Dataset: ProteOMZ nutrient, CTD, and oxygen data
Deployment: FK160115

Nutrient samples were filtered through 0.2 micron Supor filters and frozen in acid-washed 60-mL high-density polyethylene bottles until analysis. The frozen samples were thawed in a warm water bath and stored in the dark for 20– 24 h prior to analyses. This protocol has been found to increase the recovery efficiency of silicic acid in frozen samples and has no observed adverse effects on the other nutrients. Immediately before analysis, aliquots of the samples were transferred to 15-mL polypropylene cups and an Alpkem autosampler. Technicon AutoAnalyzer IITM components were used to measure phosphate and ammonium; and Alpkem rapid flow analyzer (RFA) 300TM components were used for silicic acid, nitrate + nitrite, and nitrite. All five of the macronutrients were analyzed simultaneously. The nutrient methods were essentially those employed by the Oregon State University lab during the World Ocean Circulation Experiment and Southern Ocean Joint Global Ocean Flux Study (JGOFS) cruises. The phosphate method was a modification of the molybdenum blue procedure of Bernhardt and Wilhelms (1967), in which phosphate was determined as reduced phosphomolybdic acid employing hydrazine as the reductant. The nitrate + nitrite analysis used the basic method of Armstrong et al. (1967). Sulfanilamide and N-(1-napthyl) ethylenediamine dihydrochloride react with nitrite to form a colored diazo compound. For the nitrate + nitrite analysis, nitrate is first reduced to nitrite using an open tubular cadmium reductor and imidazole buffer as described by Patton (1983). Nitrite analysis was performed on a separate channel, omitting the cadmium reductor and the buffer. The determination of silicic acid was based on that of Armstrong et al. (1967) as adapted by Atlas et al. (1971). Addition of an acidic molybdate reagent forms silicomolybdic acid, which is then reduced by stannous chloride. An indophenol blue ammonium method was modified from Alpkem RFA methodology, which references Methods for Chemical Analysis of Water and Wastes, March 1984, EPA-600/4-79-020, ‘‘Nitrogen Ammonia,’’ Method 350.1 (Colorimetric, Automated Phenate). A detailed description of the continuous segmented flow procedures used can be found in Gordon et al. (1994).

Data were collected using the Trace Metal Rosette (TMR, Sea-Bird SEACAT 19+), equipped standard conductivity, temperature and pressure sensors, as well as an added optional SBE 43 dissolved oxygen sensor. All four sensors were factory refurbished/calibrated immediately prior to the expedition in November of 2015 by Sea-Bird Electronics (Bellevue WA). 

R/V Falkor CTD data are described at the R2R repository: http://www.rvdata.us/catalog/FK160115