Texas drought visible in new national groundwater maps

ScienceDaily (Nov. 30, 2011) — The record-breaking drought in Texas that has fueled wildfires, decimated crops and forced cattle sales has also reduced levels of groundwater in much of the state to the lowest levels seen in more than 60 years, according to new national maps produced by NASA and distributed by the National Drought Mitigation Center at the University of Nebraska-Lincoln.

The latest groundwater map, released on Nov. 29, shows large patches of maroon over eastern Texas, indicating severely depressed groundwater levels. The maps, generated weekly by NASA's Goddard Space Flight Center in Greenbelt, Md., are publicly available on the Drought Center's website.

"Texas groundwater will take months or longer to recharge," said Matt Rodell, a hydrologist based at Goddard. "Even if we have a major rainfall event, most of the water runs off. It takes a longer period of sustained greater-than-average precipitation to recharge aquifers significantly."

The maps are based on data from NASA's Gravity Recovery and Climate Experiment (GRACE) satellites, which detect small changes in Earth's gravity field caused primarily by the redistribution of water on and beneath the land surface. The paired satellites travel about 137 miles (220 km) apart and record small changes in the distance separating them as they encounter variations in Earth's gravitational field.

To make the maps, scientists used a sophisticated computer model that combines measurements of water storage from GRACE with a long-term meteorological dataset to generate a continuous record of soil moisture and groundwater that stretches back to 1948. GRACE data goes back to 2002. The meteorological data include precipitation, temperature, solar radiation and other ground- and space-based measurements.

The color-coded maps show how much water is stored now as a probability of occurrence in the 63-year record. The maroon shading over eastern Texas, for example, shows that the level of dryness over the last week occurred less than two percent of the time between 1948 and the present.

The groundwater maps aren't the only maps based on GRACE data that the Drought Center publishes each week. The Drought Center also distributes soil moisture maps that show moisture changes in the root zone down to about 3 feet (1 meter) below the surface, as well as surface soil moisture maps that show changes within the top inch (2 cm) of the land.

"All of these maps offer policymakers new information into subsurface water fluctuations at regional to national scales that has not been available in the past," said the Drought Center's Brian Wardlow. The maps provide finer resolution or are more consistently available than other similar sources of information, and having the maps for the three different levels should help decision makers distinguish between short-term and long-term droughts.

"These maps would be impossible to generate using only ground-based observations," said Rodell. "There are groundwater wells all around the United States and the U.S. Geological Survey does keep records from some of those wells, but it's not spatially continuous and there are some big gaps."

The maps also offer farmers, ranchers, water resource managers and even individual homeowners a new tool to monitor the health of critical groundwater resources. "People rely on groundwater for irrigation, for domestic water supply, and for industrial uses, but there's little information available on regional to national scales on groundwater storage variability and how that has responded to a drought," Rodell said. "Over a long-term dry period there will be an effect on groundwater storage and groundwater levels. It's going to drop quite a bit, people's wells could dry out, and it takes time to recover."

The maps are the result of a NASA-funded project at the Drought Center and NASA Goddard to make it easier for the weekly U.S. Drought Monitor to incorporate data from the GRACE satellites. NASA's Jet Propulsion Laboratory, Pasadena, Calif., developed GRACE and manages the mission for NASA. The groundwater and soil moisture maps are updated each Tuesday.

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Is it Alzheimer's disease or another dementia? Marker may give more accurate diagnosis

ScienceDaily (Nov. 30, 2011) — New research finds a marker used to detect plaque in the brain may help doctors make a more accurate diagnosis between two common types of dementia -- Alzheimer's disease and frontotemporal lobar degeneration (FTLD). The study is published in the November 30, 2011, online issue of Neurology®, the medical journal of the American Academy of Neurology.

"These two types of dementia share similar symptoms, so telling the two apart while a person is living is a real challenge, but important so doctors can determine the best form of treatment," said study author Gil D. Rabinovici, MD, of the University of California San Francisco Memory and Aging Center and a member of the American Academy of Neurology.

