Displays

The knowledge of Lagrangian motion is of a great importance due to their impact on the properties of transported material like the Essential Ocean Variables (phytoplankton, temperature, pCO2, etc), or other material like plastics debris, oil spill pollution, etc. In this study we analyze the influence of the wind and waves in the transport and mixing properties at the upper layers of the Mediterranean Sea. In this context, we propose a new approach for current velocity where we take into account the wind-wave interaction and the variability that it inserts into the current velocity through Ekman and Stokes components.

Surface currents, Ekman, Stokes, Lyapunov exponent

How to cite: Morales Márquez, V., Hernández Carrasco, I., Rossi, V., and Orfila, A.: Wind and wave effects on surface currents in the Mediterranean Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2607, https://doi.org/10.5194/egusphere-egu2020-2607, 2020.

The circulation in the Levantine Eastern Mediterranean basin is characterized by a complex system of sub-basin and mesoscale features. The most predominant and persistent eddy is an anticyclonic feature located south of Cyprus and identified as the Cyprus Eddy (CE). Previous studies based on in-situ data, satellite and model outputs confirm the presence of this warm core eddy centered around 33°E, 33.5°N. Although the center of the CE might be found slightly shifted to the west /east for different years of analysis, the anticyclonic eddy appears always above the Eratosthenes seamount whose peak lies at the depth of ~ 690 m and it rises ~ 2500 m above the surrounding seafloor. The presence of a cyclonic and anticyclonic eddy named South Shikmona (SSE) and North Shikmona (NSE) eddy, respectively has been also detected east of the CE and west of the Lebanese and Israeli coasts. Here, we present a hypothesis that attempts to explain the formation mechanism of the three eddies described above. Specifically, for an eastward stratified current on a b plane, the isolated seamount forces a Taylor column above it which can be identified as the CE. A standing wake downstream is also formed, and embedded eddies are associated with the SSE and NSE. These sub-basin features are probably part of a Rossby wave system. The analytical model of McCartney 1976 supports this hypothesis. Reanalysis and sea glider data collected during the CINEL project sponsored by the U.S. Office of Naval Research (ONR) are used to investigate McCartney’s solution. Preliminary results confirm the presence of a series of eddies above and downstream the sea mountain supporting therefore, the advanced hypothesis.

How to cite: Pirro, A., Gerin, R., Mauri, E., Hayes, D., and Poulain, P.-M.: The analytical model of McCartney applied in the eastern Levantine basin: formation of the Cyprus eddy and associated sub-basin and mesoscale features , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15463, https://doi.org/10.5194/egusphere-egu2020-15463, 2020.

A large anticyclonic eddy formed in April 2019 in the Algero-Provencal basin between Mallorca and Sardinia, and lasted until November 2019. While mesoscale activity is usually high in this part of the Mediterranean basin, the formation of such large (about 150 km in diameter) and long-lived eddies is not common. The eddy formed from a filament originated in the Algerian coast and was visible in multiple sources of satellite data, including sea surface temperature and ocean colour from Sentinel-3, until summer. Because of the warming of the surface layer, during summer months the eddy remained as a subsurface structure, evidenced by the sea level anomaly derived from altimetry data. A surface signal developed again in November, and the eddy finally dissipated in December 2019. According to CMEMS model data, in its strongest period the eddy reached about 300 m in depth, and during its sub-surface period the center was located at about 100 m depth. While at the surface the temperature signal was very clear, model data suggest the salinity anomaly was stronger than temperature, especially at depth. Such large and long-lived eddies have an impact in the basin currents, specifically in the transport of cold water from the northern to the southern part of the western Mediterranean basin, influencing the ecosystem there. The impact of the presence of this eddy, its long duration and the additional mesoscale and submesoscale activity that originated in its surroundings are investigated using a combination of remote sensing data, in situ data and model data.

How to cite: Alvera-Azcárate, A., Barth, A., Troupin, C., Beckers, J.-M., Evers-King, H., Pascual, A., Aguiar, E., and Tintoré, J.: Multiplatform analysis of a large anticyclonic eddy in the Algero-Provencal basin in 2019, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13744, https://doi.org/10.5194/egusphere-egu2020-13744, 2020.

The monitoring of the sea surface salinity (SSS) in the semi-enclosed seas has a significant impact in the study of the climate change. In those basins the oceanographic processes occur at higher temporal scales than in the open ocean, and therefore, trends and anomalies can be detected before. The Mediterranean Sea is a strongly evaporative basin (evaporation exceeds the precipitation and river run-off). Converserly, in the Black Sea the river run-off and precipitation exceeds the evaporation. Based on a 4-year time series (2015-2019) of SMAP SSS, a recent study has shown that there is an increase of the salinity in the Eastern Mediterranean [Grodsky, et al. 2019]. On the other hand, the Black Sea exhibits a rich variability in space and time from (sub)mesoscale to larger scales (interannual and larger)  that needs to be appropriately taken into account when trying to identify long-term trends.

We present new estimates of SSS trends in the Mediterranean and Black Seas. These estimations are based on 10-year series obtained from the European Soil Moisture and Ocean Salinity (SMOS) mission. Two new SMOS SSS regional products have been generated. On the one hand, we have generated a new realease of SMOS SSS regional product for the Mediterranean Sea. The new release of SMOS SSS regional product for the Mediterranean Sea provides better coverage in the Eastern Mediterranean than the previous version of this product (see [Olmedo et al 2018]). The new dedicated SMOS SSS product for the Black Sea has been developed under the currently on-going ESA EO4BIS contract (An Earth Observation Data for Science and Innovation in the Black Sea). The Black Sea and the Eastern Mediterranean are strongly affected by Radio Frequency Interferences (RFI) sources, which hamper the salinity retrieval. We have applied specific methodologies to diminish the strong RFI effects in these two basins [González-Gambau et al 2017].  The new realase of these two SMOS SSS regional products will be available soon in the Barcelona Expert Center website (http://bec.icm.csic.es ).

At this conference we will present the methodologies that we have used for the generation of both regional SMOS SSS products. We will also present a quality assessment over the two regions consisting of comparing with in situ salinity measurements. Finally, we will show the SSS trends that are obtained in the different basin (and sub-basins) as well as the significance of the results with respect to the accuracy of the new SMOS SSS products.

[Grodsky, et al. 2019] Grodsky S., et al. (2019), “Eastern Mediterranean salinification observed in satellite salinity from SMAP mission”, Journal of Marine Systems,  198
[Olmedo et al 2018] Olmedo, E, et al. , (2018) “Improving SMOS Sea Surface Salinity in the Western Mediterranean Sea through Multivariate and Multifractal Analysis,” Remote sensing,  10(3), 485.
[González-Gambau et al 2017] González-Gambau, V. et. al, (2017), "Improvements on calibration and image reconstruction of SMOS for salinity retrievals in coastal regions," in IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 10, 7, 3064-3078

How to cite: Olmedo, E., González-Gambau, V., Turiel, A., González-Haro, C., Martínez, J., Gabarró, C., Alvera-Azcárate, A., Grégoire, M., and Rio, M.-H.: Sea Surface Salinity trends in the Mediterranean and Black Seas from 10 years of SMOS measurements , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21636, https://doi.org/10.5194/egusphere-egu2020-21636, 2020.

