Constantine Alexander's blog

Coral reef thriving in sediment-laden waters

		A new study has established that Middle Reef – part of Australia’s iconic Great Barrier Reef – has grown more rapidly than many other reefs in areas with lower levels of sediment stress. This image shows Middle Reef, from under the sea. Credit: University of Exeter

Rapid rates of coral reef growth have been identified in sediment-laden marine environments, conditions previously believed to be detrimental to reef growth. A new study has established that Middle Reef – part of Australia's iconic Great Barrier Reef – has grown more rapidly than many other reefs in areas with lower levels of sediment stress.

Led by the University of Exeter, the study by an international team of scientists is published today (1 August 2012) in the journal Geology.

Middle Reef is located just 4 km off the mainland coast near Townsville, Australia, on the inner Great Barrier Reef shelf. Unlike the clear waters in which most reefs grow, Middle Reef grows in water that is persistently 'muddy'. The sediment comes from waves churning up the muddy sea floor and from seasonal river flood plumes. The Queensland coast has changed significantly since European settlement, with natural vegetation cleared for agricultural use increasing sediment runoff. High levels of sediment result in poor water quality, which is believed to have a detrimental effect on marine biodiversity.

The research team collected cores through the structure of Middle Reef to analyse how it had grown. They used radiocarbon dating to map out the precise growth rate of the reef. Results show that the reef started to grow only about 700 years ago but that it has subsequently grown rapidly towards sea level at rates averaging nearly 1 cm per year. These rates are significantly higher than those measured on most clear water reefs on the Great Barrier Reef and elsewhere. Most intriguingly, the periods of most rapid growth – averaging 1.3 cm a year – occurred when the accumulation rates of land-derived sediment within the reef structure were also at their peak. They discovered that, while the reef faced high sediment levels after the European settlers arrived in the 1800s, these same conditions were also part of the long-term environmental regime under which the reef grew.

Although there is evidence that other reefs have suffered degradation from high levels of sediment, these findings suggest that in some cases reefs can adapt to these conditions and thrive. For Middle Reef, rapid rates of vertical reef growth have, paradoxically, probably been aided by the high sedimentation rates. The team believe this is because the accumulating sediment rapidly covers the coral skeletons after their death, preventing their destruction by fish, urchins and other biological eroders, thus promoting coral framework preservation and rapid reef growth.

		Rapid rates of coral reef growth have been identified in sediment-laden marine environments, conditions previously believed to be detrimental to reef growth. A new study has established that Middle Reef – part of Australia’s iconic Great Barrier Reef – has grown more rapidly than many other reefs in areas with lower levels of sediment stress. This image shows Middle Reef from above the water. Credit: University of Exeter

Professor Chris Perry of Geography at the University of Exeter said: "Our research challenges the long-held assumption that high sedimentation rates are necessarily bad news in terms of coral reef growth. It is exciting to discover that Middle Reef has in fact thrived in these unpromising conditions. It is, however, important to remain cautious when considering what this means for other reefs. Middle Reef includes corals adapted to deal with high sedimentation and low light conditions. Other reefs where corals and various other reef organisms are less well adapted may not do so well if sediment inputs increased.

"Our research calls for a rethink on some of the classic models of reef growth. At a time when these delicate and unique ecosystems are under threat from climate change and ocean acidification, a view endorsed in a recent consensus statement from many of the World's coral reef scientists, it is more important than ever that we understand how, when and where reefs can grow and thrive."

This study was conducted by a team from the University of Exeter (UK), James Cook University, Townsville, Queensland (Australia), and the NERC Radiocarbon Laboratory, Scotland (UK). It was funded by the Leverhulme Trust and Natural Environment Research Council (NERC).

Reef facts

• A coral reef is made up of thin layers of calcium carbonate (limestone) secreted over thousands of years by billions of tiny soft bodied animals called coral polyps.
• Coral reefs are the world's most diverse marine ecosystems and are home to twenty-five percent of known marine species, including 4,000 species of fish, 700 species of coral and thousands of other plants and animals.
• Coral reefs have been on the planet for over 400 million years.
• The largest coral reef is the Great Barrier Reef, which stretches along the northeast coast of Australia, from the northern tip of Queensland, to just north of Bundaberg. At 2,300km long, it is the largest natural feature on Earth.
• Coral reefs occupy less than one quarter of one percent of the Earth's marine environment, yet they are home to more than a quarter of all known fish species.
• As well as supporting huge tourist industries, coral reefs protect shorelines from erosion and storm damage.

