Alexander Theocharis

• Hellenic Centre for Marine Research

Coastal lagoons are among the most important, but also threatened, marine systems of our planet. Rainfall, wind, seawater, and freshwater discharges control water circulation in lagoons, determining the water properties that are vital for the lagoon’s biodiversity. The present work is the first study on the circulation patterns and seasonal variabi...

The Mediterranean Sea is among the most affected areas of our planet by microplastic (MP) pollution. However, some regions are still underrepresented in the current literature. This work studied the fate of microplastics (MPs) released from major populated areas within the NE Ionian Sea, an area that contains highly significant biodiversity. This w...

Antinioti is a shallow Mediterranean coastal lagoon located on the island of Corfu in West Greece. For several years, the lagoon has been exploited for fish stocks by the local community. Therefore, the lagoon presents regional economic importance. However, studies on the physical, chemical, and biological properties of the lagoon are limited. Our...

The Aegean Sea’s hydrological and circulation characteristics are as complex as its geomorphological setting. All major Eastern Mediterranean (EMed) water masses can be found inside the basin, while the Aegean Sea is a producer of dense intermediate and in some cases deep water masses that are exported to the EMed. The role of the Aegean Sea as a d...

Mesozooplankton vertical pattern was studied down to 2000 m along an east-west transect in the oligotrophic Mediterranean Sea in June 1999. Depth-stratified samples were collected by a WP-2 net (200 µm mesh size). In addition, the copepod grazing impact on autotrophs was assessed in the epipelagic zone by measurement of small and large copepod gut...

The appearance of low salinity, temperature, oxygen and nutrient-rich waters inside the Cretan Sea at depths below the saline intermediate water layer is a recurrent phenomenon related to the intrusion of Transitional Mediterranean Water (TMW) from the Eastern Mediterranean Sea. The inflow of TMW through the Cretan Straits acts as compensation for...

A review of the recent theories for thermohaline variability in the Eastern Mediterranean, presented in Ca’Foscari University, Venice

Data collected from different platforms in the Cretan Sea during the 2000’s decade present evidence of gradually increasing salinity in the intermediate and deep intermediate layers after the middle of the decade. The observed gradual salt transport towards the deeper layers indicates contributions of dense water masses formed in various Aegean Sea...

Recent studies have shown increasing salinities in the surface and intermediate layers of the eastern part of Eastern Mediterranean Sea after the middle of the 2000’s decade. In – situ data collected from different platforms in the Cretan Sea during the 2000’s decade, almost 15 years after the end of the Eastern Mediterranean Transient (EMT), prese...

This paper is the outcome of a workshop held in Rome in November 2011 on the occasion of the 25th anniversary of the POEM (Physical Oceanography of the Eastern Mediterranean) program. In the workshop discussions, a number of unresolved issues were identified for the physical and biogeochemical properties of the Mediterranean Sea as a whole, i.e., c...

This chapter, based on numerical modeling and field observations, aims at proposing a different mechanism that drives the alternation of the two competitive dense-water sources, the Adriatic and the Aegean, at quasi-regular, almost decadal, time intervals. The proposed mechanism consists of a thermohaline pump that disturbs the eastern Mediterranea...

Dense water produced in the Aegean Sea during the late 2000’s supports the existence of a rather permanent thermohaline pump mechanism that regulates the production of dense/deep waters in the Adriatic and Aegean Seas. The mechanism disturbs the Eastern Mediterranean (EMed) upper thermohaline cell modifying their hydrological structure which altern...

The importance of the Mediterranean Sea for the world ocean has long been recognized. First, the Mediterranean sea has a profound impact on the Atlantic ocean circulation and, consequently, on the global thermohaline conveyor belt. Maps of the Mediterranean salty water tongue exiting from the Gibraltar strait at intermediate depths and spreading th...

