CARBON SINK

FROM:  NATIONAL SCIENCE FOUNDATION 
Tropical forest carbon sink hinges on 'odd couple'

A unique housing arrangement between a specific tree species and carbo-loading bacteria may determine how well tropical forests can absorb carbon dioxide from the atmosphere, says new research today in an advance online publication of the journal Nature.

The findings suggest that the role of tropical forests in offsetting the atmospheric buildup of carbon from fossil fuels depends on tree diversity, particularly in forests recovering from exploitation.

Tropical forests thrive on natural nitrogen fertilizer pumped into the soil by trees in the legume family, a diverse group of plants that includes beans and peas, the researchers report.

"Fast-growing nitrogen-fixing trees are not common outside of the tropics, but are found in surprisingly high diversity there," said Henry Gholz, program director in the National Science Foundation's (NSF) Division of Environmental Biology, which funded the research.

"These findings place the trees' ability to capture atmospheric nitrogen and to use it to stimulate growth in the context of long-term tropical forest development," Gholz said. "This process not only allows these trees to get out of the gate quickly after a disturbance, but to maintain dominance decades to centuries later."

The researchers studied recovering forests in Panama that had been exploited five to 300 years earlier.

The presence of legume trees ensured rapid forest growth, and thus a substantial carbon sink, in the first 12 years of recovery.

Tracts of land that were pasture only 12 years before had already accumulated as much as 40 percent of the carbon found in fully mature forests. Legumes contributed more than half the nitrogen needed to make that happen.

These fledgling woodlands had the capacity to store 50 metric tons of carbon per hectare, which equates to roughly 185 tons of carbon dioxide, or the exhaust of some 21,285 gallons of gasoline.

That much fuel would take the average car in the United States more than half a million miles.

Though the legumes' nitrogen fertilizer output waned in later years, the species nonetheless took up carbon at rates that were up to 9 times faster than non-legume trees.

The legumes' secret is a process known as "nitrogen fixation" carried out in concert with infectious bacteria known as rhizobia, which dwell in small pods, known as root nodules, inside the tree's roots.

As a nutrient, nitrogen is essential for plant growth, but tropical soil is short on nitrogen and surprisingly non-nutritious for trees.

Legumes use secretions to invite rhizobia living in the soil to infect their roots, and the bacteria signal back to initiate nodule growth.

The rhizobia move into the root cells of the host plant and--in exchange for carbohydrates produced by photosynthesis in the tree--convert nitrogen from the air into fertilizer plants need.

Excess nitrogen from the legume eventually creates a nitrogen cycle that benefits neighboring trees.

By nurturing bigger, healthier trees that take up more carbon, legumes have a newly realized importance when it comes to influencing atmospheric carbon dioxide, said paper co-author Lars Hedin of Princeton University.

Scientists recently assigned numbers to track how much carbon forests as a whole absorb, suggesting that the world's forests took up 2.4 quadrillion tons of carbon from 1990 to 2007.

"Tropical forests are a huge carbon sink," said Hedin.

"If trees could just grow and store carbon, you could have a rapid sink, but if they don't have enough nitrogen they don't take up carbon," he said, adding that nitrogen-fixing trees are uncommon in temperate forests such as those in most of North America and Europe.

"Legumes are a group of plants that perform a valuable function in tropical forests, but no one knew how much they help with the carbon sink," Hedin said. "This work shows that the level of biodiversity in a tropical forest determines the size of the carbon sink."

First author Sarah Batterman of Princeton said that legumes, or "nitrogen-fixers," are especially important for forests recovering from agricultural use, logging, fire or other human activities.

The researchers studied 16 forest plots that were formerly pasture and are maintained by the Smithsonian Tropical Research Institute (STRI).

Forest degradation, however, comes with a loss of biodiversity that can affect nitrogen-fixers, too, even though legumes are not specifically threatened, Batterman said.

If the number and diversity of nitrogen-fixers plummet, the health of the surrounding forest would likely be affected for a long time, she said.

"This study shows that there is an important place for nitrogen-fixation in these disturbed areas," Batterman said.

"Nitrogen-fixers are a component of biodiversity and are important for the function of these forests, but we don't know enough about how this valuable group of trees influences forests. While some species may thrive on disturbance, others may be sensitive to human activities."

The researchers found that the nine legume species they studied did not contribute nitrogen to surrounding trees at the same time.

