Carbonyl sulfide (OCS) and carbon disulfide (CS2) are
volatile sulfur gases that are naturally formed in seawater and exchanged
with the atmosphere. OCS is the most abundant sulfur gas in the atmosphere,
and CS2 is its most important precursor. They have attracted increased interest due
to their direct (OCS) or indirect (CS2 via oxidation to OCS)
contribution to the stratospheric sulfate aerosol layer. Furthermore, OCS
serves as a proxy to constrain terrestrial CO2 uptake by vegetation.
Oceanic emissions of both gases contribute a major part to their atmospheric
concentration. Here we present a database of previously published and
unpublished (mainly shipborne) measurements in seawater and the marine
boundary layer for both gases, available at 10.1594/PANGAEA.905430 (Lennartz et
al., 2019). The database contains original measurements as well as data
digitalized from figures in publications from 42 measurement campaigns, i.e.,
cruises or time series stations, ranging from 1982 to 2019. OCS data cover
all ocean basins except for the Arctic Ocean, as well as all months of the
year, while the CS2 dataset shows large gaps in spatial and temporal
coverage. Concentrations are consistent across different sampling and
analysis techniques for OCS. The database is intended to support the
identification of global spatial and temporal patterns and to facilitate the
evaluation of model simulations.
Introduction
Carbonyl sulfide (OCS) is the most abundant sulfur gas in the atmosphere
with a tropospheric mixing ratio around 500 ppt (Kremser et al., 2016).
Carbon disulfide (CS2) is a short-lived sulfur gas, which is oxidized
within hours to days. Because OCS is a major product of this oxidation, with
a yield of 82 % (i.e., 82 molecules of OCS produced from 100 CS2
molecules), CS2 oxidation is a major source of OCS in the atmosphere.
Atmospheric mixing ratios of OCS show larger annual than interannual
variations (Montzka et al., 2007). Small negative trends
between 10 % and 16 % decrease, derived from firn air and flask measurements, have
been reported for the 1980 to 2000 period (Montzka et al., 2004).
Since 2001, small positive trends <10 % per decade were derived
from OCS observations in the Southern Hemisphere (Kremser et al.,
2015).
Due to its long tropospheric lifetime of 2–7 years, OCS is entrained into
the stratosphere. In volcanically quiescent periods, OCS (and indirectly
CS2) is thought to be a major contributor to stratospheric sulfate
aerosols that influence the radiative budget of the Earth (Crutzen, 1976;
Brühl et al., 2012). In addition, OCS can be used as a proxy to quantify
the CO2 uptake of plants (gross primary production), which is a major
source of uncertainty in climate modeling (Whelan et al., 2018). Both
scientific interests benefit from a well-constrained atmospheric budget. OCS
and CS2 are produced naturally in the ocean, and their oceanic
emissions contribute substantially to their atmospheric concentrations
(Chin and Davis, 1993; Watts, 2000; Kremser et al., 2015).
Oceanic source estimates of OCS and its precursor CS2 still contain
large uncertainties (Kremser et al., 2016; Whelan et al., 2018). Current
efforts to model surface concentrations of OCS in seawater diverge in their
results (Launois et al., 2015; Lennartz et al., 2017). Most measurements
of oceanic OCS and CS2 were performed in the 1980s and 1990s, and data
are often not available or stored inaccessibly, hampering model
evaluation or analysis of global spatial and temporal concentration
patterns. Therefore, a combined database for marine measurements of OCS and
CS2 has been given high priority in a recent review on using OCS as a
tracer for gross primary production (Whelan et al., 2018). Here, we aim to
provide such a comprehensive database by compiling previously reported, as
well as unpublished data, from corresponding authors of the original studies
or via digitalization from pdf documents.
Both OCS and CS2 show a pronounced variability in seawater, which
implies a need for highly resolved observations. Therefore, we pay special
attention to the temporal resolution of measurements in the database. The
seasonal variability is a direct result of the marine cycling of both gases.
Photochemical reactions involving chromophoric dissolved organic matter
(CDOM) lead to the formation of OCS, as does a light-independent production
pathway (Ferek and Andreae, 1984; Weiss et al., 1995a; Von Hobe et al.,
2001). OCS is efficiently hydrolyzed in seawater. The temperature dependence
of the hydrolysis reaction leads to high degradation rates in warm waters
(Elliott et al., 1989; Radford-Knoery and Cutter, 1994; Kamyshny et al.,
2003). The efficient photochemical production and fast
degradation in warm waters result in strong diurnal and seasonal cycles of
OCS in the surface ocean (Kettle et al., 2001;
Ulshöfer et al., 1995). CS2 is photochemically produced in seawater
as well, but diurnal cycles are not as pronounced due to lower efficiency of
the sink processes. Concentrations of CS2 and OCS in seawater differ
strongly depending on the time of day and season measured. To facilitate
interpretation of concentration measurements on larger scales in relation to
the processes described above, ancillary data coinciding with trace gas
measurements are also reported if available, such as meteorological or
physical seawater properties. The database is described with respect to
number of data, range, and patterns of concentrations; analytical methods;
temporal and spatial coverage; and sampling frequency for each dataset.
