Operational monitoring and forecasting system for global and regional oceans, including the Arctic, combines observations from different satellite remote sensing techniques and in-situ open ocean measurements with ocean circulation models through advanced assimilation techniques. Satellites can sufficiently monitor changes in surface properties of the polar oceans, while the interior of the ocean is poorly observed since the water mass is opaque to electromagnetic waves and Argo floats cannot yet be used in the Arctic. Correspondingly, the internal of the Arctic Ocean is not monitored on a systematic basis, and this represents a significant gap in the Global Ocean Observing System. It is recommended to design and implement a cost-efficient, multi-purpose acoustic infra- structure for ocean acoustic tomography, navigation/positioning of gliders and floats under ice, and monitoring of ambient noise and marine mammals.