Coastal morphology plays a significant role on how the ocean dynamics are shaped, especially in regional seas. A high resolution (1.5 km) version of ROMS (Regional Ocean Modeling System) is used for Black Sea circulation with two different scenarios to analyze the morphological changes on Rim Current and eddy formation along the Black Sea southern coastline. First case (Base Case) is the existing Black Sea morphology and the second case (Test Case) is where Sinop Peninsula is removed from the coastline as a ”theoretical study” in order to understand the effects of coastline morphology on Black Sea dynamics. Simulations were conducted between 2012 and 2022, with atmospheric forcing, rivers, and initialized with the climatological values of salinity and temperature. The results reveal that the Rim Current around Sinop Peninsula is affected in both transport and width between cases. Since the Test Case lacks the headland features, the mean flow around the Sinop Peninsula shows up to 11% stronger transport and the width of the Rim Current is increased up to 20% east of Peninsula. Similarly, Peninsula affects the number of eddies produced. Sinop Peninsula causes headland wakes and creates approximately 12% more eddies compared to the Test Case. Test Case results reveal a reduction of mean Eddy Kinetic Energy (EKE) by approximately 15%, indicating a fundamental shift towards a more stable and inertially efficient boundary current regime. This study demonstrates that morphological features play a critical role in circulation patterns and eddy formation significant for the coastal-open ocean exchange processes.

There is a consensus that the Black Sea is affected by climate change in many ways. The Black Sea Physical Reanalysis system and Argo measurements are used for analyzing not only sea surface temperature (SST), but also the entire Black Sea over the period from 1993 to 2019. Linear regression and Mann-Kendall tests are used for detecting trends and the Pearson-correlation coefficient is used for detecting correlation between data sets. Results show that the entire Black Sea has been warming with few abrupt exceptions such as in 2012 and 2017. In addition, water masses in the upper water column have been warming (CIL = 0.012 °C/year, BSSW (Black Sea Surface Water) and BSCW (Black Sea Coastal Water) = 0.096 °C/year). However, there is no statistically significant trend in deeper parts of the Black Sea. The western shelf, especially its west coasts, is the region that is most open to seasonal changes in the Black Sea.

In this study, a high-resolution eddy resolving regional ocean + sea ice coupled model (MITgcm) is used to study the effects of increasing westerlies along the Southern Ocean. Previous studies only focused on increasing wind stress, thus not taking into account of atmosphere-to-ocean heat and freshwater fluxes. Here, we conduct two concurrent simulations; i) 1.5 times increased wind stress (i.e. increased only mechanical forcing) ii) 1.2247 times increased wind speed (i.e. both mechanical and thermal flux forcing). Model domain covers whole Southern Hemisphere with lateral open boundary conditions from ECCOv2 ocean reanalysis and surface boundary conditions from ECMWF ERA-5 atmospheric reanalysis. In both sensitivity scenarios, due to the increase in the wind stress, the Ekman transport towards Equator towards north is increased. This caused increased upwelling of warmer North Atlantic Deep Water (NADW) near the Antarctic ice sheet. Both scenarios show reduced sea ice formation with up to 2 million km2 in the austral summer and up to 4 million km2 during the austral winter. Sea ice extent is reduced more in the mechanical forcing simulation than the mechanical+thermal forcing one. This is a clear result that increased wind anomalies should be studied with increased wind rather than increased stress. The reduction in the sea ice coverage that is attributed to the warmer water mass can also be observed through the Sea Surface Temperature (SST) values. The first case shows up to 1 – 1.5 °C very close to the Antarctica, whereas the second case shows a much limited SST change around 0.5 °C.Both sensitivity scenarios show an increase of the transport along Drake Passage. However, the mechanical+thermal case shows larger increase in the Drake transport compared to the mechanical case. This indicates that a change in the Antarctic Circumpolar Circulation also modifies the meridional density gradient along with the upwelling characteristics. Finally, overturning transport in the density space shows that Subtropical Cell and ACC upper Cell strengthen in the mechanical+thermal case, while there are no significant changes in the thermal case. In both simulations, Subpolar Cell increases and Lower Cell decreases. We conclude that studying increased westerlies with two different approaches show significant changes in the surface and deep circulation. Previous studies which taken into only mechanical forcing part are missing thermal component of the wind effects.

Global climate models struggle to accurately represent the dynamics of the Black Sea because it's so isolated from the open ocean, connected only by the narrow Turkish Straits. To overcome this limitation and study how the Black Sea will be affected by future climate change, we need to use high-resolution regional models. We've developed a new 5km resolution regional model of the Black Sea using the NEMO 4.2.1 ocean circulation model. To validate our new model, we compared it against a well-established 2.5-km resolution model from the Copernicus Marine Service model setup. Both models share the same numerical core, vertical layers, horizontal and vertical parameterizations. In our first comparison, we used historical ERA5 atmospheric data from 1980 to 2015. The new 5km model performed very well, with biases that were remarkably similar to those of the higher-resolution 2.5-km model. While the 2.5-km model revealed finer details like the Batumi Gyre and specific features near the Crimea Peninsula, both models provided comparable results for deep-ocean dynamics. This confirms that our 5-km model is reliable enough for long-term climate simulations.Next, we simulated three different future climate scenarios—RCP2.6, RCP4.5, and RCP8.5—using atmospheric data from the 0.01 degree CNRM-ALADIN model in the CMIP5 CORDEX-Europe project. All three scenarios show that the Black Sea surface will get warmer and saltier. In the model simulations, the surface temperature increases 1.5, 2.0, 3.5 degrees between different RCP scenarios respectively, and also gets saltier up to 3 psu. Notably, the Cold Intermediate Layer (CIL), a distinct oceanographic feature which is characterized by a layer of relatively cold water is projected to disappear after 2040 in the RCP8.5 scenario. The warming isn't limited to the surface; it penetrates deep, reaching down to 700 meters. Likewise, the Black Sea is becoming saltier, with this salinification also extending to 700 meters. To increase the robustness of our findings, we also performed an additional RCP8.5 simulation using a different atmospheric model, the SMHI-RCA4 from the CMIP5 CORDEX-Europe project. This ensemble approach helps us account for model uncertainties and strengthens our confidence in the projected climate changes for the Black Sea.These findings suggest that under a high-emission scenario like RCP8.5, the Black Sea's temperature and salinity profiles will change dramatically. These changes could significantly alter its circulation patterns, stratification, and overall ecosystem dynamics.