MethodsData collection
Data were obtained either from authors of previous studies directly or
digitalized with a web-based digitalization tool from pdf documents. Web of
Science was searched for the key words “carbonyl sulfide” (both sulfide and
sulphide), “carbon disulfide” (both sulfide and sulphide) in connection with
“ocean” or “seawater”. When data could not be obtained directly from
authors, relevant figures were identified and digitalized with the
WebPlotDigitizer Automeris (https://apps.automeris.io/wpd/, last access:
January 2019). When digitalizing the data from documents, concentration data
were rounded to the integer to account for uncertainty in the digitalization
method introduced, e.g., by misalignment of the axes in case of old scanned
pdf documents. Here we include only shipborne measurements or observations
from stations with a marine signal (i.e., research platforms in the North Sea,
ID15; on Amsterdam Island, ID6; and in Bermuda, ID39). For atmospheric OCS data from
aircraft campaigns or continental time series stations, i.e.,
HIAPER-Pole-to-Pole-Observations (HIPPO, Montzka, 2013),
Atmospheric Tomography Mission (ATom, Wofsy et al., 2018), and the
NOAA time series stations from the Earth System Research Laboratory –
Global Monitoring Division (NOAA-ESRL, Montzka, 2004, Montzka et al., 2007), we refer to the respective
repositories accessible online (HIPPO:
https://www.eol.ucar.edu/field_projects/hippo, last access: 1 August 2019; ATom:
https://espo.nasa.gov /atom/content/ATom, last access: 1 August 2019; NOAA-ESRL:
https://www.esrl.noaa.gov/gmd/, last access: 1 August 2019).
Concentration data were converted to the unit picomole OCS/CS2 L-1, accounting for molar masses of sulfur (32.1 g), OCS (60 g), and
CS2 (76.1 g). Data were collected together with the following metadata
(if reported in the original publication or otherwise available):
latitude of measurement;
longitude of measurement;
date, including year, month, day, hour, and minute;
name of the cruise and/or ship;
contributor;
main reference for data;
method description;
main reference for method;
sample depth;
any ancillary data (meteorological, physical, biological data);
flag describing the sampling resolution (see Table 1).
It should be noted that several commonly used materials, such as any
rubber parts, may lead to contaminations when measuring OCS and CS2. A
non-exhaustive list of problematic materials is available here:
http://www.cosanova.org/materials-to-avoid.html (last access: February 2019).
We paid attention to the method description of each dataset, and data were
only included when blank measurements are reported or the description of the
material was provided (e.g., Teflon used). An overview of the dataset is
provided in Table 2 (methods) and Table 3 (sampling details). A filling value
of -999 was introduced for concentrations below the respective detection
limit of each individual dataset. Missing additional data (physicochemical
parameters, meteorological parameters, etc.) was filled with NaN (not a
number) to facilitate readability in data handling software. The database
can be accessed at the data repository PANGAEA (10.1594/PANGAEA.905430, Lennartz et
al., 2019). Available additional data are listed in Table 4.
Flags used to describe sampling frequency of each individual
dataset.
0not reported1min215 min3hourly41–4 hourly5>4 hourly to daily6monthly7seasonally8annually9irregularTrace gas analysisCarbonyl sulfide in seawater
Carbonyl sulfide (OCS) concentrations in seawater were commonly measured
with a method to separate gaseous OCS from the seawater connected to a
detection system. Two main principles were applied to separate OCS from
seawater: (1) purging the water sample with an OCS-free gas to transfer the
total dissolved OCS into the gas phase or (2) using an equilibrator, where a
gas phase is brought into equilibrium with the seawater sample. The OCS
concentration in water is then calculated using Henry's law and the
temperature during the equilibration process. Sampling using method 1 is
usually performed discretely and has sometimes been replaced by method 2
with automated (semi)continuous sampling with a sampling resolution of
<15 min since 2015 (Ulshöfer et al., 1995; Von Hobe et
al., 2008; Lennartz et al., 2017). OCS detection in discrete samples used
gas chromatography (GC). Most GCs were then coupled to a flame photometric
detector (GC-FPD) or, less frequently, to an electron capture detector
(GC-ECD). Commonly, samples were cryogenically pre-concentrated (e.g., with
liquid N2) prior to injection into the GC. A new technique using
off-axis integrated cavity output spectroscopy (OA-ICOS) has only recently
been developed to continuously measure dissolved OCS in seawater with the
use of an equilibrator (Lennartz et al.,
2017).
For the majority of the samples in the database, the precision was reported
to be better than 10 %, and the limit of detection are around 2 pmol L-1 (see Table 2 for details on individual datasets). The instability of
OCS in water makes the comparison with liquid standards difficult, which is
why most of the studies used permeation tubes to calibrate their
instruments. Unfortunately, no intercalibration between cruises is reported
(see Sect. 3.1 for a discussion of quality control of the data).
Description of all cruises or campaigns contributing measurements
to this database. Cruises are given a unique ID for identification.
Reference refers to the publication where the data were reported first.
Methods are reported using the same specifications and level of detail as
given in the original publication. Specifications for analytical methods are
listed together with the method referenced in the main reference: di (or)
stands for digitalized (original) data, S stands for sampling, An stands for analysis,
Det stands for details, and R stands for reference of instrumentation. Letters in the last column
indicate direct comparability of the datasets, as studies were performed
with either identical analytical systems (i.e., same method reference) or
performed by the same laboratory through further development of analytical
systems (i.e., different method reference) but intercomparison within
laboratory.
