More than 6000 profiles from profiling floats in the Black Sea over the 2005-2020 period were used to study the ventilation of this basin from the top to the very bottom. In the upper layers and in the main pycnocline, water masses show a strong interannual variability following intermittent events of cold water formation. The density ratio decreased three times during the last 15 years, revealing the decreasing role of temperature in the vertical layering of the Black Sea halocline. The deep transition layer (DTL) between 700 and 1700 m acts as an interface between the baroclinic layer and the largest bottom convective layer (BCL) of the world oceans. On top of DTL are the warm intermediate layer (WIL) and deep cold intermediate layer (DCIL). They both showed strong trends in the last fifteen years due to warmer climate and intensification of warmer intrusions from Bosporus. A “salinity wave” was detected in 2005-2009 below ~1700 m, which evidenced for the first time the penetration of gravity flow from Bosporus down to the bottom. The layering of water masses was explained as resulting from the different distribution of sources of heat and salt, double duffusion and balances between the geothermal and salinity flows in the BCL.

How to cite: Stanev, E., Chtirkova, B., and Peneva, E.: Water Masses in the Black Sea as Seen by Profiling Floats. A revisit of the role of winter, slope and geothermal convectio., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1510, https://doi.org/10.5194/egusphere-egu21-1510, 2021.

The deep chlorophyll maximum (DCM) is a well known feature of the global ocean. However, its description and the study of its formation are a  challenge, especially in the peculiar environment that is the Black Sea. The retrieval of chlorophyll a (Chla) from fluorescence (Fluo) profiles recorded by biogeochemical-Argo (BGC-Argo) floats is not trivial in the Black Sea, due to the very high content of colored dissolved organic matter (CDOM) which contributes to the fluorescence signal and produces an apparent increase of the Chla concentration with depth.

Here, we revised Fluo correction protocols for the Black Sea context using co-located in-situ high-performance liquid chromatography (HPLC) and BGC-Argo measurements. The processed set of Chla data (2014–2019) is then used to provide a systematic description of the seasonal DCM dynamics in the Black Sea and to explore different hypotheses concerning the mechanisms underlying its development.

Our results show that the corrections applied to the Chla profiles are consistent with HPLC data. In the Black Sea, the DCM begins to form in March, throughout the basin, at a density level set by the previous winter mixed layer. During a first phase (April-May), the DCM remains attached to this particular layer. The spatial homogeneity of this feature suggests a hysteresis mechanism, i.e., that the DCM structure locally influences environmental conditions rather than adapting instantaneously to external factors.

In a second phase (July-September), the DCM migrates upward, where there is higher irradiance, which suggests the interplay of biotic factors. Overall, the DCM concentrates around 45 to 65% of the total chlorophyll content within a 10 m layer centered around a depth of 30 to 40 m, which stresses the importance of considering DCM dynamics when evaluating phytoplankton productivity at basin scale.

How to cite: Capet, A., ricour, F., D'Ortenzio, F., Delille, B., and Grégoire, M.: Dynamics of the Deep Chlorophyll Maximum in the Black Sea as depicted by BGC-Argo floats, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3191, https://doi.org/10.5194/egusphere-egu21-3191, 2021.

Straits connecting two large water bodies present a highly strong, complex, and stratified flow structure. The barotropic (related to water level) and baroclinic (related to density) structure of the neighboring seas and the morphology of the strait are decisive on the exchange flow properties through the strait.

As it is a typical example of hydrodynamically complex straits, in this paper, the annual flow structure of the Bosphorus is analyzed. A long-term (one year) current profiles (at three locations), water levels (close to both entrances), CTD measurements at some measurement stations (both at the surface and on the bottom), meteorological (wind speed, wind direction, and atmospheric pressure variation at both entrances) measurements and discharges of the Danube River, which controls the water level of the strait during the late spring, were analyzed.

The Bosphorus is one of the most strategic and busiest waterways in the world connecting the Blacksea to the Mediterranean with the Dardanelles. It presents a two-layer flow structure and the upper layer flow is incomparably much dynamic than the lower one. The results of the study may be highlighted as follows:

1) The water level difference (Δη) between both entrances of the Bosphorus, which is the driving forcing for the southward upper layer flow, shows notable fluctuations throughout the year.

2) The meteorological set-up (wind speed, and atmospheric pressure) is much severe and decisive over Δη during the autumn and the winter, which causes large fluctuations in order of 40 cm (O(40 cm)) over a few day scales. During this period of the year, the typical two-layer flow structure of the strait frequently disappears, and one layer, either southward or in the opposite direction depending on the wind directions, dominates the water column at the measurement locations.

3) The freshwater intrusion to the Blacksea from the major rivers (especially the Danube River) reaches the Bosphorus with around one-month phase (time) lag and controls the water level difference and, so, the current structure of the strait for around 40-45 days from late Spring to early Summer. This period of the year and the rest of the summer is meteorologically calm and, as a result, the water level difference and the current structure is much stable during this time compared to the rest of the year.

4) The seasonal salinity and temperature variations are higher at the surface compared to the bottom. The notable fluctuations are observed both in salinity (> 5 PSU) and in temperature (~ 5 °C) over a short-term period (from a few days to a week) due to severe meteorological conditions which are evident during the fall and winter.

5) The salinity of both layers show temporal variation. The salinity of the top layer was around 17 PSU at the Blacksea entrance of the strait. Due to the mixing, this value increased to 22 PSU at the Sea of Marmara entrance. The salinities of the bottom layer starts from 38 PSU at the south entrance and drops to 32-35 PSU at the north one.

Keywords: stratified flows, measurement, The Bosphorus, hydrodynamics, the Danube River.

How to cite: Altaş, F. and Öztürk, M.: Seasonal Variation of Stratified Flow Behavior in A Sea Strait: A Field Study, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-369, https://doi.org/10.5194/egusphere-egu21-369, 2020.

The Black Sea is a small enclosed basin where coastal regions have a large influence and mesoscale signals dominate the dynamics (the Rossby radius of deformation is about 20km). Large riverine inputs, mainly on the northwestern shelf, induce well-marked horizontal gradients in the distribution of the Black Sea salinity and optical characteristics: coastal and shelf waters have very low salinity and contain large amounts of optically active materials (e.g. coloured dissolved organic matter) and its oligotrophic deep sea has a salinity around 18.2. The presence of these contrasting water characteristics in a relatively small enclosed environment, combined with land contamination and the specificities of its atmospheric composition(e.g. high cloud coverage, aerosols) make the Black Sea a challenging area for the development of high quality satellite products. 

We present first results from a 2-year on-going ESA-funded project, EO4SIBS (Earth Observation for Science and Innovation in the Black Sea) dedicated to the development, and subsequent scientific analysis, of new algorithms and products. In particular, ocean colour products (chlorophyll-a and total suspended matter concentrations, turbidity) were produced from Sentinel 3 (S3) OLCI data combining different algorithms selected based on an automatic water mass classification procedure (case-1 versus case-2 waters). In specific areas, S3-OLCI and Sentinel 2-MSI data were merged to address local features. A revised gridded altimetry product based on 5-Hz along track data (combining Cryosat and S3 SAR) was produced and validated in the coastal zone with tide gauge data. Sea Surface Salinity was derived from the L-Band measured by SMOS and compared with in-situ surface salinity data from field sampling and Argo. 

All these products are now being integrated to further understand the Black Sea physical and biogeochemical functioning (e.g., plume and productivity patterns, mesoscale dynamics, deoxygenation). For instance, the Black Sea mesoscale dynamics are inferred from the 5-Hz altimetry product using an eddy detection and tracking algorithm. The quality of the eddy mapping is assessed by comparison with visible and infrared satellite products while the derived velocities are compared with drifters. Also, the benefit of assimilating ocean colour data in the Black Sea operational model (also known as CMEMS BS-MFC BIO) for the prediction of the Black Sea ecosystem will  be illustrated.

Gridded products are archived as CF-compliant NetCDF files and disseminated through ncWMS protocol. In-situ data are modeled as vector points in a PostGIS database. A web portal is being implemented in order to propose an efficient spatiotemporal exploration of both data sources in a user-friendly interface, including interactive map layers and export possibilities.

We conclude with a set of recommendations for observational requirements needed  to increase the quality of satellite products in the Black Sea and to be able to use the full potential of current and new information provided by  satellites. 

How to cite: Grégoire, M. and the EO4SIBS consortium (ESA project): Earth Observation products  for Science and Innovation in the Black Sea, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10237, https://doi.org/10.5194/egusphere-egu21-10237, 2021.

The aim of the work is to study the mechanisms of the Black Sea mesoscale variability based on an analysis of Lorenz energy cycles calculated from the density and currents velocity obtained by the results of three numerical experiments. An eddy-resolving z-model with a horizontal resolution of 1.6 km was used. Three experiments were carried out with different atmospheric forcing: 1) - climatic data; 2) - SKIRON data for 2011; 3) – SKIRON data for 2016. The mean current kinetic energy MKE, the eddy kinetic energy EKE, the mean available potential energy MPE, the eddy available potential energy EPE and the rates of energy conversion, generation and dissipation were considered in detail.