For the study, 107 people with early onset Alzheimer's disease or FTLD underwent a brain PET scan using a PIB marker, which detects amyloid or plaque in the brain that is the hallmark of Alzheimer's disease but not related to FTLD. The participants underwent another PET scan using a FDG marker, which detects changes in the brain's metabolism and is currently used to help differentiate between the two types of dementia.

The study found the PIB PET scan performed at least as well as the FDG PET scan in differentiating between Alzheimer's disease and FTLD, but had higher sensitivity and better accuracy and precision with its qualitative readings. The study found PIB had a sensitivity of 89.5 percent compared to 77.5 percent for FDG.

"While widespread use of PIB PET scans isn't available at this time, similar amyloid markers are being developed for clinical use, and these findings support a role for amyloid imaging in correctly diagnosing Alzheimer's disease versus FTLD," said Rabinovici.

The study was conducted at the University of California (UC) San Francisco, UC Berkeley and Lawrence Berkeley National Laboratory, and supported by the National Institute on Aging, the California Department of Health Services, the Alzheimer's Association, John Douglas French Alzheimer's Foundation and the Consortium for Frontotemporal Dementia Research.

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Chemical warfare of stealthy silverfish: Parasites hide by covering themselves in ants' scent

ScienceDaily (Nov. 30, 2011) — A co-evolutionary arms race exists between social insects and their parasites. Army ants (Leptogenys distinguenda) share their nests with several parasites such as beetles, snails and spiders. They also share their food with the kleptoparasitic silverfish (Malayatelura ponerophila). New research published in BioMed Central's open access journal BMC Ecology shows that the silverfish manage to hide amongst the ants by covering themselves in the ant's chemical scent.

Myrmecophilous (ant-loving) silverfish live their lives in and amongst army ants. To avoid being killed or rejected from the nest the silverfish must be able to somehow persuade the ants to believe that they are not invaders. These ants have limited eyesight and live in a world of chemical cues, recognizing their colony members by scent. Christoph von Beeren and Volker Witte from the Ludwig Maximilian University, Munich, collected L. distinguenda ants and M. ponerophila silverfish from the tropical rainforests of Ulu Gombak, Malaysia and found that, while the ants had 70 distinct hydrocarbon compounds on their cuticles, silverfish had none that are distinct for them. Instead, they carried the host colony scent, a phenomenon known as chemical mimicry.

By tracking the transfer of tagged hydrocarbon from host ants to silverfish, it became apparent that the latter pilfered their host's scent, preferably by rubbing against defenseless 'callows' (immature ants). To avoid ant aggression silverfish must continually top-up this scent. Isolating silverfish from the colony resulted in them losing their protective scent and being targeted for chasing, seizing and biting by worker ants, sometimes resulting in their death.

Prof. Witte explained, "It seems that silverfish and ants are engaged in a co-evolutionary arms race. The ants have equipped themselves with a complicated scent recognition system to safeguard their nest from predators and parasites. While the ants were developing their nest protection strategy the silverfish evolved elaborate behavioral patterns, pilfering the hosts own recognition cues, to outwit the ant's chemical defenses. Consequently, the silverfish have access to food and shelter in the inner part of the ants nest without giving anything in return."

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Christoph von Beeren, Stefan Schulz, Rosli Hashim, Volker Witte. Acquisition of chemical recognition cues facilitates integration into ant societies. BMC Ecology, 2011; (in press) [link]

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Climate change may happen more quickly than expected

ScienceDaily (Nov. 30, 2011) — As global temperatures continue to rise at an accelerated rate due to deforestation and the burning of fossil fuels, natural stores of carbon in the Arctic are cause for serious concern, researchers say.

In an article scheduled to be published Dec. 1 in the journal Nature, a survey of 41 international experts led by University of Florida ecologist Edward Schuur shows models created to estimate global warming may have underestimated the magnitude of carbon emissions from permafrost over the next century. Its effect on climate change is projected to be 2.5 times greater than models predicted, partly because of the amount of methane released in permafrost, or frozen soil.

