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Wave-induced sediment resuspension potential in the Finnish Archipelago; Baltic Sea: integrating field measurements with large-scale numerical model simulations
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DOI：10.5194/os-22-2123-2026.png)
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Abstract
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Abstract. Sediment resuspension; driven by wind-wave-induced shear stress; is a key process influencing coastal water quality; biogeochemical cycles; and the transport of pollutants and organisms. The critical shear stress; τcr; is a central parameter in sediment transport models; since initiation of motion can occur when wave-induced shear stress exceeds the critical value. In this study; we implemented a high-resolution (20 m) spectral wave model to simulate near-bottom orbital velocities across the complex archipelago of southwestern Finland. We then used laboratory measurements from in situ sediment samples to determine a model for the critical shear stress that accounts for physical properties using the median grain size and the dry bulk density; and the time-varying biological variation using chlorophyll a. Our proposed model; τcrd50; ρB; Chla(t) ; explained 66 % of the variation of the measured critical shear stress for our data collected from three different sediment types (Mud; Sand and Mixed sediments). The modelled mean critical shear stress differed between sediment classes; with values of 0.49 N m−2 for Mud; 1.56 N m−2 for Sand; and 1.02 N m−2 for Mixed sediments. The variability in the critical shear stress around the mean values driven by a non-constant biological contribution was approximately 30 % for Mud and Sand; and approximately 50 % for Mixed sediments. Finally; we used a class-level map of the sea floor and the in situ grain size data to translate the wave model orbital velocities to near-bottom shear stresses. Based on the numerical model data; the critical shear stresses from the newly proposed model; τcr(d50; ρB; Chla(t)) ; were rarely exceeded based on only wave-induced motions in most of the model grid; but could; nonetheless; be exceeded to up around 10 % of the times in smaller areas. This study highlights the importance of incorporating both physical and biological factors – and their temporal dynamics – into sediment transport models to achieve reliable predictions of critical shear stresses and resuspension potential.
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