Dec. 10, 1998 When Jack Frost starts nipping at your nose, consider this: Perennially frozen material lurks beneath at least one-fifth, and perhaps as much as one-fourth of the Earth's land surface.
Ongoing studies of these "permafrost" regions may help cold-weather communities prepare for potentially hazardous thawing events, says Frederick E. ("Fritz") Nelson, a professor of geography at the University of Delaware.
And, more accurate global-climate predictions should result from new information on seasonal freezing and thawing and the release of "greenhouse" gas precursors currently trapped within permafrost, says Nelson, who will take part Dec. 7 in the American Geophysical Union's (AGU) 1998 fall meeting in San Francisco.
A permafrost region around Barrow, Alaska, the northernmost settlement in the United States, thawed more deeply during the 1960s, than in the 1990s," says Nelson, whose AGU presentation was prepared with Kenneth M. Hinkel of the University of Cincinnati and Ron F. Paetzold of the U.S. Department of Agriculture's Natural Resources Conservation Service.
Today's slightly more shallow "active layer"-the seasonally thawing ground above permafrost-is strongly related to summer air temperatures recorded near Barrow by the National Oceanic and Atmospheric Administration (NOAA), Nelson says. But, the active layer also is influenced by subsurface processes, which occur over periods longer than the annual temperature cycle, he adds.
"We have found a decade-to-decade variability in the depth of summer thawing in this particular region," Nelson explains. "Over a series of years, we can use summer air temperatures to predict the depth of thaw. Yet, for some reason, the thawing depth seems to `reset' from time to time, and then the active layer will hover around that thickness for another series of years."
Deeper thawing predicted
By the year 2050, the active, seasonally thawing layer over large parts of the Northern Hemisphere could grow 20 to 30 percent thicker if temperatures follow trends predicted by large-scale climate models, Nelson reported, with Oleg Anisimov of St. Petersburg, Russia, and UD graduate student Nikolai Shiklomanov, in a recent issue of the journal, Global and Planetary Change (Vol. 15, 1997).
Because large amounts of organic carbon, the precursor for carbon dioxide and methane emissions, is sequestered within permafrost, a thicker active layer could affect global-warming predictions, Nelson notes.
"Estimates of total carbon stocks in the Arctic may need to be revised upward because the large amounts of carbon stored in permafrost could prove to be a more significant source of greenhouse gases than we previously had assumed," he says, citing work by colleagues, Jim Bockheim of the University of Wisconsin and Chien-Lu Ping of the University of Alaska.
Hinkel cautions, however, that scientists still are uncertain how warmer temperatures might affect permafrost, or how thawing ground ice could affect climate. Warmer, wetter weather might, for example, increase vegetation growth, which could actually insulate the permafrost, keeping the near-surface ground layers frozen. "The bottomline," Hinkel says, "is that we need to learn more about these vast regions of perennially frozen material and their impacts on our planet."
Understanding the polar zone
Described by Hinkel as "any subsurface materials that remain frozen over extended periods of time," permafrost underlies much of Siberia and the Himalayan Mountains. In North America, permafrost can be found well beyond the southern margins of the Hudson Bay, and beneath parts of the Rocky Mountains as far south as Colorado. Before scientists can accurately predict thawing events-and the potential climate impacts of gases escaping from permafrost- they must first understand the subsurface, free-and-thaw cycles in the Earth's cold regions.
During a recent presentation at the 1998 International Permafrost Association conference in Yellowknife, Canada, Hinkel, Nelson and several other colleagues reported that between 1964 and 1968, the thickness of the active layer atop permafrost near Barrow ranged from 35 to 43 centimeters. Yet, between 1991 and 1997, the active layer was 25 to 35 centimeters thick.
What could have caused such a dramatic change? Although the research team can't say for sure, Nelson suggests that a series of relatively cold summers may allow the underlying permafrost to grow upward slightly, while also developing an ice-rich layer that resists thawing in subsequent years.
Over the longer term, however, permafrost regions are expected by many researchers to thaw more deeply, Nelson says. Heated buildings and other engineered structures may accelerate thawing, resulting in damage to roads, house foundations and pipelines.
Already, some studies point to a "geographically variable but distinct increase in the temperature of lowland permafrost," Nelson, Hinkel and colleagues wrote in the journal, Arctic and Alpine Research (Vol. 29, No. 4, 1997). Within specific regions, thawing permafrost has caused visible damage to buildings.
And, recent findings by a group of researchers at San Diego State University indicate that "the arctic tundra may have changed from a net sink to a source of carbon dioxide, at least regionally," Nelson says.
Because permafrost may vary dramatically from region to region, experts are examining its properties over large geographic areas. Nelson and Hinkel's group is investigating Alaska's coastal Kuparuk River basin, from the Arctic Ocean over the coastal plain, into the foothills of the Brooks Range.
This research was supported by the Office of Polar Programs at the National Science Foundation (NSF). The NSF funds the Circumpolar Active Layer Monitoring Program (CALM)-administered by the University of Cincinnati's Department of Geography, involving 11 countries and 69 research sites. The NSF also supported the modeling work by Nelson and Anisimov. And, the UD group participates in the NSF-supported Teachers Experiencing the Arctic (TEA) program, which annually provides high-school science teachers and students with opportunities for Arctic field investigations.
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