OS Ocean Science OS 1812-0792 Copernicus GmbH Göttingen, Germany 10.5194/os-9-83-2013 Salinity in the Sicily Channel corroborates the role of the Adriatic–Ionian Bimodal Oscillating System (BiOS) in shaping the decadal variability of the Mediterranean overturning circulation Gačić M. 1 Schroeder K. 2 Civitarese G. 1 Cosoli S. 1 Vetrano A. 2 Eusebi Borzelli G. L. 1 Istituto Nazionale di Oceanografia e di Geofisica Sperimentale – OGS, 34010 Sgonico (Trieste), Borgo Grotta Gigante 42/c, Italy Istituto di Scienze Marine – ISMAR, Consiglio Nazionale delle Ricerche (CNR), Arsenale – Tesa 104, Castello 2737/F, 30122 Venice, Italy/Forte Santa Teresa, 19032, Lerici (SP), Italy 29 01 2013 9 1 83 90 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.ocean-sci.net/9/83/2013/os-9-83-2013.html The full text article is available as a PDF file from http://www.ocean-sci.net/9/83/2013/os-9-83-2013.pdf

Previous studies have demonstrated that the salinity in the Levantine basin depends on the intensity of the Atlantic water (AW) inflow. Moreover, its spreading eastward (to the Levantine basin) or northward (to the Ionian Sea) is determined by the Ionian circulation pattern, i.e. by the Adriatic–Ionian Bimodal Oscillating System (BiOS) mechanism. The aim of this paper is to relate salinity variations in the Levantine basin to the salt content variability in the core of the Levantine Intermediate Water (LIW) passing through the Sicily Channel (SC) and its possible impact on the Western Mediterranean Transition – WMT (i.e. the sudden salinity and temperature increase in the deep layer of the Algero-Provençal subbasin occurring since 2004). From the historical data set MEDAR/MEDATLAS in the Levantine and northern Ionian, we present evidence of decadal occurrences of extreme salinities associated with the varying influx of AW over the last 60 yr. Furthermore, we show that the salinity variations in the two subbasins are out of phase. High-salinity episodes in the Levantine are a pre-conditioning for the potential occurrence of the events like the Eastern Mediterranean Transient (EMT). Cross-correlation between the salinity time series in the Levantine basin and in the SC suggests that the travel time of the LIW is between 10 and 13 yr. Comparing the timing of the salinity increase associated with the WMT and the salinity in the LIW core in the SC, we estimate that the total time interval needed for the signal propagating from the Levantine to reach the deep mixed layers of the Algero-Provençal subbasin is about 25 yr. We also showed that the extra salt input from the eastern Mediterranean contribute up to about 60% to the salt content increase in the bottom layer of the western Mediterranean.

 References Artale, V., Calmante, S., Malanotte-Rizzoli, P., Pisacane, G., Rupolo, V., and Tsimplis, M.: The Atlantic and Mediterranean Sea as connected systems, in Mediterranean Climate Variability, Dev. Earth Environ. Sci., 4, 283–323, edited by: Lionello, P., Malanotte-Rizzoli, P., and Boscoli, R., Elsevier, Amsterdam, 2006. Astraldi, M., Balopoulos, S., Candela, J., Font, J., Gacic, M., Gasparini, G. P., Manca, B., Theocharis, A., and Tintoré, J.: The role of straits and channels in understanding the characteristics of Mediterranean circulation, Prog. Oceanogr., 44, 65–108, 1999. Ben Ismail, S., Sammari, C., Gasparini, G.