A new pathway for methane production has been uncovered in the oceans, and this has a significant potential impact for the study of greenhouse gas production on our planet. The article, published in the journal Nature Geoscience, reveals that aerobic decomposition of an organic, phosphorus-containing compound, methylphosphonate, may be responsible for the supersaturation of methane in ocean surface waters.

Methane is a more potent greenhouse gas than CO₂ on a per weight basis. Although the volume of methane in the atmosphere is considerably less than CO₂, methane is much more efficient at trapping the long wavelength radiation that keeps our planet habitable but is also responsible for enhanced greenhouse warming. Today, between 20-30% of the total radiative forcing of the atmosphere is due to methane. Terrestrial sources of methane production are well known and studied (including extraction from natural gas deposits and fermentation of organic matter), but those known sources did not account for the levels of methane observed in the atmosphere.

David Karl, an Oceanographer in the School of Ocean and Earth Science and Technology at the University of Hawai’i at Mânoa and lead author of this paper, was interested in this “methane enigma” and why the surface ocean was loaded with methane, over and above levels found in the atmosphere. When looking at the literature, Karl found a possible solution to the enigma, in the compound methylphosphonates, a very unusual organic compound only discovered in the 1960s. In the laboratory, the aerobic growth of certain bacteria on methylphosphonate can lead to the production of methane, but until now this process of methylphosphonate degradation in the ocean had not been suggested as a possible pathway for the aerobic production of methane in the sea.

“When people began measuring methane in the ocean, they found that methane concentrations varied with geographical location and with water depth”, says Karl. “If methane was inert in the ocean, its concentration should be constant and nearly equal to the concentration in the atmosphere. What the scientists found was that methane was lower than expected in deep waters, implying net consumption by microbes. However the big surprise was that near surface concentrations were higher than in the overlying atmosphere which indicated a local production of methane in the sea. Because methane is produced only in regions devoid of oxygen and since the surface ocean contains high oxygen levels this was very perplexing.”

Karl was able to combine a long term interest in methane, 20 years of ocean observing data at the Hawaii Ocean Timeseries site Station Aloha, and new technology that Massachusetts Institute of Technology co-author Edward DeLong and colleagues have developed to produce methane in aerobic marine environments. “I think this work nicely demonstrates the complementarity of different methods and approaches, which include oceanography, microbial ecology, and genomics techniques,” says DeLong. “In the case of genomics, the growing databases of marine microbial genomic and metagenomic data have great potential to help us link which organisms, and which genes, are responsible for driving important nutrient and elemental cycles in the sea, like aerobic methane generation.

With our colleagues at the Center for Microbial Oceanography: Research and Education (C-MORE, of which Karl is the Director, and DeLong the Co-Director), we plan next to learn how and when microbial communities turn on and off their methane production genes, in response to the methane precursors, like methylphosphonate, in their natural environment. This should provide new insights about the ‘who’ and the ‘how’ of this newly discovered methane generating process in the sea.”

Although the implications for global climate change are still being studied, the warming and further stratification of the ocean seem likely to affect marine methane production. “This is a newly recognized pathway of methane formation that needs to be incorporated into our thinking of global climate,” says Karl. “Since our oceans cover ¾ of the planet, you just need to stimulate this pathway a little bit and you’re going to create more methane. And one way you can tweak it is to stratify the oceans, which we know will happen. All of the climate models show that the ocean will become more nutrient limited over time.”

Phil Taylor, Acting Head of the Ocean Section, Division of Ocean Sciences at the National Science Foundation (NSF) agrees. “This remarkable discovery about methane production where we thought there would be none is a harbinger of many new insights on the ocean’s changing biogeochemical nature, and the intricate microbiological reasons for those changes.”

Interest in this research crosses many specialties. Oceanographers will be excited because it offers a solution to the long standing methane paradox. Microbiologists will be excited because it shows an aerobic production pathway of methane, which goes against everything that is currently known about methane, and Climatologists will be interested because it’s a potent greenhouse gas that we don’t have constraints on, and this new pathway is very exciting.

“NSF funded C-MORE with the hope that its scientists would make new discoveries about the vast genomic diversity and complexity in the microbial world, and its impacts from cellular to global scales,” says Matt Kane, Program Director for the NSF Division of Environmental Biology. “These findings are an example of the payoffs that come from an interdisciplinary and integrative approach to microbial oceanography.”

This research was supported by the Gordon and Betty Moore Foundation and the National Science Foundation.

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Scientists have argued about the origins of Mercury’s smooth plains and the source of its magnetic field for more than 30 years. Now, analysis of data from the January 2008 flyby of the planet by the Mercury Surface, Space Environment, Geochemistry and Ranging (MESSENGER) spacecraft have shown that volcanoes were involved in plains formation and suggest that its magnetic field is actively produced in the planet’s core.

