The Bogs Are Breathing Out

For reasons unknown, San Diego's institutions of higher education harbor a surprising number of scientists with arctic specialties. Among them is Waiter C. Oechel of San Diego State University, who annually leads a team of researchers to Alaska's north. One of their important study subjects is the carbon dioxide emitted by arctic tundra.

Measuring exhalations from tundra is especially interesting to scientists and the agencies funding them nowadays because of the attention paid to the possibility of global warming. Headlines concentrate on how burning up jungle and chopping down rain forest may be leading to an overall heating of the climate because such activities increase the amount of heat-trapping carbon dioxide in the atmosphere. Yet it turns out that far colder, less impressive-looking plant communities also may have important implications for the process.

To see why this is so, envision a typical northern terrain of the type that seems to be heaven for mosquitoes. It's on the soggy side, or downright boggy; it's well endowed with plants, but no towering forests or waving plains of grass. Also, it's not green for much of the year. A lot of the greenery produced during the short summer can be found lying brown and dead on the ground during the long winter.

That brown vegetation can be found there the winter after that, and the one after that, and so on for decades, centuries, even millennia. In the cold soggy conditions found in much of the Arctic, some dead plant material doesn't decompose. It gets buried instead, building up as peat, for example. The carbon making up most of that damp buried plant matter isn't given back to the atmosphere as carbon dioxide, which is what happens when organic decomposers can work freely on it. Thus scientists have understood that the far north is a net sink for carbon; it is taken out of the atmosphere by growing plants in summer, but it is not all returned by the microbes working to decay the dead leaves and other litter.

The San Diego State research turned up some bad news for people worried about global warming. Over the last few decades, Alaska's tundra in summertime has been releasing more carbon dioxide than it has been storing. Instead of a carbon sink, it's become a carbon source, helping speed the greenhouse effect.

Oechel has speculated that warmer summers since about the 1970s in northern Alaska have dried the soils, letting the decomposer organisms do more thorough work and thus crank out more carbon dioxide, which should lead to an increase in warm summers in northern Alaska.

The San Diego researchers assumed that the tiny decomposers would do what work they could during summer, which is not only logical but convenient, since that is also when scientists prefer to study the Arctic. Decomposition, like photosynthesis, should shut down when everything is solid.

However, nature sometimes refuses to be either logical or convenient. According to some Siberian researchers, the microbes responsible for emitting carbon dioxide from tundra soil stay busy all winter long. S. A. Zimov and his colleagues from the Pacific Institute for Geography in Vladivostok reported varying but not insignificant emissions of the gas from tundra lying only 100 kilometers south of the Arctic Ocean during the months of December, January, and February.

The Siberian surprise apparently came from a small area, so something else may be going on but no one can guess what that might be. To compare techniques with Zimov, Oechel hopes to visit Siberia this summer and to extend his own team's work later during fall to see if Alaska's microbes keep the carbon dioxide flowing out past freeze-up.