How Water Could Have Flowed on Mars

English

 

A satellite image of Olympus Mons, Mars, the largest volcano in the solar system at about three times the height of Mount Everest. Around 3.5 to 4.0 billion years ago, the release of volcanic gases, especially the greenhouse gas sulfur-dioxide, may have warmed the surface of Mars episodically, thereby explaining the presence of geomorphological features indicative of the flow of water on the planet's ancient surface

 
Why does the cold, barren surface of Mars contain geological features that appear to have been formed by flowing water: river valleys, lake basins and deltas? A new model, which was published online in Nature Geoscience this week, suggests that sulfur spewed into the Martian atmosphere by ancient volcanoes could have periodically warmed the surface enough for the ice to melt and water to flow.
 
Indeed, the signs of flowing water have been a puzzle, as the latest generation of climate models portrays Mars as an eternally ice-cold planet with all of its water frozen solid, especially early in its history, when the Sun was weaker than it is today. Today, most of that water is locked in the polar caps. Drs. Itay Halevy of the Weizmann Institute’s Earth and Planetary Science Department and James Head III of Brown University, Rhode Island, thought the answer might lie in the now dormant volcanoes on the planet’s surface, which could have played a larger role than thought in shaping its climate.
 
On Earth, volcanic emissions – sulfur compounds and ash – tend to cool the climate. But in the presumably dusty early atmosphere of Mars, the net effects might have been different. To understand their impact, Halevy and Head first calculated the size of ancient volcanic eruptions, based on the volcanic rock formations observed on the planetary surface today. Their estimations show that the eruptions were violent – hundreds of times the force of the average eruption on Earth – and may have lasted up to a decade. This means that the amounts of gases spewed from the mouths of these volcanoes, from what we know of Earthly eruptions, must have been enormous.
 
The team’s simulations showed large amounts of the greenhouse gas sulfur-dioxide mixing into the atmosphere. But warming by the sulfur-dioxide was thought to be outweighed by cooling due to the creation of sun-blocking sulfuric acid particles, which form as the sulfur-dioxide reacts in the atmosphere. Halevy and Head showed that in an atmosphere already as dusty as that of Mars, the sulfuric acid mostly forms thin coatings around particles of mineral dust and volcanic ash, subduing the added cooling. The net effect, according to the model the scientists created, was modest warming – just enough to allow water to flow at low latitudes on either side of the planet’s equator.
 
Liquid water may have flowed in these regions for tens to hundreds of years during and immediately after volcanic eruptions. The model suggests that during these brief, but intense wet periods, the surface of the planet could have been carved by flowing rivers and streams.

 
Dr. Itay Halevy’s research is supported by the Sir Charles Clore Research Prize; the Carolito Stiftung; the Wolfson Foundation; the Wolfson Family Charitable Trust; the estate of Olga Klein Astrachan; and the European Research Council.




 
 
A satellite image of Olympus Mons, Mars, the largest volcano in the solar system at about three times the height of Mount Everest. Around 3.5 to 4.0 billion years ago, the release of volcanic gases, especially the greenhouse gas sulfur-dioxide, may have warmed the surface of Mars episodically, thereby explaining the presence of geomorphological features indicative of the flow of water on the planet's ancient surface
Chemistry
English
  • Chemistry
  • Climate record
  • Earth and Planetary Sciences
  • Itay Halevy

Microbes Take their Sulfur Light

English

On the ocean floor, where oxygen is in short supply, live microbes that “breathe” sulfur instead of oxygen. Far from the world’s forests, these microbes play a vital role in the planet’s carbon cycle, digesting around half of the organic matter that sinks to the seabed. New research that was recently published as a “feature article” in the Proceedings of the National Academy of Sciences (PNAS) combines biochemical principles and stable isotope theory to create a new approach to understanding what the metabolic activity of these common microorganisms tells us about their environment. This approach may prove to be a valuable tool for helping decipher crucial processes in the planet’s ecology – in the past, as well as the present and future.


Drs. Itay Halevy of the Weizmann Institute’s Earth and Planetary Sciences Department and Boswell Wing of McGill University, Montreal, sought to explain phenomena that had been observed in experiments for almost 60 years: So-called sulfur-reducing microbes discriminate between the four stable isotopes of sulfur in ways that depend on the microbes’ growth conditions. Through respiration the microbes take in a sulfur compound, sulfate, from their environment and use it to fuel their metabolic reactions. But the microbes prefer using sulfate with the lighter isotopes of sulfur, so they “fractionate” these isotopes, generating metabolic products that are enriched in 32S and depleted in 34S. The experiments reveal that fractionation drops off as respiration rates speed up, and increases as sulfate concentrations increase. These patterns have been used to interpret the geologic record of sulfur isotopes and thus past environmental conditions, but a comprehensive model that can explain and predict the patterns has been lacking.  