IDCampaign, ship, date, regionReferenceMethodData sourceGrouping1RV Robert Conrad June 1982 ETSPFerek and Andreae (1983)OCS S: gas bubbler in glass column An: GC-FPD Det: precision <10 %, st. dev. of triplicates 6 % R: Ferek and Andreae (1983),diA2RV Cape Hatteras April 1983 Chesapeake BayFerek and Andreae (1984)OCS S: gas bubbler in glass column An: GC-FPD R: Ferek and Andreae (1983)diA3RV Discoverer March–June 1982 PacificJohnson and Harrison (1986)OCS S: glass syringes and bucket An: GC-FPD Det: standard from permeation tubes, l.o.d. 0.04 ngS, reproducibility within 2.5 %, not georeferenced R: Johnson (1985)diB4RV Discoverer March–June 1983 PacificJohnson and Harrison (1986)OCS S: glass syringes and bucket An: GC-FPD Det: standard from permeation tubes, l.o.d. 0.04 ngS, reproducibility within 2.5 %, not georeferenced R: Johnson (1985)diB5RV Columbus Iselin April–May 1986 AtlanticKim and Andreae (1992)CS2 S: purged with N2 An: GC-FPD Det: liquid CS2 standard cross checked with gas standard Metronic Associates Inc.(Santa Clara, CA), precision 9 %, l.o.d. 2 pmol S L-1 R: Kim and Andreae (1987)diC6Coastal 1987–1888 Amsterdam Island, Indian OceanMihalopoulos et al. (1991)OCS S: pressurized electropolished stainless steel canisters An:GC-FPD/FPD Det: gas standard Matheson Union Carbide, l.o.d. 0.4 ng OCS =53 ppt, reproducibility <5 % (8 repeats), accuracy 10 %, not fully georeferenced R: Belviso et al. (1987)diD7RV Polarstern 1988 Atlantic, Southern OceanStaubes et al. (1990)OCS, CS2 S: purged with N2 An: GC-FPD Det: l.o.d. 3–4 pptv and 0.5–1 ngS L-1, not georeferenced R: Staubes et al. (1990)diE8RV Cape Hatteras April 1989 North AtlanticRadford-Knoery and Cutter (1994)OCS S: sampling with Go-Flo bottles, acidified, stripped with He An: GC-FPD Det: l.o.d. 1.3 pmol L-1, precision 5 % R: Cutter and Radford-Knoery (1993)diF9RV Cape Hatteras November 1989 Estuary, North AtlanticRadford-Knoery and Cutter (1994)OCS S: sampling with Go-Flo bottles, acidified, stripped with He An: GC-FPD Det: l.o.d. 1.3 pmol L-1, precision 5 % R: Cutter and Radford-Knoery (1993)diF
Continued.
IDCampaign, ship, date, regionReferenceMethodData sourceGrouping10RV Cape Henlopen June 1990 North AtlanticCutter and Radford-Knoery (1993)OCS S: Go-Flo bottles, gas-tight syringes, stripped with He An: GC-FPD Det: l.o.d. 1,3 pmol L-1, precision 5 %, R: Cutter and Radford-Knoery (1993)diF11RV Polarstern November 1990 Southern OceanStaubes and Georgii (1993)OCS S: air – directly to sample loop, water – into gas stripping column with N2 An: GC-FPD Det: l.o.d. 3.5 ppt, 6.4 % precision R: Staubes et al. (1989)diE12OCEAT II+III, diverse 1987–1991 Mediterranean Sea, Red Sea, Indian OceanMihalopoulos et al. (1992)OCS S: pressurized electropolished stainless steel canisters An: GC-FPD Det: lod: 0.4 ng S, precision 10 %, not georeferenced R: Mihalopoulos et al. (1992)diD13Chesapeake Bay time series 1991–1994 Chesapeake BayZhang et al. (1998)OCS S: depth profiles with pump, Go-Flo, cubitainer, stripped with He An: GC-FPD C: standard permeation tubes, precision <5 %, l.o.d. 10 pmol OCS L-1 R: Cutter and Radford-Knoery (1993)diiF14RV Meteor – M21 April 1992 North Atlantic, North SeaUlshöfer et al. (1995)OCS S: equilibrator An: GC-FPD Det: standard permeation tubes, l.o.d. OCS: 100 ppt, reproducibility 15 % R: Uher (1994)orG15FP Nordsee September 1992 North SeaUher and Andreae (1997)OCS S: equilibrator An: GC-FPD Det: standard permeation tubes, l.o.d. 100 pg OCS =105 ppt, precision <15 % R: Ulshöfer et al. (1995), Uher (1994)orG16RV Aegaio, EGAMES July 1993 Mediterranean SeaUlshöfer et al. (1996)OCS S: equilibrator An: GC-FPD Det: standard permeation tubes, detection limit OCS: 4 pmol L-1, precision 15 % R: Uher (1994)orG17RV Surveyor November 1993 PacificWeiss et al. (1995b)OCS S: glass syringe, purge-and-trap An: GC-ECD Det: standard permeation tubes, l.o.d. 115 ppt cruise1, 23 ppt cruise 2, uncertainty 6 %–10 %, reproducibility of blanks 7 % R: Weiss et al. (1995a)diB18RV Meteor – M27 January 1994 North Atlantic, North SeaUlshöfer et al. (1995)OCS S: equilibrator An: GC-FPD Det: standard permeation tubes, l.o.d. OCS: 100 ppt, reproducibility 10 % R: Uher (1994)orG
Continued.
