Advances in Geosciences www.adv-geosci.net 1680-7340 1680-7359 26 11th EGU Plinius Conference on Mediterranean Storms (2009) 2010 10.5194/adgeo-26-53-2010 http://www.adv-geosci.net/26/53/2010/ http://www.adv-geosci.net/26/53/2010/adgeo-26-53-2010.html http://www.adv-geosci.net/26/53/2010/adgeo-26-53-2010.pdf 53 59 2010-07-07 Violent storms within the Sea: dense water formation episodes in the NW Mediterranean J. Salat salat@icm.csic.es P. Puig M. Latasa Insitut de Ciències del Mar (CSIC), P. Marítim, 37–49, 08003 Barcelona, Spain Centro Oceanográfico de Gijón (IEO), Avda. Príncipe de Asturias 70 bis, 33212 Gijón – Asturias, Spain Heat and water exchanges in the ocean occur almost exclusively at the surface. As water compressibility is very low, stratification of the fluid is expected and horizontal motion is predominant in the sea interior. Among the few processes that may introduce a vertical component in the water motion are those that increase surface water density by freezing, cooling or evaporation. Those processes triggering convective motion are enhanced by cold surface air, dry wind and low solar radiation. Therefore, convective cells are more likely to occur when the temperature of the air at the sea surface is lower than sea surface temperature. Conversely, rain, river runoff, solar heating, calm and condensation at surface enhance stratification. Convective motion at sea has several scales ranging from few meters at the upper ocean, causing the surface mixed layer, to the entire water column, in what is known as deep convection. Only few places in the world ocean are suitable for deep convection, and only under particular weather conditions. In this paper, a brief review of the response to these particular conditions in the NW Mediterranean is presented in what is known as dense water formation. The violent sinking and spreading of water parcels that reach the deep sea floor in few hours is described. These are "hidden" mediterranean storms, occurring under the sea surface, "on the other side of the mirror". % vor jede Referenz Allain, C.: Topographie dynamique et courants généraux dans le bassin occidental de la Méditerranée, Rev. Trav. Inst. Pêches Marit., 24, 121–145, 1960. Bougis, P. and Ruivo, M.. Sur une descente des eaux superficielles en profondeur (cascading) dans le sud du Golfe du Lion. Bulletin d'Information du Comité Central d'Océanographie et d'Etude des Côtes, 6, 147–154, 1954. Bryden, H. L. and Stommel, H. M.: Origin of the Mediterranean outflow, J. Mar. Res., Suppl., 40, 55–71, 1982. Canals, M., Puig, P., Durrieu de Madron, X., Heussner, S., and Fabres, J.: Flushing submarine canyons, Nature, 444, 354–357, 2006. CIESM: Tracking long-term hydrological change in the Mediterranean Sea, CIESM Workshop Series, 16, 134 pp., Monaco, 2002. CIESM: Dynamics of Mediterranean deep waters, No. 38, in: CIESM Workshop Monographs, edited by: Briand, F., 132~pp., Monaco, 2009. Colacino, M.: Mediterranean meteorology, in: Winds and currents of the Mediterranean basin, Reports of Meteorology and Oceanogrphy, edited by: Charnock, H., Harvard University, 40, 1–38, 1992. Durrieu de Madron, X., Zervakis, V., Theocharis, A., and Geogopoulos, D.: Comments on "cascades of dense water around the world ocean", Prog. Oceanogr., 64, 83–90, 2005. Fieux, M.: Formation d'eau dense sur le plateau continental du Golfe du Lion, Colloq. Internat, du CNRS sur la formation des eaux océaniques profondes, 215, 165–189, 1974. Font, J., Puig, P., Salat, J., Palanques, A., and Emelianov, M.: Sequence of hydrographic changes in NW Mediterranean deep water due to the exceptional winter of 2005, Sci. Mar., 