Dataset: AT42-05 Water column chemistry

1) Nutrients (DOC, TDN, NOx, NO2, NH4, PO4, TDP): Water sample was filtered through a pre-rinsed 0.2 um regenerated cellulose Target2 syringe filter (Thermo Scientific, Prod. No. F25047), collected into an HDPE bottle and stored frozen at -20°C until analysis.  Individual analytes were analyzed as follows:

DOC (Dissolved Organic Carbon) was determined using high temperature catalytic combustion and an NDIR detector following the method described in Sugimura and Suzuki, 1988 (A high-temperature catalytic oxidation method for the determination of non-volatile dissolved organic carbon in seawater by direct injection of liquid sample. Mar. Chem., 24: 105-131). 

TDN (Total Dissolved Nitrogen) was determined using high temperature combustion and a chemiluminescence detector following the method described in Watanabe et. al, 2007 (Conversion efficiency of the high-temperature combustion technique for dissolved organic carbon and total dissolved nitrogen analysis.  Intern. J. Environ. Anal. Chem., 87: 387-399).

NOx (Nitric oxides) was determined using chemical reduction and a nitric oxide detector following the method described by Garside, 1982 (A chemiluminescent technique for the determination of nanomolar concentrations of nitrate and nitrite in seawater. Mar. Chem. 11: 159-167). 

NO2 (Nitrite) was determined using the colorimetric method described by Bendschneider and Robinson, 1952 (A new spectrophotometric method for the determination of nitrite in sea water. J. Mar. Res., 11: 87) as reproduced by Parsons, Marta, and Lalli, 1984 (Determination of Nitrite.  A manual of chemical and biological methods for seawater analysis pp. 7-9).

NH4 (Ammonium) was determined using the colorimetric method described by Solorzano, 1969 (Determination of ammonia in natural waters by the phenolhypochlorite method.  Limnol. Oceanogr., 14: 799-801).

PO4 (Phosphate) was determined using the colorimetric method described by Strickland and Parsons, 1972 (Determination of reactive phosphorus. A practical handbook of seawater analysis. Fisheries Research Board of Canada, pp. 49-52).

TDP (Total Dissolved Phosphorous) was determined using the colorimetric method described by Solorzano and Sharp, 1980 (Determination of total dissolved phosphorous and particulate phosphorous in natural waters.  Limnol. Oceanogr., 25: 754-758).

2) H2S (Hydrogen Sulfide): Water sample was collected into a 15 mL centrifuge tube containing 2M zinc acetate and stored at 5°C until analysis.  H2S was determined using the colorimetric method described by Cline, 1969 (Spectrophotometric determination of hydrogen sulfide in natural waters.  Limnol. Oceanogr., 14: 454-458).

3) Alkalinity was determined colorimetrically by the method described in Sarazin, 1999 (A rapid and accurate spectroscopic method for alkalinity measurements in sea water samples. Water Research 33: 290-294).

4) CH4 (Methane): A 1L water sample was collected from the Niskin bottle using gas tight tubing and standard collection methods for dissolved gases. Subsequently in the lab, a 700 mL sub-sample was transferred to an evacuated 1L media bottle. The water was sonicated under vacuum for 1 minute and then shaken; this process was repeated twice to transfer dissolved gases into the bottle headspace. The bottle pressure was equilibrated with helium purged saturated salt brine and the volume of recovered dissolved gas was recorded. The gas sample was transferred to an evacuated serum vial for storage until analysis on the gas chromatograph. CH4 was determined by headspace analysis using an SRI 8610C gas chromatograph equipped with a flame ionization detector (Crespo-Medina et al. 2014, Nature Geoscience, 7:423-427).

5) Salinity and pH: Salinity was determined with a refractometer, and pH was measured with a Ross electrode calibrated with NBS standard buffers.

6) Calculated Values (NO3, DIN, DON, DOP):  These values were calculated as follows:
NO3 = NOx - NO2
DIN = NOx + NH4
DON = TDN - DIN
DOP= TDP - PO4​