-P., Béranger, K., Brahim, M., and Aleya, L.: Water masses exchanged through the Channel of Sicily: Evidence for the presence of new water masses on the Tunisian side of the channel, Deep-Sea Res. I, 63, 65–81, http://dx.doi.org/10.1016/j.dsr.2011.12.009doi:10.1016/j.dsr.2011.12.009, 2012. Beuvier, J., Sevault, F., Herrmann, M., Kontoyiannis, H., Ludwig, W., Rixen, M., Stanev, E., Beranger, K., and Somot, S.: Modeling the Mediterranean Sea interannual variability during 1961–2000: Focus on the Eastern Mediterranean Transient, J. Geoph. Res., 115, C08017, http://dx.doi.org/10.1029/2009JC005950doi:10.1029/2009JC005950, 2010. Borzelli, G. L. E., Gači\'c, M., Cardin, V., and Civitarese, G.: Eastern Mediterranean transient and reversal of the Ionian Sea circulation, Geophys. Res. Lett., 36, L15108, http://dx.doi.org/10.1029/2009GL039261doi:10.1029/2009GL039261, 2009. Brankart, J.-M. and Brasseur, P.: The general circulation in the Mediterranean Sea: A climatological approach, J. Marine Syst., 18, 41–70, 1998. CIESM: Dynamics of Mediterranean deep waters, in: CIESM Workshop Monographs no 38, edited by: Briand, F., Monaco, 132 pp., 2009. Demirov, E. and Pinardi, N.: Simulation of the Mediterranean Sea circulation from 1979 to 1993: Part I. The interannual variability, J. Marine Syst., 33–34, 23–50, http://dx.doi.org/10.1016/S0924-7963(02)00051-9doi:10.1016/S0924-7963(02)00051-9, 2002. Gači\'c, M., Borzelli, G. L. E., Civitarese, G., Cardin, V., and Yari, S.: Can internal processes sustain reversals of the ocean upper circulation?: The Ionian Sea example, Geophys. Res. Lett., 37, L09608, http://dx.doi.org/10.1029/2010GL043216doi:10.1029/2010GL043216, 2010. Gači\'c, M., Civitarese, G., Eusebi Borzelli, G. L., Kovačevi\'c, V., Poulain, P.-M., Theocharis, A., Menna, M., Catucci, A., and Zarokanellos, N.: On the relationship between the decadal oscillations of the Northern Ionian Sea and the salinity distributions in the Eastern Mediterranean, J. Geophys. Res., 116, C12002, http://dx.doi.org/10.1029/2011JC007280doi:10.1029/2011JC007280, 2011. Gasparini, G. P., Ortona, A., Budillon, G., Astraldi, M., and Sansone, E.: The effect of the Eastern Mediterranean Transient on the hydrographic characteristics in the Strait of Sicily and in the Tyrrhenian Sea, Deep-Sea Res. I, 52, 915–935, 2005. Grignon, L., Smeed, D. A., Bryden, H. L., and Schroeder, K.: Importance of the variability of hydrographic preconditioning for deep convection in the Gulf of Lion, NW Mediterranean, Ocean Sci., 6, 573–586, http://dx.doi.org/10.5194/os-6-573-2010doi:10.5194/os-6-573-2010, 2010. Josey, S. A.: Changes in the heat and freshwater forcing of the eastern Mediterranean and their influence on deep water formation, J. Geophys. Res. 108, 3237, http://dx.doi.org/10.1029/2003JC001778doi:10.1029/2003JC001778, 2003. Lacombe, H., Tchernia, P., and Gamberoni, L.: Variable bottom water in the western Mediterranean basin, Prog. Oceanogr., 14, 319–338, 1985. Leaman, K D. and Schott, F A.: Hydrographic structure of the convection regime in the Gulf of Lions: Winter 1987, J. Phys. Oceanogr., 21, 575–598, 1991. Malanotte-Rizzoli, P., Manca, B. B., Ribera d'Alcala', M., Theocharis, A., Bergamasco, A., Bregant, D., Budillon, G., Civitarese, G., Georgopoulos, D., Korres, G., Lascaratos, A., Michelato, A., Sansone, E., Scarazzato, P., and Souvermezoglou, E.: A synthesis of the Ionian Sea hydrography, circulation and water mass pathways during POEM-Phase I, Prog. Oceanogr., 39, 153–204, http://dx.doi.org/10.1016/S0079-6611(97)00013-Xdoi:10.1016/S0079-6611(97)00013-X, 1997. Manzella, G. M. R., Gasparini, G. P., and Astraldi, M.: Water exchange through the eastern and western Mediterranean through the Strait of Sicily, Deep Sea Res. I, 35, 1021–1035, 1988. Menna, M. and Poulain, P. M.: Mediterranean intermediate circulation estimated from Argo in 2003–2010, Ocean Sci., 6, 331–343, http://dx.doi.org/10.5194/os-6-331-2010doi:10.5194/os-6-331-2010, 2010. Millot, C.: Circulation in the Western Mediterranean Sea, J. Marine Syst., 20, 423–442, 1999. Ovchinnikov, I. M.: The renewal of the principal water masses of the Mediterranean, Oceanology, 23, 719–721, 1983. Pinardi, N., Korres, G., Lascaratos, A., Roussenov, V., and Stanev, E.: Numerical simulation of the interannual variability of the Mediterranean Sea upper ocean circulation, Geophys. Res. Lett., 24, 425–428, http://dx.doi.org/10.1029/96GL03952doi:10.1029/96GL03952, 1997. Rixen, M., Beckers, J.