Low Oxygen and Molybdenum Levels in Ancient Oceans Delayed Evolution of Life by Two Billion Years


UCR-led study tracked biogeochemical signatures preserved in ancient sedimentary rocks to establish nature and timing of oxygenation of Earth’s atmosphere

A deficiency of oxygen and the heavy metal molybdenum in the ancient deep ocean may have delayed the evolution of animal life on Earth by nearly two billion years, a study led by UC Riverside biogeochemists has found.

The researchers arrived at their result by tracking molybdenum in black shales, which are a kind of sedimentary rock rich in organic matter and usually found in the deep ocean. Molybdenum is a key micronutrient for life and serves as a proxy for oceanic and atmospheric oxygen amounts.

Study results appear in the March 27 issue of Nature.

Following the initial rise of oxygen in the Earth’s atmosphere 2.4 billion years ago, oxygen was transferred to the surface ocean to support oxygen-demanding microorganims. Yet the diversity of these single-celled life forms remained low, and their multicellular descendants, the animals, did not appear until about 600 million years ago, explained Timothy Lyons, a professor of biogeochemistry in the Department of Earth Sciences and one of the study’s authors.

Suspecting that deficiencies in oxygen and molybdenum might explain this evolutionary lag, Lyons and his colleagues measured abundances of molybdenum in ancient marine sediments over time to estimate how much of the metal had been dissolved in the seawater in which the sediments formed.

The researchers found significant, firsthand evidence for a molybdenum-depleted ocean relative to the high levels measured in modern, oxygen-rich seawater.

“These molybdenum depletions may have retarded the development of complex life such as animals for almost two billion years of Earth history,” Lyons said. “The amount of molybdenum in the ocean probably played a major role in the development of early life. As in the case of iron today, molybdenum can be thought of as a life-affirming micronutrient that regulates the biological cycling of nitrogen in the ocean.

“At the same time, molybdenum’s low abundance in the early ocean tracks the global extent of oxygen-poor seawater and implies that the amount of oxygen in the atmosphere was still low.

“Knowing the amount of oxygen in the early ocean is important for many reasons, including a refined understanding of how and when appreciable oxygen first began to accumulate in the atmosphere,” Lyons said. “These steps in oxygenation are what gave rise ultimately to the first animals almost 600 million years ago – just the last tenth or so of Earth history.”

Earth’s oxygenation

For animal life to commence, survive and eventually expand on Earth, a threshold amount of oxygen – estimated to be on the order of 1 to 10 percent of present atmospheric levels of oxygen – was needed.

Past research has shown that Earth’s oxygenation occurred in two major steps:

The first step, around 2.4 billion years ago, took place as the ocean transitioned to a state where only the surface ocean was oxygenated by photosynthesizing bacteria, while the deep ocean was relatively oxygen-free.

The second step, around 600 million years ago, marked the occasion when the entire ocean became fully oxygenated through a process not yet fully understood.

“We wanted to know what the state of the ocean was between the two steps,” said Clinton Scott, a graduate student working in Lyons’s lab and the first author of the research paper. “By tracking molybdenum in shales rich in organic matter, we found the deep ocean remained oxygen- and molybdenum-deficient after the first step. This condition may have had a negative impact on the evolution of early eukaryotes, our single-celled ancestors. The molybdenum record also tells us that the deep ocean was already fully oxygenated by around 550 million years ago.”

According to Scott, the timing of the oxygenation steps suggests that significant events in Earth history are related. Scientists have long speculated that the evolution of the first animals was linked somehow to the so-called Snowball Earth hypothesis, which posits that the Earth was covered from pole to pole in a thick sheet of ice for millions of years at a time. “The second oxygenation step took place not long after the last Snowball Earth episode ended around 600 million years ago,” Scott said. “So one question is: Did this global glaciation play a role in the increasing abundance of oxygen which, in turn, enabled the evolution of animals?”

Scott and Lyons were joined in the research by A. Bekker of the Carnegie Institution of Washington, DC; Y. Shen of the Université du Québec à Montréal, Canada; S.W. Poulton of Newcastle University, Newcastle upon Tyne, United Kingdom; X. Chu of the Chinese Academy of Sciences, Beijing, China; and A.D. Anbar of Arizona State University, Tempe, Ariz.

The research was supported by grants from the U.S. National Science Foundation Division of Earth Sciences and the NASA Astrobiology Institute.

More about molybdenum as a proxy for ocean chemistry

Molybdenum, a metal abundant in the ocean today but less so at times in the past, is an excellent tracer of ancient chemistry for two reasons. First, the primary source of molybdenum to the ocean is oxidative weathering of continental crust, requiring oxygen in the atmosphere. Second, molybdenum is removed primarily in marine sediments where oxygen is absent and sulfide is abundant. Thus the enrichment of molybdenum in ancient organic-rich shales requires oxygen in the atmosphere but high sulfur and very low or no oxygen in the deep ocean. This combination is relatively rare today but may have been common when oxygen was less abundant in the earlier atmosphere.

When oxygen is available in the atmosphere, the amount of dissolved molybdenum in seawater is determined by the extent of hydrogen-sulfide-containing sediments and bottom waters (the colder, more isolated, lowermost layer of ocean water). Where sulfidic environments are widespread, the pool of molybdenum remaining in seawater is small, growing as the sulfidic environments shrink. The amount of molybdenum in the seawater is reflected in the magnitude of molybdenum enrichment in shales deposited in the deep ocean.

