Wednesday, May 9, 2012

Hearing Footsteps under the Ocean

Published May, 2012 SIO News Explorations

Around 5 p.m. every evening the usual humdrum of the day starts to wind down at Birch Aquarium at Scripps. As the guests leave, voices and footsteps gradually fade away. A sealed underwater microphone switches on in a behind-the-scenes tank.
By night there is a cacophony of noises–munching, grabbing, calling or just moving. Simon Freeman wants nothing more than to hear this late night cacophony. He would like to understand what these sounds can tell us about the animals and their ecosystem
Freeman is a graduate student in the Marine Physical Laboratory at Scripps Institution of Oceanography. Working with Michael Buckingham, a professor of acoustics, he uses sound to monitor animal populations under the sea, noting that sound travels better and for longer distances in water than in air.
The idea of recording noises in the ocean is not new. Using hydrophones, specially designed microphones to record underwater sounds, scientists have been listening to animal sounds in the ocean since the 1940s. A pattern has emerged in the oceans: during the day, the noise level is low. After dark, the noise level increases.
At night, smaller marine animals take advantage of the fact that predators cannot see them. They come out of their hiding places to feed making incidental noises as they move about. These noises have features that are different than other sounds these animals make, such as mating calls. Freeman believes that incidental noise can be used to estimate the number and species of animals in a given area.
The technique could come just in time to document rapid changes in ecologically sensitive ocean areas such as coral reefs, which face threats from ocean acidification, pollution, and abrupt changes in ocean water temperature. One indication of the health of reefs is the number of animals present there. Annual surveys involving dives and underwater photography are conducted to monitor different aspects of coral reef health. The surveys are costly and require long planning and coordination.
Freeman’s research on ocean noise aims to develop a low-cost method to continuously monitor numbers of organisms on coral reefs. For his experiment, he is using hydrophones in shrimp tanks at Birch Aquarium at Scripps to record incidental sound.
“Shrimp have tough skeletons and when they walk on hard coral surfaces, it makes clearly recordable noise,” said Freeman.
In the tanks, there are a known number of shrimp so it is an ideal location to calibrate the noise to the number of animals. For the next year, Freeman will continue to listen to hours of underwater sound. He will be pondering questions such as how scientists can successfully record incidental noise made by animals in the ocean, how one can use recorded noise to estimate the number of individuals and whether particular species make noises that have distinct characteristics.
The process, however, is time-consuming. To get a two-minute recording of useful incidental noise, a researcher may have to record continuously for 48 hours.
“But the low cost of the measuring devices and potential for having a continuous record of ecological parameters more than makes up for it,” said Freeman.

– Atreyee Bhattacharya has a Ph.D. in earth science from Harvard University and is a visiting student at the Geosciences Research Division at Scripps

