The Aranda’s expedition provided new information about sea ice motion and compression

The marine research vessel Aranda returned from an expedition to the Bothnian Bay on 7 March. During the voyage, scientists obtained new information on ice field compression and collected observation data for the verification of measurements made by new remote-sensing satellites.

Photo: Ilkka Lastumäki

Important new observations could be collected during the voyage since strong winds, prevailing almost throughout the expedition, kept pushing sea ice towards the Finnish coast of the Kvarken and the Bothnian Bay. “Radar observations indicate that there are great local variations in sea ice motion and the ice field may be split along navigation channels,” says Jari Haapala, expedition leader at the Finnish Meteorological Institute.

Ice field compression is an intense, short-lived situation caused by ice motion, ice thickness and the size of ice rafts. The present models make it possible to predict the areas where compression will take place. However, the predictions do not give very accurate estimates of the local forces, which are important on the scale of individual ships. The research conducted on the Aranda is part of the Safewin project, where the aim is to construct a forecasting system for warning ships about difficult conditions.

Sea ice several metres thick in places

The second research topic for the voyage was the development of new methods for measuring the thickness of sea ice. Ice thickness was measured using various methods: an echo sounder installed on the seabed; a device measuring the strength of the electromagnetic radiation field; and by means of the CryoSat-2 radar satellite. Thickness measurements were made during the Aranda’s voyage using, in particular, a measurement device installed in a helicopter. “The strong winds that have been blowing during the past few weeks have created new areas of ridged ice in the Finnish coastal areas. In these areas, individual ice walls can be as much as 20 metres thick, and the average regional thickness of ice is 3–4 metres in an area measuring several square kilometres. At least in the Bothnian Bay, the awkward ice situation with continue until April,” Haapala predicts.

To observe ice field motion and compression, the scientists used buoys placed in the sea, the Aranda’s radar observations, and local observations on a drifting ice station.

Additional information:

The Aranda’s expedition leader, Senior Researcher Jari Haapala, tel. +358 40 757 3621; jari.haapala@fmi.fi