<rahmann et al.
The analytical technique for measuring this tracer is similar to
that of the transient tracers CFC-12 and SFe. Both transient (ie.,
CFC-12 and SF6) and released (CF3SFs5) tracers were measured
an 9 of the SFB 754 cruises. The tracers were measured using
gas chromatograph/purge-and-trap techniques modified from
3ullister and Weiss (1988). The sampling for CF3SFs was focused
around the density where the tracer was released, whereas the
transient tracer sampling covered the whole depth of the CTDO
profiles. The sampling volume for transient tracers was around
200 ml, whereas the sampling volume for CF3SFs5 varied with
time after injections (i.e., based on the expected concentration
range) from 20 to 1000 ml.
Water Column Measurements of NO
ixtensive discrete sampling for measurements of NO was
carried out on seven cruises during the time span of
the SFB 754 (Tanhua and Mehrtens, 2021; see Table 2
and Supplementary Table 10). Samples were collected with
either the CTD/rosette or a pump-CTD system (see Löscher
zt al., 2012; Kock et al., 2016) and measured directly on
board or at the Chemical Oceanography department of
GEOMAR. Samples were analyzed by means of a headspace
equilibration method coupled to gas chromatography with
electron capture detection (for details, see Kock et al., 2016 and
references therein).
Dissolved Silicate, Nitrate, and Nitrite Isotopes
Seawater samples for stable isotopes measurements of dissolved
silicate (8°°Si), nitrate (5”NO37) and nitrite (8'°”NO27) were
collected from the CTD/rosette on a number of SFB 754 cruises
(Grasse et al., 2021; see Table 2 and Supplementary Table 11).
Samples for 850S;i were collected during M77/3, M77/4, M90,
and M93 and immediately acidified to pH 2 after filtration
(Ehlert et al., 2012; Grasse et al., 2013, 2016). Sample preparation
was in accordance the GEOTRACES’ protocol and samples for
5506; were measured at GEOMAR on a Nu Plasma MC-ICP-
MS (Nu Instruments !M, Wrexham, United Kingdom). 8SPNO3
and 8”NO;- samples were collected during M77/3, M77/4, M90,
M92, and M93. Samples containing nitrite concentrations below
0.1 wmol/l were acidified with 25% HCI (pH 1-2), otherwise
samples were kept frozen until analysis (Altabet et al., 2012;
Zyabenko et al., 2012; Bourbonnais et al., 2015; Hu et al., 2016).
The isotopic composition of both N-species was measured using
the Cd reduction/azide method (MelIlvin and Altabet, 2005).
Radiogenic Isotopes
Seawater samples for Rare Earth Element (REE) concentrations
and neodymium (Nd) isotopes were collected during M77/3
and M77/4 off Peru (Grasse et al., 2012) and during M90
in the Panama Basin (Grasse et al., 2017, 2021; see Table 2
and Supplementary Table 12). Samples were collected with the
CTD/rosette and filtered through 0.45 (m nitrocellulose acetate
filters (Millipores) shortly after sampling. For analysis of Nd
isotopes 20 1 of seawater were collected for each sample and
treated following GEOTRACES protocol (van de Flierdt et al.,
"https://www.geotraces.org
-rontiers in Marine Science | www. frontiersin.orm
SFB754 Data Legacy
SFB 754 cruises 2008-2011
Nr“ "m
— — M77M |
„M77/2
——_M77B
—— M7714 |
D°
r
6°S5
12°8
18°5 -
ws} a a
90°W 85°W 80°W "— 75 70°W 65°W
FIGURE 5 | Cruise tracks of four SFB 754 cruises in the Pacific in the first
fundina period of the project (2008-201 1}
2012). Nd isotope measurements were carried out on a Nu plasma
MC-ICPMS as well as on a Thermo Scientific TIMS TRITON.
The concentrations of dissolved REEs in seawater were measured
with a SeaFAST online preconcentration system (Elemental
Scientific Inc.) connected to an Agilent 7500ce quadrupole ICP-
MS at GEOMAR (Hathorne et al., 2012).
Underway Trace Gas Measurements
Continuous measurements of the climate-relevant trace
gases carbon dioxide (CO„2), nitrous oxide (N,O), and
carbon monoxide (CO) in the surface ocean and overlying
atmosphere were conducted during 9 SFB 754 cruises
(Arevalo-Martinez and Mehrtens, 2021; see Table 2
and Supplementary Table 13) spanning the North,
South, and equatorial Atlantic, as well as the South and
2quatorial Pacific. Trace gases were analyzed by laser
spectroscopy-based gas analyzers coupled to air-water
equilibration chambers as described in Arevalo-Martinez
st al. (2013) and Arevalo-Martinez et al. (2019). All trace
gas measurements were quality-controlled to achieve the
international standards for marine CO,» (Bender et al.,
2002), N;O (Bange et al., 2019), and atmospheric CO
(Zellweger et al., 2019; to date there is no accepted
standard for seawater measurements). The final quality-
controlled data are available through the Surface Ocean CO2
Atlas (SOCAT®°) and the MarinE MethanE and NiTrous
A SAT ANfAL
Zentember 2021 | Volume 8 | Article 722R0-