The semi-enclosed nature of the Mediterranean Sea, together with its small inertia which is due to the relatively short residence time of its water masses, make it highly reactive to external forcings and anthropogenic pressure. In this context, several rapid changes have been observed in physical and biogeochemical processes in recent decades, partly masked by episodic events and high regional variability. To better understand the underlying processes driving the Mediterranean evolution and, anticipate changes, the measurement, and integration of many biogeochemical variables are mandatory.

The development of new BGC sensors implemented on in situ autonomous platforms allows to increase the acquisition of essential biogeochemical variables. However, the measurements carried out by in situ autonomous platforms (e.g. profiling floats, gliders, moorings) are not exhaustive.

Recently, deep learning techniques and in particular neural networks have been developed. The CANYON-MED (for Carbonate system and Nutrients concentration from hYdrological properties and Oxygen using a Neural-network in the MEDiterranean Sea) neural network-based method provides estimations of nutrients (i.e. nitrates, phosphates, and silicates) and carbonate system variables (i.e. total alkalinity, dissolved inorganic carbon, pH_T) from systematically measured oceanographic variables such as in situ measurements of pressure, temperature, salinity, and oxygen together with geolocation and date of sampling.

This regional approach, therefore, using quality-controlled in situ measurements from more than 35 cruises. CANYON-MED obtains satisfactory results: accuracies of 0.73, 0.045, and 0.70 µmol.kg^-1 for the nitrates, phosphates and silicates concentrations respectively, and 0.016, 11 µmol.kg^-1 and 10 µmol.kg^-1 for pH_T, total alkalinity and dissolved organic carbon respectively. CANYON-MED thus generates “virtual” data of parameters not yet measured by autonomous platforms, while ably reproducing the data already sampled, emphasizing its ability to fill the gaps in time-series.

Hence, by applying it to the large and growing network of autonomous platforms in the Mediterranean Sea, this method allows us to gain new insights into nutrients and carbonate system dynamics in targeted areas. In particular, in the northwestern Mediterranean Sea, the impact of deep convection on biogeochemistry (e.g., nutrient replenishment and pH_T variability) is highly variable over time and poorly covered by observing networks. In this case, CANYON-MED would improve our observations and understanding of the dynamic and coupled system.

How to cite: Fourrier, M., Coppola, L., and D'Ortenzio, F.: New insights into nutrients dynamics and the carbonate system using a neural network approach in the Mediterranean Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9520, https://doi.org/10.5194/egusphere-egu2020-9520, 2020.

   Runoff from rivers and coastal plains delivers significant amounts of nutrients to the Mediterranean Sea from the agricultural activities and urban waste waters. Several recent studies show that variations in rivers inputs may play a significant role on the marine biogeochemical cycles and planktonic food web in the entire basin. The aim of this study is to estimate the release of nutrients (N & P) to the Mediterranean Sea from basin-wide agriculture and urbanization through the implementation of the biogeochemical land-sea nutrient transfer processes within the agro-ecosystem model LPJmL. This is a contribution to the LaSeR-Med project (Towards an integrated prediction of Land & Sea Responses to global change in the Mediterranean Basin).

A compilation of a new input data set of fertilizer, manure and wastewater nutrients content [1961-2005] has been added to the LPJmL forcing data set, with a new land use patterns produced by an econometric model. The representation of the nutrient transfer from land to sea has been introduced into LPJmL by considering the following processes: mineralization, denitrification, adsorption, remineralization, nitrification, and phytoplankton dynamics.

First basin-wide LPJmL simulation at 1/12°, indicates that the model succeeds in simulating the temporal variations of water discharge for the main rivers flowing to the Mediterranean Sea, and shows a good consistency between the simulated nutrients concentration (NO3 and PO4) and available in-situ data. Preliminary results show that wastewater strongly contribute to the phosphorus fluxes (as PO4), while both agriculture and wastewater control the nitrogen fluxes (mainly as NO3). Alternative scenarios for land-use will allow to explore the future amounts of terrestrial nutrients that will reach the sea through rivers discharge and water runoffs and impact the marine ecosystems.

How to cite: Ayache, M., Bondeau, A., Pagès, R., and Baklouti, M.: A new estimation of water and nutrients (N & P) discharge to the Mediterranean Sea from the LPJmL model: modelling the dynamics of the land-sea nutrient transfer, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9138, https://doi.org/10.5194/egusphere-egu2020-9138, 2020.

Over the last decade, an intensification of extreme warm temperature events, termed as marine heatwaves (MHWs), has been reported in the Mediterranean Sea, itself a “Hot Spot” region for climate change. In the summer of 2003, a major MHW occurred in the Mediterranean with abnormal surface temperature anomalies of 2-3 Cº persisting for over a month. In 2015, an undocumented but more intense summer MHW affected almost the entire Mediterranean Sea with regional temperatures anomalies reaching 4-5 Cº. Here, we apply a MHW detection algorithm for long-lasting and large-scale summer events, on the hindcast output of a fully-coupled regional climate model (RCSM). We first examine the spatial variability and temporal evolution of both the 2003 and 2015 events. Then a basin-scale analysis of the mixed layer heat budget during each MHW is performed. The ocean and atmospheric components’ contribution is investigated separately during the onset, peak, and decay phases of both events, in order to disentangle the dominant physical processes behind each event. On the large-scale, our results indicate a key role of the wind forcing and the air-sea heat fluxes, while advection processes become more important at local scales. This study provides a comparison of the underlying mechanisms behind the two most intense MHW detected in the Mediterranean Sea during the last decade, constituting key information for the marine ecosystems of the region.

How to cite: Darmaraki, S., Somot, S., Waldman, R., Sevault, F., Nabat, P., and Oliver, E.: Mediterranean Marine heatwaves: On the comparison of the physical drivers behind the 2003 and 2015 events, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12104, https://doi.org/10.5194/egusphere-egu2020-12104, 2020.

Sapropels S5 and S7 formed in the semi-enclosed Eastern Mediterranean Sea  during peak interglacial periods MIS5e and MIS7a, respectively. This study investigates the dynamics of  water column redox change during their formation, through Fe isotope and Fe speciation studies of cores taken at 2550 m depth at site ODP-967 south of Cyprus. Both sapropels show an inverse correlation between δ⁵⁶Fe and Fe_T/Al, with slopes mostly matching that found for the Black Sea, pointing to a benthic shelf to basin shuttle of Fe and subsequent precipitation of Fe sulphides in highly euxinic bottom waters. An exception to these Black Sea-type trends occurs during the later, peak stages of S7, where the negative δ⁵⁶Fe - Fe_T/Al slope shallows. Fe speciation studies reveal that the dominant highly reactive Fe phase (Fe_HR) in the sapropels is pyrite, with Fe (oxyhydr)oxides forming the second major mineral component. Fe_HR/Fe_T plots show increased strengthening of anoxic water conditions during the transformation from pre-sapropel sediment into the sapropel. Nevertheless, despite the evidence for highly euxinic conditions from both Fe isotopes and high Mo concentrations in the sapropels, Fe_py/Fe_HR ratios remain below values commonly used to identify water column euxinia. This apparent contradiction is ascribed to the sedimentary preservation of a high flux of crystalline Fe (oxyhydr)oxide minerals to the basin, which resulted in a relatively low degree of sulphidation, despite the presence of euxinic bottom waters.  Thus, the operationally defined ferruginous/euxinic boundary for Eastern Mediterranean Sea sapropels is better placed at Fe_py/Fe_HR = 0.6, which is somewhat below the usually ascribed lower limit of 0.7. Consistent with the significant presence of crystalline Fe (oxyhydr)oxides, the change in the δ⁵⁶Fe - Fe_T/Al slope during peak S7 is ascribed to an enhanced monsoon-driven flux of detrital Fe(III) oxides from the River Nile into the Eastern Mediterranean basin. The euxinic water column conditions that developed in sapropels S5 and S7 are interpreted to reflect the positive balance between dissolved sulphide formation and rates of reductive dissolution of Fe (oxyhydr)oxide minerals. Both of these parameters in turn depend on the extent to which water overturn times are reduced during sapropel formation. Water overturn rate is therefore considered to define the strength of euxinic water column conditions during these periods of organic carbon-rich sedimentation.

