PHYSICOCHEMICAL INTERACTIONS BETWEEN THE ADRIATIC AND THE IONIAN SEAS

Ekaterini Souvermezoglou 1* and Evangelia Krasakopoulou 1 1 Hellenic Centre for Marine Research Institute of Oceanography - [email protected]

Abstract The ability of the Adriatic in renewing the deep waters of the Eastern Mediterranean is investigated in relation to the properties of the LIW entering from the Ionian Sea. This study is based on oxygen and nutrient data collected in the Otranto strait and the surrounding area between 1987 and 2000.

Keywords: Oxygen, Nutrients, Intermediate waters, Otranto Strait

The Adriatic Sea is a semi-enclosed basin shallow in the north and deep in the south. It communicates with the Ionian Sea thought the Strait of Otranto, a 70 km wide and 800 m deep channel. The general circulation in the Adriatic basin is cyclonic [1] consisting from a rather weak current along the eastern coast (the Eastern Adriatic Current - EAC) and a fast mainly coastal current along the western coast (the West Adriatic current - WAC). The Ionian Sea is a deep (up to 4000m) and wide basin which receives salty and warm waters from the easternmost part of the Mediterranean and fresher and relatively colder water from the western Mediterranean. The EAC bring Levantine Intermediate Water (LIW) and Ionian Surface Water (ISW) into the Adriatic [2]. Adriatic is prone to strong winter outbreaks of cold dry northerly winds which induce extended heat losses and evaporation, that drive to deep water formation events. During cold winters and restricted fresh water input, the densest water in the whole of the Mediterranean, the North Adriatic Dense Water (NAdDW) is formed over the shallow northern shelf of the Adriatic [3]. Fig. 2. Dissolved oxygen and nitrate plotted against sigma-theta in the station o o In addition, in the Southern Adriatic Pit, the Adriatic Deep Water (ADW) is 40 00’N 19 00’ E in Otranto strait for the period 1994-2000. produced through open ocean deep convection [4]. The capacity of the Adriatic Sea to form dense water depends to: - the incorporation of saline intermediate waters References - the intensity of the winters. 1 - Orlic M., Gacic M., LaViolette P.E.,1992. The currents and circulation of the During the Eastern Mediterranean Transient (EMT) the salinity of the Adriatic Sea. Oceanol. Acta 15(2), 109–124. intermediate layers (200-700 m) entering in the Adriatic Sea became reduced by 2 - Gacic M., Lascaratos A., Manca B., Mantziafou A., 2001. Adriatic deep the upwelling of the deep waters in the Eastern Mediterranean, due to the water and interaction with the Eastern Mediterranean Sea. In: Cushman-Roisin massive dense water supply from the Cretan Sea [5]. The reduction of salt B., Gacic M., Poulain P.-M., Artegiani A. (Eds.), Physical Oceanography of the content in combination with milder winters limited the capacity of the Adriatic Adriatic Sea: Past, Present and Future. Kluwer Academic Publishers, Sea to form dense water [6]. Dordrecht /Boston /London, pp. 111–142. The systematic study of the nutrient and oxygen regime from 1987 in the 3 - Vilibic, I., 2003. An analysis of dense water production on the North Otranto strait in the frame of national and international research programs Adriatic shelf. Estuarine Coastal Shelf Sci. 56, 697–707. permitted to follow the temporal evolution of oxygen and nutrients in the Strait 4 - Vilibic I., Orlic M., 2002. Adriatic water masses, their rates of formation and of Otranto (Fig. 1 & 2) and the surrounding area [7] and [8]. transport through the Otranto Strait. Deep-Sea Res. I 49, 1321–1340. Our observations show that the ability of the Adriatic in renewing the deep 5 - Roether W., Klein B., Beitzel V., Manca B.B., 1998. Property distributions waters of the Eastern Mediterranean is closely linked to the properties of the and transient tracer ages in Levantine Intermediate Water in the Eastern LIW entering from the Ionian Sea. The modulation of the LIW characteristics Mediterranean. J. Mar. Systems 18, 71-87. entering in the Adriatic Sea due to the reversal of the North Ionian Gyre (NIG) 6 - Klein, B., Roether, W., Civitarese, G., Gacic, M., Manca, B.B., Ribera from anticyclonic during the period of 1987-1995, to cyclonic during the period d’Alcala, M., 2000. Is the Adriatic returning to dominate the production of of 1996-2005 [9] is also examined. Eastern Mediterranean Deep Water? Geophys. Res. Lett. 27 (20), 3377–3380. 7 - Souvermezoglou E., Krasakopoulou E., Pavlidou A., 1999. Chemical status of the Eastern Mediterranean Transient during the period 1997-1998. Fourth Workshop of the Mediterranean Targeted Project, 28-30 October 1999, Perpignan, France, p.169. 8 - Souvermezoglou E., Spyres G., Civitarese G., Kress N., Krom M.D., Ribera d’Alcala M., Yilmaz A. 2009. Trends of nutrients and nutrients ratios in the deep water of the Eastern Mediterranean Sea from 1986 to 2006. ASLO Aquatic Sciences Meeting, Nice 26 -30 January 2009, p. 55. 9 - Civitarese G., Gacic , M., Lipizer M., Eusebi Borzelli G.L., 2010. On the impact of the bimodal oscillating system (BiOS) on the biogeochemistry and biology of the Adriatic and Ionian Seas (Eastern Mediterranean). Biogeosciences 7, 3987–3997.

Fig. 1. Dissolved oxygen and nitrate plotted against sigma-theta in the station 40o 00’N 19o 00’ E in Otranto strait for the period 1987-1991.

191 Rapp. Comm. int. Mer Médit., 40, 2013

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