The long-term monitoring of basic hydrological parameters (temperature and salinity), collected as time series with adequate temporal resolution (i.e. with a sampling interval allowing the resolution of all important timescales) in key places of the Mediterranean Sea (straits and channels, zones of dense water formation, deep parts of the basins),...

MedCLIVAR has become an independent platform for scientific discussion, the exchange of information and the coordination of activities across scientific groups around the Mediterranean. The scientific objects of the programme include past climate variability, connections between the Mediterranean and global climate, the Mediterranean Sea circulatio...

This work focuses on the interdependence among the Dense Water Formation (DWF) activity in the Adriatic and Aegean Seas (Dense Water source areas), the changes in the characteristic water mass circulation patterns and the salinity oscillations occurring in all basins of the Eastern Mediterranean. We use both numerical model results (1960-2000 hindc...

The long-term monitoring of basic hydrological parameters (temperature and salinity), collected as time series with adequate temporal resolution (i.e. with a sampling interval allowing the resolution of all important time scales) in key-places of the Mediterranean Sea (straits and channels, zones of dense water formation, deep parts of the basins),...

Located between subtropical and mid-latitude climates, the Mediterranean region acts as a transition area and is very sensitive to global climate change: As global temperatures have risen, the Mediterranean region has warmed, particularly in the west and in the summer, where surface temperatures in some locations increased at a rate greater than 0....

We study the impact of decadal inversions of the Ionian upper layer circulation (denominated as Adriatic-Ionian Bimodal Oscillation System) on thermohaline properties of the Levantine and Cretan Seas. Lagrangian drifter data and surface geostrophic currents show that the Atlantic Water (AW) flow is well organized and most intense when the Ionian ci...

Aiming at portraying the Aegean's water mass structure and identifying Dense Water Formation processes, two winter cruises were conducted in 2005-2006, across the plateaus and depressions of the Aegean Sea. The most prominent feature of the water mass distribution in the basin is a distinct "X-shape" of the Θ-S characteristics, suggesting a complic...

The migration of Lessepsian species, which was the result of the opening of the Suez Canal in 1869 and further facilitated by human activities and environmental conditions, seems to play a key role for fisheries particularly in the Levant basin. However, there is still lack of accurate data for most of the Lessepsian species in order to evaluate th...

The analysis of a compilation of deep CTD cast conducted in the western Mediterranean from 1998 to 2009 have documented the role that dense shelf water cascading off the Gulf of Lions plays in transporting suspended particulate matter from the coastal regions down to the basin. Deep CTD casts revealed that after the 1999 and 2005-2006 major cascadi...

Using long-term data of 149 warm alien species since 1924, we show that the introduction of warm and tropical alien species has been exacerbated by the observed warming of the eastern Mediterranean Sea. The phenomenon has accelerated after an abrupt shift in both regional and global temperatures that we detect around 1998, leading to a 150% increas...

Atmospheric time series are used to explain the observed behaviour of upper ocean temperatures in the Mediterranean Sea. The purpose of the analysis is to determine the extent observed variations of oceanic temperature during recent decades are linked with changes of the in situ atmospheric temperatures and identify the synoptic conditions leading...

Four years of CTD surveys and profiling float measurements were conducted in various Aegean Sea basins, supplemented by numerical model experiments, in order to monitor the circulation and stratification of the complex environment in the Aegean Sea. There is a remarkable difference of the Θ-S characteristics between the north and south Aegean sub-b...

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 T...

Cited By (since 1996): 6, Export Date: 15 January 2013, Source: Scopus, doi: 10.1016/S1571-9197(06)80007-8, Language of Original Document: English, Correspondence Address: Tsimplis, M.N.; James Rennell Division for Ocean Circulation and Climate, National Oceanography Centre, Southampton, United Kingdom; email: mnt@noc.soton.ac.uk, References: Artal...

A detailed description of the evolution of the hydrography and of the circulation of the deep waters that resulted from the huge and unique influx into the East Mediterranean basin of dense waters originating from and formed inside the Aegean Sea in the 1990s, the so called Eastern Mediterranena Transient (EMT).