-M., Levitus, S., Antonov, J., Boyer, T., Maillard, C., Fichaut, M., Balapoulos, E., Iona, S., Dooley, H., Garcia, M.-J., Manca, B., Giorgetti, A., Manzella, G., Mikhaolov, N., Pinardi, Zavatarelli, M., and the MEDAR Consortium: The western Mediterranean Deep water: A proxy for climate change, Geophys. Res. Lett., 32, L12608, http://dx.doi.org/10.1029/2005GL022702doi:10.1029/2005GL022702, 2005. Robinson, A., Leslie, W., Theocharis, A., and Lascaratos, A.: Mediterranean Sea circulation, in: Encyclopedia of Ocean Sciences, 3, 1689–1705, Elsevier, New York, 2001. Roether, W. and Lupton, J. E.: Tracers confirm downward mixing of Tyrrhenian Sea upper waters associated with the Eastern Mediterranean Transient, Ocean Sci., 7, 91–99, http://dx.doi.org/10.5194/os-7-91-2011doi:10.5194/os-7-91-2011, 2011. Roether, W., Klein, B., Beitzel, V., and Manca, B. B.: Property distributions and transient-tracer ages in Levantine Intermediate Water in the Eastern Mediterranean, J. Marine Syst. 18, 71–87, 1998. Roether, W., Klein, B., Manca, B. B., Theocharis, A., and Kioroglou, S.: Transient Eastern Mediterranean deep waters in response to the massive dense-water output of the Aegean Sea in the 1990s, Prog. Oceanogr. 74, 540–571, 2007. Schroeder, K., Gasparini, G. P., Tangherlini, M., and Astraldi, M.: Deep and Intermediate Water in the Western Mediterranean under the influence of the Eastern Mediterranean Transient, Geophys. Res. Lett., 33, L21607, http://dx.doi.org/10.1029/2006GL027121doi:10.1029/2006GL027121, 2006. Schroeder K., Gasparini, G. P., Borghini, M. M., and Ribotti, A.: Experimental evidences of the recent abrupt changes in the deep Western Mediterranean Sea,~in: Dynamics of Mediterranean Deep Waters, CIESM Workshop Monographs, no. 38, Qwara, Malta, 2009. Schroeder, K., Josey, S. A., Herrmann, M., Grignon, L., Gasparini, G. P., and Bryden, H. L.: Abrupt warming and salting of the Western Mediterranean Deep Water after 2005: atmospheric forcings and lateral advection, J. Geophys. Res., Vol. 115, C08029, http://dx.doi.org/10.1029/2009JC005749doi:10.1029/2009JC005749, 2010. Skliris, N., Sofianos, S., and Lascaratos, A.: Hydrological changes in the Mediterranean Sea in relation to changes in the freshwater budget: A numerical modelling study, J. Marine Syst., 65, 400–416, http://dx.doi.org/10.1016/j.jmarsys.2006.01.015doi:10.1016/j.jmarsys.2006.01.015, 2007. Vetrano A., Gasparini, G. P., Molcard, R., and Astraldi, M.: Water flux estimates in the central Mediterranean Sea from an inverse box model, J. Geophys. Res., 109, C01019, http://dx.doi.org/10.1029/2003JC001903doi:10.1029/2003JC001903, 2004. Wu, P. and Haines, K.: Modeling the dispersal of Levantine Intermediate Water and its role in Mediterranean deep water formation, J. Geophys. Res., 101, 6591–6607, 1996. Zunino, P., Schroeder, K., Vargas-Yáñez, M., Gasparini, G. P., Coppola, L., García-Martínez, M. C., and Moya-Ruiz, F.: Effects of the Western Mediterranean Transition on the resident water masses: pure warming, pure freshening and pure heaving, J. Marine Syst., 96–97, 15–23, doi:j.jmarsys.2012.01.011, 2012.