Interpretation of Arctic North Slope Permafrost Borehole Thermal Evolution in Light of Spatial and Temporal Variation in Surface Temperature Fields
Permafrost is ground that has remained below 0°C for more than two years. It has the greatest areal extent of any component of the cryosphere in the Northern Hemisphere. Feedbacks between permafrost, the hydrologic cycle, and the atmosphere are key components of the Arctic system. As the health of permafrost is directly dependent upon temperature, the thermal state of permafrost is one of the key signals of climate change. In addition, the thickness, distribution and temperature of permafrost influences both ecology and engineering in the Arctic. Between the atmosphere and the top of the permafrost is the active layer, which freezes and thaws on an annual basis. This active layer translates the climate signal at the Earth's surface into heat flow into or out of the underlying conductive permafrost. The heat flux at the base of the active layer can be determined from profiles of temperature within the active layer, based on well-known physics of conduction. The goal in this project is to identify both spatial and temporal patterns of change in the permafrost of Alaska's Arctic North Slope, and the critical processes that govern these patterns. Temperature profiles documented in the 1970s from abandoned exploratory boreholes suggested that the permafrost had warmed significantly to depths of many tens of meters, in a pattern that could be best explained by a 2-4°C surface warming over the prior half century. Since then, an array of 21 boreholes, spanning the National Petroleum Reserve-Alaska (NPR-A), has been repeatedly re-logged by USGS researchers, providing a record of dramatic change. The simplest interpretation of these profiles suggests yet more rapid increases in surface temperature, with a change of 3°C/decade occurring in the 1990s. The surface meteorology and active layer thermal structure has simultaneously been documented in an array of automated surface stations that span the region, and have been maintained for periods ranging from one to two decades. Nine of these surface stations are co-located with deep boreholes; all are embedded in international efforts to monitor the thermal state of the globe?s permafrost. The USGS network represents both the largest array of deep boreholes in the world used for monitoring the thermal state of the permafrost, and the densest array of surface stations in the global network. The investigators will integrate the observations of temperature profiles collected periodically from the deep boreholes, and 1-2 hourly observations of near surface meteorology and near surface soil temperature, to constrain the spatial and temporal record of the energy going into the permafrost. It will also extract the cleanest climate signal possible from the borehole measurements over the measurement interval (1970s onward) with the aim of answering questions about the thermal state of the landscape and the processes responsible for its evolution. To accomplish these goals the PI will first work with USGS colleagues to finalize quality control of their observations (preliminary data available at: http://data.usgs.gov/climateMonitoring/region/ show?region=alaska). He will then develop numerical models that predict the thermal disturbance from site-specific effects (e.g., length of time drilling, presence of lakes). Finally, using the "cleanest" climate signal of warming and heat flow into the permafrost, the team will analyze the spatial and temporal pattern of this signal. Results will be available through both the scientific literature, and the Community Surface Dynamics Modeling System (CSDMS, http://csdms.colorado.edu/wiki/Main_Page) Educational repository. Researchers will develop interactive models, animations, and classroom exercises based on this dataset, modeling effort, and final analysis.