"We're talking about carbon that's in soil, just like in your garden where there's compost containing carbon slowly breaking down, but in permafrost it's almost stopped because the soil is frozen," Schuur said. "As that soil warms up, that carbon can be broken down by bacteria and fungi, and as they metabolize, they are releasing carbon and methane, greenhouse gases that cause warmer temperatures."

As a result of plant and animal remains decomposing for thousands of years, organic carbon in the permafrost zone is distributed across 11.7 million square miles of land, an amount that is more than three times larger than previously estimated. The new number is mainly based on evidence the carbon is stored much deeper as the result of observations, soil measurements and experiments.

"We know the models are not yet giving us the right answer -- it's going to take time and development to make those better, and that process is not finished yet," Schuur said. "It's an interesting exercise in watching how scientists, who are very cautious in their training, make hypotheses about what our future will look like. The numbers are significant, and they appear like they are plausible and they are large enough for significant concern, because if climate change goes 20 or 30 percent faster that we had predicted already, that's a pretty big boost."

The survey, which was completed following a National Science Foundation-funded Permafrost Carbon Network workshop about six months ago, proposed four warming scenarios until 2040, 2100 and 2300. Researchers were asked to predict the amount of permafrost likely to thaw, how much carbon would be released, and what amount would be methane, which has much more warming potential than carbon dioxide.

The occurrence of carbon in northern soils is natural and the chemical does not have an effect on climate if it remains underground, but when released as a greenhouse gas it can add to climate warming. However, humans could slow warming temperatures as the result of greenhouse gas emissions from deforestation and the burning of fossil fuels, which are what speed up the process of permafrost thaw.

"Even though we're talking about a place that is very far away and seems to be out of our control, we actually have influence over what happens based on the overall trajectory of warming. If we followed a lower trajectory of warming based on controlling emissions from the burning of fossil fuels, it has the effect of slowing the whole process down and keeping a lot more carbon in the ground," Schuur said. "Just by addressing the source of emissions that are from humans, we have this potential to just keep everything closer to its current state, frozen in permafrost, rather than going into the atmosphere."

The survey shows that by 2100, experts believe the amount of carbon released will be 1.7 to 5.2 times greater than previous models predict, under scenarios where Arctic temperatures rise 13.5 degrees Fahrenheit. Some predicted effects of global warming include sea level rise, loss of biodiversity as some organisms are unable to migrate as quickly as the climate shifts and more extreme weather events that could affect food supply and water resources.

"This new research shows that the unmanaged part of the biosphere has a major role in determining the future trajectory of climate change," said Stanford University biology professor Christopher Field, who was not involved in the study. "The implication is sobering. Whatever target we set for atmospheric CO2, this new research means we will need to work harder to reach it. But of course, limiting the amount of climate change also decreases the climate damage from permafrost melting."

When carbon is released from the ground as a result of thawing permafrost, there is no way of trapping the gases at the source, so action to slow its effect must be taken beforehand.

"If you think about fossil fuel and deforestation, those are things people are doing, so presumably if you had enough will, you could change your laws and adjust your society to slow some of that down," Schuur said. "But when carbon starts being emitted from the permafrost, you can't immediately say, 'OK, we've had enough of this, let's just stop doing it,' because it's a natural cycle emitting carbon whether you like it or not. Once we start pushing it, it's going to be releasing under its own dynamic."

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The above story is reprinted from materials provided by University of Florida. The original article was written by Danielle Torrent.

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Journal Reference:

Edward A. G. Schuur, Benjamin Abbott. Climate change: High risk of permafrost thaw. Nature, 2011; 480 (7375): 32 DOI: 10.1038/480032a

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Earthquakes: Water as a lubricant

ScienceDaily (Nov. 30, 2011) — Geophysicists from Potsdam have established a mode of action that can explain the irregular distribution of strong earthquakes at the San Andreas Fault in California. As the science magazine "Nature" reports in its latest issue, the scientists examined the electrical conductivity of the rocks at great depths, which is closely related to the water content within the rocks. From the pattern of electrical conductivity and seismic activity they were able to deduce that rock water acts as a lubricant.

