OS2.4

The Levantine basin is the area of formation of the Levantine Intermediate Water. In this study, a 3D hydrodynamic-biogeochemical model (Symphonie/Eco3MS) was used to gain understanding in the dynamics of dissolved oxygen in the Levantine basin and estimate its annual budget and its interannual variability over the period of 2012-2020. Comparisons of model results with compiled in situ data from cruises and Argo floats showed that the model was able to reproduce well the seasonal variability of the dissolved oxygen. They also show that during winter, surface temperature decreased, generating  oxygen  undersaturation in the Levantine basin that absorbed atmospheric oxygen. From March to September, due to the increase of surface temperature the basin became oversaturated and released oxygen into the atmosphere. The estimate of the annual oxygen budget revealed that the Levantine basin acted as a sink of atmospheric oxygen. Gain of oxygen in the upper layer through air-sea exchanges and biogeochemical processes were counterbalanced by the loss of oxygen through physical processes via downward export into  intermediate depths and lateral transport towards the western regions. At the annual scale, the air-sea oxygen exchange term dominated the biogeochemical process term in the budget. Regarding the spatial distribution, maximum annual atmospheric oxygen uptake and biogeochemical fluxes were found in the Levantine Intermediate Water formation area of the Rhodes gyre where oxygen-poor and nutrient-rich waters were supplied in the upper layer and surface temperature was minimum. The current study revealed high interannual variability with large oxygen uptakes and physical exports during winters marked by intense heat losses.

How to cite: Habib, J., Ulses, C., Estournel, C., Marsaleix, P., Coppola, L., and Fakhri, M.: Dissolved oxygen budget in the eastern Mediterranean over the period of 2012 - 2020 using a 3D physical-biogeochemical model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-505, https://doi.org/10.5194/egusphere-egu22-505, 2022.

The Mediterranean is connected to the Black Sea through the Turkish Straits, and to the Atlantic Ocean through the Strait of Gibraltar. The hydrological cycle of the Mediterranean-Black Sea system is driven by fresh water exchanges between the atmosphere, continents and oceans, and by salty water mass exchange among the ocean basins. In this study, we estimate the water-mass fluxes through these straits as  residuals in the water balance equation. To do so, the freshwater fluxes are estimated from the time-variable gravity fields inferred from the Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On satellites, and precipitation and evaporation data from ERA5 atmospheric reanalysis products. This study covers the 18 years period from 2002 to 2020. In the Black Sea, rivers introduce an average water volume of 391 ± 12 km³/year, one third of which escape through the atmosphere and two thirds go to the Mediterranean Sea. In the latter, 1787 ± 23 km³/year are lost via net evaporation. The rivers runoff (502 ± 27 km³/year), and the inflow of Atlantic waters (1020 ± 56 km³/year; 0.0323 ± 0.0018 Sv), finally restore the Mediterranean water budget. The balance is not reached instantaneously, and this delay introduces a seasonal variability in all the fluxes. In particular, the net water flux from the Atlantic Ocean increases up to 2660 ± 111 km³/year in August/September, and reverses to –407 ± 140 km³/year in April/May. On top of the climatology, the mean annual Atlantic water flux varies significantly in time ranging from 706 to 1262 km³/year.

The work of DGG, IV, MT and JV was partially supported by Spanish Project RTI2018-093874-B-100 funded by MCIN/AEI/10.13039/501100011033,  DGG and IV were partially supported by Grant PROMETEO/2021/030 (Generalitat Valenciana) and JMS was supported by the Generalitat Valenciana  and the European Social Fund under Grant APOSTD/2020/254.

How to cite: Garcia-Garcia, D., Vigo, I., Trottini, M., Vargas, J., and Sayol, J. M.: Net water-mass transport through the Strait of Gibraltar and the Turkish Strait, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8686, https://doi.org/10.5194/egusphere-egu22-8686, 2022.

Mesoscale eddies are ubiquitous energetic features that alter the biogeochemical regimes of the oceans by blending large-scale gradients, isolating and transporting water masses over large distances, and by locally shallowing or deepening isopycnals [1]. While several studies highlighted mesoscale biogeochemical mechanisms in the open ocean, the difficulties affecting altimetry products in nearshore regions constitute a strong barrier to the observation-based characterization of nearshore biogeochemical eddy dynamics.

Because of their transitional nature, capturing observational snapshots of eddies with satisfactory coverage is challenging. To overcome this difficulty, composite analyses consist of gathering a large number of near-eddy data instances (from observation or model results) and analyzing their variations according to their relative position to nearby eddies. The method thus aims at characterizing average eddy-induced perturbations and provided the basis for many of the recent advances in the field [2].

