Slide 1

M.H Young 1, C.J. Abolt 1,2, T.G. Caldwell 1, T.E. Larson 2 High-Resolution Carbon Inventory and Dynamics in Permafrost Soils: North Slope, Alaska 1 Bureau of Economic Geology 2 Department of Geological Sciences Slide 2 Motivation and Goals Obvious scientific interest in Arctic tundra soil and potential impacts of carbon fate and transport, given climate dynamics. Generate high-resolution data set of soil organic carbon stocks that incorporate the effects of microtopographic land surface features. Predict release of soil from evolution of ice-wedge polygons. Better understand mechanisms of subsurface C transport. Slide 3 Outline of Research Done To Date Year Activity 2011 Original field survey including lake volumes using fathometer 2012High resolution lidar survey across 480 km 2 area 2013 Field sampling of soil pits across 100 km 2 area, subsequent laboratory analyses 2014 Field sampling of soil, water and gas; GPR survey; instrument installation 2015 Data collection; ground truthing site conditions with NASA JPL Slide 4 Ice Wedge Polygon Evolution Low-Centered High-Centered source: www.awi.de source: permafrost.gi.alaska.edu Slide 5 August 2012 Lidar Survey 400 kHz pulse rep. rate ~13 billion data points across 480 km 2 ~15-20 points/m 2 Slide 6 2013 Sampling and Wetland Survey Features surveyed Vegetation Soil Type Wetland Hydrology ~100 sites examined, pits dug and soil profile described 1-2 soil horizons (organic and mineral) encountered at each site, samples sent to UT-Austin for analysis: Particle size distribution Total organic carbon, including isotopic signatures and carbon isotope values Slide 7 2014 Field Characterization Active layer thickness: GPR (400 MHz) 20x20 m grid Static cone penetrometer readings to ice layer Soil cores for OC transport and thermal/hydraulic properties Characterize CO 2 and methane fluxes with in-field static chambers and lab analysis of methane dynamics in undisturbed soil core Slide 8 Preliminary Results: Carbon Distribution Organic Carbon (kg/m 3 of soil) Carbon distribution estimation assumes: Active Layer thickness = 0.5 m Organic Horizon = 0.3 m thick, when overlying mineral soil; 0.5 m thick where mineral horizon is absent b organic horizon = 300 kg/m 3 b mineral horizon = 1,000 kg/m 3 Estimated total organic carbon at study site = 2.4 million Mg Slide 9 Thermo-erosion: Low- to High-centered Slide 10 Field Plot - 2014 Slide 11 Active Layer Thickness Penetrometer Dark = thicker (80 cm) Light = thinner (35 cm) Ground penetrating radar Ice = strong reflector (red) Highly variable travel time Slide 12 Preliminary Results Polygon Evolution Transition from low-centered to high-centered form Measured low-centered, t 0 Measured high-centered, t 0 Predicted high-centered, t 38yrs Slide 13 Optimizing on Diffusivity and Trough Depth Best fit: D = 0.0125m 2 /month and trough depth = 29 cm Objective Function (RMSE) as function of two parameters Slide 14 Analytical Model Results Sediment Loss/Polygon Polygon 1: Area = 281.65 m 2 ; Sediment Loss = 43.18 m 3 Polygon 2: Area = 198.41 m 2 ; Sed Loss = 30.89 m 3 Polygon 3: Area = 175.0 m 2 ; Sediment Loss = 25.48 m 3 PolygonVolume Loss/AreaCarbon Loss (~3 kg/m 2 ) 10.15 m 3 /m 2 845 kg 20.16 m 3 /m 2 595 kg 30.15 m 3 /m 2 525 kg Slide 15 Hillslope model approach mimics morphologies and rates observed in the field and described by Raynolds et al. (2014; GCB) and Jorgensen et al. (2006; GRL) 2015 field campaign with NASA JPL and CARVE mission should provide better data for thermo-erosion approach Field results will be extrapolated to >1000 km 2 area of permafrost environments, SW of Prudhoe Bay, and eventually connected to DOE NGEE-Arctic and NSF Toolik Lake sites Lateral and 1D (vertical) models for transport and/or biogeochemical cycling of C to be done. Going Forward: Integrating carbon flux, hydrology, and heat flux to predict subsurface C transport Slide 16 Questions and Comments Acknowledgements: Support provided by Jackson School of Geosciences, UT- Austin; Great Bear Petroleum Operating LLC; ASRC Energy Services