How to cite: Matthews, A., Benkovitz, A., Teutsch, N., Poulton, S., Bar-Matthews, M., and Almogi-Labin, A.: Fe isotope and Fe speciation study of water column redox dynamics during Eastern Mediterranean sapropel events S5 and S7, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1864, https://doi.org/10.5194/egusphere-egu2020-1864, 2020.

Coastal ocean ecosystems are major contributor to the global biogeochemical cycles and biological productivity. Physical
factors induced by the turbulent flow play a crucial role in regulating marine ecosystem. However, while large scale dynamics
in the open ocean is well described by geostrophy, the role of small scale transport processes in coastal regions is still
poorly understood due to lack of continuous high-resolution observations. Here, the influence of small-scale coastal dynamics
on surface phytoplankton structuring is studied using Lagrangian metrics computed from HF Radar currents and satellite
chlorophyll-a (Chl). The combination of complementary Lagrangian diagnostics, including the accumulated divergence of the
flow along fluid trajectories, provides an improved description of the 3D flow geometry which facilitates the interpretation of two
non-exclusive physical mechanisms affecting phytoplankton patchiness. Attracting submesoscale fronts, unveiled by backwards
Lagrangian Coherent Structures, are associated to negative Lagrangian divergence where particles and Chl standing stocks
cluster. Filaments of positive Lagrangian divergence, representing large accumulated upward vertical velocities and suggesting
accrued injection of subsurface nutrients, match areas with large Chl concentrations. Our findings demonstrate that an accurate
description of small-scale transport processes is necessary to comprehend bio-physical interactions in coastal seas and to
estimate biological productivity.

How to cite: Hernández-Carrasco, I., Orfila, A., Rossi, V., and Garçon, V.: Small scale transport processes from HF-Radar, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6722, https://doi.org/10.5194/egusphere-egu2020-6722, 2020.

There are numerous health hazards arising from recreational exposures to microbiologically polluted marine environments. Microbial contaminants from catchment areas of coastal and submarine springs (due to leakages of private septic tanks and/or faults in sewage systems) could be a cause of microbial marine quality worsening after heavy rainfalls. Before testing this hypothesis groundwater dynamics should be known. Stable isotopes of water have been proven to be a very useful tool in karst hydrology and we used them as a mediator variable in predicting marine coastal water microbial contamination. 
We refer to the problem of the pollution from the position of environmental economics and economic institutional mechanism design, where such ecological problems are described as either stock or flow problems. Stock pollution is strongly dependent on the concentration potentials of the pollutant in the medium. Flow pollution depends on the speed of emission of the pollutant in the medium, as well as on the rate of its depletion by natural causes. On the example of fecal indicator bacteria Escherichia coli and enterococci propagating through karstic underground and finally ending in seawater we show how stable isotope composition of coastal springs’ water can be used to differentiate marine pollution into stock or flow. 
We tested the approach on two close coastal locations located at the Kvarner Bay (the Northern part of the Croatian part of the Adriatic Sea). Locations differ in terms of the open and closed sea as well as anthropogenic pressure. Groundwater and marine samples were collected during two consecutive bathing seasons (mid-May – mid-September). The Panel Data Pairwise Granger Causality test was used to test for statistical associations. Static Estimated General Least Squares (EGLS) and dynamic Generalised Method of Moments (GMM) statistical methods were used to distinguish between stock and flow pollution. 

This work was partially supported by the University of Rijeka as part of the research projects uniri-pr-prirod-19-24 and uniri-biomed-18-292.

How to cite: Mance, D., Mance, D., and Vukić Lušić, D.: Coastal groundwater stable isotope composition as predictor and measure of marine pollution , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7700, https://doi.org/10.5194/egusphere-egu2020-7700, 2020.

The Southern Adriatic (SA) is the deepest part of the Adriatic Sea (1242 m) and one of three sites of open-sea deep convection in the Mediterranean. Due to winter convection events, the dense water formation processes in the open SA result in a homogenization of the water column, which determines the nutrient input into the euphotic zone, enhances phytoplankton growth and consequently, the abundance of zooplankton.

By analyzing zooplankton samples, together with acoustic data (ADCP) and data from sediment traps (at 125 m and 1150 m) taken in the SA from November 2015 to June 2016, we investigated the relationship between the distribution of zooplankton abundance and the flow of organic carbon in the deep open southern Adriatic Sea. During the pre-convection period (November 2015), the highest organic carbon flux (C org flux) was found at both depth (125 m, 1150 m), which is probably related to the autumn phytoplankton bloom and consequently an increase in zooplankton abundance. During the winter mixing phase, a lower C org flux was recorded in the upper trap samples which was a consequence of the reduced growth of phytoplankton and the transport of the cells to the deeper aphotic layers; where some increase of org C flux in the lower trap was recorded. Thus, the deepest layers were enriched leading to a minimum vertical zooplankton-migration (DVM). In spring, during the post-convection period (March, April), high abundance of mesozooplankton, mostly copepods, was registered in the upper layer, as well as an evident increase of C org flux. Other species than copepods (which remain at the food rich surface), probably ostracods and euphausiids, played a significant role in the DVM because they are more abundant in the deeper layers. The increase in C org flux in the upper samples in May is in accordance with a recorded salp bloom (also evident through a strong backscatter signal). Salp fecal pellets were observed to contribute significantly to vertical carbon flux in various ocean regions.

The relationship between vertical zooplankton distribution, zooplankton migration and carbon export has generally been poorly studied in the Adriatic Sea. Preliminary results for the open SA are presented here, but for more accurate knowledge of this topic, a long term study is needed.

How to cite: Batistić, M., Garić, R., Miserocchi, S., Langone, L., Ursella, L., and Cardin, V.: On the relationship between the vertical distribution-migration of zooplankton and the organic carbon flux, before, during and after convective events, in the open southern Adriatic Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9066, https://doi.org/10.5194/egusphere-egu2020-9066, 2020.

The South Adriatic is one of the dense water formation site in the Mediterranean Sea. The variations of its thermohaline properties are relevant not only from an oceanographic and climatic point of view but also for the local impact on the vertical distribution of the biogeochemical parameters.

The South Adriatic Pit has been extensively sampled during the last forty years by traditional shipboard techniques. Float and glider measurements became part of the investigation only in the last ten years, providing a more detailed and more uniform spatio-temporal dataset. From the analysis, evidences of important changes of the South Adriatic Pit salinity vertical distribution emerge in the last 5 years. In the past, the Levantine Intermediate Water (LIW) entered the South Adriatic at a depth between 100 and 300 m, highlighted by a maximum in the salinity. The recent findings suggest that the LIW is no longer characterized by the highest salinity along the vertical profiles, which is present instead in shallower subsurface layers. In addition, in most of the seasons a thick low salinity layer is evident in the top 50-100 m. Among those changes, some peculiar haline characteristics occur in 2012 and 2017; they will be analyzed in concert with auxiliary data and model outputs.

