The influence of seasonal sea ice on the physics of the coastal waters : Gulf of Finland

• Main Author: Merkouriadi, Ioanna
• Other Authors: Myrberg, Kai, University of Helsinki, Faculty of Science, Department of Physics, Atmospheric sciences and Geophysics, Helsingin yliopisto, matemaattis-luonnontieteellinen tiedekunta, fysiikan laitos, Helsingfors universitet, matematisk-naturvetenskapliga fakulteten, institutionen för fysik, Leppäranta, Matti
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Helsingin yliopisto 2014
• Subjects: geophysics; Sea ice
• Online Access: http://hdl.handle.net/10138/136368

The Gulf of Finland is located in the seasonal sea ice zone (SSIZ), were sea ice forms in the wintertime and melts in late spring. This seasonality entitles this sea as a key area regarding the impact of climatic changes. When the basin of interest is located at the climatological edge of the SSIZ, there is also high inter-annual variability in the ice conditions. The aim of this study was to examine the influence of the sea ice on the physics of the coastal waters in the Gulf of Finland. Three sites were chosen, two located at each side of Hanko Peninsula, northwest entrance of the Gulf, and one at the estuaries of River Kymijoki, northeast side of the Gulf. Long-term hydrographic and sea ice data were examined in order to study the inter-annual variability and trends of the hydrographic characteristics, heat content, freezing and break-up days and ice thickness during the last century in the coastal zone of the Gulf of Finland. The influence of the seasonal sea ice on the physics of the water body hydrography, circulation, atmosphere-ocean interaction was evaluated. The results showed significant decrease of the ice season length by almost 30 days in the last century. The maximum annual sea ice thickness decreased by 8 cm in the last 40 years. In the last 85 years, surface water temperature increased by 1 ˚C and surface salinity increased by 0.5 PSU. The water body stratification in the coastal zone was strongly affected by the limited wind mixing in the wintertime. The circulation under ice became weaker by almost 1 cm s-1. The ice cover was a good control measure of the net surface heat exchange. Solar radiation had a strong seasonal cycle with monthly maximum at 160 W m-2 and minimum below 10 W m-2. Terrestrial radiation was mostly between 40 and 60 W m-2. Latent heat exchange was much more important than sensible heat exchange, similar to the net terrestrial radiation values in summer and autumn.