Year of Award

2018

Document Type

Thesis

Degree Type

Master of Science (MS)

Degree Name

Geography

Department or School/College

Geography

Committee Chair

Dr. Anna E. Klene

Commitee Members

Dr. Fernando Sanchez-Trigueros, Dr. Jennifer Watts

Keywords

Arctic, vegetation, climate, remote sensing

Subject Categories

Physical and Environmental Geography | Remote Sensing

Abstract

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 differences within (willow) and adjacent (dwarf birch) to the WT.

Incorporating air and soil-surface temperatures, ALT, and vegetation dynamics into a time series demonstrates the complexity of feedbacks in a changing Arctic environment. The results of this study are consistent with other studies reporting an increase in vegetation and biomass in this region. This increase in greenness (particularly within and adjacent to the WT), likely influences snow trapping and winter SST conditions, promoting overwinter decomposition and nutrient mineralization. These results may have strong implications for biogeochemical feedbacks and ecosystem processes.

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© Copyright 2018 Brianna Rick