IDCampaign, ship, date, regionReferenceMethodData sourceGrouping19RV Valdivia April 1994 North SeaUlshöfer and Andreae (1998)OCS S: Weiss-type equilibrator An: GC-FPD Det: standard from permeation tubes, precision <10 % R: Ulshöfer et al. (1995), Uher (1994)orG20RV Columbus Iselin August 1994 North Atlantic (Florida)Ulshöfer and Andreae (1998)OCS S: Weiss-type equilibrator An: GC-FPD Det: standard from permeation tubes, precision <10 % R: Ulshöfer et al. (1995), Uher (1994)orG21RV Meteor – M30 September 1994 North Atlantic, North SeaUlshöfer et al. (1995)OCS S: equilibrator An: GC-FPD Det: standard permeation tubes, l.o.d. 100 ppt, reproducibility <10 % R: Ulshöfer et al. (1995)orG22RV Cape Hatteras March 1995 North Atlantic, BermudaUlshöfer and Andreae (1998)OCS S: Weiss-type equilibrator An: GC-FPD Det: standard from permeation tubes, precision <10 % R: Ulshöfer et al. (1995)orG23RV Hudson July 1995 Atlantic, PacificXie and Moore (1999)CS2 S: bucket and submersible pump An: GC-MS Det: gravimetrically prepared liquid standard, l.o.d. CS2 1.5 pmol L-1 S, rel.st.dev. 1.4 % at 10 pmol L-1 level R: Moore and Webb (1996)orH24RV Discoverer October 1995 Atlantic, PacificXie and Moore (1999)CS2 S: stainless steel Knudsen bottles An: GC-MS Det: gravimetrically prepared liquid standard, l.o.d. CS2 1.5 pmol L-1 S, rel.st.dev. 1.4 % at 10 pmol L-1 level R: Moore and Webb (1996)orH25RV Shirase November 1996 Indian Ocean, Southern OceanInomata et al. (2006)OCS S: PTFE-tubing, Flek-sampler An: GC-FPD Det: standard gas (Nippon Sanso Co. Ltd.), l.o.d. 0.06 nmol L-1/12 ppt, uncertainty 6 % R: Inomata et al. (1999)diI26RV Prof. Vodyanitsky, ACE-2 June 1997 North AtlanticVon Hobe et al. (1999)OCS S: Weiss-equilibrator An: GC-FPD, Det: standard permeation tubes, l.o.d. 30 ppt/0.4 pmol L-1, precision <10 % R: Von Hobe et al. (1999)orG27KH97-2 July 1997 North PacificAranami (2004)OCS, CS2 S: Tedlar-bags An: GC-FPD Det: gas cylinder standard Takachiho Kogyo Co. Ltd., precision 5 % R: Aranami (2004)orJ28RV Polarstern ANTXV-1 November 1997 Atlantic transectXu et al. (2001)OCS, CS2 S: equilibrator An: GC-FPD Det: standard permeation tubes, precision 3 %, uncertainty 10 % R: Xu et al. (2001)orK
Continued.
IDCampaign, ship, date, regionReferenceMethodData sourceGrouping29RV Polarstern ANTXV-5 May 1998 Atlantic transectXu et al. (2001)OCS, CS2 S: Teflon-equilibrator An: GC-FPD Det: standard permeation tubes, precision 3 %, uncertainty 10 % R: Xu et al. (2001)orK30RV Mirai MR98-K01 November 1998 North PacificAranami (2004)OCS, CS2 S: air – Tedlar bags, seawater – plastic bucket, glass syringe An: GC-FPD Det: gas cylinder standard Takachiho Kogyo Co. Ltd., precision 5 % R: Aranami (2004)orJ31RV Endeavor 327 April 1999 North Atlantic, BATSVon Hobe et al. (2001)OCS S:equilibrator An: GC-FPD Det: precision <2 %, standard from permeation tubes, lod: 30 ppt/0.4 pmol OCS R: von Hobe et al. (2000)orG32BATS August 1999 North Atlantic, BATSCutter et al. (2004)OCS S: Go-Flo bottles, submersible pumping system An: GC-FPD Det: l.o.d. 1 pmol L-1, precision <10 % R: Radford-Knoery and Cutter (1994)orF33RV James Clark Ross, AMT-7 September 1999 AtlanticKettle et al. (2001)OCS, CS2 S: equilibrator An: GC-FPD C: permeation tubes R: Ulshöfer et al. (1995)diG34RV Poseidon P269 February 2001 Atlantic Oceanpartially published in Von Hobe et al. (2008)OCS, CS2 S: equilibrator An: GC-FPD Det: precision 1.9 % for COS and 2.2 % for CS2, standard from permeation tubes, lod: 20 ppt/0.3 pmol OCS and 10 ppt CS2 R: Von Hobe et al. (2008)orG35RV Sonne, SHIVA November 2011 Pacific, Indian OceanunpublishedOCS S: gas canister An: GC-MS Det: referenced to NOAA standard, precision 1 %, calibration accuracy 10 % R: de Gouw et al. (2009)orL36RV Sonne, SPACES-OASIS July 2014 Indian OceanLennartz et al. (2017)OCS S: equilibrator An: OA-ICOS Det: standard permeation tubes, 15 ppt precision, l.o.d. 4 pmol L-1=∼200 ppt, standard within 2 % of NOAA scale R: Lennartz et al. (2017)orM37RV Atlantic Explorer September 2014 North Atlantic, BATSBerkelhammer et al. (2016)OCS S: air via tube to instrument An: OA-ICOS Det: referenced against NOAA standard, std. dev. 12.7 ppt R: Berkelhammer et al. (2016)orN
Continued.
IDCampaign, ship, date, regionReferenceMethodData sourceGrouping38RV Hesperides, TransPEGASO October 2014 AtlanticLennartz et al. (2017)OCS, CS2 S: glass bottles An: GC-MS Det standard gas (OCS), liquid (CS2), l.o.d. OCS: 1.8 pmol L-1, CS2: 1.4 pmol L-1, precision ∼5 % R: Lennartz et al. (2017)orO39Tudor Hill Observatory December 2014–March 2015 BermudaBerkelhammer et al. (2016)OCS S: air via tube to instrument An: OA-ICOS Det: referenced against NOAA standard, std. dev. 12.7 ppt R: Berkelhammer et al. (2016)orN40RV Sonne, ASTRA-OMZ August 2015 ETSPLennartz et al. (2017)OCS, CS2 S: OCS: equilibrator, CS2: Niskin bottles An: OCS: OA-ICOS, CS2: GC-MS Det: OCS standard permeation tubes, 15ppt precision, l.o.d. 4 pmol L-1=∼200 ppt, standard within 2 % of NOAA scale, CS2: l.o.d. 1 pmol L-1, precision 5 %–10 % R: Lennartz et al. (2017)orM41RV Tangaroa February–March 2018 Southern OceanunpublishedOCS S: equilibrator An: OA-ICOS Det: standard permeation tubes, 15 ppt precision, l.o.d. 4 pmol L-1=∼200 ppt R: Lennartz et al. (2017)orM42RV Xue Long November 2018–March 2019 Pacific, Southern OceanunpublishedOCS S: Spray-head equilibrator An: OA-ICOS Det: standard permeation tubes, accuracy <18 %, l.o.d. 4 pmol L-1 R: Lennartz et al. (2017)orMCarbonyl sulfide in the marine boundary layer
Quantifying the OCS concentration in the sampled gas is performed in a
similar way with the same analytical systems, as described in Sect. 2.2.1
for dissolved concentration measurements. The database consists mainly of
shipborne measurements but includes measurements from two land-based
stations with strong marine influence. These two datasets are (1) ID6 from
Amsterdam Island in the Southern Ocean and (2) ID39 from Tudor Hill,
Bermuda.
