areas – from plans to construct a nuclear power station on the coast of South Africa to a series of coal-fired power plants proposed for the coast of Chile.

And Climate change is seen as a major challenge facing the surfing industry.

“The unfortunate truth is that the threats to surfing habitat are now growing exponentially due to the impacts of man-made climate change,” says the California-based Sustainable Surf organisation. – Climate News Network

Hungry invader fish stripping Mediterranean bare

Hungry invader fish stripping Mediterranean bare

Warming seas are extending the range of tropical rabbitfish, whose voracious appetite for seaweed and other marine vegetation is turning areas of the Mediterranean Sea into rocky barrens.

LONDON, 3 October, 2014 − Scientists in Australia, Europe and the US have identified a new menace in the Mediterranean. The tropical rabbitfish has arrived in the eastern Mediterranean Sea and − wherever the waters are warm enough −  threatens to do to the marine vegetation what the terrestrial rabbit did to Australia’s tender grasses: eat the lot.

A team of researchers led by Adriana Vergés, a marine ecologist at the University of New South Wales in Sydney, Australia, and Fiona Tomas, assistant professor at the Mediterranean Institute for Advanced Studies in Mallorca, Spain, report in the Journal of Ecology that they surveyed 1,000 kilometres of coastline around Turkey and Greece.

Dominant species

They found that two species of rabbitfish have become dominant in the region, and they think the invader is likely to claim more territory as the world’s climate changes and the waters warm.

The range expansion of the rabbitfish, which first entered the Mediterranean basin from the Red Sea via the Suez Canal, provides a good example of how tropical herbivorous fish can impact on the structure of rocky bottoms in temperate seas.

“The study identified two clearly distinct areas −  warmer regions with abundant rabbitfish, and colder regions where they are rare or absent,” Dr Vergés said.

”The regions with abundant rabbitfish had become rocky barrens. There was a 65% reduction in large seaweeds, a 60% reduction in other algae and invertebrates, and a 40% reduction in the overall number of species present.”

The hungry herbivores were first reported in the eastern Mediterranean in 1927, and have recently been found off the coast of Croatia and even the south of France.

The invaders are a threat to ecosystems because seaweed forests − like terrestrial forests − provide food and shelter for hundreds of species.

Feeding behaviour

The researchers recorded fish feeding behaviour and noted that the rabbitfish were not noticeably more greedy than the natives. But whereas the native temperate herbivores grazed only on adult algae, the two species of rabbitfish consumed both the adult and the juvenile seaweeds. The consequence is that the full-grown species were not replaced.

In the long run, such seaweed clearance could be a threat not just to Mediterranean ecosystems but also to the Mediterranean diet, because these ecosystems ultimately support the shoals of sardines, anchovies, red mullet, sea bass, bream, tuna and other specialties of the tables of Spain, Greece and Italy.

“This research highlights the need to work out how the interactions between different species will change in a warming world,” Dr Vergés said. − Climate News Network

Ice melt dilutes Arctic sea’s CO2 clean-up role

Ice melt dilutes Arctic sea’s CO2 clean-up role

New scientific research confirms that global warming is melting increasingly larger areas of Arctic sea ice − and reducing its vital function of removing CO2 from the atmosphere.

LONDON, 26 September, 2014 − The Arctic ice cap has just passed its summer minimum – and it’s the sixth lowest measure of sea ice recorded since 1978, according to scientists at the US space agency NASA.

For three decades, the shrinking Arctic ice – and the growing area of clear blue water exposed each summer – has been a cause of increasing alarm to climate scientists.

Polar seasonal changes are measured annually by NASA, but reliable satellite data goes back only to 1978, For much of the 20th century, the Arctic was part of the Cold War zone, so only Soviet naval icebreakers and US nuclear submarines took consistent measurements − and neither side published the data.

But studies of 17th and 18th century whaling ships’ logbooks and other records make it clear that the ice once stretched much further south each summer than it does today.

Steady decline

In the last 30 years, the thickness and the area of the ice have both been in steady decline, with predictions that in a few decades the Arctic Ocean could be virtually ice free by September, opening up new sea routes between Asia and Europe.

This year could have been worse, although the area of ice fell to little more than 5 million square kilometres − significantly below the 1981-2010 average of 6.22 million sq km.

“The summer started off relatively cool, and lacked the big storms or persistent winds that can break up ice and increase melting,” said Walter Meier, a research scientists at NASA’s Goddard Space Flight Centre. “Even with a relatively cool year, the ice is so much thinner than it used to be. It is more susceptible to melting.”

Warming in the Arctic is likely to affect climate patterns in the temperate zones, and the state of the polar ice has become of such concern that researchers are using ground-based and sea-based monitors to explore the physics of the phenomenon.

But there is another reason for the attention: as polar ice diminishes, so does the planet’s albedo − its ability to reflect sunlight back into space.

