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Circulation of the Levantine Intermediate Water; Mediterranean Sea geography and nomenclature of the major sub-basins and straits (adapted from Millot and Taupier-Letage, 2005).
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Data from 38 Argo profiling floats are used to describe the intermediate Mediterranean currents for the period October 2003-January 2010. These floats were programmed to execute 5-day cycles, to drift at a neutral parking depth of 350 m and measure temperature and salinity profiles from either 700 or 2000 m up to the surface. At the end of each cyc...
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... AW and becomes the main component of Mediterranean outflow to the Atlantic. From Rhodes ( Fig. 1), the LIW flows along the southern continental slope of the Cretan Arc islands to the Peloponnese, and can be found in the Ierapetra and Pelops wind-induced eddies. Part of the LIW, that continues circulating along the north-eastern slope, penetrates in the Southern Adriatic where it mixes with the AW and influences the deep water formation processes. The remainder bypasses the Southern Adriatic and continues along slope as far as the Sicily Channel, where most of it outflows into the western basin. Within the Sicily Channel, the LIW flows along the Sicil- ian slope, skirts Sicily and enters in the Tyrrhenian, where it circulates roughly at 200–600 m. A vein flows out through the Corsica Channel (sill at ∼ 400 m) while the remainder continues and flows out through the Sardinia Channel. When this vein enters the Algerian sub-basin, part of it can be en- trained offshore by Algerian eddies, the remainder continues along the western Sardinia and Corsica slopes, joins with the vein issued from the Corsica Channel, and enters in the Ligurian and the Proven ̧al sub-basins. The still-recognisable LIW continues along the Spanish slope (Liguro-Proven ̧al- Catalan Current) and most of it outflows through the Strait of Gibraltar (Millot and Taupier-Letage, 2005). The LIW plays an important role in the functioning of the Mediterranean Sea because it is the warmest and saltiest Mediterranean water formed with large amount, and because it mainly flows along the northern continental slopes of both basins, thus being in- volved in the offshore formation of all deep Mediterranean water (Millot and Taupier-Letage, 2005). The southern continental slopes of western and eastern basins are characterised by narrow and unstable currents located respectively in the Algerian (Algerian Current) and Levantine (Libyo-Egyptian Current) sub-basins, that flow from west to east and lead to the generation of cyclonic and anticyclonic eddies (Mejdoub and Millot., 1995; Hamad et al., 2005; Taupier-Letage et al., 2007; Gerin et al., 2009). These currents extend as deep as the LIW core depth (200– 500 m). During the last decades, direct measurements (moorings) of intermediate currents in some regions of the Mediterranean Sea were performed. The results of these in situ observations, summarized below, provide however only a par- tial view of the intermediate flows, with main focus in channels and dominant currents. The intermediate current (300– 400 m) in the northern Tyrrhenian Sea was investigated using three moorings, deployed between 1989 and 1990, that measured velocities values less then 1 cm/s (Artale et al., 1994). One year of current measurement in the Corsica Channel (between October 1986 and September 1987), obtained from three moorings deployed in the area north of Corsica and off the eastern Ligurian coast, produced respectively a mean velocity of 8.4 , 5.6 and ∼ 10 cm/s at depth of 300 m (Astraldi et al., 1990). An array of nine moorings, deployed in the eastern Algerian Basin between July 1997 and July 1998, measured a mean current of 4.8 cm/s and a maximum current of 14.73 cm/s (Testor et al., 2005). Two years (1994–1995) of direct current measurements were collected by six moorings in the Otranto Channel; in the intermediate layer (290– 330 m), speed showed the minimum values in the central region of the channel (between 0.3 and 0.8 cm/s), maximum value along the eastern boundary (4.4 cm/s) and a mean value of 1.3 cm/s at the western boundary (Kova cević et al., 1999). In the same period, moorings located in the southern Adriatic recorded mean velocities between 1.4 and 5 cm/s (Kova cević et al., 1999). In the Sicily Channel, over the western sill of the strait, the outflow of Eastern Mediterranean intermediate water was characterised by an intensity of 12.5 cm/s, whereas at the southern entrance of the Tyrrhenian Sea the intermediate current showed a speed of ∼ 8 cm/s (Astraldi et al., 2001). In summary, we can state that the intermediate speeds measured by moorings in the Mediterranean Sea vary essentially between 1 and 15 cm/s. Two types of profiling floats were operated in Mediterranean: the Apex (manufactured by Webb Research Corpo- ration, USA) and the Provor (produced by NKE Electronics, France). All floats were equipped with Sea-Bird CTD sen- sors. Among all the floats deployed in the Mediterranean Sea, we have selected 38 instruments according to their cycle characteristics. They were deployed as part of the MFSTEP project in 2003 and are referred to as MedArgo floats. Each float descents from the surface to a programmed parking depth of 350 m, where it remains for about 4.5 days before reaching the profile depth, that is generally 700 m but extends to 2000 m every ten cycles. At the end of each cycle the float remains for about 5–7 h at the sea surface (Solari et al., 2008), where it is localised by, and transmit the data to, the Argos satellite system. Argos is a global data location and collection system carried by the NOAA polar orbit- ing satellites; this system provides the float positions with an accuracy between 250 and 1500 m (see Appendix A for details). The data used in this work contain information on three dimensional movement of float: a set of coordinates of the float during its transmissions from the sea surface to the satellites and the pressure recorded during the parked phase of the cycle. These data are utilized to determine the float surface and intermediate displacements and, consequently to estimate the parking depth velocities. Figure 2 shows the surface and intermediate trajectories of the 38 selected floats (black line) filtered to remove cycles located over water depth less then 350 m and anomalous cycles larger than 5 days. There are 14 Apex and 24 Provor floats with a total of 3431 cycles covering the period ...