Contact: Sarah Hoyle
s.hoyle@exeter.ac.uk
44-013-927-22062
University of Exeter

 

 

'Superbird' stuns researchers

Bird was fitted with tiny camera by conservationists

		Imperial cormorants from Punta León in Argentina. Credit: Wildlife Conservation Society

A team of researchers from the Wildlife Conservation Society (WCS) and the National Research Council of Argentina recently fitted a South American sea bird called an imperial cormorant with a small camera, then watched stunned as it became "superbird" – diving 150 feet underwater in 40 seconds, feeding on the ocean floor for 80 seconds where it eventually caught a snakelike fish, before returning to the surface 40 seconds later.

This is the first time researchers have been able to watch first-hand the amazing feeding techniques of these fascinating birds, which occur off the coast of Argentina.

The footage shows the cormorant briefly on the surface before diving for the bottom. The camera is attached to the bird's back, so the view is of its head as it pumps its feet to swim deeper. When it finally reaches the ocean floor, it explores a vast area searching for food. It eventually finds an elongated fish, which it brings to the surface to eat.

The footage came from Punta León in Patagonia, Argentina, a coastal protected area supporting more than 3.500 pairs of imperial cormorants. A WCS scientific team, led by Dr. Flavio Quintana, has been studying the cormorants' feeding behavior for the past ten years. The team was joined by Dr. Carlos Zavalaga along with Ken Yoda from the University of Nogoya, Japan to fit the camera on the bird.

The WCS team has tracked more than 400 cormorants along the Patagonian Coast of Argentina using cutting edge technological tools such as multi-channel archival tags and high resolution GPS-loggers. This information will help identify priority feeding areas to help design new protected areas and to understand environmental conditions that affect cormorant populations.

WCS has worked in Patagonia for more than five decades and has helped establish a series of protected areas to safeguard local wildlife, including penguins, albatross, and elephant seals.

With the support of the Liz Claiborne and Art Ortenberg Foundation, Mitsubishi Corporation Foundation for the Americas, and other generous donors, WCS has worked in Patagonia for more than five decades. Our efforts have helped establish a series of protected areas to safeguard local wildlife, including penguins, albatross, and elephant seals.

 

Contact: John Delaney
jdelaney@wcs.org
718-220-3275
Wildlife Conservation Society

 

 

Report: Captive lion reintroduction programs in Africa operate under 'conservation myth'

		This shows a handler with a captive male lion, Namibia. Credit: © Luke Hunter/Panthera

A new report published in the international conservation journal Oryx concludes that commercial 'wildlife encounter' operations across Africa promoting the reintroduction of captive lions do little to further the conservation of African lions in the wild.

Released 'Early Online' on July 31, 'Walking with lions: Why there is no role for captive-origin lions (Panthera leo) in species restoration,' was authored by a blue-ribbon panel of lion conservationists and wild cat biologists from Panthera, the IUCN Cat Specialist Group and a team of university-based lion researchers. Demonstrating that no lions have been successfully released as a result of this process, the report determines that commercial captive lion reintroduction programs operate largely under a 'conservation myth.'

The last two decades has seen a rapid growth of such operations especially across Southern Africa. Advertised as 'wildlife encounters,' the programs typically charge tourists and paying volunteers to pet, feed and walk with hand-raised and so-called tame lions. To the paying public, the stated objective is the eventual release to the wild of lions.

The Oryx paper assesses the potential of these programs to assist wild lion conservation by evaluating the role and suitability of captive lions for release. The report concludes that captive-bred lions are simply unnecessary for reintroduction projects. For more than two decades, wild lions have been translocated and rigorously monitored in over 40 parks across southern Africa with high success rates. Over 500 wild lions have been re-established by this process. More importantly, the evaluation shows that captive-bred lions and their offspring are poorly suited for survival and release compared to their wild-born counterparts.