Los Angeles moves toward San Francisco at a pace of about six centimeters per year, because the Pacific plate with Los Angeles is moving northward, parallel to the North American plate which hosts San Francisco. But this is only the average value. In some areas, movement along the fault is almost continuous, while other segments are locked until they shift abruptly several meters against each other releasing energy in strong earthquakes. After the San Francisco earthquake of 1906, the plates had moved by six meters.

The San Andreas Fault acts like a seam of the Earth, ranging through the entire crust and reaching into the mantle. Geophysicists from the GFZ German Research Centre for Geosciences have succeeded in imaging this interface to great depths and to establish a connection between processes at depth and events at surface. "When examining the image of the electrical conductivity, it becomes clear that rock water from depths of the upper mantle, i.e. between 20 to 40 km, can penetrate the shallow areas of the creeping section of the fault, while these fluids are detained in other areas beneath an impermeable layer," says Dr. Oliver Ritter of the GFZ. "A sliding of the plates is supported, where fluids can rise."

These results suggest that significant differences exist in the mechanical and material properties along the fault at depth. The so-called tremor signals, for instance, appear to be linked to areas underneath the San Andreas Fault, where fluids are trapped. Tremors are low-frequency vibrations that are not associated with rupture processes as they are typical of normal earthquakes. These observations support the idea that fluids play an important role in the onset of earthquakes.

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The above story is reprinted from materials provided by Helmholtz Centre Potsdam - GFZ German Research Centre for Geosciences.

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Michael Becken, Oliver Ritter, Paul A. Bedrosian, Ute Weckmann. Correlation between deep fluids, tremor and creep along the central San Andreas fault. Nature, 2011; 480 (7375): 87 DOI: 10.1038/nature10609

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Abrupt permafrost thaw increases climate threat, experts say

ScienceDaily (Nov. 30, 2011) — As the Arctic warms, greenhouse gases will be released from thawing permafrost faster and at significantly higher levels than previous estimates, according to survey results from 41 international scientists published in the Nov. 30 issue of the journal Nature.

Permafrost thaw will release approximately the same amount of carbon as deforestation, say the authors, but the effect on climate will be 2.5 times bigger because emissions include methane, which has a greater effect on warming than carbon dioxide.

The survey, led by University of Florida researcher Edward Schuur and University of Alaska Fairbanks graduate student Benjamin Abbott, asked climate experts what percentage of the surface permafrost is likely to thaw, how much carbon will be released and how much of that carbon will be methane. The authors estimate that the amount of carbon released by 2100 will be 1.7 to 5.2 times larger than reported in recent modeling studies, which used a similar warming scenario.

"The larger estimate is due to the inclusion of processes missing from current models and new estimates of the amount of organic carbon stored deep in frozen soils," Abbott said. "There's more organic carbon in northern soils than there is in all living things combined; it's kind of mind boggling."

Northern soils hold around 1,700 billion gigatons of organic carbon, around four times more than all the carbon ever emitted by modern human activity and twice as much as is now in the atmosphere, according to the latest estimate. When permafrost thaws, organic material in the soil decomposes and releases gases such as methane and carbon dioxide.

"In most ecosystems organic matter is concentrated only in the top meter of soils, but when arctic soils freeze and thaw the carbon can work its way many meters down, said Abbott, who studies how carbon is released from collapsed landscapes called thermokarsts -- a process not accounted for in current models. Until recently that deep carbon was not included in soil inventories and it still is not accounted for in most climate models.

"We know about a lot of processes that will affect the fate of arctic carbon, but we don't yet know how to incorporate them into climate models," Abbott said. "We're hoping to identify some of those processes and help the models catch up."

Most large-scale models assume that permafrost warming depends on how much the air above the permafrost is warming. Missing from the models, say the authors, are processes such as the effects of abrupt thawing that can melt an ice wedge, result in collapsed ground and accelerate additional thawing.