71(2), 339–346, 2007. Furnestin, J.: Hydrologie de la Méditerranée occidentale: Golfe du Lion, Mer Catalane, Mer d'Alboran et Corse Orientale, Rev. Trav. Inst. Pêches marit., 24, 5–119, 1960. Gascard, J. C.: Mediterranean deep water formation, baroclinic instability and oceanic eddies, Oceanol. Acta, 1(3), 315–330, 1978. Gascard, J. C.: Open ocean convection and deep water formation revisited in the Mediterranean, Labrador, Greenland and Weddell Seas., Elsev. Oceanogr. Series, 57, 157–181, 1991. Herrmann, M. and Somot, S.: Relevance of ERA40 dynamical downscaling for modeling deep convection in the Mediterranean Sea, Geophys. Res. Lett., 35, L04607, doi:10.1029/2007GL032442, 2008. Hopkins, T. S.: Physical processes in the Mediterranean basins, in: Estuarine transport processes, edited by: Kjerfve, B., Univ. of South Carolina Press, 7, 269–310, 1978. Killworth, P. D.: The mixing and spreading phases of MEDOC I, Progr. Oceanogr., 7, 59–90, 1976. Lacombe, H., Gascard, J. C., Gonella, J., and Bethoux, J. P.: Response of the Mediterranean Sea to the water and energy fluxes across its surface, on seasonal and interannual scales, Oceanol. Acta,, 4(2), 247–255, 1981. Leaman, K. D. and Schott, F.: Hydrographic structure of the convection regime in the Gulf of Lions, winter 1987, J. Phys. Oceanogr., 21, 575–598, 1991. Marshall, J. and Schott, F.: Open-ocean convection: Observations, theory and models, Rev. Geophys., 37, 1–64, 1999. Millot, C.: Circulation in the western Mediterranean Sea, J. Marine Syst., 20, 423–442, 1999. MEDOC Group: Observations of formation of deep water in the Mediterranean Sea, 1969, Nature, 227, 1037–1040, 1970. Palanques, A., Puig, P., Latasa, M., and Scharek, R.: Deep sediment transport induced by storms and dense shelf water cascading in the northwestern Mediterranean basin, Deep-Sea Res. I, 56, 425–434, 2009. Puig, P., Palanques, A., Orange, D. L., Lastras, G., and Canals, M.: Dense shelf water cascades and sedimentary furrow formation in the Cap de Creus Canyon, northwestern Mediterranean Sea, Cont. Shelf Res., 28, 2017–2030, 2008. Puig, P., Palanques, A., Font, J., Salat, J., Latasa, M., Scharek, R.: Interactions between open-sea convection and shelf cascading dense waters in the formation of the Western Mediterranean Deep Water, in: CIESM Workshop Monographs No. 38 "Dynamics of Mediterranean Deep Waters", edited by: Briand, F., 81–89, 2009. Salat, J., Emelianov, M., and López-Jurado, J. L.: A typical Western Mediterranean Deep Water formation during winter 2005, Rapp. Comm. Int. Mer Médit., 38, 197, 2007. Salat, J. and Font, J.: Water mass structure near and offshore the Catalan Sea during winters of 1982 and 1983, Ann. Geophys., 5B(1), 49–54, 1987. Schott, F. and Leaman, K.: Observations with moored acoustic Doppler current profilers in the convection regime in the Gulf of Lions, J. Phys. Oceanogr., 21, 558–574, 1991. Schroeder, K., Ribotti, A., Borghini, M., Sorgente, R., Perilli, A., and Gasparini, G. P.: An extensive western Mediterranean deep water renewal between 2004 and 2006, Geophys. Res. Lett., 35, L18605, doi:10.1029/2008GL035146, 2008. Swallow, J. C. and Caston, G. F.: The preconditioning phase of MEDOC 69, Part I: Observations, Deep-Sea Res., 20, 429–448, 1973. Tchernia, P.: L'eau intermédiaire dans le bassin Algéro-Provençal, Bull. Inf. COEC., 10, 19–22, 1958. Testor, P. and Gascard, J. C.: Post-convection spreading phase in the Northwestern Mediterranean Sea, Deep-Sea Res. I, 53, 869–893, 2006. Voorhis A. D. and Webb D. C.: Large vertical currents observed in a winter sinking region of the northwestern Mediterranean, Cah. Oceanogr., 22, 571–580, 1970.