The report's senior author and Panthera's President, Dr. Luke Hunter, explained, "The simple fact is, 'lion encounter' type programs do little to help conserve wild lions. We show that any sincere effort to re-establish lions simply has no reason to resort to captive animals; wild lions are already much better equipped to be wild. Releasing captive animals unnecessarily increases the costs, risks of failure and the danger - to both lions and humans."

		A tourist is attacked at a lion encounter program in Zimbabwe. Credit: ©Peter Lawson/Eastnews/Rex USA

The report also claims that captive-lion enterprises divert critical resources and attention from projects making a real impact on declining wild lion populations. Dr Paula White, an author of the paper and Director of the Zambia Lion Project at the University of California notes, "These operations charge the public to spend time with tame lions claiming that it contributes meaningfully to lion conservation. Imagine if that funding, and the sincere interest of the people paying it, was devoted to addressing the real reasons that wild lions are declining and threatened. Spending money to breed lions behind fences is not helping."

While perhaps more than 200,000 wild lions lived in Africa over a century ago, their numbers are now thought to be fewer than 30,000. Listed as 'Vulnerable' by the International Union for the Conservation of Nature and extirpated from over 80% of its natural range, the lion is now on track to share the fate of its distant cousin, the Endangered tiger.

Dr. Matthew Becker, CEO of the Zambian Carnivore Programme (and not an author on the report) notes "Certainly interacting with tame lions is a unique experience, but it's not conservation. We have such 'Walking with Lions' programs in Zambia and they require a continual stream of young imported lions, which live out their days in captivity because they are not suitable for release. Zambia doesn't need captive-bred lions versus increased protection of its wild populations and ecosystems. Help lions by supporting the classic walking safaris that occur in our magnificent protected areas - that's the real walking with lions."

Along with Panthera's team of lion experts and Paula White, the Oryx publication was co-authored by Cole Burton (University of Alberta), Andrew Loveridge (Oxford University), and Panthera's Cat Advisory Council Member's Laurence Frank, and Christine and Urs Breitenmoser, who additionally chair the International Union for the Conservation of Nature/Species Survival Commission's Cat Specialist Group.

• Download The paper Walking with lions - Why there is no role for captive-origin lions in species restoration

Panthera, founded in 2006, is the world's leading organization devoted exclusively to the conservation of wild cats and their ecosystems. Utilizing the expertise of the world's premier cat biologists, Panthera develops and implements global conservation strategies for the largest, most imperiled cats – tigers, lions, jaguars, and snow leopards. Representing the most comprehensive effort of its kind, Panthera works in partnership with local and international NGOs, scientific institutions, local communities and governments around the globe.

 

Contact: Susie Weller
sweller@panthera.org
646-786-0417
Panthera

 

 

Critically endangered whales sing like birds; New recordings hint at rebound

This bowhead whale is a member of the population that lives in the Alaskan Beaufort Sea. The bowheads that were the subject of this study are rarely seen. Credit: Kate Stafford

When a University of Washington researcher listened to the audio picked up by a recording device that spent a year in the icy waters off the east coast of Greenland, she was stunned at what she heard: whales singing a remarkable variety of songs nearly constantly for five wintertime months.

Kate Stafford, an oceanographer with UW's Applied Physics Lab, set out to find if any endangered bowhead whales passed through the Fram Strait, an inhospitable, ice-covered stretch of sea between Greenland and the northern islands of Norway. Only around 40 sightings of bowhead whales, which were hunted almost to extinction, have been reported there since the 1970s.

Stafford and colleagues put two hydrophones, or underwater microphones, on moorings attached to the seafloor in Fram Strait, leaving them there for as long as the batteries would last: nearly a year. Since the population of bowhead whales likely to pass through was thought to number in the tens, they didn't anticipate much interesting data.

"We hoped to record a few little grunts and moans," Stafford said. "We were not expecting to get five months of straight singing."

Not only did they record singing nearly every hour of the day and night, they picked up more than 60 unique songs.

A paper detailing their discoveries appears Tuesday (July 31) as the feature article in Endangered Species Research and is openly accessible online.