The BGC-Argo program provides a powerful asset for eddy composite studies, resulting from 1) the large availability of data provided under the hood of common technical protocols, 2) the richness of characterized biogeochemical variables, and 3) the continuity of data acquisition which facilitates the characterization of local anomalies.

Here, we evaluate three Black Sea altimetry data sets (2011-2019) and compare their adequacy to characterize eddy-induced subsurface oxygen and salinity signatures by applying a common composite analysis framework exploiting in-situ data acquired by BGC-Argo profilers.

The locations, contours, and properties of eddies are obtained by applying the py-eddy-tracker procedure [3] to three altimetric sets, that differ in terms of along-track and gridding processing, and spatial resolution. For comparison, we consider equivalent CMEMS BS-MFC model products [4]. Oxygen and salinity subsurface anomalies are then obtained from BGC-Argo profiles and relocated in eddy-centric coordinates specifically for each altimetric product.

The most recent altimetric data set, issued from the ESA EO4SIBS project, provides eddy properties that are closer to model simulations, in particular for coastal anticyclones. More importantly, subsurface signatures reconstructed from BGC-Argo are more consistent when EO4SIBS is used to express eddy-centric coordinates.

We propose that the estimated error on the reconstructed mean anomaly may serve to qualify the accuracy of gridded altimetry products and that BGC-Argo data provide a strong asset in that regard.

Besides, we reveal intense subsurface oxygen anomalies whose structure supports the hypothesis that the mesoscale contribution to Black Sea oxygen dynamics extends beyond transport and involves net biogeochemical processes.

[1] D. J. McGillicuddy, (2016), Ann. Rev. Mar. Sci., 8, 125–159.

[2] P. Gaube, D. J. McGillicuddy, Jr, D. B. Chelton, M. J. Behrenfeld, P. G. Strutton, (2014), J. Geophys. Res. C: Oceans, 119, 8195–8220.

[3] E. Mason, A. Pascual, J. C. McWilliams, (2014), J. Atmos. Ocean. Technol., 31, 1181–1188.

[4] Ciliberti, S. A., et al. (2021), Journal of Marine Science and Engineering, 9(10), 1146.

How to cite: Capet, A., Taburet, G., Mason, E., Pujol, M.-I., D'Ortenzio, F., Grégoire, M., and Rio, M.-H.: Using Argo to characterize altimetric products: a study of eddy-induced subsurface oxygen anomalies in the Black Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13265, https://doi.org/10.5194/egusphere-egu22-13265, 2022.

The aim of this work is to study the seasonal variability of 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 for basin-scale and eddy circulation regimes in the Black Sea. The basin-scale circulation is a regime when the entire basin is covered by the cyclonic Main Black Sea Current (the Rim Current), which spread over the continental slope. The eddy circulation is a regime when the Rim Current is partially or completely destroyed and intense mesoscale eddies evolve in the abyssal part of the sea. Monthly energy characteristics are calculated based on eddy-resolving simulation data derived under atmospheric forcing SKIRON. Analysis of the reconstructed current fields showed that the basin-scale and the eddy circulation regime are realized in 2011 and in 2016, respectively.

Seasonal signal is weakly manifested in the variability of the MKE; its value depends on the wind forcing and current velocities, which are higher in the basin-scale circulation regime. The distribution of the MPE is predominantly seasonal; temporal variability is qualitatively similar for both regimes and is caused by increase in the density anomaly due to warming up of seawater. The energy transport MPE→MKE due to the buoyancy work is provided in the subsurface layer for all seasons and the Cold Intermediate Layer for the warm seasons in both regimes.

Seasonal variability of the EKE and the mechanisms of its intensification are different for two circulation regimes. The EKE is maximal in spring and summer in the basin-scale circulation regime, and in the cold season in the eddy circulation regime. In winter, when the Rim Current or its elements are most intense, irrespective of the circulation regime, the mesoscale eddies develop mainly due to energy transport MKE→EKE via barotropic instability mechanism. In summer, the mesoscale variability in the basin-scale circulation regime is due to commensurate contributions of barotropic and baroclinic instability, and in the eddy circulation regime only by the energy transport MPE→EKE due to baroclinic instability.

The reported study was funded by the Marine Hydrophysical Institute state task No. 0555-2021-0004.

How to cite: Dymova, O. and Demyshev, S.: Seasonal variability of energy transport in the Black Sea for the basin-scale and eddy circulation regimes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-763, https://doi.org/10.5194/egusphere-egu22-763, 2022.

Tidal forcing in numerical models is necessary to correctly forecast the ocean, since tides are a significant source of energy and driver of mixing in the global ocean. In the Mediterranean Sea, the amplitude of tides is lower than in many other regions of the global ocean, with the exception of the Alboran Sea, North Adriatic, and Gulf of Gabes, but the effects of tides are not limited to parts of the basin with high tidal amplitude. Analysis of the relationship between tidal forcing and measures of vertical motion including mixed layer depth, vertical velocity, and vertical diffusivity have not previously been carried out throughout the Mediterranean Sea.

