Geophysical investigations in the ultra-slow spreading environment of the Arctic Ocean during the last five years revealed new and astonishing insights into the fabric of the crustal and upper mantle composition.Data from icebreaker investigations and aero-geophysical experiments show how variable the ultra-slow oceanic crust and may be even the upper mantle is. Areas of focussed magmatism have formed elongated ridges, which reach far into the adjacent basins. However, this zone of enhanced magmatism seems to have distinct boundaries in the upper mantle, since adjacent to them amagmatic segments are present. Variations in crustal thickness vary strongly from 2-6 km with the presence of elongated traversal ridge or along axis volcanoes. That such kind of different spreading environments are stable can be shown by on- and off-axis investigations. However, gravity modelling suggests that the composition of the mantle just below the seismic Moho might be more variable than along faster ridges. To fit the recorded data large-scale density variation had to be incorporated into the model.The westernmost termination of the Gakkel Ridge is named Lena Trough. It is located between Svalbard and North Greenland. Magnetic data along the Lena Trough show that this ultra-slow segment propagated southwards during the Cenozoic while opening the Fram Strait. Like other ridge system, ultra-slow spreading systems are obviously able to propagate into a continent. This indicates that the eastern termination of the Gakkel Ridge off the Laptev Sea shelf might not be a typical scenario for a termination of an ultra-slow spreading systems. One hypothesis might be that how such a ridge proceeds into a continent depends more on the geology and the general plate movements.Recent results from geophysical investigations along the Gakkel Ridge and Lena Trough will be shown and discussed.