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.
|Seabird 911+ CTD Sensors & Rosette Bottle Samples|
|CTD Sensors:||Seawater Samples:|
|Temperature x 2||Salinity|
|Conductivity x 2||Oxygen|
|Oxygen x 2||Nutrients|
|Altimeter||LTER Additional Sampling|
Current sensor complement includes:
• Dual Temperature - SBE 3plus
• Dual Conductivity - SBE 4
• Dual Oxygen - SBE 43
• Fluorometer - Wetlabs Fluorometer
• Nitrate Sensor - Satlantic ISUS V2
• pH Sensor - SBE 18
• Transmissometer - WetLabs 25cm 650nm
• Underwater PAR - Biospherical QSP-2300
• Surface PAR - Biospherical QSP-240
• Carousel Water Sampler - SBE 32
Seabird CTD-Carousel Setup & Deck Unit Diagnostics
SIO-CalCOFI’s method of terminating the sea cable uses a 4-pin custom pig-tail to terminate a multi-strand conductive wire that allows each individual conductor to be used in any combination. Terminating the sea cable using this technique may be viewed on in the CalCOFI Handbook: CTD Termination Section.
Conventional two-pin Seabird pigtail terminations are standard on NOAA vessels and usually performed by the ET. So interfacing the CTD deck unit only requires the attachment of the sea cable to the deck unit. This is done by connecting a two-conductor wire, such as Seabird part no. 31371 (http://www.seabird.com/sales_info/Cables/31371b.pdf) or a coaxial cable equipped with MS3106A connector, from the winch junction box in the CTD lab to the Sea Cable port on the back of the deck unit.
Once the sea cable is connected to the Seabird 9+ and Seabird 11 deck unit, the deck unit can be powered on. If cabled properly and all electronics are functioning, the numeric LED panel of the deck unit should display non-zero numbers. These values are different for each channel which can be selected by rotating the Word Select dial to the right of the LED panel.
If the LED panel displays “0.0.0.0.0.0.0.0” then the deck unit and CTD “fish” are not handshaking correctly. Turn the deck unit off and wait 60secs before touching any exposed wire. Typically, with only two pins, the problem is reversed polarity so switching the wires in the junction box will correct this issue. Please note that powering on the deck unit with reversed polarity may blow the fuse(s). So after switching the wires and before re-powering on the deck unit, check both the 1/2A and 2A fuses on the back of the deck unit & replace if necessary. It is prudent to keep a good supply of these fuses on hand. Power on the deck unit and hopefully, the LED panel has numbers.
Please note in the photos, yellow tape is used to keep the deck unit Signal Source set to Fish. If the switch is toggled to Tape, the deck unit will not communicate with the CTD. The yellow tape prevents the switch from changing from Fish to Tape unintentionally.
(CTDOperator Duty List2017.doc 08/09/2017 - CURRENT VERSION)
These instructions are designed for use by CalCOFI CTD operators and describe our step-by-step protocol for CTD operations at sea. They outline our preferred method but are not considered "gospel" - there are many techniques that result in good data from the Seabird 911+ CTD. But based on our long history of using Seabird hardware & software, we've established these guidelines for our CTD operators to follow. Standardizing our methodology between operator improves our data continuity, format consistency, and makes problems with our system easier to catch.
1). CTD Prep: ~20 minutes before station arrival, rally the troops for CTD prep. If weather-decks are secured because of rough weather, wait until arrival to station.
2). Prep Seasave on CTD Computer:
3). Upon station arrival:
Since 1993, the CalCOFI program has deployed a Seabird 911 CTD mounted on a 24-bottle rosette during seasonal, quarterly cruises off California. The CTD-rosette is lowered into the ocean to 515m, depth-permitting, on 75 hydrographic stations using the ship's conductive-wire winch. Data from the sensors are transmitted up the conductive wire and displayed real-time on a data aquistion computer. Discrete seawater samples are collected in 10L bottles at specific depths determined by the chlorophyll maximum and mixed layer depth. These samples are analyzed at sea and used to assess the CTD sensor data quality plus measure additional properties. Processed CTD sensor data are compared to the seawater sample data and corrected when necessary. Preliminary data are available on CalCOFI's website, calcofi.org, while the cruise is at sea when internet is available. Preliminary processed data files are online shortly after the cruise returns. Final, publication-quality bottle & CTD data are available once the bottle data have been fully processed & scrutinized.