Soil surface organic layers in the Arctic foothills: development, distribution and microclimatic feedbacks

Abstract

Accumulated organic matter at the ground surface plays an important role in Arctic ecosystems. These soil surface organic layers (SSOLs) influence temperature, moisture, and chemistry in the underlying mineral soil and, on a global basis, comprise enormous stores of labile carbon. Understanding the dynamics of SSOLs is a prerequisite for modeling the responses of arctic ecosystems to climate changes. Here we ask three questions regarding SSOLs in the Arctic Foothills of northern Alaska: 1) What environmental factors control their spatial distribution? 2) How long do they take to form? 3) What is the relationship between SSOL thickness and mineral soil temperature during the growing season? Results show that the best predictors of SSOL thickness and distribution are duration of direct sunlight during the growing-season, upslope-drainage-area, slope gradient, and elevation. SSOLs begin to form within decades but require 500-700 years to reach steady-state thicknesses. SSOL formation has a positive feedback on itself by causing rapid soil cooling. Once formed, mature SSOLs lower the growing-season temperature and mean annual temperature of underlying mineral soils by 8° and 3° C, respectively, which reduces growing degree days by 78%. How climate change in northern Alaska will affect the region's SSOLs is an open and potentially crucial question.