Five locations in the Eastern Mediterranean, situated in the Ionian Sea, Cretan passage and Levantine basin, were characterized for their physical and biogeochemical properties on the basis of the data collected during an oceanographic cruise in June 2007. Basinwide, subbasin and mesoscale surface dynamic features are described in terms of absolute dynamic topography of the sea surface, sea surface temperature and chlorophyll-a distribution. Additional information along the ship's track was acquired via the vessel-mounted thermosalinograph and the Acoustic Doppler Current Profiler, providing data on temperature, salinity and marine current. The latter helped identify the depth penetration (< 300 m) of some dynamic structures revealed by satellite imagery. The principal water mass characteristics of the Eastern Mediterranean are described in terms of thermohaline properties and inorganic nutrient concentrations. Mixing of the principal water masses at each location was estimated by means of optimum multiparameter analysis. The June 2007 thermohaline properties are compared with those from previous studies that have described the evolution of the Eastern Mediterranean Transient from the early 1990s through the early 2000s. The processes of horizontal and vertical mixing that tend to decrease temperature and salinity of the deep waters with respect to the maximum reached during or some time after the Eastern Mediterranean Transient seem still to persist in 2007. (c) 2012 Elsevier Ltd. All rights reserved.

The basin-scale distribution of ultraphytoplankton (<10 μm) was determined in the upper 200 m of the eastern Mediterranean Sea during the winter season. Four clusters were resolved by flow cytometry on the basis of their optical properties and identified as Synechococcus, Prochlorococcus, pico- (<3 μm) and nanoeukaryotes (3–10 μm). Synechococcus was the most abundant population (maximum abundance of about 37 000 cells cm−3) and contributed up to 67.7% to the overall ultraphytoplanktonic carbon biomass, whereas the contribution of Prochlorococcus never exceeded 6.5%. The maximum integrated carbon biomass was 1763, 453, 58 and 571 mg C m−2 for nanoeukaryotes, picoeukaryotes, Prochlorococcus and Synechococcus respectively. Water mass properties were analyzed on the basis of temperature and salinity distributions in order to account for the general circulation and locate the main hydrodynamic structures (fronts, gyres, transition between western and eastern basins). The effect of the main hydrodynamic structures and nutrients on the ultraphytoplankton distribution was investigated. No positive correlation between nutrients and phytoplankton could be established when considering large scales. However, below 50 m depth, nutrient ratios between particular stations were correlated to corresponding density ratios. In contrast, significant relationships were found between Synechococcus abundance and density, resulting from the impact of a gyre in southern Adriatic basin and a thermohaline front in the Ionian basin. A significant relationship was also found between picoeukaryotes and salinity in the comparison of western and eastern Mediterranean Sea.

Ultraphytoplankton distribution and upper ocean dynamics in the eastern Mediterranean during winter M. Denis, M. Thyssen, V. Martin, B. Manca, and F. Vidussi Laboratoire de Microbiologie, Géochimie et Ecologie Marines, Université de la Méditerranée, CNRS UMR 6117, 163 avenue de Luminy, Case 901, 13288 Marseille cedex 9, France Istituto Nazionale di Oceanografia e Geofisica Sperimentale – OGS, Borgo Grotta Gigante, 42/c, 34010 Sgonico (Trieste), Italy Laboratoire d’Océanographie de Villefranche, CNRS UMR 7093, Université de Paris VI, quai de la Darse, B.P. 28, 06234 Villefranche-sur-mer cedex, France present address: Ecosystèmes lagunaires, CNRS, UMR 5119, Université Montpellier II, CP 093, Place Bataillon, 34095 Montpellier cedex 5, France Received: 12 May 2009 – Accepted: 6 June 2009 – Published: 13 July 2009 Correspondence to: M. Denis (michel.denis@univmed.fr) Published by Copernicus Publications on behalf of the European Geosciences Union.

