Upwellings and Downwellings Caused by Mesoscale Water Dynamics in the Coastal Zone of Northeastern Black Sea

Abstract

The paper analyzes quasiperiodic upwellings and downwellings on the shelf and upper part of continental slope of the northeastern Black Sea. It is shown that these processes are related to changes in intensity and direction of alongshore current and the following geostrophic adjustment of the density field. The source of such changes is the meandering of the Black Sea Rim Current (RC). It leads to a quasiperiodic change in direction of the alongshore current, from northwestern (cyclonic RC meander) to southeastern (anticyclonic RC meander, or eddy). These cycles, or phases, have an average duration of about 10 days. During the northwestern phase, the permanent Black Sea pycnohalocline (hereafter pycnocline) and seasonal thermocline descend, their thickness increases, and so does the thickness of the upper mixed layer (UML). During the southeastern phase, both the pycnocline and seasonal thermocline ascend and become thinner, along with the UML, which also becomes thinner. In both phases, isopycnals in the pycnocline and isotherms in the thermocline demonstrate quasi-in-phase vertical oscillations, which have a good correlation with the speed and direction of the alongshore current. These correlations allow estimation of the magnitude of upwellings and downwellings in the shelf–slope area of the northeastern Black Sea using data series of current velocity profiles.