Blue Planet II – Secrets of the Deep

As with the other 10.8 million viewers last Sunday night, I made sure to book my evening off from all form of work as it was time to watch the second instalment of Blue Planet II. The last episode, titled “Secrets of the Deep”, provides us which an insight into all that is weird and wonderful at the bottom of our oceans. In the opening Sir David Attenborough brings to light how we know more about the surface of Mars than we do about the deepest parts of our seas, hinting at the alien-like lifeforms which are found as far as 5 miles below the ocean’s surface!

Image: BBC

A total of 1,000 hours was spent filming this episode, in two small submarines which can only hold a maximum of 3 people during a single expedition. We initially start in Antarctica, one of the most hostile environments on earth, bitterly cold and barren. Yet below the colossal icebergs and sea ice lies a world we could not even imagine, providing much of the life-giving oxygen for the bottom of our oceans, transported around the globe via deep-water currents. Throughout the researchers’ time filming here, they were constantly on high alert from the dangers of icebergs (even when 1km down)! In the final section of the episode they show the problems associated with the use of submarines; including puddles forming from leaks 500 metres below the surface and shockwaves vibrating the vessel as two large masses of ice colliding! The scariest danger, in my opinion, was the threat of “drop stones”, which are car-sized boulders that fall from icebergs that pass by. You can fix a leak, but even if you get a crack on one of the submarines 1km down, the pressure will force open that weakness and there will be nothing that you can do about it!

Just 200 metres below the surface of the water we reach the twilight zone, a realm where there is barely enough light to see your hand in front of your face. Here you can find 90% of all the fish in the ocean, highlighted by a fleet of Humboldt squid some 2 metres long decimating a shoal of lantern fish.

We then travel down to the midnight zone, 1 kilometre below the surface, where no light reaches and the organisms present rely on sinking debris and marine snowfall as a source of sustenance. This place is not pitch black all the time, instead it is lit up by a display of bioluminescent flashes which are given off by the organisms which reside there. The submarines then follow the path of a dead sperm whale as it sinks to the bottom of the ocean and is slowly consumed by 30 different species over the course of 4 months. These species are extremely resourceful, making sure to get to every scrap of flesh as they do not know when their next meal will be.

The deeper that you travel, the more hostile and extreme conditions become. At these depths movement is slow, with some organisms (such as the toadfish) actually adapting to grow small limbs instead of fins, as they shuffle across the sea floor. Corals exist on the floor at rocky outcrops too, acting as an oasis for life as they catch nutrients which pass by in the slow-moving currents. Here growth rates are as little as the width of a human hair every year, allowing some corals to survive as long as 4000 years! Again, we are reminded about the ever-present threat of human disruption on the longevity of these ecosystems, with fishing trawlers carving up the sea bed.

We are then taken to a scene which looks almost like the beach of Bikini Bottom (Spongebob) where there are pools within our oceans, as a result of super-salty brine accumulating and creating a toxic layer where no organisms can possibly survive. As you travel out across the seabed eventually you will come across a steep drop-off, at which the plate boundaries meet and create deep ocean trenches. One of which, the Marinara Trench, is 11 kilometres deep (that’s deep enough to comfortably fit Mount Everest in)! Here the pressure is supposedly equivalent of 50 jumbo jets (25,000 tonnes) on top of you, which bring me to the next reality; if life can survive these hostile environments, then what about the seas which are found on the moons of Jupiter and Saturn? Many theories indicate that life itself originated on this planet some 2.4 billion years ago within the deep ocean, through hydrothermal vents forming and providing the basis of life to form, so why can’t it happen elsewhere?

This week we will be introduced to the coral reefs of this world, so be sure to book off your Sunday evening and turn the television to BBC One at 8pm!


James Deed