Hydrographic, nutrient and oxygen data from CTD bottles during R/V Pelican cruises from 2016-06-29 to 2018-06-24 (NCEI Accession 0278811)

Acquisition Description:
Nutrient Analysis Equipment and Techniques:

Nutrient samples were collected, filtered (0.2 µm Acropak-200 polyethersulfone filters, Pall) and frozen on board until analysis on shore up to 3 months later. Nutrient analyses (phosphate, silicate, nitrate+nitrite, nitrite, ammonium, and urea) were performed on 6-channel Astoria-Pacific autoanalyzer using standard methods (WHPO 1994). Ammonia analyses were based on Solorzano (1969), using phenol/hypochlorite in alkaline medium with a sodium nitroprusside catalyst. Urea analyses were based on Aminot and Kerouel (1982) using diacetyl monoxime in acid solution.

Dissolved Oxygen Analysis Equipment and Techniques:

Samples were collected for dissolved oxygen analyses soon after the rosette was brought on board. Using a Tygon or silicone drawing tube, nominal 125 ml volume-calibrated iodine flasks were rinsed 3 times with minimal agitation, then filled and allowed to overflow for at least 3 flask volumes. Reagents (MnCl2 then NaI/NaOH) were added to fix the oxygen before stoppering. The flasks were shaken twice (>1 minute inversions) to assure thorough dispersion of the precipitate. The lip of the flask stopper was the filled with ultrapure water to prevent access to atmospheric oxygen during the up to 3 hours between sample collection and analysis.

Oxygen flask volumes were determined gravimetrically to determine flask volumes at TAMU Geochemical and Environmental Research Group (GERG). This is done once before using flasks for the first time and periodically thereafter when a suspect volume is detected.

Dissolved oxygen analyses were performed with an automated Winkler oxygen titrator (Langdon Enterprises, Miami) using amperometric end-point detection. Thiosulfate (nominally 0.01 N) was standardized against 0.01 N potassium iodate prior to sample analysis.

Salinity Analysis Equipment and Techniques:

Salinity samples were drawn into 200 mL Kimax high-alumina borosilicate bottles, which were rinsed three times with sample prior to filling to the shoulder. The bottles were sealed with plastic insert thimbles to reduce evaporation. PSS78 salinity (UNESCO 1981) was calculated for each sample from the measured conductivity ratios.

A Guildline Autosal 8400B salinometer (S/N 65715) was used for salinity/conductivity measurements. The salinity analyses were performed after samples had equilibrated to laboratory temperature, usually within 6 weeks after collection. The salinometer was standardized for each group of analyses using OSIL standard seawater, with frequent use of a secondary deep water standard to check for drift during runs.