Dataset: Discrete C and N near Station P

Particulate Nitrogen and Carbon
Analyses were conducted using a Costech Analytical Technologies Zero Blank carousel attached to a Carlo Erba NA1500 Series 2 elemental analyzer (EA). The instrument precision was estimated from Acetanilide standards (189 measurements over 24 unique sampling dates) as the standard deviation of weight percent measurements for both carbon and nitrogen multiplied by the mean total weight.

The data obtained from the Carlo Erba NA1500 Series 2 elemental analyzer were calibrated using Acetanilide standard composed of 10.36 Wt. % N and 71.09 Wt. % C.

K-factor (KF) method was used to correct all unknown data using 6 acetanilide standards using the following equations.
Where:   KF = (mass mg * 10.36)/(Area N – Area N blank)
               KF = (mass mg * 70.09)/(Area C – Area C blank)

Sample C and N concentrations were calculated as follows: 
Where:   μg/L N = {(Average KF * (Area N – Area N blank))/Volume Filtered (L)} x (1000 μg / 1 mg)
               μg/L C = {(Average KF * (Area C – Area C blank))/Volume Filtered (L)}
 

Dissolved Inorganic Carbon (DIC)
DIC was analyzed using a custom automated system in which a Kloehn V6 syringe pump (5 mL syringe) handles fluid control, delivering 1.75 mL of sample to a custom designed CO₂ stripping chamber. 200 µL of 5% phosphoric acid (H₃PO₄) is subsequently added to the CO₂ stripping chamber for acidification of the sample. CO₂-free gas is then bubbled through the acidified sample and the evolved CO₂(g) is delivered to a LiCOR 7000 Nondispersive Infrared gas analyzer for measurement. Carrier gas flow rate is controlled using a mass flow controller. The DIC concentration of the sample is proportional to the integral of the LiCOR CO₂(g) sample peak. The LiCOR 7000 is calibrated annually using WMO traceable standard gases containing known CO₂ mole fractions. The average accuracy of the instrument relative to CRMs is better than than 1μmol kg^-1.

Sampling precision (σ_s) was estimated by analyzing sets of replicate samples drawn from the same Niskin bottle during rosette casts. The average standard deviation between replicate sets was found to be ±1.5 μmol kg^-1 (n = 8).  Analytical precision (σ_i) was estimated as the standard deviation of CRM samples, post calibration factor implementation, analyzed intermittently with the cruise samples over the course of a few days. The analytical precision was found to be ±0.7 μmol kg^-1 (n = 23). The overall measurement precision of 1.6 μmol kg^-1 was estimated by combining the sampling precision and analytical precision [(σ_s² + σ_i²)^0.5], which is the square root of the sum of the squares. 

Total Alkalinity (TA)
Total Alkalinity was analyzed using a Metrohm 855 automated titrator following standard open cell alkalinity titration procedures. The titrant was comprised of 0.1 M hydrochloric acid (HCl) in a 0.7 M sodium chloride (NaCl) background solution. The titration temperature was held constant at 20.0 ± 0.2°C throughout the titration. The temperature of the sample was measured immediately upon delivery to the jacketed cell for later sample mass determination using density and volume. The average accuracy of the instrument relative to Certified Reference Material (CRM) is better than 1 μmol kg^-1. 

Sampling precision (σ_s) was estimated by analyzing sets of replicate samples drawn from the same Niskin bottle during rosette casts. The average standard deviation between replicate sets was found to be ±1.5 μmol kg^-1 (n = 8).  Analytical precision (σ_i) was estimated as the standard deviation of CRM samples, post calibration factor implementation, analyzed intermittently with the cruise samples over the course of a few days. The analytical precision was found to be ±1.4 μmol kg^-1 (n = 13). The overall measurement precision of 2.1 μmol kg^-1 was estimated by combining the sampling precision and analytical precision [(σ_s² + σ_i²)^0.5], which is the square root of the sum of the squares. 

pH
pH was analyzed using an Agilent 8453 spectrometer in an automated system designed after the one described in Carter et al., (2013). The temperature of the sample was held constant at 20°C using a 10-cm jacketed cell, and every sample was immersed in a 20°C water bath for at least 25 minutes before analysis. An indicator dye (purified m-cresol purple from Sunburst Sensors - lab batch 6) solution (2 mM) was used to assess sample pH. The sample pH perturbation caused by dye addition was quantified by adding both the normal amount and twice the amount of dye to seawater solutions of ~pH 7.4, 7.8, and 8.1. The pH perturbation caused by dye addition to the sample was quantified by adding both the normal amount and twice the amount of dye to a subset of seawater samples. The average precision of the instrument is ±0.004. 

Sampling precision (σ_s) was estimated by analyzing sets of replicate samples drawn from the same Niskin bottle during rosette casts. The average standard deviation between replicate sets was found to be ± 0.0031 (n = 9). Instrument precision (σ_i) is estimated to be ±0.004. The overall measurement precision of 0.005 was estimated by combining the sampling precision and instrument precision  [(σ_s² + σ_i²)^0.5], which is the square root of the sum of the squares. 

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BCO-DMO Processing:

• Imported data from source file "LineP_QCd_bottle_data.xlsx" into the BCO-DMO data system.
• Data file imported using missing data identifiers "NaN”. The missing data identifier "NaN" in the original source file will be displayed as appropriate based on the type of file you download from the BCO-DMO data system. For example, missing data will be shown as blank (null) values in the csv files. In MATLAB .mat files it will be displayed as NaN. When viewing data at BCO-DMO the missing value will be shown as "nd" meaning "no data."
• Adjusted dates to be four digit years, and padded time column with leading zeros.  Then converted separate date and time to single datetime column with ISO8601 format.  
• Added column for vessel/ship
• Added conventional header with dataset name, PI name, version date.
• Modified parameter (column) names to conform with BCO-DMO naming conventions. (The only allowed characters are A-Z,a-z,0-9, and underscores. No spaces, hyphens, commas, parentheses, or Greek letters).