The majority of studies used a GC-FPD system; GC-ECD and OA-ICOS were less
frequently used. Detection limits and precision were comparable or identical
to seawater measurements described in the previous section. Details on each
individual method are listed in Table 2. Quantification was achieved with
standards produced from permeation tubes and from gas cylinders from various
manufacturers (see Table 2 for specifications of individual studies). No
intercalibration for the complete database is available.
Carbon disulfide in seawater
Sampling of carbon disulfide (CS2) was performed discretely from both
continuously pumped water and containers such as Niskin bottles.
Concentrations of CS2 were measured with a sampling frequency of up to
15 min. Most frequently, a GC-MS system was used; GC-FPD was less
common. Prior to the injection in the GC, samples were either purged with
CS2-free gas, and a cooled trap was used for preconcentration
(purge+trap system), or the gas and liquid phase were brought to
equilibrium with an equilibrator. Detection limits ranged down to 1 pmol L-1, and the precision was around 3 %–5 % (see Table 2 for specification
of the individual datasets). Standard measurements include permeation tubes
or liquid standards prepared in ethylene glycol, but no intercalibration
has been reported.
Carbon disulfide in the marine boundary layer
Samples were commonly taken discretely from the vessel's deck, directly into
air canisters, or sampled directly from air drawn with tubing into the
laboratory. Altitudes where samples were taken ranged from 10–25 m. The
detection of CS2 in the gas phase was similar to the analytical methods
described in the Sect. 2.2.3, without the step of purging the gas out of
the water. GC-MS or GC-FPD were used for detection. As described above,
detection limits range down to 1 ppt, and the precision is ∼3 %–5 % (see Table 2 for specification of the individual datasets). Standards
were either permeation tubes or gas cylinders, detailed in Table 2.
Description of dataset
All datasets included here provide some means of quality control, and
calibration procedures including primary gravimetric standards from
permeation tubes or by certified gas standards are described in the original
publications. However, the database compiled here includes measurements made
by different laboratories and thus different measurement systems. One
limitation of the database is the missing intercalibration across these
different measurement systems. Since many of these systems were built and
deployed in the 1990s and no longer exist, such an intercalibration is
not possible anymore. We strongly recommend undertaking efforts for
intercalibration across laboratories for future oceanic measurements of OCS
and CS2. Since no practical quality control is possible, we assess the
quality of the database by its internal consistency.
Carbonyl sulfide in seawater
Measurements of OCS in seawater were collected from 32 cruises, resulting in
7536 individual measurements (Fig. 1, Tables 2 and 3). OCS concentrations were
measured in the picomolar range in the surface and subsurface ocean, with a
mean concentration of 32.3 pmol L-1 (n=7536, Fig. 2a), ranging from
below the detection limit to 1466 pmol L-1 in the Rhode Island river
estuary.
Tracks of all cruises with OCS and/or CS2 measurements
included in the database (points depict stationary measurements). Labels
indicate the cruise ID (compare Table 1).
The majority of measurements were made in the Atlantic Ocean, with the least being taken from the
Indian Ocean. No measurements are available for the Arctic Sea. The sampling
was heavily biased towards surface ocean measurements shallower than 10 m
depths, and only a few measurements (<3 %) were obtained from
concentration profiles in the water column (144 measurements). The available
profiles range down to a water depth of 2000 m (Table 3). Reporting the
sampling depth is critical for photochemically produced substances such as
OCS and the penetration depths of UV light, and hence the photoproduction
varies spatially and temporally. Samples that were obtained from depths
shallower than 10 m are referred to as “surface samples”, and most of them were
obtained at a depth of 3–5 m. Maintaining a continuous water supply despite
water level changes by waves on a moving vessel is a challenge and currently
hinders continuous sampling at shallower depths. Profile measurements from
the North Atlantic indicated that differences in concentration within the
surface of the mixed layer <10 m are in a range of about 5 pmol L-1 (Cutter et al., 2004) but might potentially become
larger with surface stratification and high irradiation
(Fischer et al., 2019).
Quantitative sampling details for each individual dataset:
no. is the number of samples, depth and height are water depth below sea surface and
height above sea surface, t.r. is the flag for temporal resolution (see Table 1),
mbl is the marine boundary layer, and t.d. is the top deck (height not specified).
* Original paper in sampling frequency of seconds, averaged for this database.
OCS measurements were reported at 12 min to monthly resolution (Fig. 3e). Hence, the majority of the database has the required temporal
resolution to cover the full range of the diurnal variation, i.e., a
measurement interval of 4 h or less is needed to minimize averaging errors
due to interpolation.
Georeferenced data for (a) surface ocean OCS concentrations, (b) marine boundary layer OCS mixing ratios, (c) surface ocean CS2
concentrations, and (d) marine boundary layer CS2 mixing ratios. Only
surface data (shallower than 10 m) are shown.
