Dataset: Niskin Bottle Hydrography
Deployment: B4-2008

Data processing and analysis details from each cruise are reported for that platform deployment.

CTD data are reported as cast number and not as station number.

Temperature and salinity (parameter names temp and sal): On the R/S Bjarni Saemundsson cruises, only one CTD unit was present, so salinity and temperature were de-spiked using a 21-point (3.5 s) median filter. An additional 81-point (13 s) median filter was applied where the signal was particularly variable. For more details on temperature and salinity processing, see Ship_TS_despiking-NAB08.pdf.

Dissolved oxygen, O2 (parameter name O2_uncal): The sensor was calibrated immediately before the cruise. The factory calibration was applied to SBE43 oxygen sensor voltage, with units of µmol kg-1. Although the sensor was calibrated immediately before the cruise, the absolute concentrations were not verified by Winkler oxygen.

Particulate attenuation coefficient, cp (parameter name beam_cp): C-Star s/n 284 did not have a recent factory calibration. On the subsequent R/V Knorr cruise in May, it was cross calibrated with the newly calibrated C-Star s/n 1090 through a series of simultaneous ship/Biofloat48 calibration profiles. The final products for all three C-Stars are cross-calibrated cp coefficients with units of m-1. Complete details of the transmissometer intercalibration procedure are in C-Star calibration report (C-Star_Calibration-NAB08.pdf).

Particulate backscattering coefficient, bbp (parameter name bbp700): Backscattering voltage was converted to β at 140° by subtracting dark voltages (median in-situ dark voltage, 0.078 V) and multiplying by factory calibration scale factors, modified based on measurements and calculations of Sullivan et al. (subm.). The calibration factor did not change between pre-cruise and post-cruise factory calibration. β at 140° was converted to bbp (m-1) by subtracting β of seawater (Zhang et al., 2009) and multiplying by 2π (where π = 1.132). See calibration report for more details: Backscatter_Calibration-NAB08.pdf.

Chlorophyll fluorescence (parameter name chl_raw) is reported as the raw instrument voltage output minus dark voltage (median in situ dark voltage = 0.083 volts.

Water column photosynthetically active radiation (parameter name PAR): The sensor was new and freshly calibrated before the cruise. For more details, see Radiometry_and_PAR_Calibration-NAB08.pdf.

Nutrients (parameter names NO3_NO2 and Si_acid): Nutrient samples for nitrate plus nitrite (NO3-+ NO2-) and silicic acid (Si(OH4)) were collected in acid-washed LDPE bottles; unfiltered samples were frozen immediately and stored for up to 8 mo. Samples were thawed at room temperature in the dark for 24 h and vigorously vortexed (Gordon et al., 1993). Samples were analyzed with a Lachat Quickchem 8000 Flow Injection Analysis System using standard absorptiometric techniques (Smith and Bogren, 2001; Wolters, 2002; QuikChem Method 31-107-04-1-C for nitrate plus nitrite; QuikChem Method 31-114-27-1-B for silicic acid). All Lachat spectra were manually inspected for irregularities in baseline or the presence of bubbles. Any offending samples were rejected. Profiles of silicic acid and nitrate concentrations for all casts were also examined, following the recommendation of the IODE workshop on quality control of chemical oceanographic data (IOC, 2010). Concentrations that were clearly out of range without temperature or salinity intrusions were rejected. Phosphate baselines as a whole were not sufficiently stable to be accepted and hence phosphate data are not reported. For additional details on laboratory analysis of discrete water samples see: Laboratory_analysis_report-NAB08.pdf.

Fluorometric pigments (parameter names chl_a_fluor and phaeo): Water samples for fluorometric analysis of chlorophyll and pheopigments were filtered through Whatman GF/F filters. Filters were extracted in 5 ml of 90% acetone at -20? C for 24 h and read on a Turner Designs Model 10-AU Digital fluorometer. The fluorometer was calibrated before and after the field program with Turner Designs chlorophyll standards. Chlorophyll and pheopigment were determined following JGOFS protocol procedures (Knap et al., 1996). For additional details on laboratory analysis of discrete water samples see: Laboratory_analysis_report-NAB08.pdf.

Particulate organic carbon (parameter name POC): Samples were collected from Niskin bottles using a sampling bell to minimize particle contamination from air. They were immediately filtered, using closed bottles fitted with Biochem Fluidics caps with 2 tubing ports, through a Millipore Swinnex in-line filter holder onto pre-combusted Whatman GF/F filters. All plastics were washed in RBS. Samples were stored frozen for up to 5 mo. Before analysis, samples were dried at 50°C for 4 h, fumed with hydrochloric acid (HCl, 11.65 N) for 12 h, and stored in a desiccator for up to 12 h. Filters were rolled and placed in pre-combusted tin cups shortly before analysis on a Perkin Elmer 2400CHN analyzer (Knap et al., 1996). For additional details on laboratory analysis of discrete water samples see: Laboratory_analysis_report-NAB08.pdf.

HPLC pigment samples (see various parameter names) were filtered onto Whatman GF/F filters and preserved in -80°C (liquid nitrogen) until analysis. Samples were stored for up to 5 mo. HPLC analysis was performed by Horn Point laboratories using a methanol-based reversed-phase gradient C8 chromatography column system and appropriate standards (Hooker et al., 2009; Van Heukelem and Thomas, 2001). For additional details on laboratory analysis of discrete water samples see: Laboratory_analysis_report-NAB08.pdf.

Particulate and phytoplankton absorption coefficients (parameter names ap(λ) and aph(λ): Water samples for absorption spectra were filtered onto Whatman GF/F filters and scanned at sea on a Varian Cary 50 UV-Visible Spectrophotometer with a xenon flash lamp and a 1.5nm slit width for measurement of total particulate absorption spectra, ap(λ) (Mitchell and Kiefer, 1988). Filters were subsequently extracted in methanol and re-analyzed to determine residual detrital particulate absorption, ad(λ); the difference spectra are reported as phytoplankton absorption spectra, aph(λ) (Kishino et al., 1985). For each sample and blank, the average absorbance between 750-800 nm was subtracted as the zero baseline for that spectrum. For additional details on laboratory analysis of discrete water samples see: Laboratory_analysis_report-NAB08.pdf.