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... a mean velocity of 2 cm/s (MKE less than 10 cm /s , Fig. 7a), following the western coasts of Sardinia and Corsica, while another branch proceeds to the west (bin-averaged speed between 3 and 7 cm/s, Fig. 5b; MKE between 10 and 25 cm 2 /s 2 , Fig. 7a) and enters the Algerian Basin. In the Liguro-Proven ̧al sub-basin intermediate mean velocities describe a cyclonic circulation that, according to Astraldi et al. (1994), typically involves both the surface and the intermediate layer; in this region LIW participates with surface Atlantic Water (AW) in the wintertime formation of West Mediterranean Intermediate Water (WIW) (Robinson et al., 2001). The float velocities vary between 3 cm/s in the eastern branch (in agreement with Astraldi et al., 1994) and 11 cm/s in the western branch. The main cyclonic path (41 ◦ –44 ◦ N; 0 ◦ –8 ◦ E) contains a re-circulation cyclonic cell located between 42 ◦ –44 ◦ N and 6 ◦ 30 –8 ◦ 30 E (Fig. 5b). Along the French and Spanish slopes, the float velocities follow the Liguro-Proven ̧al-Catalan Current (or North- ern Current), and reach the maximum bin-averaged speed ( ∼ 11 cm/s) and the maximum value of MKE ( ∼ 65 cm 2 /s 2 , Fig. 7a) recorded in the float dataset. In the Balearic Sea, around the islands of Majorca and Menorca, the intermediate mean current describe an anticyclonic circulation following the isobaths; south of the Ibiza Channel the current merges into the Liguro-Proven ̧al-Catalan flow, towards the Alborán Sea. In the Algerian Basin the floats follow the Algerian Current along the coast from west to east, with a maximum velocity of ∼ 7 cm/s (Fig. 5a and b) and MKE values between 15 and 30 cm 2 /s 2 (Fig. 7a). More offshore they describe two cyclonic gyres (AG1 and AG2 in Fig. 5b), defined as Eastern Algerian and Western Algerian Gyres (Testor et al., 2005; Testor and Gascard, 2005) with a geographical extension of 100–300. The water masses recognised in AG1 and AG2 are composed by highly modified LIW and Tyrrhenian Deep Water (TDW). The mean float velocities in the Algerian Gyres at 350 m are in agreement with Testor et al. (2005) results (mean value ∼ 5 cm/s; maximum value ∼ 10 cm/s). In the southern Ionian Sea, the float velocities show a dominant anticyclonic circulation between 32 ◦ –36 ◦ N and 16 ◦ –20.5 ◦ E, in which the southern limb corresponds to a north-westward flow located on the African continental slope (speeds between 1.5 and 9 cm/s, Fig. 5a; MKE values between 10 and 40 cm 2 /s 2 , Fig. 7a).This north-westward current is in opposite direction compared to the circulation patterns described by Millot and Taupier-Letage (2005) and depicted in Fig. 1. In the south of Levantine Basin (Fig. 5c), along the Libyan and Egyptian slopes, the mean currents flow eastward and turn into several eddies, ...