Monday, April 9, 2012

Complex Choices in Medicare Advantage Program May Overwhelm Seniors

Published August 2013

In health care, more choice may not always lead to better choices, particularly for the elderly.
In a new study, researchers from Harvard Medical School’s Department of Health Care Policy found that the large variety of managed care plans offered by the Medicare Advantage program may be counter-productive. Elderly patients, particularly those with low cognitive ability, often make poor decisions—or no decisions at all—when faced with an overwhelming number of complex insurance choices. Ironically, those with impaired cognition may benefit most from the more generous coverage often offered by Medicare Advantage plans.
“We are providing the most complex insurance choices to the very population that is least equipped to make these high-stakes decisions,” says J. Michael McWilliams, assistant professor of health care policy and medicine at Harvard Medical School and a practicing general internist in the Division of General Medicine at Brigham and Women’s Hospital.  “Most other Americans choose from just a few health plans, but elderly Medicare beneficiaries often have to sift through dozens of options.”
The study will appear online August 18 in the journal Health Affairs. It will also appear in the September print edition of Health Affairs.
The Medicare Modernization Act of 2003 initiated a series of payment increases to the Medicare Advantage program. These payment hikes dramatically increased the number of private plans participating in the program and encouraged plans to compete for enrollees by offering lower premiums and more generous benefits, such as prescription drug coverage.
In order to examine the effects of these expanded choices and benefits of enrollment in Medicare Advantage versus traditional Medicare, McWilliams and his team looked at 21,815 enrollment decisions from 2004 to 2007 made by 6,672 participants in a national longitudinal survey, and compared enrollment decisions between participants with different cognition levels and different plan offerings in their area.
The researchers found that, on average, an increase in the number of plans was associated with increased Medicare Advantage enrollment, provided the number of available plan options was fewer than 15. When the number of options surpassed 30, as it did in 25 percent of U.S. counties, such increases were actually associated with decreased enrollment. More importantly, beneficiaries with low cognitive function were substantially less likely than their peers with high cognitive function to appreciate the advantages offered by these plans, choosing to remain in the traditional Medicare program instead.
The authors suggest the reason for lower enrollment could be that beneficiaries became overwhelmed and chose traditional Medicare by default. Furthermore, elderly Medicare beneficiaries with limited cognitive abilities may have difficulty identifying the most valuable option from a complex set of Medicare alternatives. This is particularly concerning given the high and rising prevalence of cognitive impairment and dementia in the aging Medicare population.
The findings also have important policy implications as health insurance exchanges are established under the recent national health reform legislation, the Affordable Care Act.  These exchanges, the authors say, could be helpful to seniors and the Medicare program if expanded to handle enrollment in Medicare Advantage plans.
“Efforts to limit choice and guide seniors to the most valuable options could especially benefit those with cognitive impairments, who without more help appear to be leaving money on the table,” McWilliams said. “Better enrollment decisions could in turn strengthen competition by rewarding high-value plans with more enrollees.”
This research was funded by the Beeson Career Development Award Program, National Institute on Aging and American Federation for Aging Research.
—Atreyee Bhattacharya

Thursday, February 23, 2012

Scripps Graduate Wins Sustainability Prize

 Published, SIO News, 23rd Feb, 2012

Ayana Johnson is on a mission to find sustainable solutions for problems that affect oceans and coastal communities.
The Scripps Institution of Oceanography, UC San Diego graduate, along with fellow conservationist Tim McClanahan, is this year’s recipient of the global Solution Search prize sponsored by Rare, a nonprofit organization dedicated to ocean sustainability, in association with the National Geographic Society. Johnson won for her research creating a low-tech solution to reduce accidental trapping of untargeted fish known as bycatch while preserving the livelihoods of fishermen in the Caribbean.
Johnson grew up in Brooklyn, New York. Like many children, she first fell in love with marine life as a little girl visiting aquariums with her parents. However, unlike most children whose weekend visits to aquariums amount to just a day out with parents, Johnson’s visits to aquariums propelled her into a passionate journey of marine conservation.
“I would not be doing what I do if I did not love the ocean,” said Johnson.
In 2011, Rare announced “Solution Search: Turning the Tide for Coastal Fisheries,” a contest to recognize conservation success stories around the world. Johnson and McClanahan put forward their solution, “Bycatch Escape Gaps for Fish Traps in Curaçao and Kenya” —describing an elegant alteration of fishing traps that reduces bycatch by around 80 percent.
Johnson received her PhD in marine biology from Scripps in 2011. She started investigating the idea of how to reduce the bycatch associated with fish traps during her graduate student years at Scripps. Johnson has focused on addressing issues that lay at the intersection of socioeconomics and ocean conservation in developing countries.
Fishermen build traps to capture high-value fish such as groupers and snappers, but they also capture juveniles of non-targeted species such as parrotfish that enter traps but cannot exit. Many of the juvenile fish killed in such traps have little or no market value, but are herbivores extremely important for the ecological health of the ocean.
Johnson’s solution was to retrofit traps with vertical, rectangular escape gaps that allow narrow-bodied, compressible fish to escape. Her research demonstrated that escape gaps are a low-cost, low-tech solution to increase fishery selectivity and sustainability. In fact, Johnson’s research in Curaçao, which was replicated by McClanahan in Kenya, showed that traps fitted with gaps reduced bycatch up to 80 percent, without reducing (and potentially increasing) catch value.
“We plan to continue working with fishermen to expand the number of locations where escape gaps are used,” said Johnson. “In the long term, we hope escape gaps are used in coral reef trap fisheries all over the world.”
Johnson’s proposal was one of the ten finalists chosen from more than 100 entries by a review panel of ocean conservation experts. By popular voting, Johnson’s proposal was declared the winner on Jan. 6. The runners-up were Off the Hook Community Supported Fishery in Canada and the Misool Baseftin Foundation in Indonesia. The winners received their awards at a ceremony in Washington, D.C., on February 8.
“I was thrilled to win this award, and I hope that any publicity gained will help to spread this idea for making fishing with traps more sustainable,” Johnson said. “Ocean conservation seems like a daunting problem, but the solutions can be simple.”
At present, Johnson is the Director of Science and Solutions for the Waitt Foundation in Washington D.C.
– Atreyee Bhattacharya has a Ph.D. in earth science from Harvard University and is a visiting student at the Geosciences Research Division at Scripps