To create their model, the researchers had to incorporate information about biochemical reactions, the various environmental factors that regulate metabolic processes in sulfate-reducing microorganisms and the chemistry of sulfur isotopes, which are taken up in one chemical form and expelled in another (much like inhaling O2 and exhaling it in the form of CO2). Among other things, says Halevy, he and Wing made use of principles developed in part in the Plant and Environmental Sciences Department by Prof. Ron Milo’s group, which tie biological reaction rates to the energetics of the reactions and the dynamics of the enzymes involved in those reactions.

The ability to model the processes that control microbial isotope fractionation has many possible implications. If the testing that is now underway supports the model, it will be an invaluable tool for understanding microbial activity in present-day, as well as ancient, environments. The researchers suggest that it would enable geoscientists to decode ancient history by understanding how sulfur-reducing microbes left their mark long ago in sulfur-bearing rock formations. Moreover, Halevy points out, the approach may open doors to other areas of research: “The method can be applied to the microbial metabolism of many additional elements,” he says. “For example, it could be used to model the nitrogen isotope fractionation of the denitrifying bacteria that drive an important part of the planet’s nitrogen cycle, or that of the microorganisms which produce the greenhouse gas methane.”

Dr. Itay Halevy’s research is supported by the Sir Charles Clore Research Prize; the Carolito Stiftung; the Wolfson Foundation; the Wolfson Family Charitable Trust; the estate of Olga Klein Astrachan; and the European Research Council.

Dr. Boswell Wing worked in the lab of Dr. Itay Halevy through the Feinberg Foundation Visiting Faculty Program.

 
Chemistry
English
  • Biochemistry
  • Earth and Planetary Sciences
  • Itay Halevy
  • Metabolism

The Coral Sweepstakes

English

04-11-2014

 

coral sweeping
Vortical ciliary flows enhance the exchange of oxygen and nutrients between corals and their environment. Paths of tracer particles between two adjacent polyps of the reef coral Pocillopora damicornis, spaced about 3 mm apart, are color coded to reflect local flow velocity

 

 
 

Corals get their oxygen and nutrients from the water that flows around them. Research in the group of Dr. Assaf Vardi of the Weizmann Institute’s Plant and Environmental Sciences Department and Prof. Roman Stocker of the Massachusetts Institute of Technology (MIT) now reveals a surprise dimension of reef-bound coral life: The polyps (corals are actually a symbiotic combination of polyp and alga) use their cilia – tiny hairs covering their surface – to sweep the surrounding water. This sweeps in nutrients as well as sweeping away waste products.

 

 

 

 

The motion of tracer particles (1m diameter, imaged by dark field microscopy; 4x magnification) reveals the rapid vortical flows driven by cilia covering the surface of a reef-building coral. By actively mixing their boundary layer, corals enhance the exchange of oxygen and nutrients with the environment

 

By adding tracer particles to the corals’ environment and filming them with high speed videography and powerful microscopy techniques, Dr. Orr Shapiro of Vardi’s lab – at the time a guest of Stocker’s group – and Dr. Vicente Fernandez of Stocker’s lab captured, for the first time, the polyps’ cilia in action.


The findings, which appeared in the Proceedings of the National Academy of Sciences (PNAS), help explain the long evolutionary success of corals and give some hope for their future.

 

 

 

Coral Cilia. Cilia covering the surface of reef-building corals beat synchronously to drive rapid vortical flows (150x magnification)

 

 

 

Dr. Assaf Vardi’s research is supported by the Human Frontiers Science Program (HFSP); Roberto and Renata Ruhman, Brazil; Selmo Nussenbaum, Brazil; the Brazil-Israel Energy Fund; the Lord Sieff of Brimpton Memorial Fund; the European Research Council; and the estate of Samuel and Alwyn J. Weber. Dr. Vardi is the incumbent of the Edith and Nathan Goldenberg Career Development Chair.

Environment
English
  • Assaf Vardi
  • Nutrition
  • Ocean
  • Plant and Environmental Sciences

The Ocean’s Living Carbon Pumps

English

When we talk about global carbon fixation –"pumping" carbon out of the atmosphere and fixing it into organic molecules by photosynthesis – proper measurement is key to understanding this process. By some estimates, almost half of the world’s organic carbon is fixed by marine organisms called phytoplankton – single-celled photosynthetic organisms that account for less than one percent of the total photosynthetic biomass on Earth.  


Dr. Assaf Vardi, a marine microbiologist in the Weizmann Institute’s Plant and Environmental Sciences Department, and Prof. Ilan Koren, a cloud physicist, and Dr. Yoav Lehahn, an oceanographer, both from the Earth and Planetary Sciences Department, realized that by combining their interests, they might be able to start uncovering the role that these minuscule organisms play in regulating the carbon content of the atmosphere.
 
