Séminaire LOPS: Antje Voelker

Oxygen and Hydrogen Stable Isotope Signatures of Northeast Atlantic Water Masses – the OVIDE 2010, Iberia-Forams and GA03 GEOTRACES sections

Résumé: The stable isotope values of fresh or marine waters can be used to evaluate changes in the hydrological cycle, which in the marine environment relates mostly to more/less evaporation/ precipitation in the region where a water mass is formed. The global hydrological cycle has intensified during the last decades as reflected by the increased salinity in the surface waters of evaporation dominated regions, such as the Atlantic’s subtropical gyres, and enhanced freshening in precipitation dominated regions (Durack et al., 2012). Evaluating how these changes affected the stable isotope signatures of water masses and isotope/salinity mixing lines is, however, hampered by the scarcity of available data. In the years between the GEOSECS program (early 1980’s) and the ongoing GEOTRACES program, only few hydrographic campaigns collected seawater samples for stable isotope analyses, in particular in the eastern North Atlantic basin. To fill this gap of understanding the distributions of stable isotopes in the NE Atlantic and their relationship to the prevailing water masses, δ18O and δD profiles were generated along three intersecting hydrographic sections: 1) the OVIDE 2010 section from the Reykjanes ridge to the Portuguese margin; 2) the Iberia-Forams transect along the western and southern Portuguese margin; and 3) the GEOTRACES GA03_e section from the Portuguese margin to the Azores front region near Madeira and southward to the Cape Verde islands. In this presentation we will look at the distribution of the isotopic signatures along the sections, the different water masses identified and how the isotopic signal of a water mass might change with distance from the source region. Furthermore, potential mixing line changes between the subpolar and subtropical gyre will be evaluated.