Sea Ice Station Umeä, Winter 2005 
35 
Umea Marine Sciences Centre for atmospheric surface layer, ice, and oceanographic 
measurements, but unfortunately this float then was destroyed in heavy storm in January 2005 
with much of the atmospheric data lost. In 31 March - 1 April a short field trip was made with 
manual measurements of ice sampling and the light transfer. The throughflow of ice in the 
Northern Quark was examined by mathematical modelling. 
The automatic station data showed that the water body cooled in the first two weeks. Ice 
formed at December 10th, and still after that there was a warm water inflow from the Sea of 
Bothnia. The salinity of the water was 4.0^L6% o . At the time of the fast ice break-up the ice 
thickness was 10 cm, too small to be able to resist strong wind forcing. As a whole the winter 
was mild, and at the time of the field trip the ice thickness was only 25 cm, almost all 
congelation ice but most of it already porous. The albedo of the bare ice was 0.3, and the light 
penetration depth was 35 cm for clear ice and 10 cm for porous ice. In optics of natural water 
bodies the euphotic zone is taken as the level where the irradiance has dropped to 1% of the 
surface value. In practice this means 4-5 penetration depths, i.e. in the present case the ice 
takes just half of that amount. The model simulations for the ice dynamics showed that the 
geometry of the Northern Quark, in particular the fast ice boundary, is critical for the dynamics 
of the ice there. If the fast ice boundary is taken as the 10-m depth contour, almost no ice floes 
through the strait if the ice cover is initially compact. 
The experience with the fast ice breakage was another good lesson, and also future studies 
need to be performed with low risk levels to obtain a good basic data set of the ice season in 
the Northern Quark. Anyway, winter 2004/2005 data as well as the model outcome are now 
being analysed for the final results. 
Acknowledgement. This work has been supported by a grant from the Umea Marine Sciences 
Centre of the Umea University (project Seasonal evolution of sea ice, wintertime hydrography, 
and light conditions). Dr. Amund E. B. Lindberg from the Centre is thanked for his help in the 
recovery of the automatic station. 
References 
Arst, H., 2003. Optical Properties and Remote Sensing of Multicomponental Water Bodies. 
Springer, Praxis-Publishing, Chichester U.K, 231 p. 
Granskog, M., M. Lepparanta, J. Ehn, T. Kawamura and K. Shirasawa, 2004. Sea ice structure 
and properties in Santala Bay, Baltic Sea. Journal of Geophysical Research, 109, 
C02020. 
Kawamura, T., K. Shirasawa, N. Ishikawa, A. Lindfors, K. Rasmus, J. Ehn, M. Lepparanta, T. 
Martma and R. Vaikmae, 2001. A time series of the sea ice structure in the Baltic Sea. 
Annals of Glaciology 33, 1-4. 
Lepparanta, M., 2004. The Drift of Sea Ice. 290 p. Springer-Praxis, Heidelberg, Germany. 
Lepparanta M., A. Reinart, A. Erm, H. Arst, M. Hussainov and L. Sipelgas. 2003. Investigation 
of ice and water properties and under-ice light field in fresh and brackish water bodies. 
Nordic Hydrology, 34(3), 245-266.