Dataset: CTD - Nutrients

Refer to SAGE Voyage Report

CTD-related instrumentation consisted of:
- a Seabird Electronics (SBE) 911plus CTD with:
- SBE-5 pumped SBE-3 temperature, SBE-4 conductivity and SBE-43 dissolved oxygen sensors.
- SBE-5 pumped secondary SBE-3 temperature and SBE-4 conductivity sensors.
- Seapoint Sensors, Inc. SCF chlorophyll fluorometer.
- 25-cm Wetlabs C-star transmissometer.
- Biosherical Instruments Inc. photosynthetic ally active radiation (PAR) sensor, model QSP200L4S.
- Datasonics sonar altimeter, model PSA-900D.
- a SBE 32 24x10-litre Carousel water sampler.
- Ocean Test Equipment Standard BES external-spring Niskin-type water-sampling bottles.
- Salinity sample bottles.
- CTD winch with 10-km 10.5-mm single-core seacable.

Performance: With the exception of issues noted below, the CTD-related instrumentation apparently functioned to specification and was operated essentially according to accepted practices for the duration of the voyage. A total of 85 one-cast CTD stations were completed, labelled u3502 to u3743.

PAR Sensor: The initial CTD PAR sensor experienced an intermittent fault that manifested as a time variable offset, both cast to cast and, less evidently, within casts. It was eventually replaced with a formally identical spare unit for station u3719 cast 1 and subsequent casts.

Secondary Conductivity Sensor: The initial secondary conductivity sensor eventually developed a clear fault (during station u3740 cast 1). It was replaced with a formally identical spare unit for station u3740 cast 1 and subsequent casts. The development of this fault was perhaps somewhat progressive, as possibly indicated by slight shifts in the primary-secondary conductivity difference on casts before station u3740 cast 1.

Methods:
Nutrient samples were analysed using an Astoria Pacific API 300 micro-segmented flow analyser with digital detector, and methods developed for trace seawater analysis. Duplicate depth profile samples were filtered through acid washed
Whatman GF/F filters into clean 250ml polyethylene bottles for analysis. Samples for underway analysis were drawn from the Tangaroa's surface supply at 7m, via a continuous filter (3.0um pore size) and using a LabPro computer controlled switching valve connected to the auto analyser sample line. Nitrate was reduced to nitrite by cadmium metal and determined (as nitrate plus nitrite) using an azo dye (API method 305-A177). Dissolved reactive phosphorus and dissolved reactive silicic acid were measured using the molybdenum blue method (API Methods 305-A204, 305-A221 respectively).