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Biological organisms are prevalent on and near the seabed; however, most predictive theoretical models do not explicitly address the acoustic behavior of biologically active marine sediments. Sediment-acoustics models, such as those based on Biot theory or grain-shearing theory, allow for parameterization of various physical properties including bulk density, porosity, shear strength, or pore fluid viscosity, all of which can be modified by the presence of biological organisms or bioturbation. Other models can include the effects gas bubble distributions, which can also be associated with the presence of benthic biology, on compressional and shear wave propagation. In this paper, we examine sediment-acoustics models in comparison with data from a field experiment focused on a muddy sediment containing infauna. The model parameters are partially constrained by physical data from core samples collected at the field experiment sites. Empirical relations between the core data parameters and acoustic data are also examined. [ABSTRACT FROM AUTHOR]

This talk presents results from an acoustic propagation experiment conducted in the Lower Laguna Madre to characterize the acoustical properties of a seagrass meadow. At the location of the experiment, the water was one meter deep, and the seabed was covered by a dense growth of Thalassia testudinum, a type of seagrass that grows from a long, jointed rhizome buried 5 cm to 10 cm below the seafloor. The biological processes and physical characteristics associated with seagrass are known to affect acoustic propagation due to bubble production, which results in dispersion, absorption and scattering of sound. During the experiment, a Combustive Sound Source was used to produce broadband signals at ranges of 20 m to 1000 m from the receiver location. Three sensors were positioned at the receiver location: two hydrophones located within and above the seagrass canopy, and a single-axis geophone. The data were analyzed for the purposes of predicting acoustic propagation in seagrass meadows and for estimating environmental parameters in very shallow, biologically active environments. Additionally, seagrasses are a vital part of the global carbon cycle and this work explores the feasibility of using of acoustic signals to estimate carbon stores. [ABSTRACT FROM AUTHOR]

Benthic infauna perform important ecological functions such as water filtration, the recycling of organic matter, and forage for larger predators. However, how infauna affect bulk acoustical properties of the sediment is less studied and warrants further investigation. During a field experiment conducted in Petit Bois Pass, AL, multiple cores of fine-grained sediments containing infauna were collected by divers and analyzed using a core and resonance logger (CARL). CARL is a core-logger capable of performing both conventional pitch-catch measurements radially along the core as a function of depth and lower frequency resonance measurements. Resonance measurements were performed by exciting acoustic modes within the core and sensing them externally along the core's length. By utilizing both pitch-catch transducers as receivers, symmetric and asymmetric modes can be identified, and sound speed can be inferred as a function of frequency. The frequency ranges for the pitch-catch and resonance measurements were 100 kHz to 300 kHz and 8 kHz to 23 kHz, respectfully. Subsequently, the cores were sectioned and were either sieved for infauna or analyzed for porosity and grain size distribution. The measured sound speeds will be compared with biological and geological properties of each individual core. [ABSTRACT FROM AUTHOR]