Extensive airborne ice-thickness surveys have been performed in various regions of the Arctic Ocean for almost 10 years, using electromagnetic induction sounding. Results show some significant thinning of up to 53% in the region of the North Pole, while ice thicknesses north of the coast of Canada remain almost constant, in contrast to the apparent present public perception. This presentation summarizes the results of the most recent thickness surveys carried out north of Ellesmere Island in May 2010, and compares them to observations performed in the same region since 2004, as well as to results obtained in various other regions between Svalbard and Alaska. Due to logistical constraints, ice-thickness surveys are often carried out during different seasons. Therefore, seasonal changes have to be taken into account when comparing them. We will present data obtained over the same icefields in May and August 2009 north of, and within, Nares Strait to study seasonal ice-thickness changes in this region. In addition, we present data obtained on an individual ice floe over the course of a year. For the latter, systematic ground-based electromagnetic ice-thickness sounding was performed along the same, initially 2 km long profiles from April to October 2007 around the schooner Tara which was frozen into, and drifted with, the ice of the Transpolar Drift. During the observation period, modal ice thickness decreased by 0.6 m, from 2.1 to 1.5 m. This result is in very good agreement with results from an ice mass-balance buoy, which measured ice-thickness change at one location by means of sonic rangefinders below and above the ice. The good agreement between those measurements points to the feasibility of each method to obtain representative data which can be used to correct seasonal variations in ice-thickness data obtained in different seasons.