Mesoscale eddies in the Black Sea: Characteristics and kinematic properties in a high-resolution ocean model

2021-11-01
Sadighrad, Ehsan
Fach Salihoğlu, Bettina Andrea
Arkin, Sinan S.
Salihoğlu, Barış
Hüsrevoğlu, Y. Sinan
Mesoscale eddies are ubiquitous features of oceanic circulation and important contributors to the transport of water and heat as well as chemical and biological constituents. In the Black Sea, mesoscale eddies, filaments and meanders are recognized as main agents facilitating the transport and distribution of nutrients and biomass between coastal regions and the open, deep sea. In this study, a high-resolution ocean model, Nucleus for a European Model of the Ocean (NEMO), is implemented for the Black Sea and used to create a hindcast simulation of circulation dynamics for the 1985–2014 period. This hindcast simulation is validated and then used to produce a detailed statistical investigation of the occurrence and behavior of mesoscale eddies in the Black Sea. For this purpose, an eddy identification and tracking algorithm (EddyScan) is applied and the kinematic properties of all eddies are detected, including eddy number, size, lifetime, excursion distance and their spatial distribution. The analysis shows that, on average, anticyclonic eddies are larger in diameter, have a longer lifetime and travel farther distances from the generation site than cyclonic eddies. However, the number of anticyclonic eddies generated is less than cyclones. Spatial distribution of eddies shows that cyclonic and anticyclonic eddies occupy much of the open Black Sea but few are found on the northwestern shelf. The density of anticyclonic eddies is especially high in the Sevastapol, Sinop, Kizilirmak and Batumi regions; while cyclonic eddy densities are high in the northern Black Sea along the Rim Current, north of the Batumi region, as well as in the center of the western and eastern Black Sea gyres. The number of eddies generated increases in spring and summer and decreases again in fall and winter due to changes in wind stress curl and its impact on Rim Current strength. The temporal evolution of long-lived eddies (>30 days) shows that after their creation, the diameters of cyclonic eddies increase for a period of 2–3 months, after which they reach a stable diameter. On the other hand, anticyclonic eddy diameters increase, on average, for a 5–6-month period and then reach a stable value. The vertical effects of these long-lived eddies generated in the Black Sea generally reach down to 150-200 m and hence intersect with the nitrate maximum and oxygen minimum zone. A first estimation shows that the simulated anticyclonic eddies in the Black Sea may have transported up to four times more water than cyclonic eddies over one year. The mean vertical flux induced by all cyclones generated in one year upwell ~ 0.63 Sv of water, while all anticyclones generated in one year downwell two times as much water or ~ 1.27 Sv over the top 100 m of the water column. This highlights the importance of eddies for the vertical transport of water and associated biochemical properties. In addition, eddies are able to connect different regions of the Black Sea as well as offshore/onshore regions along their paths and are of great importance for nutrient distribution and availability in the Black Sea.
Journal of Marine Systems

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Citation Formats
E. Sadighrad, B. A. Fach Salihoğlu, S. S. Arkin, B. Salihoğlu, and Y. S. Hüsrevoğlu, “Mesoscale eddies in the Black Sea: Characteristics and kinematic properties in a high-resolution ocean model,” Journal of Marine Systems, pp. 0–0, 2021, Accessed: 00, 2021. [Online]. Available: https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85111076200&origin=inward.