Suspended particle characteristics during a severe storm event

Storm events are key disturbances in coastal and estuarine systems, capable of drastically altering hydrographic conditions and suspended particulate matter (SPM) dynamics. However, high-resolution, in situ data during such events remain scarce due to logistical constraints. Here, we present rare observational data from an automated pole-mounted station in the Elbe Estuary (German North Sea coast) that captured hydrographic and particle dynamics during Storm Christian on October 28, 2013. We compare this dataset to other data from the same region collected on a research cruise in 2018 under calm to moderate wind conditions. Our results show that the SPM concentration (SPMC) increased fivefold (from ∼400 to 2000 mg/L) during the storm, while the turbidity remained surprisingly stable. Furthermore, we observed a massive increase in inorganic grain size (from ∼6 to 100 μm) during the storm, as well as an unusually low organic content (loss on ignition <11%), indicating the mobilization of predominantly inorganic large sand particles from the riverbed. The observed decoupling of SPMC and turbidity may be explained by a reduced specific scattering efficiency as particle properties are drastically altered during the storm. These findings challenge the common use of turbidity as a proxy for SPMC under severe storm conditions and highlight how extreme hydrodynamic forcing can fundamentally alter the optical and compositional properties of suspended matter, with possible implications for biogeochemical processes. • High-resolution dataset of a pole-mounted automated sampling station capturing hydrographic and SPM dynamics during a severe storm event (Storm Christian, October 2013) in the Elbe Estuary. • Fivefold increase in SPM concentration (from ∼400 to 2000 mg/L) during the storm, without a corresponding rise in turbidity, indicating a decoupling of commonly linked parameters. • Strong increase in grain size (from ∼6 μm to ∼100 μm) observed during the storm, likely due to resuspension of coarser sand grains from the riverbed. • Loss on Ignition (LOI) values dropped below typical thresholds, indicating erosion and mobilization of purely inorganic material during the storm.