Satellite image showing a patch of bright waters associated with a bloom of phytoplankton in the Barents Sea off Norway. Image courtesy of Norman Kuring, Ocean Color Group at Goddard Space Flight Center, NASA
 
 
 
Tiny as they are, phytoplankton can be seen from space: They multiply in blooms that can reach thousands of kilometers in area, coloring patches of the ocean that can be tracked and measured by satellites. These blooms have a tendency to grow quickly and disappear suddenly. How much carbon does such a bloom fix, and what happens to that carbon when the bloom dies out? That depends, in part on what kills the bloom. If it is mostly eaten by other marine life, for example, its carbon will be passed up the food chain. If the phytoplankton are starved or infected with viruses, however, the process is more complicated. Dead organisms that sink may take their carbon to the ocean floor with them. But others may be scavenged by certain bacteria the in surface waters; these remove the organic carbon and release it back into the atmosphere through their respiration.

Vardi, Koren and Lehahn asked whether one can use the satellite data to detect the signs of the demise of a bloom due to viral infection, an occurrence that Vardi has investigated in natural oceanic blooms and in the lab. During a recent research cruise near Iceland with colleagues from Rutgers University and Woods Hole Oceanographic Institute, the researchers were able to collect data on the algal-virus interactions and their effect on carbon cycles in the ocean.

By combining satellite data with their field measurements, they were able, for the first time, to measure the effect of viruses on phytoplankton blooms on large, open ocean areas. To do this, the scientists first had to identify a special subset of ocean patches in which such physical processes as currents did not affect the blooms – so they could observe just the biological effects. Then, following a bloom in one of these patches, they managed to trace its whole life cycle. This enabled them to quantify the role of viruses in the demise of this particular bloom. Their conclusions were verified in data collected in a North-Atlantic research expedition.

The scientists estimated that an algal patch of around 1,000 sq km – which forms within a week or two – can fix around 24,000 tons of organic carbon – equivalent to a similar area of rain forest. Since a viral infection can rapidly wipe out an entire bloom, the ability to observe and measure this process from space may greatly contribute to understanding and quantifying the turnover of carbon cycle and its sensitivity to environmental stress conditions, including marine viruses.

Prof. Ilan Koren’s research is supported by the J&R Center for Scientific Research; the Scholl Center for Water and Climate Research; and the estate of Raymond Lapon.
 
Dr. Assaf Vardi’s research is supported by Roberto and Renata Ruhman, Brazil; Selmo Nussenbaum, Brazil; the Brazil-Israel Energy Fund; the Lord Sieff of Brimpton Memorial Fund; the European Research Council; and the estate of Samuel and Alwyn J. Weber. Dr. Vardi is the incumbent of the Edith and Nathan Goldenberg Career Development Chair.
 
 
 
Satellite image showing a patch of bright waters associated with a bloom of phytoplankton in the Barents Sea off Norway. Image courtesy of Norman Kuring, Ocean Color Group at Goddard Space Flight Center, NASA
Environment
English
  • Assaf Vardi
  • Atmosphere
  • Carbon dioxide
  • Earth and Planetary Sciences
  • Ilan Koren
  • Ocean
  • Phytoplankton
  • Plant and Environmental Sciences›Plant and Environmental Science

The Real Price of Steak

English
 
We are told that eating beef is bad for the environment, but do we know its real cost? Are the other animal or animal-derived foods better or worse? New research at the Weizmann Institute of Science, conducted in collaboration with scientists in the US, compared the environmental costs of various foods and came up with some surprisingly clear results. The findings, which appear today in the Proceedings of the National Academy of Sciences (PNAS), will hopefully not only inform individual dietary choices, but those of governmental agencies that set agricultural and marketing policies.

Dr. Ron Milo of the Institute’s Plant Sciences Department, together with his research student Alon Shepon, in collaboration with Tamar Makov of Yale University and Dr. Gidon Eshel in New York, asked which types of animal based-food should one consume, environmentally speaking. Though many studies have addressed parts of the issue, none has done a thorough, comparative study that gives a multi-perspective picture of the environmental costs of food derived from animals.
 
Chicken vs Beef
 
The team looked at the five main sources of protein in the American diet: dairy, beef, poultry, pork and eggs. Their idea was to calculate the environmental inputs – the costs – per nutritional unit: a calorie or gram of protein. The main challenge the team faced was to devise accurate, faithful input values. For example, cattle grazing on arid land in the western half of the US use enormous amounts of land, but relatively little irrigation water. Cattle in feedlots, on the other hand, eat mostly corn, which requires less land, but much more irrigation and nitrogen fertilizer. The researchers needed to account for these differences, but determine aggregate figures that reflect current practices and thus approximate the true environmental cost for each food item.  
 
The inputs the researchers employed came from the US Department of Agriculture databases, among other resources. Using the US for this study is ideal, says Milo, because much of the data quality is high, enabling them to include, for example, figures on import-export imbalances that add to the cost. The environmental inputs the team considered included land use, irrigation water, greenhouse gas emissions, and nitrogen fertilizer use. Each of these costs is a complex environmental system. For example, land use, in addition to tying up this valuable resource in agriculture, is the main cause of biodiversity loss. Nitrogen fertilizer creates water pollution in natural waterways.
 
When the numbers were in, including those for the environmental costs of different kinds of feed (pasture, roughage such as hay, and concentrates such as corn), the team developed equations that yielded values for the environmental cost – per calorie and then per unit of protein, for each food.

