1. The French Service facility for oceanic Total Alkalinity and
Dissolved Inorganic Carbon analyses (SNAPO-CO2).
J. Fin, N. Metzl, C. Mignon, M. Herbal et C. Lo Monaco.
OSU-Ecce-Terra, Sorbonne Universités (UPMC)-CNRS-IRD-MNHN, LOCEAN/IPSL, Paris, France
Since 2004, about samples have been collected for total alkalinity (TA) and dissolved inorganic carbon (CT) from research vessels, VOS lines, time-series stations (both coastal and open ocean) and during mesocosm experiments. The samples (500 ml) are analyzed at SNAPO-CO2 facility supported by INSU (Institut National des Sciences de l’Univers) and OSU-Ecce-Terra (Observatoire des Sciences de l’Univers at University Paris VI). All analyses are performed using a potentiometric method (in a closed-cell developped at LOCEAN) and calibrated with Certified Reference Material (CRMs) provided by Pr. A.Dickson (Scripps, USA). Those analyses have been used in many studies (~55 peer-review publications and ~ 20 phD thesis), including topics such as pCO2 long-term trends, air-sea CO2 fluxes, ocean process studies and acidification relevant for ICOS.
Instrumentation
LabWiew control
Standards - CRMs
The LabVIEW program controls and records (with real-time graphics) the running of each measurement (~ 20 mn), and at the end calculates the TA and CT concentrations using a non-linear method (DOE, 1994). All records are stored for post-processing.
TA and CT concentrations for CRM Batch-139 measured in 2015
(Number: 118, Sigma: 3.9 µmol/kg for both TA and CT)
The closed-cell, developped at LOCEAN, is motorized for various steps (rincing, dosing).
Reproductibility
Comparing measured and calculated pCO2
Intercomparison
Intercomparison of TA measurements (LOCEAN/SNAPO-CO2 and IIM/Vigo, PI F. Perez) for samples taken in surface and water column during the GEOVIDE-2014 cruise in the North Atlantic (PIs G.Sarthou/IUEM, P. Lherminier/LPO, Brest). For all samples (57) the mean difference is 3.94 µmol/kg.
Sea surface pCO2 recorded at location BOUSSOLE in the Mediterranean Sea in Colors show pCO2 measured by CARIOCA sensor, circles show pCO2 values calculated from TA/CT discrete samples: the mean difference is ~ 4.4 µatm (J.Boutin & L. Merlivat/LOCEAN, in prep., project Biocarex)
Example of duplicate TA and CT analyses (2016 samples at location SOMLIT-Point-B at 1m or 50m in Mediterranean coastal waters, PIs J.-P. Gattuso, L. Mouseeau – LOV, Villefranche/Mer). Average differences: 3.9 µmol/kg for TA, 3.3 µmol/kg for CT
Time-series, long-term trends and acidification
Exploring new oceanic regions
(Solomon Sea - PANDORA July 2012)
In July 2012 the multidisciplinary PANDORA cruise was conducted on French R/V L’Atalante through a France-USA collaboration, to document physical and geochemical water properties in the Solomon Sea (Ganachaud et al, sub. 2016). Very few observations of the inorganic carbon system have been previously conducted in this region. Discrete samples (180) were collected for TA and CT at selected locations and measured back at LOCEAN/SNAPO-CO2 in January Figures below show the TA and CT profiles along with estimates of both anthropogenic carbon (Cant) and anthropogenic pH (pH-ant). Below the surface, a pronounced TA subsurface maximum around 150 m is clearly recognized in the maximum salinity layer. In deep waters (> 1000 m) TA and CT concentrations present, like nutrients, a maximum around m. The results show a significant penetration of anthropogenic carbon down to about 1500 m. Between 200 and 1000 m Cant concentrations decrease sharply from about 50 µmol/kg to 10 µmol/kg. Below 1500 m, the Cant concentrations are low and within the error of the method (+/-7 µmol/kg). A large pH decrease of about -0.1 units is estimated in upper layers (200 m) and is also significant at depth (-0.05 units at 500 m). (Note that for scaling purpose, pH-ant values are multiplied by (i.e. 100 = -0.1 unit pH change).
