More than 40 researchers recently visited a sparsely populated part of the western tropical Pacific Ocean—near the island of Guam—known as the "global chimney." The area boasts the world’s warmest ocean temperatures and vents massive volumes of warm gases from the surface high into the atmosphere, which may shape global climate and air chemistry enough to impact billions of people worldwide. Until the project’s recent start, scientists were only vaguely aware of the scale and impact of the global chimney. The warm waters in this area feed thunderstorms with heat and moisture, which loft all sorts of gases above the lowest layer of atmosphere, known as the troposphere, into the stratosphere.
At that altitude gases move horizontally, rather than vertically, as they do in the troposphere, and can therefore spread much further around the globe. Better understanding the chemical composition and transport within the chimney, however, could greatly advance our knowledge of the atmosphere and how it may respond to a changing climate. The researchers hope an added bonus could be understanding how pollutants are transported and transformed as air is pushed along the tropics, which could have a direct effect on people living downwind of major air pollution sources. "There are a lot of consequences from this type of air motion," says Elliot Atlas, professor of marine and atmospheric chemistry at the University of Miami and a principal investigator for the project. "There is a link between the chemistry that goes on in this type of air motion and the subsequent effects on the trace gases and aerosols in the atmosphere that ultimately impact climate."
The scientists investigated the waters near Guam last winter using three different high-tech aircraft to collect air samples and examine the abundance, distribution and transformation of various gases in the tropical atmosphere. Some of those gases in the chimney system such as chlorofluorocarbons (found in refrigerants and aerosols) and bromine compounds (found in products such as fire extinguishers) are man-made and can become trapped in the stratosphere, lingering there for years. Those compounds alone can destroy ozone, which helps block the sun’s ultraviolet radiation. (Those rays can contribute to the destruction of crops as well as human skin cancer.) Other compounds, especially the more reactive bromine compounds, can be made naturally, however. Over the last decade scientists have more closely looked at the amount of bromine in the stratosphere and realized it must have sources beyond the long-lived, man-made compounds. The consensus was that natural bromine compounds were being produced by marine organisms and released into the atmosphere. These compounds are relatively short-lived, however, so the scientists suggest that they react in the tropical atmosphere to form inorganic bromine containing compounds, such as bromine monoxide, which can eventualy lead to ozone depletion. Phytoplankton and other plants in the surface ocean can emit gases containing bromine and also chlorine and iodine into the water, which then escape into the atmosphere. Although the distribution of these emissions is still uncertain, measurements have indicated that the tropical oceans could be major sources, lofting them into the atmosphere where they can ultimately contribute to reactions that control tropospheric and stratospheric ozone.
So, the scientists are actively trying to understand how ocean biology might respond to changes in water circulation, nutrient supply, temperature and other factors, all of which could influence the reactive gas emissions and, in turn, feed into the chemical cycles that further influence climate through changes in greenhouse gases. The planet’s climate ultimately becomes altered when these gases start to affect the amount of energy from the sun that is allowed to reach Earth’s surface or is stored in the atmosphere.
Besides increasing or decreasing the levels of ozone in the upper atmosphere, some of the chemicals also contribute directly to the greenhouse effect. For example, added water vapor pumped into the upper atmosphere from the chimney increases the amount of energy trapped there, in turn heating the planet further. Another principal investigator for the project, Laura Pan, senior scientist at the National Center for Atmospheric Research in Boulder, Colo., believes storm clusters over this area of the Pacific are likely to influence climate in new ways, especially as the warm ocean temperatures (which feed the storms and chimney) continue to heat up and atmospheric patterns continue to evolve. "Understanding the impact of these storms will help us gain ground truth for improving the chemistry–climate models we use to project future climate," she says. Defining those linkages, however, is an obviously complex task, according to Ross Salawitch, a University of Maryland, College Park, professor of atmospheric and oceanic sciences and another principal investigator. "The various processes and feedbacks between the physical forcing factors in the climate system are under active investigation by a whole community of climate scientists," he says. "The addition of biological interactions adds another layer of complexity (and uncertainty) to the eventual outcomes of changing temperatures, circulations and so on. Rising temperatures, for example, could either increase or decrease biological productivity," Salawitch says, as well as the emission of certain less-prevalent gases that are exchanged between the air and ocean. "Perhaps increased ocean acidification could be another controlling factor," he adds.
Only one other major circulation has been considered a "global chimney." The other (much smaller) major pathway for transporting air from the lower atmosphere to the stratosphere is the Asian monsoon circulation, which prevails in the summer. Efforts are underway to conduct similar aircraft observations in the region of the Asian monsoon. The researchers have also identified smaller circulations that could significantly affect atmospheric chemistry such as the North American monsoon and convections over Africa. The idea for this type of project dates back to 1999, according to Salawitch. He says the project didn’t swing into action until recently, however, because work involving multiple complex aircraft and research teams takes a long time to plan (especially for high-altitudes). And although the collection process is now over, the scientists have a lot of data to sift through before they can say for sure what exactly is happening in this chimney and what its future impact on the world’s climate could be. "The data collected during these missions will stand as benchmarks for testing how well the tropics are represented in computer simulations and in forecasts of future climate," Salawitch says. The complete analysis, he notes, could last two years or more. More
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