So, as the ice shrinks, the seas warm, making it more difficult for new ice to form. And greater exposure to sunlight increases the probability that permafrost will thaw, releasing even more greenhouse gases locked in the frozen soils.

Now researchers have found another and unexpected example of climate feedback that could affect the cycle of warming. Climate scientist Dorte Haubjerg Søgaard, of the Greenland Institute of Natural Resources and the University of Southern Denmark, and research colleagues have discovered that sea ice itself is an agency that removes carbon dioxide from the atmosphere.

That the oceans absorb the stuff, and tuck it away as calcium carbonate or other marine minerals, is old news.

“But we also thought that this did not apply to ocean areas covered by ice, because the ice was considered impenetrable,” Søgaard said. “However, new research shows that sea ice in the Arctic draws large amounts of CO2 from the atmosphere into the ocean.”

The research is published in four journals, Polar Biology, The Cryosphere, The Journal of Geophysical Research: Atmospheres and Marine Ecology Progress Series.

Two-stage pattern

The Danish research team observed a complex, two-stage pattern of gas exchange as ice floes formed off southern Greenland. They measured the role of atmospheric carbon dioxide in the formation and release of calcium carbonate crystals form in the sea ice, and kept a tally during a 71-day cycle of the carbon dioxide budget.

In the course of this complicated bit of natural cryo-chemistry, they found that some CO2 was carried deep into the ocean with dense, heavy brines, as the ice froze and some was captured by algae in the thawing ice.

They also identified a third factor: the “frost flowers” that formed on the new ice had an unexpectedly high concentration of calcium carbonate.

The profit-and-loss accounting meant that every square metre of ice effectively removed 56 milligrams of carbon from the atmosphere during the 71-day cycle. Over an area of 5 million sq km, this would represent a significant uptake.

But the real importance of the discovery is that scientists have identified yet another way in which the ice – while it is there – helps keep the Arctic cold, and yet another way in which carbon dioxide is absorbed by the oceans.

“If our results are representative, then the sea ice plays a greater role than expected, and we should take account of this in future global CO2 budgets,” Søgaard said. – Climate News Network

Acidic seas block fishes’ survival mechanism

Acidic seas block fishes' survival mechanism

Scientific studies show that the sense of smell so vital for the survival of predators such as sharks, as well as for their prey, is being impaired as carbon dioxide increases acidification of oceans.

LONDON, 18 September, 2014 − Global warming could be bad for sharks, too. These ocean-going creatures that have survived 420 million years of natural climate change could be at risk from increasingly acidic seas, according to two entirely different scientific studies.

The sharks are already in trouble everywhere. They are pursued as food or feared as a threat, and the habitat they favour is gradually being degraded or destroyed.

But Danielle Dixson, a marine conservation biologist at the Georgia Institute of Technology in the US, and colleagues report in Global Change Biology that changes in the pH value of water – in other words, as the seas became more acidic – have interfered with a shark’s ability to smell food.

Behaviour change

Dr Dixson has already shown that increasing acidification, due to greater levels of carbon dioxide in the atmosphere, could change the behaviour of reef fish, seemingly making them less afraid of predators because the acidic waters disrupt a specific receptor in the fish’s nervous system.

This time, she experimented with a shark known as the smooth dogfish (Mustelus canis), which is found in the Atlantic waters off the US coast. She tested 24 sharks in a 10-metre tank with two currents or plumes of water. One was normal sea water, and the other was rich in the odour of squid. As expected, the sharks showed a distinct preference for the smell of food.

Then she and her colleagues enriched the water with carbon dioxide − to levels predicted for mid-century as greenhouse emissions continue to rise, and the seas become more rich in carbonic acid.

When released into the most acidic water, the sharks actually avoided the plume of squid odour. Once again, the change in the water’s pH seemed to have disrupted an all-important receptor, and thus the sharks’ interest in hunting.

“Sharks are like swimming noses, so chemical cues are really important for them in finding food,” Dr Dixson said.

Less aggressive

Overall activity did not change significantly, but shark attack behaviour did. The squid odour was pumped through bricks to give the sharks something to push against, but the sharks in the most acidic waters responded less aggressively.

“They significantly reduced their bumps and bites on the bricks, compared to the control group,” Dr Dixson said. “It’s like they’re uninterested in their food.”

There is always the chance that, as acidity levels slowly rise, sharks will adjust or adapt. But increasing acidification may not even give them the chance to adapt.

In a second paper, this time in the Proceedings of the Royal Society, Rui Rosa, senior researcher at the Centre for Oceanography in Cascais, Portugal, and colleagues considered the impact of warmer and more acidic seas on the survival of the newly-hatched tropical bamboo shark (Chiloscyllium punctatum), normally found in the intertidal zones of the western Pacific.

