Water quality profiling with a WETLabs Autonomous Moored Profiler (AMP)

Operational details are described and results are presented from a deployment of a WETLabs AMP (Autonomous Moored Profiler) in Chesapeake Bay. The AMP (figure 1) is anchored and nominally stationed at depth throughout a deployment. An onboard processor schedules and controls profiling; collects, processes, and stores data collected from instrument sensors; and communicates with a remote host during profiler surface intervals. The profiler is tethered to an anchor by an HMPE cable /winch system. When a profile is initiated, sensors are activated and the winch spools out, allowing a controlled ascent by the buoyant package. At the surface, profile, winch control, status, and position data are transferred to the remote host, new instructions may be downloaded, and the instrument is winched back to the bottom, awaiting the next profile in low-power mode. The AMP is easily deployable from a small boat by 3-4 persons, requiring only a 50 kg anchor. Communications in this deployment are via CDMA modem. Onboard sensors include a Seabird SBE 49 Temperature / Conductivity / Pressure, Aanderaa 4330F Dissolved Oxygen, and WETLabs ECO chlorophyll, backscattering, and CDOM fluorescence sensors. Results from a deployment during July and August 2010 in mid-Chesapeake Bay are shown and discussed. For example, Figure X shows dissolved oxygen concentration during a 10-day period of hourly continuous profiling, with the profiler anchored in 20 meters of water. Missing data near the surface confined to daylight hours were discovered to be due to light saturation of the Aanderaa optode; this has since been corrected by a protective housing that also enhances flow over the sensor film. Studies are under way to accurately determine and correct for the relative lags between Temperature/Conductivity and Dissolved Oxygen sensor response. During the deployment time period, the lower water column displayed hypoxic conditions, with the depth of the oxycline strongly modulated by semidiurnal tides. Dynamics of the observed conditions are analyzed with the aid of a nearby buoy mooring providing wind, wave, current profiles, and surface and bottom water quality data. Additional deployments during Spring/Summer 2011 are scheduled to capture the onset of hypoxic conditions.