The variety of tunes was so surprising that the researchers compared the whales' song catalog to that of birds. "Whether individual singers display one, multiple or even all call types, the size of the song repertoire for… bowheads in 2008-2009 is remarkable and more closely approaches that of songbirds than other… whales," they wrote in the report.

They have yet to learn why the whales sang so consistently last year.

Scientists believe that bowhead whale song comes from males during mating season. In most other kinds of whales, individuals either sing the same song their whole lives or all members of a population sing the season's same popular tune. If bowheads are like the former, that would mean more than 60 males were in the Fram Strait. If the population is evenly split between males and females, there could have been more than 100 whales -- far more than anyone thought comprised this population.

With further study, the scientists instead could discover that individual bowhead whales have a repertoire of songs that they sing during a season. That would be equally interesting because it would make the bowheads the only known whales to sing a variety of songs in the same season.

The findings also hint at the possibility of a rebound in bowhead whales.

"If this is a breeding ground, it would be spectacular," said Stafford. "For such a critically endangered species, it's really important to know that there's a reproductively active portion of the population."

In addition, since the whales are difficult to study given their year-round residence in the Arctic, virtually nothing was known about where they spend their winters. The research offers a clue about the whales' migration path.

Only a handful of bowhead whale populations remain. The largest historic population, which includes the individuals studied for this report, once possibly numbered more than 30,000 members but was hunted to near-extinction from the 1600s through the 1800s. Commercial whaling reduced bowhead whale populations in other regions as well; combined, the four remaining populations are thought to number fewer than 10,000 members.

Bowhead whales are massive creatures. They grow to over 60 feet long, may live to 200 years old and can weigh 200,000 pounds. They use their huge skulls to break through ice as thick as 1.5 feet.

Bowhead whale song is unique in that the whales appear to sing with "two voices," simultaneously producing high- and low-frequency sounds. The whales sometimes repeat the same tune for hours at a time.

Stafford and her colleagues deployed the two hydrophones 60 miles apart. They made 2,144 hours of simultaneous recordings from September 2008 through July 2009. In order to conserve battery power and take recordings for a longer period of time, the hydrophones worked for nine minutes out of every half hour.

The hydrophone in the west, covered in dense ice and in colder water, picked up far more singing than the one in the east, where there was spotty ice coverage and warmer water. The greatest frequency of song occurred in the darkest, coldest period.

"It's clear there's a habitat preference," Stafford said. The thick canopy of ice may provide better acoustics than the loose pack ice and therefore might be favored by singing whales, she said.

"As Arctic sea ice declines, there may be some places like this that are important to protect in order to preserve a breeding ground for the bowhead whales," Stafford said.

To answer new questions that the data opens up – including how many whales make up this North Atlantic population – Stafford hopes to do additional study.

Co-authors of the paper include Sue Moore and Catherine Berchok from the National Oceanic and Atmospheric Administration; Øystein Wiig of the University of Oslo; Christian Lydersen, Edmond Hansen and Kit M. Kovacs from the Norwegian Polar Institute; and Dirk Kalmbach with the Alfred Wegener Institute of Polar and Marine Research in Germany. The research was funded by NOAA and supported by the Norwegian Polar Institute and the Alfred Wegener Institute.

Listen to the bowheads repeat their other-worldly song as they cross the Fram Strait:

• Bowhead whale song 1
• Bowhead whale song 2

Contact: Nancy Gohring
ngohring@uw.edu
206-543-2580
University of Washington

 

 

Camouflage of moths: Secrets to invisibility revealed

		Fig. 1 shows two species of moths that, according to the recent study of evolutionary biologists from Seoul, “know” how to find a spot on a tree bark to become invisible to predators: (a) – Hypomecis roboraria; (b) – Jankowskia fuscaria. Credit: ©entomart NonCommercial-ShareAlike 2.0 Generic (CC BY-NC-SA 2.0)

Moths are iconic examples of camouflage. Their wing coloration and patterns are shaped by natural selection to match the patterns of natural substrates, such as a tree bark or leaves, on which the moths rest. But, according to recent findings, the match in the appearance was not all in their invisibility.

