Hydrographic Measurements

All CTD pressure, temperature, salinity, and oxygen values for the bottle data tabulations were obtained by averaging CTD data for a brief interval at the time the bottle was closed on the rosette. All reported CTD values were calibrated with reference to the International Temperature Scale of 1990 and processed with the methodology described in the documentation accompanying the final CTD data report for the TUNES-3 Expedition. The full cruise report, that includes details about processing the hydrographic data, and the final CTD data are available from the WOCE Hydrographic Program Office (WHPO) or the WHP Special Analysis Center (SAC).

Salinity samples were drawn into 200-mL Kimax high-alumina borosilicate glass bottles with custom-made plastic insert thimbles and Nalgene screw caps which provided low container dissolution and sample evaporation. These bottles were rinsed three times before filling, and measurements were usually made within 8-36 h after collection. Salinity was determined on the basis of electrical conductivity measured by an SIO Oceanographic Data Facility (ODF)-modified Guildline Autosal Model 8400A salinometer, and the values were obtained according to the equations of the Practical Salinity Scale of 1978 (UNESCO 1981).

Water samples for oxygen analyses were collected shortly after the rosette sampler was brought on board and after the samples for CFCs and 3H were drawn. Sampling flasks (100-125 mL), calibrated before the expedition, were carefully rinsed, and then filled using a drawing tube after allowing to overflow for at least two flask volumes. Reagents were added to fix the oxygen before sealing the flasks with stoppers. The flasks were shaken immediately after being sealed, and again after 20 min to ensure thorough dispersion of the manganous hydroxide [Mn(OH)2] precipitate. The oxygen concentration in these solutions was determined within 4-36 h using the Winkler titration methods of Carpenter (1965) with modifications by Culberson and Williams (1991). The titrator was calibrated with 0.01 N potassium iodate standard solutions prepared using preweighed potassium iodate crystals. Oxygen concentrations were converted from milliliter per liter to micromoles per kilogram of seawater using the in situ temperature. A molar volume at STP of 22.3914 L/mol (Kester 1975) was used for this purpose.

Nutrient analyses were performed by analysts from OSU using a Technicon AutoAnalyzer II. The AutoAnalyzer used was provided by the ODF of SIO. A data acquisition system and the software used to process the nutrient data were developed and supplied by OSU. The chemical methods used on Leg 3 of the TUNES Expedition were essentially and deliberately the same as those used on the first two legs. All of the reagent and standard materials were provided by ODF of SIO. The methods used are described in Atlas et al. (1971) but with modifications in analytical protocols as employed by ODF.


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