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... Proven whereas ̧al-Catalan the Liguro-Proven basin and in ̧al, some Algerian eddies and of the Libyan- eastern Egyptian basin, whereas Currents the are Liguro-Proven characterised ̧al, by maximum Algerian and speeds Libyan- of 15 Egyptian cm/s. Currents are characterised by maximum speeds of 15 The cm/s. pseudo-Eulerian statistics, computed with V end 350 , show typical The circulation pseudo-Eulerian pathways statistics, related computed to Mediterranean with V end 350 inter- , show mediate typical currents. circulation The pathways mean circulation related to mapped Mediterranean by floats inter- is almost mediate everywhere currents. in The agreement mean circulation with the description mapped by of floats inter- is mediate almost circulation everywhere provided in agreement by the with framework the description of various of inter- international mediate circulation projects and provided by several by the authors framework in the past. of various There in- is ternational an important projects exception and by in several the southern authors Ionian, in the along past. There the Libyan is an important coast, where exception floats follow in the a southern north westward Ionian, current, along the which Libyan is coast, in opposite where direction floats follow compared a north to westward the circulation current, patterns which described is in opposite by Millot direction and Taupier-Letage compared to the (2005) circulation and depicted patterns in described Fig. 1. The by Millot LIW flow and south Taupier-Letage of Crete and (2005) north- and ward depicted pathway in Fig. toward 1. The the Adriatic LIW flow Sea south was of not Crete confirmed and north- by the ward float pathway data, due toward to the the presence Adriatic of Sea Ierapetra was not eddy confirmed and the by scarcity the float of data, data in due the to northeast the presence Ionian of Sea. Ierapetra eddy and the scarcity In the of Western data in Mediterranean the northeast Ionian basin, Sea. the velocity field shows In the the characteristic Western Mediterranean cyclonic paths basin, in the the velocity Tyrrhenian, field Liguro-Proven shows the characteristic ̧al and Algerian cyclonic sub-basins, paths in as the well Tyrrhenian, as in the Algerian Liguro-Proven and Liguro-Proven ̧al and Algerian ̧al-Catalan sub-basins, Currents, as well where as in it the reaches Algerian the and maximum Liguro-Proven intensities ̧al-Catalan ( ∼ 10–12 cm/s). Currents, High where val- it ues of EKE ( ∼ 80 cm 2 /s 2 ) and velocity variance are ...
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... Mediterranean Sea, depicted in Fig. 1, is a semi- enclosed basin connected to the Atlantic Ocean by the narrow Strait of Gibraltar and to the Black Sea by the Dardanelles- Marmara Sea-Bosphorus system. The whole Mediterranean is a concentration basin (evaporation exceeds precipitation and runoff) divided in two sub-basins (Western and Eastern Mediterranean) by the shallow ( ∼ 400 m) sill of the Sicily Channel. The water deficit is supplied by the inflow of the Atlantic Water (AW), that flows from the Strait of Gibraltar eastward along the North African coast and enters in the eastern basin through the Sicily Channel (Millot, 1999; Lascaratos et al., 1999) (not shown). The net result of the air-sea interactions in the entire Mediterranean is an outflow of salty water through the Strait of Gibraltar; the main water mass that constitute this salty and relatively warm outflow is the Levantine Intermediate Water (LIW). The LIW, formed in the eastern Levantine sub-basin, sinks to a depth between 200 and 500 m and spreads out across the entire Mediterranean basin at this intermediate depth (Fig. 1). The LIW proceeds essentially westward along several pathways and eventually outflows in the Atlantic Sea and influences the formation of North Atlantic Deep Water (NADW) (Reid, 1994; Lozier et al., 1995; Potter and Lozier, 2004). Hence, the salty LIW is a crucial component of the Mediterranean thermohaline “conveyor belt” circulation (Poulain et al., 2007) and it can influence the NADW formation in the global thermohaline cell. Traditional knowledge on the nature and motion of the intermediate water masses in the Mediterranean Sea is almost entirely based on hydrographic properties, with only spo- radic direct current measurements mainly made with moorings in the major channels (Corsica, Sicily, Otranto) and in the Strait of Gibraltar. Since the turn of the century profiling floats have provided data to study the intermediate ...
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... Mediterranean Sea, depicted in Fig. 1, is a semi- enclosed basin connected to the Atlantic Ocean by the narrow Strait of Gibraltar and to the Black Sea by the Dardanelles- Marmara Sea-Bosphorus system. The whole Mediterranean is a concentration basin (evaporation exceeds precipitation and runoff) divided in two sub-basins (Western and Eastern Mediterranean) by the shallow ( ∼ 400 m) sill of the Sicily Channel. The water deficit is supplied by the inflow of the Atlantic Water (AW), that flows from the Strait of Gibraltar eastward along the North African coast and enters in the eastern basin through the Sicily Channel (Millot, 1999; Lascaratos et al., 1999) (not shown). The net result of the air-sea interactions in the entire Mediterranean is an outflow of salty water through the Strait of Gibraltar; the main water mass that constitute this salty and relatively warm outflow is the Levantine Intermediate Water (LIW). The LIW, formed in the eastern Levantine sub-basin, sinks to a depth between 200 and 500 m and spreads out across the entire Mediterranean basin at this intermediate depth (Fig. 1). The LIW proceeds essentially westward along several pathways and eventually outflows in the Atlantic Sea and influences the formation of North Atlantic Deep Water (NADW) (Reid, 1994; Lozier et al., 1995; Potter and Lozier, 2004). Hence, the salty LIW is a crucial component of the Mediterranean thermohaline “conveyor belt” circulation (Poulain et al., 2007) and it can influence the NADW formation in the global thermohaline cell. Traditional knowledge on the nature and motion of the intermediate water masses in the Mediterranean Sea is almost entirely based on hydrographic properties, with only spo- radic direct current measurements mainly made with moorings in the major channels (Corsica, Sicily, Otranto) and in the Strait of Gibraltar. Since the turn of the century profiling floats have provided data to study the intermediate ...