We present a detailed account of the changing hydrography and the large-scale circulation of the deep waters of the Eastern Mediterranean (EMed) that resulted from the unique, high-volume influx of dense waters from the Aegean Sea during the 1990s, and of the changes within the Aegean that initiated the event, the so-called ‘Eastern Mediterranean Transient’ (EMT). The analysis uses repeated hydrographic and transient tracer surveys of the EMed in 1987, 1991, 1995, 1999, and 2001/2002, hydrographic time series in the southern Aegean and southern Adriatic Seas, and further scattered data. Aegean outflow averaged nearly 3×106m3s−1 between mid-1992 and late 1994, and was largest during 1993, when south and west of Crete Aegean-influenced deep waters extended upwards to 400m depth. EMT-related Aegean outflow prior to 1992, confined to the region around Crete and to ∼1800m depth-wise, amounted to about 3% of the total outflow. Outflow after 1994 up to 2001/2002, derived from the increasing inventory of the tracer CFC-12, contributed ∼20% to the total, of ∼2.8×1014m3. Densities in the southern Aegean Sea deep waters rose by 0.2kg/m3 between 1987 and 1993, and decreased more slowly thereafter. The Aegean waters delivered via the principal exit pathway in Kasos Strait, east of Crete, propagated westward along the Cretan slope, such that in 1995 the highest densities were observed in the Hellenic Trench west of Crete. Aegean-influenced waters also crossed the East Mediterranean Ridge south of Crete and from there expanded eastward into the southeastern Levantine Sea. Transfer into the Ionian mostly followed the Hellenic Trench, largely up to the trench’s northern end at about 37°N. From there the waters spread further west while mixing with the resident waters. Additional transfer occurred through the Herodotus Trough in the south. Levantine waters after 1994 consistently showed temperature–salinity (T–S) inversions in roughly 1000–1700m depth, with amplitudes decreasing in time. The T–S distributions in the Ionian Sea were more diverse, one cause being added Aegean outflow of relatively lower density through the Antikithira Strait west of Crete. Spreading of the Aegean-influenced waters was quite swift, such that by early 1995 the entire EMed was affected. and strong mixing is indicated by near-linear T–S relationships observed in various places. Referenced to 2000 and 3000dbar, the highest Aegean-generated densities observed during the event equaled those generated by Adriatic Sea outflow in the northern Ionian Sea prior to the EMT. A precarious balance between the two dense-water source areas is thus indicated. A feedback is proposed which helped triggering the change from a dominating Adriatic source to the Aegean source, but at the same time supported the previous long-year dominance of the Adriatic. The EMed deep waters will remain transient for decades to come.

Hydrographic measurements obtained in March-April 2002 indicate a new ventilation of the deep layers in the Adriatic and Ionian Seas, following abrupt changes in the thermohaline circulation of the eastern Mediterranean observed since the beginning of the last decade. The water masses that reside in the Southern Adriatic basin were renewed by open ocean winter convection of water with potential density excess (sigma(theta)) > 29.18 kg m(-3) at depths 600 to 800 m and by a vein of still denser (29.26 kg m(-3)) and oxygen-rich (230 to 232 mmol m(-3)) water flowing into the southern Adriatic depression (similar to 1200 m), presumably from the north, When compared to 1999, a moderate increase in salinity (similar to 0.05) and a much stronger dissolved oxygen increase (> 29 mmol m(-3)) were found in the bottom layer of the southern Adriatic Sea. The cold, fresh and highly oxygenated water of Adriatic origin, overflowing the Otranto Strait sill (similar to 935 m) with a potential density of 29.24 kg m(-3), was dense enough to sink into the deep Ionian basin. Multiparameter analysis based on the fundamentals of the mixing processes was applied using temperature, salinity, oxygen and nutrient data to investigate the spatial distribution of water masses and to quantify the fractional contributions of distinctive source water types along specific sections running from the Adriatic to the Ionian Sea. The results clearly indicate that the dense water of Adriatic origin, which was recently in contact with the atmosphere, have again replenished the volume of the deep Ionian basin by more than 50%.

Vertical profiles of dissolved organic carbon (DOC) in different areas of the Mediter- ranean Sea were studied during 6 oceanographic surveys conducted between January 1999 and Sep- tember 2001. The study areas were located at key points of water mass circulation of the entire Mediterranean basin. DOC showed similar behaviors at all hydrological stations, with highest values in surface waters, a minimum in the intermediate layers and slightly increasing values in deep waters. Important links were found between DOC distribution in the water column and hydrological structures. In particular, distinctive DOC concentrations were detected in the different water masses. This finding was attributed to the age, origin and route of each water mass.

