The decrease of Arctic sea ice volume is investigated using a dynamic-thermodynamic sea ice model. The model was forced with NCEP/NCAR reanalysis winds and surface air temperatures in a hindcast simulation of the period 1958--1998. The simulation reveals pronounced decadal variability (10--12 years) along with a significant linear negative trend of total Arctic sea ice volume which amounts to -4%/decade. The decrease is apparent throughout the annual cycle with largest amplitudes from September to December. Regionally the strongest thinning of ice thickness occurs in the East Siberian Sea with magnitude up to -30 cm/decade. The simulation also reveals some positive trends in the Baffin Bay/Labrador Sea and north of the Canadian Archipelago. ¿ 2000 American Geophysical Union