Emerging Issue Summary
PERMAFROST

Highlights:

  • Existing data and current techniques for permafrost measurement are not yet sufficient to address most management concerns.
  • Active layer depth and subsidence, and their relation to threshold conditions in the active layer-permafrost system, may be of more immediate importance to land managers than broad permafrost conditions.
  • All relevant data should be centralized in an accessible location.
  • Combining ground observations with remote sensing techniques may hold some promise. For instance, combining Synthetic Aperture Radar (SAR) with active layer monitoring results may lead to improved understanding of permafrost dynamics relevant to land managers.

Permafrost
Permafrost degradation on the North Slope. (Ken Dunton, University of Texas)

Overview and Management Relevance:

The most important and basic finding of the STAP is that current measurement techniques, extent of monitoring, and availability of data for permafrost are not adequate. Current permafrost science has only a limited understanding of the distribution of permafrost on the North Slope and a similarly limited sense of the trajectory of change of that permafrost. In other words, current knowledge of the distribution of permafrost and an understanding of how it is changing is insufficient to address most of the more specific management concerns and questions. Prediction and detection of subsidence is especially problematic. Furthermore, before advances can be made in the ability to predict future conditions and detect change, we need to have a better understanding and to some degree a standardization of how and where permafrost is monitored.

Currently, available information comes primarily from index sites operated by USGS, boreholes monitored by the Permafrost Laboratory at the University of Alaska in Fairbanks, and a network of roughly 125 index sites throughout the Arctic (see Circumpolar Active Layer Monitoring Network, http://www.udel.edu/Geography/calm) where the active layer thickness is measured at the end of each summer. Industry also monitors a number of sites, but the data from these sites are not widely distributed. If at all possible, all relevant data should be centralized in one accessible location, in part because development of change trajectories and model testing require large, spatially distributed data sets. Only then can science begin to address questions both general (e.g., How widespread is thermokarsting?) and local (e.g., Will the permafrost thaw under a specific section of pipeline?).

A noteworthy STAP observation is that while questions of permafrost trends across the North Slope seem to be of general interest, it may be that site-specific issues will drive agency agendas as the permafrost thaws. For example, the thawing of permafrost near a critical habitat lagoon could lead to sudden drainage. If this is the case, it will be important for managers to clarify these specific concerns, identify sensitive areas, and consider whether there are potential confounding factors. For instance, an ice cellar may thaw because of urban heat island effects, rather than because of global warming.

Hybrid methods combining several types of measurements may offer the best hope for future monitoring. For example, combining Circumpolar Active Layer Monitoring (CALM) data with SAR data has shown some potential to augment traditional measures of active layer change. Preliminary examination of SAR data collected near CALM active layer depth measurements show a positive correlation—an increase in active layer thickness correlates with an increase in backscatter return. The opportunity may exist to extend the area coverage of the CALM measurements by combining them with SAR-derived values. Other remote sensing techniques may allow spatial extrapolation of spot measurements and help to address management issues such as habitat and vegetation changes due to changing permafrost or the effects of fire on permafrost. It should be recognized, however, that there are currently no standoff technologies that can directly determine the state of the ground, and even on-the-ground geophysical methods (Ground Penetrating Radar and Resistivity) have limitations.

Another important STAP observation relevant to the discussion of whether the focus is on broad-scale and long-term or finer-scale and short-term, is that 10- to 20–year-out questions actually relate to the active layer, rather than specifically to the permafrost itself. In 20 years, North Slope permafrost will almost certainly be still regionally intact, but the active layer may change in either thickness and/or the degree to which frost heave and thaw subsidence occur. It is these changes to the active layer and shallow permafrost, rather than overall changes to permafrost, that have the most important implications for ecosystem change and relevant management and engineering concerns.

Perhaps critical questions relevant to management concerns are “Is there some threshold state or thickness of the active layer beyond which current rates of change might accelerate?” and, “Are there threshold conditions in the active layer-permafrost system that trigger rapid ecosystem change?” These questions are at the heart of the issue of rate of change. Among permafrost scientists, there is a strong sense that this threshold might occur when the active layer begins to thaw deeper each year than can freeze back the following winter, leaving a thawed gap or discontinuity between the active layer and the deeper soils and earth that remain permanently frozen.

Recent observations suggest that one impact of accelerated thickening of the active layer is, in fact, changes in ecosystem structure through altered hydrology. For example, a change in active layer thickness may lead to a rapid down-slope sliding of the organic layer and thawed mineral soil, exposing the underlying permafrost. This in turn begins to thaw rapidly, leading to several meters of down-wasting of ice-rich soils, a process known as thermal erosion. The change in surface topography alters the drainage network, which feeds back into changes in vegetation. These changes may occur in just a few years. In sum, the altered drainage network means the hydrology of the area is now different. The incidence of these types of change appears to be increasing, and to have been particularly notable in relation to recent large tundra fires on the North Slope.

Finally, there are regulatory issues to consider. For instance, to move forward with new research on permafrost conditions and winter travel, there needs to be a serious consideration of the rules used to open tundra travel and the assumptions that underlie these decision-making tools. The potential ramifications of any new science (such as finding that results indicate a shortening or lengthening of the season) will provide an important context for resource commitment decisions.

Recommendations:

  1. Inventory and evaluate existing data and document monitoring techniques.
  2. Centralize these data in an accessible location.
  3. Support research that explores hybrid techniques in which standoff (remote sensing) technology is combined with in-situ measurements to achieve wider spatial coverage.
  4. Recognizing the heterogeneity of permafrost (especially variability in ice content), identify sensitive areas where changes in the active layer or soil ice content could result in important ecosystem or infrastructure changes. Take measures to better monitor changes in these areas.
  5. Undertake work on threshold conditions in active layer state beyond which thawing accelerates.
  6. Develop a more integrated understanding of how thermokarst and thermal erosion impact vegetation and hydrology.

 

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