DOI: 10.17882/82165
title: Isotopic composition of dissolved inorganic carbon in sea water analyzed since 1990 at LOCEAN (DICisotopes)

description: LOCEAN has been in charge of analyzing the isotopic composition of the dissolved inorganic carbon (DIC) in sea water collected during a series of cruises or ships of opportunity mostly in the southern Indian Ocean , the North Atlantic, and the equatorial Atlantic, but also in the Mediterranean Sea and in the equatorial Pacific.
The LOCEAN sea-water samples for δ13CDIC were collected in 125/25 ml glass bottles until 2022/since then and poisoned with HgCl2 (1 ml of saturated solution) before storage in a dark room à 4°C until their measurement. The DIC was extracted from the seawater by acidification with phosphoric acid (H3PO4 85%) and CO2 gas that was produced was collected in a vacuum system following the procedure described by Kroopnick (1974). The isotopic composition of CO2 was determined using a dual inlet-isotopic ratio mass spectrometer (SIRA9-VG) by comparing the 13C/12C ratio of the sample to the 13C/12C ratio of a reference material, the Vienna-Pee Dee Belemnite (V-PDB). The isotopic composition is expressed in the δ-unit defined by Craig (1957)(method type 2).  Experience showed that samples older than 3-4 years are likely to have experienced conservation issues and have been dismissed. The mass spectrometer has worked very well until 2014-2015. Afterwards, its aging as well as the aging of the preparation line resulted in more data loss, and often less accurate results. The preparation line was renovated in 2019, and analyses in 2020 were run manually, often repeating the measurement a second time for each sample.
Up to 2007-2008, δ13CDIC values have a precision of±0.01 ‰ (Vangriesheim et al.,2009) and a reproducibility of±0.02 ‰. After an interlaboratory comparison exercise led by Claire Normandeau (Dalhousie  University),  results  suggest  that  recent  LOCEAN  samples have a slightly poorer reproducibility (±0.04 ‰ ) as well as an offset of -0.13‰ (details available in Reverdin et al., ESSD 2018) that is confirmed by Becker et al. 2016 work by comparison with other cruises after removing the anthropogenic signal. Recent comparisons in early May 2021 with Orsay GEOPS facility samples suggest that the current offset is much smaller and might be +0.03‰.
LOCEAN has installed in 2021 a new measurement device by coupling a Picarro G2131-I cavity ring down spectrometer (CRDS) with a CO2 extractor (Apollo SciTech) that will measure at the same time DIC (method type 3) (Leseurre, 2022). Since then, all water samples have been analyzed on this device.
Part of the data set, as well as a scientific context and publications are also presented on the WEB site https://www.locean-ipsl.upmc.fr/oceans13c.
Individual files correspond to regional subsets of the whole dataset. The file names are based on two letters for the region followed by (-) the cruise or project name (see below) followed by –DICisotopes, followed by either -s (surface data) or -b (subsurface data), and a version number (-V0, …): example SI-OISO-DICisotopes-s-V0; the highest version number corresponds to the latest update of the cruise/project data set, and can be directly downloaded. Earlier versions can be obtained on request, but are not recommended. The region two letters are the followings:
 
- SI: station and surface data in the Southern Indian Ocean that include cruises :
INDIGO I (1985 – stn) (https://doi.org/10.17600/85000111)
CIVA I (1993 – stn & surf) (https://doi.org/10.17600/93000870) (Archambeau et al., JMS 1998)
ANTARES (1993 – stn & surf) (https://doi.org/10.17600/93000600)
OISO (*) (since 1998 – stn & surf) (https://doi.org/10.18142/228) (Racapé et al., Tellus 2010, Leseurre, 2022)
 
- EA: station and surface data in the Tropical Atlantic Ocean that include cruises :
EQUALANT (1999 & 2000 – surf) (https://doi.org/10.18142/98)
EGEE (2005 to 2007 – stn & surf) (https://doi.org/10.18142/95)
PIRATA (since 2013 – stn & surf) (https://doi.org/10.18142/14)
EUMELI 2 (1991 – stn) (https://doi.org/10.17600/91004011)  (Pierre et al., JMS 1994)
BIOZAIRE 3 (2003 – stn & surf ) (https://doi.org/10.17600/3010120) (Vangriesheim et al., DSRII, 2009)
TARA-Microbiomes (2021 - stn & surf)
 
- NA : station and surface data in the North Atlantic Subpolar gyre that include cruises :
OVIDE (**) (since 2002 – stn & surf) (https://doi.org/10.17882/46448) (Racapé et al., 2013)
RREX (2017 – stn & surf) (https://doi.org/10.17600/17001400)
SURATLANT (since 2010 - surf) (https://doi.org/10.17882/54517) (Racapé et al., BG 2014 ; Reverdin et al., ESSD 2018, Leseurre, 2022)
NUKATUKUMA (since 2017- surf)
 
- MS: station data in the Mediterranean sea that include cruises :
ALMOFRONT 1 (1991 – stn) (https://doi.org/10.17600/91004211)
VICOMED 3 (1990 – stn) (https://doi.org/10.17600/90000711)
 
- PO: tropical Pacific that include cruises :
PANDORA (2012 – stn) (https://doi.org/10.17600/12010050)
ALIZE2 (1991 – stn & surf) (https://doi.org/10.17600/91002711) (Laube-Lenfant and Pierre, Oceanologica Acta 1994)
 
- SO: station and surface data in the Southern Ocean (except OISO) that include cruises:
TARA-Microbiomes (2021-2022, stn & surf)
AGULHASII-072022 (2022, stn)
CONFLUENCE (1993-1994, stn)
 
- AO: station and surface data in the Arctic Ocean and nearby seas that include cruises: GREENFEEDBACK (2024, stn&surf) TCA (2024, stn) REFUGE ARCTIC (2024, stn)
(*) The values for cruises OISO19, 21 and 22 are doubtful (for some, too low) and will require further investigation to find whether adjusted values can be proposed.
(**) Some of the OVIDE cruises are also referred to as or GEOVIDE (in 2014), and BOCATS (in 2016). CATARINA, BOCATS1 and BOCATS2 (PID2019-104279GB-C21/AEI/10.13039/501100011033) cruises were funded by the Spanish Research Agency  The values of the OVIDE 2010 stations are doubtful (too low), but no particular error was found, and they have been left in the files.
 
Data
The files are in csv format reported as:
 - Cruise name, station id, (bottle number), day, month, year, hour, minute, longitude, latitude, pressure (db), depth (m), temperature (°C), temperature qc, salinity (pss-78), salinity qc, d13CDIC, d13CDIC qc, method type
 - Temperature is an in situ temperature
 - Salinity is a practical salinity
 - Method type (1) acid CO2 extraction from helium stripping technique coupled to mass spectrometer, (2) acid CO2 extraction in a vacuum system coupled to mass spectrometer,(3) CO2 extractor (Apollo SciTech) coupled to CRDS measurements.
Temperature qc, salinity qc, d13CDIC qc are quality indices equal to:
 - 0 no quality check (but presumably good data)
 - 1 probably good data
 - 2 good data
 - 3 probably bad data
 - 4 certainly bad data
 - 9 missing data (and the missing data are reported with an unlikely missing value)