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Abstract: This study investigates the impact of atmospheric deposition on the marine ecosystem of the East Mediterranean Sea. Atmospheric deposition has been suggested to be more important than land inputs of nutrients to the East Mediterranean Sea. For the first time, atmospheric deposition measurements of dissolved inorganic phosphorous and nitrogen over Crete are used together with marine ecosystem observations in the Cretan Sea and a one-dimension physical/biogeochemical marine model. The adopted model configuration successfully reproduces observations of production rates and biomasses of phytoplankton and bacteria in the region. The atmospheric deposition of N and P to the East Mediterranean is shown to increase the primary production by 1–35% depending on season with the maximum impact calculated for summer and fall. Biomasses subsequently increase by 2–26% for phytoplankton and up to 7% for bacteria. The total organic carbon integrated year-around in the first 200m of the water column increases by about 30%. The results also show the importance of the rate of P preferential to N remineralization in the upper sea water layer for the marine productivity. Simulations indicate that continuous atmospheric inputs of nutrients over several decades can maintain the anomalously high N-to-P ratio observed in the East Mediterranean seawater. [Copyright &y& Elsevier]

Abstract: The semi-enclosed environment of Pagasitikos Gulf was the object of a holistic study during 1998–1999 following the appearance of mucilaginous events during summer. A major part of the INSEA project was the development and implementation of a coupled modeling system capable of reproducing all the major characteristics both in physical and biological environments. In the present work the hydrodynamic model based on the Princeton Ocean Model (POM) code is presented while the functioning of Pagasitikos Gulf is analyzed through the assessment of model results. Model results indicate intense seasonal variability with moderate flow patterns and substantial horizontal and vertical gradients. The main known climatological circulation features are found to be reproduced quite well by the model with a rich eddy field controlled by surface buoyancy and momentum fluxes. The ultimate goal is the development of a future operational forecasting system encompassing a detailed description of the ecosystem processes and advanced data assimilation techniques. [Copyright &y& Elsevier]

Abstract: Pagasitikos gulf is a semi-enclosed basin highly influenced both by anthropogenic activities (inflow of nutrients at the north and west parts) as well as by water exchange between the gulf and the Aegean Sea at its south part (Trikeri channel) resulting in the development of functional sub-areas within the gulf. Thus the inner part is characterised by eutrophic conditions with sporadic formation of harmful algal blooms whilst the central part acts as a buffer with mesotrophic characteristics influenced by the outer area. In a companion paper, the circulation fields and the development of water masses in the Pagasitikos gulf were explored. The aim of this study is to investigate the interactions between the physical and biogeochemical systems in the Pagasitikos gulf by coupling advanced hydrodynamic and ecological models. The simulation system comprises two on-line coupled sub-models: a three-dimensional hydrodynamic model based on the Princeton Ocean Model (POM) and an ecological model adapted from the European Regional Seas Ecosystem Model (ERSEM) for this specific ecosystem. After a model spin up period of 10years, the results from an annual simulation are presented. Emphasis is given to the description of the spatial and temporal variability of the ecosystem parameters as well as to the relationship between physical forcing and the evolution of the ecosystem along with other factors affecting the nutrient cycling and primary production. A cost function is used for the validation of model results with field data. Simulation results are in good agreement with in-situ data illustrating the role of the physical processes in determining the evolution and variability of the ecosystem, as well as highlighting the potential usefulness of the model as an operational tool to support environmental management decisions. [Copyright &y& Elsevier]

Abstract: In order to support management decisions for aquaculture, a modeling tool capable of simulating the ecosystem response was developed and is presented here. The impact on the Pagasitikos gulf ecosystem from two marine fish farms, one in a well protected cove and one in a more exposed area of the gulf, is explored and analyzed in the framework of the INSEA EU project. Model results show little effects of nutrient inputs near the exposed site. It appears that effluents from the exposed site may affect more distant areas due to hydrodynamic transport, while effects in the well protected site are more localized and intense (hot spot). Additionally, as the system dynamics are driven to large extent by the seasonal physical variability, the effect depends not only on the location of the farm but also on the season. Planning decisions for coastal areas require integrated management policies based on holistic approaches that include as many system components as possible. The tool capabilities illustrated by the simulation results demonstrate its role in supporting management decisions. [Copyright &y& Elsevier]

