High-Resolution Topography-Following Chemical Mapping of Ocean Hypoxia by Use of an Autonomous Underwater Vehicle: The Santa Monica Basin Example

Andreas F. Hofmann, Peter M. Walz, Hans Thomas, Edward T. Peltzer, Peter G. Brewer
2013 Journal of Atmospheric and Oceanic Technology  
This paper reports on the execution of a combined chemical sensing/high-resolution terrain-following autonomous underwater vehicle (AUV) survey to explore the fine structure and functional boundaries of the Santa Monica Basin suboxic zone and its relationship to topography. An AUV mapping vehicle is used in a novel configuration-combining the mapping vehicle tail section, with precision inertial navigation and acoustic communications systems, with CTD/O 2 , NO 3 sensing, and Gulper water
more » ... Gulper water sampling systems. The challenge was to perform a long-distance near-bottom physical/chemical survey in deep water without any intermediate surfacing to disrupt the survey or require the vehicle to surface in areas of heavy ship traffic. Some 210 km of AUV cruise track at '10 m above bottom were accomplished during a 3-day survey. The dissolved oxygen concentration [O 2 ] data are combined with temperature T, salinity S, and hydrostatic pressure P to produce maps of oxygen partial pressure pO 2 that help define the limits at which the oceanic supply of O 2 can match the O 2 demands required to sustain various forms of marine life. The chemical NO 3 sensing was included to define the critical pO 2 boundary at which NO 3 reduction occurs. The combination of a high-resolution terrain-following AUV with chemical sensors is important for a diverse array of investigations, including the study of vent sites, and for locating the source of chemical signals originating from the seafloor. The hypoxic basin example here permits better discrimination between general climate/ circulation controls on hypoxia and more specific point-source-driven processes.
doi:10.1175/jtech-d-12-00249.1 fatcat:xskgp475zbedhbrp74o7a5tdaa