Fig. S1.

Zero curtain assessment. Soil temperatures at BES (20 cm, left), BEO (10 cm, center), and IVO (15 cm, right), recorded during 2013 and 2014. The red curves show the time derivative of temperature (°C/d), illustrating the effect of latent heat in stabilizing the temperature when the soils are poised in the zero curtain (0 ± 0.75 °C, light blue shading and horizontal dashed lines). Temperature data have been smoothed using a locally weighted least-squares linear trend (“lowess” filter) with a window of 35 d, roughly equivalent to a two-sided moving average of ±1 wk.