Articles | Volume 10, issue 5
The Cryosphere, 10, 2241–2274, 2016
The Cryosphere, 10, 2241–2274, 2016

Research article 27 Sep 2016

Research article | 27 Sep 2016

Modeling the spatiotemporal variability in subsurface thermal regimes across a low-relief polygonal tundra landscape

Jitendra Kumar1, Nathan Collier2, Gautam Bisht3, Richard T. Mills4, Peter E. Thornton1, Colleen M. Iversen1, and Vladimir Romanovsky5 Jitendra Kumar et al.
  • 1Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA
  • 2Computer Science and Mathematics Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA
  • 3Lawrence Berkeley National Laboratory, Berkeley, CA, USA
  • 4Intel Corporation, Hillsboro, OR, USA
  • 5Geophysical Institute, University of Alaska Fairbanks, AK, USA

Abstract. Vast carbon stocks stored in permafrost soils of Arctic tundra are under risk of release to the atmosphere under warming climate scenarios. Ice-wedge polygons in the low-gradient polygonal tundra create a complex mosaic of microtopographic features. This microtopography plays a critical role in regulating the fine-scale variability in thermal and hydrological regimes in the polygonal tundra landscape underlain by continuous permafrost. Modeling of thermal regimes of this sensitive ecosystem is essential for understanding the landscape behavior under the current as well as changing climate. We present here an end-to-end effort for high-resolution numerical modeling of thermal hydrology at real-world field sites, utilizing the best available data to characterize and parameterize the models. We develop approaches to model the thermal hydrology of polygonal tundra and apply them at four study sites near Barrow, Alaska, spanning across low to transitional to high-centered polygons, representing a broad polygonal tundra landscape. A multiphase subsurface thermal hydrology model (PFLOTRAN) was developed and applied to study the thermal regimes at four sites. Using a high-resolution lidar digital elevation model (DEM), microtopographic features of the landscape were characterized and represented in the high-resolution model mesh. The best available soil data from field observations and literature were utilized to represent the complex heterogeneous subsurface in the numerical model. Simulation results demonstrate the ability of the developed modeling approach to capture – without recourse to model calibration – several aspects of the complex thermal regimes across the sites, and provide insights into the critical role of polygonal tundra microtopography in regulating the thermal dynamics of the carbon-rich permafrost soils. Areas of significant disagreement between model results and observations highlight the importance of field-based observations of soil thermal and hydraulic properties for modeling-based studies of permafrost thermal dynamics, and provide motivation and guidance for future observations that will help address model and data gaps affecting our current understanding of the system.

Short summary
Microtopography of the low-gradient polygonal tundra plays a critical role in these ecosystem; however, patterns and drivers are poorly understood. A modeling-based approach was developed in this study to characterize and represent the permafrost soils in the model and simulate the thermal dynamics using a mechanistic high-resolution model. Results shows the ability of the model to simulate the patterns and variability of thermal regimes and improve our understanding of polygonal tundra.