Saturday, October 8, 2011

Circadian clock--Timekeeper of 24-hour Cycle in Mammals

Focus, June 2011

Unmasking Timekeeper of 24-hour Cycle in Mammals

Key player in genetic loop behind circadian clock identified
Researchers at Harvard Medical School have identified what may be the key switch in mammals’ 24-hour clock: a simple protein that leads to the demise of its own genetic precursor. Their work provides interesting clues to a fundamental and longstanding mystery regarding a genetic mechanism known to drive this 24-hour biological clock, otherwise known as the circadian rhythm.
Scientists believe that circadian rhythms operate on a series of interlocked genetic reactions that define what researchers call a feedback loop. However, the precise mechanism of this process—that is, how and what closes this genetic loop—has eluded scientists for decades. The answer, the researchers propose, may be a well known protein, one that plays a secret role in sustaining the ubiquitous circadian cycle.
“Our research solves a mystery about how the genetic feedback loop works in mammals,” said Charles Weitz, the Robert Henry Pfeiffer Professor of Neurobiology at HMS and senior author on a paper published June 17 in Science.
First described in the 17th century, the term circadian is derived from the Latin circa, meaning around, and diem, meaning day. Circadian clocks govern physiology and behavior in mammals (sleeping, waking and feeding, for example) and play a critical role that allows these animals to synchronize their metabolic cycles with the environment. Present in ancient life forms, including blue-green algae, such clocks are thought to have originated almost a billion years ago, possibly as a means of scheduling DNA replication for nighttime in order to protect genes from harmful solar radiation that penetrated the era’s thin atmosphere.
In the paper, Weitz, with lead authors Hao Duong and Maria Robles, and co-author Darko Knutti, all postdoctoral fellows at HMS, suggest that the key to the circadian riddle may be a novel function of a common protein known as Polypyrimidine tract–binding protein–associated splicing factor, or PSF.
Working with mouse models, Weitz and his team found that the protein PSF resides within a tangle of proteins called the PERIOD, or PER, complex. PER complexes are created by transcription factors of the PER gene. (A transcription factor is a protein that causes particular genes to be turned on or off.) The PER gene is activated by two other proteins residing on it: CLOCK and BMAL1.  Once turned on, PER protein has the ability to inhibit, or turn off, CLOCK and BMAL1, the very transcription factor that created it, closing the genetic loop for a certain period. This operation is crucial for maintaining a 24-hour clock in mammalian cells.
However, the PER protein cannot perform this operation unless it is carried to the site of CLOCK and BMAL1. The PSF protein within the PER complex plays the critical role of carrier: PSF protein carries the PER cargo back to CLOCK and BMAL1. The PER complex then turns the two proteins off for a limited time. “Without the presence of PSF, the whole loop ceases to function—or functions in ways that do not maintain the 24-hour clock,” said Weitz.
The series of genetic reactions takes roughly 24 hours. At the end of that time span, CLOCK and BMAL1 are turned on once again, and the circadian cycle begins anew.
A billion years after the circadian clock originated and centuries after scientists and philosophers learned of its existence, researchers finally have a mechanism that potentially explains how mammals maintain 24-hour clocks.
The work is far from over, however. “In fact, it has only just begun, now that we have a sense of the mechanism,” said Weitz. “There may be more PSF-like proteins.” Researchers in his laboratory are looking into potential functions of previously unknown proteins that may provide insights into the genetic interactions governing 24-hour mammalian circadian rhythms.
—Atreyee Bhattacharya


