1. Mercury and methylmercury in the Atlantic sector of the Southern Ocean João Canário 1, Juan Santos-Echeandia 2, Ana Padeiro 1, Eduardo Amaro 1, Volker Strass 3, Christine Klaas 3, Mario Hoppema 3 Sharyn Ossebaar 4, Boris P. Koch 3, Luis M. Laglera 5, 1 Centro de Química Estrutural, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1, 1049-001 Lisboa, PORTUGAL 2 Instituto Español de Oceanografía, Centro Oceanográfico de Murcia, Apdo. 22, C/ Varadero 1, San Pedro del Pinatar, Murcia. SPAIN 3 Alfred-Wegener-Institut – Helmholtz-Zentrum für Polar und Meeresforschung, Am Handelshafen 12, 27570 Bremerhaven, GERMANY 4 NIOZ - Royal Netherlands Institute for Sea Research, Landsdiep 4, 1797 SZ ’t Horntje (Texel) and 5 Utrecht University, Utrecht, Utrecht THE NETHERLANDS 5 FITRACE. Departamento de Química, Universidad de las Islas Baleares, Cra. De Valldemossa, Palma, Balearic Islands, 07122, SPAIN *joao.canario@tecnico.ulisboa.pt The oceans constitute one of the most important reservoirs for Hg. While many studies have been published about the Hg cycling in the world's oceans much less attention has been given to the abiotic compartments in the Southern Ocean (SO). In order to provide a first insight into the concentrations of Hg species in the SO and to understand the processes responsible for their distribution, partitioning and speciation,. a sampling campaign was carried out south of the Polar Front (Atlantic sector of the SO). Introduction Conclusions Results and Discussion Water samples taken at discrete depths from the surface down to 300 m at five stations (84, 91, 140, 143, 163 and 174) were analysed for total Hg (HgT), methylmercury (MeHg) and other interpretative parameters (e.g. salinity, temperature, dissolved and particulate organic carbon, etc). Materials and Methods Acknowledgements Chief scientist Dieter Wolf-Gladrow, Captain and crew of R/V Polarstern, FCT (UID/QUI/00100/2013), MINECO of Spain (Grant CGL2010-11846-E) and the Government of the Balearic Islands (AAEE083/09, co-funded by FEDER). Vertical profiles of Hg and MeHg The results obtained in this study shows that Hg distribution in the Atlantic sector of the SO are comparable (or in some sites higher) to the ones published for the other oceanic regions, however MeHg species present in this area are more dependent of the environmental conditions than the amount of Hg present in the water. Sites location Ranges of Hg and MeHg concentrations These results are published in DSRII - DOI: http://dx.doi.org/10.1016/j.dsr2.2016.07.012 StationLatLong ML Depth (m) Direct Radiation (W m -2 ) HgT (ng L -1 ) MeHg (ng L -1 ) MeHg (%) Features 84-53.00-10.015500.70 – 3.600.18 – 0.5611 - 33South of the SPF 91-51.20-12.675634 ± 280.69 – 1.230.12 – 0.2210 - 27 Phytoplankton bloom (PB) 140-51.20-12.6668399 ± 1170.23 – 0.560.10 – 0.1422 - 32PB medium-final stage 143-53.5-36.405900.31 – 1.130.09 – 0.3114 - 37Island effect 163-50.40-39.403900.36 – 0.910.10 – 0.1912 - 36Bloom decay 174-49.65-38.2939795 ± 280.21 – 0.540.09 – 0.1925 - 37Phytoplankton bloom With the exception of stations 84 (unfiltered water), 91 and 143 the concentrations of both Hg and MeHg are comparable to the ones obtained in the world oceans Phytoplankton bloom stages influence the amount of both Hg and MeHg levels in water column (Sts. 91 and 140) Hg availability could be a limiting factor for MeHg in the water column With the exception of st. 84, MeHg concentrations increase continuously with depth indicating net methylation in deeper waters The substantial increase on MeHg levels at 200m in st. 84 appears to be related to intrusion of UCDW with lower DO – favorable conditions for Hg methylation The high variability of Hg and MeHg in this sector of the SO is explained by the huge quantity of undergoing physical and biogeochemical processes such as lateral advection, upwelling of water masses or more or less favourable conditions for Hg methylation