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... characteristics (Notarstefano and Poulain, 2009) and currents more or less continuously throughout the Mediterranean Sea. We hereafter present a novel quantitative description of the intermediate currents related to the LIW in most areas of the Mediterranean Sea based on the displacements of profiling floats. Autonomous profiling floats were operated in the Mediterranean starting in 2000 (Poulain et al., 2007) and contributed to the global Argo program. In 2003, as part of the MFSTEP project, a significant number of floats were deployed to provide temperature and salinity data in real time to op- erational prediction models ( These floats, also referred to as MedArgo floats, were programmed to execute 5-day cycles and to drift at a neutral parking depth of 350 m. This depth was chosen because it corresponds approximately to the depth of the LIW core in most of the basin. More specifically a recent study on Argo float salinity data recognizes the LIW core close to the surface in the Levantine basin, at 300–350 m in the centre of Mediterranean Sea and deeper then 350 m in the Liguro- Proven ̧al basin (Notarstefano and Poulain, 2009). Hence, drifts at 350 m allow to study the LIW pathways from its ori- gin in the northern Levantine sub-basin to its outflow through the Strait of Gibraltar (Poulain et al., 2007). In this paper, we describe quantitatively the Mediterranean Sea circulation at the float parking depth and refer to 350 m currents as intermediate currents. Float surface positions are used to determine surface and intermediate displacements. The estimation of surface displacement includes the use of satellite fixed positions. The estimation of intermediate displacement requires the determination of the exact surfacing and diving times and the extrapolation in time of the satellite- derived positions, using a simple model based on linear displacement and inertial motion. From these, the intermediate velocities at the 350 m parking depth are estimated and fi- nally used to compute pseudo-Eulerian circulation statistics and to produce maps of mean intermediate circulation and eddy variability in the Mediterranean Sea. The paper is organised as follows. Background on the Mediterranean intermediate circulation is given in Sect. 2. The float database and the methodology used to process the data are described in Sect. 3. Fast currents, pseudo-Eulerian maps of mean flow, eddy variability, energy levels and the bathymetry-controlled currents are presented and discussed in Sect. 4. The conclusions are summarized in Sect. 5. Technical details are given in the Appendix A. The most exhaustive descriptions of the intermediate circulation in the Western Mediterranean Sea arose in the framework of various international projects (La Violette, 1990; Millot, 1995, 1999; Fusco et al., 2003, Millot and Taupier- Letage, 2005), whereas for the Eastern Mediterranean they were described as part of the POEM and MFSPP projects (Malanotte-Rizzoli and Hetch, 1988; Malanotte-Rizzoli and Robinson, 1988; Robinson et al., 1991, 2001; Malanotte- Rizzoli et al., 1999; Fusco et al., 2003). The Mediterranean (Fig. 1) is governed by a large scale anti-estuarine buoyancy- driven circulation (Myers and Haines, 2000): the salinity increase due to evaporation over the Mediterranean surface is compensated by an outflow of salty water in the Atlantic Ocean. Inflowing Atlantic Water (AW) flows across the western and eastern basins into the Levantine sub-basin. Cooling in winter causes convection to intermediate depths mainly in the Rhodes gyre forming the LIW (Ovchinnikov, 1984; Malanotte-Rizzoli and Robinson, 1988; Lascaratos, 1993; Lascaratos et al., 1993, 1999; Nittis and Lascaratos, 1998; Malanotte-Rizzoli et al., 1999, Myers and Haines, 2000). This salty intermediate water returns to the west ...
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Data from 38 Argo profiling floats are used to describe the subsurface Mediterranean currents for the period 2003-2009. These floats were programmed to execute 5-day cycles, to drift at a neutral parking depth of 350 m and measure temperature and salinity profiles from either 700 or 2000 m up to the surface. At the end of each cycle the floats rema...
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... While the PM observed in the traps is predominantly supplied by flash floods and resuspension by shelf waves, cross-shore flow is also required in order to transport the PM to the deep basin. At the EMS, mid-depth water hosts the socalled LIW (Levantine Intermediate Water) water mass (150-350 m, Hazan et al., 2018;Ozer et al., 2017), which is indeed believed to derive from the margins (Fach et al., 2021;Menna & Poulain, 2010); however, its temporal pattern and dynamics are hardly known. Current velocities measured during the present study, although unfortunately limited only to the DeepLev site, 50 km offshore, clearly show that while average westward velocities are relatively low (1.7 and 1.5 km d 1 at 100 and 280 m, respectively), there are several velocity peaks (up to 40 and 17 km d 1 , respectively, Figures 8b and 8c), which could allow the arrival of PM at DeepLev within several days, in agreement with the above. ...
