There exists no other way of navigating through the Arctic Ocean than to send an icebreaker ahead to open a passage through the ice. The cargo ships that are Siberia's vital link to the rest of the world rely upon the nuclear-powered icebreakers inherited by Russia when the Soviet Union broke up. As they plough through the icy desert up to four metres in depth, convoys of ships carrying the mineral treasures of Siberia to the outside world form in their wake. The Russian economy depends on the northern sea routes being kept open all year round.