The UCR-led team of researchers estimated the size of the oceanic reservoir, and thus the extent of sulfidic bottom waters and sediments, based on the concentration of molybdenum in ancient black shales. They did so by dissolving the samples in a cocktail of acids and analyzing the dissolved rock for concentration using a mass spectrometer. The amount of this metal in the shales tracks the oxygen state of the early ocean and atmosphere and also points to the varying abundance of this essential ingredient of life. Molybdenum limitations may have delayed the development of eukaryotes, including the first animals, our earliest multicellular cousins.

Dramatic developments at Kilauea Volcano: Scientists work to keep public safe and informed

Explosive eruptions and noxious gas emissions at Kilauea Volcano in Hawaii this week have prompted scientists to work around the clock to understand what will happen next and how to keep the public out of harm’s way.

Scientists are monitoring gas emissions and seismic activity at Kilauea, which on March 19 experienced its first explosive eruption since 1924. The volcano is also emitting sulfur dioxide at toxic levels.

The National Park Service has closed Crater Rim Drive through the south caldera area until further notice. The U.S. Geological Survey is issuing frequent updates, which can be accessed at http://hvo.wr.usgs.gov/kilauea/.

Sulfur dioxide emissions at the volcano’s summit have increased to a rate that is likely to be hazardous for areas downwind of Halema’uma’u crater. Future explosions from Halema’uma’u Crater are possible.

“This historic activity has created new hazards that did not exist before – explosive eruptions as well as toxic sulfur dioxide emissions – in the middle of a national park,” said U.S. Geological Survey Volcano Hazards Program Coordinator John Eichelberger. “Our job is to give emergency responders and the civil defense community the very best information we can provide about what the volcano is doing and what it is likely to do in the future.”

Under the sea

Scientists explore huge volume of molten rock now frozen into the crust under the ocean’s floor.

For the first time scientists have mapped the layers of once molten rock that lie beneath the edges of the Atlantic Ocean and measure over eight miles thick in some locations.

The research, reported in this week’s edition of Nature, gives us a better understanding of what may have happened during the break up of continents to form new mid-ocean ridges. The same volcanic activity in the North Atlantic may also have caused the subsequent release of massive volumes of greenhouse gases which led to a spike in global temperatures 55 million years ago.

The scientists, led by Professor Robert White, FRS at the University of Cambridge, also developed a new method of seeing through the thick lava flows beneath the seafloor to the sediments and structures beneath. The technique is now being employed to further oil exploration of the area which was previously restricted by the inability to image through the lava flows.

When a continent breaks apart, as Greenland and Northwest Europe did 55 million years ago, it is sometimes accompanied by a massive outburst of volcanic activity due to a ‘hot spot’ in the mantle that lies beneath the 55 mile thick outer skin of the earth. When the North Atlantic broke open, it produced 1-2 million cubic miles (5-10 million cubic kilometres) of molten rock which extended across 300,000 square miles (one million square kilometres). Most of the volcanic rock is now underwater and buried by more recent sediments. However the edge of this huge volcanic region is visible on land in a few places including the Giant’s Causeway in Northern Ireland.

For the first time scientists mapped the huge quantities of molten rock in the North Atlantic. The rock had been injected into the crust of the earth at a depth of 5-10 miles (10-20 kilometres) beneath the surface along the line of the continental breakup 55 million years ago. Using seismic methods, they were able to map the layers of lava flows both near the surface and deep into the earth.

There is a considerable controversy at present as to whether the large scale volcanism was caused by abnormally hot mantle deep in the earth (a ‘hot spot’) or whether it was caused by some other means, such as a compositional change in the mantle that mean it could more easily be melted. The researchers demonstrate in this paper that the volcanic activity requires a temperature anomaly, supporting the ‘hot spot’ model.

Additionally, the scientists hope that a better understanding of what happened 55 million years ago will also provide insight into the changes that occur to the atmosphere and biosphere during volcanic activity.

Professor White said: “At the time of the break-up of the North Atlantic 55 million years ago there was a very sudden increase in global temperatures: in fact the earth has never been as hot since then, although the global warming that humans are now causing is likely to take the earth back to the same high temperatures as existed for a short period then.

“The increases in global temperatures are thought to have been caused by a massive release of methane from under the seabed – methane is almost 25 times worse than carbon dioxide as a greenhouse gas. A better understanding of volcanism and the underlying hot spot will help us understand how such activity might have triggered the methane release and subsequent global warming.”

The researchers’ findings also have implications for oil exploration in the region. Large volumes of oil have already been discovered (and are being extracted) in the sediments under the seabed between the Shetland Islands and the Faroe Islands. If these same sediments extend westward towards the Faroe Islands, as geological models suggest they do, there may be a lot more oil to be found.

However, because the sediments had thick layers of lava flows (molten rock) poured over them at the time the north Atlantic broke open, conventional exploration techniques have not been able to see through the lavas because they reflect the seismic energy. The scientists succeeded in developing a method of seeing through these thick lava flows to the sediments and structures that lie beneath them.

