AGU journal highlights -- 31 August 2012

(Press-News.org) The following highlights summarize research papers that have been recently published in Geophysical Research Letters (GRL), Journal of Geophysical Research - Biogeosciences (JGR-G), Journal of Geophysical Research - Atmospheres (JGR-D), Water Resources Research (WRR), and Space Weather (SW).

In this release:

1. Trade-offs between water for food and for curbing climate change 2. Low calcification in corals in the Great Barrier Reef 3. The Everglades still threatened by excess nutrients 4. Wetlands the primary source of Amazon Basin methane 5. Old fractures caused rare 8.6 magnitude earthquake 6. Solar storms can destabilize power grids at midlatitudes

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1. Trade-offs between water for food and for curbing climate change

Earth's growing human population needs fresh water for drinking and food production. However, fresh water is also needed for the growth of biomass, which acts as a sink of carbon dioxide and thus could help mitigate climate change. Does the Earth have enough freshwater resources to meet these competing demands?

Rockstrom et al. estimate the order of magnitude of freshwater consumption needed to feed a population of 9 billion people by 2050 and the amount of water needed to realize the planet's full biomass carbon sequestration potential. They analyze these uses of freshwater in a framework of "planetary boundaries" within which the Earth system is resilient; beyond the boundaries, abrupt and irreversible change could take place. For instance, river ecosystems can collapse if water levels become too low due to water withdrawal for human uses.

On a global level, they find that achieving global food security and maximizing carbon sequestration together would require increasing water consumption by 3,250 cubic kilometers (780 cubic miles) per year. Combined with the current use of 2,600 cubic kilometers (624 cubic miles) per year, this would be above the safe planetary boundary level of about 5,000 cubic kilometers (1,200 cubic miles) per year.

They stress the need for societies to recognize the trade-offs between using water for food production and for increasing carbon sequestration through biomass. They conclude that since food production is essential, large-scale carbon sequestration through increasing biomass might not be realistic as a major mode of climate change mitigation.

Source: Geophysical Research Letters, doi: 10.1029/2012GL051688
http://dx.doi.org/10.1029/2012GL051688

Title: The planetary water drama: Dual task of feeding humanity and curbing climate change

Authors: J. Rockstrom: Stockholm Resilience Centre, Stockholm University, Stockholm, Sweden;

M. Falkenmark: Stockholm Resilience Centre, Stockholm University, Stockholm, Sweden, Stockholm International Water Institute, Stockholm, Sweden;

M. Lannerstad: Stockholm Environment Institute, Stockholm, Sweden;

L. Karlberg: Stockholm Resilience Centre, Stockholm University, Stockholm, Sweden, Stockholm Environment Institute, Stockholm, Sweden.

2. Low calcification in corals in the Great Barrier Reef

Reef-building coral communities in the Great Barrier Reef-the world's largest coral reef-may now be calcifying at only about half the rate that they did during the 1970s, although live coral cover may not have changed over the past 40 years, a new study finds. In recent decades, coral reefs around the world, home to large numbers of fish and other marine species, have been threatened by human activities such as pollution, overfishing, global warming, and ocean acidification; the latter affects ambient water chemistry and availability of calcium ions, which are critical for coral communities to calcify, build, and maintain reefs.

Comparing data from reef surveys during the 1970s, 1980s, and 1990s with present-day (2009) measurements of calcification rates in One Tree Island, a coral reef covering 13 square kilometers (5 square miles) in the southern part of the Great Barrier Reef, Silverman et al. show that the total calcification rates, i.e., the rate of calcification minus the rate of dissolution, in these coral communities have decreased by 44 percent over the past 40 years; the decrease appears to stem from a threefold reduction in calcification rates during nighttime.

The authors suggest that reduced calcification, particularly during nighttime, could be caused by boring and other erosional activities brought about by a change in the type or the number of boring organisms (e.g., sea cucumbers) that live on these coral reefs. Another possibility is that warming water temperatures and ocean acidification could be causing increased dissolution of coral reefs over the past 40 years. The study is consistent with previous estimates and predictions of reduced calcification rates of coral communities in the Great Barrier Reef.

Source: Journal of Geophysical Research - Biogeosciences, doi:10.1029/2012JG001974, 2012
http://dx.doi.org/10.1029/2012JG001974

Title: Carbon turnover rates in the One Tree Island reef: A 40 year perspective

Authors: Jacob Silverman: Institute for Oceanographic and Limnological Research, Haifa, Israel;

David Kline: Scripps Institution of Oceanography, University of California San Diego, La Jolla, California, USA;

Leah Johnson: School of Oceanography, University of Washington, Seattle, Washington, USA;

Tanya Rivlin: The H. Steinitz Marine Biology Laboratory, The Interuniversity Institute for Marine Sciences, The Hebrew University of Jerusalem, Eilat, Israel;

Kenneth Schneider: Department of Global Ecology, Carnegie Institution for Science, Stanford, California, USA;

Jonathan Erez: The Fredy and Nadine Herrman Institute of Earth Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel;

Boaz Lazar: The Fredy and Nadine Herrman Institute of Earth Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel;

Ken Caldeira: Department of Global Ecology, Carnegie Institution for Science, Stanford, California, USA.