"This survey is part of the scientific process, what we think is going to happen in the future, and how we come up with testable hypotheses for future research," Schurr said. "Our survey outlines the additional risk to society caused by thawing of the frozen North and the need to reduce fossil fuel use and deforestation."

By integrating data from previous models with expert predictions the authors hope to provide a frame of reference for scientists studying all aspects of climate change.

"Permafrost carbon release is not going to overshadow fossil fuel emissions as the main driver of climate change" said Schuur, "but it is an important amplifier of climate change."

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Journal Reference:

Edward A. G. Schuur, Benjamin Abbott. Climate change: High risk of permafrost thaw. Nature, 2011; 480 (7375): 32 DOI: 10.1038/480032a

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Archaeologists find new evidence of animals being introduced to prehistoric Caribbean

ScienceDaily (Dec. 1, 2011) — An archaeological research team from North Carolina State University, the University of Washington and University of Florida has found one of the most diverse collections of prehistoric non-native animal remains in the Caribbean, on the tiny island of Carriacou. The find contributes to our understanding of culture in the region before the arrival of Columbus, and suggests Carriacou may have been more important than previously thought.

The researchers found evidence of five species that were introduced to Carriacou from South America between 1,000 and 1,400 years ago. Only one of these species, the opossum, can still be found on the island. The other species were pig-like peccaries, armadillos, guinea pigs and small rodents called agoutis.

Researchers think the animals were used as sources of food. The scarcity of the remains, and the few sites where they were found, indicate that the animals were not for daily consumption. "We suspect that they may have been foods eaten by people of high status, or used in ritual events," says Dr. Scott Fitzpatrick, an associate professor of anthropology at NC State and co-author of a paper describing the research.

"Looking for patterning in the distribution of animal remains in relation to where ritual artifacts and houses are found will help to test this idea," said Christina Giovas, lead author and a Ph.D. student at the University of Washington.

The team, which also included Ph.D. student Michelle LeFebvre of the University of Florida, found the animal remains at two different sites on the island, and used carbon dating techniques to determine their age. The opossum and agouti were the most common, with the latter remains reflecting the longest presence, running from A.D. 600 to 1400. The guinea pig remains had the shortest possible time-frame, running from A.D. 985 to 1030.

These dates are consistent with similar findings on other Caribbean islands. However, while these species have been found on other islands, it is incredibly rare for one island to have remains from all of these species. Guinea pigs, for example, were previously unknown in this part of the Caribbean. The diversity is particularly surprising, given that Carriacou is one of the smallest settled islands in the Caribbean, though the number of remains is still not that large -- a pattern seen on other islands as well.

This combination of small geographical area and robust prehistoric animal diversity, along with evidence for artifact trade with other islands and South America, suggests that Carriacou may have had some significance in the pre-Columbian Caribbean as a nexus of interaction between island communities.

The animal remains are also significant because they were found in archaeological digs at well-documented prehistoric villages -- and the remains themselves were dated, as opposed to just the materials (such as charcoal) found near the remains.

"The fact that the dates established by radiocarbon dating are consistent with the dates of associated materials from the villages means the chronology is well established," says Fitzpatrick, who has been doing research on Carriacou since 2003. "In the future we'd like to expand one of the lesser excavated sites to get more information on how common these species may have been, which could shed light on the ecological impact and social importance of these species prehistorically."

The paper, "New records for prehistoric introduction of Neotropical mammals to the West Indies: evidence from Carriacou, Lesser Antilles," is published online in the Journal of Biogeography and was co-authored by Fitzpatrick, Giovas and LeFebvre. The research was supported by the National Science Foundation, NC State, the University of Washington and the University of Florida.

NC State's Department of Sociology and Anthropology is part of the university's College of Humanities and Social Sciences.

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Journal Reference:

Christina M. Giovas, Michelle J. LeFebvre, Scott M. Fitzpatrick. New records for prehistoric introduction of Neotropical mammals to the West Indies: evidence from Carriacou, Lesser Antilles. Journal of Biogeography, 2011; DOI: 10.1111/j.1365-2699.2011.02630.x

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