A detailed description of the evolution of the hydrography and of the circulation of the deep waters that resulted from the huge and unique influx into the East Mediterranean basin of dense waters originating from and formed inside the Aegean Sea in the 1990s, the so called Eastern Mediterranena Transient (EMT).

Evidences of temperature-controlled dense water cascading off the Gulf of Lion shelf, in the northwestern Mediterranean, and several Aegean shelves in the northeastern Mediterranean are reported. Together with the Adiatic shelf, already listed by Ivanov, Shapiro, Huthnance, Aleynik, & Golovin (2004), these zones represent the major coastal areas of...

This work is an effort to identify significant dense water formation events over the Aegean Sea for the period 1949-present. The Aegean Sea is one of the major dense wa-ter formation sites of the Mediterranean Sea. The interannual variability of its dense-water production appears to be remarkably large, ranging from being the major con-tributor for...

This paper is a review of the circulation in the seas surrounding the Hellenic Peninsula, constituting a chapter of the volume "State of the Hellenic Marine Environment", published by the Hellenic Centre for Marine Research in 2005, editors E. Papathanassiou and A. Zenetos.

The Aegean Sea is a region of special interest for the Mediterranean oceanographic community, as one of the dense-water formation sites of the Mediterranean, driving its thermohaline circulation. Early oceanographic literature exhibits significantly varying opinions regarding the role of the Aegean as a contributor to the water masses of the easter...

During the CIESM workshop (Monaco, 22–24 April 2002) entitled “Monitoring Hydro- logical 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 m...

The Mediterranean Sea as a whole is known to be very sensitive to atmospheric forcing and far from a stationary state. Long-term variability, ranging from interannual to multiannual, of water-mass characteristics and currents, has been documented in the last century throughout the whole Mediterranean Sea. However, recent studies based on observatio...

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...

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...

[1] 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 wate...

[1] Dense water formation processes in the Aegean Sea (eastern Mediterranean) are studied using a three-dimensional numerical ocean model. The simulations cover the period 1979–1994 during which major changes that affected the thermohaline circulation of the whole Mediterranean Sea were recorded. Sensitivity studies that focus on the role of freshw...

Buoyancy exchanges in the Aegean Sea lead to the formation of deep and bottom water, which occasionally overflows in the eastern Mediterranean. In this study we attempt an assessment of the buoyancy exchange between the North and South Aegean through budget estimations. This will provide a first-order estimate of the North Aegean contribution to th...

The main outputs of a multidisciplinary and integrated studies are summarised. The results incorporate the latest biogeochemical researches, at basin scale, in the Aegean Sea (including thermohaline circulation studies, SPM dynamics, mass and energy fluxes, acknowledge biochemical processes in the euphotic and the benthic layer and benthic response...

The Eastern Mediterranean Transient (EMT) was the major climatic event in the circulation and water mass properties of the Mediterranean in the last century. In this paper, we describe the present status of the EMT and its evolution since 1995 using hydrological and tracer data from 1997 to 1999. Few but important changes have been observed in the...

Four seasonal oceanographic cruises were carried out in the Eastern Mediterranean Sea, within the framework of the CEC/MAST-MTP Project PELAGOS, during 1994–1995. The surveys covered the South Aegean Sea and the adjacent open sea regions (southeastern Ionian, northwestern Levantine). Analysis of CTD data revealed that a multiscaled circulation patt...

Five research cruises were undertaken incorporating ADCP sections along the Cretan Arc Straits and CTD surveys covering the entire area of the Straits and the Cretan Sea. In addition, six moorings (with 15 current meters) were deployed within the Straits, which monitored flows in the surface (50 m), intermediate (250 m), and deep (50 m from the bot...

A simple hydraulic model is used to estimate the deep water fluxes of Cretan Deep Water (CDW), through the Cretan Arc Straits and into the Eastern Mediterranean Basins. The input to the model consists of the height of the deep water reservoir above sill depth and its density difference from the overlying water masses. Data from four hydrographic cr...