Certain species were more active in the youngest forests, others in middle-aged forests, and still other species went into action mainly in 300-year-old tracts, though not nearly to the same extent as legumes in younger plots.

The researchers found that individual trees reduced their fixation as nitrogen accumulated in soils, with the number of legumes actively "fixing" nitrogen dropping from 71 to 23 percent between 12- and 80-year-old forests.

"The diversity of species present in the forest is critical because it ensures that there can be fixation at different time periods of forest recovery," Batterman said.

"If you were to lose one of those species and it turned out to be essential for a specific time period, fixation might drop dramatically."

Such details can improve what scientists know about future climate change, Batterman said.

Computer models that calculate the global balance of atmospheric carbon dioxide also must factor in sinks that offset carbon, such as tropical forests.

And if forests take up carbon differently depending on the abundance and diversity of legumes, models should reflect that variation, she said.

"Other researchers can now put this role of nitrogen-fixation into their models and improve predictions about the carbon sink," Batterman said.

Batterman and Hedin worked with Michiel van Breugel and Jefferson Hall at STRI, Johannes Ransijn at the University of Copenhagen and Dylan Craven at Yale University.

The work was also supported by grants from the National Oceanic and Atmospheric Administration; the Smithsonian Tropical Research Institute; and the Cooperative Institute for Climate Science and the Carbon Mitigation Initiative, both at Princeton University.

-NSF-

AMOUNT OF WATER TREES NEED AND THE CHANGING ATMOSPHERE

On the ground: looking into Harvard Forest's trees from a less lofty perch.  Credit: NSF Harvard Forest LTER Site

FROM:  NATIONAL SCIENCE FOUNDATION
Changing Atmosphere Affects How Much Water Trees Need

Spurred by increasing levels of atmospheric carbon dioxide, forests over the last two decades have become dramatically more efficient in how they use water.

Scientists affiliated with the National Science Foundation's (NSF) Harvard Forest Long-Term Ecological Research (LTER) site report the results in this week's issue of the journal Nature.

Harvard Forest is one of 26 such NSF LTER sites in ecosystems from deserts to grasslands, coral reefs to coastal waters, around the world.

Studies have long predicted that plants would begin to use water more efficiently, that is, lose less water during photosynthesis, as atmospheric carbon dioxide levels rose.

A research team led by Trevor Keenan and Andrew Richardson of Harvard University, however, has found that forests across the globe are losing less water than expected and becoming even more efficient at using it for growth.

Using data collected in forests in the northeastern United States and elsewhere around the world, Keenan and Richardson found increases in efficiency larger than those predicted by state-of-the-art computer models.

The research was done in collaboration with scientists from the USDA Forest Service, Ohio State University, Indiana University and the Karlsruhe Institute of Technology in Germany.

"This could be considered a beneficial effect of increased atmospheric carbon dioxide," said Keenan, the first author of the Nature paper.

"What's surprising is we didn't expect the effect to be this big. A large proportion of the ecosystems in the world are limited by water--they don't have enough water during the year to reach their maximum potential growth.

"If they become more efficient at using water, they should be able to take more carbon out of the atmosphere due to higher growth rates."

While increased atmospheric carbon dioxide may benefit forests in the short-term, Richardson emphasized that the overall climate picture would remain grim if levels continue to rise.

"We're still very concerned about what rising levels of atmospheric carbon dioxide mean for the planet," Richardson said.

"There is little doubt that as carbon dioxide continues to rise--and last month we just passed a critical milestone, 400 parts per million for the first time in human history--rising global temperatures and changes in rainfall patterns will, in coming decades, have very negative consequences for plant growth in many ecosystems around the world."

How do increasing carbon dioxide levels lead to more efficient water use?

The answer, Keenan said, is in the way photosynthesis works.

To take in the carbon dioxide they need, plants open tiny pores, called stomata, on their leaves. As carbon dioxide enters, however, water vapor is able to escape.

Higher levels of carbon dioxide mean the stomata don't need to open as wide, or for as long, so the plants lose less water and grow faster.

To take advantage of that fact, commercial growers have for years pumped carbon dioxide into greenhouses to promote plant growth.

To test whether such a "carbon dioxide fertilization effect" was taking place in forests, Keenan, Richardson and others turned to long-term data measured using a technique called eddy covariance.