For all experiments the generation and dissipation rates of the MKE and EKE are close to each other, so the kinetic energy from wind dissipated inside the sea. A buoyancy work (described by the conversion between the MPE and MKE) increase the MKE. The EKE was increasing due to the energy transport from the mean current into eddies and the transport from the EPE to the EKE for all experiments. It is shown that these two energy fluxes were comparable in the experiment 1, while the ratio between of them has changed almost six times in the experiments 2 and 3. The c(MKE, EKE) prevailed in 2011, but the c(EPE, EKE) dominated in 2016.

The maps analysis of the EKE spatial distribution showed that its maximum in the climatic field was located above a continental slope and in areas of the biggest mesoscale eddies. The mesoscale variability of the climatic circulation was due to the influence of both baroclinic and barotropic instability. The zones of the EKE maximum were located in the abyssal part of the sea in the experiments 2 and 3. EKE was increasing in 2011 mainly due to the inflow from the mean current through barotropic instability. The growth of EKE in 2016 was due to conversion of EPE induced by baroclinic instability.

The difference in the EKE variability by the results of climatic and real forcing experiments is associated with the wind forcing. The contribution of the wind stress work to MKE was decreased for the experiments 2 and 3, so as a result, it was observed weakening in the mean current, intensive stream meandering and generation of mesoscale eddies not only in the coastal zones but also in the abyssal part of the sea. Thus, the Black Sea mesoscale variability is determined by barotropic instability or by the combined contribution of barotropic and baroclinic instability processes under intense wind action. The mesoscale variability is due to baroclinic instability under weak wind action.

The reported study was funded by RFBR and Government of the Sevastopol according to the research project No 18-45-920019 and the state task No. 0555-2021-0004.

How to cite: Dymova, O., Demyshev, S., and Alekseev, D.: Analysis of mean and eddy energy of the Black Sea circulation derived under account the climatic and real atmospheric forcing, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-358, https://doi.org/10.5194/egusphere-egu21-358, 2020.

The recently upgrated CMEMS product Black Sea Physical Reanalysis (BLKSEA_MULTIYEAR_PHY_007_004) covers the period 1993-2019 presenting a base for reliable long-term estimates on different aspects of the Black Sea physical processes. The data archive provides monthly and daily fields for the Black Sea basin including 3D variables (temperature, salinity, zonal and meridional velocity components) and 2D variables (mixed layer depth, bottom temperature and sea surface height). 

The good spatial and temporal resolution of the reanalysis gives possibility to evaluate the trend and variability of the subsurface temperature and salinity, as well as the general circulation changes. In the last two decades significant tendency for warming is observed at the surface and in deeper layers, reaching down ~100 m depth. This trend is associated with a slight positive salinity trend seen down to ~200 m depth, which is present almost in the entire Black Sea except for the north-western shelf close to the Danube and Dnestr river delta. Both temperature and salinity show strong interannual variability.  

The calculated Ocean Heat Content (OHC) in the Black Sea basin over the last ~30 year period suggests that the Black Sea water had experienced a general heating tendency after 2013. The increase of OHC is mostly due to the layer 0-200 m and the deeper layers are rather conservative in time. Nevertheless, the cold winter conditions in 2006, 2012 and 2017 led to significant surface water cooling and replenishment of the Cold Intermediate Layer. 

The variation in the main dynamic feature of the basin, the Black Sea Rim current, is studied using the reanalysis data. It shows that the surface current speed varies within ~30% in the period 1993-2019 with a slight positive tendency. The main factor which triggers the inter-annual variability of the Rim current is found to be the atmospheric forcing. Comparison with the surface wind curl from the ERA5 reanalysis data shows significant correlation, predominantly positive (cyclonic) curl for both sea and atmosphere circulation and similar positive trend of the wind/current speed. This proves that the Black Sea Rim Current could be considered a Sverdrup balanced flow and thus strongly related to the regional air circulation.

How to cite: Peneva, E., Lima, L., Aydogdu, A., Masina, S., Stanev, E., Ciliberti, S., Azevedo, D., Coppini, G., Palazov, A., Marinova, V., and Valcheva, N.: The use of CMEMS Black Sea Physical Reanalysis (1993-2019) to understand better the Black Sea variability, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6057, https://doi.org/10.5194/egusphere-egu21-6057, 2021.

Marmara Sea including Bosphorus and Dardanelles Straits (i.e. Turkish Strait Systems, TSS) is the connection between the Black Sea and the Mediterranean. The exchange flow that occurs in the Straits is crucial to set the deep water properties in the Black Sea and the surface water conditions in the Northern Aegean Sea. We have developed a new high-resolution unstructured grid model (U-TSS) for the Marmara Sea including the Bosporus and Dardanelles Straits using the System of HydrodYnamic Finite Element Modules (SHYFEM). Using an unstructured grid in the horizontal better resolves geometry of the Turkish Straits. The new model has a resolution between 500 meter in the deep to 50 meter in the shallow areas, and 93 geopotential coordinate levels in the vertical. We conducted a 4 year hindcast simulation between 2016 and 2019 using lateral boundary conditions from CMEMS (https://marine.copernicus.eu/) analysis, in particular Black Sea Forecasting System (BS-FS) for the northern boundary and Mediterranean Sea Forecasting System (MS-FS) for the southern boundary. Atmospheric boundary conditions fare from the ECMWF dataset.

Mean averaged surface circulation shows that there is a cyclonic gyre in the middle of the basin due to Bosphorus jet flowing to the south and turning to west after reaching the southern Marmara coast. The U-TSS model has been validated against the seasonal in situ observations obtained from four different cruises between 2017 and 2018. The maximum bias occurs at around halocline depth between 20 to 30 meters.  We also found that root mean square error field is higher in the mixed layer interface. We conclude that capturing shallow mixed layer depth is very in the Marmara Sea due to the interplay of air-sea fluxes and mixing parametrizations uncertainties. Maximum salinity bias and rms in the new U-TSS model are around 3 psu which is a significant improvement with respect to previous studies. This new model will be used as an operational forecasting system and will provide lateral boundary conditions for the BS-FS and MS-FS models in the future.

How to cite: Ilicak, M., Federico, I., Barletta, I., Pinardi, N., Ciliberti, S. A., Clementi, E., Coppini, G., Lecci, R., and Mutlu, S.: Evaluation of the new high resolution unstructured grid Marmara Sea model, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7194, https://doi.org/10.5194/egusphere-egu21-7194, 2021.

This study analyzes the evolution of the wave climate in the Black Sea basin in a 31-year long hindcast (1988-2018) performed with the third-generation wave model WaveWatchIII v5.16, forced by the ECMWF-ERA5 reanalysis winds at 30km of spatial resolution and 1-hour frequency. The wave model is implemented on a grid covering the whole Black Sea, with 3km grid step and is off-line coupled with a NEMO based hydrodynamical model. The wave spectrum is discretized using 24 directional sectors, and 30 frequencies, with 10% increment starting from 0.055Hz. The model is implemented to solve deep water processes, following the WAM Cycle4 model physics, with Ultimate Quickest propagation scheme and GSE alleviation, which is implemented in WWIII. Wind input and dissipation are based on Ardhuin et al. (2010), wave-wave interactions are based on Discrete Interaction Approximation. Currents and air-sea temperature difference are provided to the wave model to account for Doppler shift and atmospheric stability above the sea. Model validation and statistical analysis have been carried out to describe the wave climate of the Black sea, considering the following wave fields: significant wave height (Hs), mean wave period (Tm) and mean wave direction. Statistics as Mean, Maximum, 5^th percentile and 95^th statistics have been computed to produce monthly climatologies. The work considers also the evaluation of trends for Hs and Tm, and the evaluation of tendency in the occurrence frequency of mean and max fields for Hs and Tm.

There is no evidence about an overall trend in Hs and Tm, but tendencies can be highlighted in some months and seasons. The most evident trend occurs in Summer on the whole wave spectrum, with reduction of Hs and Tm in the Eastern basin, and increasing in the South-Western basins. Even the evaluation of occurrence frequencies suggests that Black Sea is subjected to a change in the wave regime.

How to cite: Causio, S., Lionello, P., Ciliberti, S. A., and Coppini, G.: Wave climate in the Black Sea: description and trend evaluation using new ECMWF-ERA5 reanalysis and wave-current interaction., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10000, https://doi.org/10.5194/egusphere-egu21-10000, 2021.

