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SFB754 Data Legacy 
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FIGURE 1 | The two working areas of the SFB 754 overlaid on the climatological content of dissolved oxygen on the potential density surface sigmag 26.9 (between 
200 and 500 m depth in tropical regions). The map is based on data from the World Ocean Atlas 2018 (Garcia et al., 2018}. 
Conductivity-Temperature-Depth-Oxygen (CTDO) 
Measurements 
Conductivity-temperature-depth-oxygen (CTDO) 
measurements were acquired on 32 of the major research 
cruises performed as part of the SFB 754 or other collaborative 
or complementary projects (Krahmann and Mehrtens, 2021c; 
see Table 2 and Supplementary Table 1). Seabird 911plus 
systems equipped with dual temperature-conductivity-oxygen 
sensors were employed. All systems had a 24-bottle water 
sampling rosette with 10 1 Niskin bottles. On some cruises only 
22 bottles were mounted to accommodate a lowered Acoustic 
Doppler Current Profiler for deep ocean current observations. 
Water sampling, processing, and calibration followed GO- 
SHIP recommendations (McTaggart et al., 2010; Swift, 2010; 
Jchida 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, as well as Derivation of Calculated 
Properties, After these steps, conductivity and oxygen readings 
were calibrated against values determined with salinometry (see 
section “Salinometry”) and Winkler titration [see section 
“Discrete Oxygen Measurements (Winkler Titration)”], 
respectively. Finally, the downcast data were averaged over 
1 dbar wide intervals. An independent upcast calibration was 
used to obtain calibrated CTDO values coincident with the 
discrete water samples. These values entered the bottle file 
described in section “Chemical Oceanography.” 
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 
-rontiers in Marine Science | www.frontiersin.orc 
cruises or casts, depending on the availability of the sensors and 
‘heir pressure ratings. SUNA data were processed following the 
procedures outlined in Sakamoto et al. (2009) and Sakamoto et al. 
(2017) and calibrated against Nitrate measurements from discrete 
bottle samples (see section “Nutrient Measurements”). To CHL- 
a and CDOM fluorescence, turbidity, transmissometer beam 
attenuation, and PAR data only the manufacturer’s calibrations 
were applied in the published data sets. Details about the sensors 
used on each cruise can be found in the respective cruise 
reports (see Table 1). 
Lowered Acoustic Doppler Current Profiler (LADCP) 
Measurements 
Lowered acoustic doppler «current profiler (LADCP) 
measurements were performed on all research cruises that 
concentrated on open ocean areas (Krahmann and Mehrtens, 
2021d; see Table 2 and Supplementary Table 2) while on 
cruises that worked mostly in shallow waters, ocean current 
measurements by the shipboard ADCP [see section “Shipboard 
Acoustic Doppler Current Profiler (SADCP) Measurements”] 
were deemed suflicient. GEOMAR used a two-instrument 
LADCP configuration with two Teledyne RDI 300 kHz 
workhorse ADCPs mounted in down- and up-looking positions. 
Data collection and processing was performed according to 
recommendations in the GO-SHIP best practices manual 
(Thurnherr et al., 2010). 
Moored Instrument Measurements 
Almost all long-term moored observations of the SFB 754 were 
conducted in the tropical Atlantic between the equator and 18° 
N, except for one mooring that was deployed in the tropical 
South Pacific (Hahn et al., 2021; see Table 2 and Supplementary 
Table 3). Moorings were typically equipped with instruments 
recording pressure, temperature, conductivity, dissolved oxygen, 
and current velocity. The moorings at 17.6° N, 24.2° W 
which have been deployed in the same location for several 
3eptember 2021 | Volume 8 | Article 72330«