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 (βT) 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 βT on the rate of local soil warming being stronger after (mean βT = 0.8 ± 0.1) than before (βT = 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.
Highlights
In the Arctic, climate is warming at twice the rate as lower latitudes, and where the increase in synoptic temperature might have a strong effect on near-surface thermal conditions (Post et al 2009, IPCC 2013)
While near-surface soil and air temperatures generally respond to temporal fluctuations in ambient air temperature (AAT) (Pollack et al 2005), locally they can substantially differ due to effects of both physiographic and biophysical processes (Korner 2003, Dobrowski 2011, Lenoir et al 2017)
Our results provide new insights into the factors determining Soil temperature (ST) in the Arctic throughout a complex network of biogeophysical processes affecting soilatmosphere thermal offset (ΔT) and coupling
Summary
In the Arctic, climate is warming at twice the rate as lower latitudes, and where the increase in synoptic temperature might have a strong effect on near-surface thermal conditions (Post et al 2009, IPCC 2013). Soil temperature (ST) is fundamentally linked to various aspects of ecosystem functioning, plant growth and reproduction (Bowman and Seastedt 2001, Korner 2003), soil biogeochemistry (nutrient enrichment and microbial activity; Starr et al 2008, Saito et al 2009) and frost-related geomorphological processes (French 2007). Near-surface thermal conditions do not necessarily follow synoptic temperature variations (Geiger et al 2009), with consequences for biotic and abiotic responses to climate warming (Lawrence and Swenson 2011, Lenoir et al 2017). While near-surface soil and air temperatures generally respond to temporal fluctuations in ambient air temperature (AAT) (Pollack et al 2005), locally they can substantially differ due to effects of both physiographic and biophysical processes (Korner 2003, Dobrowski 2011, Lenoir et al 2017) a.
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