1. What is the acidification level in the Mediterranean Sea? Abed El Rahman HASSOUN 1*, Elissar GEMAYEL 1,2,3, Evangelia KRASAKOPOULOU 4, Catherine GOYET 2,3, Marie ABBOUD-ABI SAAB 1, Véronique GUGLIELMI 2,3, Franck TOURATIER 2,3, Cédric FALCO 2,3 1 National Council for Scientific Research, National Center for Marine Sciences, P.O.Box 534, Batroun, Lebanon 2 IMAGES_ESPACE-DEV, Université de Perpignan Via Domitia, 52 avenue Paul Alduy, 66860 Perpignan Cedex 9, France 3 ESPACE-DEV, UG UA UR UM IRD, Maison de la télédétection, 500 rue Jean-François Breton, 34093 Montpellier Cedex 5, France 4 University of the Aegean, Department of Marine Sciences, University Hill, Mytilene 81100, Greece. *e-mail: abedhassoun@cnrs.edu.lbabedhassoun@cnrs.edu.lb Summary Despite the knowledge of its potential impacts on biological and chemical processes by the scientific community, estimations of the acidification level in the Mediterranean Sea are still scarce. This poster presents the results of a new study that is estimating the actual anthropogenic CO 2 (C ANT ) concentrations sequestered in the Mediterranean waters, as well as the variations of both calcite and aragonite saturation states based on hydrographic and carbonate system data collected during the May 2013 MedSeA cruise. Under the excessive anthropogenic pressures in the Mediterranean area, the actual acidification levels (ΔpH = pH 2013 - pH pre-industrial ) are estimated to vary from -0.055 to -0.156 pH unit in this sea. Introduction Ocean acidification is a direct consequence of increasing levels of CO 2 in Earth’s atmosphere. This phenomena, which occurred since the beginning of the industrial revolution in the early 1800s, is altering seawater chemistry and affecting the life cycles of many marine organisms. Although there are already some quantifications of the C ANT in the Mediterranean Sea and some studies about the acidification evolution in its waters [1, 2 and 3], there is still a lack of data to get a complete picture of the evolution of the C ANT and the acidification in this semi-enclosed sea. Objectives 1 - Quantifying the C ANT concentrations in the Mediterranean Sea, 2 - Calculating the variations of calcite and aragonite saturation states between the preindustrial period and 2013, 3 - Estimating the current acidification level in the Mediterranean waters. Study area Data sets and Methodology -Data used in this study were collected during the MedSeA oceanographic cruise between 2 May and 2 June 2013. -S, T (ºC) and O 2 were measured in Situ, and θ (ºC) was calculated based on: S, T (ºC), and pressure (db). : -The saturation state of calcite (ΩCa) and aragonite (ΩAr) were also computed via the “CO2SYS” program. - Results Conclusions All Mediterranean seawaters are invaded by anthropogenic CO 2 (with concentrations ranging between 35.2 and 101.9 µmol kg -1 ) which indicates that C ANT is efficiently transferred from the atmosphere to the Mediterranean waters. ΩCa decreases from -0.37 to -2 while ΩAr decreases from -0.24 to -1.3 between the preindustrial period and 2013. This phenomenon reflects the effect of the ocean acidification on the calcium carbonate dissolution, particularly in the sub-basins invaded by high C ANT concentrations (i.e. the Western basin). The acidification level varies between −0.055 and −0.156 pH unit in the Mediterranean Sea. All Mediterranean Seawaters are already acidified, especially those of the Western basin. This study's results are already published by [6]. More researches related to the carbonate system of the Mediterranean Sea are also recently published [7 and 8]. References [1] Touratier, F., Goyet, C., 2009. Decadal evolution of anthropogenic CO2 in the NorthWestern Mediterranean Sea from the mid-1990s to the mid-2000s. Deep-Sea Research Part I, 56, 1708-1716. [2] Rivaro P., Messa R., Massolo S., Frache R., 2010. Distributions of carbonate properties along the water column in the Mediterranean Sea: Spatial and temporal variations. Marine Chemistry, 121, 236–245. [3] Schneider A., Tanhua T., Körtzinger A., Wallace D.W.R., 2010. High anthropogenic carbon content in the eastern Mediterranean. Journal of Geophysical Research, 115, C12050, doi: 10.1029/2010JC006171. [4] DOE: Handbook and methods for the analysis of the various parameters of the carbon dioxide system in seawater, 1994. [5] Touratier F., Goyet C., 2004. Applying the new TrOCA approach to assess the distribution of anthropogenic CO2 in the Atlantic Ocean. Journal of Marine Systems, 46, 181–197. [6] Hassoun A.E.R., Gemayel E., Krasakopoulou E., Goyet C., c, Abboud-Abi Saab M., Guglielmi V., Touratier F., Falco C., 2015b. Acidification of the Mediterranean Sea from anthropogenic carbon penetration. Deep Sea Research Part I, 102,1–15, doi:10.1016/j.dsr.2015.04.005. [7] Hassoun A.E.R., Gemayel E., Krasakopoulou E., Goyet C., Abboud-Abi Saab M., Ziveri P., Touratier F., Guglielmi V., Falco C., 2015a. Modeling of the Total Alkalinity and the Total Inorganic Carbon in the Mediterranean Sea. Journal of Water Resources and Ocean Science, 4 (1), 24–32, doi: 10.11648/j.wros.20150401.14. [8] Gemayel E., Hassoun A.E.R., Benallal M.A., Goyet C., Rivaro P., Abboud-Abi Saab M., Krasakopoulou E., Touratier F., Ziveri P., 2015. Climatological variations of total alkalinity and total dissolved inorganic carbon in the Mediterranean Sea surface waters. Earth System Dynamics, 6, 789-800, doi:10.5194/esd-6-789-2015. Acknowledgments This work was funded by the EC FP7 “Mediterranean Sea Acidification in a changing climate” project (MedSeA ; grant agreement 265103 ; medsea-project.eu). -For A T and C T measurements, seawater samples were collected into washed 500 ml borosilicate glass bottles, and poisoned with a saturated solution of HgCl 2. Their analysis was performed via a potentiometric titration using a closed cell [4]_mechanism summarized in the above scheme. -C ANT was estimated via TrOCA approach [5], according to the following equation h h