<rahmann et al.
SFB754 Data Legacy
m
*300
6
IM
| 250 ®
w
fr
»"
200
150
100 '
50
ü
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«