Britain’s biggest meteorite impact found

Evidence of the biggest meteorite ever to hit the British Isles has been found by scientists from the University of Aberdeen and the University of Oxford.

The scientists believe that a large meteorite hit northwest Scotland about 1.2 billion years ago near the Scottish town of Ullapool.

Previously it was thought that unusual rock formations in the area had been formed by volcanic activity. But, the team report in the journal Geology that they found evidence buried in a layer of rock which they now believe is the ejected material thrown out during the formation of a meteorite crater. Ejected material from the huge meteorite strike is scattered over an area about 50 kilometres across, roughly centred on the northern town of Ullapool.

Ken Amor of Oxford University’s Department of Earth Sciences, co-author on the Geology paper, said: “Chemical testing of the rocks found the characteristic signature of meteoritic material, which has high levels of the key element iridium, normally only found in low concentrations in surface rocks on Earth. We found more evidence when we examined the rocks under a microscope; tell-tale microscopic parallel fractures that also imply a meteorite strike.”

The proposed volcanic origin for the rock formations has always been a puzzle as there are no volcanic vents or other volcanic sediments nearby. Scientists took samples from the formations during fieldwork in 2006 and have just had their findings published.

Professor John Parnell, Head of Geology & Petroleum Geology at the University of Aberdeen, also a co-author on the paper, said: “These rocks are superbly displayed on the west coast of Scotland, and visited by numerous student parties each year. We’re very lucky to have them available for study, as they can tell us much about how planetary surfaces, including Mars, become modified by large meteorite strikes. Building up the evidence has been painstaking, but has resulted in proof of the largest meteorite strike known in the British Isles.

Scott Thackrey,a PhD studentin Geology and Petroleum Geology at the University of Aberdeen, and also co-author of the paper, added: “The type of ejected deposit discovered in North West Scotland is only observed on planets and satellites that possess a volatile rich subsurface, for example, Venus, Mars and Earth. Due to the rare nature of these deposits, each new discovery provides revelations in terms of the atmospheric and surface processes that occur round craters just after impact.”

“If there had been human observers in Scotland 1.2 billion years ago they would have seen quite a show,” continued Ken Amor. “The massive impact would have melted rocks and thrown up an enormous cloud of vapour that scattered material over a large part of the region around Ullapool. The crater was rapidly buried by sandstone which helped to preserve the evidence.”

Since the formation of the solar system leftover space material has collided regularly with the Earth and other planets. Some of these impacts are large enough to leave craters, and there are about 174 known craters or their remnants on Earth.

Ken Amor added: “This is the most spectacular evidence for a meteorite impact within the British Isles found to date, and what we have discovered about this meteorite strike could help us to understand the ancient impacts that shaped the surface of other planets, such as Mars.”

Would You Like a Large Shake with that Little Mac?

Shake Per View â€
Shake Per View — Participants in a project led by SDSC’s Network for Earthquake Engineering Simulation Cyberinfrastructure Center (NEESit) demonstrate iSeismograph, a new software tool for students to study, store and share data using a widely available, cost-efficient and compact platform — a laptop computer. The video camera in all newer laptops shows a view of a shaking board (top) while the computer’s sudden motion sensor records real-time motions on a graph (bottom). – Credit: San DiegoSupercomputerCenter, UC San Diego.

Researchers Turn SeisMac Feature on Apple Laptops into an Innovative Learning Tool

What began as a way to prevent damage to the hard drive from a dropped laptop has led to an innovative project that lets seismology and engineering students or researchers study, store and share data to better understand the science of structural dynamics – be it a gentle tap or a full blown temblor.

Researchers with the Network for Earthquake Engineering Simulation Cyberinfrastructure Center (NEESit) at the San Diego Supercomputer Center created a new application by writing dedicated, open source software programs that combine the tri-axis accelerometer, or sudden motion sensor built into every recent Apple laptop, with the iSight video camera that’s used in newer Intel-based laptops for videoconferencing.

While free downloads of the SeisMac 2.0 software, developed under a separate grant from the National Science Foundation, are available to turn Apple’s OS X application laptops into real-time seismographs, the SDSC’s iSeismograph project was envisioned as providing researchers with a data acquisition system for acceleration measurement using a widely available, cost-efficient and compact platform – a laptop computer.

“We believe this initiative has strong potential as an educational and research tool to stimulate interest in engineering and science at the earliest levels, and to promote the development of future leaders, particularly in the field of earthquake research,” said Lelli Van Den Einde, assistant director of the NEESit program based at SDSC, an organized research unit at the University of California, San Diego. “In addition, the combination of commercially available technology and open source software creates an ideal environment for worldwide collaboration and access at the university and post-graduate levels.”

SDSC researchers have already conducted a pilot classroom project with about 90 UCSD students participating as part of an undergraduate earthquake engineering course. The students, who had little or no experience in measuring structural dynamics, benefited from the visual and quantitative demonstrations, enabling researchers to suggest curriculums for future classroom demonstrations and study.

Specifically, SDSC researchers found a way to link the existing accelerometer and video sensor in all newer Macintosh laptops to its NEESit Real-time Data Viewer (RDV), which provides a graphical display of the movement. That, in turn, was linked to the Open Source Data Turbine, a streaming middleware system funded by the National Science Foundation used for sensor-based observing of a full range of environmental events, from structural analysis to weather data.