Sediment trap data set and ²³⁴Th profiles (deep water excesses and deficits) reveal that particulate organic carbon (POC) export at the highly oligotrophic Levantine Sea is dominated by lateral transport from the nearby margin. These intermediate nepheloid layers (INL) operate at multi‐depth, with the silt‐to‐clay size particulate matter (PM) fraction transported at water depths of about 100–500 m, while finer fraction arrives also at deeper depths. The shallow NIL is triggered by winter storms, manipulated by coastal flash floods and shelf resuspension and assisted by cross‐shore currents, which allow the arrival of PM at a distance of 50 km within about 10 days. The deeper INL could be related to sediments initially driven to depth by density currents. Our data show that inter‐annual differences in sediment trap fluxes were related to changes in both the intensity of coastal floods and current velocity. The frequent observation of deep‐water ²³⁴Th excesses during a (relatively) low export winter (2018) is related to lessened cleansing of the water column, that is, reduced removal of fine‐grained PM by sinking coarser‐grained material. These observations highlight the importance of winter storm intensity in the POC budget of marginal seas like the Levantine Basin (LB) even in areas with limited river discharge. This further suggests that the anticipated increase in extreme weather events due to the on‐going climate change should have an impact on this coastal‐deep sea conveyor and on POC export in the LB.
... The classical Mediterranean circulation model involves a shallow influx of Atlantic Water moving eastward from Gibraltar towards North African coasts, which then enters the eastern basin through the Sicily Channel, transforming into the deeper Levantine Intermediate Water. This water subsequently moves westward until it exits into the Atlantic Ocean through the Strait of Gibraltar (Pinardi & Massetti, 2000;Menna & Poulain, 2010). Surface circulation in the southeastern Mediterranean is dominated by large anticyclonic gyres with seasonal variation (Pinardi & Massetti, 2000), affecting the southern coasts of Crete. ...
In the Mediterranean Sea, the genus Pinna encompasses two large fan-shaped bivalve species, Pinna nobilis and Pinna rudis. Historically, both species coexisted in the western Mediterranean until a Mass Mortality Event brought P. nobilis to the brink of extinction. Notably, P. rudis remained unaffected by the MME, and its recent successful recruitment and further spread has been hypothesized to be linked to the local extinction of P. nobilis. Although P. rudis has been sparsely recorded in the eastern Mediterranean Sea (but with some of these records being doubtful), reports emerging in the summer of 2023 from researchers and citizens have unveiled its sudden spread in Greece. This study presents an updated review of the distribution of P. rudis in the Mediterranean Sea, integrating data from literature and online repositories. Additionally, the recent presence of the species within Greek waters was documented through a dedicated survey and molecularly confirmed through two distinct molecular methods. For the distribution mapping of P. rudis in Greece, we also included information derived from a citizen science initiative, following photo-identification of the species. Consequently, this research confirms the recent spread of P. rudis in South Crete and the Greek Ionian Sea (first verified records of the species in both regions), in marine areas where P. nobilis has become extinct, further strengthening the hypothesis that P. rudis has benefited from the collapse of P. nobilis populations.
... The Mediterranean Sea is a semi-enclosed continental sea that is considered as a laboratory for climate change studies [5] from how it has been changing faster than the global ocean, creating a strong impact on the marine environment [50,33]. It consists of two basins, the Western Mediterranean (WMED) and the Eastern Mediterranean Sea (EMED) connected through the narrow and shallow Sicily Strait, which supports the mixing of the surface water and intermediate water [31,40]. EMED is made by its own seas at the edge, the Aegean Sea and the Adriatic Sea, that facilitate the formation of the deep water [40]. ...
... The circulation in the Mediterranean Sea starts with the Atlantic Water (AW) entering the Mediterranean Sea through the Gibraltar Strait [44,20,31] and continues to the Alboran Sea feeding two Alboran gyres, separated by the well-known front of Almera-Oran [1], that makes it continues near the coast of North Africa as Algeria Current (AC). The AC is a narrow and unstable current that flows from west to east leading to the generation of cyclonic and anticyclonic severe large eddies that prevail for several months [3,43]. ...
... The AC is a narrow and unstable current that flows from west to east leading to the generation of cyclonic and anticyclonic severe large eddies that prevail for several months [3,43]. The AC transports AW toward the east through Sicily Channel [31,28]. The Mediterranean is governed by a large-scale anti-estuarine buoyancy-driven circulation" from [31]; this leads to the fact that some properties have to be changed to facilitate equilibrium, such as evaporation which leads to salinity increase and the exit of salty and deep water toward the Atlantic Ocean. ...
