Hydrographic observations from four separate expeditions to the Arctic Ocean between 1991 and 2001 show 300-700 m thick homogenous bottom layers in the Eurasian Basin. The layers are characterized by slightly warmer temperatures (~7x10^-3C) compared to ambient, overlying water masses, indicating that they may have formed by convection, induced by geothermal heat supplied from Earth’s interior. The layers are present in the deep central parts of the Nansen and Amundsen Basins, away from continental slopes and ocean ridges. The layers are seen in data from all four expeditions and are spatially coherent across the length of the interior parts of the deep basins. From all observations we find a mean layer thickness and temperature surplus of 502±105 m and 7.0±2.1x10^-3C, respectively. Different mechanisms for generating and maintaining these layers are discussed. We argue that the most likely scenario is that the layers are constantly developing in time, becoming thicker and warmer until some exchange of bottom water occurs and a new layer forms. Simple numerical simulations using an observed geothermal heat flux of 80 mWm^-2 indicate that it is possible to generate a layer similar to the observations in a period of 4-5 years, starting with a hypothetical initial profile without a warm homogeneous bottom layer. The observations also suggest that new deep water may have been advected into the Amundsen Basin between 1991 and 2001, with warmer water being present over the entire deep-water column. We speculate that the renewal most likely occurred between 1996 and 2001.