What Happens in the Depths of the Oceans?

Sometimes the world feels, boring. We've visited all the remote islands, conquered the Arctic, and penetrated the deepest jungles. But there is still one place to explore. It's a wet and deadly desert inhabited by mysterious creatures living in total darkness. The deep sea. Let's dive down. When we look at the sheer scale of the Earth's oceans, it’s hard to believe that less than 2% of all biomass on Earth lives here. And of that small percentage, around 90% is located close to the surface in the first 200 meters. This is where we begin our journey.

Here, light can still penetrate the water which allows photosynthesis to occur. Phytoplankton, trillions and trillions of single-celled algae and bacteria make up the foundation of the ocean's ecosystem, and they're consumed by bigger plankton, who are consumer by other species. The seafloor at this depth is akin to the Amazon rainforest, and is often covered with coral reefs, algae, and other sea plants that are home to a plethora of sea animals. So far, we've focused most of our attention on this comparatively pleasant environment, where we fish, swim, pollute, and do science.

let's dive deeper. Moving from familiar coastal waters into deeper, more remote waters, we eventually reach the edge of the continental shelf, where we're confronted with the continental slope, the long descent down to the deep sea. With every additional meter of water, light fades drastically, which means there are basically no more plants, and the seemingly steep continental slope begins to remind us of the surface of the Moon. Looking out we're faced by what seems to be endless open water. Let's leave the slope behind us, and enter what's known as the Twilight Zone, the portal to the deep sea. As we sink down further, the water pressure rises to deadly levels.

 The deepest scuba dive ever came in at 332 meters. At that depth, the pressure is like having 200 cars stacked on top of you. Yet we've only completed 3% of our journey. While this region seems pretty grim, many fish and other animals actually spend at least half their lives down here. During the day, it's a good place to rest and recover, hidden from predators in the vast dark waters. At night, they can travel more safely into shallower zones to feed in the food-rich surface waters. In this transition zone between Twilight and Darkness, light becomes a powerful tool. Over 90% of the species indigenous to this deep environment use bioluminescence chemicals to create light.

They do so as camouflage against the very faint sunlight, to send signals to potential mates, or to confuse and scare attackers. Or, they use lights to hunt. Another tool for survival in the dark is teamwork. At around 700 meters, we encounter a colony of siphonophores. They can be up to 50 meters in length, but are only as wide as a broomstick. To attract prey, a colony creates a tragically beautiful bright blue or red light, and deploys a curtain of tentacles filled with toxic needles that kill anything that comes too close. But most species living down here have to rely on an unlikely resource: Marine Snow. White flaky stuff that constantly sinks from the surface to the bottom of the ocean.

It consists of dead plant or animal parts, fecal matter, shells, sand, or dust. Even though this doesn't sound very tasty, without this crucial resource, life in the deep sea would starve. It's in this area that the most fascinating battles between two unlikely enemies could happen. Sperm whales hunt and attack giant squid the size of a house. While the squid fight back ferociously, they probably don't stand a chance, but they do leave permanent marks on their killer's skin. As we reach 1,000 meters, deeper than the tallest structure built by humans, we need to be careful. This is the Midnight Zone, a place of utter darkness. A barely explored wet wasteland consisting of nothing but endless black open water.

At these depths, it's harder for a human to take a swim than to take a walk-in space. Finding food down here is really hard, so life had to adapt, and become extremely energy-efficient. Like the 30-centimeter-long vampire squid that floats through the water without motion, with long and slender catching arms extended. They're covered in tiny stiff hairs, which brush food from the water. This saves a lot of energy compared to actively catching food. For carnivorous fish, it's much harder to find food since living prey is quite rare down here. the hunters have to get a perfect grip on their victim on first strike. Otherwise, it will escape into the dark. Many deep-sea predators have several sets of long and deadly teeth. Like the viperfish, which uses its long fangs to trap even large prey and swallow it whole.

Or the frilled shark, with its impressive set of 300 teeth, which are curved backwards to hook their victims in their mouths. We sink further. Below the 3800 marks, as deep as the grave of the Titanic, we are now at abyssal depths. Here, life happens in slow motion. Preserving every last bit of energy is crucial for survival. Everything down here hovers motionless, or swims in a slow, elegant fashion. The only time the animals living in this zone move fast is when they have to escape danger. Like the Dumbo octopod paddling with its ear-like fins, or the grenadier’s fish with its slow eel-like tail beats. At 4,000 meters, we've finally reached ground again. The Abyssal Plain.

It's covered in grey mud and rocks dusted with the remains of marine snow, which is consumed by animals like sea cucumbers, shrimp, sea urchins, and sea worms. In some regions of the seafloor, small dark mineral deposits can be seen. These are manganese nodules. Deep-sea corals and sponges use them to anchor themselves on the bottom of the sea. Though life is sparse on the deep-sea floor, even down here there are oases. In the rift valleys, where tectonic plates are splitting apart, magma heats up seawater and creates dark jets of water and minerals as hot as 400℃ (752℉), that form elaborate chimneys and towers. Extremophile bacteria use the minerals to create organic substances, that are the bases for unique ecosystems.

As we descend further, we reach the deepest point of the abyssal plain at 6,000 meters. For most of the seafloor, this is as deep as it gets, but if we want to get to the deepest point of the oceans, we're actually only halfway there. Let's enter the Hadal Zone, the underworld of the sea. It consists of long narrow trenches that only make up around 0.25% of the oceans, and are among the most extreme environments on Earth. Only extremophiles exist down here, like the ethereal snailfish, that holds the record for deepest living fish ever seen, at around 8,000 meters. We see spiky and sharp black rocks rush by as we sink down to more than 10,000. Until we reach the final slope, a trench inside the larger Mariana Trench with gently-sloping sides that enflame a valley about 1.6 kilometers wide.

This is it. The deepest point, the Challenger Deep. 11,000 meters below the surface. The water pressure here is 1,086 bar. Taking a swim here is like having to balance 1,800 elephants on top of you. But even here, life has found a way to thrive. Next to sea cucumbers, white and light pink amphipods wiggle their way through the water. Their size is astounding. While their shallow-water cousins are maybe a few centimeters long, the deep-sea version can reach up to 30 centimeters. And there are other things floating elegantly through the water. Plastic bags that were found by scientists in 2018. Even the remotest place on Earth is not safe from human influence.