Reconstructing 3D geostrophic currents using satellite altimetric data and in-situ temperature and salinity measurements from Argo floats is the focus of this research. The study is centered on the Mediterranean Sea, spanning from 29.5N to 46.5N and 5.5W to 36.5E, encompassing depths ranging down to 2000 m. The investigation spans two decades, from 2001 to 2021, employing a spatial resolution of 1◦×1◦. The outcomes highlight the contribution of Atlantic water to the dynamics of the Mediterranean Sea’s thermohaline circulation. By analyzing data across seasonal and annual averages, distinctive patterns emerge at different locations and depths. The initial focus is on the western Mediterranean Sea, where currents in the Alboran Sea display retrograde movement towards the Atlantic Ocean. Notably, velocities surpass 20 cm s−1 at depths above 300 m, while deeper layers, around 1000 m, witness maximum mean velocities of approximately 14 cm s−1.The southern and northern coasts of the Alboran Sea exhibit heightened dynamics, propelling a robust Algerian current toward the east. This phenomenon influences circulation patterns in the southern Tyrrhenian Sea and evolves into the Atlantic-Ionian Stream (AIS). This current gains momentum along the southern coast of the Sicily channel, maintaining a velocity exceeding 20 cm s−1 across all datasets. Within the Adriatic Sea, a cyclonic circulation prevails in its southern segment, accompanied by a more robust current along the western coast, reaching mean velocities of about 13 cm s−1 during summer and even higher values in winter. Transitioning to the central Mediterranean Sea, the Mid-Ionian Jet exhibits varied behavior during summer and winter. However, the mean dataset reveals a well-defined current with anti-cyclonic attributes, characterized by an average velocity of 6 cm s−1.
In the eastern Mediterranean, the focus turns to the Rhodes gyre, which displays seasonal variations in width, being wider during winter and narrower in summer. Along the coasts of Libya and Egypt, situated south of the Levantine basin, geostrophic currents attain velocities surpassing 14 cm s−1 in both summer and winter, although they are more pronounced during the warmer months. Throughout the entire Mediterranean Sea, substantial disparities between the uppermost 300 m and deeper layers are observed in terms of variability.
... where N is the Brunt-Väisälä frequency ( 2 = 0 ⁄ ⁄ ), z is the depth, ρ the potential density and h the maximum depth of integration which we have chosen to be 650 m because it is right below the LIW layer (150-600 m; Menna and Poulain, 2010). 170 ...
Dense water formation in the Eastern Mediterranean (EMed) is essential in sustaining the Mediterranean 10 overturning circulation. Changes in the sources of dense water in the EMed point to changes in the circulation and the water properties of the Mediterranean Sea. Here we examine with a regional climate system model the changes in the dense water formation in the EMed through the twenty-first century under the RCP8.5 emission scenario. Our results show a shift in the dominant source of Eastern Mediterranean Deep Water (EMDW) from the Adriatic Sea to the Aegean Sea at the first half of twenty-first century. The projected dense water formation reduces by 75% for the Adriatic Sea, 84% for the Aegean Sea and 15 83% for the Levantine Sea by the end of the century. The reduction in the intensity of deep water formation is related to hydrographic changes of surface and intermediate water, that strengthen the vertical stratification hampering the vertical mixing and thus the convection. Those changes have an impact on the water that flows through the Sicilian Strait to the Western Mediterranean and therefore on the whole Mediterranean system.
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... We set a minimum threshold at To calculate the organic carbon budget, the water column was divided into two layers. The surface layer is defined as the euphotic layer covering the surface to 150 m of depth, and the intermediate layer, from 150 to 400 m (Ozer et al., 2016;Menna et al., 2010Menna et al., , 2021, includes the LIW. Organic carbon englobes dissolved and particulate organic carbon (DOC and POC, respectively). ...
The Rhodes Gyre is a cyclonic persistent feature of the general circulation of the Levantine Basin in the eastern Mediterranean Sea. Although it is located in the most oligotrophic basin of the Mediterranean Sea, it is a relatively high primary production area due to strong winter nutrient supply associated with the formation of Levantine Intermediate Water. In this study, a 3D coupled hydrodynamic-biogeochemical model (SYMPHONIE/Eco3M-S) was used to characterize the seasonal and interannual variability of the Rhodes Gyre’s ecosystem and to estimate an annual organic carbon budget over the 2013–2020 period. Comparisons of model outputs with satellite data and compiled in situ data from cruises and BioGeoChemical-Argo floats revealed the ability of the model to reconstruct the main seasonal and spatial biogeochemical dynamics of the Levantine Basin. The model results indicated that during the winter mixing period, phytoplankton first progressively grow sustained by nutrient supply. Then, short episodes of convection driven by heat loss and wind events, favoring nutrient injections, organic carbon export, and inducing light limitation on primary production, alternate with short episodes of phytoplankton growth. The estimate of the annual organic carbon budget indicated that the Rhodes Gyre is an autotrophic area with a positive net community production in the upper layer (0–150 m) amounting to 31.2 ± 6.9 g C m-2 year-1. Net community production in the upper layer is almost balanced over the seven-year period by physical transfers, (1) via downward export (16.8 ± 6.2 g C m-2 year-1) and (2) through lateral transport towards the surrounding regions (14.1 ± 2.1 g C m-2 year-1). The intermediate layer (150–400 m) also appears to be a source of organic carbon for the surrounding Levantine Sea (7.5 ± 2.8 g C m-2 year-1) mostly through the subduction of Levantine Intermediate Water following winter mixing. The Rhodes Gyre shows high interannual variability with enhanced primary production, net community production, and exports during years marked by intense heat losses and deep mixed layers. However, annual primary production appears to be only partially driven by winter vertical mixing. Based on our results, we can speculate that future increase of temperature and stratification could strongly impact the carbon fluxes in this region.
