During the RV Polarstern cruise ARK-XXIII-3 in summer of 2008, geophysical data of a nearly 1200 km long seismic transect along 81 N including the Amundsen Basin, Lomonosov Ridge, Makarov Basin, Mendeleev Ridge and Canada Basin could be acquired. The objective was to understand the tectonic evolution of the Makarov Basin in relation to the evolution of the adjacent Lomonosov and Mendeleev ridges in the Amerasia Basin. The data acquisition involved seismic reection and refraction data, gravity, bathymetry, and magnetics. The seismic survey set-up included a 300 m streamer and a 32 liter airgun cluster. Because of ice conditions, gaps remained between the proles but for the rst time it was possible to get a nearly complete overview over the three main features within the Arctic Ocean. In addition to reection seismic data, eight sonobuoys were deployed along the proles to better resolve the seismic velocities in the sedimentary column. The seismic sections are dominated by an unconformity that persists across the entire transect and that separates the at-lying well-stratied upper unit of Cenozoic age from the lower Mesozoic sediment sequences, which are dominated by pervasive normal faulting. The unconformity marks the break-up of the Lomonosov Ridge from the Siberian/Barents shelves between 56-65 Ma ago. The developed velocity depth functions indicate sediment thicknesses from 1200-2000 m on the Lomonosov Ridge to 5500-6300 m within the deepest point of the Makarov Basin around 168 E, to 1000-1500 m on the western ank of the Mendeleev Ridge, to 4000 m within the Canada Basin. The continental origin of the Lomonosov Ridge could be approved. The fact that evidences for oceanic origin are missing leads to the assumption that the Makarov Basin is created only by extension of continental crust between the opening of the Canada Basin and the initiation of the Eurasia Basin, 120 - 56 Ma ago. However, the possibility of a partly oceanic crust can not be ruled out. The high velocities of the basement (> 6.4 km/s), the density characteristics and the uniform crust within the 2D gravity modeling leads to the conclusion that the Mendeleev ridge has an oceanic origin. The modeled thick crust (33 km) could be explained by the theory of a Large Igneous Province (LIP) around 89 Ma ago. All interpretations support the rotational models.