Abstract
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.
Highlights
Coastal Arctic landscapes – dominated by wetlands and patterned ground – cover approximately 5–10 % of Earth’s land surface and play an important role in the hydrology, geomorphology, biogeochemistry and vegetation dynamics of the vast Arctic region
The low-gradient topography of the polygonal tundra characteristic of these landscapes is a complex mosaic of microtopographic features created by icewedge polygons
This microtopography leads to strong finescale variability in thermal and hydrological regimes of landscapes underlain by continuous permafrost
Summary
Coastal Arctic landscapes – dominated by wetlands and patterned ground – cover approximately 5–10 % of Earth’s land surface and play an important role in the hydrology, geomorphology, biogeochemistry and vegetation dynamics of the vast Arctic region. The low-gradient topography of the polygonal tundra characteristic of these landscapes is a complex mosaic of microtopographic features created by icewedge polygons. This microtopography leads to strong finescale variability in thermal and hydrological regimes of landscapes underlain by continuous permafrost. Complex surface drainage patterns lead to heterogeneous soil moisture and substrate conditions, supporting a wide range of vegetation composition across the landscape. Hobbie et al (2000) studied the controls over carbon storage and turnover in Arctic soils and found temperature, microtopography and vegetation composition to be the primary controls at regional scale Arctic tundra soil pools are estimated to contain ∼ 190 Pg of carbon (Post et al, 1982), much of which is under risk of rapid release to the atmosphere in a warming climate. Hobbie et al (2000) studied the controls over carbon storage and turnover in Arctic soils and found temperature, microtopography and vegetation composition to be the primary controls at regional scale
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