This method, which relies on sophisticated instruments mounted on tall towers extending above the forest canopy, allows researchers to determine how much carbon dioxide and water are going into and out of the ecosystem.

With more than 20 years of data, the towers at the NSF Harvard Forest LTER site--which have the longest continuous record in the world--are an important resource for studying how forests have responded to changes in atmospheric carbon dioxide levels, scientists say.

"A goal of the NSF LTER program is understanding forest ecosystems and the basis for predicting fluxes of energy and materials in these ecosystems," said Matt Kane, program director in NSF's Division of Environmental Biology, "as well as distributions of forest biota as a result of global climate change."

"Findings from this study are important to our understanding of forest ecosystems--and how they can be managed more effectively now and in the future."

Though more than 300 towers like Harvard Forest's have sprung up around the globe, many of the earliest--and hence with the longest data records--are in the northeastern United States.

When the researchers began to look at those records, they found that forests were storing more carbon and becoming more efficient in how they used water.

The phenomenon, however, wasn't limited to a single region. When the scientists examined long-term data sets from all over the world, the same trend was evident.

"We went through every possible hypothesis of what could be going on, and ultimately what we were left with is that the only phenomenon that could cause this type of shift in water-use efficiency is rising atmospheric carbon dioxide," Keenan said.

Going forward, Keenan, who is now at Macquarie University in Sydney, Australia, is working to get access to data collected from yet more sites, including several that monitor tropical and arctic systems.

"This larger dataset will help us better understand the extent of the response we observed," he said.

"That in turn will help us build better models, and improve predictions of the future of the Earth's climate.

"Right now, all the models we have underrepresent this effect by as much as an order of magnitude, so the question is: What are the models not getting? What do they need to incorporate to capture this effect, and how will that affect their projections for climate change?"

The research was also supported by NOAA. Field measurements at the sites, which are part of the AmeriFlux network, have also been funded by the U.S. Department of Energy and the USDA Forest Service.

-NSF-

GLOBAL WARMING AND RAINFALL

 

Model simulations spanning 140 years show that warming from carbon dioxide will change the frequency that regions around the planet receive no rain (brown), moderate rain (tan), and very heavy rain (blue). The occurrence of no rain and heavy rain will increase, while moderate rainfall will decrease. Credit: NASA's Goddard Space Flight Center Scientific Visualization Studio

FROM: NASA

NASA Study Projects Warming-Driven Changes in Global Rainfall

WASHINGTON -- A NASA-led modeling study provides new evidence that global warming may increase the risk for extreme rainfall and drought.

The study shows for the first time how rising carbon dioxide concentrations could affect the entire range of rainfall types on Earth.

Analysis of computer simulations from 14 climate models indicates wet regions of the world, such as the equatorial Pacific Ocean and Asian monsoon regions, will see increases in heavy precipitation because of warming resulting from projected increases in carbon dioxide levels. Arid land areas outside the tropics and many regions with moderate rainfall could become drier.

The analysis provides a new assessment of global warming's impacts on precipitation patterns around the world. The study was accepted for publication in the American Geophysical Union journal Geophysical Research Letters.

"In response to carbon dioxide-induced warming, the global water cycle undergoes a gigantic competition for moisture resulting in a global pattern of increased heavy rain, decreased moderate rain, and prolonged droughts in certain regions," said William Lau of NASA's Goddard Space Flight Center in Greenbelt, Md., and lead author of the study.

The models project for every 1 degree Fahrenheit of carbon dioxide-induced warming, heavy rainfall will increase globally by 3.9 percent and light rain will increase globally by 1 percent. However, total global rainfall is not projected to change much because moderate rainfall will decrease globally by 1.4 percent.

Heavy rainfall is defined as months that receive an average of more than about 0.35 of an inch per day. Light rain is defined as months that receive an average of less than 0.01 of an inch per day. Moderate rainfall is defined as months that receive an average of between about 0.04 to 0.09 of an inch per day.

Areas projected to see the most significant increase in heavy rainfall are in the tropical zones around the equator, particularly in the Pacific Ocean and Asian monsoon regions.

Some regions outside the tropics may have no rainfall at all. The models also projected for every degree Fahrenheit of warming, the length of periods with no rain will increase globally by 2.6 percent. In the Northern Hemisphere, areas most likely to be affected include the deserts and arid regions of the southwest United States, Mexico, North Africa, the Middle East, Pakistan, and northwestern China. In the Southern Hemisphere, drought becomes more likely in South Africa, northwestern Australia, coastal Central America and northeastern Brazil.

