Friday, February 26, 2010
2/26/2010 11:09:00 AM Publicado por Alquimia
New data provides the strongest evidence to date that the world's biggest mud volcano, which killed 13 people in 2006 and displaced thirty thousand people in East Java, Indonesia, was not caused by an earthquake, according to an international scientific team that includes researchers from Durham University and the University of California, Berkeley.
Drilling firm Lapindo Brantas has denied that a nearby gas exploration well was the trigger for the volcano, instead blaming an earthquake that occurred 280 kilometers (174 miles) away. They backed up their claims in an article accepted this week for publication in the journal Marine and Petroleum Geology, by lead author Nurrochmat Sawolo, senior drilling adviser for Lapindo Brantas, and colleagues.
In response, a group of scientists from the United Kingdom, United States, Australia and Indonesia led by Richard Davies, director of the Durham Energy Institute, have written a discussion paper in which they refute the main arguments made by Nurrochmat Sawolo and document new data that provides the strongest evidence to date of a link between the well and the volcano. That paper has been accepted for publication in the same journal.
"The disaster was caused by pulling the drill string and drill bit out of the hole while the hole was unstable," Davies said. "This triggered a very large 'kick' in the well, where there is a large influx of water and gas from surrounding rock formations that could not be controlled.
"We found that one of the on-site daily drilling reports states that Lapindo Brantas pumped heavy drilling mud into the well to try to stop the mud volcano. This was partially successful and the eruption of the mud volcano slowed down. The fact that the eruption slowed provides the first conclusive evidence that the bore hole was connected to the volcano at the time of eruption."
The Lusi volcano, which first erupted on May 29, 2006, in the Porong sub-district of Sidoarjo, close to Indonesia's second city of Surabaya, East Java, now covers seven square kilometers – nearly three square miles and is 20 meters (65 feet) thick. The mud flow has razed four villages and 25 factories. Thirteen people have died as a result of a rupture in a natural gas pipeline underneath one of the holding dams. The Lusi crater has been oozing enough mud to fill 50 Olympic size swimming pools every day. All efforts to stem the mud flow have failed, including the construction of dams, levees, drainage channels, and even plugging the crater with concrete balls. Lusi may continue to erupt for decades, scientists believe.
Arguments over the causes of the Lusi volcano have stalled the establishment of liability for the disaster and delayed compensation to thousands of people affected by the mud. The Yogyakarta earthquake that occurred at the time of the volcano was cited by some as a possible cause of the eruption, but the research team rejected this explanation.
The Durham University-led group of scientists believe that their analysis resolves the cause beyond all reasonable doubt. According to their discussion paper, 'The pumping of heavy mud caused a reduction in the rate of flow to the surface. The reason for pumping the mud was to stop the flow by increasing the pressure exerted by the mud column in the well and slowing the rate of flux of fluid from surrounding formations.'
"An earthquake trigger can be ruled out because the earthquake was too small given its distance, and the stresses produced by the earthquake were minute smaller than those created by tides and weather," said co-author Michael Manga, professor of earth and planetary science at the University of California, Berkeley.
The group of scientists has identified five critical drilling errors as the causes of the Lusi mud volcano eruption:
•having a significant open hole section with no protective casing
•overestimating the pressure the well could tolerate
•after complete loss of returns, the decision to pull the drill string out of an extremely unstable hole
•pulling the bit out of the hole while losses were occurring
•not identifying the kick more rapidly
"This is the clearest evidence uncovered so far that the Lusi mud volcano was triggered by drilling," Davies said. "We have detailed data collected over two years that show the events that led to the creation of the Lusi volcano."
"The observation that pumping mud into the hole caused a reduction in eruption rate indicates a direct link between the wellbore and the eruption," he added. "The decision was made to pull the drill bit out of the hole without verifying that a stable mud column was in place and it was done while severe circulating mud losses were in progress. This procedure caused the kick."
