A series of permafrost-related projects have been funded as part of the National Science Foundation's Arctic System Science (ARCSS) program. Larry Hinzman, University of Alaska, solicited and submitted the following summaries.
Progress in developing climatic simulations of large areas in the Arctic is restricted by physical constraints of data collection, by a limited understanding of the interdependence and interaction of the physical and biological processes, and by limitations in our technical ability to extend our measurements and understanding across a range of scales. NSF, as part of its ARCSS global change program, is funding a multi-year program focused on northern Alaska. The program, Land-Atmosphere-Ice Interactions (LAII), involves a group of projects concerned with research on boundary layer processes associated with the vegetative cover, active layer and near-surfice permafrost. Many of the study sites are along the route of the oil pipeline and road to Prudhoe Bay and the adjacent Kuparuk River watershed, in which an intensive vegetation-soil-atmospheric gas exchange program known as the Flux Study of the LAII is underway. Details can be obtained from individuals and the LAII project office at the University of Alaska (email@example.com).
An important component of several active layer studies was the establishment of 1-x 1-km grids surveyed and marked every 100 m. These grids, installed at Toolik Lake, Imnavait Creek, Happy Valley, West Dock, Betty Pingo, Barrow and Atkasuk, are the U.S. contribution to CALM (see page 21). Thaw depths have been measured at every node on these grids each autumn, and in some cases several times throughout the summer, by many of the cooperating LAII-Flux Study scientists.
Donald Walker, University of Colorado, and his associates have established permanent vegetation plots at inland sites at Toolik Lake, Imnavait Creek and Happy Valley and at coastal sites at Prudhoe Bay, Barrow and Barter Island. Site factors, including soil properties, plant cover, and active layer depth in August, are available. A regional vegetation map of the Kuparuk River basin (8140 km²) was prepared using existing vegetation classifications and aerial and satellite imagery. Additional plots along the north-south Flux Study transects were established in 1995 to serve as verification for the regional scale extrapolations.
Frederick Nelson, State University of New York-Albany, Ken Hinkel, University of Cincinnati, and colleagues are collaborating on two related projects concerning the spatial variations and temporal trends of the active layer on the ARCSS 1- x 1-km grids and the Flux Study 100- x 100-m plots. These studies involve intensive probing using formal hierarchical sampling designs. Near-surface (0-120 cm) temperatures and soil moisture are monitored hourly at several of these locations. Temporal (interannual and interdecadal) variations of active layer thickness are being investigated using coupled-flow models of soil thermal evolution, driven by local weather records at Barrow. Heat and mass transport measurements in the active layer and upper permafrost indicate that coupled-flow processes are especially active during snowmelt and when the active layer is thawed, and that these effects extend into the upper permafrost. When the annual field is modeled, the difference between measured and simulated temperatures indicates that nonconductive processes can cause episodic residuals of ± 2°-3°C and, while infiltration of snow meltwater is occurring, can displace the entire thermal field in the upper soil column. Soil moisture appears to be the crucial dynamic parameter. Using historical core data taken at Barrow in 1963 and a replicate sampling in 1993 suggests an average volumetric water (ice) enrichment of up to 5% in the upper few decimeters of permafrost. Stratigraphic analysis of the structures suggested downward movement of water through a network of cracks.
Tom Osterkamp, University of Alaska, and associates are pursuing research to improve understanding of the coupling of climate to permafrost through the intervening snow cover. A model using Barrow air temperatures applied to the ground surface with no snow cover predicted little change in permafrost temperatures. This result disagrees with observations confirming that air temperatures alone cannot account for the observed warming of the permafrost over the last century. Modeling the effects of the snow cover showed that the variable depth hoar fraction can change the daily and mean annual ground surface temperatures by several degrees and the date of active layer freeze-up by several weeks. Permafrost temperatures, obtained from a series of shallow boreholes, have cycled since 1983 over a range of 4°C with a period of at least 11 years, about in phase with the sunspot cycle and with the patterns of cyclonic and anticyclonic circulation in the Arctic Ocean. This range is about the same as the observed warming of the last century and the predicted warming for the next half-century due to greenhouse gases in the atmosphere. Active layer thicknesses also varied systematically, changing by up to a factor of two. About one-third of the active layer freezes from the bottom upwards.
