GEOVIDE: AN INTERNATIONAL GEOTRACES STUDY IN THE NORTH ATLANTIC AND THE LABRADOR SEA (GA01 GEOTRACES SECTION)

GEOVIDE (GA01 GEOTRACES section) is an international programme which aims to better disentangle the uncertainties on water masses, heat fluxes and Trace Element and Isotope (TEI) cycles in the North Atlantic and Labrador Sea. To achieve these objectives, interdisciplinary (physical oceanography, biogeochemistry and geochemistry) and multi-proxy approaches were used and a high resolution hydrographical section was carried out during a 47-day oceanographic cruise on board RV “Pourquoi Pas?” in May-June 2014. In total, 78 stations were occupied, including the Iberian, Greenland, and Canadian shelves, and more than 500 on-board operations were realized.

A very sharp front separating the subpolar and the inter-gyre domains was observed at 49°30’N. This is the first time over the last 15 years that the subarctic front was found so far to the South and the branches of the North Atlantic Current so concentrated geographically. The central Irminger and Labrador Seas were marked by a recently ventilated water mass down to 1000 m and 1500 m-depth, respectively, capped by a thin fresh layer. The first results on TEI distributions along the cruise transect show that different waters masses were found to have characteristic signatures for some elements, in particular dissolved aluminium, iron, lead, and particulate iron. Trace metal inputs from the atmosphere, ice and iceberg melting, weathering, coastal runoff, benthic nepheloid layers, as well as potential hydrothermal activity were identified. Atmospheric deposition was very low, reflected by very low concentrations of aluminium in the surface waters and in the aerosols. Mercury concentrations found in the recently ventilated water masses were among the lowest ever measured, suggesting that atmospheric mercury deposition to the North Atlantic has decreased in the past decades. This finding shows the efficiency of global anti-pollution policies implemented in Europe and North America.