Spatial Autocorrelation Analysis of a 28 Year Active Layer Thickness Record from North-Central Alaska

Active layer thickness (ALT) has been monitored annually at seven 1 km2 Circumpolar Active Layer Monitoring (CALM) sites in north-central Alaska for 28 consecutive years, employing a systematic sampling strategy. The sites represent the main climatic, geomorphic and landscape types of the North Slope of Alaska. Spatial autocorrelation analysis of data from two years (1995-1996) conducted previously concluded that topography, acting through changes in the soil moisture, is a prime determinant of ALT formation. A more nuanced conclusion emerges from the current study. We analyzed the full 28-year records from the same sites using two-dimensional correlograms to assess spatial and temporal changes in the active layer at each study site. We observed more pronounced and persistent ALT patterns in the coastal plain sites compared to those located in northern foothills of the Brooks Range. Significant interannual differences in spatial ALT patterns are related primarily to variations in cumulative summer warmth and precipitation. The results of this work indicate that site-specific factors, such as topography and vegetation cover, impact the active layer system over long (30 years) time periods. Spatial autocorrelation analysis can be used to compare active layer data across sites of varying topographic and environmental conditions to explore how past and current trends in the active layer may be impacted by shifts in local conditions.