Tuesday, June 28, 2011

How Do Bacteria Handle Mixed Signals? With Surprising Simplicity

Focus, June 2011

How Do Bacteria Handle Mixed Signals? With Surprising Simplicity
Kishony lab explores cell’s response to drug pairs

You say yes, I say no. You say stop and I say go, go, go.
Mixed signals can be confusing, as the Beatles’ refrain has it. But when the signals come from antibiotic drug combinations, cells react in surprisingly simple ways, HMS researchers have found. Even when drug pairs affect different genes in a single cell in complex ways, the cell as a whole responds in a manner that’s predictable—an insight that could improve drug design.
So-called combination drug therapy is a staple for treating many infectious diseases. Doctors treating tuberculosis, for example, might prescribe one drug to break down the pathogen’s protective barriers and a second to deliver the knockout punch. But identifying effective combinations for a particular disease has relied on guesswork—and the excruciatingly slow accumulation of data.
Roy Kishony, professor of systems biology at HMS, and Tobias Bollenbach, a postdoctoral fellow in his lab and now an assistant professor at the Institute of Science and Technology Austria, wondered whether there was a better way to explain —and perhaps predict—why some drugs work better together while other pairings are less powerful or even counterproductive. Using a systems approach, Kishony and Bollenbach investigated how, within a living cell, gene expression responds to drug pairings.
“The possibility of predicting how cells respond to multi-drug treatments opens the door to a more rational approach for the design of new drug combinations,” Kishony said.
Average Or Prioritize?
Kishony and Bollenbach measured how the single-celled bacterium E. coli responded when subjected to a combination of two drugs. The effect could be either additive, with the drugs’ combined inhibitory effect equal to the sum of their individual effects, or antagonistic, in which case the drugs have a weaker effect when combined. In either case, the bacterial cell’s response to one of the drugs may prove incompatible with its response to the other. For example, a specific gene in the cell may be “turned off” by drug A but “turned on” by drug B. So how do cells as a whole respond, the researchers wondered, when A says stop and B says go?
In a study published in the May 20 issue of the journal Molecular Cell, Kishony and Bollenbach report that bacterial cells respond in surprisingly simple ways, which can be reasonably predicted by monitoring only a handful of their responses.
When drugs enter a bacterial cell’s environment, the researchers found that the response can be broken down to two components: the first, comprising about 70 percent of the cell’s response, involves processes resulting from the total inhibition of the cell’s growth by the two drugs. In the remaining 30 percent, the cells focus on resolving conflicts that arise when paired antibiotics caused mixed genetic responses. This conflict resolution depends on the nature of the signals sent by particular drug pairs.
Kishony and Bollenbach found that bacterial cells resolve conflicting signals from drug combinations by either “averaging” or “prioritizing.” For a drug pair that is additive, the cell averages the conflicting effects of the two drugs. (For example, when one drug’s effect on the regulation of a gene is a four-fold increase and the other’s is a two-fold decrease, their combined effect on the cell is a two-fold increase.) But for the antagonistic drug pair, the cell responds only to the stronger drug signal, ignoring the other. Particularly surprising was that, no matter the drug pairing, almost all genes within a bacterial cell were in agreement about which conflict-resolution strategy to use and which signal was strongest.
These findings demonstrate that it is possible to quickly predict bacterial responses to combined drugs, simply by measuring just a few aspects of how a cell responds to individual drugs. Thus the most effective combinations can be more easily determined.
—Atreyee Bhattacharya

Friday, June 17, 2011

The World Bank at Scripps Institution of Oceanography- ‘What do we need to know before funding a project in the developing world?’

