High resolution measurements of the epi- and mesopelagic ocean by a profiling vehicle equipped with environmental sensors and a broadband echosounder

Abstract

Collecting detailed surveys of the physical and biological heterogeneity in the epi and mesopelagic ocean is critical to describe the ecosystems within these vast and three-dimensional habitats. Common ocean sampling platforms (e.g., net systems, moored and shipboard sensors) are often unable to resolve marine biota at scales comparable to the variability existing in their physical environment. We have integrated a dual-frequency split-beam echosounder (Simrad EK80 with 70 and 200 kHz transducers) into the Wire Flyer profiling vehicle to achieve concurrent hydrographic and acoustic sections in environments between 0 and 1000 m. The Wire Flyer provides high-resolution repeat profiling (0–2.5 m/s vertical velocity, ∼1 km horizontal repeats) within specified water column depth bands typically spanning 300–400 m. This system can provide acoustic backscatter data at depths unavailable to shipboard surveys and can be operated in tandem with shipboard echosounders to provide overlapping acoustic coverage with concurrent hydrographic sections near the surface. The side-looking transducer orientation samples orthogonal to the vehicle's profiling survey path provide a direct measurement of horizontal heterogeneity. The collected data have proven the system’s capacity to resolve migrating layers, biological patches, and single targets in the horizontal, rising gas plumes, and scattering layer distributions tightly coupled to submesoscale environmental features.