... Generation mechanisms, regions and times of the intermediate water formation, time rates of its generation, volumes and thermohaline characteristics, as well as circulation routes within a basin are addressed in a number of investigations. The most detailed studies were published on the Mediterranen Sea (Lascaratos et al., 1999;Menna & Poulain, 2010), the Black Sea (Korotaev et al., 2014;Oguz & Besiktepe, 1999;Stanev & Staneva, 2001;Stanev et al., 2003;Staneva & Stanev, 1997) and the Aral Sea (Izhitskiy et al., 2014). In this context, the investigations of the Cold Intermediate Layer (CIL) of the Baltic Sea look very fragmentary and sparse. ...
... In contrast to the evolution of the intermediate and cold intermediate layers of other seas (e.g., in the Mediterranean (Lascaratos et al., 1999;Menna & Poulain, 2010) or the Black Sea (Korotaev et al., 2014;Oguz & Besiktepe, 1999;Stanev & Staneva, 2001;Stanev et al., 2003;Staneva & Stanev, 1997)), a modelling study of the formation of the Baltic CIL has not been carried out yet, and we suggest two reasons for that. The first is a quite simplified general understanding of the Baltic CIL as a local and seasonal feature, which arises due to solar heating of the top of the cool winter mixed layer. ...
Vertical thermohaline structure in the southeast part of the Baltic Sea is complicated: The salinity field has two layers due to the general estuarine circulation, while the water temperature stratification changes seasonally from two-layered to three-layered. Simulation of the re-stratification processes in such a basin is still a challenging problem, even for the most advanced models. In this study, using a comparison with the independent field data, we have examined how well the structure of the Baltic Sea Cold Intermediate Layer (CIL) is reproduced by the Copernicus Marine Environment Monitoring Service (CMEMS) reanalysis data. It was found that the water salinity within the CIL and the halocline is overestimated, and the upper CIL boundary (the thermocline) in the reanalysis data is considerably shallower than that in the field data. These conclusions are similar to other studies comparing model and field data in the Baltic Sea for various applications. The reanalysis data demonstrate certain deviations in the water temperature, salinity, and depth values at the CIL upper and lower boundaries. However, the general structure of the CIL is reproduced well, including its salinity-homogeneous and salinity-gradient sublayers. Moreover, the T-S diagrams indicate that the salinity-gradient sublayer in the south-eastern and central basins in summer contains waters similar to those observed within the upper mixed layer in spring in the south-western sea basins. This confirms the applicability of the CMEMS reanalysis (with certain caution regarding the temperature/salinity/depth values) for the investigation of such a complicated process as the formation of the Baltic CIL in spring when the seasonal vertical mixing ceases and denser waters from the eastern part of the sea are expected to renew the lower part of the CIL in the Baltic Proper.
... Eventually, the AW reaches the easternmost part of the Mediterranean Sea, showing salinity two units higher than at the Gibraltar Strait [1]. During the wintertime in the area southwest of Rhodes, the intermediate vertical convection takes place and the Levantine Intermediate Water (LIW) forms [2], starting its westward spreading [3,4] at a depth of around 300-400 m ( Figure 1A). Then, it exits through the Gibraltar Strait in the layer below the surface, which is occupied by the inflowing AW. ...
