Dataset: Sediment resuspension acoustics

We resuspended the surface 5 cm of natural muddy sediment cores in the lab and compared temporal changes in sediment compaction to changes in surface and subsurface cohesion over 30 days post resuspension. Sediment-water interface (SWI) height and acoustic sound speed through sediment, which depends on bulk density, provided continuous and nondestructive metrics of compaction, and sediment porosity and grain size were measured destructively to characterize sediment physical structure. We determined surface cohesion by measuring both eroded mass and turbidity resulting from increasing shear stress. Subsurface cohesion was determined from the force required for sediments to fail in tension. We compared surface and subsurface exopolymeric substance (EPS) concentrations to surface and subsurface cohesion measurements. We differentiated between water-soluble (colloidal) and sediment-bound EPS as we expected bound EPS to contribute more to sediment-organic matrix development and thus cohesion because they are directly bound to sediment grains rather than dissolved in porewater.

These data include the repeated acoustic measurements on the cores processed on day 30 from this experiment. A summary of data collected on cores processed over time points 0 days (no resuspension), then 1, 2, 3, 7, 14, and 30 days post resuspension is given in dataset 1. Detailed data on erosion measurements, as well as repeated non-destructive measurements of sediment-water interface height on cores processed on day 30 are provided in separate datasets.

We performed acoustic measurements following methods from Dorgan et al. (2020). Within a seawater tank, a 400 kHz three-cycle sinusoidal tone burst was transmitted horizontally through sediment cores to a receiver at 3 depths below the sediment surface (2.5, 5, 10 cm) (see Fig. 1 in Dorgan et al., 2020). To account for sound speed differences due to temporal variability in temperature and salinity, sound speed through sediment was normalized by the sound speed in seawater to obtain sound speed ratio (SSR). Each day, we also performed acoustic measurements on cores filled with seawater and with no core present. Sound speed in seawater and the lag time between the transmitted and received signals (time of flight) through sediment and seawater cores were used to calculate sound speed in sediment (νp):

    ν_p=c_w/(1-(c_w * ∆t/d_s )

where cw is sound speed in water, Δt is the difference in time of flight between seawater core (tw) and sediment core (ts), and ds is the inner diameter of the core (Jackson and Richardson, 2007; Dorgan et al., 2020). SSR was then calculated by dividing νp by cw, where a higher SSR indicates more compact sediment.

Acoustics measurements done following Dorgan et al. 2020, JASA.