An autonomous, bottom-transecting vehicle for making long time-series measurements of sediment community oxygen consumption to abyssal depths

We have developed and successfully collected data with a unique, bottom-transecting vehicle (ROVER) that permits the first long time-series measurements of sediment community oxygen consumption (SCOC). This instrument has the following capabilities: (1) it operates as an autonomous, free vehicle on the sea floor to 6,000-m depth for periods up to 6 months; (2) it transits across the sea floor, minimizing the impact that a long-term, free-vehicle structure would have on measurement sites; (3) it measures SCOC by using duplicate benthic chambers at up to 30 different sites over a single deployment period; (4) it measures sediment porewater oxygen concentration as an independent measure of SCOC by using a microprofiler at up to 30 different sites over a single deployment period; (5) it has an incubation period of programmable duration for each SCOC measurement; (6) it monitors operation of instruments and the surrounding area with time-lapse still and video cameras; (7) it has the flexibility to be used as an autonomous programmable platform for a wide variety of benthic boundary-layer measurements; and (8) it collects a water sample for oxygen and other analyses at the end of the deployment. The ROVER resembles a small forklift with a forward-mounted instrument assembly, a current meter, double-tread propulsion system, central battery and controller electronics, flotation, acoustic releases, and disposable ballast. The ROVER was deployed for a 4-month period (January-May 1996) to measure SCOC at 4,100-m depth in the eastern North Pacific. During this deployment the ROVER occupied 17 sites with each benthic chamber incubation lasting 152.3 h and a 17-h interval between incubations for repositioning and transit. SCOC ranged from 0.50 to 0.91 mmol O-2 m(-2) d(-1), generally declining from January until the end of February and then increasing irregularly to the end of the deployment in late May. These measurements show good agreement with those made at the same site with another autonomous instrument, the free-vehicle grab respirometer, at the beginning and end of the ROVER deployment.