Once data from an event is captured in the Data Turbine server’s archive, it is automatically transferred using the laptop’s wireless network interface into the NEEScentral database repository, where students and researchers can collaborate on a global scale by analyzing, processing and sharing information. NEEScentral is a high-level data storage model that is universal to all earthquake engineering disciplines and contains information on how to archive and share data.

Software from the iSeismograph project can be downloaded for free by accessing it online at http://it.nees.org/software/iSeismograph for installation in any MacBook laptop. Data can be shared through the NEESit Data Repository (NEEScentral) after a user account is established by accessing https://central.nees.org/acct/index.php.

Researchers are scheduled to present full details of the iSeismograph project this October at the 38th annual ASEE/IEEE “Frontiers in Education” conference in Saratoga Springs, New York.

The iSeismograph initiative was funded by the NSF through the NEES Consortium, Inc., which manages NEES as a national, shared-use research facility encompassing 15 universities for the earthquake engineering community.

In addition to Van Den Einde, other SDSC researchers for the iSeismograph project include Wei Deng, production infrastructure support manager, and Paul Hubbard, with the Cyberinfrastructure Laboratory for Environmental Observing Systems (CLEOS) group. Additional members include Professor Ahmed Elgamal and graduate student Patrick Wilson, with UCSD’s Jacobs School of Engineering; Terry Weymouth, an associate research scientist with the University of Michigan; and Jason Hanley, formerly with the University at Buffalo.

Antarctic Ice Shelf Disintegrating As Result Of Climate Change, Scientists Say

This series of satellite images shows the Wilkins Ice Shelf as it begins to break up. The large image is from March 6. The images at right, from top to bottom, are from Feb. 28, Feb. 29 and March 8. The images were processed from the MODIS satellite sensor flying on NASA's Earth Observing System Aqua and Terra satellites. Images courtesy NSIDC, NASA, University of Colorado.
This series of satellite images shows the Wilkins Ice Shelf as it begins to break up. The large image is from March 6. The images at right, from top to bottom, are from Feb. 28, Feb. 29 and March 8. The images were processed from the MODIS satellite sensor flying on NASA’s Earth Observing System Aqua and Terra satellites. Images courtesy NSIDC, NASA, University of Colorado.

Satellite imagery from the University of Colorado at Boulder’s National Snow and Ice Data Center shows a portion of Antarctica’s massive Wilkins Ice Shelf has begun to collapse because of rapid climate change in a fast-warming region of the continent.

While the area of collapse involves 160 square miles at present, a large part of the 5,000-square-mile Wilkins Ice Shelf is now supported only by a narrow strip of ice between two islands, said CU-Boulder’s Ted Scambos, lead scientist at NSIDC. “If there is a little bit more retreat, this last ‘ice buttress’ could collapse and we’d likely lose about half the total ice shelf area in the next few years.”

In the past 50 years, the western Antarctic Peninsula has experienced the biggest temperature increase on Earth, rising by 0.9 degree F per decade. “We believe the Wilkins has been in place for at least a few hundred years, but warm air and exposure to ocean waves are causing a breakup,” said Scambos, who first spotted the disintegration activity in March.

Satellite images indicate the Wilkins began its collapse on Feb. 28. Data revealed that a large iceberg, measuring 25.5 by 1.5 miles, fell away from the ice shelf’s southwestern front, triggering a runaway disintegration of 220 square miles of the shelf interior. The Wilkins Ice Shelf is a broad sheet of permanent floating ice on the southwest Antarctic Peninsula roughly 1,000 miles south of South America.

The edge of the shelf crumbled into the sky-blue pattern of exposed deep glacial ice that has become characteristic of climate-induced ice shelf breakups such as the Larsen B ice shelf breakup in 2002, said Scambos. A narrow beam of intact ice about 3.7 miles wide was protecting the remaining shelf from further breakup as of March 23.

Scientists track ice shelves and study collapses carefully because some of them hold back glaciers, which if unleashed, can accelerate and raise sea level, Scambos said. “The Wilkins disintegration won’t raise sea level because it already floats in the ocean, and few glaciers flow into it. However, the collapse underscores that the Wilkins region has experienced an intense melt season. Regional sea ice has all but vanished, leaving the ice shelf exposed to the action of waves.”

With Antarctica’s summer melt season drawing to a close, scientists do not expect the Wilkins to further disintegrate in the next several months. “This unusual show is over for this season,” Scambos said. “But come January, we’ll be watching to see if the Wilkins continues to fall apart.”

After images from NASA’s Moderate Resolution Imaging Spectroradiometer, or MODIS, and data from the ICESat satellite showed that a portion of the ice shelf was in a state of collapse in March, Scambos alerted colleagues around the world.

The British Antarctic Survey flew over the shelf, collecting video footage and other observations. BAS glaciologist David Vaughan, who said the ice shelf is supported by a single strip of ice strung between two islands, said the Wilkins is the largest ice shelf on West Antarctica yet to be threatened. “This shelf is hanging by a thread.”