Douglas Kane and Larry Hinzman, University of Alaska, and associates focus upon developing models of hydrologic and thermal processes. The modeling efforts include simulations of meteorologic data, areal extrapolation, soil moisture, stream runoff, active layer thaw depth, and soil temperatures. Data necessary to understand the hydrologic, meteorologic and thermal processes are being collected throughout the Kuparuk River basin. Specific parameters measured include subsurface temperatures and variables necessary to establish the surface energy balance. Soil samples were analyzed in the laboratory for bulk density and hydraulic conductivity. Automated time domain reflectometry (TDR) probes are installed in the active layer to measure unfrozen soil moisture daily during the summer. Depth of thaw of the active layer is measured several times throughout the summer and surface condition is noted in an attempt to relate thaw rates to surface characteristics. Physically based, spatially distributed models of hydrologic and thermal processes have been developed and verified for portions of the Kuparuk River basin. The primary control on the depth of thaw appears to be hydrologic factors. In very wet soils, the depth of thaw is greater than in drier soils, all other factors being nearly the same. Under conditions of running water in surficid drainages the depth of thaw is geaterthan in drier soils. An extensive network of shallow wells around the Prudhoe Bay site (Betty Pingo) revealed that hydraulic gradients changed from early to late summer. Just after spring melt, the surrounding wetlands supplied water to the tundra ponds; in late summer, however, the gradients were reversed, with water moving from the ponds to the wetlands. The total volumes of water movement were quite low due to low hydraulic conductivities and low hydraulic gradients; however, this supply of water and heat may be important for areas adjacent to small thermokarst features.
James Bockheim, University of Wisconsin, and other LAII investigators have found that nonacidic tundra soils are more extensive in the Kuparuk River basin, accounting for as much as 54% of the total vegetation cover. Properties of 30 soils in moist nonacidic and acidic tundra and 8 soils in nonacidic and acidic shrublands were compared. Although the organic layer is thicker in acidic tundra, the thickness of the A horizon, the maximum thaw depth, and the pH of the upper mineral soil layer are greater in the nonacidic moist tundra and shrubland than in their acidic counterparts. Many of the soils in nonacidic tundra contain a thick, dark-colored surface mineral horizon and abundant base cations. These soils may be more susceptible to carbon release and permafrost table recession in the event of global warming then adjacent acidic, lighter colored soils. The factors controlling the distribution of nonacidic soils are poorly understood but may include distribution of calcareous dust in snowfall, the age of the geomorphic surface and vegetation succession.
Chien-Lu Ping, University of Alaska, and colleagues are studying the relationship between the permafrost table and soil formation in more than 70 pedons excavated to a meter or more from arctic Alaska and associated sites in northwest Canada, and northeast Russia (see Cryosol Working Group report). Field evidence indicates that the zone of permafrost table fluctuation ranges from a few to more than 50 cm,
depending on the vegetation type and successional stage, latitude, and landform position. During a cooling period the permafrost table rises and sequesters the soil carbon which was frost-churned or cryoturbated to the lower part of the active layer. During a warmer period, the permafrost table is expected to be depressed and release carbon and other nutrients to biogeochemical cycling. The increased active layer results in deeper root penetration. Reducing conditions generally occur above the permafrost table. When the saturated zone fluctuates with the rise and fall of the permafrost table, a redox zone is created and mineral weathering is enhanced. Moderately to strongly developed cryogenic structures, including ice lenses and ice nets, commonly occur above the permafrost table. After thawing, these structures become platy and blocky, which provides channels and pores for water and root penetration.
William Reeburgh, University of California-Irvine, and his students measured methane fluxes, using static chambers, at weekly intervals at 43 sites during the 1994 and 1995 thaw seasons. Five vegetation cover classes were used in the sampling site selection: barrens, moist non-acidic tundra, moist acidic tundra, shrublands, and wet tundra. The methane fluxes were integrated over the thaw season to produce annual methane emission estimates. The vegetation-classified methane fluxes were used to define four general methane emission categories (sink and low-, moderate-, and high-source) and were combined with the Kuparuk River basin vegetation map to produce a regional methane emission map. Field water table manipulation experiments are in progress near Toolik Lake. These experiments involve lowering (and raising) wet meadow water tables inside 1- x 1-m cofferdams to determine the effect of water table level changes on methane and carbon dioxide emissions.