The calculations showed that the biggest culprit, by far, is beef. That was no surprise, say Milo and Shepon. The surprise was in the size of the gap: In total, eating beef is more costly to the environment by an order of magnitude – about ten times on average –  than other animal-derived foods, including  pork and poultry. Cattle require on average 28 times more land and 11 times more irrigation water, are responsible for releasing 5 times more greenhouse gases, and consume 6 times as much nitrogen, as eggs or poultry. Poultry, pork, eggs and dairy all came out fairly similar. That was also  surprising, because dairy production is often thought to be relatively environmentally benign. But the research shows that the price of irrigating and fertilizing the crops fed to milk cows – as well as the relative inefficiency of cows in comparison to other livestock – jacks up the cost significantly.
 
Milo believes that this study could have a number of implications. In addition to helping individuals make better choices about their diet, it should hopefully help inform agricultural policy. And the tool the team has created for analyzing the environmental costs of agriculture can be expanded and refined to be applied, for example, to understanding the relative cost of plant-based diets, or those of other nations. In addition to comparisons, it can point to areas that might be improved. Models based on this study can help policy makers decide how to better ensure food security through sustainable practices.

Dr. Ron Milo’s research is supported by the Mary and Tom Beck-Canadian Center for Alternative Energy Research; the Lerner Family Plant Science Research Endowment Fund; the European Research Council; the Leona M. and Harry B. Helmsley Charitable Trust; Dana and Yossie Hollander, Israel; the Jacob and Charlotte Lehrman Foundation; the Larson Charitable Foundation; the Wolfson Family Charitable Trust; Charles Rothschild, Brazil; Selmo Nissenbaum, Brazil; and the estate of David Arthur Barton. Dr. Milo is the incumbent of the Anna and Maurice Boukstein Career Development Chair in Perpetuity.
 
 
Chicken vs Beef
Environment
English
  • Agriculture
  • Environmental Sciences and Energy Research›Environment
  • Mathematical model
  • Plant Sciences
  • Ron Milo

No Limits to Human Effects on Clouds

English

Understanding how clouds affect the climate has been a difficult proposition. What controls the makeup of the low clouds that cool the atmosphere or the high ones that trap heat underneath? How does human activity change patterns of cloud formation? The research of the Weizmann Institute’s Prof. Ilan Koren suggests we may be nudging cloud formation in the direction of added area and height. He and his team have analyzed a unique type of cloud formation; their findings, which appeared recently in Science indicate that in pre-industrial times, there was less cloud cover over areas of pristine ocean than is found there today.


Clouds need tiny particles called aerosols that rise in the atmosphere, in order to form. These aerosols – natural ones like sea salt or dust, or such human-made ones as soot – form nuclei around which the cloud droplets condense. In relatively clean environments, clouds can only grow as large as the amount of aerosols in the atmosphere allows: They will be the limiting factor in cloud formation.

The question is: Does the current load of aerosols in the atmosphere already exceed that limit, in which case adding extra particles should not greatly affect cloud formation; or do they continue to be a limiting factor as pollution rises, so that added aerosols would continue to influence the clouds? A model developed by Koren and his team showed that an increase in aerosols, even in relatively polluted conditions, should result in taller, larger clouds that rain more aggressively. But proving the model was another story: Experimenting on clouds, or even finding ways to isolate the various factors that go into their formation in real time, is a highly difficult undertaking.

Koren, research student Guy Dagan and Dr. Orit Altaratz in the Earth and Planetary Sciences Department looked to an unlikely place to test their model: near the horse latitudes. These are subtropical regions far out in the oceans that were reviled in the past by sailors because the winds that carried their sails would die out there for weeks on end. Here was a lab for them to test the basic physics of their model: an atmospheric region controlled by well-defined meteorological conditions, which was sometimes pristine, sometimes containing low levels of aerosols. If the model was correct, transitions from one to the other should be dramatic. And they wanted to test their theory on the clouds that do form in this region – warm convective clouds that are fuelled by the ocean’s moisture.
 
Convective clouds forming over the Amazon in a blanket smoke. Image: Prof. Ilan Koren
 

 

 
With other potential factors – wind, large temperature swings or land formations – out of the way, the team could concentrate on the aerosols, comparing daily satellite images of cloud cover and measurements of the aerosol load to the predictions of the model. Using many different types of analysis, they found that their model closely matched the satellite observations.

They then looked at another source of data: that of the Clouds’ and the Earth’s Radiant Energy System (CERES) satellite instruments which measure fluxes of reflected and emitted radiation from the Earth to space, to help scientists understand how the climate varies over time. When analyzed together with the aerosol loading over the same area at the same time, the outcome, says Koren, was a “textbook demonstration of the invigoration effect” of added aerosols on clouds. In other words, the radiation data fit the unique signature of clouds that were growing higher and larger. Such clouds show a strong increase in cooling due to the reflected short waves, but that effect is partly cancelled out by the enhanced, trapped, long-wave radiation coming from underneath.

