CTD Hydrocasts were performed with a Sea-Bird SBE 911/917 plus CTD mounted near the base of a Niskin 24 Bottle Rosette. The CTD instrumentation included Conductivity (S/N 2147 & 2768), Temperature (ITS-90, S/N 4195 & 4252), Pressure (S/N 63505 SBE090462), Oxygen (SBE 43, S/N 0264), Fluorescence (Wetlab ECO-AFL/FL, S/N FLNTURTD-304), and Beam Transmission (Chelsea/Seatech/Wetlab CStar, S/N CST-1118DR). Processing firmware is SBE11plus v 5.

At each station, a hydrocast was conducted with a rosette carrying 24 10-L Niskin bottles. The rosette was instrumented with sensors for conductivity, temperature, pressure, oxygen, fluorescence, and beam transmission, as listed above. The downcast was conducted at 30 m per minute in the upper 100 m and increased to 60 m per minute to a maximum depth of ~5 m above the seafloor (based on altimeter data). Features were selected from the downcast data for sampling on the upcast. These features included oxygen minimum layer(s), chlorophyll maximum layer(s), and the thermocline. In addition, standard depths of bottom, 50 m above bottom, 5000 m, 4000 m, 3000 m, 2000 m, 1500 m, 1000 m, 300 m, 200 m, 100 m, 50 m, 10 m, and surface were sampled.

The vent plugs were removed and replaced with t-fittings. A ring of plastic tubing (1/4" inner diameter) was used to construct a manifold to deliver pressure to each Niskin bottle. Each bottle was connected individually to the manifold to prevent any potential mixing between bottles. The compressor was connected to the initial t-valve in the series and the final t-valve was plugged. The compressor was set to 8 - 10 psi.

Cylindrical, 0.2 um retention membrane filters (Sterivex) were attached to the petcock valve of the Niskin bottles with 1/4" tubing (Fig. 8). The valves were opened and the water was pushed through the filters with the compressed air. The filtration rate is ~200 mL per minute. When the water stopped dripping through the filter, the filters were removed, capped at both ends, placed into freezer boxes and stored at -70 degrees C in the main lab freezer.

KN223_CTD.csv