Overview of the OCS datasets: Boxplots of concentrations per
latitudinal bin for (a) water and (b) marine boundary layer measurements. Blue
boxes show range of 25 and 75 percentile, horizontal bar indicates the
median, and red crosses show outliers. The seasonal variation averaged over
all years for (c) water and (d) marine boundary layer (note that in panel c
and d, red indicates Northern Hemisphere data, whereas light blue indicates
Southern Hemisphere data). Note that measurements >150 pmol L-1 were excluded from these statistics (i.e., coastal samples). Numbers
of days with observations for temporal resolution from minute-scale to annually
for (e) water and (f) marine boundary layer measurements. (Note that for the
boxplots in a and b, only completely georeferenced data were included).
NH stands for Northern Hemisphere, and SH stands for Southern Hemisphere.
Ancillary information available for the individual datasets.
Physicochemical and meteorological data (water temperature, salinity,
relative humidity, atmospheric pressure at sea level, wind speed, absolute
wind direction, dew point temperature, chlorophyll a concentration,
fluorescence, radiation, pH, and precipitation) are directly included in the
database. Availability of other trace gas measurements is indicated, but the
data are not included in the database (others, available upon request).
The global variability of the available measurements shows the lowest
concentrations in tropical and subtropical waters, especially compared to
concentrations at higher latitudes of the Southern Hemisphere (Fig. 3a). The
pattern of highest OCS concentrations in coastal and shelf regions has been
reported for individual datasets (Cutter and Radford-Knoery,
1993) but is also recognizable in this global database. In particular, the data
from cruise ID10 (Cutter and Radford-Knoery, 1993), which covers
estuaries and shelves, is 10–1000-fold higher than in oligotrophic warm
waters (Fig. 4a). This pattern is also evident in elevated concentration in
the North Sea (Uher and Andreae, 1997), the Mediterranean Sea
(Ulshöfer et al., 1996) and the coastal waters of Amsterdam
Island in the Indian Ocean (Mihalopoulos et al., 1992).
Concentration profiles in the water column show a typical photochemical
behavior and decrease with depth, although subsurface peaks occur
occasionally (Von Hobe et al., 1999; Cutter et al., 2004; Lennartz et
al., 2017). Despite the still limited size of the database, it already
covers a large part of the global variability, as it includes measurements
from a variety of different biogeochemical regimes, i.e., from oligotrophic
waters (Cutter et al., 2004; Lennartz et al., 2017; Von Hobe et al.,
2001) to higher trophic stages in shelf (Uher and Andreae, 1997),
estuary (Cutter and Radford-Knoery, 1993), and upwelling regions
(Ferek and Andreae, 1983; Mihalopoulos et al., 1992; Von Hobe et al.,
1999; Lennartz et al., 2017).
The annual pattern illustrated in Fig. 3c is different for the Southern Hemisphere and
Northern Hemisphere. The lowest median concentrations in the Southern Hemisphere
are present during austral winter months and increase up to five times
during austral summer. In the Northern Hemisphere, the lowest concentrations are
present during late boreal summer (August, September, October) and late boreal winter (January, February, March).
The range of observed concentrations is similar for both hemispheres.
Compared to the spatial pattern in Fig. 3a, the seasonal variability in the
database is larger than the spatial variability.
Figure 4a illustrates the concentration range of each dataset for OCS in
seawater. The internal consistency of the database is supported by (1) the
variation in concentration in this database being consistent with the current
process understanding and thus reflecting actual variability. The majority of
the global measurements (60 %) fall into a very narrow range of 8.7–43.0 pmol L-1, and outliers of this 20–80 percentile range are explicable by
location or time of measurement. For example, OCS concentrations during
cruise ID2, ID10, ID13, and ID19 were much higher than observed by other
cruises (Fig. 4), which can be explained by the location of Chesapeake Bay
(ID2, ID13), the Petaquamscutt estuary (ID 10), and the North Sea (ID19) in shelf
areas or close to estuaries, where high CDOM abundance enhances
photochemical production and increases concentration. An example for a
particularly low concentration is cruise ID18, which took place during
winter. The authors refer the low concentration as due to low
photoproduction at that time (Ulshöfer et al., 1995). (2) Measurements obtained from cruises that cover a similar temporal and spatial
area yield comparable results, such as cruises ID3 and ID4 (Pacific Ocean);
cruises ID27 and ID28 (Atlantic transects; or cruises ID20, ID26, and ID32
from the North Atlantic (Fig. 4). (3) Reported OCS concentrations in
seawater and the marine boundary layer are consistent across different
laboratories and methods. The introduction of new methods, e.g., OA-ICOS
(cruiseID 36 and 39), yields results that are comparable to previous
measurements using GC-FPD. To facilitate comparison of individual datasets,
they are grouped according to the analysis system used in Table 2 (capital
letters in last table column).
Boxplots of measured OCS concentrations in (a) seawater and (b) marine boundary layer. Marked in red is the median of each individual
dataset, the edges of the box represent the 25th and 75th
percentile, and outliers are indicated by red dots. The patch in the
background indicates the 20th and 80th percentile of the whole
dataset. Note the break in the y axis in (a).
Carbonyl sulfide in the marine boundary layer
The dataset of OCS in the marine boundary layer includes 14 291 measurements
from 30 cruises (Fig. 3f, Table 3). The average mixing ratio in the marine
boundary layer is 548.9 (209–1112) ppt. All major ocean basins were covered,
except for the Arctic Ocean. The North Atlantic Ocean, including the North
Sea, was sampled most frequently.
