The rise in sea level of the Mediterranean is accelerating

In this image, scientists are collecting samples during the RADMED campaign. -  IEO
In this image, scientists are collecting samples during the RADMED campaign. – IEO

At the end of the 20th century, the rise in sea level of the Mediterranean sea was lower than in the rest of the world due to atmospheric pressure, but since the start of the 21st century the levels of the Mediterranean have regained pace and seem to be accelerating. This has been demonstrated by the updated results from the second edition of the book Cambio Climático en el Mediterráneo Español (Climate Change in the Spanish Mediterranean).

“The sea level in the Mediterranean has risen by between 1 and 1.5 millimetres each year since 1943, but this does not seem set to continue, because it now seems that the speed at which it rises is accelerating”, Manuel Vargas Yáñez, main author of the book Cambio Climático en el Mediterráneo Español, and researcher in the Spanish Oceanography Institute (IEO), tells SINC.

The publication, which in its second edition includes, for the first time, climate figures from 1943 to 2008 using a marine observation system which is unique in Spain and pioneering in Europe, confirms that the Mediterranean is becoming warmer. Its salinity is also increasing, and the rise in sea level is accelerating. Since the start of the 21st century the level has already risen by 20 centimetres.

However, “during the last three years which were added to the study (from 2005 to 2008) the rise in temperatures has been slower than at the end of the 20th century, when the sea temperatures rose significantly”, points out Vargas Yáñez, who insists on the necessity to study long series of figures to show the impact of climate change in the Mediterranean.

According to the book, presented today in Malaga by the Spanish Foundation for Science and Technology (FECYT) and the IEO to mark the third anniversary of SINC, the changes which occurred in the temperatures are not only due to the effects of climate change, but also to natural and “normal” atmospheric changes. “These are changes which are always going to happen; the atmosphere and oceans are chaotic systems”, explains the expert.

Something human beings can no longer avoid

On the sea’s surface layer, the temperature has risen throughout the 20th century to a level similar to that of the air, in other words roughly 0.7 or 0.8ºC. “It is rising at a speed of almost one degree per century, but it is not possible to extrapolate for the 21st century, because it depends on what human beings do and responds only to the laws of nature”, explains Vargas-Yáñez.

Even if humans were to release less CO2 into the atmosphere during this century, emerging countries were to reduce their emissions, and the burning of fossil fuels fell and green economies were promoted, “in the short-term, temperatures would continue to rise”, concludes the scientist.

“The climate on Earth is experiencing inertia to a certain extent. Even though we have now decreased greenhouse gas emissions to the levels of the 1990s, during the next 30 years the rise in temperatures and in sea level will continue at the same level as if we did nothing”, the physicist points out, who adds, nonetheless, that “the future is not set in stone, and we can still take action to fix it”.

Vargas Yáñez and his team plan to continue updating the climate figures for the Mediterranean year after year, thereby consolidating the observation and monitoring system. The next step will be to present a report which is similar but “more multidisciplinary”, and which includes a study of the impact of climate change on the Mediterranean’s ecosystems.

Drier conditions projected to accelerate dust storms in the southwest

Drier conditions projected to result from climate change in the Southwest will likely reduce perennial vegetation cover and result in increased dust storm activity in the future, according to a new study by scientists with the U.S. Geological Survey and the University of California, Los Angeles.

The research team examined climate, vegetation and soil measurements collected over a 20-year period in Arches and Canyonlands National Parks in southeastern Utah. Long-term data indicated that perennial vegetation in grasslands and some shrublands declined with temperature increases. The study then used these soil and vegetation measurements in a model to project future wind erosion.

The findings strongly suggest that sustained drought conditions across the Southwest will accelerate loss of grasses and some shrubs and increase the likelihood of dust production on disturbed soil surfaces in the future. However, the community of cyanobacteria, mosses and lichens that hold the soil together in many semiarid and arid environments-biological soil crusts-prevented wind erosion from occurring at most sites despite reductions in perennial vegetation.

“Accelerated rates of dust emission from wind erosion have large implications for natural systems and human well-being, so developing a better understanding of how climate change may affect wind erosion in arid landscapes is an important and emerging area of research,” said Seth Munson, a USGS ecologist and the study’s lead author.

