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Biogeosciences An interactive open-access journal of the European Geosciences Union
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
13 Nov 2017
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Biogeosciences (BG).
Mercury distribution and transport in the North Atlantic Ocean along the GEOTRACES-GA01 transect
Daniel Cossa1, Lars-Eric Heimbürger2, Fiz F. Pérez3, Maribel I. García-Ibáñez3, Jeroen E. Sonke4, Hélène Planquette5, Pascale Lherminier6, and Géraldine Sarthou5 1ISTerre, Université Grenoble Alpes, CS 40700, 38058 Grenoble Cedex 9, France
2Aix Marseille Université, CNRS/INSU, Université de Toulon, IRD, Mediterranean Institute of Oceanography (MIO) UM 110, Marseille, France
3Instituto de Investigaciones Marinas, CSIC, Eduardo Cabello 6, 36208 Vigo, Spain
4CNRS, GET-OMP, 14 Ave. E. Belin, 31240 Toulouse, France
5LEMAR, Université de Bretagne Occidentale, 29280 Plouzané, France
6IFREMER, Brittany Center, LPO, BP 70, 29280 Plouzané, France
Abstract. We report here the results of total mercury (HgT) determinations along the 2014 GEOTRACES GEOVIDE cruise (GA01 transect) in the North Atlantic Ocean (NA) from Lisbon (Portugal) to the Labrador coast (Canada). Ninety-seven percent of the HgT concentrations of unfiltered samples (HgTUNF) ranged between 0.16 and 1.00 pmol L−1. The geometric mean was 0.51 pmol L−1 for the 535 samples analysed. The dissolved fraction (< 0.45 μm) of HgT, determined on 141 samples, averaged 78 % of the HgTUNF for the whole water column. HgTUNF concentrations increased eastwards and with depth from Greenland to Europe and from sub-surface to bottom waters, respectively. The Hg distribution mirrored that of dissolved oxygen concentration, with highest HgTUNF levels associated with oxygen-depleted zones. The statistically significant (p < 0.01) relationship between HgTF (filtered samples) and the apparent oxygen utilization confirms the nutrient-like behavior of Hg in the NA. An extended Optimum Multiparameter Analysis allowed us to characterize HgTUNF concentrations in the different Source Water Types (SWTs) present along the transect. Mean HgTUNF concentrations ranged from 0.26 ± 0.03 pmol L−1 in the Irminger Subpolar Mode Water to 1.02 ± 0.02 pmol L−1 in the lower North East Atlantic Deep Water. Anthropogenic Hg-enriched SWTs were found in the upper oceanic layers (i.e., East North Atlantic Central Water and Subarctic Intermediate Water). The change in anthropogenic Hg concentrations in the Labrador Sea Water, during its eastward journey, suggests a continuous decrease of Hg content in this water mass over the last decades. Calculation of the water transport driven by the Atlantic Meridional Overturning Circulation across the Portugal-Greenland transect indicates a northward Hg transport within the upper limb, and a southward Hg transport within the lower limb, with a resulting net transport from low latitudes to the polar zones of about 111 kmol yr−1.

Citation: Cossa, D., Heimbürger, L.-E., Pérez, F. F., García-Ibáñez, M. I., Sonke, J. E., Planquette, H., Lherminier, P., and Sarthou, G.: Mercury distribution and transport in the North Atlantic Ocean along the GEOTRACES-GA01 transect, Biogeosciences Discuss.,, in review, 2017.
Daniel Cossa et al.
Daniel Cossa et al.
Daniel Cossa et al.


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Short summary
We report first high-resolution description of mercury distribution in the water section across the subpolar and subtropical gyres of the North Atlantic Ocean (GEOTRACES-GA01 transect). It allows the characterisation of various sea-water types in term of mercury content, and the quantification of mercury transport associated with the Atlantic Meridional Overturning Circulation. It shows the nutrient-like biogeochemical behavior of mercury in this Ocean.
We report first high-resolution description of mercury distribution in the water section across...