Basic characteristics of larg multiparameter ocean database for the Mediterranean and Black Sea are described.

r The EU-MAST/MEDAR/MEDATLAS II project (Mediterranean Data Archeology and Rescue of temperature, salinity and bio-chemical parameters, 1998-2001) provided the most updated and comprehensive data set and climatological atlas of physical, biological and chemical oceanographic parameters for the Mediterranean and Black Sea. The MEDAR/MEDATLAS II is a distributed data-management structure made up of the NODC/DNA from 20 countries, four regional data centres (in charge of data compilation in the Eastern, Central, and Western Mediterranean and the Black Sea, respectively) and a global assembling centre (responsible for the overall integration). These centres have strengthened the IOC/IODE network at national and regional level, enhancing the overall capacity in data rescue and validation. The multidisciplinary hydrographic data set, globally assembled, was checked for quality by common compatible and coherent procedures, based on international standards. The validation process, fully implemented for temperature, salinity, dissolved oxygen, nitrate, phosphate, and silicate, was extended to other biological and chemical parameters, which include alkalinity, ammonium, chlorophyll-a, nitrite, pH, total phosphorus and total nitrogen. New broad-range check values in the sub-domains' discretisation of the Central Mediterranean were defined. The global analysis of the biological and chemical core parameters defined very wide ranges at the surface, rather wide ones for the intermediate layer, while the ranges are narrow in the deep layer. The statistical results obtained here could be used to improve data management practices, by providing trustworthy intervals to substantiate studies on spatial-temporal variations of selected physical, biological and chemical properties over the past 80 years.

Basic characteristics of larg multiparameter ocean database for the Mediterranean and Black Sea are described.

Since the beginning of 90’s a large climatic event, widely known as Eastern Mediterranean Transient, established in the Cretan Sea (Southern Aegean) an additional source of dense waters [Roether et al., 1996]. This event has been largely attributed to an increase of salinity in the Aegean Sea since the mid 80’s [Theocharis et al, 1999]. The basic belief was that important meteorological anomalies acting in the Eastern Mediterranean changed the circulation patterns of the main water masses, which drive the salt distribution in the different sub-basins both at surface and intermediate layers [Malanotte-Rizzoli et al., 1999]. Concurrently, altered fresh water budgets and exceptional cold winters over the Aegean Sea might have played favourable conditions to move the predominant source of dense waters of the Eastern Mediterranean from the Adriatic into the Aegean Sea during the early 90’s [Josey, 2003].

Reconstructions of Mediterranean ocean temperature fields back to 1950 show a proxy relationship between heat content changes in the North Atlantic and the Western Mediterranean Deep Water (WMDW) formed in the Gulf of Lions in winter, because of consistent air‐sea heat fluxes over these areas, strongly correlated to the North Atlantic Oscillation (NAO).

Seasonally and spatially averaged vertical profiles of temperature, salinity, dissolved oxygen, nutrients and chlorophyll-a have been computed from in situ observations in different regions of the Mediterranean Sea using the recently released EU/MEDAR/MEDATLAS II and EU/MTPII/MATER databases. The regions have been defined according to known dynamics important in the formation, transformation and spreading of the main water masses that circulate in the upper, intermediate and deep layers. The climatological characteristics of temperature and salinity reflect the water mass structures and the general thermohaline circulation patterns. Spatial and temporal variations on a seasonal basis of nutrients and principal biological parameters are described along with some aspects of the trophic conditions of the Mediterranean Sea. The strongest signal of variability is along the vertical; however, horizontal inhomogeneities are mostly associated with the internal dynamics. The distribution of the biochemical elements, in conjunction with hydrographic measurements of temperature and salinity, may serve as appropriate tracers for the characterisation of the main water masses (Atlantic Water, Levantine Intermediate Water and Bottom Water in the eastern and eastern basins) throughout the Mediterranean Sea. In a first approach, adequate descriptors of water properties have been obtained, useful for the quality control of incoming data in large databases and in setting-up documented procedures to improve future data management practices. Secondly, the biochemical climatological characteristics addressed in this paper are verified to be consistent with the physics of the Mediterranean Sea and are conceived useful to initialise coupled physical–biological models. The full set of spatially averaged vertical profiles can be found and downloaded from the World Wide Web data server established at OGS (http://doga.ogs.trieste.it/medar/climatologies/).