On an unusually gloomy morning of 25th June this year, members of the International Finance Corporation (IFC)–the private arm of the World Bank–and experts of climate science from the Scripps Institution of Oceanography (SIO)–a leading institution in climate research in San Diego–met over breakfast to discuss ways to promote sustainable private sector growth, particularly in the developing world. Established in 1956 the IFC is the largest source of funding for the private sector, primarily through financing projects/ companies and providing advisory service to businesses and governments on sustainable and cleaner energy solutions in the developing world.
So what brings in a group of economists and bankers to an oceanographic institute? Mainly, questions such as, ‘is sustainable private sector growth in a rapidly evolving economy of developing nations–like India and China- really a win-a-win situation? One that mitigates the impacts of climate change without hampering financial returns for corporate houses and banks?’ Prof. Richard Somerville, a leading authority of several, Intergovernmental Panel on Climate Change (IPCC) reports, and author of the popular book, ‘ The forgiving air’, says that it isn’t so. At least not in all situations. However, he emphasized that such arguments are necessary to push corporate houses and governments to investigate ways to promote economic growth at a lower cost to the climate than they are doing at present.
Over the last few years the World Bank has come under mounting media and public scrutiny concerning its loan practices to developing nations. NGO’s and non-profit organizations have argued that revenues generated from projects funded by the World Bank- and its private farm sectors–rarely reach the poor. The Ecologist said in 2000, ‘..the poor are often displaced from their homes, suffer loss or damage to their natural resource base, and are placed in the front line of climatic destabilization that the Bank’s support for fossil fuels is helping to cause’. It is because of such intense media scrutiny that the visiting members of the IFC were grilled for two hours in a seminar session at the Sumner auditorium in SIO by an audience, comprising of graduate students, scientists and faculty members, on issues ranging from policies that the IFC/ World Bank adopts to fund projects to how it plans to deal with biodiversity conservation. Currently, the IFC is sponsoring sustainable projects like the clean technology employment in the public transit system of Mexico city, wind energy projects in China, solar panels in India, fuel cells in Africa, geothermal risk insurance in Turkey, waste management technologies in the steel industry, watershed management in China and Nepal which are being affected by melting Himalayan mountain glaciers and in products pertaining to the carbon market (also called cap and trade, it is an administrative approach using the market in order to control pollution by providing economic incentives for achieving reduction in emissions of pollutants).
Given that at present 1.4 billion people all over the world use dirty energy and a staggering 1.6 billion people lived without any energy at all, how does the IFC decide on which projects to fund? Financial returns from a project within a window of 8-12 years of the loans being released, socio-political landscape in which a project is to take place and how that might be affected by climate change in the future, evaluating population growth of a region in terms of per capita carbon footprint and finally if the proposed projects are aimed at utilizing the best possible technique under a given set of circumstance, says Vikram Widge, the global head of the Carbon Finance unit at the IFC.
Does this mean that the IFC/ World Bank would venture to fund projects on fossil fuel in developing countries that destabilize the climate in major ways, as it has done so in the past? The answer to this question lies in the nature of the project and the country involved. While the IFC would consider funding a coal plant in a country in the sub-Sahara region, they would probably not do so in India and china’, says Patricia Bliss-Guest, program manager of the administrative unit of the climate investment fund at the IFC.
Staff members of the IFC/World Bank such as Shilpa Patel, Vikram Widge and Patricia Bliss-Guest, who find themselves involved in the discourse about climate change as a part of their daily job, need more than just a working knowledge on climate change. The two-day course at the Scripps seaside forum from 25th-26th June was designed to impart in-depth but non-technical description of climate science. Over the two days as experts on climate and biodiversity from the SIO explained in simple words the current level of understanding of the climatic system, projections of the impact of climate change on global temperature, precipitation patterns, sea level rise, ocean acidification, marine ecosystems and quelled some of the long standing misconceptions perpetuated by the media and used as an excuse by governments and corporate houses who choose to maximize short term returns at the cost of severe climate degradation.
