Biogeophysical controls on soil-atmosphere thermal differences: implications on warming Arctic ecosystems

Abstract

Soil temperature (ST) has a key role in Arctic ecosystem functioning and global environmental change. However, soil thermal conditions do not necessarily follow synoptic temperature variations. This is because local biogeophysical processes can lead to a pronounced soil-atmosphere thermal offset ( ∆T ) while altering the coupling (β T ) between ST and ambient air temperature (AAT). Here, we aim to uncover the spatiotemporal variation in these parameters and identify their main environmental drivers. By deploying a unique network of 322 temperature loggers and surveying biogeophysical processes across an Arctic landscape, we found that the spatial variation in ∆T during the AAT≤0 period (mean ∆T = 6.0 °C, standard deviation ± 1.2 °C) was directly and indirectly constrained by local topography controlling snow depth. By contrast, during the AAT>0 period, ∆T was controlled by soil characteristics, vegetation and solar radiation ( ∆T = −0.6 °C ± 1.0 °C). Importantly, ∆T was not constant throughout the seasons reflecting the influence of β T on the rate of local soil warming being stronger after (mean β T = 0.8 ± 0.1) than before (β T = 0.2 ± 0.2) snowmelt. Our results highlight the need for continuous microclimatic and local environmental monitoring, and suggest a potential for large buffering and non-uniform warming of snow-dominated Arctic ecosystems under projected temperature increase.

Keywords

• thermal variability
• microclimate
• soil-atmosphere decoupling
• soil temperature
• structural equation model
• snow cover