3. The Everglades still threatened by excess nutrients

Since 1985, a state agency has constructed and continues to maintain hundreds of square kilometers of wetlands built to regulate the amount of nutrients reaching the Everglades in southern Florida. But this is proving to be ineffective in controlling concentrations of phosphorous, a key nutrient, in the surface waters of the wetland, a new study by Zapata-Rios et al. shows. Historically, the Everglades have been a nutrient-poor environment, a characteristic that determines the delicate ecological balance and distinct flora and fauna in this region.

Agricultural development and urbanization since the 1800s have not only claimed two-thirds of the natural Everglades (only 6,000 square kilometers (2,300 square miles) now exist in their natural form) but have also dramatically increased phosphorus levels in surface water, at times exceeding the acceptable limit of 10 micrograms per liter by severalfold.

Using a database containing more than 360,000 individual measurements of water quality from various sources between 1985 and 2007, the authors demonstrate that over the long term (about 13 years), phosphorus levels in surface waters have decreased by 5 percent during the dry season in several protected areas, as well as in Everglades National Park. Yet on shorter timescales (approximately 4 to 5 years), the levels continue to increase in Everglades National Park. In fact, the highest phosphorus concentrations were in the dry and wet seasons of 1999 and 2003, when levels reached 200 micrograms per liter. In 65 percent of the natural Everglades, phosphorus levels in surface water remain above 10 micrograms per liter. The study shows that measures undertaken thus far have been insufficient in regulating phosphorus and nutrient levels in the surface waters of the Everglades. The authors emphasize the need to further increase the area of constructed wetlands that help regulate nutrient flow into the Everglades.

Source: Water Resources Research, doi:10.1029/2011WR011421
http://dx.doi.org/10.1029/2011WR011421

Title: Spatial and temporal phosphorus distribution changes in a large wetland ecosystem

Authors: Xavier Zapata-Rios, Rosanna G. Rivero, Ghinwa M. Naja: Everglades Foundation, Science Department, Palmetto Bay, Florida;

Pierre Goovaerts: BioMedware, Inc. Ann Arbor, Michigan.

4. Wetlands the primary source of Amazon Basin methane

The Amazon basin is an important sink of carbon dioxide, but it is also a substantial source of atmospheric methane. Tropical wetlands, including those in the Amazon, are one of the largest sources of biogenic methane and globally represent roughly 13 percent of annual emissions of the greenhouse gas. Other sources of methane include fossil fuel or biomass burning. Through two intensive atmospheric methane sampling campaigns, Beck et al. determine the sources of Amazonian methane.

During 27 flights split between November 2008 and May 2009 the authors measured 150 vertical profiles of the atmospheric methane concentration, spanning 500 to 4,000 meters (roughly 1,600 to 13,000 feet) altitude. During both sets of flights they collected atmospheric samples, and during the 2009 flights they also produced the first continuous measurement of Amazon basin methane, accurate to within 2 parts per billion and sampled at three-second intervals. Using isotopic analyses of the collected gas samples, the authors find that Amazon basin methane is predominantly biogenic. Based on carbon monoxide measurements made concurrently with the methane observations, they calculate that biomass burning was not a major contributor to methane emissions.

They find that wetlands were the primary source of methane. However, they note that other biogenic sources, such as waste decomposition or sewage and cattle operations, could easily be confused with wetland emissions. The authors note that their two airborne campaigns are not enough on which to base an assessment of the Amazon's annual methane emissions.

Source: Journal of Geophysical Research - Atmospheres, doi:10.1029/2011JD017345, 2012 http://dx.doi.org/10.1029/2011JD017345

Title: Methane airborne measurements and comparison to global models during BARCA

Authors: Veronika Beck, Christoph Gerbig, Olaf Kolle, and Thomas Koch: Max Planck Institute for Biogeochemistry, Jena, Germany;

Peter Bergamaschi: European Commission, Joint Research Centre, Institute for Environment and Sustainability, Ispra, Italy;

Huilin Chen, Lori Bruhwiler: National Oceanic and Atmospheric Administration, Boulder, CO, USA;

Sander Houweling: Institute for Marine and Atmospheric Research Utrecht, Utrecht University, Utrecht, Netherlands and SRON Netherlands Institute for Space Research, Utrecht, Netherlands;

Thomas Rockmann, Celia J. Sapart, Carina van der Veen: Institute for Marine and Atmospheric Research Utrecht, Utrecht University, Utrecht, Netherlands;

Christian Frankenberg: Jet Propulsion Laboratory, California Institute of Technology, Pasadena, USA;

Meinrat O. Andreae: Max Planck Institute for Chemistry, Mainz, Germany;

Julia Steinbach: Department of Applied Environmental Science, Stockholm University, Stockholm, Sweden;

Paulo Artaxo: University Sao Paulo, Sao Paulo, Brazil;

Karla M. Longo: Center for Earth System Science (CCST), National Institute for Space Research (INPE), Sao Jose dos Campos, Brazil;

Steven C. Wofsy: Harvard University, Cambridge, MA, United States.

