Tracing suspended sediment fluxes using a glider: observations in a tidal shelf environment

Abstract. Underwater gliders equipped with current profilers and optical turbidity sensors offer a low-energy solution for high-resolution measurements of currents, suspended particle properties, and sediment transport in coastal waters. Because the spatial structure of hydrosedimentary processes often changes on short time scales (hours to weeks), especially in coastal areas, validating the distribution of glider observations is required to assess our capacity to represent hydrosedimentary processes. Here we propose to validate in a shelf tide-dominated environment, both i) glider-based currents, and ii) glider-based acoustic backscatters and optical turbidities in full resolution delayed mode, using in situ colocated and synchronous ancillary observations. The deployed glider system correctly measures the periodic pattern of the tidal current, with a satisfying RMSD of O(3 cm s ^-1). Glider optical turbidities highly correlate with the ancillary observations (R² up to 0.83). They also correlate well with their glider acoustic counterpart for most of the campaign period (R² = 0.76), allowing an estimation of suspended particulate matter concentrations from the acoustic. In this study, we showed the presence of bottom nepheloid layers of several mg·l^-1 on the shelf probably due to advection of coastal turbid waters as evidenced by estimated glider sediment fluxes. These results highlight the potential of gliders for quantifying sediment fluxes and advancing our understanding of coastal hydrosedimentary processes.