An example of a fruitful international intercomparison

The reliability of the GEOTRACES data products including the eGEOTRACES Electronic Atlas is strongly related to the quality of the data acquired by the different laboratories contributing to this international effort. A key aspect for assessing this quality relies on the good intercomparison of the trace metal data. Iron (Fe) concentrations and moreover Fe isotopes count among the most delicate parameters to be measured in seawater.

Conway (Switzerland), John (USA) and Lacan (France) (2016, see reference below) present the first comparison of dissolved Fe stable isotope ratio profiles in the oceans, analyzed at different depths at 3 different GEOTRACES crossover stations in the Atlantic Ocean (Bermuda Atlantic Time Series Station, off Cape Verde and in the Cape Basin, south Atlantic).

Having assessed the strong agreement between data and profiles measured by 5 different laboratories at Bermuda Atlantic Time Series (BATS), the authors discuss the temporal variability observed at the three locations, taking advantage of reoccupation of the stations by multiple cruises on a 1-3 year timescale. The authors find that the deep ocean at these locations is largely invariant for Fe isotopes on these timescales, but that there is variability in surface waters and near low-oxygen margins.

16 Conway l
Figure: Comparison of δ56Fe (relative to IRRM-014) and Fe data from Bermuda Atlantic Time Series (BATS) in the subtropical North West Atlantic (31.75°N 64.17°W) from the U.S. GEOTRACES IC1 (June 2008) and GA03 cruises (USGT11, Nov. 2011). Data are reproduced from Boyle et al. (2012); Conway and John (2014a); Conway et al. (2013a; 2013b); John and Adkins (2012). Please click on the figure to view it larger.


Conway, T. M., John, S. G., & Lacan, F. (2016). Intercomparison of dissolved iron isotope profiles from reoccupation of three GEOTRACES stations in the Atlantic Ocean. Marine Chemistry. doi:10.1016/j.marchem.2016.04.007

Figure references:

Boyle et al., 2012: E.A. Boyle, S.G. John, W. Abouchami, J.F. Adkins, Y. Echegoyen-Sanz, M.J. Ellwood, A.R. Flegal, K. Fornace, C. Gallon, S. Galer, M. Gault-Ringold, F. Lacan, A. Radic, M. Rehkämper, O. Rouxel, Y. Sohrin, C. Stirling, C. Thompson, D. Vance, Z. Xue, Y. Yhao. GEOTRACES IC1 (BATS) contamination-prone trace element isotopes Cd, Fe, Pb, Zn, Cu, and Mo intercalibration. Limnol. Oceanogr. Methods, 10 (2012), pp. 653–665. doi: 10.4319/lom.2012.10.653

Conway and John, 2014a: T.M. Conway, S.G. John. Quantification of dissolved iron sources to the North Atlantic Ocean Nature, 511 (2014), pp. 212–215. doi:  10.1038/nature13482

Conway et al., 2013a:  T.M. Conway, A.D. Rosenberg, J.F. Adkins, S.G. John. A new method for precise determination of iron, zinc and cadmium stable isotope ratios in seawater by double-spike mass spectrometry Anal. Chim. Acta, 793 (2013), pp. 44–52. doi: 10.1016/j.aca.2013.07.025

Conway et al., 2013b: T.M. Conway, A.D. Rosenberg, J.F. Adkins, S.G. John. Corrigendum to “A new method for precise determination of iron, zinc and cadmium stable isotope ratios in seawater by double-spike mass spectrometry.” Anal. Chim. Acta, 801 (97) (2013). doi: 10.1016/j.aca.2013.09.010

John and Adkins, 2012: S.G. John, J.F. Adkins. The vertical distribution of iron stable isotopes in the North Atlantic near Bermuda Glob. Biogeochem. Cycles, 26 (2) (2012) doi: 10.1029/2011GB004043

Latest highlights

Science Highlights

Thorium-Protactinium fate across the tropical Atlantic Ocean: what reveals the water column-sediment coupling

Twenty seawater profiles and twenty core-top 231-protactinium and 230-thorium analyses were realised by Ng and colleagues along five depth transects across the northern tropical Atlantic open ocean.


Science Highlights

Constraining Oceanic Copper Cycling through Artificial Intelligence and Ocean Circulation Inverse Model

Using available observations of dissolved copper, artificial neural networks, and an ocean circulation inverse model, authors calculated a global estimate of the 3-dimensional distribution and cycling of dissolved copper in the ocean


Science Highlights

Particulate rare earth elements distributions, processes and characterisation of nepheloids in the North Atlantic

Lagarde et al. realised the first basin scale section of particulate rare earth elements concentrations across the North Atlantic Ocean.


Science Highlights

Isopycnal mixing controls protactinium and thorium distributions in the Pacific Southern Ocean

Pavia and co-workers determined the physical and chemical speciation as well as the vertical distribution of Protactinium-231 and Thorium-230 at 12 stations across the Southern Pacific Antarctic Circumpolar Current…