Thermal characterisation of active layer across a soil moisture gradient in the McMurdo Dry Valleys, Antarctica

Heat transport into active layer soils is important to understanding potential responses to changes in surface energy balance, particularly in the context of changing climate. Here we present results of a study to characterise soil thermal properties along a soil moisture gradient adjacent to Lake Fryxell in Taylor Valley, Antarctica. Our goals were to characterise the thermal characteristics of these relatively wet soils (compared to the rest of the McMurdo Dry Valleys landscape), and to assess the response of the active layer to possible increases in soil moisture. We measured subsurface temperatures at depths from 3 to 50 cm at four locations along a natural gradient of wet to dry soils adjacent to Lake Fryxell from January 2006 to January 2007. We used a numerical model to estimate apparent thermal diffusivity (ATD) and simulate observed temperature time series. Calculations of ATD at discrete locations yielded values ranging from 1.0 × 10−9 – 2.4 × 10−5 m2 s−1, and the corresponding range of bulk (i.e. depth averaged at a single surface location) ATD was 2.9 × 10−9–1.2 × 10−7 m2 s−1. Thawed soils had a range of bulk ATD during warming of 2.9 × 10−9–3.8 × 10−8 m2 s−1, and during cooling of 2.9 × 10−9–4.8 × 10−8 m2 s−1. When soils were frozen, however, the range of bulk ATD was 7.6 × 10−9–1.2 × 10−7 m2 s−1 during warming, and 7.8 × 10−9–1.1 × 10−7 m2 s−1 during cooling. Estimated bulk ATD values were consistently greater in locations of enhanced soil moisture, so lakeside soils were more likely to conduct energy into the subsurface. Increased soil moisture across the landscape would likely increase ATD, allowing for greater heat exchange between the atmosphere and the subsurface. Copyright © 2009 John Wiley & Sons, Ltd.