"Large changes in moderate rainfall, as well as prolonged no-rain events, can have the most impact on society because they occur in regions where most people live," Lau said. "Ironically, the regions of heavier rainfall, except for the Asian monsoon, may have the smallest societal impact because they usually occur over the ocean."

Lau and colleagues based their analysis on the outputs of 14 climate models in simulations of 140-year periods. The simulations began with carbon dioxide concentrations at about 280 parts per million -- similar to pre-industrial levels and well below the current level of almost 400 parts per million -- and then increased by 1 percent per year. The rate of increase is consistent with a "business as usual" trajectory of the greenhouse gas as described by the United Nations' Intergovernmental Panel on Climate Change.

Analyzing the model results, Lau and his co-authors calculated statistics on the rainfall responses for a 27-year control period at the beginning of the simulation, and also for 27-year periods around the time of doubling and tripling of carbon dioxide concentrations.
They conclude the model predictions of how much rain will fall at any one location as the climate warms are not very reliable.

"But if we look at the entire spectrum of rainfall types we see all the models agree in a very fundamental way -- projecting more heavy rain, less moderate rain events, and prolonged droughts," Lau said.

EPA PUBLISHES U.S. GREENHOUSE GAS INVENTORY

FROM: U.S. ENVIRONMENTAL PROTECTION AGENCY

 

 

EPA Publishes 18th Annual U.S. Greenhouse Gas Inventory


WASHINGTON – Today, the U.S. Environmental Protection Agency (EPA) released its 18th annual report of overall U.S. greenhouse gas (GHG) emissions showing a 1.6 percent decrease in 2011 from the previous year. Recent trends can be attributed to multiple factors including reduced emissions from electricity generation, improvements in fuel efficiency in vehicles with reductions in miles traveled, and year-to-year changes in the prevailing weather.

Under this Administration, EPA has taken a number of common sense steps to help reduce GHG emissions. This includes increasing fuel efficiency for cars that will reduce America’s dependence on oil by an estimated 12 billion barrels by 2025, and increasing energy efficiency through the Energy Star program that saved Americans $24 billion in utility bills in 2012.

GHGs are the primary driver of climate change, which can lead to hotter, longer heat waves that threaten the health of the sick, poor or elderly; increases in ground-level ozone pollution linked to asthma and other respiratory illnesses; as well as other threats to the health and welfare of Americans. GHG emissions in 2011 showed a 6.9 percent drop below 2005 levels. Total emissions of the six main greenhouse gases in 2011 were equivalent to 6,702 million metric tons of carbon dioxide. These gases include carbon dioxide, methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons and sulfur hexafluoride.

The Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2011 is the latest annual report that the United States has submitted to the Secretariat of the United Nations Framework Convention on Climate Change since it was ratified by the United States in 1992. The treaty sets an overall framework for intergovernmental efforts to address the challenge posed by climate change. EPA prepares the annual report in collaboration with other federal agencies and after gathering comments from stakeholders across the country.

The inventory tracks annual GHG emissions at the national level and presents historical emissions from 1990 to 2011. The inventory also calculates carbon dioxide emissions that are removed from the atmosphere through the uptake of carbon by forests, vegetation, soils, and other natural processes (called carbon "sinks").

Emissions and Trends

Since 1990, U.S. greenhouse gas emissions have increased by about 8%. From year to year, emissions can rise and fall due to changes in the economy, the price of fuel, and other factors. In 2011, U.S. greenhouse gas emissions decreased compared to 2010 levels. This decrease was primarily due to a decrease in the carbon intensity of fuels consumed to generate electricity due to a decrease in coal consumption, with increased natural gas consumption and a significant increase in hydropower used. Additionally, relatively mild winter conditions, especially in the South Atlantic Region of the United States where electricity is an important heating fuel, resulted in an overall decrease in electricity demand in most sectors.

THE OPTIMIZATION OF CELL BASED CENSORS

Photo:  Cells.  Credit:  Wikimedia Commons

FROM: U.S. NAVY
Recruiting Engineered Cells to Work for Warfighters
Date: 4/8/2013 3:27:00 PM
By Katherine H. Crawford, Office of Naval Research

ARLINGTON, Va. (NNS) -- The Office of Naval Research (ONR) launched a collaborative initiative with university researchers April 8 focused on synthetic, or engineered, cells as part of a larger effort to use the smallest units of life to help Sailors and Marines execute their missions.

