Variability of synoptic-scale quasi-stationary thermohaline stratification patterns in the Gulf of Finland in summer 2009

[摘要] We present and analyze high-resolution observational data of thermohalinestructure and currents acquired in the Gulf of Finland (Baltic Sea), usingan autonomous buoy profiler and bottom-mounted acoustic Doppler currentprofiler during July–August 2009. Vertical profiles of temperature andsalinity were measured in the upper 50-m layer with a 3 h time resolution,and vertical profiles of current velocity and direction were recorded with a10 min time resolution. Although large temporal variations of verticaltemperature and salinity distributions were revealed, it was possible todefine several periods with quasi-stationary vertical thermohalinestructure. These quasi-stationary stratification patterns persisted for4–15 days and were dominated by certain physical processes: upwelling,relaxation of upwelling, estuarine circulation and its wind-inducedreversal, and downwelling. Vertical profiles of current velocities supportedthe concept of synoptic-scale, quasi-stationary periods of hydrophysicalfields, characterized by distinct layered flow structures and currentoscillations. To estimate the contribution of different processes to thechanges in stratification, a simple conceptual model was developed. Themodel accounts for heat flux through the sea surface, wind mixing,wind-induced transport (parallel to the horizontal salinity gradient) in theupper layer, and estuarine circulation. It reproduced observed changes invertical stratification reasonably well. The largest discrepancies betweenobservations and model results were found when water motions across the Gulfand associated vertical displacements of isopycnals (upwelling ordownwelling) were dominant processes.

[学科分类] 海洋学与技术