The deep-sea dive, which began at 2.55pm, reaches its climax as an unmanned submersible descends into an underwater canyon 2,000m beneath the waves of Monterey Bay. Meanwhile, the yellow submarine with Kate Humble aboard is used to lure a deep-water shark in the Caribbean, and the tiny protective bubble containing Alastair Fothergill bobs around a massive black smoker (hydrothermal vent) at the bottom of the Atlantic.

Throughout the day, viewers can email questions to the team in Monterey at [email address removed] or text them on [number removed].
Highlights of today's dives at 11pm.