This work investigates the effects of tides on vertical motion in the Mediterranean Sea, using the hydrodynamic model corresponding to the Copernicus Monitoring Environment Marine Service (CMEMS) system, a baroclinic forecasting model for the Mediterranean Sea, integrated over 5 years. Several regions were selected for separate study, based on their tidal amplitude and the local importance of vertical dynamics, such as deep water formation. The inclusion of tides increased the mean mixed layer depth in winter in the Mediterranean Sea, as well as in most of the selected regions. The magnitude of vertical velocity was also increased by tides on a basin level, but did not increase consistently throughout the selected regions. Vertical diffusivity, Brunt-Väisälä frequency, and Richardson number results were also explored.

The relationship between tidal amplitude and vertical velocity was additionally studied from a theoretical perspective. This work developed a prognostic equation for vertical velocity which was then compared to model results.

Our improved understanding of the effects of tidal forcing on vertical motion in the Mediterranean Sea highlights the necessity of including tides in high resolution ocean models, and allows for the separation of their effects from the impact on vertical mixing due to other modelling choices such as the chosen parametrization of vertical diffusivity. 

How to cite: McDonagh, B., Clementi, E., Pinardi, N., Goglio, A. C., and Cessi, P.: The effects of tides on vertical motion in the Mediterranean Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7628, https://doi.org/10.5194/egusphere-egu22-7628, 2022.

Ocean biomass distribution has a growing importance in the world economy as a global strategic reserve, due to environmental and industrial applications and its variability related to climate change. Satellite imagery allows multi-resolution methodologies to obtain estimation, and hopefully classification, of biomass content over sea surface. This information is largely used in numerical simulations and nowadays represents an important contribute to future projections. Nevertheless, satellite, models and classical in situ monitoring resolution/accuracy sometimes cannot provide data at the finer spatial scales needed to describe the complex threedimensional water column system. On the other hand, glider surveys allow scientists to collect observations of ocean phenomena at very high resolution along the water column, to assess numerical simulations reliability and, eventually, to assimilate these data into ocean models. In this study, we present a quantitative comparison between the glider observations collected in the Algerian Basin (Western Mediterranean Sea) during the ABACUS surveys from 2014 to 2018, and the daily outputs of two co-located CMEMS model products (i.e., GLB and IBI).
The achieved results point out that model products are well correlated with glider potential temperature measurements but they still need improvements to provide a correct representation of the chlorophyll concentration variability in the study area. Generally, IBI daily simulations present higher linear correlation with concurrent glider in situ data than GLB ones. IBI products also reproduce better the pattern of the local maxima of chlorophyll concentration across the Algerian Basin. Nevertheless, they largely underestimate glider chlorophyll measurements and present significant differences that limit their capability to reproduce its upper ocean concentration that is needed for accomplishing advanced ecological studies.

How to cite: Aulicino, G., Cesarano, C., Zerrouki, M., Ruiz, S., Budillon, G., and Cotroneo, Y.: On the use of ABACUS high resolution glider observations for theassessment of phytoplankton ocean biomass from CMEMS model products, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3942, https://doi.org/10.5194/egusphere-egu22-3942, 2022.

On 7 April 2021, an exceptional bloom of the scyphomedusa Rhizostoma pulmo was observed in the Gulf of Trieste (Italy). Blooms of these species in the northern Adriatic Sea have been reported since the late 1800s, however, the density of jellyfish observed in 2021 reached dozens of specimens per cubic meter. In this work, we analyze the bloom from a multi-platform approach using observation and model data at different time scales. This study aims to contextualize the oceanographic/environmental conditions that may have contributed to the exceptional aggregation of the scyphomedusa Rhizostoma pulmo along the northernmost coast of the Adriatic Sea. Our study shows that 1) the bloom was probably enabled by anomalous warm sea conditions during winter 2020, allowing specimens that reproduced in 2020 to survive and reach considerable abundance and sizes by early 2021; 2) strong wind events, such as the Bora wind for the Gulf of Trieste, enhanced upwelling and mixing processes in the gulf thus bringing the jellyfish present in deeper waters to the surface and clustering them along the coast.

How to cite: Reyes Suarez, N. C., Ursella, L., Tirelli, V., Ličer, M., Querin, S., and Cardin, V.: How physical properties can unveil the biological processes in the water column: a multi-platform study of the extreme bloom of Rhizostoma pulmo jellyfish in the Gulf of Trieste,  April 2021 case study., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2337, https://doi.org/10.5194/egusphere-egu22-2337, 2022.