The most important question that the members of the IFC had was whether climate change is really caused by humans or is it a natural phenomenon which the human race has witnessed in the geological past (for example the earth was periodically warmer than over the last two million years) and survived. To this, Prof. Jeff Severinghaus, professor of geosciences at SIO and director of Climate-Ocean-Atmosphere (COAP) had a simple answer; “It is not whether we can survive, but at what cost?” Prof. Richard Somerville said that the reason for so much misinformation floating around regarding the recent pace of climate change and the plethora of arguments denying the extent of its impact is because scientists are poor communicators of scientific finding and the media has not caught up with the pace of research in this fast evolving field. Recent research on deep sea and lake sediment cores, tree rings, coral records, ice core, speleothems (calcium carbonate deposits from drip water in caves)—all of which provide accurate annual scale of resolution of past variations in temperature, precipitation, greenhouse gas content of the atmosphere and numerous other climate change parameters—bear evidence that is overwhelmingly suggestive of a strong anthropogenic component in the current climatic degradation.
One such compelling study involves looking air bubbles trapped in ice cores from Greenland and Antarctica. Scientists like Prof. Severinghaus, look at isotopes of Carbon, Oxygen, Nitrogen and other gases in these air bubbles to unravel the climatic history of the earth over the past 20,000 years. The most important information regarding the nature of modern day carbon dioxide and its influence on global temperature comes mainly from
isotopes of Carbon: Carbon has two varieties – the heavy variety with an atomic mass of 13 (C-13) and light variety of atomic mass 12 (C-12). C-13 is heavier because of presence of a neutron in the Carbon atom. Organisms prefer to store the lighter C-12. When we burn fossil fuels like coal and petroleum, the CO2 that is released is rich in the lighter isotope C-12 compared to natural CO2. Over time air bubbles get trapped in the ice depositing in the polar regions. It is by looking at the ratio of the C-13 to C-12 in air bubbles in those ice cores that scientists can tell the nature of the carbon dioxide that is present in the atmosphere and that today it is dominated by anthropogenic emissions. The rate at which CO2 is rising in the modern day climate system is alarming rate. In the past 20,000 years there has been very abrupt changes with very small pace of CO2 changes. Although climate models, particularly those from IPCC, suggest a gradual but rapid increase in temperature, archival records show that climate change has actually been very abrupt. For example, about 13,000 years back there have been repeated short intensely cold events (called the Younger Dryas). The air temperature abruptly dropped by ~ 15C following a warm event preceding it. And given the accelerated pace of rise of CO2 today, it is difficult to estimate the response of the climate system. But one thing is certain. It is going to get warmer.
Modern day sophistication has made us increasingly reliant on the perfect workings of nature than ever before and even slight changes in the climate system (e.g. a small rise is sea level due to melting of continental ice sheets) will be at a tremendous cost to human life and resources. Even a few hundred years back, human civilization was not nearly half as vulnerable as it is today. Prof. Somerville encapsulates this in an ominous warning, “…. nothing short of a natural disaster is going to rouse people from their stupor, but by then it may be too late”. Besides such catastrophic fallouts global warming will also relocate rainfall belts substantially, spelling doom for many countries, which depends on natural rainfall for their economy. We see that already happening in the Sahel, north-west America, the Middle East and Australia. Seasons are readjusting in terms of its onset and duration. Although the human race did survive such drastic changes in climate before, it is foolhardy to expect a double whammy.
The colossal cost associated with climate change and related relocation, war and food crises puts a major responsibility on us to use our money wisely. The IFC/ World Bank staff members find themselves in the midst of this responsibility under an increasingly aware public and media scrutiny. It’s a staggering job, to say the least, to promote clean energy and sustainability in a scenario of increasing global population and complicated financial structure. Administering such major changes in a matter of few decades is a humongous task, says Prof. Somerville. But a small step for a long journey was taken at the Scripps Seaside forum that day, as top bracket climate scientists and the World Bank got together to understand the impacts of climate change and the responsibility of financing organizations to distribute funds. Only through such interaction between the academia and policy makers can we hope to take on what threatens to be the biggest challenge humanity has ever faced.
Atreyee Bhattacharya
Graduate student at Harvard University currently a visiting student at Scripps Institution of Oceanography, San Diego