Despite a long history of research on these iconic insects, whether moths behave in a way to increase their invisibility has not been determined. A research team from the Laboratory of Behavioral Ecology and Evolution at the Seoul National University has conducted an experiment to directly answer this question. Chang-ku Kang, Jong-yeol Moon, Sang-im Lee and Piotr Jablonski have found out that moths are walking on the tree bark until they settle down for resting; the insects seem to actively search for a place and a body position that makes them practically invisible.

Instead of placing moth specimens on a tree bark in various positions to see how body orientation of moths make them invisible to birds, which has been done by several researchers, "we let the moths to do the job for us" says Changku Kang, the PhD student who conducted the experiment. The researchers let inchworm moths of two species (Jankowskia fuscaria and Hypomycis roboraria; Fig. 1) to land on a tree bark and to freely choose the final resting spot and body orientation. Many moths did not remain at the spot of landing. They walked around with stretched wings as if they were looking for that one perfect spot that may make them invisible to predators.

To determine whether this final spot indeed made the moth really invisible, the researchers photographed each moth at its landing spot (initial spot) and at the final spot at which the moth decided to rest. Next, the researchers asked people to try to locate the moth from the photograph as quickly as possible. People had more difficulty finding the moths at their final spots than the same moths at their initial landing spots. Amazingly, this was even true for the species (Hypomecis roboraria) that only changed its resting spot on the tree bark without changing its body orientation. Therefore, the researchers concluded, that moths seems to actively choose the spot that makes them invisible to predators. How do they know how to become invisible? The research team is now trying to answer this question as the next step.

 

Reference: CK Kang, JY Moon, SI Lee, P.G. Jablonski, 2012, Camouflage through an active choice of a resting spot and body orientation in moths. Journal of Evolutionary Biology. Article first published online: 6 Jul 2012. DOI: 10.1111/j.1420-9101.2012.02557.x

Contact: S.J.Lee
82-108-028-7799
Laboratory of Behavioral Ecology and Evolution at Seoul National University

 

 

To know a tiger is at least to start tolerating them, study shows

		Neil Carter, a doctoral student at Michigan State University's Center for Systems Integration and Sustainability, (left) tests a camera trap set in Chitwan National Forest in Nepal, where he studies interactions between people and tigers. Credit: Sue Nichols, Michigan State University CSIS

To protect a dangerous and endangered animal -- be it a tiger in Nepal or a wolf in Michigan - you really do have to ask people "how do you FEEL about your predatory neighbor?"

Effective conservation calls for not only figuring out what protected species need – like habitat and food sources. It also requires an understanding of what it takes for their human neighbors to tolerate them. A Michigan State University doctoral student studying tigers in Nepal found that those feelings can provide critical information on how best to protect species.

"People have complex psychological relationships with wildlife," said Neil Carter, researcher in MSU's Center for Systems Integration and Sustainability (CSIS). "Picking apart these complex relationships is the best way to get a really good idea of what's affecting their tolerance of the animal."

The paper, "Utility of a psychological framework for carnivore conservation," is published Tuesday in Oryx, an international journal of conservation. Co-authors are Shawn Riley, MSU associate professor of fisheries and wildlife, and Jianguo "Jack" Liu, MSU University Distinguished Professor of fisheries and wildlife, who holds the Rachel Carson Chair in Sustainability and is CSIS director.

		In the buffer zone which runs along Nepal's Chitwan National Forest, people and tigers closely coexist, both depending on the forest for their livelihoods. It is here doctoral student Neil Carter at Michigan State University's Center for Systems Integration and Sustainability study tiger/human interactions. Credit: Sue Nichols, Michigan State University CSIS

Carter has conducted research in Nepal's Chitwan National Park, home to some 125 adult tigers that live close to people. And tigers, like all wild animals, have little regard for borders or fences. Likewise, the tigers' human neighbors depend on the forests for their livelihoods. Conflict is inevitable. There were 65 human deaths due to tiger attacks from 1998 to 2006 and tigers are known to kill livestock. People sometimes kill tigers in response to these threats

Carter's work has developed a novel tool to help figure out where to direct conservation resources -- not just in Nepal, but also for conserving carnivores that live next to people in many regions of the world.

