Identifying Decadal Time-scale Patterns and Controls of Tundra Land Surface Stability Across the North Slope of Alaska using Repeat Terrestrial Light Detection and Ranging (T-LiDAR)

Abstract:

Thaw of ice rich permafrost in the Arctic is causing widespread permafrost degradation that is decreasing surface stability and dramatically transforming Arctic tundra landscapes. Changes to terrestrial landscapes include but are not limited to, impacts to surface hydrology, trace gas fluxes, nutrient cycling, vegetation dynamics, and infrastructure. Additionally, permafrost thaw has the potential to amplify climate warming by releasing stored soil organic carbon to the atmosphere. The majority of remote sensing technologies used to capture land surface variability and change are inadequate for advancing high spatiotemporal resolution change (< 50 cm). However, Terrestrial LiDAR (T-LiDAR) systems are capable of capturing surface microtopographic features at acquisition rates of more than 100,000 data points/sec and at millimeter accuracy and precision. Research utilizing T-LiDAR for quantifying thaw subsidence over multiple years and locations and that combine rates of change with field-based measurements in permafrost regions is lacking. Our study aims to fill this research gap and improve understanding of the spatiotemporal patterns and biophysical drivers associated with land surface microtopographic change in permafrost landscapes on the North Slope of Alaska using T-LiDAR and field based observations (i.e. surface temperature and active layer thaw depth (ALT)) between 2010 and 2019. Results from initial preliminary analysis of peak season annual T-LiDAR scans at seven distinct sites across northern Alaska show variable rates of heave and subsidence across Atqasuk, Toolik and Imnaviat and overall net subsidence trends ranging from -0.25 to -1cm per year in Utqiaġvik. Annual surveys of the Mobile Instrumented Sensor Platform (MISP) transect in Utqiaġvik associated with the International Tundra Experiment (ITEX)- Arctic Observing Network (AON) revealed little to no subsidence in some years and subsidence of up to -0.5cm in other years. Overall, 97.7 % of the MISP site in Utqiaġvik, between 2010-2019, subsided by 7cm ±2cm. MISP sites located in Atqasuk and Imnaviat show varying rates of subsidence and heave across eight and 5-year time spans, respectfully. The only MISP study site to show little to no surface change over a 5-year time period, is located in Toolik Lake. Results from this analysis also highlight the impact of surface vegetation, standing water, surface temperature and ALT on the T-LiDAR instrument. Future directions will expand the analysis to quantify vegetation phenology from spectral analysis of digital imagery and coupled spectral reflectance measurements. The methodology presented here highlights the significant potential of T-LiDAR to document the impact of site-level terrestrial change across tundra landscapes.