Dust carried by the wind has received recent attention because of its far-reaching effects, including the loss of nutrients and water-holding capacity from source landscapes, declines in agricultural productivity and health and safety concerns. Dust is also a contributing factor in speeding up the melting of snow, which affects the timing and magnitude of runoff into streams and rivers.

Scientists find increase in microearthquakes after Chilean quake

By studying seismographs from the earthquake that hit Chile last February, earth scientists at the Georgia Institute of Technology have found a statistically significant increase of microearthquakes in central California in the first few hours after the main shock. The observation provides an additional support that seismic waves from distant earthquakes could also trigger seismic events on the other side of the earth. The results may be found online in the journal Geophysical Research Letters.

It has been well known that microearthquakes can be triggered instantaneously by distant earthquakes. However, sometimes the triggered events could occur long after the passage of the direct surface waves that take the shortest path on the earth surface. There are several other explanations out there about how such delayed triggering occurs. Some involve the redistribution of pore fluids and triggered aseismic creep, while others simply consider them as aftershocks of the directly triggered events. But the group from Georgia Tech found something different.

“From our research, we’ve concluded the delayed triggering that occurs in the first few hours after an earthquake could be caused by multiple surface waves traveling back and forth around the earth multiple times,” said Zhigang Peng, assistant professor in the School of Earth and Atmospheric Sciences at Georgia Tech.

In a previous paper, also published in Geophysical Research Letters last December, Peng’s research group found that the direct surface waves of the Chilean earthquake triggered seismic activity in central California. In this new study, Peng’s group looked beyond the direct surface waves and focused on secondary and tertiary waves that return after traveling across the globe multiple times. In addition, they went beyond earthquake information published in the U.S. Geological Survey catalog and instead studied the seismographs.

“So when you look at the events that have been reported in the catalog, you won’t see this effect,” said Peng. “But if you look at the seismographs, you’ll see many small events and notice that they occurred mostly when those multiple surface waves arrived.”

Peng said that the finding is significant because it also suggests that scientists can look beyond the direct surface waves and understand that those later-arriving waves could affect the seismic activity on the other side of the earth. But his team believes that seismic waves circle the globe only for large earthquakes. They are currently examining other regions and quakes to see just how widespread this effect is.

Soot packs a punch on Tibetan Plateau’s climate

In some cases, soot – the fine, black carbon silt that is released from stoves, cars and manufacturing plants – can pack more of a climatic punch than greenhouse gases, according to a paper published in the journal Atmospheric Chemistry and Physics.

Researchers at the Department of Energy’s Pacific Northwest National Laboratory, the University of Michigan and NOAA found that soot landing on snow on the massive Tibetan Plateau can do more to alter snowmelt and monsoon weather patterns in Asia than carbon dioxide and soot in the air. Soot on snow causes the plateau’s annual glacial melt to happen sooner each year, causing farmers below it to have less water for their crops in the summer. In a domino effect, the melting then prods two of the region’s monsoon systems to become stronger over India and China.

“On the global scale, greenhouse gases like carbon dioxide cause the most concern related to climate change,” said Yun Qian, the paper’s lead author and an atmospheric scientist at PNNL. “But our research shows that in some places like the Tibetan Plateau, soot can do more damage.”

Roof of the Earth

Qian and his colleagues focused their research on the Tibetan Plateau, a giant outcropping of land between China and India that’s nicknamed the “Roof of the Earth.” About five times the size of Texas and as much as 5 miles high in places, the Tibetan Plateau greatly influences the Asia’s weather, including the annual deluge of rain and strong winds that come with monsoons. It’s also home to the largest volume of ice outside of the north and south poles. Glaciers and snow on the plateau grow and melt as seasons change, providing runoff that feeds most of the region’s major rivers, including the Yangtze in China and the Ganges in India.

Soot has increasingly dirtied the Tibetan Plateau’s winter-white surfaces in the past two decades. A byproduct of the region’s rapid growth in industry and agriculture, soot leaves smokestacks and burning fields in developing Asian countries before it floats into the sky, where winds carry it toward the plateau. Soot is dark and absorbs far more heat from sunlight than pristine white snow. Soot’s ability to soak up more solar rays causes the snow it lands on to melt faster. The Tibetan Plateau also receives more direct sunlight than the distant north and south poles, meaning soot’s snow-melting powers are be more pronounced on the plateau.

