Sampling and Analytical Methodology:
A single SBE9plus CTD (S/N 831) was used for all casts and was deployed with all sensors and pumps as recommended by SBE. In situ salinity and dissolved oxygen check samples were collected to calibrate conductivity and dissolved oxygen sensors (see MV1310 Preliminary Cruise Report).
The primary conductivity and temperature sensors failed on the up-casts of stations 19, 21-27 and on the down-cast of stations 28 and 29. The secondary sensors were chosen for consistent reporting.
In addition to the 0.0073 second temperature and conductivity standard alignment factor an offset of 0.08 seconds was applied for each station and sensor configuration.
CTD Pressure: Paroscientific Digiquartz pressure transducer (S/N 831-99677) last calibrated in November 2012 at the SIO/STS Calibration Facility. Residual pressure offsets indicated that an offset of -0.84350 dbar be applied to pressure sensor calibration.
CTD Temperature: A SBE35RT Digital Reversing Thermometer sensor was not used, therefore only standard laboratory calibrations were used for T1 and T2 sensors. The secondary sensors were chosen for consistency. An offset observed in cast 12/3 was adjusted based on data from adjacent casts at the same station. Sensors used: The SBE3plus secondary (T2/03-2309) was swapped for (T2/03-4307) after cast 12/1. The SBE3plus secondary (T2/03-4307) was swapped for (T2/03-2309) after station/cast 12/3. The SBE3plus secondary (T2/03-2309) was swapped for (T2/03-2322) after cast 28/1.
The 95% confidence limits for the MV1310 data mean low-gradient differences are +- 0.00137C for T1-T2 .The 95% confidence limit for deep temperature residuals (where pressure > 1800 dbars) is +- 0.00105C for T1-T2 .
CTD Conductivity: Pre-cruise calibration coefficients were applied to convert raw frequencies to conductivity. Secondary sensors were compared to conductivity calculated from check sample salinities using CTD pressure and temperature. Sensors used: The SBE4C secondary (C2/04-2819) was swapped for (C2/04-2765) after cast 28/1. The 95% confidence limits are ± 0.00445 relative to bottle salinities for all salinities, where T1-T2 is within +- 0.01C; and +- 0.000781 relative to bottle salinities for deep salinities, where pressure is more than 1800 decibars. Within the context of having only a small number of salinity check samples, when questionable check samples were ignored, the final CTD salinities (and temperatures) appear to meet a reasonable standard, though less reliable than the reference cruises (P16N (2009) and P17N (2001)).
CTD Dissolved Oxygen: SBE43 dissolved oxygen sensor (DO/43-0275) was calibrated to dissolved oxygen bottle samples taken at bottle stops. At the end of the cruise, standard and blank values for bottle oxygen data were smoothed, and the bottle oxygen values were recalculated (changes were less than 0.01 ml/l for most stations). Standard deviations were 3.142 umol/kg for all oxygens and 1.365 umol/kg for deep oxygens. CTD dissolved oxygen ml/l data are converted to umol/kg units.
Salinity (in situ): To calibrate conductivity CTD sensors, salinity was determined at the Marine Chemistry Laboratory at the University of Washington’s School of Oceanography. Water was collected from Niskin bottles directly into acid leached, 500 mL HDPE bottles and stored at room temperature until analysis at shore-based laboratories. Samples were collected at the surface and/or mixed layer of the CTD profile and at least three samples evenly spaced below the high gradient region with one sample at the bottom of the cast. Analyses were run on Guildline models 8400B and 8410 Portasal - Calibration is with IAPSO Standard Seawater. Limit of Detection: 0.002PSU.
Dissolved Oxygen (in situ): To calibrate oxygen CTD sensors, dissolved oxygen was sampled and measured onboard by Winkler titration using the amperometric technique (Langdon 2010). At least six oxygen samples were sampled on full depth stations from the surface, bottom and major min/max inflection points with-in the profile. There were insufficient bottle oxygen samples of usable quality available from this cruise to provide reasonable assurance of values of dissolved oxygen at a given level from a given profile. Because the final data do match the shape of P17N data, there is, however somewhat more confidence in the shape and gradients revealed in the final CTD oxygen probe data.
TOC and TDN: TOC and TDN concentrations were determined in the Hansell lab at the University of Miami. Water was collected from Niskin bottles directly (unfiltered) into acid leached, 60-mL polycarbonate bottles and stored frozen at –20°C in volatile organic-free freezers until analysis at shore-based laboratories. TOC was measured by high temperature combustion (HTC) using a Shimadzu TOC-L with auto injection (CV of 1.5-2.5%), following the method described in Dickson et al. (2007). TOC was combusted to CO2 upon injection and the resulting gas stream scrubbed of water vapor and halides and the magnitude of CO2 detected with a non-dispersive infrared detector. TDN was determined by HTC where TDN was converted to nitric oxide (NO) gas, which then reacted with ozone producing an excited chemiluminescence NO2 species. The fluorescence signal was then detected with a Shimadzu TNM-1 chemiluminescence detector. TON is calculated as the difference between TDN concentrations and dissolved, combined inorganic (nutrient) nitrogen. Four point standard curves using KHP for C and KNO3 for N were run daily to calibrate the response of the high temperature combustion systems. Both measurements were quality controlled using consensus reference materials (CRMs) distributed to the international community (Hansell, 2005). The CRMs were analyzed at regular intervals during each analytical day. Low C (and N) reference water was employed to determine system blanks.
Nutrients: Nutrient concentrations were determined in the Marine Chemistry Laboratory at the University of Washington School of Oceanography. Water was collected from Niskin bottles directly into acid leached 60-mL HDPE bottles and stored at –20C in volatile organic-free freezers or at 4°C refrigerators (silicate only) until analysis at shore-based laboratories. Analyses and calibration follow the protocols of the WOCE Hydrographic Program using a Technicon AAII system (UNESCO 1994).
Detection Limits:
Phosphate: 0.03µM, 0.0009mg/L
Silicate: 0.59µM, 0.0166mg/L
Nitrate: 0.15µM, 0.0021mg/L
Nitrite: 0.02µM, 0.0003mg/L
Ammonium: 0.12µM, 0.0017mg/L
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