How to cite: Mauri, E., Menna, M., Notarstefano, G., Gerin, R., Martellucci, R., and Poulain, P.-M.: Recent changes of the salinity distribution in the South Adriatic, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9874, https://doi.org/10.5194/egusphere-egu2020-9874, 2020.

Continuous measurements are essential to assess the interannual variability of the thermohaline circulation, water masses properties and transports, and biochemical contents. The need for high-frequency sampling to resolve events and rapid processes (on different time scale) and the long-sustained measurements of multiple interrelated variables from the sea surface to the seafloor is provided by Southern Adriatic Node. It is formed by the observatory E2M3A located in the area of the Southern Adriatic Pit (Eastern Mediterranean) at 41°32'N, 18°04'E together with a system of moorings positioned along the Bari Canyon (mooring BB lat. 41°20.49’N long. 17°11.64’E at 605 m depth; mooring FF lat 41°48.35’N long 17°02.29’E at 751 m depth) and the open-slope. The Canyon is generally assumed to play an important role in dense water sinking and sediment transfer to the deep Southern Adriatic basin.

The dense waters of North Adriatic origin flow southwards, mostly intermittently, along the Adriatic shelf and sink into the basin, both along the open slope and, more markedly, through the canyon of Bari. Thus, the basin due to its morphology, is considered as a reservoir that collects these waters together with those formed in-situ by open deep water formation (DWF) processes, exiting the Adriatic as the ADW that feeds the thermohaline circulation of the Eastern Mediterranean.

Signals of transport through the canyon to the deep pit layer are evident, in particular environmental conditions as for winter 2012, from the physical and biogeochemical data measured simultaneously at high frequency by the various system components (E2M3A and BB and FF moorings). From BB’s mooring data after this event until 2018 do not show us very significant events but are episodes of lower intensity that are not clearly identified in the E2M3A time series.

The intrusion of very dense waters of North Adriatic origin (cascading) evidenced at the E2M3A, occurred in late march 2014, January 2015 and winter 2016 is remarked from salinity homogenization at the 900 -1000 m depth. This has most likely contributed to enhance the lithogenic material fluxes at the bottom trap.  However, this intrusion has not been clearly detected by BB mooring but might have sunk across the open-slope.

How to cite: Langone, L., Brunetti, F., Conese, I., Giordano, P., Miserocchi, S., Siena, G., Ursella, L., and Cardin, V.: The South Adriatic observatory: towards a multidisciplinary seafloor and water column research infrastructure , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11665, https://doi.org/10.5194/egusphere-egu2020-11665, 2020.

The regionalization of the Mediterranean Sea has been the subject of many studies. It is a miniature ocean where most of the processes of the global ocean are encountered (Lejeusne et al., 2010). Several features of the Mediterranean (near-tropical ocean in summer with a well-formed thermocline, near-polar ocean in winter with deep convection, multiple basins with different characteristics) make it a hotspot of marine biodiversity (Coll and al., 2010) and consequently vulnerable to climate change. It is therefore important to characterize the present state of the Mediterranean Sea with robust estimators in order to study the long-term evolution of this mesocosm.

We present a partitioning of the Mediterranean Sea in regions having well defined characteristics with respect to Sea Surface Temperature and surface chlorophyll observed by satellite, and Argo mixed layer depth. This regionalization was performed by using an innovative classification based on neural networks, the so-called 2S-SOM. Its major advantage is to consider the specificity of the variables by adding automatically, through machine learning, specific weights to each of them, which facilitates the classification and consequently highlights the regional correlations. The 2S-SOM provided a well differentiated regionalization of the Mediterranean Sea waters into seven bioregions governed by specific physical and biogeochemical processes such as Intermediate-water formation in the Aegean Sea, large surface currents in the Adriatic and the Alboran, deep winter convection phenomena in the Balearic and stratification phenomena during summer in the eastern part of the Mediterranean Sea.

Besides, in order to highlight the phytoplankton diversity in these regions, we processed the satellite ocean color observations with a specific neural network approach (SOM-PFT, El Hourany et al., 2019). As a result, specific phytoplankton communities characterized by their seasonal variability are associated with the obtained Mediterranean bioregions; the dominance of the Nanophytoplankton groups is largely observed in the western basin during the period ranging from autumn to spring. While the dominance of different types of cyanobacteria Synechococcus and Prochlorococcus is highlighted in summer and more precisely in the waters of the eastern basin. Diatoms dominate throughout the year in the coastal and shallow regions, which can be explained by the presence of terrigenous input necessary for the development of this type of phytoplankton. Diatoms also largely benefit from the strong deep convection in the Balearic Sea marked by a large bloom at the end of winter convection in March.

This work will be further extended to study the phytoplankton diversity at global scale using various data set from the Tara Oceans.

How to cite: El Hourany, R., Bowler, C., Mejia, C., Crépon, M., and Thiria, S.: A neural-based bio-regionalization of the Mediterranean Sea using satellite and Argo-float records, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12004, https://doi.org/10.5194/egusphere-egu2020-12004, 2020.

The Mediterranean Sea is characterized by a combination of long-term trends and climatic shifts known in the literature as “transients”, that impact the biogeochemical processes.  We focus on the dissolved oxygen (DO) concentration, as it is an essential oceanic parameter for the marine ecosystem functioning. Dissolved oxygen distribution in the ocean interior is controlled by air-sea interaction processes, ocean circulation patterns, and biological effects. Understanding the related mechanisms and the variability of the above processes requires systematic oceanographic measurements over long periods and at high spatial resolution. Taking advantage of the Mediterranean monitoring systems, we can examine the sensitive physical and biogeochemical processes in the Mediterranean ecosystem. In this study, we investigate and combine all available data of temperature, salinity and dissolved oxygen over the period 1960-2011 (taking into consideration the scarcity of the available DO observations during the last years). In order to receive a direct and accurate evaluation of the interannual changes in the Mediterranean Sea, we constructed a gridded dataset interpolated into 1/8^ο x 1/8^ο grid using Data-Interpolating Variational Analysis (DIVA). At the surface layer, the solubility-driven changes determine the dissolved oxygen concentration. In deeper layers, the interannual variability is more related to dynamical processes that may involve dense-water convection, biological consumption or mixing, rather than temperature trends. The observed changes in minimum/maximum oxygen zones are mostly related to abrupt shifts. The attribution of the observed variability involves complex physical and biogeochemical processes as well as anthropogenic activities and requires further analysis using modeling techniques and available operational tools.

How to cite: Mavropoulou, A.-M., Vervatis, V., and Sofianos, S.: Basin scale dissolved oxygen interannual variability of the Mediterranean Sea: Analysis of long-term observations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15189, https://doi.org/10.5194/egusphere-egu2020-15189, 2020.

Climate change investigation, protection of marine ecosystems and mitigation of natural risks are the main research objectives of the Levante Canyon Mooring (LCM), a deep submarine multidisciplinary observatory, installed in September 2019 in the Eastern Ligurian Sea (Lat 44°05.443'N, Long 009°29.900'E at 608 m depth), inside the Pelagos Sanctuary. The observatory consists of a stand-alone station, with an instrumented mooring line ending with a submerged buoy. It operates in delayed-mode and is equipped with sensors that measure physical and biogeochemical parameters continuously and it is expected to provide data in the long-term. Temperature and salinity monitoring is carried out at three depth levels (about 80, 335 and 580 m depth), while turbidity is recorded at 580 m depth. LCM is also equipped with a sediment trap and two acoustic current profilers, able to measure direction and speed of currents in nearly the entire water column.