Associate Professor Cheng-Chien Liu at Taiwan’s National Cheng-Kung University used high-resolution color satellite images of the area from Taiwan’s Formosat-2 satellite operated by the National Space Organization to analyze the activity. “It looks as if something is slicing the ice shelf piece by piece on an incredible scale, kilometers long but only a few hundred meters in width,” Cheng-Chien said.

In addition, Andrés Rivera and Gino Cassasa at the Laboratory for Glaciology and Climate Change at the Center of Scientific Study in Chile acquired images of the Wilkins from the ASTER instrument aboard NASA’s Terra satellite.

The combined efforts have begun to provide observational data that will improve scientific understanding of the mechanisms behind ice shelf collapse, Scambos said. “The Wilkins is an example of an event we don’t see very often, but it’s a key process in being able to predict how sea level will change in the future.”

The Wilkins is one of a string of ice shelves that have collapsed in the West Antarctic Peninsula in the past 30 years. The Larsen B became the most well-known of these, disappearing in just over 30 days in 2002. The Prince Gustav Channel, Larsen Inlet, Larsen A, Wordie, Muller and Jones ice shelf collapses also underscore the unprecedented warming in this region of Antarctica, said Scambos.

New findings from Tibetan Plateau suggest uplift occurred in stages

 UCSC graduate student Peter Lippert and coworker Igor Villa of the University of Bern collect samples from an outcrop in Tibet - Credit: Xixi Zhao
UCSC graduate student Peter Lippert and coworker Igor Villa of the University of Bern collect samples from an outcrop in Tibet – Credit: Xixi Zhao

The vast Tibetan Plateau–the world’s highest and largest plateau, bordered by the world’s highest mountains–has long challenged geologists trying to understand how and when the region rose to such spectacular heights. New evidence from an eight-year study by U.S. and Chinese researchers indicates that the plateau rose in stages, with uplift occurring first in the central plateau and later in regions to the north and south.

“The middle part of the plateau was uplifted first at least 40 million years ago, while the Himalayan Range in the south and also the mountains to the north were uplifted significantly later,” said Xixi Zhao, a research scientist at the University of California, Santa Cruz.

The team found marine fossils suggesting that the now lofty Himalayas remained below sea level at a time when the central plateau was already at or near its modern elevation, Zhao said. The average elevation of the plateau today is more than 4,500 meters (14,850 feet).

The researchers published their findings in the Proceedings of the National Academy of Sciences (online the week of March 24 and later in a print edition). Zhao, who is affiliated with the Institute of Geophysics and Planetary Physics at UCSC, is the second author of the paper. First author Chengshan Wang of the China University of Geosciences in Beijing has been collaborating with Zhao and other UCSC researchers since 1996.

Known as “the roof of the world,” the Tibetan Plateau was created by the ongoing collision of tectonic plates as India plows northward into Asia. Coauthor Robert Coe, a professor of Earth and planetary sciences at UCSC, said ideas about how the uplift of the plateau occurred have been evolving since well before his first visit to Tibet in 1988.

“People used to talk about the whole plateau coming up at once, but it has become clear that different parts of the plateau were elevated at different times,” Coe said. “Our work shows that the central part of the plateau was uplifted first, and it seems to fit pretty well with other studies.”

The rise of the Tibetan Plateau led to dramatic changes in the climate, both regionally and globally. For climate researchers trying to understand major episodes of global climate change in Earth’s past, the timing of the uplift is a crucial piece of information.

“One of the traditional views of when Tibet became a high plateau is that it’s a relatively recent phenomenon that happened in the last 15 million years,” said coauthor Peter Lippert, a UCSC graduate student who has spent five field seasons studying the geology of the plateau. “The existence of a high plateau at least 40 million years ago could have important climatic implications.”

The team of U.S. and Chinese geologists based their findings on extensive field studies conducted mostly in a remote interior region of the Tibetan Plateau. They focused on an area called the Hoh Xil Basin in the north-central part of the plateau. The area’s geologic history is recorded in layers of sedimentary rock 5,000 meters thick. Now a part of the high plateau, it was once a basin on the northern edge of the central plateau, Lippert said.

“The structure of the basin and way the sediments were deposited show that it is the type of basin that forms at the base of large mountains. So we’ve shown that there was high topography to the south of the Hoh Xil Basin at least 40 million years ago,” he said.

Several lines of evidence support the team’s conclusions. In addition to field studies, the researchers used a variety of laboratory techniques to analyze and date the rocks. Past changes in Earth’s magnetic field, recorded in the magnetization of the rocks, provide one method of dating. Called magnetostratigraphy, this analysis was performed in Coe’s laboratory at UCSC. Another dating technique used in the study, called apatite fission-track analysis, is based on the damage trails left in apatite crystals by the decay of radiogenic isotopes.

The researchers also discovered volcanic rock in an area of the central plateau south of the Hoh Xil Basin. The flat bed of hardened lava lies on top of tilted and folded layers of sedimentary rocks; geochronology techniques dated it to 40 million years ago.

“The presence of these flat-lying volcanic rocks tells us that the sedimentary rock was deformed prior to the volcanism, and it extends the age of volcanism in this part of Tibet from 15 million to 40 million years ago,” Lippert said.