Scientists additionally took their first look at the chemical composition of the planet’s surface. The tiny craft probed the composition of Mercury’s thin atmosphere, sampled charged particles (ions) near the planet, and demonstrated new links between both sets of observations and materials on Mercury’s surface. The results are reported in a series of 11 papers published in a special section of Science magazine July 4.

The controversy over the origin of Mercury’s smooth plains began with the 1972 Apollo 16 moon mission, which suggested that some lunar plains came from material that was ejected by large impacts and then formed smooth “ponds.” When Mariner 10 imaged similar formations on Mercury in 1975, some scientists believed that the same processes were at work. Others thought Mercury’s plains material came from erupted lavas, but the absence of volcanic vents or other volcanic features in images from that mission prevented a consensus.

Six of the papers in Science report on analyses of the planet’s surface through its reflectance and color variation, surface chemistry, high-resolution imaging at different wavelengths, and altitude measurements. The researchers found evidence of volcanic vents along the margins of the Caloris basin, one of the solar system’s youngest impact basins. They also found that Caloris has a much more complicated geologic history than previously believed.

The first altitude measurements from any spacecraft at Mercury also found that craters on the planet are about a factor of two shallower than those on Earth’s moon. The measurements also show a complex geologic history for Mercury.

Mercury’s core makes up at least 60 percent of its mass, a figure twice as large as any other known terrestrial planet. The flyby revealed that the magnetic field, originating in the outer core and powered by core cooling, drives very dynamic and complex interactions among the planet’s interior, surface, exosphere and magnetosphere.

Remarking on the importance of the core to surface geological structures, Principal Investigator Sean Solomon at the Carnegie Institution of Washington said, “The dominant tectonic landforms on Mercury, including areas imaged for the first time by MESSENGER, are features called lobate scarps, huge cliffs that mark the tops of crustal faults that formed during the contraction of the surrounding area. They tell us how important the cooling core has been to the evolution of the surface. After the end of the period of heavy bombardment, cooling of the planet’s core not only fueled the magnetic dynamo, it also led to contraction of the entire planet. And the data from the flyby indicate that the total contraction is a least one-third greater than we previously thought.”

The flyby also made the first-ever observations of the ionized particles in Mercury’s unique exosphere. The exosphere is an ultrathin atmosphere in which the molecules are so far apart they are more likely to collide with the surface than with each other. The planet’s highly elliptical orbit, its slow rotation and particle interactions with the magnetosphere, interplanetary medium and solar wind result in strong seasonal and day-night differences in the way particles behave.

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The ESA/NASA SOHO spacecraft has just discovered its 1500th comet, making it more successful than all other comet discoverers throughout history put together. Not bad for a spacecraft that was designed as a solar physics mission.

SOHO’s record-breaking discovery was made on 25 June. The small and faint Kreutz-group comet was discovered by US-based veteran comet hunter and amateur astronomer Rob Matson.

Kreutz-group comets, or sungrazing comets have been observed for many hundreds of years. They travel very close to the Sun (if they were to hit it, they would become ’sunstrikers’), with perihelion distance less than 0.01 Astronomical Units (the mean distance between the Earth and the Sun), or some 1460000 km.

When it comes to comet catching, the SOlar and Heliospheric Observatory has one big advantage over everybody else: its location. Situated between the Sun and Earth, it has a privileged view of a region of space that can rarely be seen from Earth. From the surface, we can see regions close to the Sun clearly only during an eclipse.

Roughly 85% of SOHO discoveries are fragments from a once-great comet that split apart in a death plunge around the Sun, probably many centuries ago. The fragments are known as the Kreutz group and now pass within 1.5 million km of the Sun’s surface when they return from deep space.

At this proximity, which is a near miss in celestial terms, most of the fragments are finally destroyed, evaporated by the Sun’s fearsome radiation – within sight of SOHO’s electronic eyes. The images are captured by the Large Angle and Spectrometric Coronograph (LASCO), one of 12 instruments on board.

Of course, LASCO itself does not make the detections; that task falls to an open group of highly-skilled volunteers who scan the data as soon as it is downloaded to Earth. Once SOHO transmits to Earth, the data can be on the Internet and ready for analysis within 15 minutes.

Enthusiasts from all over the world look at each individual image for a tiny moving speck that could be a comet. When someone believes they have found one, they submit their results to Karl Battams at the Naval Research Laboratory, Washington DC, who checks all of SOHO’s findings before submitting them to the Minor Planet Center, where the comet is catalogued and its orbit calculated.

The wealth of comet information has value beyond mere classification. “This is allowing us to see how comets die,” says Battams. When a comet constantly circles the Sun, it loses a little more ice each time, until it eventually falls to pieces, leaving a long trail of fragments. Thanks to SOHO, astronomers now have a plethora of images showing this process. “It’s a unique data set and could not have been achieved in any other way,” says Battams.

All this is on top of the extraordinary revelations that SOHO has provided over the 13 years it has been in space, observing the Sun and the near-Sun environment. “Catching the enormous total of comets has been an unplanned bonus,” says Bernhard Fleck, ESA SOHO Project Scientist.

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