The research is unique in that it explores peoples' attitudes about protected animals. Work has been done to understand how people feel about their wildlife neighbors, such as deer or coyotes. But the relationship with protected animals, especially those that can be dangerous, is more complicated. Issues of fear, risk and control make for a volatile mix, as do the constraints on solutions.

"You can't just remove all the tigers, or the grizzly bears, or other carnivores that may pose a risk to people. Managing animal populations in this fashion is not a viable option for protected species," Carter said. "It's imperative to come up with ways that people and carnivores can get along."

		This shows a tiger in Nepal's Chitwan National Forest. Credit: Michigan State University Center for Systems Integration and Sustainability

Policy and laws aren't enough, he says. Carter said that in Nepal and around the world, people kill protected animals or turn a blind eye to poachers.

Carter, with his collaborators, surveyed 499 people living near Chitwan about how they feel about future tiger population size and factors that may influence preferences, like past interactions with tigers as well as beliefs and perceptions about tigers.

Among the findings:

While more study is needed, this work hints that it's not fear that drives people's preferences for the number of future tigers. Rather, it's a combination of psychological responses that focus on the benefits and pragmatic costs of having tigers nearby.

"We expected that interactions – real experiences with tigers in the wild would be most influential," Carter said. "Someone who had three cattle killed would have different tolerance than someone who hasn't. Perhaps, if you're exposed to something all the time, the fear stops becoming the powerful predictor."

The survey identifies opportunities. For example, it was clear that people's beliefs that tigers weren't beneficial to the forest influenced their acceptance of tigers, a belief that had nothing to do with risk.

"That's a real simple educational opportunity," Carter said. "People can be shown that tigers regulate the populations of deer and boar, which cause real economic damage to crops. If they don't see the connection then that's a lost opportunity."

In addition to Carter's work on attitudes, he also has spent considerable time in Chitwan setting up camera traps to better understand the tiger populations, as well as understanding how people move in and out of tiger territory. His blending of social sciences and ecological studies is characteristic of CSIS, which works in the innovative new field of coupled human and natural systems to find sustainable solutions that both benefit the environment and enable people to thrive.

The research was funded by the National Science Foundation, NASA, and the U.S. Fisheries and Wildlife Rhinoceros and Tigers Conservation Fund. It was part of the Partnership for International Research and Education among MSU, the University of Michigan and seven other institutions in the United States, Nepal, and China.

The Center for Systems Integration and Sustainability integrates ecology with socioeconomics, demography and other disciplines to conduct cutting-edge research on ecological sustainability on local, national and global scales.

Michigan State University has been advancing knowledge and transforming lives through innovative teaching, research and outreach for more than 150 years. MSU is known internationally as a major public university with global reach and extraordinary impact. Its 17 degree-granting colleges attract scholars worldwide who are interested in combining education with practical problem solving.

Contact: Neil Carter
cartern7@msu.edu
858-414-0434
Michigan State University

 

 

 

Ecosystems reveal radiation secrets

The transfer of radioactive compounds is not straightforward

A new study by Tiina Tuovinen, from the University of Eastern Finland, and her colleagues casts doubt over the validity of models used to assess the impact of radiation on human health. Their work is published online in Springer's journal Hydrobiologia.

The Chernobyl accident in 1986 led to a discharge of radioactive compounds into terrestrial, freshwater and marine environments. Over a period of time, these compounds have been taken up by organisms and have made their way into the food chain.

Since the accident, the fall-out from the power plant accident has been used as a major source of information for models which predict the transfer of these radioactive compounds into ecosystems, estimating their doses and assessing their potential effects on human health and wildlife.

The authors explain: "The ability of models to accurately predict concentrations and doses depends critically on the empirical data on the behavior of radioactive compounds in the biosphere and also on the correctness of basic assumptions used in the models."

Their analysis of the contamination of two Finnish lakes by radioactive compounds (137Cs in particular) suggests that the models used to predict consequences on human health are based on a false premise. Their work therefore questions the validity of the models used and the conclusions that can be drawn from them.

