Q The growth and composition of pack-ice in the Baltic Sea is not well known. Even though sporadic observations exist, systematic investigations should be performed. Such basic questions as sea ice and snow thickness distribution, textural and > /@? O composition need to be addressed along with chemical and biological investigations.
Q The presence of a snow cover on sea ice, as well as its seasonal development, especially during spring melt-freeze cycles, deserves more attention. Further data are relevant both for the observa-tion of superimposed ice formaobserva-tion, as well as development and validaobserva-tion of thermodynamic sea ice models with the formation of snow-ice and superimposed ice layers included (see also Cheng, 2002). The inclusion of rain in the models seem also relevant at the Baltic Sea conditions.
Q The low porosity of Baltic Sea ice will evidently affect its hydraulic properties, therefore in situ studies of the permeability of Baltic Sea ice at different salinities and temperatures should be per-formed. This is important for e.g. the infiltration of seawater to the ice-snow interface (snow-ice formation) as well as exchange processes of sea ice with the snow pack and under-ice water. Trans-port of surface meltwaters through the ice is imTrans-portant for the nutrient dynamics, but should also be taken into account in thermodynamic models with snow-ice and superimposed ice formation, because this transport provides a sink of surface melt that is not used for surface ice growth.
Q To examine the exact role of sea ice in geochemical cycling and budgets there is a need for con-current snow, sea ice cover, and under-ice water column hydrochemical studies throughout the ice season. Especially important is the spring melt season, and the transition from ice coverage to open water. This applies to both landfast and pack ice areas in the Baltic Sea.
Q Studies on the microstructure, i.e. the distribution and the sizes of brine pockets and channels on Baltic Sea ice would be needed.
Q Detailed studies on the in situ composition and properties of sea ice brine in the Baltic Sea ice should be undertaken. This could be accomplished by sampling brine using e.g. refrigerated centrifuges. Measurements could include physical properties of the brine, such as viscosity and density, and detailed analysis of its chemical composition.
Q Virtually no studies have been undertaken where detailed hydrochemical observations have been performed during the period of snow and sea ice melt, when substances accumulated onto and possibly (photo)chemically transformed , are released to the underlying waters. There is clearly a need for such studies, as well as investigations looking at uptake and bioaccumulation of pollutants in ice-associated organisms as observed in the Arctic (Borgå et al.,2002)
Acknowledgements
All through my scientific career, professor Matti Leppäranta has played an important role. He first introduced me to the field of sea ice geophysics when I was a (young) undergraduate student and there was no turning back. Ever since he has given support, independence and therefore also responsibility in making this work. Without his support, this thesis would never have been completed.
This work has been carried out at the Division of Geophysics at the University of Helsinki, and the Arctic Centre at the University of Lapland. I would like to express my gratitude to the staff at both departments for providing support and an inspiring atmosphere.
I also want to express my gratitude to all those involved in producing the final outcomes of this thesis, that is all the publications, both to co-authors and all others who helped in producing the relevant material. A complete list of all would take too much space. However, in particular I would like to thank the staff of the Tvärminne Zoological Station and the Bothnian Bay Research Station, who helped in solving many practical problems, provided a nice environment for working out on the ice and in laboratories, and also fed the hungry and sometimes frozen and soaked researchers. Tõnu Martma provided all the oxygen isotopic measurements, which is greatly acknowledged. Special thanks goes to two fellow postgraduate students, Jens Ehn and Hermanni Kaartokallio, for collaboration in the practical work and for many inspiring and fruitful discussions on sea ice.
Professor Harri Kuosa and Dr. Jari Haapala provided critical and constructive comments on this manuscript.
Suggestions of Dr. Johanna Ikävalko, PhD John Moore and PhD David Thomas aided in improving the manuscript. Ms. Alicia Kennedy did a great job in editing my English.
This work has been partly funded by the Academy of Finland, the Walter och Lisi Wahls Stiftelse för Naturvetenskaplig Forskning Foundation, Oskar Öflunds Stiftelse Foundation, the Jenny and Antti Wi-hurin Rahasto Foundation, and the Walter and Andrèe de Nottbeck Foundation. All are hereby greatly acknowledged.
Last but not least, I would like to express my sincerest thanks to my parents, my brothers and their families for continuous support (especially at the worst of times in autumn 2000), and to all friends and colleagues without whom life would not be worth while. Get something better to read.
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