In several locations, TA and CT were regularly sampled since many years (at weekly, monthly or seasonal scales). Here (right) we show results in Mediterranean Sea at Dyfamed (red symbols) and Point-B (blue), and in the North Atlantic Subpolar Gyre (green, Suratlant line, PI G.Reverdin/LOCEAN, see map above). In all regions we observed an increase of CT likely controlled by anthropogenic CO2 uptake, leading to a decrease of pH (calculated from TA and CT data). Obsevations at Point-B (blue) also suggest an increase in TA (~ +2 µmol/kg/yr) that modulates pH trend (Kapsenberg et al., 2016).
TA and CT data are also used to calculate fCO2: the figure below shows the fCO2 variability (interannual and trend) observed during winter months in the North Atlantic Subpolar Gyre (red dots are the atmospheric fCO2 recorded at Mace-Head station, Ireland). Adapted from Metzl et al, (2010) + extended data ( ).
A global view from TARA Ocean
Reconstructing pCO2 monthly fields
(an example in the tropical western atlantic)
Regional TA and CT data allow to estimate relation-ships with salinity (SSS) and/or temperature (SST). Such relations could be used to construct TA and CT fields (e.g. at monthly scale) and calculate pCO2 fields and air-sea CO2 fluxes over a region. Such method has been applied in various regions. Here we present a recent investigation in the Western Tropical Atlantic, WTA (Bonou et al., 2016). The map (left) shows all TA-CT data available in the WTA including data analyzed at SNAPO-CO2 (Aramis, Colibri, Pirata, Plumand, Rio-Blanco…).
In this region strong (linear) relations between TA, CT and SSS are determined, including for low salinity close to the mouth of Amazon river (figurs bottom left). The pCO2 fields (maps below, left) reconstructed from TA/CT show large seasonal variability and significant differences compared to the climatology derived from pCO2 data (see maps on right, Takahashi et al., 2014). The method, applied at regional scale is also able to resolve coastal pCO2 not evaluated in the climatology.
As part of the Tara-Ocean expedition ( ), about 700 samples were taken for TA and CT in both surface and water column. Here, we present results for sea surface from 80S to 80N in all oceanic basins covering a wide range of water masses, temperature and salinity. The concentrations for TA range between 1810 and 2650 µmol/kg, and for CT between 1680 and 2275 µmol/kg. Except near the ice (very low salinity in Arctic), TA and CT are linearly related to salinity. Data available at PANGAEA (Picheral et al., 2014). Samples are now taken during the ongoing Tara-Pacific expedition ( ).
Anthropogenic Carbon
(Dyfamed et Cascade ?)
References:
Bonou et al. 2016, Distribution of CO2 parameters in the Western Tropical Atlantic Ocean. Dynamics of Atmospheres and Oceans
Ganachaud et al., 2016, Two oceanographic cruises explore the Solomon Sea circulation, chemistry, geochemistry and biology, sub. Elementa
Metzl et al., 2010, Recent acceleration of the sea surface fCO2 growth rate in the North Atlantic subpolar gyre ( ) revealed by winter observations. Global Biogeochem. Cycles
Kapsenberg et al., 2016, Concomitant ocean acidification and increasing total alkalinity 1 at a coastal site in the NW Mediterranean Sea ( ). sub. Ocean Science
Picheral et al., 2014, Vertical profiles of environmental parameters measured on discrete water samples collected with Niskin bottles during the Tara Oceans expedition doi: /PANGAEA
Takahashi et al., 2014, Climatological Distributions of pH, pCO2, Total CO2, Alkalinity, and CaCO3 Saturation in the Global Surface Ocean, and Temporal Changes at Selected Locations. Marine Chemistry