There are presented the results from two MATER cruises during Winter and late Summer 1998 that were dedicated to the study of water mass formation in the South Aegean and the monitoring of the so called East Mediterranean Transient (EMT). The EMT is characterized by the unique, huge shift of the Deep Water Mass source of the whole Eastern Mediterra...

There are presented quantitative estimations of the Suspended Particulate Matter (SPM) in the North and in the South Aegean and are correlated to anthropogenic factors (trawling, increased terrigenous inputs from rivers due to human interventions such as construction of river dams) as well as to natural factors (organic inputs in the euphotic zone,...

There is presented an estimation of the production of Cretan Deep Water (CDW) for the period 1991-1998, based on water mass continuity and using the volume that the Cretan Deep Water (CDW) (sigma-theta > 29.2) occupied each time. Also, the outflow rates through the Cretan Straits are calculated from current meter measurements, when available

A study has been made of the distribution of terrigenous (Al and Mnex, Feex) and biogenic (POC, PNtot, Porg, Sibio, Baex) elements of suspended particulate matter (SPM) on a series of transects in three marginal areas of the Mediterranean Sea; the NW Mediterranean, the western Adriatic to the Strait of Otranto and the southern (Cretan) and northern...

Straits in the Mediterranean Sea form an important network from which one can determine the characteristics of the water exchange between all the constituent sub-basins. This includes the definition of water masses and water transport and their time variability. From 1994, all the major straits in the Mediterranean Sea (Gibraltar, Sicily, Otranto,...

The CEC/MAST-MTP PELAGOS Project, which was conducted in 1994 and 1995, found a new dynamic hydrological regime in the Cretan Sea–Cretan Straits region that is interacting with and affecting the whole basin of the Eastern Mediterranean. In the Cretan Sea, the upper thermocline general circulation shows no significant seasonal signal, but the circul...

We present definitive observational evidence that the startling change of the Eastern Mediterranean deep circulation observed in winter 1995 and documented by [Roether, W., Manca, B.B., Klein. B., Bregant, D., Georgopoulos, D., Beitzel, V., Kovacevich, V., Luchetta, A., 1996. Recent changes in the Eastern Mediterranean deep water. Science 271, 333-...

Recent changes of water mass characteristics in the south Aegean Sea have considerably influenced the Eastern Mediterranean thermohaline circulation. A combi-nation of salinity increase (1987-92) and temperature drop (1992-94) caused massive dense water formation and strong outflow towards the deep and bottom parts of the Eastern Mediterranean. Thi...

Internal waves have been detected on ERS-1 SAR images obtained during late summer over the eastern Cretan Straits, an area characterised by complex regional physiography, bottom topography, flow regime and stratification patterns of the upper part of the water column. Analysis of the imaged characteristics of the internal waves has revealed a stron...

In early spring of 1986, 1992 and 1995, newly formed deep water masses were observed in the cyclonic Rhodes Gyre of the Eastern Mediterranean at depths reaching ∼1000 m in 1995 and exceeding 1000 m in 1986 and 2000 m in 1992. Levantine Intermediate Water (LIW) formation was observed at localized source areas south of the East Cretan Straits at the...

During the period 18-December-1994 to 20-April-1995, a multinational collaborative experiment was carried out in the NW Levantine Sea with main objective to study the Levantine Intermediate Water (LIW) formation process. During this POEM (Physical Oceanography of Eastern Mediterranean) coordinated experiment, the Rhodes Gyre area and the adjacent s...

Within the framework of the POEM-BC program, a multinational collaborative experiment LIWEX’ 95 in the Levantine basin was undertaken in winter-spring 1995, focussing on the different phases of the process of formation of the Levantine Intermediate Water (LIW). This paper presents the results obtained pertaining to the water exchange between the Ae...