To find out how much soot is affecting the Tibetan Plateau’s region, Qian and colleagues used a global climate computer model, the Community Atmosphere Model. The model allowed them to examine a mixture of possible scenarios, including if soot sat on the Tibetan Plateau’s snow, if soot was floating in the air above the plateau and if increased carbon dioxide was in the air as a result of industrialization.

More heat, melting

The model’s calculations showed that the average air temperature immediately above the plateau increased when all the scenarios were combined. Alone, both soot on snow and carbon dioxide increased temperatures about 2 degrees Fahrenheit. But while carbon dioxide increased temperatures fairly evenly throughout the region, including the ocean, soot on snow only significantly heated up the Tibetan Plateau and north Asia. Researchers concluded that soot on snow can increase the temperature differences between air over land and air over the ocean, which drive monsoons.

Soot on snow also stood out when the model investigated water runoff. Smaller changes were observed when just carbon dioxide or soot in the air were examined, but soot on snow by itself increased runoff substantially during the late winter and early spring and then decreased it during the late spring and early summer. With all three scenarios combined, the runoff increased by 0.44 millimeters (or nearly two-one hundredths of an inch) daily between February and April and then decreased by 0.57 millimeters daily between May and July. These changes provide more water in the winter, when it’s not particularly useful to farmers, but less in the summer when it’s needed to grow crops.

The researchers reasoned that soot on snow is more efficient in melting the plateau’s snowpack because of its close proximity to the snow. Like a warm blanket covering the plateau, soot on snow can almost immediately warm and melt the snow beneath it. But carbon dioxide and soot in the atmosphere have to transfer the heat they absorb way down to the plateau below, with some heat inevitably being lost.

Nature’s heat pump

Before this research, scientists knew that the Tibetan Plateau acted like a natural heat pump for the region’s weather. The plateau reaches 5 miles high in some places, allowing the air above it to be warmer than other air at the same elevation. The warm air strengthens air circulation around the plateau and causes the iconic, drenching monsoons that move through the region every year.

But with soot on snow causing more snowmelt on the plateau, the plateau is increasingly bare. Less snow covering to reflect solar heat means the Tibetan Plateau is absorbing more sunlight, which the researchers hypothesized was causing the atmosphere above the plateau to warm up even more. They used climate models to find out of this affects the area’s monsoons.

Stronger monsoons

The surface temperature above the plateau increased by more than 2 degrees Fahrenheit in May due to soot on snow alone. The researchers found that this warmer air above the plateau rises and air is drawn from India to replace it. In turn, moist air hanging above Arabian Sea and Indian Ocean blows in over India. Known as the South Asian Monsoon system, this southwest-northeast flow also brings in more soot from India to the Tibetan Plateau that perpetuates the cycle. As a result, the researchers found that the South Asian Monsoon system is starting earlier and bringing more rain to central and Northern India in May than it would without soot on the plateau’s snow.

The soot-on-snow effect lingers throughout the summer and causes another weather shift in the East Asian Monsoon system over China. By July, much of the plateau’s snow has already melted. The plateau’s bare soil is warmer and further heats the plateau’s air. Coupled with cool ocean air nearby, the plateau’s heat strengthens the East Asian Monsoon. The models showed that rain increases 1 to 3 millimeters per day over southern China and the South China Sea. The strengthened monsoon advances to northern China, which also receives more rain than it would otherwise, while the rains mostly skip central East China, including the Yangtze River Basin.

More work needs to be done to refine these findings, however. Qian and his co-authors noted that existing global climate models don’t allow for the close-up, detailed resolution needed to accurately portray the Tibetan Plateau’s many varying peaks. The model’s coarse resolution likely resulted in the plateaus’ snowpack being overestimated, meaning the researchers’ results represent the maximum amount that soot on snow could potentially impact hydrological and weather systems in the region.

Future research could also factor in dust, which blows throughout Asia with the wind. While soot is believed to have a larger impact on snowmelt than dust per unit mass, the region likely has more total dust than soot. However, dust is more challenging to represent in models, since its sources can’t be as easily measured as the polluting smokestacks and burning fields that cause soot.

“The Tibetan Plateau is an amazing, dynamic place where many things come together to develop large climate systems,” Qian said. “Our research indicates that soot on snow can be a large player in the region’s climate, but it’s not the only factor. Many other elements need to be studies before we can say for sure what is the leading cause of snowmelt – which also contributes to retreating glaciers – on the plateau.”

