The world's best-known wildlife expert Sir David Attenborough returns to tell us all about the planet's oceans. Blue Planet II explores the latest scientific discoveries, from the icy Arctic seas to the bluest coral reefs. From the green Atlantic artline to the undiscovered, murky depths of the ocean. In four years, more than 6000 hours of underwater footage was shot on more than 125 expeditions, in 39 different countries.