During the RV Polarstern cruise ARK-XXIII-3 in the summer of 2008, seismic reflection and refraction data along an almost 1200 km long transect along 81�N latitude were acquired across the Amundsen Basin, Lomonosov Ridge, Makarov Basin, Mendeleev Ridge and parts of the Canada Basin. The seismic data are dominated by an unconformity/reflector band that is observed along the entire transect that separates a flat-lying well-stratified upper unit from the underlying sediment sequences. In our interpretation this reflector band spans a time interval from breakup of the Lomonosov Ridge from the Siberian/Barents shelves around 56 - 65 Ma to the top of the Oligocene. The velocity-depth functions indicate total sediment thicknesses ranging from 1200 to 2000 m on the Lomonosov Ridge, to 5500-6300 m within the deepest part of the Makarov Basin around 168�E, to 1000 e1500 m on the western flank of the Mendeleev Ridge, and, finally, to ~4000 m within the Canada Basin. The data show that stretched continental crust of the Lomonosov Ridge extends farther into the Makarov Basin than previously known. Horst and graben structures indicate that approximately 50% of the Makarov Basin along the 81�N transect is underlain by stretched continental crust. These structures most likely formed during a rift phase which is older than 56 Ma. Thick Mendeleev Ridge crust (up to 33 km) occupies the remaining portion of the basin. It is likely that the formation of this magmatic crust overprinted older oceanic crust during the Cretaceous Quiet Period (84e120 Ma).