Category: Climate

Image credit: NASA
As two rovers scour Mars for signs of water and the precursors of life, geochemists have uncovered evidence that Earth’s ancient oceans were much different from today’s. The research, published in this week’s issue of the journal Science, cites new data that shows that Earth’s life-giving oceans contained less oxygen than today’s and could have been nearly devoid of oxygen for a billion years longer than previously thought. These findings may help explain why complex life barely evolved for billions of years after it arose.

The scientists, funded by the National Science Foundation (NSF) and affiliated with the University of Rochester, have pioneered a new method that reveals how ocean oxygen might have changed globally. Most geologists agree there was virtually no oxygen dissolved in the oceans until about 2 billion years ago, and that they were oxygen-rich during most of the last half-billion years. But there has always been a mystery about the period in between.

Geochemists developed ways to detect signs of ancient oxygen in particular areas, but not in the Earth’s oceans as a whole. The team’s method, however, can be extrapolated to grasp the nature of all oceans around the world.

“This is the best direct evidence that the global oceans had less oxygen during that time,” says Gail Arnold, a doctoral student of earth and environmental sciences at the University of Rochester and lead author of the research paper.

Adds Enriqueta Barrera, program director in NSF’s division of earth sciences, “This study is based on a new approach, the application of molybdenum isotopes, which allows scientists to ascertain global perturbations in ocean environments. These isotopes open a new door to exploring anoxic ocean conditions at times across the geologic record.”

Arnold examined rocks from northern Australia that were at the floor of the ocean over a billion years ago, using the new she had method developed by her and co-authors, Jane Barling and Ariel Anbar. Previous researchers had drilled down several meters into the rock and tested its chemical composition, confirming it had kept original information about the oceans safely preserved. The team members brought those rocks back to their labs where they used newly developed technology -called a Multiple Collector Inductively Coupled Plasma Mass Spectrometer-to examine the molybdenum isotopes within the rocks.

The element molybdenum enters the oceans through river runoff, dissolves in seawater, and can stay dissolved for hundreds of thousands of years. By staying in solution so long, molybdenum mixes well throughout the oceans, making it an excellent global indicator. It is then removed from the oceans into two kinds of sediments on the seafloor: those that lie beneath waters, oxygen-rich and those that are oxygen-poor.

Working with coauthor Timothy Lyons of the University of Missouri, the Rochester team examined samples from the modern seafloor, including the rare locations that are oxygen-poor today. They learned that the chemical behavior of molybdenum’s isotopes in sediments is different depending on the amount of oxygen in the overlying waters. As a result, the chemistry of molybdenum isotopes in the global oceans depends on how much seawater is oxygen-poor. They also found that the molybdenum in certain kinds of rocks records this information about ancient oceans. Compared to modern samples, measurements of the molybdenum chemistry in the rocks from Australia point to oceans with much less oxygen.

How much less oxygen is the question. A world full of anoxic oceans could have serious consequences for evolution. Eukaryotes, the kind of cells that make up all organisms except bacteria, appear in the geologic record as early as 2.7 billion years ago. But eukaryotes with many cells-the ancestors of plants and animals- did not appear until a half billion years ago, about the time the oceans became rich in oxygen. With paleontologist Andrew Knoll of Harvard University, Anbar previously advanced the hypothesis that an extended period of anoxic oceans may be the key to why the more complex eukaryotes barely eked out a living while their prolific bacterial cousins thrived. Arnold’s study is an important step in testing this hypothesis.

“It’s remarkable that we know so little about the history of our own planet’s oceans,” says Anbar. “Whether or not there was oxygen in the oceans is a straightforward chemical question that you’d think would be easy to answer. It shows just how hard it is to tease information from the rock record and how much more there is for us to learn about our origins.”

Figuring out just how much less oxygen was in the oceans in the ancient past is the next step. The scientists plan to continue studying molybdenum chemistry to answer that question, with continuing support from NSF and NASA, the agencies that supported the initial work. The information will not only shed light on our own evolution, but may help us understand the conditions we should look for as we search for life beyond Earth.

Original Source: NSF News Release

Image credit: NASA
Using measurements from a NASA aircraft flying over the Arctic, Harvard University scientists have made the first observations of a molecule that researchers have long theorized plays a key role in destroying stratospheric ozone, chlorine peroxide.

Analysis of these measurements was conducted using a computer simulation of atmospheric chemistry developed by scientists at NASA’s Jet Propulsion Laboratory (JPL), Pasadena, Calif.

The common name atmospheric scientists use for the molecule is “chlorine monoxide dimer” since it is made up of two identical chlorine-based molecules of chlorine monoxide, bonded together. The dimer has been created and detected in the laboratory; in the atmosphere it is thought to exist only in the particularly cold stratosphere over Polar Regions when chlorine monoxide levels are relatively high.

“We knew, from observations dating from 1987, that the high ozone loss was linked with high levels of chlorine monoxide, but we had never actually detected the chlorine peroxide before,” said Harvard scientist and lead author of the paper, Rick Stimpfle.

The atmospheric abundance of chlorine peroxide was quantified using a novel arrangement of an ultraviolet, resonance fluorescence-detection instrument that had previously been used to quantify levels of chlorine monoxide in the Antarctic and Arctic stratosphere.

We’ve observed chlorine monoxide in the Arctic and Antarctic for years and from that inferred that this dimer molecule must exist and it must exist in large quantities, but until now we had never been able to see it,” said Ross Salawitch, a co-author on the paper and a researcher at JPL.

