What lies deep beneth the ocean?
It is a sobering fact that more people have walked on the moon’s surface than have visited Earth’s lowest spot. During six Apollo missions between 1969 and 1972, 12 humans did the moonwalk. Jacques Piccard and Don Walsh reached a 10,916 m depth in their Trieste bathyscaphe in 1960. The first unmanned vehicle to reach the Deep was controlled by the Woods Hole Oceanographic Institution’s researchers, reaching up to 10,902 meters.
Oceanographers divide the majority of the ocean midwater into five broad zones. The very deepest depth of the ocean is roughly 2,000 meters deeper than Mount Everest is tall—36,070 feet deep (10,994 m)! Each zone has a different mix of species adapted to its specific light level, pressure, temperature, and community. About three-fourths of the area covered by ocean is deep, permanently dark, and cold. This is the deep sea.
Most are familiar with the surface layer, which extends down 650 feet (200 m) and receives the most sunlight, allowing photosynthetic organisms like phytoplankton to convert sunlight to energy. It is the home of pods of dolphins, schools of fish, and shoals of sharks. Scientists refer to this highly productive area as the epipelagic zone.
But the majority of the space in the ocean is a dark world. Dive below the epipelagic and you will enter the mesopelagic zone. Also known as the twilight zone, this area receives only faint, filtered sunlight, allowing no photosynthetic organisms to survive. Many animals have adapted to the near darkness with large eyes and counterillumination.
The ocean floor
Seventy percent of the Earth’s surface is below the ocean, yet 95 percent of it remains unexplored to the human eye. Although the oft-heard statistic is that we know more about the surface of Mars than we do about the ocean seabed, scientists have been able to map the entire ocean floor—but the resolution is incredibly poor, so we can only visualize features larger than three miles. Ongoing research like Seabed 2030 aims to bring the ocean floor into greater focus, so we can better see and understand what’s really down there. For now, we can just marvel at the most stunning deep-sea sights in the world.
Running between Greenland and Siberia, the Gakkel ridge is the deepest mid-ocean ridge in the world, reaching depths of up to three miles. It’s no surprise then that the darkest corners of the Gakkel Ridge remain largely unexplored. Despite this, the underwater mountain chain is where scientists found the first Arctic hydrothermal vents, only in 2003.
Hydrothermal vents are a hot-spot for sea organisms, with up to 100,000 times higher density of organisms than the surrounding ocean, and with those in the Gakkel ridge being so isolated from other oceans, these vents are likely to contain species found nowhere else on the planet. In 2007 researchers conducted the AGAVE (Arctic Gakkel Vents Expedition) mission, in which they discovered large amounts of pyroclastic volcanic deposits, which appear as glass-like structures on the sea floor. The group used an under-water robot to explore the area and found “mats” of large amounts of microbial life.
Deep beneath the ocean’s surface, towers spew scalding water from within the earth’s crust. These are hydrothermal vents.
Hydrothermal vents exist in volcanically active areas. Seawater makes its way through the cracks in the earth’s crust until it reaches hot magma. As the water heats it absorbs metals like iron, zinc, copper, lead, and cobalt from the surrounding rocks. Hot water rises, carrying these minerals to the surface of the sea floor. There, it meets cool ocean water, an event that sparks chemical reactions and forms solid deposits. Over time the deposits create towers—forming the classic image of a hydrothermal vent. Some spew water filled with black iron sulphide and are aptly named “black smokers,” while others spew white coloured elements like barium, calcium, and silicon and are called “white smokers.”
At first inspection, it seems unlikely that anything could live in such an environment—spewing from cracks in the earth’s crust is scalding water that has been heated to temperatures up to 752 degrees Fahrenheit (400 degrees Celsius), a temperature hot enough to melt lead. These vents are also so deep that they never see a glimmer of light from the sun. Despite these obstacles, clams, mussels, shrimp, and gigantic worms thrive in these habitats. Their existence is thanks to bacteria.
Could these be the sea monsters of yore? This snake-like creature is the longest bony fish on Earth and can grow up to 56 feet and weigh 600 pounds. But because they live at depths around 3,300 feet, not much is known about the rarely-seen-alive creature. Two dead oarfish were found on California shores in 2013, prompting scientists to wonder if ominous forces were at work to beach the normally deep-sea animals, as they have been rumoured to wash up before earthquakes. But instead, the incident turned out to be a boon for scientists to be able to study the specimens—since they don’t even know how many species of the fish exist, DNA samples could help researchers figure that out.
Located in the middle of Iceland, this is the only place where you can swim in the crack between two continents. It is here that the Eurasian and North American plates meet, creating a crevice with a depth of up to 63 metres. Its fissure gets 2cm wider every year, building tension between the plates and the Earth, which is released by earthquakes.
The freshwater is claimed to be the ‘clearest water on Earth’, with visibility up to 100m, and as a consequence the fissure is a popular snorkelling and diving location – despite the water temperature reaching as low as two degrees Celsius. The water within the fissure is particularly clean as the glacial water has been filtered through porous rock, clean enough to drink as you dive in fact.
Ocean Reef Mask
For much of the deep ocean, food rains down from above in the form of marine snow. The term ‘marine snow’ is used for all sorts of things in the ocean that start at the top or middle layers of water and slowly drift to the seafloor. This mostly includes waste, such as dead and decomposing animals, poop, silt and other organic items washed into the sea from land.
As this material drops deeper and deeper, the particles can grow in size as smaller flakes clump together. The larger size causes them to fall more quickly through the water column—but, even so, the journey to the bottom can take several weeks to years. Scientists have learned more about the travels of marine snow by using sediment traps on the ocean floor. Data from these traps have shown that 815 million tons of carbon reaches the ocean floor every year. These layers of ocean ooze are important carbon sinks—drawing down the decomposing bits of carbon, laying them to rest on the seafloor, and finally burying them.
But not all particles get that far. They are often eaten by fish or marine mammals during their slow fall, just to be digested and pooped out elsewhere in the ocean to begin the cycle all over again. Once the trip is complete, this decomposing hodgepodge can be a welcome food source for animals in deep water and on the sea floor that don’t have reliable food in the sparse darkness. Some animals, such as the vampire squid and its special feeding filaments, have special adaptations to help them better catch and eat the falling particles. The snow is also important to small, growing animals, such as eel larvae, which rely on the snow for months during their development. Marine snow clumps are also swarming with microbes—tiny organisms ranging from algae to bacteria—that form communities around the sinking particles.
These and many more discoveries over the years reveal how little we knew of our watery world – and many more marine frontiers remain to be explored. Unless we manage our oceans in a more precautionary manner, we may never know what riches they contain.