The Mediterranean Sea is considered a hot spot of global warming because it has been changing faster than the global ocean, creating a strong impact on the marine environment. Recent studies agree on the increase in the sea level, in the sea surface temperature, and in the sea surface salinity in the Mediterranean Sea over the last two decades. In this research, the possible interconnection between these and other parameters that contribute to the regulatory effect of the sea on the climate are identified and discussed. Spatio-temporal variability of four oceanographic and air–sea interaction parameters (sea-level, sea surface temperature, sea surface salinity, and freshwater flux) are estimated over the last 27 years by performing the empirical orthogonal function analysis. Climatic trends, and interannual and decadal variability of the different datasets are delineated and described in the whole Mediterranean and in its sub-basins. On the climatic scale, the Mediterranean and its sub-basins behave in a coherent way, showing the seal level, temperature, salinity, and freshwater flux rise. On the interannual scale, the temporal evolution of the sea level and sea surface temperature are highly correlated, whereas freshwater flux affects the variability of sea level, temperature, and the salinity field mainly in the Western and Central Mediterranean. The decadal signal associated with the Northern Ionian Gyre circulation reversals is clearly identified in three of the four parameters considered, with different intensities and geographical extents. This signal also affects the intermediate layer of the Eastern Mediterranean, from where it is advected to the other sub-basins. Decadal signal not associated with the Northern Ionian Gyre reversals is strongly related to the variability of main sub-basin scale local structures.
... The expected increase in temperature and salinity accelerates from 2040 at 150-600 m (Figures 3b and 3d). The 150-600 m depth range corresponds to the equilibrium depth of LIW (Menna & Poulain, 2010) in the western Mediterranean. ...
Deep water formation (DWF) in the North Western Mediterranean (NWMed) is a key feature of Mediterranean overturning circulation. DWF changes under global warming may have an impact on the Mediterranean biogeochemistry and marine ecosystem. Here we analyze the deep convection in the Gulf of Lions (GoL) in a changing climate using a regional climate system model with a horizontal resolution high enough to represent DWF. We find that under the RCP8.5 scenario the NWMed DWF collapses by 2040–2050, leading to a 92% shoaling in the winter mixed layer by the end of the century. The collapse is related to a strengthening of the vertical stratification in the GoL caused by changes in properties of Modified Atlantic Water and Levantine Intermediate Water, being their relative contribution to the increase of the stratification 57.8% and 42.2%, respectively. The stratification changes also alter the Mediterranean overturning circulation and the exchange with the Atlantic.
... Besides these eddies that are deterministic in their place of appearance and long-lasting (they are sometimes described as permanent), many anticyclones do not seem to be related to the wind but rather to the instability of the slope current. A first zone of formation of small and short-lived anticyclones was named by Mkhinini et al. (2014) Benghazi Eddies around 20 • E. Further east, Mkhinini et al. (2014) and Gerin et al. (2009) noted the recurrent presence of anticyclones in the Herodotus Trough which they finally named Herodotus Trough Eddies which include the anticyclone classically named Mersa Matruh (Hamad et al., 2005) or sometimes Egyptian Eddy (Menna and Poulain, 2010). This "structure" corresponding either to an accumulation of locally or upstream formed eddies and sometimes even Ierapetra, was named by Millot and Taupier-Letage (2005) "SLw" (accumulation in the western Levantine) and attributed to the shape of the deep isobaths that would trap the eddies in this pit. ...
A simulation of the Mediterranean circulation between 2011 and 2020 at a resolution of 3 - 4 km in the Eastern basin was compared to vertical profiles and horizontal distributions of temperature and salinity from Argo profilers distributed throughout the basin. The comparison is marked by high temporal (∼0.9) and spatial (0.6-0.8) correlations and low biases. Comparisons of SST with satellite imagery have also shown strong similarities for numerous structures over a wide range of spatial scales. The simulation is used to describe the mean circulation of surface Atlantic Waters and Intermediate Waters in winter and summer.
The surface circulation is cyclonic alongslope, stronger and more stable in winter. In summer, the current veins are sometimes interrupted and replaced by trains of eddies like in the South Ionian. In other cases, the current becomes very narrow and stuck to the coast as along the Ionian east coast or the Middle East coast. In winter, surface and Levantine Intermediate Waters exit from the Levantine mainly through the Aegean, while in summer, they exit westward south of Crete. The Aegean tends in summer to be isolated by eddies that develop on both sides of the Cretan Arc. The juxtaposition of Ierapetra, the Rhodes Gyre and the Mersa-Matruh Eddies produces a southward path across the Levantine basin at about 27 - 28°E which delimits a large cyclonic circulation to the east which tends to separate the two parts of the basin (west and east Levantine). Concerning the Levantine Intermediate Waters, the alongslope cyclonic circulation all around the Levantine basin in winter is no longer maintained in summer as a large anticyclonic circulation occupies the southeast of the basin. The intermediate waters entering the Ionian either through southern Crete in summer or through the Aegean in winter, are submitted to a strong northward, southward and even westward dispersion by Pelops and the nearby anticyclonic areas. The presence of recurrent anticyclones between 35 and 37°N along a band extending from west to east of the Ionian also produces a vertical dispersion of intermediate water. Finally, the circulation of intermediate water in the South Ionian is marked by an important seasonality with the presence in summer of a large anticyclonic circulation that seems to be wind induced and finally drives a secondary branch to the Sicily Channel. A climatology for the transport through the different straits is discussed and simplified representations of the circulation are proposed.