At least over the oceans, the pre-industrial cloud conditions would have been considerably different from those of today; this implies that the aerosols we have been adding to the atmosphere may have had a significant effect on global patterns of cloud formation and rain.  

Koren: “We showed that convective clouds do not necessarily stop being aerosol-limited; under relatively polluted conditions the increase in aerosol loading will make the clouds taller, larger and their rain-rate stronger. As the area of this cloud cover grows, it reflects more of the shortwave radiation; but as the clouds get taller, their greenhouse effect becomes more significant, counteracting about half of their total cooling effect.”   

 
Prof. Ilan Koren’s research is supported by the J & R Center for Scientific Research; and the estate of Raymond Lapon.
 
Convective clouds forming over the Amazon in a blanket smoke. Image: Prof. Ilan Koren
Environment
English
  • Climate change
  • Cloud formation
  • Ilan Koren
  • Satellite image

Exchange Rates

English

 

Prof. Dan Yakir
We know that green plants are important for keeping our planet cool: Around the globe, they consume billions of tons of the greenhouse gas carbon dioxide (CO2), converting it, through photosynthesis, to sugars and ultimately to wood. But CO2 is also released back into the atmosphere in a process called respiration, both from living plants and from the decomposition of detritus. Thus the total amount of CO2 plants take out of the atmosphere equals the quantity they absorb for photosynthesis, minus the amount they return to the atmosphere through respiration. It sounds like a simple equation, but until now, measuring its components has been anything but simple; scientists have been stumped for years trying to come up with an accurate means to tease out the two components of the “simple equation” – an analysis that is critical to predicting the future impact of plants on our climate.

Recently, a research team in the lab of Prof. Dan Yakir of the Environmental Sciences and Energy Research Department demonstrated a new method for just measuring how much CO2 is taken up, independent of the amounts released back in respiration. This method, based on another chemical compound in the atmosphere – one found in extremely tiny amounts – should help scientists around the world clarify the picture of the ongoing exchange of carbon between plants and the atmosphere, hopefully leading to better climate models and predictions. Measuring the levels of this compound, COS, involved developing new, ultra-precise tools to reveal its presence.

In the commonly used methods for figuring carbon exchange, only the net difference between photosynthesis and respiration can be directly measured in the air above vegetation. But that doesn’t indicate specifically how much CO2 is lost or gained – information that is critical when trying to understand how patterns change daily or seasonally, across regions or in response to climate change. Researchers trying to tease apart CO2 fluxes have used various “tricks” – for example, measuring at night, when photosynthesis shuts down; but the results have still been only approximations.

Yakir and his team decided to act on an idea that had come up several years earlier but was considered too impractical to be of use: Measure the flux of another substance, carbonyl sulfide (COS) into the plant biosphere. COS is similar to CO2, except that instead of two oxygen atoms attached to the carbon, the molecule contains an oxygen and a sulfur atom. Plants absorb COS along with the CO2; but they don’t release it again in respiration, so measurements could serve as a good proxy for CO2 uptake. The only problem was that there is about a million times less COS in the atmosphere than CO2: If CO2 is measured in parts per million, COS must be measured in parts per trillion (that is one molecule of COS for every trillion molecules of gas in the atmosphere).
 
Yakir infographic
 
 
Though these figures were daunting, the researchers convinced a scientific instrument company in the US to build them a tool – called a quantum cascade laser (QCL) – capable of accurately measuring minute amounts of COS. Research student Keren Stimler then spent around five years testing the QCL with plants in the lab, “developing the ‘language’ of COS exchange, the instrument, and the analysis of its results,” says Yakir.

In the team’s recent work, which appeared in Nature Geoscience, Yakir and postdoctoral fellow Dr. David Asaf decided it was time to take the QCL on the road. They loaded it into the Biosphere-Atmosphere Mobile Research Lab (see below) and took it to various sites to see how well it works in real conditions – in pine forests in a variety of climate regions and in agricultural fields. Their results demonstrate that COS measurements based on the new QCL technology are able to provide the numbers on CO2 uptake that scientists have been seeking for years. Indeed, the team can now confirm their previous finding that pine forests in Israel are as effective in carbon storage (carbon sequestration) as European pine forests: While the semi-arid local forests take up much less CO2 in photosynthesis than European ones, they also lose much less CO2 in respiration, so the net carbon storage is the same in both forests.
 

Going mobile pays off

Biosphere-Atmosphere Mobile Research Lab
 
 
Two years ago, when Prof. Dan Yakir together with staff scientist Dr. Eyal Rotenberg and their team finally (after two years of development) started up the four-by-four, 12-ton truck that houses the Biosphere-Atmosphere Mobile Research Lab, they knew they were taking a bit of a risk. Although they had visions of the exciting contributions the one-of-a-kind transportable lab could be making to global research on the exchange of materials between forests and the atmosphere, there were no guarantees that the new approach would be widely endorsed or that other researchers in this field would be lining up on their doorstep.