(Photo: Channel 9 Australia)
University of California, Berkeley
2/26/2010 11:09:00 AM Publicado por Alquimia
Evidence from the Challenger Deep– the deepest surveyed point in the world's oceans– suggests that tiny single-celled creatures called foraminifera living at extreme depths of more than ten kilometres build their homes using material that sinks down from near the ocean surface.
The Challenger Deep is located in the Mariana Trench in the western Pacific Ocean. It lies in the hadal zone beyond the abyssal zone, and plunges down to a water depth of around 11 kilometres.
"The hadal zone extends from around six kilometres to the deepest seafloor. Although the deepest parts of the deepest trenches are pretty inhospitable environments, at least for some types of organism, certain kinds of foraminifera are common in the bottom sediments," said Professor Andrew Gooday of the National Oceanography Centre, Southampton (NOCS) and member of a UK-Japanese team studying these organisms in samples collected in 2002 during a Japan-USA-Korea expedition to study life in the western depression of the Challenger Deep.
The researchers, whose findings appear in the latest issue of the journal Deep Sea Research, used the remotely operated vehicle KAIKO, operated by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC), to take core samples from the soft sediment of the trench floor. Among many foraminiferans with an organic shell (or 'test'), they found four undescribed specimens with agglutinated tests.
"The Challenger Deep is an extreme environment for agglutinated foraminifera, which construct their tests from a wide range of particles cemented together by calcareous or organic matter," said Gooday. "At these great depths, particles made from biologically formed calcite and silica, as well as minerals such as quartz, should dissolve, leaving only clay grains available for test building."
The researchers were therefore surprised to discover that foraminiferan tests sampled from the Challenger Deep contained calcareous components, including the dissolved remnants of coccoliths, the calcium carbonate plates of tiny algae called coccolithophores, and planktonic foraminiferan test fragments.
The organic test surface of one species was densely pitted with imprints, which the researchers interpreted as representing mineral grains of various types, including quartz, which subsequently dissolved. Agglutinated particles, presumed to be clay minerals, survived only in one specimen.
"Our observations demonstrate that coccoliths, and probably also planktonic foraminiferan tests, reach the Challenger Deep intact," said Gooday. "These particles were probably transported to these extreme depths in rapidly sinking marine snow, the aggregated remains of phytoplankton that lived in the sunlit surface ocean, or in faecal pellets from zooplankton."
It seems likely, therefore, that at least some agglutinated foraminifera living at extreme hadal depths build their homes from material that sinks down from the ocean above, rather like manna from heaven.
(Photo: National Oceanography Centre)
National Oceanography Centre
2/26/2010 11:07:00 AM Publicado por Alquimia
A research team led by biogeochemists at the University of California, Riverside has developed a detailed and dynamic three-dimensional model of Earth's early ocean chemistry that can significantly advance our understanding of how early animal life evolved on the planet.
Working on rock samples from the Doushantuo Formation of South China, one of the oldest fossil beds and long viewed by paleontologists to be a window to early animal evolution, the research team is the first to show that Earth's early ocean chemistry during a large portion of the Ediacaran Period (635-551 million years ago) was far more complex than previously imagined.
Their work is the first comprehensive geochemical study of the Doushantuo Formation to investigate the structure of the ocean going from shallow to deep water environments. It is also one of the most comprehensive studies for any Precambrian interval. (The Precambrian refers to a stretch of time spanning from the inception of the Earth approximately 4.5 billion years ago to about 540 million years ago. It was in the Precambrian when the first single-celled microbes evolved 3.5 billion years ago or earlier, followed by the first multicellular animals much later, around 700 million years ago.)
The researchers' model for the ancient ocean argues for a stratified marine basin, one with a chemically layered water column. While the surface ocean was oxygen-rich, the deep ocean was ferruginous – oxygen-deprived and iron-dominated. Further, sandwiched in this deep ocean was a dynamic wedge of sulfidic water, highly toxic to animal life, that impinged against the continental shelf.