In the Himalayas, the team found fossils of marine plankton called radiolarians that turned out to be 5 million years younger than any previously discovered marine fossils from that area. The discovery narrows the window of time during which the Himalayas could have been uplifted. When the central part of the Tibetan plateau was uplifted more than 40 million years ago, Mount Everest and the rest of the Himalayas were still part of a deep ocean basin, Zhao said.

The Himalayan region is very complicated, however, and other groups are working to determine the timing of its uplift more precisely, said Lippert. “Our main contribution has been the data we gathered from the north-central part of the plateau, which has not been well studied,” he said.

Zhao noted that the U.S. researchers could not have gained access to this area without the support of their Chinese colleagues. This long-term collaboration has included exchanges of graduate students between UCSC and Chinese universities, as well as opportunities for UCSC undergraduates to conduct field research in Tibet. “It has been a very good research collaboration, with a strong educational component as well,” Zhao said.

In addition to Wang, Zhao, Lippert, and Coe, the coauthors of the paper include Zhifei Liu of Tongji University in Shanghai; Stephan Graham of Stanford University; Haisheng Yi, Lidong Zhu, and Shun Liu of Chengdu University of Technology in Chengdu; and Yalin Li of China University of Geosciences in Beijing. This research was supported in part by grants from the National Key Basic Research Program of China, the U.S. National Science Foundation, and the Institute of Geophysics and Planetary Physics at UCSC.

Current Major Flooding in U.S. a Sign of Things to Come

Map of US spring flood risk. (Credit: NOAA)
Map of US spring flood risk. (Credit: NOAA)

Major floods striking America’s heartland in March offer a preview of the spring seasonal outlook, according to NOAA’s National Weather Service. Several factors will contribute to above-average flood conditions, including record rainfall in some states and snow packs, which are melting and causing rivers and streams to crest over their banks. The week of March 15, more than 250 communities in a dozen states are experiencing flood conditions.

The science supporting NOAA’s short-term forecasts allows for a high level of certainty. National Weather Service forecasters highlighted potential for the current major flood event a week in advance and began working with emergency managers to prepare local communities for the impending danger.

“We expect rains and melting snow to bring more flooding this spring,” said Vickie Nadolski, deputy director of NOAA’s National Weather Service. “Americans should be on high alert to flood conditions in your communities. Arm yourselves with information about how to stay safe during a flood and do not attempt to drive on flooded roadways – remember to always turn around, don’t drown.”

Nadolski called on local emergency management officials to continue preparations for a wet spring and focus on public education to ensure heightened awareness of the potential for dangerous local conditions.

Above-normal flood potential is evident in much of the Mississippi River basin, the Ohio River basin, the lower Missouri River basin, Pennsylvania, New Jersey, most of New York, all of New England, and portions of the West, including Colorado and Idaho:

Heavy winter snow combined with recent rain indicates parts of Wisconsin and Illinois should see minor to moderate flooding, with as much as a 20 to 30 percent chance of major flooding on some rivers in southern Wisconsin and northern Illinois.

Current snow depth in some areas of upstate New York and New England is more than a foot greater than usual for this time of the year, which increases flood potential in the Connecticut River Valley.

Locations in the mountains of Colorado and Idaho have 150 to 200 percent of average water contained in snowpack leading to a higher than normal flood potential.

Snowfall has been normal or above normal across most of the West this winter; however, preexisting dryness in many areas will prevent most flooding in this region. Runoff from snow pack is expected to significantly improve stream flows compared to last year for the West.

The drought outlook indicates continued general improvement in the Southeast, although some reservoirs are unlikely to recover before summer. Winter precipitation chipped away at both the western and southeastern drought. On the U.S. Drought Monitor, extreme drought coverage dropped from nearly 50 percent in mid-December to less than 20 percent in the Southeast for March.

Overall, the Southeast had near-average rainfall during the winter with some areas wetter than average. Nevertheless, lingering water supply concerns and water restrictions continue in parts of the region.

Drought is expected to continue in parts of the southern Plains despite some recent heavy rain. Parts of Texas received less than 25 percent of normal rainfall in the winter, leading 165 counties to enact burn bans by mid-March. Seasonal forecasts for warmth and dryness suggest drought will expand northward and westward this spring.

During the spring season, weather can change quickly – from drought to flooding to severe weather, including outbreaks of tornadoes.

Using Ground Penetrating Radar to Observe Hidden Underground Water Processes

Researchers present applications of radar technology for exploring the properties and movement of water beneath our feet.

To meet the needs of a growing population and to provide it with a higher quality of life, increasing pressures are being placed on the environment through the development of agriculture, industry, and infrastructures.

Soil erosion, groundwater depletion, salinization, and pollution have been recognized for decades as major threats to ecosystems and human health. More recently, the progressive substitution of fossil fuels with biofuels for energy production have been recognized as potential threats to water resources and sustained agricultural productivity.

The top part of the earth between the surface and the water table is called the vadose zone. The vadose zone mediates many of the processes that govern water resources and quality, such as the partition of precipitation into infiltration and runoff, groundwater recharge, contaminant transport, plant growth, evaporation, and energy exchanges between the earth’s surface and its atmosphere. It also determines soil organic carbon sequestration and carbon-cycle feedbacks, which could substantially affect climate change.

