Resolving environmental processes by imaging and monitoring lake ice properties of the boreal Lake Pääjärvi, southern Finland

The composition, structure, and dynamics of a transient ice sheet that forms and disintegrates on a boreal lake is influenced by meteorological and environmental processes. This includes trapping of upwelling methane from the lake sediments, which is in turn affected by eutrophication in the catchment area. Methane is a potent greenhouse gas, yet documented sources and sinks to the atmospheric budget are highly unbalanced. Here we explore a novel approach for quantifying methane ebullition from a boreal lake that combines seismic methods together with interdisciplinary observation methods.

 

The DYNALake project centerpiece is an array of ~210 seismic geophones arranged in an aperiodic tiling configuration that we deployed in February 2025 on the ~20 cm thick ice of Lake Pääjärvi some 100 km north of Helsinki. The 10-km scale lake array is complemented by a sparser network of 31 land-based sensors installed around the lake between fall 2024 and spring 2025, three dense circular arrays enabling local beamforming and estimating array derived rotation, a DAS system with a 1 km-long fibre optic cable, an underwater echosounder to monitor potential methane ebullition, a rotational seismometer, a microphone to record seismo-acoustic waves, a Ground Penetrating Radar (GPR) survey, water chemistry measurements, manual ice thickness sampling and ice coring, and meteorological data. The project popularizes the subarctic wintertime fieldwork and the science by making a professional documentary for science communication, outreach, and education.

 

We present initial results on spatial and temporal variations in lake-ice thickness and on the quality and characteristics of the recorded seismic data. The observations include distinct ice-guided wavefield signatures, including QS₀ (quasi-symmetric) and SH₀ (horizontally polarized shear) modes used to estimate elastic parameters such as Young’s modulus and Poisson’s ratio, as well as the dispersive QS (quasi-Scholte) mode that is primarily sensitive to ice thickness at higher frequencies. We compare signals from natural sources and hammer shots across the different sensor types. We show examples of noise correlation wavefields, beamforming results, and seismo-acoustic records that can be used to characterize seismic activity patterns and resolve variable ice properties. Seismic activity in the 0.03–0.2 Hz band increases during high-wind episodes, while higher-frequency signals (0.1–1000 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. The geochemical water sample analysis suggests Lake Pääjärvi is a source of methane.

 

We discuss the potential of the data quality and the sensor configuration for signal detection and for icequake and passive tomography lake ice images to resolve spatially variable air and gas bubble properties that are controlled by environmental processes. This synthesis demonstrates that the application of environmental seismology concepts can form a bridge between bottom-up ebullition monitoring and remote-sensing approaches.