Dominated by dissolved hydrogen sulfide, the sulfidic wedge was in a state of flux, varying in size and capable of encroaching on previously oxygenated areas of the continental shelf — killing all animal life there. The overall picture is a marine basin with co-existing oxygen-rich, sulfidic and ferruginous water layers.
Study results appeared Feb. 11 in Science Express.
In the modern sulfur-rich ocean, hydrogen sulfide in oxygen-poor waters reacts with iron to form the mineral pyrite, thus stripping the dissolved iron from the water column. But the researchers' results show that under specific geochemical conditions in the early ocean, when levels of dissolved sulfate (the source of hydrogen sulfide in the ocean) and oxygen were particularly low compared to the modern ocean, layers of sulfidic waters could coexist with ferruginous water masses, and even persist for long periods of time.
"This is an entirely new interpretation of ancient ocean chemistry," said Chao Li, a research specialist in UC Riverside's Department of Earth Sciences and the first/lead author of the research paper. "Our model provides a brand-new backdrop for the earliest evolution of animal life on the planet. We show that the sulfidic ocean wedge, along with an absence of oxygen, can hinder the colonization of early animals on the shallow seafloor and influence their evolution as they take a foothold. In other words, we cannot ignore hydrogen sulfide when piecing together how animals and other eukaryotes such as algae evolved on our planet."
The researchers posit that their robust pattern of a stratified marine basin is the best example of a new paradigm in studies of Precambrian ocean chemistry. They predict the record of much of the early ocean elsewhere will show similarities to the complex chemical layering seen in South China.
"This new world order asks that we take into account co-occurring spatial variations in water chemistry in an ocean basin, specifically when moving from near the shallow shoreline along continental shelves to progressively outwards into deeper waters, and when applying a diverse range of complementary geochemical analyses to elucidate these changes in ocean chemistry," said Gordon Love, an assistant professor of biogeochemistry, who collaborated on the study and in whose lab Li works.
Li explained that in the scientific literature the generally patchy fossil record of early animals observed through the Ediacaran has largely been attributed to poor preservation of fossils. The new research shows, however, that changes in environmental conditions, in this case variations in distribution of hydrogen sulfide, may explain gaps seen in the Ediacaran fossil record.
"Our model points to early animal life having to cope with changing chemical environments even in the shallow waters of the continental shelf," said Love, the principal investigator on the National Science Foundation (NSF) grant that funded the study. "At times, movement of toxic sulfide-rich waters into the shallow water would be calamitous to animal life. This well explains the patchy time record of animal fossils in most Ediacaran basins."
Timothy Lyons, a professor of biogeochemistry and a co-principal investigator on the NSF grant, explained that only an incomplete temporal record of animal microfossils has been unearthed in the Doushantuo Formation despite considerable efforts.
"Much of the unequivocal fossil evidence for animals is in the form of microfossil cysts found in only a few sedimentary layers, suggesting that the early animals were environmentally stressed," he said. "An explanation for this pattern is certain to lie in our model."
According to the researchers, a stratified marine basin was favored by an overall deficiency of dissolved sulfate in seawater following a long history of oxygen deficiency in the ocean. Ordinarily, sulfate gets introduced into the ocean from the weathering of continental sulfide minerals exposed to an atmosphere with photosynthetically produced oxygen. But the researchers argue that major glaciation events predating Doushantuo time exacerbated the scarcity of sulfate. They note that if glaciation was globally extensive, gas and chemical interactions between the oceans and atmosphere would be suppressed by a layer of ice cover in many areas.
"Ocean chemistry changes as the ice coverage acts like a pie crust sealing off the ocean interior from the atmosphere," Love said. "The effects of such ice coverage are a reduction of sulfate inputs into the ocean brought in by rivers and a buildup of dissolved iron in the deep ocean sourced by volcanic activity along the mid-ocean ridges. Later, as the ice cover abated, sulfate inputs from rivers localized the animal-inhibiting wedge of hydrogen sulfide along the shallow basin margins."
(Photo: Alex Sessions, Caltech)
University of California, Riverside