Persistent Lagrangian transport patterns in the Black Sea identified from climatological Lagrangian Coherent Structures

Abstract

The quasi-steady Lagrangian transport patterns in the Black Sea are quantified and identified from climatological Lagrangian Coherent Structures. Wind velocity and Earth observation data have been incorporated to illustrate the potential applications of these results. The persistent squeezelines show that the high aggregation of passive tracers in the coastal region is a consequence of the complex coastal configuration of the Black Sea. The continental shelf is characterized by high stirring and mixing activities. The persistent and recurrent pathway patterns on the northwestern shelf are responsible for attracting nearby water parcels and passive tracers and conducting them towards the southern platform and offshore. Along the Rim Current, fifteen regions were identified as chevrons, indicating that they are jet-like structures. The jet-like structures and the northwestern shelf play an essential role in facilitating cross-shelf transport of material to neighboring coastal regions and offshore areas. Four transport barriers were identified by the climatological Lagrangian Coherent Structures as being both efficient and critical to the Lagrangian transport, and to the protection of coastal regions. One of these barriers is also identified as the Lagrangian Front. The Rim Current accounts for 44% of the Black Sea basin’s climatological attraction strength. The Rim Current and the basin-wide climatological attraction strength show seasonal variations, with the highest values observed in winter. The distribution of persistent and recurrent mesoscale activity is also analyzed. The prevailing tendency among eddies identified is an anticyclonic orientation, typified by elevated levels of stirring and mixing. It is evident that an increase in wind speed over the basin results in a corresponding rise in the climatological attraction force exerted by anticyclonic eddies. This, in turn, leads to an enhancement in the process of stirring, mixing, and aggregation of nearby water parcels and passive tracers. However, it has been demonstrated that the presence of eddies is reduced in proportion to the velocity of the wind, particularly in the case of cyclonic eddies. The study offers valuable insights into the complex transport dynamics of the Black Sea ecosystem, with potential implications for environmental management and conservation efforts.