Water temperature, salinity, oxygen, silicate, nitrate, and other physical and hydrochemical parameters taken by CTD and Niskin bottle samples from research vessels L'Atalante, Meteor, Maria S. Merian, and Islandia in the Atlantic and Pacific Oceans from 2007-01-20 to 2017-05-06 (NCEI Accession 0206154)

This dataset contains hydrochemistry (nutrient concentrations (silicate, nitrate, nitrite, ammonium, phosphate), dissolved and particulate organic nutrients, stable isotope tracers, N2= concentration, and others) as well as physical parameters (water temperature, salinity, density, oxygen concentrations, and others) taken by CTD and Niskin bottle samples in the Atlantic and Pacific Oceans. It combines 25 cruises on research vessels L'Atalante, Meteor, Maria S. Merian, and Islandia as part of the Collaborative Research Centre SFB 754 (Climate - Biogeochemistry Interactions in the Tropical Ocean). Nitrogen, in the form of nitrate and ammonia, is supposed to be the major limiting factor in these oligotrophic areas. There is an increasing biogeochemical evidence that nitrogen fixation by marine diazotrophs contributes significantly to new production. Experimental, small-volume incubations of near-surface seawater were used to investigate rates and controls of nitrogen fixation by the plankton community. This work included sampling for metagenomic characterization of the microbial community, especially new phylotypes of the nifH gene. CTD measurements were taken at each station. They were equipped with dual temperature-conductivity-oxygen sensors and 24-bottle water sampling rosette with 10 liter Niskin bottles. Water sampling, processing, and calibration followed GO-SHIP recommendations (Swift, 2010; McTaggart et al., 2010; Uchida et al., 2010) and included the recommended steps Data Conversion, Sensor Time-Alignment, Creation of Bottle Files, Outlier Removal, Pressure Sensor Filtering, Conductivity Cell Thermal Mass Correction, Ship Roll Correction and Deck Offset Correction by Loop Editing, and Derivation of Calculated Properties. After these steps conductivity and oxygen readings were calibrated against values determined with salinometry and Winkler titration, respectively. Finally, the downcast data were averaged over 1 dbar wide intervals. In addition to the CTDO measurements basically all CTDO casts included either a Dr. Haardt or a Wetlabs FLNTU fluorometer for CHL-a fluorescence. Several other sensors, such as a Wetlabs CDOM fluorometer and turbidity sensor, a Wetlabs C-Star transmissometer, a Photosynthetically Active Radiation (PAR) sensor manufactured by Biospherical Instruments, or a Seabird/Satlantic Submersible Ultraviolet Nitrate Analyzer (SUNA) have been attached to the CTDO system on some of the cruises or casts, depending on the availability of the sensors and their depth ratings. SUNA data were processed and calibrated following the procedures outlined in Sakamoto et al. (2009) and Sakamoto et al. (2017). To CHL-a and CDOM fluorescence, turbidity, transmissometer beam attenuation, and PAR data generally only the manufacturer’s calibration was applied in the stored files. Lastly, a purposeful tracer release was conducted on several cruises, where about 100kg of a chemically inert and nontoxic substance (SF5CF3 for short SF5 in the following text) was injected and tracer surveys are planned 6, 18, and 30 months after injection. This method allows very accurate estimations of the mixing, which can be used to improve and calibrate mixing parameterizations in numerical ocean models. A regional survey of the oxygen minimum zone in the vicinity of the tracer release site in an east-west direction was conducted. See pangea_flags.pdf for data flag description. Data are in ASCII format.