The vadose zone’s inherent spatial variability and inaccessibility make direct observation of the important belowground (termed “subsurface”) processes difficult. Conventional soil sampling is destructive, laborious, expensive, and may not be representative of the actual variability over space and time. In a societal context where the development of sustainable and optimal environmental management strategies has become a priority, there is a strong prerequisite for the development of noninvasive characterization and monitoring techniques of the vadose zone.

In particular, approaches integrating water movement, geological, and physical principles (called hydrogeophysics) applied at relevant scales are required to appraise dynamic belowground phenomena and to develop optimal sustainability, exploitation, and remediation strategies.

Among existing geophysical techniques, ground-penetrating radar (GPR) technology is of particular interest for providing high-resolution subsurface images and specifically addressing water-related questions. GPR is based on the transmission and reception of electromagnetic waves into the ground, whose propagation velocity and signal strength is determined by the soil electromagnetic properties and spatial distribution. As the electric permittivity of water overwhelms the permittivity of other soil components, the presence of water in the soil principally governs GPR wave propagation. Therefore, GPR-derived dielectric permittivity is usually used as surrogate measure for soil water content.

In the areas of unsaturated zone hydrology and water resources, GPR has been used to identify soil layering, locate water tables, follow wetting front movement, estimate soil water content, assist in subsurface hydraulic parameter identification, assess soil salinity, and support the monitoring of contaminants.

The February 2008 issue of Vadose Zone Journal includes a special section that presents recent research advances and applications of GPR in hydrogeophysics. The studies presented deal with a wide range of surface and borehole GPR applications, including GPR sensitivity to contaminant plumes, new methods for soil water content determination, three-dimensional imaging of the subsurface, time-lapse monitoring of hydrodynamic events and processing techniques for soil hydraulic properties estimation, and joint interpretation of GPR data with other sources of information.

“GPR has known a rapid development over the last decade,” notes Sébastien Lambot, who organized the special issue. “Yet, several challenges must still be overcome before we can benefit from the full potential of GPR. In particular, more exact GPR modeling procedures together with the integration of other sources of information, such as other sensors or process knowledge, are required to maximize quantitative and qualitative information retrieval capabilities of GPR. Once this is achieved, GPR will be established as a powerful tool to support the understanding of the vadose zone hydrological processes and the development of optimal environmental and agricultural management strategies for our soil and water resources.”

The full article is available for no charge for 30 days following the date of this summary. View the abstract at: vzj.scijournals.org

How Iron Gets into the North Pacific

From a site 47 degrees north latitude and 160 degrees east longitude in the Western North Pacific (marked X), iron and manganese found at depths of 100-200 meters originated hundreds of miles away, from the continental shelves of the Kamchatka Peninsula and Kuril Islands. Particulate and dissolved iron and manganese hydroxides came from the upper shelf, and, after further processing, more iron (now poor in manganese) came from deeper on the slopes.
From a site 47 degrees north latitude and 160 degrees east longitude in the Western North Pacific (marked X), iron and manganese found at depths of 100-200 meters originated hundreds of miles away, from the continental shelves of the Kamchatka Peninsula and Kuril Islands. Particulate and dissolved iron and manganese hydroxides came from the upper shelf, and, after further processing, more iron (now poor in manganese) came from deeper on the slopes.

Is the Dust-Storm Theory Overblown?

Most oceanographers have assumed that, in the areas of the world’s oceans known as High Nutrient, Low Chlorophyll (HNLC) regions, the iron needed to fertilize infrequent plankton blooms comes almost entirely from wind-blown dust. Phoebe Lam and James Bishop of the Earth Sciences Division at the Department of Energy’s Lawrence Berkeley National Laboratory have now shown that in the North Pacific, at least, it just ain’t so.

In a forthcoming issue of Geophysical Research Letters, Lam, a biogeochemist at the Woods Hole Oceanographic Institution and a guest at Berkeley Lab, and Bishop, an Earth Sciences oceanographer and professor in the Department of Earth and Planetary Science at the University of California at Berkeley, report that the key source of iron in the Western North Pacific is not dust but the volcanic continental margins of the Kamchatka Peninsula and the Kuril Islands.

Can iron affect climate change?

Understanding the origins, transport mechanisms, and fate of naturally occurring iron in high-nutrient, low-chlorophyll surface waters is important in calculating climate change. For example, artificial iron-fertilization schemes, although based on inadequately tested assumptions, hope to reduce greenhouse gases by stimulating plankton blooms to suck carbon dioxide from the atmosphere and store it in the oceans.

It’s iron that enables phytoplankton to use nitrate; without it the plants are denied access to often substantial nitrogen sources in HNLC regions, of which the Subarctic North Pacific is one of three major such regions in the world.

“In the open ocean, the biopump wants to grab all the iron it can,” says Bishop. “There were two recognized natural sources of iron out there, atmospheric dust and upwelling from below. Where we’ve looked in the North Pacific, we’re seeing a new and important third source, the continental margins. The rules for the role of iron in the ocean carbon cycle need to be revised.”

The wind-blown-dust theory of iron fertilization had no direct evidentiary support until Jim Bishop himself made the first observation of dust in action. In the spring of 2001, two robotic Carbon Explorer floats recorded the rapid growth of phytoplankton in the upper layers of the North Pacific Ocean after a passing storm had deposited iron-rich dust from the Gobi Desert. The Carbon Explorers had been designed by Bishop with colleagues at the Scripps Institution of Oceanography; their measurements, radioed back to him by satellite, marked the first time wind-blown terrestrial dust had been recorded fertilizing the growth of aquatic plant life.