68 percent of New England and Mid-Atlantic beaches eroding

An assessment of coastal change over the past 150 years has found 68 percent of beaches in the New England and Mid-Atlantic region are eroding, according to a new US Geological Survey report. Scientists studied 650 miles of the New England and Mid-Atlantic coasts and found the average rate of coastal change was negative 1.6 feet per year.  Of those beaches eroding,the most extreme case exceeded 60 feet per year.
An assessment of coastal change over the past 150 years has found 68 percent of beaches in the New England and Mid-Atlantic region are eroding, according to a new US Geological Survey report. Scientists studied 650 miles of the New England and Mid-Atlantic coasts and found the average rate of coastal change was negative 1.6 feet per year. Of those beaches eroding,the most extreme case exceeded 60 feet per year.

An assessment of coastal change over the past 150 years has found 68 percent of beaches in the New England and Mid-Atlantic region are eroding, according to a U.S. Geological Survey report released today.

Scientists studied more than 650 miles of the New England and Mid-Atlantic coasts and found the average rate of coastal change – taking into account beaches that are both eroding and prograding — was negative 1.6 feet per year. Of those beaches eroding, the most extreme case exceeded 60 feet per year.

The past 25 to 30 years saw a small reduction in the percentage of beaches eroding – dropping to 60 percent, possibly as a result of beach restoration activities such as adding sand to beaches.

“This report provides invaluable objective data to help scientists and managers better understand natural changes to and human impacts on the New England and Mid-Atlantic coasts,” said Anne Castle, Assistant Secretary of the Interior for Water and Science. “The information gathered can inform decisions about future land use, transportation corridors, and restoration projects.”

Beaches change in response to a variety of factors, including changes in the amount of available sand, storms, sea-level rise and human activities. How much a beach is eroding or prograding in any given location is due to some combination of these factors, which vary from place to place.

The Mid-Atlantic coast – from Long Island, N.Y. to the Virginia-North Carolina border — is eroding at higher average rates than the New England coast. The difference in the type of coastline, with sandy areas being more vulnerable to erosion than areas with a greater concentration of rocky coasts, was the primary factor.

The researchers found that, although coastal change is highly variable, the majority of the coast is eroding throughout both regions, indicating erosion hazards are widespread.

“There is increasing need for this kind of comprehensive assessment in all coastal environments to guide managed response to sea-level rise,” said Dr. Cheryl Hapke of the USGS, lead author of the new report. “It is very difficult to predict what may happen in the future without a solid understanding of what has happened in the past.”

The researchers used historical data sources such as maps and aerial photographs, as well as modern data like lidar, or “light detection and ranging,” to measure shoreline change at more than 21,000 locations.

This analysis of past and present trends of shoreline movement is designed to allow for future repeatable analyses of shoreline movement, coastal erosion, and land loss. The results of the study provide a baseline for coastal change information that can be used to inform a wide variety of coastal management decisions, Hapke said.

The report, titled “National Assessment of Shoreline Change: Historical Shoreline Change along the New England and Mid-Atlantic Coasts,” is the fifth report produced as part of the USGS’s National Assessment of Shoreline Change project. An accompanying report that provides the geographic information system (GIS) data used to conduct the coastal change analysis is being released simultaneously.

Geology professor and research team present findings studying drought

A group of researchers have studied the history of drought in the Pacific Northwest during the last 6,000 years, a time that spans the mid-Holocene geological epoch to the present. The research team included Dr. Joseph Ortiz, associate professor of geology at Kent State University. -  Kent State University
A group of researchers have studied the history of drought in the Pacific Northwest during the last 6,000 years, a time that spans the mid-Holocene geological epoch to the present. The research team included Dr. Joseph Ortiz, associate professor of geology at Kent State University. – Kent State University

A group of researchers have studied the history of drought in the Pacific Northwest during the last 6,000 years, a time that spans the mid-Holocene geological epoch to the present. The goal of the research was to improve the understanding of drought history because the instrumental record of drought only goes back a few hundred years and at relatively few locations.