Sampling of OCS in the marine boundary layer is done either discretely by
pumping air in canisters, or continuously by pumping air directly into the
detection system (see Table 2 for details). Marine boundary layer air was
often sampled from the ship's uppermost deck, and reported sampling heights
ranged from 10–35 m (Table 3). Given the relatively stable atmospheric mixing
ratios (compared to the strong diel variations in dissolved OCS), a strong
gradient in mixing ratios towards the sea surface is not expected. Hence,
the database is suited to calculate the concentration gradient across the
air–sea boundary, making it valuable for calculating oceanic emissions. The
sampling frequency in individual datasets ranged from intervals shorter than
hourly to monthly time series (Fig. 3f). Given the weak diurnal variability
compared to the seasonal variability, the reported resolution in all of the
individual datasets is sufficient for large-scale comparisons.
The global variability of boundary layer OCS mixing ratio is less pronounced
and does not show the same spatial pattern as that of dissolved OCS in the
surface ocean (Fig. 2b). Ranges of mixing ratios are similar across all
latitude bins, with minor variations (Fig. 3b). In several individual
datasets, e.g., in the Pacific (Weiss et al., 1995b) and Atlantic
transects (Xu et al., 2001), mixing ratios in the tropics
increase compared to higher latitudes during the respective cruise (Fig. 2b). The highest atmospheric mixing ratios are reported from around Europe
(including the Mediterranean), as well as off the Falkland Islands (Fig. 2b).
The complete database includes measurements from January to December in the
Northern Hemisphere, but data for September are missing in the Southern
Hemisphere. The seasonal variability in atmospheric mixing ratio was less
pronounced compared to the variability in seawater OCS concentration, with
monthly medians ranging from 439–647 ppt in the Northern Hemisphere and 467–523 ppt in
the Southern Hemisphere. No clear seasonal pattern was observed in either of
the hemispheric datasets. The lack of such a pattern in atmospheric
concentrations might result from the limited size of the dataset and the
spatial heterogeneity of the sampling locations (i.e., influence of local
vegetation sinks or anthropogenic sources of the air mass history). It
should also be noted that small decadal trends as reported in the
introduction could influence the reported differences, as the measurements
reported here span a period of 1982–2018. Also, possible standardization and
calibration issues could potentially be larger than the range of reported
trends, so using the dataset in new trend studies should only be done with
caution.
The internal consistency of the database is of similar quality as that described
for OCS in seawater. A total of 60 % of the data (i.e., between 20 and 80 percentile)
fall in a narrow range of 477–621 ppt (Fig. 4b). Some features are present
across different datasets and thus support the internal consistency of
the dataset: for example, locally elevated mixing ratios in tropical
latitudes are present in single datasets and also globally (Figs. 2b and
4b). Elevated atmospheric mixing ratios were reported by several studies
providing measurement from around Europe (Figs. 2b and 4b).
Carbon disulfide in seawater
Measurements of dissolved CS2 in seawater are reported from 11
cruises (Fig. 1, 1813 measurements), with an average of 15.7 (1.1–376) pmol L-1. Most of the measurements were performed in the Atlantic Ocean,
comprised of three Atlantic meridional transects (Fig. 2c). No measurements
are available from the Arctic and Antarctic waters and the Indian Ocean.
The latitudinal variation in CS2 in seawater was small (Fig. 5a, on
average <5 pmol L-1), although individual studies report a
general covariation in concentrations and water temperature (Xie and
Moore, 1999; Lennartz et al., 2017). Apart from an Atlantic transect with
exceptionally high concentrations
(Lennartz et al., 2017), concentrations
tend to increase towards coastal and upwelling regions (Fig. 2c), but this
increase was less pronounced compared to the spatial variability of OCS
(Fig. 2a). Seasonal variability of CS2 water concentrations was larger
compared to the spatial variability (Fig. 5a and c) but did not show a
clear seasonal or spatial pattern. Concentrations were comparable in the
Northern Hemisphere and Southern Hemisphere. Diurnal variability of surface
concentrations was present on some but not all days within individual
datasets, likely representing the varying efficiency of the local sink
process in the mixed layer. The occurrence of diel cycles calls for a
similarly high sampling frequency to that suggested for OCS (i.e., more frequently
than 4 hourly). However, most of the dataset comprises a sampling frequency
of daily to monthly, and the sampling is biased towards daytime (Fig. 5e).
Hence, averaged concentrations might slightly overestimate diel averages.
Same as Fig. 2 but for CS2.
The database presented here indicates the common range of seawater
concentrations and covers several biogeochemical regimes. However,
limitations remain, viz., (1) a general sparsity of measurements; (2) data
gaps, especially in high latitudes; and (3) insufficient sampling frequency to
cover full diel variability in many individual datasets.
The limited size of the database for CS2 in seawater hampers internal
data comparison. The majority of the data (between 20 and 80 percentile)
falls in the range of 6.1–15.6 pmol L-1. Individual datasets from the
Southern Ocean (cruiseID 7, not georeferenced) and from an Atlantic transect
(cruiseID 38) show mean concentrations that are considerably higher than
observed on other cruises (Fig. 6a). Since data from dataset ID7 represent
the only available measurements for this location, based on this database,
we cannot determine whether this is an artifact or not. However, we see a
similar trend in the OCS data observed by dataset ID7. Also, the low
atmospheric mixing ratio measured during this specific cruise speaks against
a contamination problem. For the Atlantic transect it is evident that the
average concentration is higher compared to the other three Atlantic cruises
with a similar cruise track, i.e., dataset ID28, ID29, and ID33. However, the
minimum measured concentration in this specific dataset is 7 pmol L-1,
which makes a strong contamination unlikely. The atmospheric mixing ratios
during cruise ID38 are also lower than those during the other two Atlantic
transects, which negates a strong contamination problem. Furthermore, the
covariance with temperature is evident in this and in other datasets (Xie
and Moore, 1999; Lennartz et al., 2017). CS2 concentration in dataset
ID38 is reported twice daily, once at 08:00–10:00 and once at 15:00–18:00 local time. Potentially, the average is misleading in this respect
because it masks potential diel cycles. Daily maxima of cruise ID38 agree
with daily maxima of some parts of the other Atlantic transects
(ID28, 29, 33) but not on the majority of days. The minimum values over large
parts of the cruise ID38 were higher than those in the cruises ID28, 29, and
33. Potentially, the minima might have been missed by the coarse sampling.
Same as Fig. 4 but for CS2.