The researchers tested hatchlings in tanks at temperatures and pH values predicted for 2100, and found “significant impairment” in survival rates.

In their experiments at normal temperature conditions, mortality among the hatchlings was zero. In experimental conditions, behaviour changes were apparent from the outset and, within 30 days, more than 40% had died. – Climate News Network

Ocean acidification and GHGs hit record levels

Ocean acidification and GHGs hit record levels

New scientific evidence of the highest greenhouse gas concentrations on record is compounded by the revelation that oceans are acidifying faster than at any time in the last 300 million years.

LONDON, 9 September, 2014 – The World Meteorological Organisation (WMO) reports that the amounts of atmospheric greenhouse gases reached a new high in 2013, driven by rapidly rising levels of carbon dioxide.

The news is consistent with trends in fossil fuel consumption. But what comes as more of a surprise is the WMO’s revelation that the current rate of ocean acidification, which greenhouse gases (GHGs) help to cause, appears unprecedented in at least the last 300 million years.

The details of growing GHG levels are in the annual Greenhouse Gas Bulletin, published by the WMO – the United Nations specialist agency that plays a leading role in international efforts to monitor and protect the environment.

They show that between 1990 and 2013 there was a 34% increase in radiative forcing – the warming effect on our climate – because of long-lived greenhouse gases such as carbon dioxide (CO2), methane and nitrous oxide.

Complex interactions

The Bulletin reports on atmospheric concentrations – not emissions − of greenhouse gases. Emissions are what go into the atmosphere, while concentrations are what stay there after the complex system of interactions between the atmosphere, biosphere (the entire global ecological system) and the oceans.

About a quarter of total emissions are taken up by the oceans and another quarter by the biosphere, cutting levels of atmospheric CO2.

In 2013, the atmospheric concentration of CO2 was 142% higher than before the Industrial Revolution started, in about 1750. Concentrations of methane and nitrous oxide had risen by 253% and 121% respectively.

The observations from WMO’s Global Atmosphere Watch network showed that CO2 levels increased more from 2012 to 2013 than during any other year since 1984. Scientists think this may be related to reduced CO2 absorption by the Earth’s biosphere, as well as by the steady increase in emissions.

Although the oceans lessen the increase in CO2 that would otherwise happen in the atmosphere, they do so at a price to marine life and to fishing communities − and also to tourism. The Bulletin says the oceans appear to be acidifying faster than at any time in at least the last 300 million years.

“We know without any doubt that our climate is changing and our weather is becoming more extreme due to human activities such as the burning of fossil fuels,” said the WMO’s secretary-general, Michel Jarraud.

“We are running out of time. The laws
of physics are non-negotiable.”

“The Greenhouse Gas Bulletin shows that, far from falling, the concentration of carbon dioxide in the atmosphere actually increased last year at the fastest rate for nearly 30 years. We are running out of time. The laws of physics are non-negotiable.

“The Bulletin provides a scientific base for decision-making. We have the knowledge and we have the tools for action to try to keep temperature increases within 2°C to give our planet a chance and to give our children and grandchildren a future. Pleading ignorance can no longer be an excuse for not acting.”

Wendy Watson-Wright, executive secretary of the Intergovernmental Oceanographic Commission of UNESCO, said: “It is high time the ocean, as the primary driver of the planet’s climate and attenuator of climate change, becomes a central part of climate change discussions.

“If global warming is not a strong enough reason to cut CO2 emissions, ocean acidification should be, since its effects are already being felt and will increase for many decades to come.”

The amount of CO2 in the atmosphere reached 396.0 parts per million (ppm) in 2013. At the current rate of increase, the global annual average concentration is set to cross the symbolic 400 ppm threshold within the next two years.

More potent

Methane, in the short term, is a far more powerful greenhouse gas than CO2 − 34 times more potent over a century, but 84 times more over 20 years.

Atmospheric methane reached a new high of about 1,824 parts per billion (ppb) in 2013, because of increased emissions from human sources. Since 2007, it has started increasing again, after a temporary period of levelling-off.

Nitrous oxide’s atmospheric concentration in 2013 was about 325.9 ppb. Its impact on climate, over a century, is 298 times greater than equal emissions of CO2. It also plays an important role in the destruction of the ozone layer that protects the Earth from harmful ultraviolet solar radiation.

The oceans currently absorb a quarter of anthropogenic CO2 emissions − about 4kg of CO2 per day per person. Acidification will continue to accelerate at least until mid-century, according to projections from Earth system models. − Climate News Network

Bluefin tuna follow prey to warming high Arctic

Bluefin tuna follow prey to warming high Arctic

A research ship’s surprise catch of bluefin tuna further north than ever recorded indicates that climate change is restructuring the food web as the waters of east Greenland get warmer.

