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The Cryosphere An interactive open-access journal of the European Geosciences Union
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Volume 12, issue 11 | Copyright
The Cryosphere, 12, 3459-3476, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 08 Nov 2018

Research article | 08 Nov 2018

Interannual sea ice thickness variability in the Bay of Bothnia

Iina Ronkainen1, Jonni Lehtiranta1, Mikko Lensu1, Eero Rinne1, Jari Haapala1, and Christian Haas2 Iina Ronkainen et al.
  • 1Finnish Meteorological Institute, 00560 Helsinki, Finland
  • 2Alfred Wegener Institute, 27570 Bremerhaven, Germany

Abstract. While variations of Baltic Sea ice extent and thickness have been extensively studied, there is little information about drift ice thickness, distribution, and its variability. In our study, we quantify the interannual variability of sea ice thickness in the Bay of Bothnia during the years 2003–2016. We use various different data sets: official ice charts, drilling data from the regular monitoring stations in the coastal fast ice zone, and helicopter and shipborne electromagnetic soundings. We analyze the different data sets and compare them to each other to characterize the interannual variability, to discuss the ratio of level and deformed ice, and to derive ice thickness distributions in the drift ice zone. In the fast ice zone the average ice thickness is 0.58±0.13m. Deformed ice increases the variability of ice conditions in the drift ice zone, where the average ice thickness is 0.92±0.33m. On average, the fraction of deformed ice is 50% to 70% of the total volume. In heavily ridged ice regions near the coast, mean ice thickness is approximately half a meter thicker than that of pure thermodynamically grown fast ice. Drift ice exhibits larger interannual variability than fast ice.

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Short summary
We quantify the sea ice thickness variability in the Bay of Bothnia using various observational data sets. For the first time we use helicopter and shipborne electromagnetic soundings to study changes in drift ice of the Bay of Bothnia. Our results show that the interannual variability of ice thickness is larger in the drift ice zone than in the fast ice zone. Furthermore, the mean thickness of heavily ridged ice near the coast can be several times larger than that of fast ice.
We quantify the sea ice thickness variability in the Bay of Bothnia using various observational...