Vertical structure and seasonal evolution of the cold intermediate layer in the Baltic Proper

Abstract

Vertical T,S structure of waters of the cold intermediate layer (CIL) is examined on the base of high-resolution CTD profiles obtained in the Baltic Sea Proper in spring and early-summer periods. Basic elements of the structure of the CIL are identified and possible mechanisms responsible for their formation are suggested. Seasonal evolution of the CIL structure is considered. Its four stages are discussed: formation in early spring; late-spring adjustment; slow summer-time modification; and fall/winter-time washing-out/preconditioning to the next cycle. The mechanisms of mixing and stirring which could be responsible for the observed features of the CIL structure are discussed. It is proposed to consider the Baltic CIL not as a phenomenon which appears during the warm season only, but as a manifestation of a permanently current process of basin-scale water exchange. Further targeted investigations are urged disclosing the role of this exchange in general thermo-haline circulation of the Baltic Sea.