The Black Sea is an extraordinarily complex water body for ocean color remote sensing, as it belong to Case 2 waters, which are characterized by relatively high absorption by Colored Dissolved Organic Matter (CDOM) while the concentration of non-pigmented particulate matter does not co-vary in a predictable manner with chlorophyll a . The optical complexity of the Black Sea is the reason why the standard bio-optical algorithms developed for Case 1 waters, are the source of large uncertainties (of the order of hundreds of percent) of chlorophyll a concentration in the coastal and shelf regions. In the framework of ESA contract “BIO-OPTICS FOR OCEAN COLOR REMOTE SENSING OF THE BLACK SEA - Black Sea Color” we developed empirical ocean color algorithm for chlorophyll a retrieval from Sentinel 3A/OLCI primary ocean color products using the in situ reference bio-optical datasets collected in the Black Sea in the period 2012-2019. Results obtained from the assessment of operational S3A/OLCI chlorophyll products, highlighted and confirmed that the specific regional algorithm is essential for the Black Sea. The coefficients of the regional algorithm were derived from the regression of log-transformed pigment concentrations and remote sensing reflectance ratio at 490nm and 560 nm with determination coefficient R² =0.88 and number of samples N=186. The algorithm predicts chlorophyll a values using a cubic polynomial formulation. The result of assessment of the regional chlorophyll a product against independent in situ measurements from the data utilized for algorithm development, showed relatively high accuracy (31.7%), fewer underestimations (MPD=-9.2%) and a good agreement (R²=0.66) between datasets indicating that the regional algorithm is more effective in reproducing the  pigment concentration in the Black Sea waters in comparison to the standard Sentinel 3A/OLCI algorithms. Our analysis revealed the importance of providing regional algorithms strictly required to suit the peculiar bio-optical properties featuring this basin. However, this requires collection of accurate in situ measurements in the different parts of the Black Sea. The validity of the reported empirical algorithm obviously depends on the size of the dataset used for its development. The Black Sea waters vary at a basin level due to the sub-regional features, environmental factors and seasonal variability, consequently the presented regional algorithm might have a limited generalization capability. Clearly, more in situ data with improved spatial and temporal coverage are critically needed for further calibration and validation of the ocean color products in the Black Sea.

How to cite: Slabakova, V., Moncheva, S., Slabakova, N., and Dzembekova, N.: Regional empirical algorithm for an improved retrieval of chlorophyll a concentrations in the Black Sea using Sentinel 3 ocean color data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1743, https://doi.org/10.5194/egusphere-egu21-1743, 2021.

The Cyprus coastal ocean forecasting system, known as CYCOFOS has been providing operational hydrodynamical and sea state forecasts in the Eastern Mediterranean since early 2002. Recently, it has been improved with the implementation of new hydrodynamic and new wave modeling systems with the objective of targeting higher resolution domains, at coastal, sub-regional and regional scales in the Mediterranean and the Black Sea. For the new CYCOFOS hydrodynamic modeling system a novel parallel version of the well established POM has been implemented. The new CYCOFOS hydrodynamical models covers the entire Eastern Mediterranean with a resolution of 2 km and the Levantine Basin with a resolution of ~600 m, both nested in the Copernicus Marine Environmental Monitoring Service of the Mediterranean Forecasting Center-CMEMS Med MFC. For sea waves forecasting, CYCOFOS has implemented  the new ECMWF wave model WAM CY46R1 in the Mediterranean and the Black seas at a higher resolution of 5 km. The CYCOFOS hydrodynamical models received an extended cal/val against the parent model, Argo profiles and satellite SST time series, while in-situ wave data gathered by the HERMES buoy monitoring network in the Eastern Mediterranean and the Black Sea were used for statistical validation of the new CYCOFOS wave forecasts. The new CYCOFOS validated modeling systems,  provide higher resolution quality controlled forecasting data suiting the needs for : a) down-streaming applications supporting risk assessment for offshore platforms in the Levantine Basin and studies concerning the coastal erosion in the Eastern Mediterranean (Albania, Cyprus, Greece) and the Black Sea (Bulgaria) in the framework of the HERMES project, and b) further hierarchical downscaling applications for the development of the COASTAL CRETE operation forecasting system at a higher resolution in the Eastern Mediterranean (Crete, Greece).

How to cite: Zodiatis, G., Lardner, R., Nikolaidis, M., Sofianos, S., Vervantis, V., Zhuk, E., Spanoudaki, K., Kampanis, N., Kallos, G., and Sylaios, G.: The new CYCOFOS forecasting at coastal, sub-regional and regional scales in the Mediterranean and the Black Sea, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2392, https://doi.org/10.5194/egusphere-egu21-2392, 2021.

During quaternary, periodic organic rich layers in the Mediterranean Sea marine sediments also known as sapropels, are not only driven by African monsoon modulation. Superimposed to the main pacing associated with precession cycles (about 21 ka) many sapropels are also impacted by the 100 ka periods associated with the glacial-interglacial cycles. The last occurrence (S1) at the end of the last glacial period and the Early Holocene is an appropriate illustration of this behavior. Recent studies based on long deglaciation simulations with coupled AOGCM pointed out that reaching bottom water anoxia needs a preconditioning, throughout the last deglaciation, driven by North Atlantic Ocean freshening for a few thousand years prior to S1. Here, we investigate another important source of fresh water induced by the melting of Fennoscandian ice sheets (FIS). This run-off freshened the Black Sea, the Marmara Sea and ultimately could have an impact on the stratification and the convection over the Aegean Sea. In order to tackle this issue, we used continental hydrologic perturbation scenarios to drive a high-resolution Mediterranean Sea dynamic circulation model (1/8°) that correctly captures the convection sites and their intensity. In one hand, we rely on hydrologic reconstruction of FIS melting provided by Peltier et al. (JGR, 2015) and Patton, H. et al. (QSR, 2017) in order to derive freshwater flux since the Last Glacial Maximum - that impacted the Black Sea, and likely the Eastern Mediterranean Sea. In the other hand, we build a complete transient scenario accounting for the later enhancement of the African monsoon and we increase fresh water from Nile river. Prescribing such a scenario: first a freshwater increase from FIS during the deglaciation and second a fresh water increase from Nile river, it leads to the shutdown of the Mediterranean Thermohaline Circulation. Our results are in good agreement with Aegean reconstructions (Grant et al, QSR, 2016; Soulet e al. Proc. Natl. Acad. Sci, 3013). The methodology we developed could also be applied to sapropel S5 and S10.

How to cite: Ramstein, G., Vadsaria, T., Li, L., Dutay, J.-C., and Zaragosi, S.: Modeling new scenarios of ocean dynamics during deglaciation over Southern European Seas (Mediterranean and Black Seas), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11131, https://doi.org/10.5194/egusphere-egu21-11131, 2021.

The fine scales are defined here as oceanic dynamical features (eddies, fronts and filaments) generally induced by mesoscale interactions and frontogenesis, and often associated with intense vertical exchanges. These processes are characterized by horizontal scales of 1–10 km with a relatively short lifetime of days/weeks to months. This temporal scale is similar to that of many biological processes, such as, phytoplankton growth, suggesting a physical and biological coupling. Numerical simulations and satellite observations have allowed the characterization of this regime highlighting the role played by these fine scales on structuring the phytoplankton community. To better understand this coupling mechanism, physical and biological in situ measurements are necessary. However, the observations of fine scales remains challenging due to the difficulties of sampling at high spatio-temporal frequency (~km ~daily).

Over the past few years, the Mediterranean Sea has become a lab for developing fine scale in situ strategies. Indeed, a series of campaigns using a satellite based adaptative and Lagrangian strategy coupled with a high-resolution physical-biological sampling, have been performed in order to follow and describe fine scale structures. Following this strategy, the PROTEVSMED-SWOT 2018 cruise has been leaded in the South of the Balearic Islands, with a particular attention to correlate the Lagrangian sampling with the temporal phytoplankton growth, in order to reconstruct the phytoplankton diurnal cycle. Multidisciplinary in situ sensors have allowed to identify a frontal area with a dynamic vertical circulation. Furthermore, the presence of two Atlantic waters, at different stages of mixing associated with various abundances of several phytoplankton groups, corroborated that fine scales must be dynamical barriers to transport, as previous modeling studies have proposed. In order to better understand fine scale mechanisms, the Protevs Gibraltar cruise was performed in the Strait of Gibraltar in October 2020. This region of study is characterized by an important exchange of Mediterranean and Atlantic waters, and also by an intense circulation that generates energetic processes, which make it a favorable place for the formation of fine scale structures.

The new knowledge acquired with these studies paves the way to the future BIOSWOT-Med campaign planned for 2022 in the western Mediterranean Sea under the future SWOT satellite crossover tracks.

How to cite: Tzortzis, R., Doglioli, A. M., Barrillon, S., Petrenko, A. A., d'Ovidio, F., Izard, L., Thyssen, M., Bhairy, N., Pascual, A., Barceló-Llull, B., Cyr, F., Tedetti, M., Garreau, P., Dumas, F., Bordois, L., Comby, C., Rousselet, L., and Gregori, G.: Recent progress in the study of fine-scale physical-biological coupling in the Mediterranean Sea., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7133, https://doi.org/10.5194/egusphere-egu21-7133, 2021.