Famine Follows the plough
STIN flash, June., 2011

Famine follows the plough in Africa?

A fifty-year famine provoked by drought threatens millions in the sub-Saharan Sahel region of Africa with crop failure, cattle loss, starvation and death. As policy makers work to provide relief for the drought-ravaged nations, scientists in Europe are investigating what caused a seemingly-minor ‘dry spell’ to snowball into a drought so severe that it now threatens political stability in sub-Saharan Africa. Airborne dust, created by commercial farming practices introduced by Portuguese settlers between the 18th and the 19th centuries, may be the culprit.

New research shows that dust emission from the West African Sahel has increased almost exponentially since the early part of the 18th century.  Many factors influence the rate at which dust is released from the Sahel. Long periods of drought dry the soil, leading to increased dust emission. Some agricultural practices, like extensive cash crop farming, loosen the topsoil, releasing even more dust. Dust from North Africa is carried by trade winds across the Atlantic Ocean in seven days, mainly during the summer months. While in transit, the larger and denser dust particles settle out near the African coast. Lighter particles are lofted into higher levels of the atmosphere and travel longer distances – as far as the Caribbean and South America. In fact, windblown African dust is a major contributor to the iron rich soils of the Amazon.

Figure 1. A massive cloud of dust billows off the coast of West Africa, as seen by satellite. (Photo courtesy of NASA)
Scientists can measure the amount of dust emitted from North Africa and deposited in the ocean. Mud samples collected from the bottom of the Atlantic Ocean bordering the Western coast of Africa have a distinctive composition that can be used to track variations in dust emission over centuries. Scientists can use this data to infer changes in rainfall, wind patterns and human activities, all of which contribute to dust emission from the Sahel region. Current studies show that, for the past three thousand years, dust emission from West Africa was regulated by frequently occurring droughts in the region. High dust emission is characteristic of extensive droughts, whereas low dust emission is a feature of wetter periods.
Sahel region droughts spanning several decades are the consequence of warming ocean temperatures in the tropics and atmospheric circulation patterns over the North Atlantic. However, scientists have used coastal mud samples to measure the increase in North African dust emission over the last 150 years, and it is far greater than can be explained by changes in the amount of rainfall. Researchers believe this recent increase in dust emission may reflect the introduction of aggressive commercial farming practices to the Sahel around the mid 19th century. These farming practices release huge quantities of dust into the atmosphere – an amount that was grossly underestimated until recently. African dust is carried by wind as far as Western Europe and the United States, where it also impacts air quality. These findings may confirm what scientists have long suspected: that dust emitted from human activities like farming can increase the severity and duration of naturally occurring droughts.
How can the increase in dust emission amplify droughts in the Sahel region? During transit, dust acts as an additional layer in the atmosphere. The dust layer causes absorption of incoming solar radiation. This absorption causes localized heating in the atmosphere, but leaves the ocean surface cooler, since the sun’s rays are partially blocked by the dust layer. The heating of the atmosphere caused by the dust particles impedes atmospheric mixing, which is necessary for rainfall. Additionally, dust in the atmosphere changes cloud properties, further preventing them from raining out. Less rainfall causes drier conditions in the already arid sub-Saharan Africa. The resultant decades-long dry spells have had catastrophic effects for the expanding agriculture-based economy of the region.
These recent studies have major implications for commercial farming practices, especially in dry regions. For North Africa, scientists suggest that replacing cash crop production with local produce that are more suited to the climate of the region may help reduce dust emissions from the Sahel region. The history of the United States shows that we are not immune to these effects, either. In the southwestern United States, malpractices in farming techniques in the late 1930’s led to the dust bowl and contributed to the biggest economic downturn in American history. Today, the southwest is going through another drought period. These new findings show that dust emissions must be taken into serious consideration when planning commercial agriculture in drought-prone regions around the world.
Atreyee Bhattacharya is a PhD student at Harvard University.


1. Biasutti, M., Held, I. M., Sobel, A. H. & Giannini, A. (2008) SST forcings and Sahel rainfall variability in simulations of the twentieth and twenty-first centuries. Journal of Climate 21, 3471-3486.
2. Evan, A. T. & Mukhopadhyay, S. (2010) African Dust over the Northern Tropical Atlantic: 1955-2008 Journal of Applied Meteorology and Climatology 49, 2213-2229.
3. Giannini, A., Saravanan, R. & Chang, P. (2003) Oceanic forcing of Sahel rainfall on interannual to interdecadal time scales. Science 302, 1027-1030.
4. Held, I. M., Delworth, T. L., Lu, J., Findell, K. L. & Knutson, T. R. (2005) Simulation of Sahel drought in the 20th and 21st centuries. Proceedings of the National Academy of Sciences of the United States of America 102, 17891-17896.
5. Mulitza, S. et al. (2010) Increase in African dust flux at the onset of commercial agriculture in the Sahel region. Nature 466, 226-228.
6. Natalie Mahowald’s Dust Page.
7. “Desert, dust, dust storms and climate.”
8. “Dust plays a huge role in climate change.”
9. “Drought in the dust bowl era.”