ONR currently has multiple ongoing projects in the field of synthetic biology, which offers new tools and methods for creating new organisms with specific functions, such as threat monitoring.

Even the simplest cells can have complex functions, such as being able to move in a particular direction or glow in the dark. The idea is to make these capabilities useful to humans by directing their natural functions and adding non-natural functions to a cell's repertoire.

In one instance, ONR is examining synthetic cell circuits, which is a genetic programs designed by scientists either to make a cell perform a certain task or change the way a cell would normally do the task. For example, plants have been engineered to turn white when they detect trinitrotoluene (TNT) as a visual cue to their handlers.

"We're developing better ways to program cells to detect things we're interested in-like explosives-and then communicate that they've found that chemical to a device like a robot," said Dr. Linda Chrisey, ONR program officer for naval biosciences and bio-centric technology. "For example, you could grow these special cells on a silicon chip that's part of a robot. When the cells detect something and respond, they would communicate this information to the 'mother ship'-the autonomous robot system."

One of ONR's biggest successes to date was a TNT-detecting plant. This "plant sentinel" transitioned to the Defense Threat Reduction Agency and Department of Homeland Security in 2010. A small company was founded to modify this plant for other applications, such as chemical warfare detection and crop security.

"The grand plan is to try and take advantage of the natural capabilities of microbes to collect chemical and physical signal information of different types and process this information," Chrisey said. "We already make a lot of medicines and industrial products using cells and engineered cells. Synthetic biology is going to smarten that process up, make it less susceptible to failure and save money by allowing us greater control of the engineered cells."

Another initiative is looking at microbes that use carbon dioxide and electrical current for their metabolism and programming them to make liquid fuels.

"Eventually, in a remote location, with just a vial of these organisms and materials that most people consider to be waste products, Sailors and Marines could potentially make organic compounds, such as fuel, medicine or polymers, on demand, even under austere conditions," Chrisey said.

In the long term, synthetic circuits offer possibilities for enabling new methods for manufacturing. These new processes can be used: to make certain products, such as biofuels, pharmaceuticals and specialty chemicals; as medical devices and therapies for infection control, regenerating tissues and disease treatment; as environmental sensors and pollution treatments; and for micro-robotic systems.

The Multidisciplinary University Initiative (MURI) launched today, "Next-generation genetic devices: Model-guided Discovery and Optimization of Cell-Based Sensors," is aimed at applying tools from synthetic biology to construct high-performance and robust genetic sensors that respond to non-natural signals, such as non-visible wavelengths of light (ultraviolet and infrared) and magnetic fields.

This program is expected to contribute to the development of "smart" hybrid biological-robotic systems that will detect threats in the environment. The universities involved are the Massachusetts Institute of Technology, Penn State, Rice University, Rutgers University, California Institute of Technology and University of Minnesota.

MURI efforts involve teams of researchers investigating high-priority topics and opportunities that involve more than one technical area. This multidisciplinary approach often stimulates innovations, accelerates research progress and expedites transition of results into naval applications.

THE LAST "HOT SPELL" ON EARTH

Former dwellers in Pliocene seas: fossil coral found on modern-day Cyprus.

FROM: NATIONAL SCIENCE FOUNDATION

In Last Great Age of Warmth, Carbon Dioxide at Work...But Not Alone
Temperature patterns during Earth's last prolonged global "hot spell"--the Pliocene, some 5.3 to 2.6 million years ago--differed dramatically from those of modern times, according to results reported in this week's issue of the journal Nature.

Cloud feedbacks, ocean mixing and other factors must have played a greater role in Pliocene warming than previously recognized, and these must be accounted for to make meaningful predictions of Earth's future climate, the scientists said.

"This study shows that no one mechanism can explain all the observations," says Candace Major, a program director in the National Science Foundation's (NSF) Division of Ocean Sciences, which funded the research.

The data come from studies of the geochemistry of microfossils (microscopic shells of tiny plankton) preserved in deep-sea sediments.

The sediments were retrieved by researchers affiliated with the Deep Sea Drilling Project, the later Ocean Drilling Program and the current Integrated Ocean Drilling Program--all supported by NSF.