Using an intercalibrated set of oxygen data for the eastern Mediterranean, 1987–1999, we study the evolution of oxygen concentrations that accompanied the recent changes in the thermohaline circulation of this sea (the so‐called Eastern Mediterranean Transient (EMT)). We find that, by way of massively transferring oxygen‐rich near‐surface waters into the deep layers, the EMT by 1995 had raised oxygen concentrations considerably relative to the pre‐EMT situation in 1987. Between 1995 and 1999, however, the oxygen concentrations decreased noticeably, we identify oxygen decreases of about 5 μmol/kg for the layers below 2200 m and between about 500 and 1000 m depth, for which layers previous work found vanishing or little replenishment during 1995–1999. Supporting evidence for absence of replenishment is obtained from the temporal evolution of tritium‐3He ages. The oxygen decreases convert into utilization rates of approximately 1.3 μmol/(kg yr). An even higher rate, 2.3 μmol/(kg yr), is obtained for the deep waters of the Cretan Sea below 1000 m. The utilization rate found for the deepest waters significantly exceeds the pre‐EMT value of 0.53 μmol/(kg yr). We propose that the massive invasion of near surface waters affected by the EMT made available large amounts of dissolved organic carbon with an unusually high fraction of labile material, which in turn enhanced oxygen consumption. Supporting evidence is obtained from data of dissolved organic carbon, and from mesozooplankton ecology data. The enhanced oxygen utilization represents a further example of EMT‐related disturbances in the biogeochemistry of the eastern Mediterranean.

Dissolved organic carbon (DOC) and particulate organic carbon (POC) distribution in the water column were investigated at eight hydrological stations, located in the Ionian Sea, during January 1999. DOC and POC exhibited values in the range 50–73 μM and 0.7–2.7 μM, respectively, in the surface waters, and 31–62 μM and 0.2–0.8 μM in the intermediate and deep waters. The main water masses circulating in the Ionian were identified through potential temperature (θ) versus salinity (S) diagrams and their distribution patterns were verified in the cross‐basin longitudinal sections of temperature and salinity. In particular, the water masses formed in the Cretan Sea (southern Aegean), specifically the Cretan Intermediate Water (CIW) and the Cretan Deep Water (CDW), outflowing through the Cretan straits, occupy similar deep horizons as the Levantine Intermediate Water (LIW) and Eastern Mediterranean Deep Water (EMDW) of Adriatic origin, respectively. DOC exhibited different concentrations in each water mass; its range was 39–42 μM in the LIW, 54–62 μM in the CIW, 31–36 μM in the EMDW of Adriatic origin, 43–47 μM in the CDW, and 44–48 μM in the EMDW of the western‐central Ionian. The highest DOC concentrations were found in the water masses originated in the Aegean Sea and in the EMDW of the western‐central Ionian. Further, DOC versus apparent oxygen utilization (AOU) relationships were investigated within each water mass. In both intermediate and deep waters the results showed linear correlations between DOC and AOU, although with a different sign and slope.

This work is aimed at studying the variability of Rhodes and Ierapetra Gyres during the Levantine Intermediate Water Experiment. Sea surface temperature maps, derived from Global Area Coverage advanced very high resolution radiometer (AVHRR) data in the framework of the Pathfinder Project and sea level anomalies, derived from TOPEX/Poseidon altimeter, were used to track the evolution, both in terms of dimension and position, of the cyclonic Rhode Gyre and Ierapetra anticyclone. The analysis was performed for the period from October 1994 to the end of April 1995, i.e., from the preconditioning to the spreading phase of Levantine Intermediate Water. The description of the surface fields was complemented by a temporal evolution study of the Rhodes and Ierapetra Gyres hydrological vertical structure. European Centre for Medium‐Range Weather Forecasts AVHRR‐derived fluxes have been used as forcing for a numerical model to study the variability of the mixed layer in both gyres. The simulated upper layer dynamics remarkably matched remotely sensed and in situ observations. This work shows that using a combined analysis of observational data and model simulations, we were able to propose a dynamical scenario for the winter of 1995 where the Levantine basin was characterized by short intense heat loss events occurring during at the beginning of December. The intense air‐sea interaction contributed to deep, instead of intermediate, mixing as confirmed by remote sensing, in situ data, and model experiments. A hypothesis on the role of the lateral contribution on the water column buoyancy content in the Rhodes Gyre was formulated.

During the CIESM workshop (Monaco, 22-24 April 2002) entitled "Monitoring Hydrolouical Trends in the Mediterranean", the review of existing data sets and analyses has revealed important variability in the dynamics and hydrological characteristics, in the past century, ranging from interannual to decadal time scales. These variations are related mainly to local forcing and larger scale atmospheric parameters (NAO, ENSO, Indian monsoon). Moreover, abrupt events contribute to modification of the Mediterranean conveyor belt, also influencing the biogeochemical environment and the Mediterranean outflow in the Atlantic Ocean. The participating scientists have agreed on the need of a sustained multi-component long-term monitoring system based on both oceanographic and atmospheric observations and modelling. The group also proposed an expansion and strengthening of the ongoing relevant large operational programs by a "climatic approach" component.