This summer, any fears they may have had were laid to rest when research groups from the US, Spain, Austria and Germany all showed up to work together out of the Mobile Lab. The teams brought along their research tools – including large pieces of equipment that had to be carefully shipped halfway around the world. The idea was to combine the mobile platform, with its fully operational (and air-conditioned) laboratory, on the one hand, and, on the other hand, to make use of the mobile lab’s 28-meter-high telescopic mast, which, according to Yakir, reaches the critical layer “between the plant canopies and the airspace below the mixed atmosphere.” Each group planned to investigate one slice of the larger question: How do the volatile compounds released by trees (think of the terpenes that give pines their characteristic scent) link to CO2 exchange, and how does this affect atmospheric chemistry and ultimately cloud formation and climate?

One group, for example, took detailed measurements of the trees at ground level; another measured levels of the volatile compounds above the forest canopy; a third monitored the size of particles, which, above a certain diameter, can serve as nuclei for the condensation of water drops in clouds; and so on. Combining the data from all of the groups, says Yakir, “is beginning to give us an overall picture of the evolution of climate – from the trees to clouds and rain.”

“We were very excited by this campaign,” he says. “It was a great example of scientific collaboration in which different groups worked together out of one small traveling lab. It was a further test of our own instruments, including the new mobile platform and the QCL system, and it looks like the results will be really interesting. Most of all, it showed us that the investment in the Biosphere-Atmosphere Mobile Research Lab was worth the risk – it is clearly paying off.”
 
 

Prof. Dan Yakir's research is supported by the Cathy Wills and Robert Lewis Program in Environmental Science; the estate of Sanford Kaplan; and the
Carolito Stiftung.
 

 

 

 
Biosphere-Atmosphere Mobile Research Lab
Environment
English
  • Atmosphere
  • Carbon dioxide
  • Dan Yakir
  • Environmental Sciences and Energy Research

Sulfur Swings

English
Dr. Itay Halevy
 
Sulfur – element 16 in the periodic table – is found all over the Earth. It is released by volcanoes and burning fossil fuels, taken up by living organisms, dissolved in rain and sea water and crystallized in rock. As sulfur cycles through Earth’s atmosphere, oceans and land, it undergoes chemical changes that are often coupled to changes in such elements as carbon and oxygen. Although this affects the concentration of free oxygen, sulfur has traditionally been portrayed as a secondary factor in regulating atmospheric oxygen, with most of the heavy lifting done by carbon. However, new findings that appeared recently in Science suggest that sulfur’s role may have been underestimated.

Drs. Itay Halevy of the Weizmann Institute’s Environmental Sciences and Energy Research Department (Faculty of Chemistry), Shanan Peters of the University of Wisconsin and Woodward Fischer of the California Institute of Technology, were interested in better understanding the global sulfur cycle over the past 550 million years – roughly the period in which oxygen has been at its present atmospheric level of around 20%. They used a database developed and maintained by Peters at the University of Wisconsin, called Macrostrat, which contains detailed information on thousands of rock units in North America and beyond.
 
 
The researchers used the database to trace one of the ways in which sulfur exits ocean water into the underlying sediments – the formation of so-called sulfate evaporite minerals. These sulfur-bearing minerals, such as gypsum, settle to the bottom of shallow seas as seawater evaporates. The team found that the formation and burial of sulfate evaporites were highly variable over the last 550 million years, due to changes in shallow sea area, the latitude of ancient continents and sea level. More surprising to Halevy and colleagues was the discovery that only a relatively small fraction of the sulfur cycling through the oceans has exited seawater in this way. Their research showed that the formation and burial of a second sulfur-bearing mineral – pyrite – has apparently been much more important.

Pyrite is a shiny, yellow iron-sulfur mineral also known as "fools’ gold," which forms when microbes in seafloor sediments use the sulfur dissolved in seawater to digest organic matter. The microbes take up sulfur in the form of sulfate (bound to four oxygen atoms) and release it as sulfide (with no oxygen). Oxygen is emitted during this process, thus making it a source of oxygen in the air. This part of the sulfur cycle, however, was thought be minor. Since the other part – sulfur evaporite formation – does not release oxygen, sulfur's effect on oxygen levels was considered unimportant.
 
Iron pyrite crystal (Thinkstock photos)
 
In testing various theoretical models of the sulfur cycle against the Macrostrat data, the team realized that the production and burial of pyrite has been much more significant than previously thought, accounting for more than 80% of all sulfur removed from the ocean – rather than the 30-40% in prior estimates. As opposed to the variability they saw for sulfate evaporite burial, pyrite burial has been relatively stable throughout the period. The analysis also revealed that most of the sulfur entering the ocean has been washed in from the weathering of pyrite exposed on land. In other words, there is a balance between pyrite formation and burial, which releases oxygen, and the weathering of pyrite on land, which consumes it. The implication of these findings is that the sulfur cycle regulates the atmospheric concentration of oxygen more strongly than previously appreciated.

