Sea-ice kinematics measured with GPS drifters

Abstract

A sea-ice dynamics experiment was performed in the Baltic Sea in March 1997. A new type of drifter was constructed based on the global positioning system and mobile-phone data transmission. The drifters worked well and the accuracy was reasonable (std dev. 40 m). Five drifters were used to map ice kinematics in a 20 km size array in the coastal drift-ice zone. The study included periods of onshore motion with ridge formation, and alongshore motion with narrow shear lines. The motion of ice largely occurred in short pulses between which the field stood nearly still. The level of ice speed was much less than that of free drift, while the deformation field was more uniaxial due to the presence of the solid boundary. Drift-ice strength was estimated as 4 × 104 N m-2. Large deformation rates of up to 2% h-1 were observed.