5. Old fractures caused rare 8.6 magnitude earthquake

On 11 April 2012, an 8.6 magnitude earthquake occurred 100 kilometers (62 miles) off the coast of Sumatra. This earthquake was unusual in that it originated within the plate rather than at a plate boundary. In fact, it is the largest such earthquake in observed human history. The quake originated under the Wharton Basin in the Indian Ocean, where hundreds of kilometers of rock were under crushing tension, causing the plate to deform at its base. But this deforming zone was also absorbing tension as two plates, the Indian and Australian plates, rotated toward each other.

One month after the earthquake, Satriano et al. revisited the Wharton Basin to reconstruct the rupture history of the events of 11 April to gain a better understanding of the general nature of these rare large within-plate earthquakes. They used a comparatively new tool known as back projection analysis, which tracks radiation that emanates as new locations along a rupture path become active.

Calibrating the back projection analysis with aftershocks, which scientists use to calculate the travel time and distance of seismic P and S waves that originate at the epicenter, the authors find that the events of 11 April had their roots in the old fabric of the Wharton Basin, the floor of which is littered with old fractures. Tension deep within the deformation zone had reactivated one of the north-south aligned fractures. That rupture in turn triggered a series of ruptures of old fractures, generating a slew of strike-slip faulting that traveled westward and ended at the Ninety East Ridge, the north-south oriented seamount chain that bounds the basin, 370 kilometers (230 miles) from the epicenter and 120 seconds later-the timing of the last rupture event.

Source: Geophysical Research Letters, doi:10.1029/2012GL052387, 2012 http://dx.doi.org/10.1029/2012GL052387

Title: The 2012 Mw 8.6 Sumatra earthquake: Evidence of westward sequential seismic ruptures associated to the reactivation of a N-S ocean fabric

Authors: Claudio Satriano, Eszter Kiraly, Pascal Bernard, and Jean-Pierre Vilotte: Institut de Physique du Globe de Paris, Sorbonne Paris Cite, Universite Paris Diderot, UMR CNRS 7154, Paris, France.

6. Solar storms can destabilize power grids at midlatitudes

The Sun is capable of disrupting electrical systems on Earth in a variety of ways, from solar flares and coronal mass ejections to proton storms. Typically, it is only objects far above the Earth's surface, or systems at high altitudes at polar latitudes, that are considered at risk except during the most powerful storms. Notable recent examples include solar activity during March 1989 and October 2003 (the "Halloween Storms"), which knocked out power in Quebec, Canada, and Sweden, respectively. Research by Marshall et al., however, finds that even a moderate event can have destructive effects far from the typical regions of concern.

At 1:20 UT on 6 November 2001, a high-density pocket of solar wind, 18 nanoPascals above the background pressure, sped past the Solar and Heliospheric Observatory (SOHO) satellite, which was orbiting 197 Earth radii above the Earth toward the Sun. In half an hour, this high-pressure wave traveled more than a million kilometers (620,000 miles) to the Earth's magnetopause. The high- pressure pulse induced currents both in the magnetopause and in power lines across New Zealand, causing alarms to be tripped and a transformer to fail catastrophically. Extending from 35 degrees South to 46 degrees South, New Zealand is typically considered outside the region susceptible to such solar activity. A Northern Hemisphere equivalent would be a zone extending from Maine to North Carolina. The authors find currents of up to 27.4 amperes in transformer earth lines that were supposed to be neutral. For comparison, the Halloween Storms 2 years later caused peak currents of 23.4 amperes and no serious damage, though the authors suggest that this may have been due to damage prevention measures implemented following the 2001 event.

Source: Space Weather, doi: 10.1029/2012SW000806, 2012 http://dx.doi.org/10.1029/2012SW000806

Title: Geomagnetically Induced Currents in the New Zealand Power Network

Authors: R.A. Marshall: IPS Radio and Space Services, Bureau of Meteorology, Sydney, New South Wales, Australia;

M. Dalzell: Transpower New Zealand Limited, New Zealand;

C.L. Waters and P. Goldthorpe: School of Mathematical and Physical Sciences, University of Newcastle, Australia;

E.A. Smith: Defence Science and Technology Organisation, Edinburgh, South Australia, Australia.

Contact: Mary Catherine Adams
Phone (direct): +1 202 777 7530
Email: mcadams@agu.org ###