Yale University climate scientist Alexey Fedorov and colleagues compiled records of sea surface temperatures going back five million years, to the early Pliocene.

The records reveal a world with fairly uniform warm temperatures in the Tropics before four million years ago--a scenario that typical climate model simulations fail to show.

"If we want to understand our future climate, we have to be able to understand the climate of the past," said Fedorov, an author of this week's paper.

"The Pliocene Epoch attracts particular attention because of similar carbon dioxide levels to what we have had over the last few decades, but its climate was markedly different in several important ways," he said.

"If we're able to simulate early Pliocene climate, however, we will be more confident in our ability to predict future climate change."

Warm and temperate, the Pliocene is widely viewed as a potential analog for a future hot Earth.

Using chemical fingerprints in ocean sediments to estimate sea surface temperatures, the researchers describe long-term climate trends from the early Pliocene to the present, comparing that ancient climate with today's.

The Pliocene Earth had the same maximum temperature as today, and a similar concentration of atmospheric carbon dioxide, but waters in the Tropics--off the coast of Peru, for example--were much warmer than they are now, resembling modern El Niño conditions.

There was little to no east-to-west temperature variation along the equator. Temperature differences between high latitudes and the Tropics were also much smaller.

Kira Lawrence of Lafayette College, also an author of the paper, said that "we have been focused on changes in the global mean temperature. What our study demonstrates is the potential for climate patterns to be markedly different in a world that is not that much warmer than today's."

Previous attempts to explain Pliocene climate have emphasized tectonic changes in Indonesia and Central America.

But accounting for this in climate models still results in a conflict with actual temperature patterns.

The scientists have proposed several factors to explain warm temperatures during the Pliocene.

They include ocean mixing in subtropical waters, perhaps due to widespread hurricanes and diminished cloud reflectivity, maybe a result of a different aerosol composition. Both would tend to warm the ocean.

When combined in models with higher levels of carbon dioxide, they help replicate conditions of the warm Pliocene Earth.

But so far these factors have not been included in climate models used to make future projections, the researchers said.

A better understanding of what drove Pliocene climate, with its nearly uniform tropical ocean temperatures, will increase our confidence in the models, said Fedorov.

"We can't discount a possible future that has a vast pool of warm water covering the tropics, and the changes in atmospheric circulation and rainfall that would go along with that," said paper author Chris Brierley of the University College London.

Other authors include Zhonghui Liu of the University of Hong Kong, Petra Dekens of San Francisco State University and Christina Ravelo of University of California, Santa Cruz.

In addition to NSF, the research was supported by the U.S. Department of Energy, the David and Lucile Packard Foundation and Yale University.

-NSF-

RESEARCHERS STUDY BLUE MUSSELS AND OCEAN ACIDIFICATION

Photo:  Mussel.  Credit:  Wikimedia Commons

FROM: NATIONAL SCIENCE FOUNDATION
Blue Mussels 'Hang On' Along Rocky Shores: For How Long?

Imagine trying to pitch a tent in a stiff wind. You just have it secured, when a gale lifts the tent--stakes and all--and carries it away.

That's exactly what's happening to a species that's ubiquitous along the rocky shores of both the U.S. West and East Coasts: the blue mussel.

Mussels make use of what are called byssal threads--strong, silky fibers--to attach to rocks, pilings and other hard substrates. They produce the threads using byssus glands in their feet.

Now, scientists have discovered, the effects of ocean acidification are turning byssal threads into flimsy shadows of their former selves, leaving mussels tossed about by wind and waves.

At high levels of atmospheric carbon dioxide--levels in line with expected concentrations over the next century--byssal threads become weaker, less able to stretch and less able to attach to rocks, found scientists Emily Carrington, Michael O'Donnell and Matthew George of the University of Washington.

The researchers recently published their results in the journal Nature Climate Change; O'Donnell is the lead author.

Oceans turning caustic

The pH of the seas in which these and other marine species dwell is declining. The waters are turning more acidic (pH dropping) as Earth's oceans change in response to increased carbon dioxide in the atmosphere.

As atmospheric carbon rises as a result of human-caused carbon dioxide emissions, carbon in the ocean goes up in tandem, ultimately resulting in ocean acidification, scientists have found.

To study the effects of ocean acidification on marine organisms, Carrington has been awarded an NSF SEES (Science, Engineering, and Education for Sustainability) Ocean Acidification grant.