Ocean life relies on the loads of dissolved inorganic nutrients (nitrate, phosphate and silicate) and other micro-nutrients into the euphotic layer. They fuel phytoplankton growth that maintains the equilibrium of the food web. Ocean circulation and physical processes continually drive the large -scale distribution of chemicals toward a homogeneous distribution (Williams and Follows, 2003). The biological and biochemical processes counteract this tendency. Therefore, describing nutrient dynamics is important to understand the overall ecosystem functioning.

At global scale, most of the biogeochemical descriptions are based on model simulations and satellite data, since nutrient in situ observations are generally infrequent and not homogeneously distributed in space and time. Climatological mapping is often used to understand the biogeochemical state of the ocean representing monthly, seasonally or annual averaged fields.

Within this context, the western Mediterranean Sea climatology (BGC-WMED) presented here is a product derived from in situ observations, derived from various data sources: in total, 2253 in-situ inorganic nutrient profiles over the period 1981-2017 have been used (Medar/MEDATLAS, Fichaut et al., 2003; the CNR-WMED biogeochemical dataset, Belgacem et al., 2020; SeaDataNet data product, https://www.seadatanet.org; Mediterranean Ocean Observing System for the Environment, MOOSE, http://www.moose-network.fr/).

Annual mean gridded nutrient fields for the period 1981-2017, and sub-periods 1981-2004 and 2005-2017, on a horizontal 1/4° × 1/4° grid have been produced. The biogeochemical climatology is built on 19 depth levels and for the dissolved inorganic nutrients nitrate, phosphate and orthosilicate. To generate smooth and homogeneous interpolated fields, an advanced N-dimensional version of DIVA, DIVAnd v2.5.1 (Barth et al., 2014), which is based on the variational inverse method (VIM) (Brasseur et al., 1996), has been used.

A sensitivity analysis was carried out to assess the comparability of the data product with the observational data. The BGC-WMED has then been compared to other available data products, i.e. the medBFM biogeochemical reanalysis and the biogeochemical component of WOA18.

Keywords: Mediterranean Sea, climatology, inorganic nutrient, in situ observations. 

How to cite: Belgacem, M., Chiggiato, J., Schroeder, K., Barth, A., Troupin, C., and Pavoni, B.: Climatological distribution of dissolved inorganic nutrients in the Western Mediterranean Sea (1981-2017), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7762, https://doi.org/10.5194/egusphere-egu21-7762, 2021.

The Mediterranean Sea has been identified as a hotspot for climate change. Furthermore, its very diverse trophic regimes, in such a little area, make it an extremely interesting region from a biogeochemical perspective. Numerous studies aim at better understanding and representing the Mediterrenean dynamics and biogeochemistry through modeling. This is a crucial step in order to predict the future anthropogenic impacts on the Mediterranean Sea and their possible effects on its biogeochemistry,  and all what depends on it. The number of models that simulate the Mediterranean biogeochemistry, and the data available to compare with are now sufficient to draw an overall picture of the Mediterranean Sea biogeochemical models state of the art.

In this study, we gathered 10 biogeochemical simulations of the Mediterranean Sea, including 8 regional and 2 high-resolution global configurations. The simulations are compared with surface chlorophyll estimates derived from satellite observations; chlorophyll, nitrate, oxygen, and particulate organic carbon concentrations derived from BGC-Argo floats, and  phytoplankton group-specific  primary production estimated from ocean color satellite observations. 

Our first aim is to describe and compare all known Mediterranean biogeochemical models, and to highlight their specificity. This should give an insight into the current achievements, and expose what biogeochemical model products are hence available for further ecological analysis. 

Furthermore, a specific attention is given to how well each model performs in selected regions of the Mediterranean Sea, in order to understand which specific process is needed to adequately represent the different trophic regimes of the Mediterranean Sea.

How to cite: Palmieri, J., Mignot, A., Dutay, J.-C., Richon, C., Macias Moy, D., d’Ortenzio, F., Schmechtig, C., Uitz, J., Houpert, L., Lamouroux, J., Baklouti, M., Pages, R., Cosimo, S., Teruzzi, A., Lazzari, P., Ciavatta, S., Kay, S., Triantafyllou, G., Tsiaras, K., and Somot, S. and the BGC-Med team: Med-BGC MIP: A Mediterranean Biogeochemical models comparison., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10452, https://doi.org/10.5194/egusphere-egu21-10452, 2021.

Statistics of anticyclone activity and trajectories in the southeastern Mediterranean sea over the period 2000-2018
is created using the DYNED atlas, which links the automated mesoscale eddy detection by the AMEDA algorithm with in
situ oceanographic observations. This easternmost region of the Mediterranean sea, delimited by the Levantine coast and
Cyprus, has a complex eddying activity, which has not yet been fully characterized. Using Lagrangian tracking
to investigate the eddy fluxes and interactions between different subregions in this area, we find that the southeastern Levantine
area is isolated, with no anticyclone exchanges with the western part of the basin. Moreover the anticyclonic structure above
the Eratosthenes seamount is identified as being an anticyclone attractor, differentiated from other anticyclones and staying
around this preferred position up to four years with successive mergings. Colocalized in situ profiles inside eddies provide
quantitative information on their subsurface structure and show that similar surface signatures correspond to very different
physical properties. Despite interannual variability, the so-called "Eratosthenes attractor" stores a larger amount of heat and
salt than neighboring anticyclones, in a deeper subsurface anomaly that usually extend down to 500 m. This suggests that this
attractor could concentrate heat and salt from this sub-basin, which will impact the properties of intermediate water masses
created there.

How to cite: Barboni, A., Lazar, A., Stegner, A., and Moschos, E.: Lagrangian eddy tracking reveals the Eratosthenes anticyclonicattractor in the eastern Levantine basin, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4290, https://doi.org/10.5194/egusphere-egu21-4290, 2021.

In line with international initiatives (e.g. UN Decade of Ocean Science for Sustainable Development, UN Sustainable Developement Goal 14, OceanObs’19), one of the main objectives of the Balearic Islands Coastal Observing and Forecasting System (SOCIB) is to respond to science and society needs providing oceanographic data and added-value ocean products. In particular, SOCIB is developing a comprehensive set of multivariate sub-regional indicators in the Mediterranean Sea from past (last four decades) to present (today), with a specific interest on the Balearic Islands region and its adjacent basins (North-western Mediterranean Sea, Alboran Sea and Algerian sub-basin).

Two categories of oceanic variables are currently processed: (1) surface ocean data (sea surface temperature, chlorophyll-a concentration, currents, sea level and wind) from satellite products distributed by CMEMS, and (2) vertically integrated data (ocean heat and salt content, mixed layer depth properties, and water mass transports in key sections) from in situ platforms (gliders from SOCIB, profiling floats from Met-Office). These sub-regional indicators are an integral part of an operational product that provides continuous information about the ocean state and variability at sub-regional scale from daily (events) to interannual/decadal (climate) scales. These indicators allow to detect specific events in real time (e.g. marine heat wave, atmospheric storm, extreme river discharge, mesoscale eddy, deep convection). Long-term variations of the physical and biogeochemical components of the ocean, in response to climate change, are also addresssed as well as sub-regional differences.

An interactive and user-friendly interface has been implemented to monitor, visualize and communicate ocean information that is relevant for a wide range of sectors, applications and end-users (e.g. scientific community, educators in marine science, decision-makers and environmental agencies). The “Sub-regional Mediterranean Sea indicators” visualization tool is positioned as a complementary product to the CMEMS Ocean Monitoring Indicators at regional level addressing sub-regional variablity at various time scales and contributes to respond to the societal and environmental challenges.

How to cite: Juza, M. and Tintoré, J.: The “Sub-regional Mediterranean Sea indicators” viualization tool: from event detection to climate change estimations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8675, https://doi.org/10.5194/egusphere-egu21-8675, 2021.

Anticyclonic mesoscale eddies are often formed in the Balearic Sea towards the end of summer and autumn. In some years, these eddies become strong and persistent, modifying the ocean currents and water mass properties in the area. The generation and intensification mechanisms of two long-lived events observed in 2010 and 2017 were studied by means of the energy conversion terms associated with eddy-mean flow interactions and through complementary model sensitivity tests.

Results show that these eddies were formed through mixed barotropic and baroclinic instabilities. The former was associated with weak meandering of the shelf current near the coast produced by northwesterly wind events, and the latter with the existence of the northward intrusions of relatively warm waters through the intense Pyrenees thermal front. The intensification mechanism varied between the two events. While in 2010 it was driven by intense salinity gradients in the Balearic Sea, in 2017 it resulted from an extra barotropic energy term fed by northwesterly winds.