Their work extended the drought history of the Pacific Northwest back much longer than the tree ring record, which provides information in the region over the past 1,500 years. The team’s research also indicates that during the time period they studied, the duration of the droughts has in general increased in response to decadal oscillations in the climate system driven by marine processes.

Dr. Joseph Ortiz, associate professor of geology at Kent State University and resident of Hudson, Ohio, has spent about four years working on this research project with Dr. Mark Abbott of the University of Pittsburgh and his team. Their work is funded by the National Science Foundation. Their research findings appear in the online Early Edition (EE) of the Proceedings of the National Academy of Sciences, one of the world’s most-cited multidisciplinary scientific serials, during the week of Feb. 21.

“Climate scientists have developed several methods to evaluate changes in drought for times earlier than we have rain gauge record,” Ortiz explained. “One approach is to use trees as an integrator of this signal. When there is plenty of water, trees will grow faster and develop thicker growth rings. But trees are not found in all locations, water is not the only factor that controls tree growth, and it can be hard to find trees older than a few hundred years, so we sought to employ a different approach using sediment records from lakes.”

The researchers went out into the field and collected lake cores to measure properties of the sediment through time. For this study, they digitally photographed the lake cores to capture variations in the thickness and color of the thin layers of sediment deposited year by year at the bottom of the lake.

“We also extracted calcium carbonate from the lake to study variations in the oxygen isotopic composition of the carbonate minerals that precipitated from the surface water of the lake,” Ortiz said. “Mark Abbott and his group at the University of Pittsburgh have pioneered these types of studies at locations throughout the Americas. The relative proportion of the O18 and O16 isotopes in the carbonate recovered from the lack reflect changes in the proportion of these isotopes in the water of the lake. We were able to relate changes in these two proxies to changes in the water balance of the lake through time.

“To make sure that we had the relationship right, we compared our results with tree-ring records and instrumental data for the parts of the records that overlapped in time. We had confidence that we were on the right track because the various methods provided essentially the same result.”

Ortiz’s role in the project was to assist with the statistical analysis of the data sets using quantitative methods that let the research team explore the inter-relationships between variables and how they changed through time.

“Mark and I complement each other very well because Mark has tremendous experience in terrestrial field work and limnology, while I bring expertise in marine climate studies and quantitative methods,” Ortiz said. “Our complementary expertise turned out to be very important for this collaboration because we are able to effectively explore the relationships between what happens here on land and how oceanic processes are involved.”

The researchers’ work also has added support to the observation that the 20th century, when population in the western United States grew rapidly, was a relatively “wet” period in the West. “This has implications for public water policy because our perception of the availability of water is tied to the limited window of our historical experience,” Ortiz said. “Our work demonstrates that there can be surprises when we step back and look at variations in the climate system over a longer period. The connection to marine processes that create decadal oscillations in climate, such as El Niño, is also important because our work provides insights into how water availability in the Pacific Northwest will shift as El Niño responses to human-induced changes in the climate system.”

Ortiz is excited that the team’s work was selected to appear in the Proceedings of the National Academy of Science, allowing the research to reach a diverse audience.

“That should help bring our results to the attention of policy makers so that they can apply sound science while developing strategies to address future change,” he said.

Oscillating ‘plug’ of magma causes tremors that forecast volcanic eruptions

University of British Columbia geophysicists are offering a new explanation for seismic tremors accompanying volcanic eruptions that could advance forecasting of explosive eruptions such as recent events at Mount Pinatubo in the Philippines, Chaiten Volcano in Chile, and Mount St. Helens in Washington State.

All explosive volcanic eruptions are preceded and accompanied by tremors that last from hours to weeks, and a remarkably consistent range of tremor frequencies has been observed by scientists before and during volcanic eruptions around the world.

However, the underlying mechanism for these long-lived volcanic earthquakes has never been determined. Most proposed explanations are dependent upon the shape of the volcanic conduit – the ‘vent’ or ‘pipe’ through which lava passes through – or the gas content of the erupting magma, characteristics that vary greatly from volcano to volcano and are impossible to determine during or after volcanic activity.

Published this week in the journal Nature, the new model developed by UBC researchers is based on physical properties that most experts agree are common to all explosive volcanic systems, and applies to all shapes and sizes of volcanoes.

“All volcanoes feature a viscous column of dense magma surrounded by a compressible and permeable sheath of magma, composed mostly of stretched gas bubbles,” says lead author Mark Jellinek, an associate professor in the UBC Department of Earth and Ocean Sciences.

