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Understanding the processes that control the buoyancy fluxes of the Aegean Sea is important for various reasons. First, the Aegean is directly connected with the Black Sea and acts as a buffer between two opposite thermohaline systems, a concentration and a dilution basin (the Mediterranean vs the Black Sea), receiving and filtering the variability and changes of a much broader geographical area. Second, the Aegean is capable to produce large amounts of very dense water, having temporarily been the major originator of Eastern Mediterranean Bottom Water. These processes are controlled by the buoyancy fluxes, both through oceanic advection and atmospheric exchanges. In this work we examine the characteristics and variability of heat, freshwater and the overall buoyancy air-sea fluxes, focusing on the potential role of the interaction with the Black Sea. A thirty-year-long simulation (1985-2015) of the whole Eastern Mediterranean/Black Sea system, forced by ERA-Interim data, was used to estimate and analyze the seasonal and interannual variability of the buoyancy fluxes in the North Aegean. The climatological mean buoyancy flux over the North Aegean has been estimated to be about –10×10–6 kg m–1 s–3 (loss to the atmosphere). However, in the absence of Black Sea Water (BSW) inflow, the buoyancy loss would correspond to the high values observed over the Eastern Aegean, an area not directly affected by the presence of the BSW, i.e. about –30 ×10–6 kg m–1 s–3. It should be noted that the heat loss of the Aegean Sea to the atmosphere is much higher than all neighboring seas, including the Adriatic, the dominant dense-water formation site for the Eastern Mediterranean. Our analysis reveals that the thin surface layer of modified BSW acts as a moderator of the buoyancy loss from the upper water column. This layer not only absorbs the air-sea fluxes (acting as an effective insulator regarding dense-water formation processes), but also moderates or even reverses the buoyancy fluxes over its path. Thus, in addition to the significant lateral buoyancy input to the basin by the Black Sea inflow, an additional mechanism of reduction of winter heat losses to the atmosphere contributes to the control of dense water formation processes.

The North Aegean Sea is a sub-basin of the Mediterranean which exhibits a range of oceanic processes at various scales. Due to the inflow of very light, mesotrophic Black-Sea waters it is the most productive region of the seas around the Hellenic Peninsula, although the regular seasonal coastal upwelling along its eastern shores does not contribute to its productivity. Despite the continuous buoyancy import by the Black Sea, the North Aegean hosts the densest waters of the Eastern Mediterranean. Finally, three semi-enclosed bays located in two islands of the North Aegean exhibit an alternating behavior as sources or sinks of buoyancy for the basin, while their productivity and natural beauty support a range of coastal activities. For the above reasons, the University of the Aegean has invested over several years in the development of a coastal oceanographic observatory (AEGIS), covering both the open North Aegean Sea and the three main bays of the islands of Lesvos and Lemnos. The Observatory consists of a numerical modeling component and an observational component.The modeling component of the observatory consists of four coastal circulation models (for the three bays and the island of Lesvos) nested within a larger domain circulation model covering the whole Aegean Sea north of 37º N. Data assimilation, employing both satellite (sea-surface temperature and sea-level) and field data (employing mostly ARGO float observations) is used in the model of the extended domain (an implementation/configuration of the ROMS system), while the observations obtained in the coastal regions are currently used for coastal models’ (DELFT-3D FLOW and ROMS) validation. In addition to the above circulation models, SWAN is used to simulate the surface waves and DELFT-3D WAQ is being implemented to simulate the biochemical functioning at the various model domains.The observational component at small geographical scales (in the Bays) comprise of continuous meteorological and oceanographic observations through an oceanographic mooring in the middle of the Bay of Kalloni, sea-level observations at the Bays of Kalloni and Gera, and High-Frequency radar observations of sea-surface currents and waves in a region east of Lemnos island, aiming to monitor the Black Sea outflow into the Aegean. The above continuous measurements are supplemented by periodic hydrographic and biogeochemical measurements in the three Bays, to validate the models and calibrate the in-situ continuous data. A recent addition to the AEGIS’s observational arsenal is an ocean glider aimed to capture the variability of the open North Aegean sea.The AEGIS Observatory provides the necessary background to support strategic planning of human interventions at regional and local scales, such as Marine Spatial Planning or the construction of river dams affecting sensitive coastal basins. The implementation of the Coastal Laboratory has been supported by several projects, the most recent being the project “Coastal Environment Observatory and Risk Management in Island Regions AEGIS+” (MIS 5047038), implemented within the Operational Programme “Competitiveness, Enterpreneurship and Innovation” (NSRF 2014-2020), cofinanced by the Hellenic Government (Ministry of Development and Investments) and the European Union (European Regional Development Fund).