These eddies lasted more than two months with a radius varying between 30km and 90km and a vertical structure that reached 1500 m depth. Their presence resulted in a 3ºC anomaly between the warm core waters and the outer parts of the eddies.

How to cite: Aguiar, E., Mourre, B., Revélard, A., Juza, M., Alvera-Azcárate, A., Pascual, A., Mason, E., and Tintoré, J.: Strong long-lived anticyclonic mesoscale eddies in the Balearic Sea: formation and intensification mechanisms, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8742, https://doi.org/10.5194/egusphere-egu21-8742, 2021.

The Strait of Gibraltar is a narrow and shallow channel that controls the thermohaline and biogeochemical balances of the Mediterranean Sea. Exchanges across this strait are known to be significantly modulated by tidal currents that induce an intense vertical mixing. However, the turbulent processes that control the location, timing and magnitude of this vertical mixing are still unclear. Based on twin tidal and non-tidal simulations, we shed light on the tidal mixing at the Strait of Gibraltar, as simulated from a regional configuration of the three-dimensional numerical model MITgcm. The model domain covers the entire Mediterranean basin, the Black Sea and a part of the Atlantic Ocean, using a very high spatial resolution around the Strait of Gibraltar (1/200°). In both simulations we analyse the vertical mixing generated by the model's turbulence closure scheme based on a turbulent kinetic energy budget. As expected, tides strongly intensify the vertical mixing within the Strait of Gibraltar. Tidal currents also induce significant vertical motions that feed recirculation cells between Atlantic and Mediterranean layers. Conversely, the absence of tidal currents causes an overestimation of the velocities along with spurious mixing in the vicinity of the strait. We show that tidal mixing relies on two main ingredients: sustained vertical shear of horizontal velocities and the reduction of stratification, performed by the work of tidal currents against buoyancy forces. We conclude by proposing a revised conceptual view of tidal mixing at the Strait of Gibraltar.

How to cite: Gonzalez, N., Waldman, R., Sannino, G., Giordani, H., and Somot, S.: A new perspective on tidal mixing at the Strait of Gibraltar from a very high-resolution model of the Mediterranean Sea, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3971, https://doi.org/10.5194/egusphere-egu21-3971, 2021.

Vertical velocities associated with meso- and submeso-scale structures generate important vertical fluxes of carbon and other biogeochemical tracers from the surface layer to depths below the mixed layer. Vertical velocities are very weak and characterized by small scales which make them difficult to measure. The project entitled Coherent Lagrangian Pathways from the Surface Ocean to Interior (CALYPSO, Office of Naval Research initiative) addresses the challenge of observing, understanding, and predicting the vertical velocities and three-dimensional pathways on subduction processes in the frontal regions of the Alboran Sea. Within the framework of the CALYPSO project, we analysed the processes that give rise to vertical velocities in the Western Alboran Gyre Front (WAGF) and Eastern Alboran Gyre Front (EAGF). The periods of frontal intensification were analyzed in the perspective of the frontogenesis, instabilities, non-linear Ekman effects, and filamentogenesis using multi-platform in-situ observations and a high-resolution simulation in spring 2018. The spatio-temporal characteristics of the WAGF indicate a wider, deeper, and longer-lasting front than the EAGF. The WAGF intensification and vertical velocities development are explained through i) frontogenesis, ii) conditions for symmetric and ageostrophic baroclinic instabilities generation, and iii) nonlinear Ekman effects. These mechanisms participate to generate and strengthen an ageostrophic secondary circulation responsible for vertical velocities intensification in the front. In the case of the EAGF, the intensification and vertical velocities development are explained by filamentogenesis in both the model and glider observations. The EAGF intensification is characterized by a sharp and outcropping density gradient at the center of the filament, where two asymmetrical ageostrophic cells develop across the front with narrow upwelling region in the middle.

How to cite: Garcia-Jove, M., Mourre, B., Zarokanellos, N., Lermusiaux, P. F. J., Rudnick, D. L., Allen, J., and Tintoré, J.: Analysis of Vertical Velocities Development through High-resolution Simulation and Glider Observations in the Alboran Sea, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8945, https://doi.org/10.5194/egusphere-egu21-8945, 2021.

We present a phenomenological description and dynamical analysis of the Alboran fronts using a realistic simulation at submesoscale resolution. The study is focused on east Alboran fronts emerging within relatively strong flows that separate from the Spanish coast into the basin interior. The statistical analysis of our solution shows that strained-induced frontogenesis is a recurrent submesoscale mechanism associated with these fronts, and the process is assessed in terms of the advective Lagrangian frontogenetic tendencies associated with buoyancy and velocity horizontal gradients. Intermittency in their strength and patterns is indicative of high variability in the occurrence of active frontogenesis in association with the secondary circulation across the frontal gradient. As a result, we find many episodes with strong surface fronts that do not have much associated downwelling. Frontogenesis and the associated secondary circulation are further explored during two particular frontal events, both showing strong downwelling of O(1) cm s−1 extending down into the pycnocline. A frontogenetic contribution of turbulent vertical momentum mixing to the secondary circulation is identified in the easternmost region during the cold season, when the dynamics are strongly influenced by the intrusion of the salty Northern Current. The background vertical velocity fields observed during the analyzed events indicate other currents in the submesoscale range, including tidal and topographic Internal waves.

How to cite: Capó, E., McWilliams, J. C., Mason, E., and Orfila, A.: Intermittent frontogenesis in the Alboran Sea, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15553, https://doi.org/10.5194/egusphere-egu21-15553, 2021.

Recent improvements of satellite altimeter observations allow to approach investigations on the surface ocean circulation even in those regions where the slope associated to dynamic structures is reduced. The capability to detect the main dynamic features and their variability from satellite radar altimetry in the Ligurian Sea (Western Mediterranean) is here assessed.

Altimeter data from X-TRACK products recently released are used for this study: the time series of satellite-based- currents along the track n.044, which crosses the Ligurian Sea from the Corsica Channel to the Ligurian coast, is analysed. The temporal sampling is about 10 days and the along-track resolution is 7 km. Geostrophic currents computed from satellite radar altimetry are checked for consistency against the dynamic topography obtained from concurrent CTD casts collected during recent oceanographic campaigns carried out by the Italian Hydrographic Institute along the track. A more detailed assessment of the computed current velocities is based on the analysis of long-term ADCP measurements from a fixed mooring deployed from 2004 to 2006 in the Central Ligurian Sea (43°47.77’ N; 9°02.85’ E) 40 nm from the coast, quite close to the altimeter track. An RD&I 300 kHz upward-looking ADCP sampled the upper layer at 8 m vertical resolution. Currents in the upper layer (0-100 m) are almost barotropic with the variability due to the wind confined to the upper few meters. In order to define an appropriate metrics to compare currents from different measuring systems, EOF analysis of ADCP profiles have proved to be a good tool to filter out the high frequency and wind driven currents, thus enhancing the contribution of the geostrophic component.

How to cite: Picco, P., Vignudelli, S., Repetti, L., and Demarte, M.: Surface circulation in the Ligurian Sea: an assessment of satellite radar altimeter-derived geostrophic currents., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9785, https://doi.org/10.5194/egusphere-egu21-9785, 2021.

During the winter from 2009 to 2013, the mixed layer reached the seafloor at about 2500m in the NW Mediterranean. Intense fronts around the deep convection area were repeatedly sampled by autonomous gliders, mainly as part of the MOOSE observatory of the NW Mediterrnean Sea (https://www.moose-network.fr/). Subduction down to 200-300m, sometimes deeper, below the mixed layer was regularly observed testifying of important frontal vertical movements. Potential Vorticity dynamics was diagnosed using glider observations and a high resolution realistic model at 1-km resolution (SYMPHONIE model, https://sirocco.obs-mip.fr/ocean-models/s-model/).

During down-front wind events in winter, remarkable layers of negative PV were observed in the upper 100m on the dense side of fronts surrounding the deep convection area and successfully reproduced by the numerical model. Under such conditions, symmetric instability can grow and overturn water along isopycnals within typically 1-5km cross-frontal slanted cells. Two important hotpspots for the destruction of PV along the topographically-steered Northern Current undergoing frequent down-front winds have been identified in the western part of Gulf of Lion and Ligurian Sea. Fronts were there symmetrically unstable for up to 30 days per winter in the model, whereas localized instability events were found in the open-sea, mostly influenced by mesoscale variability. The associated vertical circulations also had an important signature on oxygen and fluorescence, highlighting their under important role for the ventilation of intermediate layers, phytoplankton growth and carbon export.

How to cite: Bosse, A., Testor, P., Damien, P., Estournel, C., Marsaleix, P., Mortier, L., Prieur, L., and Taillandier, V.: Wind-forced submesoscale symmetric instability around deep convection in the NW Mediterranean Sea, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11053, https://doi.org/10.5194/egusphere-egu21-11053, 2021.