"We need to understand the chemistry of ocean acidification and its interplay with other marine processes--while Earth's seas are still hospitable to life as we know it," says David Garrison, program director in NSF's Division of Ocean Sciences. "In the rocky intertidal zone, blue mussels are at the heart of those processes."

Land between the tides

Visit the land between the tides, and you'll see waves crashing on boulders tinged dusky blue by snapped-closed mussels.

"Their shells are a soft color, the misty blue of distant mountain ranges," wrote Rachel Carson more than 50 years ago in her best-selling book The Edge of the Sea.

For blue mussels trying to survive, the rocky intertidal zone indeed may be akin to scaling a mountain range.

The rocky intertidal is above the waterline at low tide and underwater at high tide--the area between tide marks.

It's home to such animals as starfish and sea urchins, and seaweed such as kelp. All make a living from what floats by rocky cliffs and boulders.

It can be a hard go. Rocky intertidal species must adapt to an environment of harsh extremes. Water is available when the tide washes in; otherwise residents of this no man's land between sea and shore are wide open to the elements.

Waves can dislodge them, and temperatures can run from scalding hot to freezing cold.

Hanging on for dear life

In the rocky intertidal, blue mussels hang on for dear life.

That may not always be the case.

Combining results from laboratory experiments with those from a mathematical model, Carrington and colleagues show that at high carbon dioxide concentrations, blue mussels can be dislodged by wind and wave forces 40 percent lower than what they are able to withstand today.

Mussels with this weakened ability, once dislodged from their homes, could cause ecological shifts in the rocky intertidal zone--and huge economic losses in a global blue mussel aquaculture industry valued at U.S. $1.5 billion each year.

"Mussels are among the most important species on rocky shores worldwide," says O'Donnell, "dominating ecosystems wherever they live. The properties in their byssal threads are also of interest to biochemists and have been studied as possible medical adhesives."

Blue mussels may make important contributions to the field of materials science, says Carrington.

"Some species of mussels are experts at gluing onto seagrass, some to other shells, some even adhere to rocks in the harsh conditions of deep-sea hydrothermal vents. Each may have different genes that code for different proteins, so the adhesives vary."

Will their potential be realized? Carrington, O'Donnell and George have found a disturbing answer.

The scientists allowed mussels to secrete byssal threads in a range of ocean water chemistries from present-day through predicted near-future conditions, then tested the threads to see how strong they were.

At levels considered reasonable for a near-future coastal ocean (given current rates of acidification), byssal threads were less able to stretch and therefore less able to adhere. Further testing revealed that the problem was caused by weakening of the glue where the threads attach to rocks and other hard surfaces.

Ocean acidification beyond shells and corals

"Much ocean acidification research has focused on the process of calcification," says Carrington, "through which animals and some plants make hard parts such as shells."

In acidifying oceans, marine species that depend on calcium carbonate have a more difficult time forming shells or, in the case of coral reefs, skeletons.

"But there's more to marine communities than calcified parts," says O'Donnell. Other species such as mussels and their byssal threads, he says, are equally important.

"Understanding the broader consequences of ocean acidification requires looking at a variety of biological processes in a range of species."

A need that didn't exist when Rachel Carson wrote The Edge of the Sea.

"When we go down to the low-tide line, we enter a world that is as old as the Earth itself--the primeval meeting place," mused Carson, "of the elements of earth and water."

And of mussels and rock. Fifty years hence, will the mussels still be here?

THE MARTIAN ATMOSPHERE, GONE WITH THE WIND

FROM: NASA

Billions of years ago, Mars had a lot more air than it does today. (Note: Martian "air" is primarily carbon dioxide, not the nitrogen-oxygen mix we breathe on Earth.) Ancient martian lake-beds and river channels tell the tale of a planet covered by abundant water and wrapped in an atmosphere thick enough to prevent that water from evaporating into space. Some researchers believe the atmosphere of Mars was once as thick as Earth's. Today, however, all those lakes and rivers are dry and the atmospheric pressure on Mars is only 1% that of Earth at sea-level. A cup of water placed almost anywhere on the Martian surface would quickly and violently boil away—a result of the super-low air pressure.

 

Mars Atmosphere Loss

This video illustration shows how Mars may have lost its atmosphere to the solar wind after the Red Planet's magnetic field died.