The eastern Mediterranean Sea, one of the poorly known sea regions before the ‘80s, became the object of very intensive research since 1985. The synthesis of the results based on the data sets that were collected in the frame of international (POEM, POEM-BC, EU/MAST/MTP) and national research programs revealed significant information about the circ...

The thermohaline circulation of the Eastern Mediterranean underwent a dramatic change between 1987 and 1995. In 1987 the “engine” of the Eastern Mediterranean “conveyor belt” was the convective cell of the Southern Adriatic, while in 1995 the active convection region moved to the Aegean Sea. This change actually started as early as 1991. The phenom...

A mixture of two intermediate water masses, LIW and CIW is identified as a double peak structure in the T-S diagram of many CTD stations covering the whole area of the central Ionian Sea. This mixture's path is specified via the observation of the gradual degradation of the aformentioned double peak structure.

In this paper we revisit, with a thorough in-depth analysis, the dataset collected in the hydrographic surveys of the international collaborative programme POEM (Physical Oceanography of the Eastern Mediterranean) in the period 1986–1987. The work has two major objectives. The first is to refine the dynamic picture of the Ionian upper thermocline s...

Current meter data from six moorings are analyzed to study current variability at the straits of the Cretan Arc which connect the south Aegean Sea with the eastern Mediterranean. The three layers in which the current meters were deployed show different current characteristics. The upper layer shows evidence of the Asia Minor current in the Rhodes S...

This paper presents the qualitative circulation patterns of the 'upper' and 'deeper' layers in the Cretan Sea and its environs in late winter 1994. The qualitative aspects of the flow field were determined primarily by the distribution of salinity on appropriate neutral surfaces and were supported by dynamic inferences. Water circulation presented...

Analysis of CTD data collected in the Cretan Sea and adjacent regions in late winter 1994 revealed the hydrological structure of their waters: Modified Atlantic Water (MAW) occurs in the south-eastern Ionian Sea and enters the Cretan Sea through the Antikithira Strait. Levantine Surface Water (LSW) spreads into the Cretan Sea across the Karpathos a...

During the last decade the oceanography community has focused much attention on the Mediterranean Sea. One reason for the growing interest is that the Mediterranean's impact on the Northern Atlantic Ocean is more significant than previously realized. The warm, salty Mediterranean water tongue exits the Gibraltar Straits and spreads throughout the N...

In the framework of the major multinational coordinated POEM-II-86 (March–April 1986) and POEM-V-87 (September–October 1987) cruises in the Eastern Mediterranean, high resolution hydrographic (CTD) data were collected by R.V. Aegaio in the eastern Ionian Sea, south Aegean Sea and northwest Levantine Basin. The intercalibrated data sets were analyze...

The North Aegean Sea was visited from 27 February to March 3 1987, during the late winter LIA-5-87 national cruise in the framework of the Open Sea Oceanography Research Program of NCMR. CTD data were collected from 31 stations on board R.V. Aegaio. Strong (velocities up to 17 ms−1) and cold (∼2°C) northerlies, dominating during the week before the...

A novel description of the phenomenology of the Eastern Mediterranean is presented based upon a comprehensive pooled hydrographic data base collected during 1985–1987 and analyzed by cooperating scientists from several institutions and nations (the POEM project). Related dynamical process and modeling studies are also overviewed. The circulation an...

The area is characterized by intense sub-basin and mesoscale variability. Various gyres and eddies as well as currents and jets affect the vertical and horizontal transport of the identified water masses. Furthermore, in late winter LIW is generated exclusively in this region of the Eastern Mediterranean, mainly in the Rhodes cyclonic gyre and to a...

Maps are presented for dynamic height and geostrophic flow in the upper thermocline based upon four basin-wide hydrographic surveys during 1985–1987. The data collection was coordinated, intercalibrated and pooled by the international research programme for Physical Oceanography of the Eastern Mediterranean (POEM). Objective analysis mapping was co...