Bottle Sampling Depths

Bottle Sampling Depths, based on downcast profiles

The CalCOFI CTD-rosette is equipped with a Sea-Bird Electronic carousel water sampler (SBE 32), a computer-driven, electro-magnetically-released latch system. The 24 ten-liter plastic (PVC) bottles, equipped with epoxy-coated springs & Viton (non-toxic) O-rings, connect to 24 individual triggers by lanyards which keep the bottle ends open. During the downcast, profiles of different sensor measurements vs depth are displayed real-time on a computer screen. Based on the chlorophyll maximum & mixed layer depths, bottles are closed at specific depths to isolate the seawater. The 10 meter bottle spacing shifts up or down (see table below) to resolve steep gradient features such as chlorophyll, oxygen, nitrite maxima and shallow salinity minimum. Salinity, oxygen and nutrients samples are analyzed at-sea for all depths sampled. Chlorophyll-a and phaeopigments samples from the top 200 meters, bottom depth permitting, are also extracted for 24hrs and analyzed at-sea. Most CTD-rosette casts sample 20 depths to a maximum of 515 meters, bottom depth permitting. Occasionally, additional bottle depths or multiple bottles are tripped at the same depth to provide extra water for ancillary projects or primary productivity incubations. Two basin stations, off Santa Monica & Santa Barbara, are sampled beyond 515m to within 10m of bottom. Wire-length permitting, a 3500m deep cast is performed at sta 90.90.

(more…)

Continue ReadingBottle Sampling Depths

CTD Setup & Diagnostics

Seabird CTD-Carousel Setup & Deck Unit Diagnostics

SIO-CalCOFI’s method of terminating the sea cable uses a custom 4-pin pigtail 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 in the CalCOFI Handbook: CTD Termination.

Conventional two-pin Seabird pigtail terminations are standard on NOAA vessels and are 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 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 (see the deck unit section below).
Once the sea cable is connected to the Seabird 9plus and Seabird 11plus 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 60 seconds 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.

(more…)

Continue ReadingCTD Setup & Diagnostics