Since August 1993, CalCOFI has deployed a 24 bottle CTD-Rosette. The CTD-Rosette consists of two integrated components: the Seabird 911+ CTD electronic sensor array and carousel surrounded by a ring of 24-10 liter PVC bottles that collect seawater at various depths.
The Seabird 911+ 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 several sensor measurements display on the CTD computer screen. Based on the downcast profiles, the 10 liter bottles are closed at target depths as the CTD-Rosette is brought back to surface, trapping seawater for analysis.
The CTD-Rosette is typically lowered to terminal depth of 515 meter (1690 feet), bottom-depth permitting. On basin stations or stations less than 515 meters, it is routinely deployed within ~10 meters from the seafloor. To improve the sampling resolution in areas with significant hydrological and biological gradients, the CTD-Rosette is lowered a speed of ~30 m/min for the first 100 m then ~60 m/min to depth without stopping. During retrieval, the CTD-Rosette stops for at least 20 seconds at target bottle depths to adequately flush the 10 liter sample bottle prior to closure. Seawater samples are analyzed onboard for salinity, oxygen, nutrients & chl and are used to cross-check & correct matching depth CTD sensor measurements.