“In our model, we show that as the center ‘plug’ of dense magma rises, it simply oscillates, or ‘wags,’ against the cushion of gas bubbles, generating tremors at the observed frequencies.”

“Forecasters have traditionally seen tremors as an important – if somewhat mysterious – part of a complicated cocktail of observations indicative of an imminent explosive eruption,” says Jellinek, an expert in Geological Fluid Mechanics. “Our model shows that in systems that tend to erupt explosively, the emergence and evolution of the tremor signal before and during an eruption is based on physics that are uniform from one volcano to another.”

“The role of tremors in eruption forecasting has become tricky over the past decade, in part because understanding processes underlying their origin and evolution prior to eruption has been increasingly problematic,” says Jellinek. “Because our model is so universal, it may have significant predictive power for the onset of eruptions that are dangerous to humans.”

New Zealand earthquake damage illustrates risks posed by shallow crustal faults

The terribly destructive earthquake that just hit Christchurch, New Zealand, was only a moderate 6.3 magnitude, but had certain characteristics that offer an important lesson to cities up and down the West Coast of North America that face similar risks, experts say.

The New Zealand earthquake killed dozens – and some fear the death toll may rise to the hundreds – and was an aftershock of the much more powerful 7.1 magnitude earthquake that struck that nation last September near the same area, but caused no deaths.

Even though this earthquake was weaker than last year’s event, it was much shallower; was situated directly under Christchurch; hit during the lunch hour when more people were exposed to damage; and shook sediments that were prone to “liquefaction,” which can magnify the damage done by the ground shaking.

Robert Yeats, a professor emeritus of geology at Oregon State University, who is an international earthquake expert and researcher on both New Zealand and U.S. seismic risks, says that same description nicely fits many major cities and towns in Washington, Oregon, California and British Columbia.

“The latest New Zealand earthquake hit an area that wasn’t even known to have a fault prior to last September, it’s one that had not moved in thousands of years,” Yeats said. “But when you combine the shallow depth, proximity to a major city and soil characteristics, it was capable of immense damage.

“The same characteristics that caused such destruction and so many deaths in Christchurch are similar to those facing Portland, Seattle, parts of the Bay Area and many other West Coast cities and towns,” Yeats said. “And it’s worth keeping in mind that New Zealand has some of the most progressive building codes in the world. They are better prepared for an earthquake like this than many U.S. cities would be.”

The risks from comparatively shallow “crustal” faults, Yeats said, are often given less attention compared to the concerns about the major subduction zone earthquake facing the Pacific Northwest in its future, or other major quakes on famous plate boundaries such as the San Andreas Fault. There are dozens or hundreds of faults such as this that can cause serious earthquakes in the West, Yeats said.

Associated with that is the risk of liquefaction – the characteristic of some soils, particularly sediments deposited over long periods of time, to become saturated with water and quiver like a bowl of gelatin during an earthquake. Such motions can significantly increase building damage and loss of life.

“Much of the Willamette Valley in Oregon is a prime example of soils that could liquefy, old sediments deposited during floods and coming down from the Cascade Range,” Yeats said. “It’s very similar in that sense to the area around Christchurch, which sits on sand, silt and gravel from the Southern Alps to the west. This issue, along with the risks posed by crustal faults, has to be considered in our building codes.”

The city of Portland sits astride the Portland Hills Fault – which may or may not still be active – and faces significant liquefaction concerns in many areas. Seattle faces similar risks from the Seattle Fault, which is active. And whether or not an earthquake has happened lately offers little reassurance – the New Zealand fault that just crippled Christchurch hadn’t moved in millennia.

“The damage in New Zealand in the past day has been terrible, just horrible,” Yeats said. “But as bad as it has been, it’s worth noting that it could have been a lot worse. In the earlier earthquake, as well as this one, their building codes have saved a lot of lives. If the same type of event had happened in urban areas of many developing nations, the damage would have been catastrophic.”

Like much of the West Coast, Yeats said, New Zealand sits near a major boundary of the Earth’s great plates – in this case, the junction of the Australia Plate and the Pacific Plate. Past OSU research has helped characterize parts of that plate boundary – but despite intensive seismic studies in that nation, no one had yet identified the related fault that just devastated Christchurch.