John Hobbie, Marine Biological Laboratory, and colleagues are conducting research on two major aspects of the active layer. First, the project monitors thaw depth in a small watershed at the LTER Toolik Lake site through surveys conducted in early and in late summer. The database now contains six years of information (see CALM table, page 21). Comparison of data between Barrow (coastal) and Toolik (inland foothills) shows the same depression of thaw penetration in 1991 reported by Osterkamp's project in the Prudhoe Bay area. Second, the project is monitoring soil chemistry and hydrology in the same watershed. Weekly measurements of water table, soil temperature, and soil water gases, nutrients, and dissolved organic carbon are being made at eight different sites representing upland tussock tundra and riparian birch and willow. Soil water gases reach 100,000 microatmospheres of C02 and 500,000 microatmospheres of methane due to plant and microbial respiration. Most of the nitrogen and phosphorus leaves the watershed in the dissolved organic forms. Soil water concentrations of dissolved organic carbon are correlated with different vegetation types and position of the sample in the watershed.
Terry Chapin, University of California-Berkeley, and associates are measuring water and energy exchange in all the major tundra vegetation types in the Kuparuk River basin, including those that are expected to become more common with global warming. Included in these measurements is an estimation of ground heat flux, measured as a function of vegetation type, climatic factors (e.g. temperature), and net radiation. At each site, other important variables influencing ground heat flux are also measured, including leaf area index, moss cover, soil moisture, and soil temperature. These measurements are at the same locations where Nelson's project measures active layer depth.
Walt Oechel, San Diego State University, and several associated groups obtain active layer depth measurements associated with a series of experiments. These include net CO2 flux chamber plots, several permanent meteorological sites, and a water table-surface temperature manipulation experiment at a Prudhoe Bay site (West Dock). The water table was lowered on average 7 cm below the ambient water table, and surface temperature was increased by approximately 1°C using the open-top ITEX chambers. Several of these studies are closely related to similar ones in the Russian Arctic. Descriptions of the extensive data sets and experimental designs for the San Diego projects and the other ARCSS-LAII projects will be available as part of an ARCSS data management project at the National Snow and Ice Data Center, University of Colorado.
Reports of several recent NSF-ARCSS-sponsored workshops on arctic land-shelf-basin interactions are available. The results of three workshops held in Columbus, Ohio, Arlington, Virginia, and St. Petersburg, Russia, describe research priorities for the Eurasian land-shelf system, including both onshore and subsea permafrost. The report is available as Byrd Polar Research Center Misc Series M-397, Ohio State University, Columbus, Ohio 43210-1002. The second report of a workshop held in March 1995 discusses issues and research questions for the arctic shelf-basin interactions. That report is available from the Polar Science Center-APL, University of Washington, Seattle, Washington 98105-6698.
The Transportation Research Board (TRB) Committee on Frost Action chaired by Billy Connors (Alaska Department of Transportation and Public Facilities) met on 9 January during the Seventy-Fifth Annual Meeting of the TRB. In addition to committee business, presentations were made on the IPA Global Geocryological Database (Jerry Brown), neural networks (Lufto Raad), moisture accumulation in pavements (K. Eigenbrod), and evaluation of seasonal variability in cohesive subgrades (Ken Anderson). The TRB program included a seven-paper session on Geotextiles in Cold Regions.
Jess Walker reports that on 13 April, 20 papers devoted to the cryosphere were presented in four sessions of the annual meeting of the Association of American Geographers (AAG) in Charlotte, North Carolina. Six papers were devoted to various aspects of snowfall, including such topics as snow depths in the former Soviet Union and snow cover fluctuation as derived from satellite observations. Other papers dealt with the active layer, permafrost, glaciers, rock glaciers, arctic soil development and alpine talus deposits. IPA working group chairs Roger Barry, Fritz Nelson and Antoni Lewkowicz co-chaired several sessions and presented papers. IPA Vice President Hugh French presented a paper entitled Periglacial Environments, Pleistocene and Recent.
The general consensus was that the sessions were very successful and that we should pursue attempts to form a Cryosphere Specialty Group within the AAG. To that end a petition containing the names of 106 potential members was submitted to the AAG requesting that the Cryosphere Specialty Group be established. It was subsequently approved and the group is now official. Future plans call for two or three sessions to be held at the meeting in Fort Worth (1-5 April 1997) and for expanded sessions in Boston
(25-29 March 1998). Further information is available from H.J. Walker (hwalker@unixl .sncc.lsu.edu).
Submitted by Larry Hinzman and Jerry Brown (firstname.lastname@example.org, email@example.com)