“This is the first use of Macrostrat to quantify chemical fluxes in the Earth system,” said Peters. “I met my coauthors at a lecture I gave at Caltech, and we immediately began discussing how we might apply Macrostrat to understanding biogeochemical cycling. I think this study will open the door to many more uses of Macrostrat for constraining biogeochemical cycles.”

“For me, the truly surprising result is that pyrite weathering and burial appear to be such important processes in the sulfur cycle throughout all of Earth’s history. The carbon cycle is recognized as the central hub controlling redox processes on Earth, but our work suggests that nearly as many electrons are shuttled through the sulfur cycle,” said Fischer.

Halevy: “These findings, in addition to shedding new light on the role of sulfur in regulating oxygen levels in the atmosphere, represent an important step forward in developing a quantitative, mechanistic understanding of the processes governing the global sulfur cycle.”
 
Dr. Itay Halevy’s research is supported by the Sir Charles Clore Research Prize; and the estate of Olga Klein Astrachan.
 
 
Iron pyrite crystal (Thinkstock photos)
Environment
English
  • Atmosphere
  • Environmental Sciences and Energy Research
  • Itay Halevy
  • Ocean
  • Planetary cycles

Fools’ Gold Found to Regulate Oxygen

English

 

As sulfur cycles through Earth’s atmosphere, oceans and land, it undergoes chemical changes that are often coupled to changes in other such elements as carbon and oxygen. Although this affects the concentration of free oxygen, sulfur has traditionally been portrayed as a secondary factor in regulating atmospheric oxygen, with most of the heavy lifting done by carbon. However, new findings that appeared this week in Science suggest that sulfur’s role may have been underestimated.

Drs. Itay Halevy of the Weizmann Institute’s Environmental Science and Energy Research Department (Faculty of Chemistry), Shanan Peters of the University of Wisconsin and Woodward Fischer of the California Institute of Technology, were interested in better understanding the global sulfur cycle over the last 550 million years – roughly the period in which oxygen has been at its present atmospheric level of around 20%. They used a database developed and maintained by Peters at the University of Wisconsin, called Macrostrat, which contains detailed information on thousands of rock units in North America and beyond.

The researchers used the database to trace one of the ways in which sulfur exits ocean water into the underlying sediments – the formation of so-called sulfate evaporite minerals. These sulfur-bearing minerals, such as gypsum, settle to the bottom of shallow seas as seawater evaporates. The team found that the formation and burial of sulfate evaporites were highly variable over the last 550 million years, due to changes in shallow sea area, the latitude of ancient continents and sea level. More surprising to Halevy and colleagues was the discovery that only a relatively small fraction of the sulfur cycling through the oceans has exited seawater in this way. Their research showed that the formation and burial of a second sulfur-bearing mineral – pyrite – has apparently been much more important.

Pyrite is an iron-sulfur mineral (also known as fools’ gold), which forms when microbes in seafloor sediments use the sulfur dissolved in seawater to digest organic matter. The microbes take up sulfur in the form of sulfate (bound to four oxygen atoms) and release it as sulfide (with no oxygen). Oxygen is released during this process, thus making it a source of oxygen in the air. But because this part of the sulfur cycle was thought be minor in comparison to sulfate evaporite burial (which does not release oxygen), its effect on oxygen levels was also thought to be unimportant.

In testing various theoretical models of the sulfur cycle against the Macrostrat data, the team realized that the production and burial of pyrite has been much more significant than previously thought, accounting for more than 80% of all sulfur removed from the ocean (rather than the 30-40% in prior estimates). As opposed to the variability they saw for sulfate evaporite burial, pyrite burial has been relatively stable throughout the period. The analysis also revealed that most of the sulfur entering the ocean washed in from the weathering of pyrite exposed on land. In other words, there is a balance between pyrite formation and burial, which releases oxygen, and the weathering of pyrite on land, which consumes it. The implication of these findings is that the sulfur cycle regulates the atmospheric concentration of oxygen more strongly than previously appreciated.
 
Iron pyrite. Photo: Thinkstock
                                               

 

 
 

“This is the first use of Macrostrat to quantify chemical fluxes in the Earth system,” said Peters. “I met my coauthors at a lecture I gave at Caltech, and we immediately began discussing how we might apply Macrostrat to understanding biogeochemical cycling. I think this study will open the door to many more uses of Macrostrat for constraining biogeochemical cycles.”

“For me, the truly surprising result is that pyrite weathering and burial appear to be such important processes in the sulfur cycle throughout all of Earth’s history. The carbon cycle is recognized as the central hub controlling redox processes on Earth, but our work suggests that nearly as many electrons are shuttled through the sulfur cycle,” said Fischer.

Halevy: “These findings, in addition to shedding new light on the role of sulfur in regulating oxygen levels in the atmosphere, represent an important step forward in developing a quantitative, mechanistic understanding of the processes governing the global sulfur cycle.”
 
Dr. Itay Halevy’s research is supported by the Sir Charles Clore Research Prize; and the estate of Olga Klein Astrachan.
 
