Greening of the Arctic: Plot-Scale Analysis of Interactions between Climate, Vegetation, and Permafrost at Toolik Lake, Alaska (1995 - 2017)

• Main Author: Rick, Brianna
• Format: Thesis
• Language: unknown
• Published: University of Montana 2018
• Subjects: Arctic; vegetation; climate; remote sensing; Physical and Environmental Geography; Active layer thickness; north slope; permafrost; Tundra; Alaska
• Online Access: https://scholarworks.umt.edu/etd/11262; https://scholarworks.umt.edu/context/etd/article/12316/viewcontent/Rick_Brianna_Thesis.pdf

Air temperatures across the Arctic have increased in recent decades, and through complex feedbacks, vegetation and permafrost (frozen ground) are actively responding as climate warming continues. This study investigates the trends and interactions of observed air, soil-surface temperature (SST), and active-layer thickness (ALT) at Toolik Lake on the Alaskan North Slope between 1995 and 2017, as well as vegetation change over time. Time series between 1995 and 2017 at CALM site U12B, a 1 ha plot near Toolik Lake, reveal an increase (0.50 °C/decade) in mean summer (Jun-Aug) air temperatures and a decrease (­0.23 °C/decade) in mean summer SST. In winter (Dec-Feb), the plot experienced an overall increase (2.27 °C/decade) in SST and an increase (0.84 °C/decade) in air temperatures. In nearly every winter during the 23-yr observation period, mean SST at sensors positioned along the water track (WT) within the plot remained above -6°C. Since 2009, sensors in non-WT areas have recorded mean winter SST consistently above -8°C, an increase in mean winter SST across the tussock tundra that could have important implications for winter microbial activity. Deepening mean maximum ALT (1.9 cm/decade) reflects the annual warming air and SST (0.60 °C/decade and 0.90 °C/decade, respectively) at CALM site U12B. Using airplane color-infrared aerial photographs (1995) and unmanned aerial vehicle (UAV) red-near infrared images (2017), normalized difference vegetation index (NDVI) maps were produced for peak greenness in August within the 1 ha plot. The WT, dominated by low shrubs, had the highest NDVI values compared to the surrounding tussock tundra. An increase in greenness along the edges of the WT in 2017 relative to 1995, as well as a visual comparison of the ortho-mosaics and photo-derived digital elevation models (DEMs), reveals the WT widening by nearly 4.5 m and greening of the shrubs adjacent to it, although shrub height and abundance were not directly measured. This increase in greenness could also be due to vegetation ...