Ecosystem models are recognized as valuable tools to understand marine ecosystem dynamics and address management questions, requiring an integrated approach of physical and biotic processes. In the present study, a three-dimensional basin scale Mediterranean hydrodynamic/biogeochemical model, currently operational as part of the POSEIDON forecasting system, was extensively validated against available in-situ and satellite data. The generic POSEIDON ecosystem model skill was objectively assessed, in capturing the observed seasonal variability of the main chemical ecosystem components within the planktonic food web. A cluster K-means analysis was applied to obtain an objective 'biogeography' of the Mediterranean Sea, allowing a more efficient validation of model outputs against observational data. The model presented a reasonable skill in reproducing the seasonal cycle and observed patterns of the Mediterranean inorganic nutrients and chlorophyll-a, characterized by a prominent west-to-east gradient and their increase in areas receiving lateral nutrient inputs. Despite some model deviations, validation results have demonstrated the capability of the model to represent the Mediterranean ecosystem, ranging from oligotrophic open ocean to mesotrophic conditions in productive coastal areas. [ABSTRACT FROM AUTHOR]

Operational monitoring and forecasting of marine environmental conditions is a necessary tool for the effective management and protection of the marine ecosystem. It requires the use of multi-variable real-time measurements combined with advanced physical and ecological numerical models. Towards this, a FerryBox system was originally installed and operated in the route Piraeus–Heraklion in 2003 for one year. Early 2012 the system was upgraded and moved to a new high-speed ferry traveling daily in the same route as before. This route is by large traversing the Cretan Sea being the largest and deepest basin (2500 m) in the south Aegean Sea. The HCMR Ferry Box is today the only one in the Mediterranean and thus it can be considered as a pilot case. The analysis of FerryBox SST and SSS in situ data revealed the presence of important regional and sub-basin scale physical phenomena, such as wind-driven coastal upwelling and the presence of a mesoscale cyclone to the north of Crete. In order to assess the impact of the FerryBox SST data in constraining the Aegean Sea hydrodynamic model which is part of the POSEIDON forecasting system, the in situ data were assimilated using an advanced multivariate assimilation scheme based on the Singular Evolutive Extended Kalman (SEEK) filter, a simplified square-root extended Kalman filter that operates with low-rank error covariance matrices as a way to reduce the computational burden. Thus during the period mid-August 2012–mid January 2013 in addition to the standard assimilating parameters, daily SST data along the ferryboat route from Piraeus to Heraklion were assimilated into the model. Inter-comparisons between the control run of the system (model run that uses only the standard data set of observations) and the experiment where the observational data set is augmented with the FerryBox SST data produce interesting results. Apart from the improvement of the SST error, the additional assimilation of daily of FerryBox SST observations is found to have a significant impact on the correct representation of the dynamical dipole in the central Cretan Sea and other dynamic features of the South Aegean Sea, which is then depicted in the decrease of the basin wide SSH RMS error. [ABSTRACT FROM AUTHOR]

Abstract: Pagasitikos Gulf (Greece), presents an interesting area as it depicts strongly non-linear ecosystem characteristics. It is a shallow coastal area where the marine ecosystem picture is strongly influenced by non-linear hydrodynamic interactions and instabilities. In this study, we explore and assess the major influential variables of the surface phytoplankton biomass (Chlorophyll-a). Several different physical and biogeochemical parameters were used (sea surface temperature [SST], mixed layer depth [MLD], salinity, phosphates and nitrates) to identify which variables control or significantly affect the surface Chl-a of Pagasitikos Gulf for the period of 2001–2005. The variables were derived from a coupled hydrodynamic-biogeochemical model and remotely sensed data from SeaWiFS and AVHRR sensor. Generalised Additive Models (GAMs) were used to examine the relationships between Chlorophyll-a and the environmental regime. GAM analysis showed that the combined effects of the variables used, explained 71% of the surface chlorophyll variation. The order of importance of the variables (based on GAM probability) is p =0.01 (for both phosphate and nitrate), MLD: p =0.0197, salinity: p =0.022, and SST: p =0.046. The results clearly indicated the importance of deep mixing for Pagasitikos Gulf, as the surface phytoplankton blooms appeared to be favoured by cold, nutrient rich, well mixed and higher salinity waters. GAMs indicated that SST plays a significant role having a strong negative relationship with Chl-a, where the highest concentration is reached at 12–15°C and minimum at 22–26°C. Chl-a ceases to increase after 37.9‰ of salinity and 40m of MLD, while minimum concentration is found at 10m of MLD, with a subsequent increase as the waters become more mixed. Phosphate and nitrates appeared to be of equal importance with Chl-a exhibiting an increase along with the nutrients. [Copyright &y& Elsevier]