Iron pyrite. Photo: Thinkstock
Environment
English
  • Atmosphere
  • Environmental Sciences and Energy Research
  • Itay Halevy
  • Ocean
  • Planetary cycles

Let it Rain

English

rain

 
 
 
 
 
 
 
 
 
Rain can be a blessing or a disaster. An hour of steady rainfall can water the roots of plants and percolate underground to replenish water supplies. If the same amount of water falls in a five-minute downpour, however, the results are more likely to be uprooted plants, runoff and even flooding. According to new research, the effects of human activity on the atmosphere appear to be nudging rain patterns in the direction of faster and heavier.

In a paper recently published in Nature Geosciences, Prof. Ilan Koren, research student Reuven Heiblum and Dr. Orit Altaratz of the Institute’s Environmental Sciences and Energy Research Department (Faculty of Chemistry), together with Dr. Graham Feingold of NOAA-ESRL, Lorraine Remer of NASA-GSFC and J. Vanderlei Martins of JCET University of Maryland, Baltimore County and NASA-GSFC, looked at the rain rate – how much falls in a given period of time – for a large part of the globe. They then asked whether there is any connection between this rate and aerosols – tiny floating particles in the atmosphere. Aerosols often occur naturally, and they provide the “seeds” for the condensation of cloud droplets or, higher in the atmosphere, the nuclei for ice crystals. But today’s amounts are anything but natural: Burning fuels have added many tons of aerosols to the atmosphere over the past century. “For the first time,” says Koren, “we have managed to obtain a global picture of aerosols’ ability to change rain patterns.”
 
 
Prof. Ilan Koren
 
Koren and Feingold had previously shown how these aerosols affect cloud formation: Heavier loads of airborne particles stimulate the creation of more, but smaller, droplets. But the progression from cloud formation to rainfall is far from straightforward. Many different factors contribute, and diverse patterns of rainfall – from drizzles to torrential storms – arise from quite different weather conditions. Add to this the fact that rain is a widespread but sporadic occurrence, and it becomes quite difficult to formulate any hard-and-fast rules about cause and effect.

To assess rain rates – measured in millimeters per second – around the world, the researchers turned to satellite data. These satellites cannot, as they orbit, monitor absolute rainfall amounts, but they do measure rain rates for so-called convective cloud systems – well-formed clouds that produce relatively heavy rainfall. Data amassed from several different research satellites, collected over a several-month period in 2007 (see below), enabled them to evaluate rain intensity over large parts of the earth where convective cloud systems form, and also to assess aerosol pollution levels in the same regions.

The research team then looked for possible connections between the two, comparing satellite-generated maps of rainfall intensity with those in which aerosol pollution was sorted according to clean, mildly polluted or heavily polluted. Their analysis showed a very strong correlation: In over 80% of the areas in which rain fell from convective cloud systems, more pollution went hand in hand with higher rain rates.

Were aerosol levels really affecting the rain? Or could a third factor, for example, atmospheric instability, be the cause of both higher levels of particles carried in the atmosphere and greater rainfall intensity? To address this question, the scientists undertook a detailed meteorological analysis to see if their results would stand up in light of the hundreds of possible factors affecting rainfall. Most convincingly, when they divided their findings into levels of relative atmospheric stability, they found that added aerosols were tied to increased rain rates across the board, for stable as well as neutral and unstable conditions. This strongly implies that rising aerosol levels do, indeed, intensify rainfall.

Koren believes this phenomenon is mostly felt in areas in which rainfall patterns are close to borderline. In regions that are already flood-prone, higher rain rates might not significantly affect the flooding; and in arid regions, rain is too scarce for the rate to matter much. But somewhere in the middle, as more of the annual rains fall faster than the ground can absorb them, that beneficial rain may also bring more of the less-than-favorable effects.
 

The little satellite that could

satellite data: Tropical Rainfall Measuring Mission data for a 24-hour period
 

 

 
 
 
 
 
 
 
Sometimes unplanned surprises can work in our favor. That is the case with the Tropical Rainfall Measuring Mission (TRMM), a satellite operated by NASA and the Japanese Aerospace Exploration Agency. When it was launched in 1997, carrying monitoring technology from the early 1990s, its projected life span was around three years, at the very most. In 2005, the agencies planned to destroy the TRMM with a controlled reentry, rather than letting it crash to Earth when it ran out of fuel. But scientists realized that the data it was providing were too important, and they even appealed to the US congress, getting a stay of execution to keep the TRMM in orbit. “The satellite has an orbit that allows it to cover much of the tropics and extract as much rainfall data over 24 hours (16 orbits) as possible,” says Koren. “The fact that it has refused to give up the ghost for 15 years means we were able to use it to produce a good, solid study.”
 
Artist's image of the TRMM satellite at work. Images: Jupiterimages and NASA
 

Dr. Ilan Koren’s research is supported by the Yeda-Sela Center for Basic Research.

 

 

 


 

 
rain
Environment
English
  • Aerosols
  • Climate change
  • Cloud formation
  • Environmental Sciences and Energy Research
  • Ilan Koren
  • Rain
  • Satellite image

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