Particulate trace elements in the North Atlantic along the GEOVIDE section (GEOTRACES GA01)
Hélène Planquette1, Arthur Gourain2, Marie Cheize1, Jan-Lukas Menzel Barraqueta3, Julia Boutorh1, Rachel Shelley1, Leonardo Pereira Contreira4, Francois Lacan5, Pascale Lherminier6 and Geraldine Sarthou1, (1)LEMAR, UMR 6539, Plouzané, France, (2)University of Liverpool, Earth Ocean & Ecological Sciences, Liverpool, United Kingdom, (3)GEOMAR Helmholtz-Zentrum für Ozeanforschung, Kiel, Germany, (4)Universidade Federal do Rio Grande, Rio Grande, Brazil, (5)CNRS-LEGOS, Toulouse, France, (6)IFREMER, LOPS, Plouzané, France
Abstract:
The GEOVIDE cruise (May-June 2014, R/V Pourquoi Pas?) aimed to provide a better understanding on trace metal biogeochemical cycles in the North Atlantic. Overall, 32 full vertical profiles were collected for trace metal analyses, representing more than 500 samples, collected in two size fractions, 0.45- 5µm and > 5µm. This resolution provides a solid basis for assessing concentration distributions, elemental ratios, size-fractionation, or adsorptive scavenging processes in key areas of the thermohaline circulation. A wide range of particulate trace element concentrations were measured: for example, total particulate iron (pFe) concentrations ranged from as low as 9 pmol L-1 in surface Labrador Sea waters to 304 nmol L-1 near the Iberian margin, while median pFe concentrations of 1.15 nmol L-1were measured over the sub-euphotic ocean interior. The large size fraction dominated the pFe pool and small size fraction pFe ranged between 2 pmol L-1 up to 7.74 nmol L-1, with concentrations usually higher within the euphotic layer. At most stations over the Western European and Icelandic basins, the relative concentrations of total particulate Fe, Al, Mn and P showed the near-ubiquitous influence of crustal particles in the water column. Within the Irminger and Labrador basins, suspended particles seemed to differ in composition, with higher pFe/pAl and pMn/pAl ratios being observed. This suggests a loss of lithogenic material accompanied by retention of pFe and pMn, while in the upper 100m of these stations, biological uptake likely increased these ratios. Additionally, several benthic nepheloid layers were encountered along the transect, especially in the Icelandic, Irminger and Labrador basins, delivering particles with high pFe and pAl content, reaching 58 and 138nmol L-1 respectively in the Labrador Sea. Finally, these results will also be discussed in light of dissolved trace metal distributions that were measured in parallel.