Chlorine monoxide and its dimer originate primarily from halocarbons, molecules created by humans for industrial uses like refrigeration. Use of halocarbons has been banned by the Montreal Protocol, but they persist in the atmosphere for decades. “Most of the chlorine in the stratosphere continues to come from human-induced sources,” Stimpfle added.

Chlorine peroxide triggers ozone destruction when the molecule absorbs sunlight and breaks into two chlorine atoms and an oxygen molecule. Free chlorine atoms are highly reactive with ozone molecules, thereby breaking them up, and reducing ozone. Within the process of breaking down ozone, chlorine peroxide forms again, restarting the process of ozone destruction.

“You are now back to where you started with respect to the chlorine peroxide molecule. But in the process you have converted two ozone molecules into three oxygen molecules. This is the definition of ozone loss,” Stimpfle concluded.

“Direct measurements of chlorine peroxide enable us to better quantify ozone loss processes that occur in the polar winter stratosphere,” said Mike Kurylo, NASA Upper Atmosphere Research Program manager, NASA Headquarters, Washington.

“By integrating our knowledge about chemistry over the polar regions, which we get from aircraft-based in situ measurements, with the global pictures of ozone and other atmospheric molecules, which we get from research satellites, NASA can improve the models that scientists use to forecast the future evolution of ozone amounts and how they will respond to the decreasing atmospheric levels of halocarbons, resulting from the implementation of the Montreal Protocol,” Kurylo added.

These results were acquired during a joint U.S.-European science mission, the Stratospheric Aerosol and Gas Experiment III Ozone Loss and Validation Experiment/Third European Stratospheric Experiment on Ozone 2000. The mission was conducted in Kiruna, Sweden, from November 1999 to March 2000.

During the campaign, scientists used computer models for stratospheric meteorology and chemistry to direct the ER-2 aircraft to the regions of the atmosphere where chlorine peroxide was expected to be present. The flexibility of the ER-2 enabled these interesting regions of the atmosphere to be sampled.

Original Source: NASA News Release

Image credit: NASA

When Hurricane Erin was beating up the North Atlantic last year, NASA researchers decided to take its temperature. Using a special aircraft, researchers dropped eight sensors into the area round the storm’s eye, a place that contains the most powerful winds and warmest temperatures. Using this data, they were able to create a three-dimensional image of the complete inner core.

Last year, NASA researchers took the temperature of the eye of Hurricane Erin to determine how a hurricane?s warm center fuels the strength of storms. The new data is helping scientists understand the inner workings of hurricanes at very high altitudes, and will improve future hurricane forecasts.

The researchers found that the warmest portion around a hurricane?s eye is approximately 3.5 miles high and that area in the eye corresponds with falling pressure, which is what causes the winds to spiral inward at destructive speeds.

During September 2001 while flying over the North Atlantic Ocean, scientists aboard NASA?s ER-2 aircraft dropped eight sensors into the area around Hurricane Erin?s eye, containing the strongest thunderstorms and winds, and warmest temperatures. Variations in temperatures within a hurricane provide clues about the storm?s intensity. For example, a warm center marked by a large temperature contrast compared to the rest of the hurricane is a sign of a strong storm.

The sensors measured temperature, air pressure and winds as they fell through the hurricane and transmitted their data back to the ER-2 aircraft. For the first time, the data allowed scientists to create a comprehensive 3-dimensional image of the complete inner core (including the eyewall and the eye) of a hurricane, giving scientists a better look at how heat from warm, rising air spreads out in the storm?s center. The warm, humid, rising air is the key to a hurricane?s power. This rising air draws in air from the surface to take its place, and creates winds.

?Scientists can obtain a detailed look at a hurricane?s heat engine (the warm temperatures that power a storm) by combining the aircraft data with that from satellites such as NASA?s Tropical Rainfall Measurement Mission,? said Jeff Halverson, a scientist from NASA?s Goddard Space Flight Center, Greenbelt, Md., and the University of Maryland Baltimore County.

?The data from the sensors and the satellite have given us a view of the eye?s warm air, the rain clouds that warm the air through condensation, and the spiraling surface winds which in turn create the rain clouds. We have assembled all this data in a three dimensional rendition of the hurricane which is akin to taking a detailed ?CAT scan? of the storm,? Halverson said.

?We found that this storm had a very warm eye, from the ocean to the top of the lower atmosphere at around 10 miles altitude,? said Halverson. The warmest part of Erin?s eye was almost 21 degrees (Fahrenheit) warmer than the surrounding air, a dramatic difference from the air around it. Above 7.5 miles high, the eye?s temperature dropped quickly to the same temperature as the air outside the eye.

The warming temperatures within the hurricane?s eye make the air lighter, so air pressure eases on the surface and falls. When air is cold, the air molecules are dense, and air is heavier. The falling pressure in the hurricane?s eye is what creates swirling destructive winds.

The experiment also discovered that strong rising air currents in Erin caused the tropopause (top of the lower atmosphere) to ?bubble up? or bend, south of the eye?s center. This is indicative of the strength of Hurricane Erin, which was a Category 3 storm at this time.

There are five categories in which hurricanes are classified, the fifth being the most devastating. Category 3 hurricanes, such as Erin have winds between 111-130 mph, and can bring a storm surge of water (wind driven water above tide level) between 9-12 feet to shorelines.

Halverson will be presenting these findings at the AMS Hurricane and Tropical Meteorology Conference in San Diego, Calif. on Tuesday, April 30, 2002 at 9:00 a.m. Pacific time in a session titled ?Thermal Structure of Hurricane Erin?s Core Using Dropsonde Data From 68,000 Feet and Comparison with AMSU Satellite Measurements.?

Original Source: NASA News Release