“But the plankton blooms the two Carbon Explorers saw lasted only two weeks,” Bishop says, “which raised questions about how important this transport mechanism really is.”

Further doubts arose when, beginning in 2001, Lam analyzed samples that Bishop had collected five years earlier well out in the Eastern North Pacific. In February, 1996, a rare break in the winter weather had allowed Bishop to deploy a Multiple Unit Large Volume Filtration System (MULVFS), an array of collectors lowered over the side of the research vessel by cable. What MULVFS brought back were samples that contained iron plus evidence of a vigorous plankton bloom – in the middle of the Eastern Subarctic Pacific, in the cold, dark days of midwinter.

There was no evidence dust storms could have carried terrestrial iron to the North Pacific that February, nor was the chemistry of the iron in the samples characteristic of iron from upwelling or past deposited dust. As the source of the iron, only the continental margins were logical.

Lam and Bishop and their colleagues published their studies in 2006, concluding that the iron had indeed come from the continental margins of the Aleutian Islands, 900 kilometers to the northwest of the site where the midwinter plankton bloom had been found. Iron particles and soluble iron had been carried there along a layer of denser water roughly 100 to 150 meters deep (the pycnocline), and the iron had been stirred up by storms that made it available to near-surface plankton in the dead of winter.

Lam and Bishop’s recent studies of iron in the North Pacific HNLC region were focused on a region thousands of kilometers farther west. They used samples they collected with MULVFS in the late summer of 2005, during a VERTIGO project cruise led by scientists at the Woods Hole Oceanographic Institution (VERTIGO stands for Vertical Transport in the Global Ocean). The cruise concentrated on a site in the Western Subarctic Pacific that was hundreds of kilometers south of the Kamchatka Peninsula and east of the Kuril Islands.

Like other HNLC regions, this area has low biomass compared to what might be expected for such nutrient-rich waters, although it does have higher biological productivity than the Eastern Subarctic Pacific. It also has higher iron concentrations, traditionally explained by its proximity to sources of Asian dust storms, which deposit three times as much dust in these waters as in the Eastern North Pacific.

Iron from the Ring of Fire

Lam and Bishop again found particulate iron beneath the surface, and again the concentrations peaked at depths between 100 and 200 meters. But these concentrations were six times greater than those they had found in the Eastern Subarctic Pacific. The chemistry was a giveaway: the iron was “reduced,” that is, having less oxygen than oxidized samples from the surface of the Earth (oxidized iron is better known as rust). Like material brought up from Earth’s mantle, many of these iron-rich samples had not been weathered; in fact they were characteristic of basalts found in the continental shelves of the Kurils and Kamchatka, part of the Pacific’s volcanic Ring of Fire.

Iron must be dissolved to be accessible to phytoplankton, and the reduced iron in volcanic silicates from island-arc sediments may dissolve more readily than iron in dust. As in the Eastern Subarctic Pacific, the particulate iron Lam and Bishop found in the Western Subarctic Pacific – and by inference the dissolved iron essential to plankton growth – was concentrated at depths indicating it had traveled from the ocean edges along the pycnocline. Upwelling or vertical mixing would make concentrations of continental iron at these depths readily available to plankton.

Conservative estimates of bioavailable iron (iron that can fertilize plankton) from both wind-blown dust and continental sources led Lam and Bishop to conclude that a minimum of 55 percent of the bioavailable iron they found at this site – and probably much more – comes from the nearby volcanic continental margins.

Says Lam, “It takes only a simple calculation to show that iron delivered from the continental shelf, under the surface, is at least as important here as iron from airborne dust. And we suspect this is the case for the iron supply in other, similar regions of the oceans.”

Lam and Bishop’s findings have implications far beyond correcting estimates of the iron budget in HNLCs.

“Just looking at a map and considering the history of geochemical processes like volcanism and their influence on the biology of the oceans – and what’s already happening as the climate gets warmer, the glaciers melt, and the edges of the continents are altered drastically – it’s clear how little we understand how these changes are likely to affect the productivity of the ocean and its ability to store atmospheric carbon,” Bishop says. “Before we start playing around with massive-scale, commercial iron fertilization, we have a lot of science yet to do. Natural iron, and associated elements, seem to cause a significantly different biological response than has been seen in the dozen fertilization experiment to date. It would be good to know why.”

“The Continental Margin is a Key Source of Iron to the HNLC North Pacific Ocean,” by Phoebe J. Lam and James K. B. Bishop, will appear in a forthcoming edition of Geophysical Research Letters and is now available to subscribers at www.agu.org (PDF). Once published, the paper will be available from the Geophysical Research Letters website at www.agu.org/journals/gl/.

This research was funded by the U.S. Department of Energy’s Office of Science, Biological and Environmental Research Program, and by the Woods Hole Oceanographic Institution, the Richard B. Sellars Endowed Research Fund, and the Andrew W. Mellon Foundation. Portions of the work were carried out at DOE’s Advanced Light Source at Berkeley Lab and DOE’s Stanford Synchrotron Radiation Laboratory.