“We can learn about earthquakes and help people understand the seismic risks they face,” Yeats said. “But it’s still an inexact science, the exact timing of an earthquake cannot be predicted, and the best thing we can do is prepare for these events before they happen.”

Fish provide missing piece in the marine sediment jigsaw

Research published today reveals the previously unidentified role that fish play in the production of sediments in the world’s oceans, and specifically of the carbonate sediments that contain critical records of changes in ocean chemistry and climate shifts in the geological past.

The discovery, made by a team of scientists from the UK and US, helps explain the origins of a key component of marine sediments – the fine-grained carbonates, the origins of which are often problematic to resolve.

Published today (21 Feb 2011) in The Proceedings of the National Academy of Science (PNAS), the study describes the discovery of an entirely new source of marine carbonate and one that has major implications for understanding the origins of the sediments that form ancient limestone and chalk deposits.

Until now it was believed that the fine-grained carbonates that constitute a major component of marine carbonate sediments were derived primarily from either direct precipitation out of seawater or from the breakdown of the skeletons of marine invertebrates and algae.

This study, funded by the UK’s Natural Environment Research Council (NERC), shows that large volumes of carbonate crystals are precipitated inside the intestines of marine fish and are then excreted at very high rates, releasing this lesser-known, non-skeletal carbonate into the marine environment. Although this material comes from the guts of marine fish, it is derived from calcium in the seawater they drink rather than any undigested product of their food.

However, the form and fate of these crystals after excretion by the fish was unknown. The researchers therefore conducted a “needle in a haystack” search, to look for microscopic crystals that are unique to fish within areas that are already rich in carbonate crystals from other organisms.

The study was undertaken in The Bahamas, famous for its white carbonate sands and muds, where the preservation of such crystals in shallow sediments was predicted to be good.

Measurements made on fish that were local to The Bahamas yielded conservative estimates that they produce in excess of 6 million kg of carbonate each year across the region, equivalent to an estimated 14% of its total carbonate mud production.

To reach these findings, the team combined data on regional fish biomass in different marine habitats across The Bahamas with laboratory measurements of the production rates for a range of fish species from this region. These production estimates for fish were then compared against published rates of mud production.

The study reveals that fish guts are a direct source of the most fine-grained carbonate with individual crystals generally less than 30 micrometers (or 0.03 mm) in diameter.

These crystals are also produced in an incredibly diverse array of shapes similar to rugby balls, broccoli florets and dumbbells. Despite their small size, the volumes of carbonate produced by individual fish are so immense that this carbonate has direct relevance to understanding marine carbonate budgets.

Lead author Professor Chris Perry, a marine geoscientist at Manchester Metropolitan University, said: “The recognition that fish can act as major producers of carbonate in the marine environments will be completely unexpected to a large section of the marine science community. Given how much carbonate these fish can produce, the findings also clearly have major implications for our understanding of different sources and sinks of carbonate sediment in the oceans and some exciting implications for understanding where much of the mud in limestones and chalks may derive from”.

One of the most interesting issues arising from the study is what it means for our understanding of how marine carbonate sediments accumulate in the first place. The study clearly shows fish to be a unique and novel source of the carbonate sediment in modern marine environments, but the work has equally exciting implications for understanding these processes in the geological record.

Joint corresponding author, Dr. Rod Wilson, a fish biologist at the University of Exeter, said: “An obvious area of future study in this field relates to the geological record and in particular to the role of this process in periods of the Earth’s history when ocean chemistry was very different and temperatures considerably warmer. For example, a preliminary study has estimated fish carbonate production under Cretaceous seawater conditions, the time (146-65 million years ago) when large masses of chalk were deposited (famously including the White Cliffs of Dover). These studies, although in their early stages, suggest massive increases in production of this carbonate by fish during this ancient time. Perhaps fish have been a major contributor to these iconic carbonate deposits, in addition to the better known micro-fossils of shelled organisms? However, we are yet to look for direct evidence of this unusual contribution of fish, and we are currently seeking research funds to help answer this intriguing question.”

And what about the future? The study finds clear evidence that at present such carbonates can accumulate within the marine environment, at least in warm shallow seas, but the fate of this carbonate under changing oceanographic conditions (especially marine chemistry change) is unclear.