LONDON, 8 September, 2014 − Biologists and fishermen aboard a scientific cruise in the Arctic while they investigated mackerel stocks caught more than they bargained for − three large bluefin tuna, each weighing about 100 kilograms.

The research ship was sailing through the Denmark Strait, which separates Greenland from Iceland. Bluefin tuna are very seldom found near Greenland, and there are no other scientific reports of them venturing that far north. The most recent report of a tuna anywhere near was a stranding in 1900, a long way south at Qaqortoq, on the south-western tip of Greenland.

Details of the find, during a cruise in August 2012 organised by the Center for Macroecology, Evolution and Climate at the University of Copenhagen, have now been published in the journal Global Change Biology.

Expanded range

The lead author, Professor Brian MacKenzie, said bluefin tuna usually search for prey in areas where surface temperatures are warmer than 11°C.

At the time of the catch, the Denmark Strait was unusually warm, and one of tuna’s preferred prey species, mackerel, had already expanded their range into the region.

Professor MacKenzie and his colleagues write: “Regional temperatures in August 2012 were historically high and contributed to a warming trend since 1985, when temperatures began to rise.

“The presence of bluefin tuna in this region is likely due to a combination of warm temperatures . . . and immigration of an important prey species to the region. We conclude that a cascade of climate change impacts is restructuring the food web in east Greenland waters.”

They say their data was too limited to estimate how many tuna came so far north, but because bluefins are a schooling species − with schools having from 10 to 100 individuals − and because the three tuna were caught in the same haul, it is likely there were many more present.

The report says: “Satellite imagery showing the spread of warm water from the south-east towards east Greenland suggests that recent warming and climate change may have opened a migration pathway from the European shelf towards Greenland for migratory species.”

It acknowledges that the fish may have swum to the Denmark Strait from the north-west Atlantic, and concludes: “Our results show that rising temperatures have been progressively leading a . . . trophic [high in the food chain] cascade into east Greenland waters via improved thermal conditions for migratory prey and predator species.”

New fishing quotas

Nobody knows why bluefin tuna disappeared from the waters near Denmark and in the Norwegian Sea during the 1960s, nor when they might return. But Iceland and Norway have been allocated new fishing quotas of 30 tonnes each for the species in 2014.

An adult bluefin tuna is typically 1.5m-2m long, but some have been as big as 4.5m and weighed 650 kg. The fish are highly prized for sushi, especially in Japan.

Further climate-related changes in distributions of commercial fish such as mackerel and herring will mean new fishery and ecosystem management plans are going to be needed, says the report’s co-author, Helle Siegstad, head of the Department for Fish and Shellfish at the Greenland Institute of Natural Resources.

The Denmark Strait tuna will be discussed at the annual science conference of the International Council for the Exploration of the Sea (ICES), which starts on 15 September in the Spanish coastal city of A Coruña. – Climate News Network

Fresh water causes Antarctic seas to rise faster

Fresh water causes Antarctic seas to rise faster

Researchers in the UK have established that billions of tonnes of fresh water from melting glaciers are causing Antarctic sea levels to rise much higher and faster than the global average.

LONDON, 7 September, 2014 − Sea levels around Antarctica are rising faster than anywhere else in the southern ocean. The global average rise in ocean heights in the last 19 years has been 6cms, but the rise in seas around Antarctica is 2cms higher.

This seemingly counter-intuitive finding is certainly a consequence of melting ice in the Southern Ocean, but the connection with global warming is, for the moment, tenuous. The agency that is behind the rising sea levels is simply an excess of fresh water from melting glaciers − about 350 billion tonnes of it.

“Fresh water is less dense than salt water, and so in regions where an excess of fresh water has accumulated we expect a localised rise in sea level,” says Craig Rye, an oceanography researcher at of the University of Southampton in the UK, who, with colleagues, has published the findings in Nature Geoscience.

Partly because the oceans are warmer and are therefore expanding, and partly because the terrestrial glaciers are in retreat, global sea levels on average have crept up by about 3 millimetres a year. Waters off the Antarctic shelf seem to be gaining an additional 2mm a year.

Less saline

The scientists studied satellite scans of a region of more than a million square kilometres to make their finding, and used ship-based studies of the Antarctic sea water to confirm that is has become less saline.

The melting of the Antarctic ice sheet – German scientists recently calculated that around 125 cubic kilometres of meltwater is running off the continent each year − and the thinning of the floating ice shelves is enough to explain the unexpected rise.

Computer model studies confirm the interpretation that the rise is happening because the southern seas have just got fresher. The consequences in the longer term are uncertain.

Rye, a postgraduate researcher, said: “The interaction between air, sea and ice in these seas is central to the stability of the Antarctic ice sheet and global sea levels, as well as other environmental processes, such as the generation of Antarctic bottom water, which cools and ventilates much of the global ocean abyss.” – Climate News Network