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Puget Sound Marine Monitoring

The best decisions are based on Sound information

For questions about the King County Puget Sound Marine Monitoring Program, please contact

Offshore CTD Monitoring

Map icon for active stationactive station  Map icon for inactive stationinactive station
Scientist and the CTDKing County collects monthly in situ water column profiles at its offshore monitoring stations using a CTD. A CTD is a multi-sensor array that measures dissolved oxygen, salinity, temperature, density (calculated), transmissivity, photosynthetically active radiation, and fluorescence (as a measure of chlorophyll). The sensor array is deployed on a rosette; a round metal frame that also holds 12 Niskin sampling bottles. The CTD collects water quality measurements 16 times a second (16 Hertz) as it is lowered through the water column from the surface to the bottom (downcast) and back up again (upcast). Scientists collecting water samples from Niskin bottles The CTD also triggers the closure of the 5-liter Niskin bottles on the upcast at pre-programmed depths to collect discrete water-column samples for laboratory analysis of additional parameters. The water column profile data for each cast are averaged, or binned, over each 0.5 meters of the total depth. Please click on the station map to the left to download CTD data for both current and historic sampling stations. Detection limits and methods are described in the following table.

Light Transmission data prior to May 19, 2014 were referenced to air. After this date, all Light Transmission data are referenced to water. To convert the pre-May 19, 2014 data to ‘referenced to water’, multiply the values by 1.095.

Parameter Sensor Reporting units Detection Limit
Chlorophyll WET Labs WETStar Fluorometer µg/L 0.06
Conductivity Seabird SBE 4 Conductivity Sensor S/m --
Depth Seabird SBE 29 Pressure Sensor m --
Dissolved Oxygen Seabird SBE 43 Dissolved Oxygen Sensor mg/L 0.5
Density Calculated from conductivity, temperature, and depth sensors kg/m3 --
Sigma-Theta Density Potential density (minus 1000) from conductivity, temperature, and depth kg/m3 --
Light Transmission WET Labs C-Star Transmissometer % Light 0.01
PAR (Surface) LI-COR Surface Light Intensity (PAR) LI-190-SA-50 µmol.sm3 --
PAR (Water Column) LI-COR Light Intensity (PAR) LI-193-SA-50 µmol.sm3 --
Salinity Calculated from conductivity and temperature sensors PSS --
Temperature Seabird SBE 3 Temperature Sensor °C --
Nitrite + Nitrate Seabird SUNA Nitrate Sensor (10 mm pathlength) mgN/L 0.034