The focus of this study is to analyze the probability distribution functions of model wind data over the Mediterranean Sea. The atmospheric wind data set is composed by ECWMF analyses for the period 2010-2019. A single grid point statistical method is applied to the Mediterranean Sea for both wind components and amplitude. The pdf (probability distribution function) of the wind components is Gaussian while the amplitude is Weibull. In addition, sensitivity experiments are done to compare the Weibull with the Exponential Weibull pdfs, showing almost identical patterns for both distributions. The use of two parameters Weibull distribution is widely accepted to represent the statistical structure of surface wind, while three parameters Exponential Weibull distribution mostly refers to extreme events. The pdf parameter distribution in the Mediterranean Sea is shown for the first time to be associated with specific wind structures such as Mistral and Etesian winds. This study confirms the previous results from Chu (2009) for oceanic currents and by Drobinski (2015) for wind station data, both cases showing the two parameter Gaussian pdf for wind components and Weibull pdf for wind amplitude. The knowledge of these distributions will help to improve the ensemble ocean forecast as for the setting of initial conditions of ocean forecasts where atmospheric forcing is crucial to quantify the forecast errors.

How to cite: Ghani, M. H., Pinardi, N., and Trotta, F.: Statistical analysis of model wind data for the Mediterranean Sea , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13556, https://doi.org/10.5194/egusphere-egu21-13556, 2021.

The coastal area of Crete is an area of increasing interest due to the recent hydrocarbon exploration and exploitation activities in the Eastern Mediterranean Sea and the increase of the maritime transport after the enlargement of the Suez Canal. National and local authorities, like ports and the coast guard, who are involved in maritime safety, such as oil spill prevention, the tourism industry and policy makers involved in coastal zone management, are key end users’ groups who can benefit from high spatial and temporal resolution forecasting products and information to support their maritime activities in the coastal sea area of the island. To support local end users and response agencies to strengthen their capacities in maritime safety and marine conservation, a high-resolution, operational forecasting system, has been developed for the coastal area of Crete. The COASTAL CRETE forecasting system implements advanced numerical hydrodynamic and sea state models, nested in CMEMS Med MFC products and produces, on a daily basis, 5-day hourly and 6-hourly averaged high-resolution forecasts of important marine parameters, such as sea currents, temperature, salinity and waves. The COASTAL CRETE high-resolution (~ 1km) hydrodynamic model is based on a modified POM parallel code implemented by CYCOFOS in the Eastern Mediterranean and the Levantine Basin, while for wave forecasts, the latest ECMWF CY46R1 parallel version including a number of new features, a state-of-the-art wave analysis and prediction model, with high accuracy in both shallow and deep waters has been implemented with a resolution of ~1.8 km. The COASTAL CRETE hydrodynamic model has been evaluated against the CMEMS Med MFC model and with satellite Sea Surface Temperature data with good statistical estimates. The COASTAL CRETE wave model is calibrated with in-situ data provided from the HCMR buoy network operating in the area. Both the CMEMS Med MFC products and COASTAL CRETE forecasts are made available through a customized instance of ADAM (Advanced geospatial Data Management platform) developed by MEEO S.r.l. (https://explorer-coastal-crete.adamplatform.eu/). This application provides automatic data exchange management capabilities between the CMEMS Med MFC and the COASTAL CRETE models, enabling data visualization, combination, processing and download through the implementation of the Digital Earth concept. Among the numerous functionalities of the platform, a depth slider allows to explore the COASTAL CRETE products through the depth dimension, and a sea current magnitude feature enables the visualization of the currents vectors by overlaying them to any available product/parameter, thus allowing comparisons and correlations. The downscaled high-resolution COASTAL CRETE forecasts will be used to deliver on demand information and services in the broader objectives of the maritime safety, particularly for oil spill and floating objects/marine litters predictions. Such a use case is presented for the port area of Heraklion, implementing nested fine grid hydrodynamic and oil spill models (MEDSLIK-II).

Acknowledgement: Copernicus Marine Environment Monitoring Service (CMEMS) DEMONSTRATION COASTAL-MED SEA. COASTAL-CRETE, Contract: 110-DEM5-L3.

How to cite: Spanoudaki, K., Zodiatis, G., Kampanis, N., Quarta, M. L., Folegani, M., Galanis, G., Nikolaidis, M., and Nikolaidis, A.: The high-resolution COASTAL CRETE ocean forecasting system , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2777, https://doi.org/10.5194/egusphere-egu21-2777, 2021.

Sediment archives of the Eastern Mediterranean Sea (EMed) indicate very different physical and biogeochemical conditions during the LGM and the early Holocene than for present day. The ultimate goal of the here presented project is to disentangle the controlling processes of the circulation in the EMed over the last deglacial period by applying a regional ocean model including biogeochemistry covering the entire Mediterranean Sea. This model setup will be driven by downscaled forcing fields from a simulation with the paleo version of Max Planck Institute Earth System Model (pMPI-ESM) spanning from 26 to 0 kaBP.  pMPI-ESM has unique features like automatic bathymetry adjustment due to sea level rise and transient river routing. Despite its coarse model resolution, pMPI-ESM simulations catch the humid period of the early Holocene with corresponding increased Nile river discharge, a relevant driver for the conditions in the EMed. Thus, we are convinced that pMPI-ESM can provide a long-term transient and consistent forcing which is appropriate for our aims.

Here we present first results to evaluate the performance of our regional model driven by the downscaled forcing from pMPI-ESM. Main characteristics of the present day Mediterranean circulation are well captured such as locations of deep water formation, Mediterranean and Black Sea fresh water budgets, and the baroclinic transports through the Strait of Gibraltar.  We test our model framework for different time slices of deglaciation.

How to cite: Six, K. and Mikolajewicz, U.: Towards an ocean biogeochemical modelling framework for long-term transient simulations with a focus on the Eastern Mediterranean Sea , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5933, https://doi.org/10.5194/egusphere-egu21-5933, 2021.

The ocean's turbidity and optical properties are determined by the interaction of sunlight radiation with suspended particles and dissolved matter of the water body's surface layers. Variations in the optical properties can affect the upper ocean's heat content, thus modifying the stratification and the mixed layer dynamics. These variations can be monitored using satellite products, along with in-situ observations, and their impact on ocean circulation can be analyzed through numerical modeling. For the oligotrophic Eastern Mediterranean, there is a gap of in-situ data used to evaluate remote sensing observations. Furthermore, this region receives significant atmospheric deposition of particulate inorganic matter through African dust, as well as from river discharges. These constituents' contribution in optical properties modulation is often considered negligible for oligotrophic regions, where the various parameters have been calculated based on chlorophyll variations. To fill this gap, in situ measurements of beam attenuation coefficient at 660 nm (c, in m^-1)⁽¹⁾ provided by the Hellenic Centre for Marine Research (HCMR) were assessed, and a gridded dataset was constructed using Data-Interpolating Variational Analysis (DIVA), for the Aegean Sea, Eastern Mediterranean, for the years 1991-2019. The aim is to validate the accuracy of satellite products for this region using this dataset. Towards this goal, available satellite ocean color products of the ocean's inherent optical properties will be used to estimate c values, which will be compared to the in-situ dataset.

1. A. P. Karageorgis et al., Deep Sea Res. Part I 55, 177–202 (2008).

How to cite: Metheniti, V., Karageorgis, A. P., Kampanis, N., and Sofianos, S.: Optical properties of the Eastern Mediterranean Sea, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2644, https://doi.org/10.5194/egusphere-egu21-2644, 2021.

A hydrodynamic simulation is carried out over the entire Mediterranean basin at a resolution of 3 to 4 km and a duration of about 10 years (2011-2020). The results are systematically evaluated using Argo profiles focusing on the spatial distribution of water mass properties along their path, the main mesoscale structures, the mean vertical temperature and salinity profiles by sub-basins as well as their "pseudo temporal evolution" biased by the variability of the spatial and temporal distribution of Argo observations.

The simulation has generally very low mean biases (of the order of 0.01 for salinity) and correlations on the monthly time series reconstructed from the observations, of the order of 0.9 at the scale of the eastern basin, both in surface waters and at 200 m in intermediate waters.

The evolution of salinity over the decade is then analyzed from the simulation. Particular attention is paid to the main basins of water mass formation, the Adriatic, the Levantine basin and the South Aegean Sea. The factors driving this evolution are analyzed in each of these basins. The propagation of the changes from these formation areas to the entire eastern basin is then examined, with a particular focus on the intermediate waters.

How to cite: Estournel, C., Marsaleix, P., and Ulses, C.: Variability of the hydrological characteristics of the Eastern Mediterranean over the last decade, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15927, https://doi.org/10.5194/egusphere-egu21-15927, 2021.