Tuesday, March 29, 2011

Those goosebumps on glaciers

March/April 2011

Scripps researchers monitor icequakes on Swiss glacier
Seated in her office overlooking the Pacific Ocean, Debi Kilb, an expert on earthquakes at Scripps Institution of Oceanography, UC San Diego, points out the objects of her current research--multicolored blocks that pop up rapidly on her computer screen like an ongoing video game.
The popping blocks on her computer are not earthquakes occurring, as one may have guessed. In fact they depict a chronological evolution of surface icequakes--tremors that occur almost constantly on glaciers all over the globe.
Icequakes, like earthquakes, are caused by stress changes. However, unlike earthquakes that respond to large stress changes within the earth, icequakes respond to relatively smaller stress changes driven by processes in glaciers such as surface crevasse openings, iceberg breakaway events known as calvings and the flow of water below a glacier's surface. As a result, icequakes get recorded in negative values on a scale that measures the magnitude of earthquakes.
Kilb joined glaciologist and Scripps postdoctoral fellow Fabian Walter to study icequakes in Gornersee, a glacial lake on the Gornergletscher glacier in Switzerland in the summer of 2004. Their plan was to monitor icequake activity for an extended period during a lake drainage event — a study that Kilb and Walter expected would give insights into the behavior of water under the surface of glaciers.
Glacial lakes form within, below, above, or even next to glaciers as meltwater accumulates in spaces dammed either by glacial ice or moraines. Moraines are debris carried and piled up by moving glaciers. Such ice dams are extremely unstable. Hence, glacier-dammed water bodies can drain unexpectedly, sometimes within days or even hours in a potentially catastrophic manner. In 2004, Gornersee released about 2.7 million liters (713,000 gallons) of water in a flooding event that damaged parts of Zermatt and Tasch, two Swiss towns downstream from the glacier.
"Everybody just knew that icequake activities increased during glacial lake drainages," said Kilb. "The idea was when glacial lakes drain, the excess water is injected into surrounding ice causing stress to build up that will dramatically increase icequake activity."
click here popup Her smile gives away that her research on icequakes suggests otherwise. In an unprecedented survey, Kilb's team recorded some one million tremors over three summers from 2004 to 2007 using a high-density network of seismometers that cover the western flank of lake Gornersee. Their analysis did not show strong evidence of the expected dramatic increase in icequakes during lake drainage events. But their discoveries were even more interesting.
Kilb and Walter found that during lake drainage, icequakes seem to halt in some regions and become heavily active in other regions but causing no net change in the rate of icequake activity. Kilb suggests that it is possible that during some of these drainage events, the excess water drains into locations that are already so heavily inundated that new meltwater cannot be accommodated. This forces the "new" water to find other outlets or wait until water pressures within the inundated locations abate. This could explain the temporary halt to icequake activity in certain regions and increases in others.
Although preliminary, Kilb and Walter's research suggests that an increase in the number of icequakes may not be a good predictor of lake drainage. It may be more realistic to monitor changes in icequake activity in multiple areas of the glacier to better forecast lake drainages. The team also recorded an increase in the number of icequakes during the day compared to at night that suggest day/night melt cycle has a large impact on surface seismicity within critical locations of the glaciers. These new findings challenge well-established hypotheses on movement of glaciers.
Kilb said she hopes that the new data her team has collected will not only help scientists like herself to learn the unusual ways in which icequakes operate but also contribute meaningfully toward a better understanding about behavior of glaciers that are experiencing rapid melting due to warming air temperatures in the 21st century.
"The possibilities are endless and it is so cool," Kilb said.
—Atreyee Bhattacharya
March/April 2011