The coastal marine ecosystem of Saronikos Gulf, a busy Eastern Mediterranean embayment directly impacted by the greater metropolitan area of Greece’s capital, Athens, is examined through a series of state-of-the-art numerical models that address the hydrodynamics (Delft3D-FLOW), the wave regime (SWAN), the biogeochemistry, and pollution related to species of heavy metals and polyaromatic hydrocarbons (Delft3D-WAQ).The study so far has focused on calibrating model components and on reproducing the seasonal thermohaline conditions, known circulation patterns and the variability of biogeochemical constituents (chlorophyll-a, nutrients, dissolved and particulate matter) and pollutant concentrations, focusing on the vicinity of inner Saronikos.The annual cycle ‘Nov 2009 - Oct 2010’ is simulated, forced with atmospheric data from the ERA5 database. Three sets of open boundary conditions data are tested (Mediterranean Sea Physics Reanalysis dataset by Copernicus and two implementations of the ROMS model covering the Aegean and the Eastern Mediterranean respectively), constituting three classes of numerical experiments aiming to optimize model performance. Freshwater discharges from waste treatment facilities and rivers are considered, the latter drawn from the Swedish Meteorological and Hydrological Institute (platform ‘Hypeweb’).Emphasis has been placed in compiling available information on point sources of pollution from the numerous human activities in the vicinity of the study area. These data are used as forcing in the modelling process.A comprehensive dataset of field measurements collected monthly by the Hellenic Centre for Marine Research from a network of ten stations, as well as satellite derived SST data, are used for model validation.This work is carried out within the context of the EMERGE Horizon 2020 project, that develops methodologies to evaluate, control and mitigate the environmental impacts of shipping emissions. For the scope of the project, next steps currently undertaken include the simulation of the Saronikos Gulf status for the year 2018 considering pollutant mass fluxes (a) from shipping emissions as calculated by the Ship Traffic Emission Assessment Model (STEAM) and (b) from atmospheric depositions as calculated from atmospheric modelling, both components from data provided by consortium partners.

The North Aegean Sea is one of the most interesting seas of the Mediterranean, being under the dominant impact of the Black Sea waters though the so-called Turkish Strait System (TSS – including the Dardanelles and Bosphorus Straits and the Marmara Sea). Moreover, it constitutes a potentially deep water formation site of the Eastern Mediterranean Sea along with the Adriatic Sea. Previous studies for the region focused – rightly – on the crucial role of low salinity Black Sea waters in controlling the overall thermohaline function and dynamics of the North Aegean. None of the previous modeling approaches studied the impact of tides in the mixing processes and the production of extremely dense water, especially during 1987, 1992 and 1993 when major deep water formation events took place in the region. In this work we examine the tidal impact via several long term simulations using a high resolution (1.0 km) ocean model covering the period from 1985 to 2013.The Regional Ocean Model System (ROMS) was used for two 28-year-long hindcasts. A computational grid of approximately 1.0 km horizontal resolution in both directions and 31 vertical sigma (σ) levels was develop to cover the region of interest that extends from 22.5ºE to 27.25º E in longitude and 38.35º N to 41.2º N in latitude. Atmospheric forcing fields from ECMWF ERA5 reanalysis dataset with a spatial resolution of 0.25 degrees and hourly time step were used. The inflow from the Black sea to the North Aegean was treated as an open (east) boundary condition and data from Vladimir Maderich work was used as input. The tidal forcing, in total eight (8) harmonics – four diurnal and four semidiurnal – came from Oregon State University (OSU) inverse global tidal model. Two identical simulation – in terms of model setup and input – were conducted: the first without and the second with tidal forcing.After extensive validation of the model’s results, using all available in situ data from different platforms, a comprehensive analysis was conducted and our findings reveal that model results employing tidal forcing exhibit a closer proximity to observations than non-tidal results, thus validating the necessity to incorporate tidal forcing. Furthermore, the use of barotropic tidal forcing enchanced meridional exchanges of heat, salt and buoyancy between the North and South Aegean, thus increasing the stratification and buoyancy content of the upper water column prior to winter mixing. The most significant and surprising result however is that the dense-water volumes produced using tidal forcing were much higher than the ones without tides, a fact signifying the complexity of processes involved prior to and during dense-water formation.This work was partly covered by the project “Coastal Environment Observatory and Risk Management in Island Regions AEGIS+” (MIS 5047038), implemented within the Operational Program “Competitiveness, Entrepreneurship and Innovation” (NSRF 2014-2020), co-financed by the Hellenic Government (Ministry of Development and Investments) and the European Union (European Regional Development Fund).

This paper presents the state-of-the-art research conducted as part of EN.I.R.I.S.S.T. regarding the emerging impact of shipping and transport to the environment. More specifically, it presents the digital platforms and services that are developed as part of the research infrastructure and are related to environmental sciences. The first is the “EcoMarpol Platform”, which caters for collecting and analyzing pollution-driven data as well as calculating the environmental imprint (atmospheric emissions, waste production, chemical pollution of marine waters and sediments) of maritime activities. This platform additionally includes the online monitoring of in-port emissions from shipping and pollution from ship-to-ship transfer operations or accidents and the environmental risk assessment management. The other platform is the “Passenger Sustainable Travel Platform”, as part of which a tool for calculating aircraft emissions (CO2 and air pollutants) will be developed and applied in the Greek airspace and airports.

Inter-basin water exchanges can be quite important in climatic-scale numerical studies simulating the circulation and hydrographic characteristics of neighboring oceanic basins connected through narrow straits. The crucial role of the interaction between the Mediterranean and the Black Seas is often overseen in simulations, which rely mostly on parameterizations to describe the exchange, essentially decoupling the two basins. In this study, the fully interconnected Eastern Mediterranean–Black Sea system is simulated for the historical period (1985–2015) using realistic boundary conditions (lateral, atmospheric and hydrological), with a hydrodynamic fully three-dimensional ocean modeling system. The setup of such a configuration is thoroughly described and the performance of the 30-year hindcast product is validated exhaustively against observations and model results, by evaluating the representation of surface fields, circulation, three-dimensional hydrographic characteristics, volumetric water exchanges, and the spatio-temporal variability of the above. The comparison shows exceptional performance, minimal drift, and substantial improvement compared to modeling studies that do not include the interaction. Moreover, due to the free-run configuration of the simulation (i.e., absence of assimilation schemes) no additional input is required other than the respective boundary conditions, making it possible to reliably extend the same setup for scenarios where observational data are not available, such as in future projections.