On the one hand, rising sea-surface temperatures should result in higher rates of carbonate production by fish since production increases markedly with temperature. On the other hand, increasing ocean acidity may mean more of this carbonate is dissolved, with potential knock-on effects for ocean carbon cycling and absorption of CO2 from the atmosphere.

6,000-year climate record suggests longer droughts, drier climate for Pacific Northwest

Measurement of oxygen isotope ratios (red) and grayscale (black) arranged to show drought cycle duration and intensity with 20th century wet period indicated. -  Mark Abbott
Measurement of oxygen isotope ratios (red) and grayscale (black) arranged to show drought cycle duration and intensity with 20th century wet period indicated. – Mark Abbott

University of Pittsburgh-led researchers extracted a 6,000-year climate record from a Washington lake that shows that the famously rain-soaked American Pacific Northwest could not only be in for longer dry seasons, but also is unlikely to see a period as wet as the 20th century any time soon. In a recent report in the Proceedings of the National Academy of Sciences, the team linked the longer dry spells to the intensifying El Niño/La Niña climate pattern and concluded that Western states will likely suffer severe water shortages as El Niño/La Niña wields greater influence on the region.

The researchers analyzed a sediment core from Castor Lake in north central Washington to plot the region’s drought history since around 4,000 BCE and found that wet and dry cycles during the past millennium have grown longer. The team attributed this recent deviation to the irregular pressure and temperature changes brought on by El Niño/La Niña. At the same time, they reported, the wet cycle stretching from the 1940s to approximately 2000 was the dampest in 350 years.

Lead researcher Mark Abbott, a Pitt professor of geology and planetary science, said those unusually wet years coincide with the period when western U.S. states developed water-use policies. “Western states happened to build dams and water systems during a period that was unusually wet compared to the past 6,000 years,” he said. “Now the cycle has changed and is trending drier, which is actually normal. It will shift back to wet eventually, but probably not to the extremes seen during most of the 20th century.”

Abbott worked with his former graduate student, lead author and Pitt alumnus Daniel Nelson, as well as Pitt professor of geology and planetary science Michael Rosenmeier; Nathan Stansell, a Pitt PhD graduate now a postdoctoral researcher at Ohio State University; and Pitt geology and planetary science graduate student Byron Steinman. The team also included Pratigya Polissar, an assistant research professor at Columbia University’s Lamont-Doherty Earth Observatory; Joseph Ortiz, associate professor of geology at Kent State University; Bruce Finney, a professor of geology at Idaho State University; and Jon Riedel, a geologist at North Cascades National Park in Washington.

The team produced a climate record from the lake mud by measuring the oxygen isotope ratios of the mineral calcite that precipitates from the lake water every summer and builds up in fine layers on the lake floor. More calcite accumulates in wet years than in dry years. They reproduced their findings by measuring grayscale, or the color of mud based on calcite concentration, with darker mud signifying a drier year.

The record in the sediment core was then compared to the Palmer Drought Severity Index, which uses meteorological and tree-ring data to determine drought cycles dating back 1,500 years, Abbott explained. The Castor Lake core matched the Palmer Index reconstructed with tree-ring data and expanded on it by 4,500 years, suggesting that lakebeds are better records of long-term climate change, the authors contend.

Analysis of the sediment core revealed that the climate of the Pacific Northwest fluctuated more or less evenly between wet and dry periods for thousands of years, the researchers wrote. Droughts tended to be lengthier with 25 percent of dry periods during the past 6,000 years persisting for 30 years or more and the longest lingering for around 75 years. Wet periods tended to be shorter with only 19 percent lasting more than 30 years and the longest spanning 64 years.

But since around 1000 AD, these periods have become longer, shifted less frequently, and, most importantly, ushered in more extreme conditions, Abbott said. The two driest cycles the researchers detected out of the past 6,000 years occurred within only 400 years of each other-the first in the 1500s and the second during the Great Depression. Wet periods showed a similar pattern shift with five very wet eras crammed into the past 900 years. The wettest cycle of the past 6,000 years began around the 1650s, and the second most sodden began a mere 300 years later, in the 1940s.

The change in cycle regularity Abbott and his colleagues found correlates with documented activity of El Niño/La Niña. When the patterns became more intense, wet and dry cycles in the Pacific Northwest became more erratic and lasted longer, Abbott said.