Toward the Ultrasonic Sensing of Organic Carbon in Seagrass‐Bearing Sediments

Abstract

Ten percent of all organic carbon (Corg) absorbed by the ocean each year is stored in seagrass‐bearing sediments. The preservation of these carbon stores is considered a vital method to mitigate climate change. Seagrass‐bearing sediments have been correlated with sediment geophysical properties yet have not been related to sediment acoustic properties. For this purpose, sediment cores were collected from a Thalassia testudinum seagrass meadow in South Texas, USA, where geophysical, acoustical, and Corg properties were measured. It is hypothesized that when deposits of Corg adsorb onto mineral surfaces and are stored in pore spaces, compliant layers between grain contacts and the formation of an organic‐rich suspension reduce sediment stiffness. Results from this seagrass meadow demonstrated a strong correlation between sediment P wave modulus and Corg and show promise toward the development of an in situ ultrasonic sediment probe to more rapidly quantify and monitor seagrass carbon stores.

Broadband sound propagation in a seagrass meadow throughout a diurnal cycle

“…Cores collected from a nearby area in the seagrass meadow were analyzed to compare sediment properties both underneath the seagrass and in the seagrass-free patches. 15 Solar irradiance was logged throughout the daylight hours with a blackbody thermopile pyranometer. The pyranometer was sensitive at electromagnetic wavelengths ranging from 385 to 2105 nm, which is inclusive of the photosynthetically active radiation band.…”

Acoustic propagation in gassy intertidal marine sediments: An experimental study

“…In the early days of marine sediment acoustics, studies of gas-free sediments were more common than those of gassy sediments, where the presence of gas complicated modelling and measurements [84][85][86][87]. Now, as studies of gas populations in gassy-sediments that are not subject to tidal exposures become established [4][5][6][7][8][9][10][11][12][13], it is timely to look at forward modeling for gassy intertidal sediments, and collect data suitable for acoustic inversion studies. The intertidal zone, with its specialized flora and fauna, and frequent proximity to anthropogenic factors (dredging, shipping and invasive species, civil engineering, chemical and acoustic pollutants etc.)…”

“…seafloor surveying [6][7][8], the construction of offshore structures [9], and the detection of leakages from carbon capture and storage facilities [10][11][12][13]). In situ gas generation may have pronounced environmental consequences.…”