In winter 1995 the last major field work of the Physical Oceanography of the Eastern Mediterranean (POEM) program was carried out, the Levantine Intermediate Water Experiment (LIWEX). In this study a thorough analysis is presented of the data set collected during three successive surveys in January, February, and March–April 1995. The major overall result is that the Levantine basin is shown to be the site for multiple, and different, water mass formation processes. Levantine Deep Water (LDW) was formed in the Rhodes gyre, with the preconditioning phase starting in December 1994. In late January the chimney was ventilating to the atmosphere. In February the strong mixing phase is documented by the convective cell vertically homogeneous to 900 m depth. In March–April, recapping has occurred in the upper 200 m. LDW remained confined inside the Rhodes gyre cyclonic circulation. Levantine Intermediate Water (LIW) is instead deeply affected by the upper thermocline circulation. Shallow ventilating chimneys with the LIW thermostads were found in the January survey inside the cyclonic region of the northern Levantine. The formation process of LIW does not involve deep penetrative convection. Winter surface cooling and evaporation are sufficient to produce a surface mixed layer 100 m deep with LIW characteristics. At the mixed layer basis, LIW subducts and spreads along isopycnal surfaces along pathways determined by the cyclonic/anticyclonic structures of the upper thermocline circulation.

Basin‐wide hydrographic observations performed in the eastern Mediterranean during the past 2 decades attest changes in the thermohaline circulation as well as new aspects concerning the onset and the follow up of the major transient event that occurred at the beginning of the 1990s, i.e., the change of the dense water formation site from the Adriatic to the Aegean Sea. Since 1999, the upper thermohaline circulation has indicated the restoring of the opposite flows of the Atlantic Water and the Levantine Intermediate Water, which were greatly reduced in the period 1987–1995. In the deep layer the comparison between water mass structures observed in 1995, during the mature status of the transient, and those observed in 1999 shows a damping of the event and a regained role of the Adriatic Sea as a primary source of dense waters. Separate calculations of the salt content in the Ionian and in the Levantine Seas show an overall salt redistribution. During 1987–1995 a salt loss of about 25 × 1012 kg was computed for the upper 800 m, constituting only 27% of the salt gain in the deep layer over most of the eastern Mediterranean. On the contrary, during 1995–1999 the restored upper thermohaline circulation caused a salt redistribution between the two basins of about the same amount, but in the opposite sense, while an extra quantity of 12 × 1012 kg was deposited in the deep layer. In addition, calculations of the salt concentration in the convection region of the southern Adriatic reveal a remarkable amount of the salt, not yet totally transferred into the deep layers by its interior dynamics because of mild winters.

Changes in the vertical distribution of the physical and chemical parameters observed during this study point to the continuing spatial and temporal evolution of the Eastern Mediterranean Deep Water (EMDW). These changes influenced primarily the water column below 800 m and confined the old EMDW of Adriatic origin to the 1000–2000 m in the Levantine, uplifting the minimum‐oxygen/maximum‐nutrient (Min Ox /Max Nut ) from 2500 m in 1995 to 1500 m in 1999. The denser and younger EMDW of Aegean origin (EMDW Aeg ) appeared at the bottom layer, more evident at the central eastern Mediterranean and moving prevalently into the Levantine basin. Younger water still intruded the central area at intermediate depths. In the Levantine Intermediate Waters (LIW) oxygen decreased and nutrients increased westward in agreement with its pathway across the basin. However, a temporal decrease in oxygen and concurrent increase in nutrient was found in the LIW because of its confinement in the Levantine by anticyclonic features. Temporal changes were also found in the EMDW at the western Ionian and eastern Cretan passage. The differences in the vertical placement of the Min Ox /Max Nut layer among the different areas were explained by the physical processes, but the relative displacement of the extreme points within the same area were probably a result of oxidation of particulate matter poorer in nitrogen and phosphorus in the Levantine than in the Ionian. Maximal concentrations of silicic acid were located deeper than the other nutrients because of the slower chemical dissolution of silicious tests. The N:P molar ratios at the EMDW were high (26.2–30.7), highest in the younger EMDW Aeg . These differences could not be explained by different dissolved inorganic nutrients concentration at the sources nor by the composition of particulate matter in the euphotic zone. It was suggested that DOM may have a significant role in determining those differences; however, data on DOM concentration and composition across the basin is lacking in order to test this hypothesis.