An experiment to resolve system-scale lake ice properties shaped by environmental processes

Abstract. The multi-scale composition, structure, and dynamics of seasonal ice floating on freshwater lakes are influenced by ambient conditions. Here we describe a comprehensive geoscience experiment for lake system imaging and monitoring of spatiotemporal ice property variations. We explore the resolution of meteorological and environmental driving mechanisms that can include the quantification of methane degassing from boreal lakes. The project centerpiece is a seismic array of 210 geophones arranged in an aperiodic tiling configuration that was deployed in February 2025 on the ~25 cm thick ice of Lake Pääjärvi in southern Finland. The 10-km scale lake array is complemented by three dense circular arrays, 31 land-based sensors, eight broadband seismometers, three accelerometers, a rotational seismometer, a Distributed Acoustic Sensing system with a 1 km-long fibre optic cable, an underwater echosounder, a microphone, a Ground Penetrating Radar (GPR) survey, water chemistry measurements, manual ice thickness sampling and ice coring, and meteorological observations. We observe the strongly dispersive QS flexural mode and the weakly or non-dispersive QS₀ and HS₀ modes excited by hammer shots, icequakes, and environmental sources and reconstruct the average propagation using beamforming and noise correlations. Propagation speed estimates for the three modes range approximately between 20–100 m s⁻¹, 3000–3400 m s⁻¹, and 1650–1800 m s⁻¹, respectively. High values for the Poisson's ratio ν = 0.42 and Young's modulus E = 8.59 GPa reflect the overall competent characteristics of the ice referred to as teräsjää (steel ice). Seismic activity in the 0.03–0.2 Hz band increases during high wind speed episodes, and signals above 0.1 Hz correlate with rapid air-temperature cooling events. The GPR profile images the spatial ice variability across the lake that is compatible with the in-situ measurements, and we show that seismo-acoustic observations can be inverted for similarly compatible thickness estimates. The geochemical water and ice sample analysis suggests Lake Pääjärvi is a source of methane, and localized ebullition can potentially be resolved from echosounder data. This synthesis demonstrates that the application of environmental seismology concepts can form a bridge between bottom-up ebullition monitoring and remote-sensing approaches.