Data will be used to measure flux of sediments, nutrients and organic matter and to better understand the hydrodynamic and physical conditions of the Levante Canyon, which hosts valuable and vulnerable ecosystems, such as the deep-living cold-water corals, identified by IIM and ENEA in 2014, near the LCM mooring site. The LCM site is also located in an area where surface currents are monitored in near-real time by the CNR’s High Frequency Radar network, allowing data integration from multiplatform observations.

The project, co-financed by the Liguria Region, is coordinated by the DLTM in strict collaboration, in terms of human resources, infrastructures and instruments with the associated public research bodies (CNR, ENEA, INGV) and with the IIM. The project also includes the next deployment of a cabled station in the Gulf of La Spezia (10 m depth, less than 100 m far from the coast) that will monitor the gravimetric field, temperature and marine current. The main objective of the coastal station is to provide a test site for new instruments and sensors.

How to cite: Ciuffardi, T., Berta, M., Bordone, A., Borghini, M., Celentano, P., Cocchi, L., De Fabritiis, L., Delbono, I., Delfanti, R., Demarte, M., Ivaldi, R., Kokkini, Z., Locritani, M., Marini, D., Marini, S., Muccini, F., Pannacciulli, F., Peirano, A., Raiteri, G., and Vetrano, A.: A new multidisciplinary observatory in the Eastern Ligurian Sea (NW Mediterranean Sea): a combination of deep-sea and coastal measurements, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16533, https://doi.org/10.5194/egusphere-egu2020-16533, 2020.

An important deoxygenation trend has been described in the Black Sea over the five past decades from in-situ observations [1]. While the implications for basin-scale biogeochemistry and possible future trends of this dynamics are unclear, it is important to consolidate our means to resolve the dynamics of the Black Sea oxygen content in order to assess the likelihood of future evolution scenario, and the possible morphology of low-oxygen events. 

Also, it is known that current global models simulate only about half the observed oceanic O2 loss and fail in reproducing its vertical distribution[2]. In parts, unexplained O2 losses could be attributed to illy parameterized biogeochemical processes within 3D models used to integrate those multi-elemental dynamics.

Biogeochemical processes involved in O2 dynamics are structured vertically and well separated in the stratified Black Sea. O2 sources proceed from air-sea fluxes and photosynthesis in the
photic zone. Organic matter (OM) is respired over a depth determined by its composition and
sinking, via succeeding redox reactions. Those intricate dynamics leave unknowns as regards the biogeochemical impacts of future deoxygenation on associated cycles, for instance on the oceanic carbon pump. Here we use the Black Sea scene to derive model-observation strategies to best address the global deoxygenation concern.

First, we decipher components of the O2 dynamics in the open basin, and discuss the way in which O2-based indicators informs on the relative importance of processes involved. Using 1D biogeochemical model set-up, we then conduct a sensitivity analysis to pin-point model parameters, ie. biogeochemical processes, that bears the largest part in the uncertainty of simulated results for those diagnostics. Finally, we identify among the most impacting parameters the ones that can most efficiently be constrained on the basis of modern observational infrastructure, and Bio-Argo in particular. 

The whole procedure aims at orienting the development of observations networks and data assimilation approaches in order to consolidate our means to anticipate the marine deoxygenation challenge. 

[1] Capet A et al., 2016, Biogeoscience, 13:1287-1297
[2] Oschlies A et al., 2018, Nature Geosci, 11(7):467–473

How to cite: Capet, A., Luc, V., and Marilaure, G.: Biogeochemical controls on the Black Sea oxygen dynamics : relevant diagnostics, key processes and adequacy of the monitoring infrastructure., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17933, https://doi.org/10.5194/egusphere-egu2020-17933, 2020.

Oceans contribute to the removal of 25%-30% of the atmospheric anthropogenic CO₂, which increase sea water CO₂ concentration and acidity, and decrease the Aragonite saturation state that may cause problems for calcium carbonate skeletons of marine species. The Mediterranean Sea is a specific environment with a higher alkalinity and a fast ventilation that is in favor of a more important uptake of  anthropogenic CO2 relatively to global ocean, and an acidification process impacting the whole water. The future acidification of the Mediterranean Sea has not been investigated by regional model yet.

In this study, we used an eddy-permitting regional model of the Mediterranean Sea (NEMO_MED8) coupled to an oceanic biogeochemical model (PISCES) to evaluate how climate and anthropogenic CO₂ changes will modify the acidification and its annual cycle from the 1850 period to the end of the 21^st century according to the future IPCC SRES-A2.  Evolution of boundary conditions from Rivers and exchange at the Gibraltar strait are considered. We analyse the relative influence of temperature, salinity, DIC and alkalinity on the mean and the seasonal amplitude of acidity (H+) and aragonite saturation sate (Ω_A) and their evolution following a changing climate scenario SRES-A2.

How to cite: Dutay, J.-C., orr, J., le-vu, B., palmieri, J., richon, C., and somot, S.: Acidification in the Mediterranean Sea following a transient climate change scenario simulated with a high-resolution regional model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18508, https://doi.org/10.5194/egusphere-egu2020-18508, 2020.

Dissolved oxygen dynamics in the south Adriatic pit have been investigated between 2015 and 2019 through in situ measurements and numerical models. This area is characterized by a frequent occurrence of deep water convection phenomena during winter time. Such convection phenomena represent the main source of dense waters for the Eastern Mediterranean basin modulating the oxygen advection in the deep water.

In situ glider measurements in the south Adriatic pit were performed by the OGS Glider Team since 2013. Typically, these missions covered the transect from Bari to Dubrovnik. The glider missions aim to investigate the water masses before, during and after the convection period. Pre-convection missions were carried out between the end of November and the beginning of December. Convection missions were performed between the end of January and the beginning of May.

Over 3000 profiles from the surface to 950m depth were collected and used to better understand the physical and biogeochemical highly variable processes in the southern Adriatic pit.

During the pre-convection period the water column is generally stratified; recorded data show an inverse correlation between dissolved oxygen and salinity. The pre-convection periods in 2015 and 2016 present the highest variability; the water column is mainly characterized by vertical profiles with a double oxygen minimum, which corresponds to the highest salinity concentrations. During the 2017 pre-convex mission the water column is characterized by a vertical salinity gradient, whereas dissolved oxygen profiles show a double dissolved oxygen maximum both on the surface and at 300-400 m depth. The 2018 pre-convex mission shows a thin surface layer of low salinity and high dissolved oxygen, which extends from the surface down to 50 m depth. A nucleus of high salinity and low oxygen is present close to the Italian coast at about 80-200m depth.

The 2016 convex mission revealed an inverse correlation of oxygen and salinity profiles and a double oxygen minimum with slightly different characteristics with respect to the previous pre convection period. During 2018 and 2019 the missions occurred during the convection phenomenon. The water column is well mixed from the surface down to 600 m depth, suggesting the occurrence of deep winter convection, also confirmed by the increase in oxygen and salinity concentrations along the water column.

In order to fully understand the process development in the south Adriatic Pit, which are the combinatorial result of coastal and open ocean processes, we integrated our observations with numerical model outputs provided by the Copernicus Marine Environment Monitoring Services. As the sea glider allows us to observe a high degree of variability from mesoscale to sub-mesoscale, the model output was used to evaluate mesoscale and sub basin scale phenomena.