Mediterranean marine heat waves (MHW) can be defined as abrupt but prolonged, discrete and anomalously warm water events that last for five or more days and exceed temperatures warmer than the 99th percentile (Darmaraki et al. 2019). Like their atmospheric counterpart, Mediterranean MHW have already increased in intensity, frequency and duration - a trend projected to continue under anthropogenic climate change. Recent observations of MHW demonstrated a strong influence of these extreme climatic events on marine organisms, including mass mortalities and shifts in species ranges but also economic impacts on fisheries and aquaculture. MHW can be caused by a combination of atmospheric and oceanic processes and depend on the specific season and location of occurrence. However, the main triggers are generally still not well understood and the current knowledge is largely based on these reported regional impacts. This work focuses on historical (1985 – 2014) atmospheric and marine heat waves in a high resolution CMIP6 model as well as a fully three-dimensional oceanographic hindcast of the interconnected Eastern Mediterranean – Black Sea system. We detect the atmospheric and marine heatwaves and investigate the triggering, compound/concurrent effect of the atmosphere on marine heat waves in the Eastern Mediterranean. For the analysis of atmospheric heat waves, we follow the methodology of Kuglitsch et al. (2010). We use Eastern Mediterranean atmospheric model and ERA-Interim reanalysis to calculate daily maximum (TX) and minimum (TN) air temperatures as well as to set temperature thresholds to estimate the beginning and end of the heat wave events. We identify MHWs from daily sea surface temperatures, applying the approach of Darmaraki et al. (2019). Furthermore, we calculate the heat wave frequency, duration and intensity. The two pairs of datasets are then compared with respect to the spatio-temporal occurrence of heat waves in the atmosphere and ocean, in an effort to reveal feedbacks between the two spheres which would characterize the events as compound. Finally, we estimate a threshold at which an atmospheric heat wave triggers a marine heat wave, and thus a compound event.

How to cite: Behr, L., Petalas, S., Jaeger, M., Xoplaki, E., Tragou, E., Gogou, A., and Zervakis, V.: Atmosphere-Ocean compound heat wave events in the Eastern Mediterranean, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9583, https://doi.org/10.5194/egusphere-egu21-9583, 2021.

The Mediterranean Sea is considered a relevant geostrategic region and a prominent climate change hot spot. This semi-enclosed basin has been the subject of abundant studies due to its vulnerability to sea-level rise and other coastal hazards. With the steady advent of new technologies, a growing wealth of observational data are nowadays available to efficiently monitor the sea state and properly respond to socio-ecological challenges and stakeholder needs, thereby strengthening the community resilience at multiple scales.

Nowadays, High-Frequency radar (HFR) is a worldwide consolidated land-based remote sensing technology since it provides, concurrently and in near real time, fine-resolution maps of the surface circulation along with (increasingly) wave and wind information over broad coastal areas. HFR systems present a wide range of practical applications: maritime safety, oil spill emergencies, energy production, management of extreme coastal hazards. Consequently, they have become an essential component of coastal ocean observatories since they offer a unique dynamical framework that complement conventional in-situ observing platforms. Likewise, within the frame of the Copernicus Marine Environment Monitoring Service (CMEMS), HFR are valuable assets that play a key pivotal role in both the effective monitoring of coastal areas and the rigorous skill assessment of operational ocean forecasting systems.

The present work aims to show a panoramic overview not only of the current status of diverse Mediterranean HFR systems, but also of the coordinated joint efforts between many multi-disciplinary institutions to establish a permanent HFR monitoring network in the Mediterranean, aligned with European and global initiatives. In this context, it is worth highlighting that many of the Mediterranean HFR systems are already integrated into the European HFR Node, which acts as central focal point for data collection, homogenization, quality assurance and dissemination and promotes networking between EU infrastructures and the Global HFR network.

Furthermore, priority challenges tied to the implementation of a long-term, fully integrated, sustainable operational Mediterranean HFR network are described. This includes aspects related to the setting up of such a system within the broader framework of the European Ocean Observing System (EOOS), and a long-term financial support required to preserve the infrastructure core service already implemented. Apart from the technological challenges, the enhancing of the HFR data discovery and access, the boosting of the data usage as well as the research integration must be achieved by building synergies among academia, management agencies, state government offices, intermediate and end users. This would guarantee a coordinated development of tailored products that meet the societal needs and foster user uptake, serving the marine industry with dedicated smart innovative services, along with the promotion of strategic planning and informed decision-making in the marine environment.

How to cite: Lorente, P. and the RADAR-MED: The High Frequency coastal radar network in the Mediterranean: joint efforts towards a fully operational implementation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16311, https://doi.org/10.5194/egusphere-egu21-16311, 2021.

The available historical oxygen data show that the deepest part of the South Adriatic Pit remains well-ventilated despite the winter convection reaching only the upper 700 m depth. Here, we show that the evolution of the vertical temperature structure in the deep South Adriatic Pit (dSAP) below the Otranto Strait sill depth (780 m) is described well by continuous diffusion, a continuous forcing by heat fluxes at the upper boundary (Otranto Strait sill depth) and an intermittent forcing by rare (several per decade) deep convective and gravity-current events. The analysis is based on two types of data: (i) 13-year observational data time series (2006–2019) at 750, 900, 1,000, and 1,200 m depths of the temperature from the E2M3A Observatory and (ii) 55 vertical profiles (1985–2019) in the dSAP. The analytical solution of the gravest mode of the heat equation compares well to the temperature profiles, and the numerical integration of the resulting forced heat equation compares favorably to the temporal evolution of the time-series data. The vertical mixing coefficient is obtained with three independent methods. The first is based on a best fit of the long-term evolution by the numerical diffusion-injection model to the 13-year temperature time series in the dSAP. The second is obtained by short-time (daily) turbulent fluctuations and a Prandtl mixing length approximation. The third is based on the zero and first modes of an Empirical Orthogonal Function (EOF) analysis of the time series between 2014 and 2019. All three methods are compared, and a diffusivity of approximately κ = 5 · 10⁻⁴m²s⁻¹ is obtained. The eigenmodes of the homogeneous heat equation subject to the present boundary conditions are sine functions. It is shown that the gravest mode typically explains 99.5% of the vertical temperature variability (the first three modes typically explain 99.85%) of the vertical temperature profiles at 1 m resolution. The longest time scale of the dissipative dynamics in the dSAP, associated with the gravest mode, is found to be approximately 5 years. The first mode of the EOF analysis (85%) represents constant heating over the entire depth, and the zero mode is close to the parabolic profile predicted by the heat equation for such forcing. It is shown that the temperature structure is governed by continuous warming at the sill depth and deep convection and gravity current events play less important roles. The simple model presented here allows evaluation of the response of the temperature in the dSAP to different forcings derived from climate change scenarios, as well as feedback on the dynamics in the Adriatic and the Mediterranean Sea.

How to cite: Wirth, A., Cardin, V., Khosravi, M., and Gačić, M.: South Adriatic Recipes: Estimating the Vertical Mixing in the Deep Pit, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12697, https://doi.org/10.5194/egusphere-egu21-12697, 2021.

In the recent years Adriatic Sea witnessed to different microbiological, termohaline with also the sea surface temperature changes interleaved with human impact, climate change and shifts in synoptical patterns. Adriatic Sea is under permanently modulated with Adriatic-Ionian Bimodal Oscillating System and North Atlantic Oscillation. This paper shows changes in termohaline properties in September, the period between Summer and Autumn. During summer months most cyclones that are appearing in the Adriatic basin and their tracks are classified as Genoa cyclones with a smaller number of Adriatic Cyclones. Autumn shows a different picture, with an equal number of Genoa, Adriatic, and non-Genoa and non-Adriatic cyclones. Large-scale air flow superimposed with Adriatic circulation have an impact during the transition from summer to autumn. The mix layer depth and termohaline conditions over Eastern Adriatic in the September in the period 2005 – 2020 are detected form a large database of CTD measurements. The data used in this study were collected during acoustic surveys conducted within framework of projects PELMON (2005-2012) and MEDIAS (2013-2020), carried out by Institute of Oceanography and Fisheries and supported by Croatia's Ministry of Agriculture. The CTD SBE25 probes used in the experiment were regularly calibrated and all measurements was quality controlled. In order to extract characteristic patterns from temperature and salinity vertical profiles and to connect them to wind and sea surface air pressure obtained from ERA5 reanalysis the unsupervised learning approach was utilized and the Neural gas algorithm was applied. The results show that the changes in mix layer depth are connected with interannual changes in cyclone path are connected with wind regime.

This work has been supported in part by Croatian Science Foundation under the project UIP-2019-04-1737 and project MAUD (grant number HRZZ-IP-2018-01-9849).

How to cite: Ćatipović, L., Udovičić, D., Džoić, T., Matić, F., Kalinić, H., Juretić, T., and Tičina, V.: Adriatic mix layer depth changes in September in the recent years, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2410, https://doi.org/10.5194/egusphere-egu21-2410, 2021.

