The CTD-Rosette is lowered through the water column, measuring physical parameters including temperature, salinity, oxygen, fluorescence, light transmittance, nitrate, and photosynthetically active radiation (PAR). Bottles are closed at target depths, isolating seawater for analysis.
The CTD-Rosette consists of two integrated components: the Seabird 911plus CTD electronic sensor array, and a “rosette” of 24-10 liter PVC Niskin bottles. The CTD electronic sensor array sends real-time data to a shipboard computer via the winch’s conductive wire. As the CTD-Rosette is lowered, depth profiles of sensor measurements display on the shipboard computer screen. As the CTD-Rosette is brought back to surface, the 10 liter bottles are closed at target depths, trapping seawater for analysis.
The CTD-Rosette is typically lowered to a terminal depth of 515 meters (1690 feet), bottom-depth permitting. On basin stations, or stations less than 515 meters, it is routinely deployed within 10 meters of the seafloor. To improve the sampling resolution in areas with significant hydrological and biological gradients, the CTD-Rosette is lowered at a speed of 30 m/min for the first 100 m then 60 m/min to terminal depth, without stopping.
During the upcast, the CTD-Rosette stops for at least 20 seconds at each target bottle depth to adequately flush the Niskin bottle prior to closure. Seawater samples are analyzed onboard for salinity, oxygen, nutrients & chlorophyll-a to cross-check and correct CTD sensor measurements.
Available Oceanographic Data
CalCOFI began deploying a 24-bottle CTD-Rosette in August 1993, with test casts beginning in March 1990. Prior to 1993, CalCOFI collected seawater samples using Niskin, Nansen, and “Wally” bottles (in-house design by Walt Bryant & George Anderson) with reversing thermometers. CTD Cast Files are available 1990-present and seawater sample data are available 1949-present in the Bottle Database.