Such an integration of different datasets provide information at different temporal and spatial scales of water mass dynamics, thus underlying the fundamental role of integrating multi-platform contributions to gain knowledge of the ocean processes.

How to cite: Martellucci, R., Mauri, E., Gerin, R., Notarstefano, G., and Cossarini, G.: Deep winter ventilation dynamics in the south Adriatic convection area from in situ glider observations and model output, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19256, https://doi.org/10.5194/egusphere-egu2020-19256, 2020.

The Mediterranean Sea is considered a hot spot of the global warming since it is changing faster than the global ocean, with a strong impact on the marine environment. Recent studies agree on the increase of the sea level, of the Sea Surface Temperature (SST), and of the Sea Surface Salinity (SSS) in the Mediterranean Sea over the last two decade, but no one has yet come to interconnect these and other parameters that contribute to the regulatory effect of the sea on the climate.

In this study, interannual variability and decadal climatic trends in the upper-layer of the Mediterranean Sea are estimated in the last 26 years using in-situ data (Argo float), satellite (altimetry, SST, wind vorticity, freshwater fluxes, mixed layer depth) and model (SSS) products.

Spatio-temporal variability is studied performing the Empirical Orthogonal Function analysis on the gridded, monthly, de-seasonalized maps of all satellite and model data. The contribution of the western, central and eastern regions of the Mediterranean Sea to the total trends is assessed. SSS distribution and trends derived from model reanalysis are compared with those derived from Argo float data in the upper layer.

Possible relationships between the trends in different datasets are delineated and described, i.e. the connection between the sea level rise and the SST, between the freshwater fluxes and the SSS, between the SSS and the ocean dynamics, including Ekman and geostrophic transports as well as vertical entrainment.

How to cite: Menna, M., Notarstefano, G., Mauri, E., Gačić, M., Civitarese, G., Gerin, R., and Poulain, P.-M.: Trends and interconnections of physical parameters in the upper layer of the Mediterranean Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20514, https://doi.org/10.5194/egusphere-egu2020-20514, 2020.

We present an analysis of specific water masses fluxes in the Western Mediterranean Sea issued from a twenty years (1992-2013) reanalysis (MEDRYS1V2). Water masses are identified on the base of salinity and potential density properties and computes; the fractions of each water mass involved in total flux are computed under the hypothesis assumptions of mixing lines schemes. It was first designed in order to avoid rough truncations between water masses on the T-S diagram when using fixed thermo-haline properties thresholds. The method does not use the temperature marker due to its high seasonal variability in near surface waters (0-200 m) and we consider that potential density is a better marker to discriminate deep and intermediate water masses. The algorithm discriminates successively five different water masses : the Atlantic Water (AW) incoming from the Gibraltar strait (salinity between 36,1 and 38,45 PSU), the Levantine Intermediate Waters (LIW) incoming from the Tunisia-Sicily strait (salinity between 38,45 and 39.1 PSU), the Modified Atlantic Waters (MAW) defined as near-surface waters (potential density less than 28,9 kg m-3) that are neither AW or LIW, while Western Intermediate Waters (WIW) are those remaining until the σθ = 29,10 kg m-3 threshold for Western Mediterranean Deep Waters (WMDW) is reached. Such computed fractions of each water mass, whose sum is constrained to unity, are then used to compute their water masses transports all along over twenty years of the reanalysis. The transport are assessed across computed on key transects delimiting known sub-basin entities (Ligurian Sea, Gulf of Lion, Balearic Sea...), with total transports showing balanced mass budget. The such computed total transport reveal marked differences in their seasonal to interannual variability, while the analysis of the water mass transports allows to identify those which mainly implied induced these variability. The results first show a low seasonal and no significant interannual variability at the exit of the Alboran Sea that results from the balance between the eastward AW/MAW outflow and the westward WIW and WMDW inflows. The Corsican strait, the Ligurian Sea line and Tunisia-Sardinia straits show a marked seasonal variability (0,37-0,39 Sv) mainly driven by the AW/MAW. By contrast, a strong interannual variability dominates the seasonal one (-2 to 1 Sv) between the Algerian Basin and the northern basin, correlated to the WMDW formation. The analysis of each specific water masses transport pointed out that shows this marked variability to be first driven by the intermediate and deep water masses transports. Similarly the interannual variability of the AW and MAW transports in the central part of the Western Mediterranean suggests some coupling between the deep, intermediate and surface water masses, even through the shallower Balearic Sea.

How to cite: Barral, Q.-B., Zakardjian, B., Dumas, F., Garreau, P., and Beuvier, J.: Analysis of specific water masses transports in the Western Mediterranean in the MEDRYS1V2 twenty-one-year reanalysis., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21979, https://doi.org/10.5194/egusphere-egu2020-21979, 2020.

Mesoscale to sub-mesoscale surface dynamics in the ocean is a key parameter, driving, for instance, the dispersion of pollutants emanating from heavily populated coastal areas for example. Estimating the surface velocity can be challenging especially when data is sparse. In [1], the authors developed a near real-time 3D-Var assimilation algorithm that blends in-situ Lagrangian drifters’ positions with altimetry data to improve the estimation of the surface velocity in the Eastern Levantine Mediterranean. The algorithm was tested near the Lebanese coast and in the case of an eddy between Lebanon and Cyprus. The objective of this work is to further validate the algorithm.

First, a Comparison with Ocean color satellite images shows that eddies’ shapes and location are more consistent after the assimilation of drifter data.Independent in-situ current-meter data provided from the EGYPT campaign are also used to validate the results of the algorithm in terms of velocity intensity and direction. The comparison shows an improvement of the estimated velocity, particularly in terms of direction.

We also address the question of extending the algorithm to a larger regional scale in the Eastern Levantine Mediterranean, which is subject to a high mesoscale activity but which is less densely observed than the western part.

[1] L. Issa, J. Brajard, M. Fakhri, D. Hayes, L. Mortier, P-M. Poulain. Modelling Surface Currents in the Eastern Levantine Mediterranean Using Surface Drifters and Satellite Altimetry. Ocean Modelling, May 2016. Doi: 10.1016/j.ocemod.2016.05.006

How to cite: Baaklini, G., Issa, L., Brajard, J., Fakhri, M., Menna, M., Taupier-Letage, I., and Mortier, L.: Mesoscale Activity in the Eastern Mediterranean: Blending Altimetry with in situ observations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20407, https://doi.org/10.5194/egusphere-egu2020-20407, 2020.

The action of propellers induced jets on the seabed of ports and harbors might be responsible of erosion and deposition of sediment around the port basin, potentially inducing important variations of the bottom topography in the medium to long time scales. Such dynamics constantly repeated for long periods can result in drastic reduction of ships’ clearance - in the case of deposition - or might be a threat for the stability and duration of the structures - in the case of erosion in the close vicinity of births and decks. These sediment processes are sources of problems for the port managing authorities, both for the safety of navigation and for the optimization of the management and maintenance of the ports’ bottom.

In the present work we study by means of integrated numerical modeling the erosion and sediment transport induced by naval traffic in the passenger Port of Genoa (Italy) and we propose a novel delayed-mode methodology and new science-based tools useful to optimize and efficiently plan the maintenance of the port sea bed. Fully operational real-time tools can be further developed starting from the proposed methodology in order to monitor the dynamics of the sediment on a daily basis.

