Monitoring permafrost freeze-up with ambient seismic noise

Understanding organic carbon release from permafrost soils is essential to predict the impact of permafrost thawing on our warming climate. In soils, freeze-thaw processes and the redistribution of water control how and when permafrost dissolved organic carbon is exported. In late autumn 2023, we buried 4 seismic geophones, aka seismic nodes, at the Eight Mile Lake site (Alaska, USA) at two different locations with a different level of permafrost degradation and let them freeze-in during six weeks to monitor freeze-up. Horizontal/Vertical spectral ratio analysis of the recorded ambient seismic noise and other seismological techniques show seismic velocity changes as the active layer deepens, allowing tracking the freezing front over time and depth. Although longer and replicated times series are still needed to fully understand the effect of freeze-thaw cycles on soil water movement, this tentative experiment already shows the potential of using seismic instruments for gathering permafrost time series.