Carbon disulfide in the marine boundary layer
CS2 measurements in the marine boundary layer are only available for
the Atlantic Ocean from six cruises, i.e., 1036 individual measurements.
Atmospheric mixing ratios were on average 42.2 ppt (2.5 to 275.7 ppt, Fig. 2d).
The reported CS2 concentrations are generally higher than those reported
from airborne measurements in previous studies, where values <10 ppt in the boundary layer have been reported (Cooper and Saltzman, 1993).
An influence of continental air carrying a higher concentration of CS2
might be a possible explanation for elevated values (see, e.g., compilation in
Khan et al., 2017 of up to 1200 ppt). The short atmospheric lifetime
of CS2 sets a limit on long-range transport, so this explanation would
only hold for coastal and shelf regions. The data reported here have
undergone calibration procedures as reported in the original papers, and
elevated values are consistent across different labs and locations, so
the contamination problems of the local measurement systems are unlikely but
cannot be ruled out completely as being responsible for the elevated mixing
ratios.
Since this dataset is only comprised of four individual cruises, any
perceived pattern in global variation should be taken with caution, as it
might instead reflect natural variability or differences between individual
laboratories. Spatiotemporal variability will become clearer once more data
are available. Almost no preference is given to new measurement locations or
times, as any new dataset will help to further constrain spatial and
temporal variability of CS2 concentration. Latitudinal median mixing
ratios varied between studies by a factor of 2, but due to the limited size
of the dataset, it is currently unclear if this variation is meaningful.
However, a CS2 mixing ratio of 42.2 ppt in the marine boundary layer
may become relevant for calculation of oceanic emissions. Commonly, marine
boundary layer concentrations of CS2 are assumed to be 0 due to its
short lifetime, which will lead to an overestimation of emissions in cases
where the true mixing ratio is higher, as our database indicates (at a temperature
of 20 ∘C, a salinity of 35 psu, a wind speed of 7 m s-1, and a
CS2 water concentration of 16 pmol L-1, the difference between 0
and 42 ppt CS2 in air leads to an overestimation of 21 %).
Due to the sparsity of data and the expected strong variability resulting
from the short atmospheric lifetime, we will not use this limited dataset
here for assessing the internal consistency across locations. The variation
between the two Atlantic transect datasets ID28 and ID29, with a strong
overlap in measured mixing ratios, seems reasonable (Fig. 6b), but more data
are needed to establish a comparison on larger scale.
Data availability
The data are available from the PANGEA database
10.1594/PANGAEA.905430 (Lennartz et
al., 2019).
Recommendations for oceanic OCS and CS2 measurements
The full potential of an oceanic OCS and CS2 database can be exploited
if measured concentrations are stored together with relevant metadata. As a
minimal requirement, we recommend to report (i) the exact date of each
measurement (including time of the day) and (ii) the exact location (including
latitude, longitude and sample depth). This is especially important due to
the photochemical production of both gases, as concentration in seawater
varies strongly on diurnal and seasonal scales. To obtain a full diurnal
cycle, we recommend measuring at a 4 h resolution at least to minimize
errors when interpolating and averaging over the period of 1 d. Of
secondary importance are physical parameters such as temperature, radiation,
and wind speed. When modeling marine concentrations of OCS and CS2, it
is helpful to have access to the CDOM absorbance data at a wavelength of 350 nm because parameterizations for production rates are based on this value
(von Hobe et al., 2003; Lennartz et al., 2017). In order to decipher the
history of the air mass and identify potential continental influence, it
would also be helpful to measure additional trace gases such as CO or other
anthropogenic tracers simultaneously.
In order enable the identification of large-scale patterns and the
quantification of the oceanic source strength, we identify locations for
future measurements. For OCS seawater concentration, large gaps exist in the
open Pacific Ocean and the Arctic Ocean. The Arctic Ocean would be
especially interesting due to the unique composition of dissolved organic
matter derived from river input, which could influence OCS production in the
water. Marine boundary layer OCS is required, especially from the Arctic
Ocean. The data coverage for CS2 is very scarce, and
measurements in water and marine boundary layer from high latitudes
(Southern Ocean and Arctic Ocean), as well as Indian Ocean and Southern
Pacific, would be especially helpful. Generally, for both gases, water concentration
profiles would be helpful to understand their processes in the subsurface.
This is important for CS2, which has a long lifetime in water, so that
mixing processes could bring subsurface CS2 in contact with the
atmosphere. Similarly, repeated measurements from the same locations would
be helpful to decipher any trends.
Author contributions
STL and CAM started the initiative for data compilation and long-term
storage. All coauthors contributed data from one or more expeditions. STL
wrote the manuscript with input from all coauthors.
Competing interests
The authors declare that they have no conflict of interest.
Acknowledgements
We thank all captains and crew members of all cruises that are included in this database for their support in the data collection.
Financial support
This research has been supported by the BMBF (ROMIC-THREAT; grant nos. BMBF-FK01LG1217A and 01LG1217B) and the Helmholtz-Association (TRASE-EC; grant no. VH-NG-819).
Review statement
This paper was edited by Jens Klump and reviewed by Roisin Commane and one anonymous referee.
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