The researchers collected data from two lakes in Northern Finland to investigate the transfer of 137Cs from lake water into fish during a twenty-year period after the Chernobyl nuclear power plant accident. Their results show that, contrary to what has been assumed until now, the transfer of the radioactive compounds is non-linear. In addition, the levels of these compounds appear to be three times higher in fish-eating species (piscivores) than in non-fish-eating species.

Reference: Tuovinen TS et al (2012). Transfer of 137Cs from water to fish is not linear in two northern lakes. Hydrobiologia; DOI 10.1007/s10750-012-1224-8

Contact: Joan Robinson
joan.robinson@springer.com
49-622-148-78130
Springer

 

 

 

Scientists probe link between magnetic polarity reversal and mantle processes

Earth Crust Cutaway

Scientists at the University of Liverpool have discovered that variations in the long-term reversal rate of the Earth's magnetic field may be caused by changes in heat flow from the Earth's core into the base of the overlying mantle.

The Earth is made up of a solid inner core, surrounded by a liquid outer core, in turn covered by a thicker or more viscous mantle, and ultimately by the solid crust beneath our feet. The magnetic field is generated by the motions of the liquid iron alloy in the outer core, approximately 3,000 km beneath the Earth's crust. These motions occur because the core is losing heat to the overlying solid mantle that extends up to the crust on which we live.

The mantle itself is also in motion but at much slower speeds of millimetres per year as opposed to millimetres per second in the core. This mantle motion is responsible for the drifting of the continents at the surface as well as earthquakes, volcanoes, and changes in the climate over millions of years.

At intervals of hundreds of thousands of years, the North and South magnetic poles reverse and scientists can tell from rock formations precisely at what periods in the past this took place. The most recent reversal happened 780,000 years ago. Magnetic field variations happen on timescales of months to millions of years. Much of the magnetic field's variation is thought to be sporadic but new research, led by Liverpool scientists, has found that over long timescales, this variability may be related to the changing pattern of heat loss across the core-mantle boundary occurring over millions of years.

The team performed a detailed synthesis based on latest findings from a number of different areas including the ancient geomagnetic field and its record in rocks, motions in the mantle caused by motions of the continents and the process responsible for generating the magnetic field in the core.

Dr Andrew Biggin, from the University's School of Environmental Sciences, said: "The magnetic field has undergone big changes in its behaviour that might be due to the mantle's controlling influence on the core. In particular, we focused on the time interval between around 200 and 80 million years ago – when dinosaurs were still around – when the magnetic field initially started reversing its polarity very frequently. During this period the polarity was reversing up to 10 times every million years; however 50 million years later, it stopped reversing altogether for nearly 40 million years.

"When these changes in the magnetic field were taking place, the whole of the Earth's crust and mantle, including all of the continents, were undergoing a big rotation with respect to the geographic and time-averaged geomagnetic poles – the points defining the Earth's axis of rotation. We suspect that this process, called True Polar Wander and caused by the changing density distribution in the mantle, will have changed the pattern of heat flowing out of the core in such a manner as to cause the magnetic field to first become less stable, with lots of reversals, and then become much more stable – and stop reversing."

The team believes this may not be the only explanation and conjecture that this big drop in the frequency of reversals may also be related to a similar decrease in the number of 'large igneous provinces' (LIPs) or concentrated outpourings of magma from the Earth's core, 50 million years later. The last LIP happened around 16 million years ago and produced the Columbia Plateau in the North West US. LIPs are thought to be produced by hot plumes of material rising from thermal instabilities near the bottom boundary of the mantle.

The team believes the 50 million year time lag between the magnetic field changing and the occurrence of the LIPs could represent the time it takes for the plumes to travel 2,890 km through the mantle. If this link were correct it would mean that the rather unstable magnetic field observed in the last 50 million years predicts that a considerable number of LIPs will erupt over the next 50 million years. This in turn could have major implications for the surface conditions – for climate and for life itself.

The research, published in Nature Geoscience, is a collaboration between the University of Liverpool, GFZ Potsdam, IPGP Paris, the University of Oslo and Utrecht University. Future research at Liverpool, is planned and already underway to develop a new tool for understanding the Earth's system.

Contact: Kate Mizen
kate.mizen@liv.ac.uk
0044-151-794-2247
University of Liverpool