How to cite: Guarnieri, A., Saremi, S., Jensen, J. H., Pedroncini, A., Vaccari, M., and Vincenzi, C.: Modelling sediment resuspension and transport induced by ships propellers in ports – the study case of the Port of Genoa, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4766, https://doi.org/10.5194/egusphere-egu2020-4766, 2020.

Seawater Rare Earth Element (REE) concentrations and Nd isotopic composition (ε_Nd) are increasingly applied as valuable tracers of oceanographic processes such as water mass mixing and lithogenic inputs to seawater. However, their measurements are basically lacking in the Mediterranean Sea water column. This study analyzes 9 seawater stations around the central Mediterranean Sea to clarify the relative importance of external sources, vertical (biogeochemical) processes and lateral water mass transport in controlling REE and ε_Nd distributions. Concentrations of REE do not show nutrient-like profiles with depth, likely indicative of relatively young waters with limited accumulation of remineralized REE. Light REE (LREE) present a non-conservative behavior, which largely peak at surface waters and rapidly decrease with depth. The negative correlation of surface LREE enrichment with offshore distance highlights the influence of continental input from the western Italian coast to the Tyrrhenian surface waters. In contrast to other regions with reported boundary exchange, this process does not modify the ε_Nd values here. On the other side, distributions of dissolved heavy REE (HREE) and ε_Nd display a conservative behavior that can be explained by mixing of western- (MAW and WMDW) and eastern- (LIW and EMDW) originated waters. We test this hypothesis with an Optimum Multi-Parameter Analysis (OMPA) including HREE and ε_Nd parameters. Even though the limited data set, consistent results of water mass fractions are obtained for the four main water masses although with some particularities. While LIW take on major importance when considering HREE in the model, EMDW fractions are preferentially detected with ε_Nd. This latter finding implies a noticeable deep water flux across the Sicily Strait into the Western Mediterranean that was not clearly evidenced before.

How to cite: Garcia-Solsona, E., Pena, L. D., Paredes, E., Pérez-Asensio, J. N., Quirós-Collazos, L., Lirer, F., and Cacho, I.: Rare Earth Elements and Nd isotopes as tracers of modern ocean circulation in the central Mediterranean Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5284, https://doi.org/10.5194/egusphere-egu2020-5284, 2020.

We here discuss the remarkable uplift of the Eastern Mediterranean bottom waters that flow westward, over the Malta Escarpment, and cross the sill of the Channel of Sicily (Astarldi et al., 2001; Iudicone et al., 2003; Falcini & Salusti 2015); a dynamics that is rather similar to the one occurring at the Strait of Gibraltar (Mediterranean Sea) and Bab el Mandab (Red Sea) (Siddall et al., 2002). This classical uplift, which usually occurs under a three layer system dynamics, is mostly explained by the Bernoulli suction effect (Lane-Serff et al., 2000). However, the real filed analyses suggest that this dynamics are significantly perturbed by tidal effects and or large scale storms (Smeed et al., 2004). Here consider a novel, theoretical approach to obtain a rather realistic view of natural perturbations that affect these deep flow dynamics. Our insights on uplift processes, in addition, give a contribution to the general understanding of the Mediterranean Sea deep water circulation and, on climatological grounds, heat storage dynamics. We finally remark that similar phenomena happens in several marine straits and/or in semi-enclosed, peripheral basins of particular importance for local and large-scale processes.

References

Astraldi, M., Gasparini, G. P., Gervasio, L., & Salusti, E. (2001). Dense water dynamics along the Strait of Sicily (Mediterranean Sea). Journal of Physical Oceanography, 31(12), 3457-3475.

Falcini, F., & Salusti, E. (2015). Friction and mixing effects on potential vorticity for bottom current crossing a marine strait: an application to the Sicily Channel (central Mediterranean Sea). Ocean Science, 11(3), 391-403.

Iudicone, D., Buongiorno Nardelli, B., Santoleri, R., & Marullo, S. (2003). Distribution and mixing of intermediate water masses in the Channel of Sicily (Mediterranean Sea). Journal of Geophysical Research: Oceans, 108(C9).

Lane-Serff, G. F., Smeed, D. A., & Postlethwaite, C. R. (2000). Multi-layer hydraulic exchange flows. Journal of Fluid Mechanics, 416, 269-296.

Siddall, M., Smeed, D. A., Matthiesen, S., & Rohling, E. J. (2002). Modelling the seasonal cycle of the exchange flow in Bab el Mandab (Red Sea). Deep Sea Research Part I: Oceanographic Research Papers, 49(9), 1551-1569.

Smeed, D. A. (2004). Exchange through the Bab el Mandab. Deep Sea Research Part II: Topical Studies in Oceanography, 51(4-5), 455-474.

How to cite: Falcini, F., Di Paolantonio, M., and Salusti, E.: New insights on bottom water flows crossing a marine sill under periodic or impulsive perturbations: an application to the Sicily Channel sill (Central Mediterranean Sea), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6046, https://doi.org/10.5194/egusphere-egu2020-6046, 2020.

The variability of surface dynamics has been investigated extensively in the Mediterranean Sea for different temporal and spatial coverage, whereas a specific evaluation for the area of the Tyrrhenian Sea does not exist. Thus, this study is focused on the Tyrrhenian basin, a subbasin of the western Mediterranean, which is considered sensitive to climatic variations due to its small size and isolated nature. The main scope is to provide a comprehensive and up-to-date assessment of the sea surface warming, the sea level changes and the general surface circulation in the Tyrrhenian Sea, as well as to improve the understanding of the relation to large-scale teleconnection patterns and to regional air-sea interaction. The long-term spatio-temporal variability and trends were investigated using satellite-derived, in-situ and reanalysis-based datasets up to the end of 2018. Further, the possible linkage with the occurrence of extreme weather events was assessed using observations from the European Severe Weather Database. The different datasets cover multiple temporal and spatial scales and enable the investigation of the potential physical processes related to the non-homogeneous, time-depended spatial variability. The results indicate a significant increase in sea level and sea surface temperature which appears to be linked with the North Atlantic Oscillation (NAO) and the Atlantic Multidecadal Oscillation (AMO), respectively. Moreover, analysis of the basin’s surface circulation together with local air-sea exchanges of heat, freshwater and momentum indicated a significant influence of the wind-driven Ekman pumping variability.

How to cite: Zambianchi, E., Krauzig, N., and Falco, P.: Long-term assessment of surface dynamics in the Tyrrhenian Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7459, https://doi.org/10.5194/egusphere-egu2020-7459, 2020.

The Gulf of Trieste (GoT) is shared by Italy, Slovenia and Croatia, with most of its coasts belonging to Italy and Slovenia, along with the two main harbours; the Harbour of Trieste (Italy) and Koper (Slovenia). Both are subject to heavy marine traffic and exposed to different threats including oil spills, maritime accidents and SAR operations. The GOT High frequency radar network provides near-real time data of sea surface currents and waves since 2016. In this work we provide a statistical description of surface variability in terms of Lagrangian descriptors in order to elucidate the transport and retention in the GoT as well as to provide the seasonal evolution of the residence time. Among the most widely used Lagrangian techniques, we focus the study on Lagrangian Coherent Structures and Path-integrated topological variables like Lagrangian divergence and Lagrangian vorticity.