Northern Adriatic Shelf (NAS) is a shallow, semi-enclosed northern part of the Adriatic basin, and as such rapidly responds to climate change. Multidecadal satellite and in-situ sea surface temperature (SST) time series on the NAS indicate a warming trend. During 1995-2015, SST in the Gulf of Trieste increased at a rate of 0.08°C ± 0.01°C per year (amounting to 1.6°C in 20 years), a trend indicative of the entire NAS shelf.

We use a centennial SST time series from Trieste (Raicich and Colucci, 2019) to construct a climatological year as a base for SST day-of-year anomaly estimation. We show that yearly number of discrete periods of extreme warming (Marine Heat Waves - MHW) and extreme cooling (Marine Cold Spells - MCS) exhibit clear seasonality. Both positive and negative anomalies from climatological SST manifest maximum variance in the summer months. The frequency of MHW has increased, while the number of Marine Cold Spells (MCS) is declining.

Sea warming and MHW intensification are potent agents of disturbance, particularly for sessile taxa and species residing near their warm range edges. In the NAS extreme events may force regression of habitat-forming species such as seagrass Zostera marina and increase bleaching episodes of coral Cladocora caespitosa. Warming events may be associated with the inflow of invasive non-indigenous species and expand the period of occurrence, such as harmful gelatinous invader Mnemiopsis leidyi. In contrast, a reduced number of MCS during winter may enhance survival of Aurelia polyps generating through strobilation more intense jellyfish blooms.

How to cite: Licer, M. and Malej, A.: Vulnerability of Northern Adriatic to Warming and Intensification of Marine Heat Waves, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1212, https://doi.org/10.5194/egusphere-egu21-1212, 2021.

In the framework of the European Project H2020 "ODYSSEA" (Operating a network of integrated observatory systems in the Mediterranean SEA, http://odysseaplatform.eu/) a forecasting modeling system of the coupled physical and biogeochemical conditions of the Northern Adriatic Sea is under development.

The modeling system consists of the on-line coupling of the European general circulation model - NEMO (Nucleus for European Modeling of the Ocean, https://www.nemo-ocean.eu/), with the marine biogeochemical model - BFM (Biogeochemical Flux Model, bfm-community.eu/).
The biogeochemical component of the model includes the simulation of the biogeochemical processes of both water column and sediments and their coupling. The model is run for the first time in the Northern Adriatic Sea with an explicit benthic-pelagic coupling.

The horizontal spatial discretization is defined by a rectangular grid of 315 × 278 cells, having a horizontal resolution of about 800 m. The vertical resolution is defined at 2 m, with 48 z-levels regularly spaced. Currently the atmospheric forcing are the ECMWF 6hr analysis atmospheric fields. The river supplies of fresh water and nutrient salts consider the daily runoff of the Po river, while the other rivers within the study area are included as climatological values. The open boundary conditions of the modeling system come from the Copernicus Marine Environment Monitoring Service (CMEMS, http://marine.copernicus.eu/).

In this work, the hindcast simulations encompassing the period 2000 – 2009 are validated against available observations from in situ and satellite platforms for sea surface temperature, chlorophyll-a and dissolved inorganic nutrients and, in order to evaluate the impact of a resolved benthic biogeochemical dynamics,  compared against simulations results obtained utilising a simple benthic closure parameterisation.

How to cite: Zavatarelli, M., Scroccaro, I., and Lovato, T.: Modeling the Environmental Dynamics of the Northern Adriatic Sea with an explicit benthic-pelagic coupling., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10691, https://doi.org/10.5194/egusphere-egu21-10691, 2021.

This study evaluates existing hypothesis according to which intensity of local winter primary production (may be high, influencing annual means), controlled by the degree of the spreading of Po River waters across the northern Adriatic (NAd), reflects on secondary annual production (microzooplankton and anchovy) of the ongoing year.

The analysis extends over a four-year period 2017-2020.

In 2017, in the open western NAd, close to the Po River delta, nutrients and phytoplankton abundances reached their yearly maximum in winter (February and March, respectively). By the end of winter, an anticyclonic gyre formed in the eastern part of the NAd, capturing waters advected from western NAd region. In the gyre area, microzooplankton abundance reached the yearly maximum in spring (June). A month later, at the same position, the abundance of the allochthonous Ctenophora Mnemiopsis leidyi that feeds on microzooplankton, along with the concentration of  Dissolved Organic matter and its Carbon (DOC) fraction, reached yearly peaks. In the western NAd, within another gyre (cyclonic), maxima in the microzooplankton abundances and DOC were recorded in spring. Results point to importance of winter conditions in yearly production cycle. In line with the existing hypothesis, phytoplankton abundance in winter 2017 was above the long-term average and coupled with extremely high zooplankton abundances and DOC concentrations in some of the following, spring or summer, months. Later, during summer, phytoplankton abundances were rather low.

In 2018 and 2019, the data collected in the NAd were rather scarce. In 2018 no winter data were available to test the hypothesis. In 2019, high abundances of microzooplankton was observed in March, and later in September an increase in M. leidyi, which might indicate that 2019 was again a year rich in organic production.

In 2020, the above average concentrations of nutrients and chlorophyll a in winter occurred along with very high concentrations of DOC and an abundance of M. leidyi in summer.

Data collected in 2017, 2019 and 2020 support the hypothesis, pointing to large organic outputs after winters rich in production.  Numerical models show that the NAd was mostly “separated” from the rest of the Adriatic Sea during 2017-2020 by a northern branch of a large cyclonic gyre with high salinity water (from central Adriatic and/or Kvarner Bay) entering the NAd along the eastern (Istrian) coast. Such circulation system could favour the Po River waters spreading across the NAd, inducing high primary production in winter, at the beginning of the yearly pelagic cycle, with the retention/accumulation of organic matter produced in the following months.

The NAd basin has been exposed to very high salinity water intrusions since 2015 (CMR data). These occurrences, together with the formations of specific circulation patterns described above, result from regional atmospheric and/or oceanographic processes which are not yet fully understood. However, using projections of temperature and salinity from a numerical approach, and following the observed biological relations, a prediction of the organic matter production in the NAd can be obtained.

This work has been supported in part by Croatian Science Foundation under the projects EcoRENA (IP-06-2016), MARRES (IP-2018-01-1717) and ADIOS (IP-2016-06-1955).

How to cite: Supić, N., Budiša, A., Ciglenečki, I., Čanković, M., Dautović, J., Djakovac, T., Dunić, N., Dutour-Sikirić, M., Ivančić, I., Kalac, M., Kraus, R., Kužat, N., Lučić, D., Marić Pfannkuchen, D., Mihanović, H., Njire, J., Paliaga, P., Pasarić, M., Pasarić, Z., Simonović, N., and Vilibić, I.: Hypothesis on impact of winter conditions on annual organic production in the northern Adriatic, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9040, https://doi.org/10.5194/egusphere-egu21-9040, 2021.

The Adriatic Sea is known to be under a high flooding risk due to both storm surges and meteorological tsunamis, with the latter defined as short-period sea-level oscillations alike to tsunamis but generated by atmospheric processes. In June 2017, a tide-gauge station with a 1-min sampling resolution has been installed at Stari Grad (middle Adriatic Sea), the well-known meteotsunami hot-spot, which is, also, often hit by storm surges. 

Three years of corresponding sea-level measurements were analyzed, and 10 strongest episodes of each of the following extreme types were extracted from the residual series: (1) positive long-period (T > 210 min) extremes; (2) negative long-period (T > 210 min) extremes; (3) short-period (T < 210) extremes. Long-period extremes were defined as situations during which sea level surpasses (is lower than) 99.7 (i.e. 2) percentile of sea level height, and short-period extremes as situations during which variance of short-period sea-level oscillations is higher than 99.4 percentile of total variance[J1]  of short-period series. A strong seasonal signal was detected for all extremes, with most of the positive long-period extremes appearing during November to February, and most of the negative long-period extremes during January to February. As for the short-period extremes, these appear evenly throughout the year, but strongest events seem to appear during May to July.

All events were associated to characteristic atmospheric situations, using both local measurements of the atmospheric variables, and ERA5 Reanalysis dataset. It was shown that positive low-pass extremes commonly appear during presence of low pressure over the Adriatic associated with strong SE winds (“sirocco”), and negative low-pass extremes are associated to the high atmospheric pressure over the area associated with either strong NE winds (“bora”), or no winds at all. On the other hand, high-pass sea level extremes are noticed during two distinct types of atmospheric situations corresponding to both “bad” (low pressure, strong SE wind) and “nice” (high pressure, no wind) weather.

It is particularly interesting that short-period extremes, of which strongest are meteotsunamis, are occasionally coincident with positive long-period extremes contributing with up to 50 percent to total sea level height – thus implying existence of a double danger phenomena (meteotsunami + storm surge). 

How to cite: Pervan, M. and Šepić, J.: Analysis of the eastern Adriatic sea-level extremes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5676, https://doi.org/10.5194/egusphere-egu21-5676, 2021.