How to cite: Reyes-Suarez, N. C., Hernandez-Carrasco, I., Licer, M., Cardin, V., Gacic, M., and Orfila, A.: Lagrangian dynamics in the Gulf of Trieste from high resolution HF-Radar, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11179, https://doi.org/10.5194/egusphere-egu2020-11179, 2020.

Thermaikos Gulf, located in the Northwestern Aegean Sea (Greece), is a marine ecosystem of major importance, not only environmentally (as an area of the deep water formation with contribution to the renewal of the North Aegean deep waters), but also due to the various socioeconomic activities associated with the area. Observational and simulated data are used to investigate the evolution of eutrophication events during the last two years in order to evaluate the current (2017-2019) quality state of the seawater in the Gulf. The quality of the marine environment of Thermaikos Gulf was appraised by measuring physical, chemical and biological parameters. Specific physical-chemical characteristics (temperature, salinity, density along with pH and dissolved oxygen) and biological parameters (chl-a and phytoplankton biomass) throughout the water column were evaluated by conducting in situ measurements during the sampling campaigns. Current fields, derived from a high-resolution 3-D ocean model, together with ADCP measurements, are used to describe the major circulation patterns, the river plume dynamics and the renewal pathways of the Gulf. The obtained results are discussed with regards to seasonal and spatial variability, and the water column stratification. Satellite ocean color data were also used to discuss the in-situ findings and confirm “Dirty” Sea and Red Tide phenomena, that were detected and analyzed based on the physical dynamics and especially the renewal patterns of the Gulf. Moreover, we compare these recent findings to respective observations from a previous period (1997 to 2007) to evaluate potential changes in the quality state of the Gulf with respect to meteorological and river discharge conditions.     

How to cite: Krestenitis, Y. N., Kolovoyiannis, V., Androulidakis, Y., Makris, C., and Baltikas, V.: Circulation patterns and eutrophication phenomena in the Thermaikos Gulf , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11775, https://doi.org/10.5194/egusphere-egu2020-11775, 2020.

The Mediterranean Sea (MS) is a semi-enclosed sea characterized by a zonal west-east gradient of oligotrophy, where microbial growth is controlled by phosphate availability in most situations. External inputs of nutrients including Gibraltar inputs, river inputs and atmospheric deposition are therefore of major importance for the biogeochemistry of the MS. The latter has long been considered to be driven mainly by nutrient exchanges at Gibraltar. However, recent studies indicate that river inputs significantly affect nutrients concentrations in the Mediterranean Sea, although their resulting impact on its biogeochemistry remains poorly understood. In this study, our aim was to help fill this knowledge gap by addressing the large-scale and long-term impact of variations in river inputs on the biogeochemistry of the Mediterranean Sea over the last decades, using a coupled physical- biogeochemical 3D model (NEMO-MED12/Eco3M-Med). As a first result, it has been shown by the model that the strong diminution (60%) of phosphate (PO4) in river inputs into the Mediterranean Sea since the end of the 1980s induced a significant lowering of PO4 availability in the sub-surface layer of the Eastern Mediterranean Basin (EMB). One of the main consequences of PO4 diminution is the rise, never previously documented, of dissolved organic carbon (DOC) concentrations in the surface layer (by 20% on average over the EMB). Another main result concerns the gradual deepening of the top of the phosphacline during the period studied, thus generating a shift between the top of the nitracline and the top of the phosphacline in the EMB. This shift has already been observed in situ and documented in literature, but we propose here a new explanation for its occurrence in the EMB. The last main result is the evidence of the decline in abundance and the reduction of size of copepods calculated by the model over the years 1985–2010, that could partially explain the reduction in size of anchovy and sardine recently recorded in the MS. In this study, it is shown for the first time that the variations in river inputs that occurred in the last decades may have significantly altered the biogeochemical cycles of two key elements (P and C), in particular in the EMB.

How to cite: Pagès, R., Baklouti, M., Barrier, N., Richon, C., Dutay, J.-C., Ayache, M., and Moutin, T.: ​Impact of changes in rivers inputs during the last decades on the biogeochemistry of the eastern Mediterranean basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13494, https://doi.org/10.5194/egusphere-egu2020-13494, 2020.

In this work we present the results obtained through a dynamic downscaling of the ERA5 reanalysis dataset (hindcast) of ECMWF, using high-resolution meteorological and wave models defined on unstructured computation grids along the Mediterranean coasts, with a particular focus on the North-Western Mediterranean area. Downscaling of the ERA5 meteorological data is obtained through the BOLAM and MOLOCH models (up to a resolution of 2.5 km) which force an unstructured WW3 model with a resolution of up to 500 m along the coast. Models were validated through available meteorological stations, wave buoy data and X-band wave radars, the latter for the purposes of wave spectra validation.

On the one hand, this allowed, by extracting the time series of some attack parameters of the waves along the coast, and according to the type of coast (rocky coasts, sandy coasts, coastal structures etc.), to compute the return periods and to characterize the impact of any individual storm. On the other hand, it is possible to highlight some trends observed in the last 30 years, during which recent research is showing an increasing evidence  of some changes in global circulation at regional to local scales. These changes also include effects of wind rotation, wave regimes, storm surges, wave-induced coastal currents and coastal morphodynamics. For example, in the North-Western Mediterranean extreme events belonging to cyclonic weather-types circulation with stronger S-SE components (like the storm of October 28-30th 2018 and many others), rather than events associated with perturbations of Atlantic origin and zonal circulation, are becoming more frequent. These long-term wind/wave climate trends can have consequences not only in the assessment of long-term risk due to main morphodynamic variations (ie. coastal erosion), but also in the short-term risk assessment.

This work was funded by the EU MAREGOT project (2017-2020) and ECMWF Special Project spitbran  “Evaluation of coastal climate trends in the Mediterranean area by means of high-resolution and multi-model downscaling of ERA5 reanalysis” (2018-2020).

How to cite: Brandini, C., Taddei, S., Vannucchi, V., Bendoni, M., Doronzo, B., Iannuccilli, M., Messeri, G., Pasi, F., and Capecchi, V.: Coastal climatology of the North-Western Mediterranean area for long-term and short-term risk assessment., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19382, https://doi.org/10.5194/egusphere-egu2020-19382, 2020.

High precision measurements of natural uranium isotopes in the Atlantic Ocean, Mediterranean Sea,
and Black Sea reveal isotopic makeups which differ significantly from the well-known oceanic
composition. In the Mediterranean, water masses are strongly differentiated to the extent that they
are able to be fingerprinted on the basis of δ²³⁴U. Mediterranean deep water masses show the
highest enrichment, with an offset with respect to oceanic δ²³⁴U values of just over 1 ‰. The Black
Sea shows an even higher offset of up to ~40 ‰.
This offset provides an opportunity to look into the as of yet largely unstudied uranium inputs to the
Mediterranean, in particular rivers and submarine groundwater discharge (SGD), which are thought
to play key roles in uranium input to the global ocean. A simple box model, incorporating the
Mediterranean and Black Sea data from this study is constructed to provide a first estimate of the U
concentration and δ²³⁴U signature of rivers and SGD necessary for this offset to arise. These
estimates are then compared with new measurements of various coastal and submarine springs from
along the French Mediterranean Coast as well as with existing riverine data exists to speculate on
which inputs may be most responsible for this offset.

How to cite: Border, E., Frank, N., van Beek, P., Henderson, G., and Tamborski, J.: Offsets and inputs of natural uranium isotopes in the Mediterranean Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20226, https://doi.org/10.5194/egusphere-egu2020-20226, 2020.