Welcome to the realm of the deep. We're talking deep that is so far down in the ocean it's hard to fathom* (where do you think the expression came from?). Deep so deep that it takes hours to free fall to the ocean bottom. Studying this inner space is truly extreme science. The oceans are WAY deeper than anything on land is high. Many people say that the ocean realm is truly the last frontier on earth. There is still much we don't know about the ocean depths that makes being a scientist in this exciting field such an adventure. New creatures are still being discovered while scientists seek to unravel some ancient mysteries.

 

Ocean Zones – Scientists’ have organized and classified the oceans into various zones, each with its own characteristics. These zones aren’t known to the creatures that live in the sea and they ignore the boundaries readily. But scientists have organized the sea into layers because the living environment generally changes with each different layer. Each layer is usually distinguished by the amount of sunlight it receives, the depths it occupies, and the degree of hydrostatic pressure found there. The easiest way to think of hydrostatic pressure in the sea is to think of the weight of a gallon of water, approximately 8.8 pounds. When you dive into a body of water and dive down, there are a lot of gallons of water over the top of you, and all together they add up to a lot of weight. The deeper you dive into the water, the more gallons (and weight) of water is over the top of you. The pressure of the weight of the overlying water is the hydrostatic pressure at that depth.

To best experience these life zones as they affect life in the sea, imagine that you are a diver for the day. Put on a diving suit and scuba gear and climb into the ocean for a descent into the sea to experience the life zones …

Sunlight Zone - (from the surface to about 200 meters down). As you begin your descent you see that the ocean is absolutely teeming with life forms of every sort. From the microscopic plankton and diatoms that give the ocean its murky color and limits visibility, to bony fishes of every shape and size, to starfishes, and warm-blooded, oxygen-breathing mammals. You can see the most fantastic array of colors; reds, pinks, purples, bright yellows, oranges, blues, greens. Everywhere you look the ocean is brimming with brightly colored life forms, much more so than anything on land. As you swim down deeper, it seems that the colors begin to fade and the palette of life is becoming more monochromatic. In fact, the colors are not disappearing, you simply are not able to see them. Water, especially murky, turbid water, scatters and absorbs some of the sun’s light, filtering out colors below certain depths. The first colors to go are the reds, then oranges, yellows, greens, and then finally blues. You may reach a certain depth, say about 60 feet, and it appears that everything around you is shades of brown, black, gray and white. But lucky for you – you brought a bright dive light. You turn on the light and once again marvel at the incredible variety of colors, even at that depth. The sunlight zone of the sea contains some of the most plentiful, but tiny organisms in the ocean, krill (a type of crustacean). Their existence is responsible for sustaining the largest living creatures on earth – the Blue Whales.

As you dive deeper in the sunlight life zone of the sea, you will also quickly notice the effects of hydrostatic pressure on your body. The deeper you dive the more water is over the top of you. The more gallons of water you put between you and the surface of the ocean, the greater the pressure is on your body because of the weight of the water over the top of you. You can really get a sense of hydrostatic pressure as you dive deeper because you'll feel the pressure against your ear drums, like they're being squeezed or pushed in. You’ll need to equalize the pressure against your eardrums to avoid rupturing them, so you descend slowly to prevent them from being damaged. Once you get down to about a depth of 100 feet you will feel the pressure against every square inch of your body. It really becomes noticeable as you breathe. At a depth of 100 feet, the size and volume of your lungs has been reduced to 1/3rd their capacity at sea level. You will also notice that it is much darker at 100 feet and COLD. The lack of sunlight at that depth also means the ocean is not getting warmed by sunlight, either. At a depth of about 180 feet you’ve pretty much reached the limit of safe diving for a human breathing compressed air. Because of the possible hazards of nitrogen narcosis, hypothermia, fatigue, and the need for decompression after a deep dive, you’ll need to return to the surface and put on a special suit to dive deeper into the next zone.

 

Twilight Zone - (also called the Mesopelagic zone) This life zone is also known as the midwater range and is noted for very low levels of sunlight, and virtual darkness for human eyes. This layer ranges from 600 feet to about 2,600 feet down. The plankton, which occupies the sunlight layer in profusion and provides a food source for most of the creatures living in that layer, either directly or indirectly, does not live in the twilight zone. Plankton needs adequate sunlight to thrive. The type of foods available to creatures living at these depth tend to be energy-poor and usually are characterized by detritus and bacteria, the things that drift down from the sunny creatures teeming and thriving at the surface. Most of the sea creatures living in this layer have low-energy tissues and sluggish lifestyles to cope with low food energy, since no algae can grow. Life here is noticeably sparse, the deeper you go.

The hydrostatic pressure in the twilight zone is much greater and special suits and diving crafts are necessary for humans to explore this layer of the water column. A highly specialized diving suit was designed and built for manned diving operations and exploration of these depths. Called the JIM suit, it is a type of atmospheric diving suit that creates artificial atmospheric conditions inside the suit (of 1 atmosphere, the same at sea level) regardless of the hydrostatic pressure outside the suit. It also protects the diver inside from the extreme cold temperatures at these depths and the risk of hypothermia. To date, the deepest dive for a JIM suit is 1,400 feet.

Imagine yourself inside a JIM suit – it feels like a personal sized mini-sub. As you look out into the deep, deep blue water you see that life down here is pretty sparse. Soon, you see unfolding before your eyes what looks like a light show. One of the most spectacular and awe-inspiring phenomenon that a human diver visiting this realm can experience is bioluminescence. Many organisms’ body tissues are capable of emitting their own light – they glow in the dark. The colors range from blues to greens, as some fish even emit red light as a form of infrared vision to help them see their prey in darkness. Although it isn’t completely dark in the twilight zone, many of the creatures that live in this ocean zone have developed this highly specialized adaptation for different reasons. A great many organisms throughout the water column (including those that live at the ocean surface) are capable of bioluminescence, but it plays a more critical role in the lives of creatures that exist in almost complete darkness. For example, some creatures, such as squid and octopi, emit clouds of glowing ink to evade predators. Others, such as jellyfish and some bony fish, use light to attract prey. In a world where sunlight casts just a faint blue glow for brief periods, organisms have adapted by generating their own light.

Midnight Zone - The deepest, darkest regions of the ocean are found from about 2000 meters down to the sea floor. It is a realm of perpetual darkness, where even the faintest blue tendrils of sunlight cannot penetrate. It has been called the “Midnight Zone” because it is continually plunged in utter blackness, even when the brightest summer sun is perched high above the surface, there is no “daytime” here. Life that exists in the midnight zone relies indirectly on the benefits of sunlight; organisms thriving in the sunny upper layers of the sea die their eventual deaths and rain down upon the sea floor a steady flow of organic nutrients to feed the masses living at or near the bottom. The organic “rainfall” includes dead microscopic organisms, such as phytoplankton and dinoflagellates, sinking downward, fecal pellets of fish and mammals, and carcasses of larger organisms sinking down to the sea bed. Those creatures that do not feed directly on the “leftovers” raining down from above, usually prey upon those that do. Many of the creatures thriving in the deep sea have taken on fascinating, gruesome and horrifying visages and proportions, developing special adaptations to surviving in this harsh environment.

The deep sea still remains largely unexplored. The extreme hydrostatic pressure of the overlying water at depths of 2000 meters and more demand technologies that can safely withstand the cold, crushing waters of the deep. The technologies used to explore the inner space of the deep sea have only recently been developed in the last 30 years, and are just now becoming more widely available to a non-civilian community of scientific explorers. There have been many, manned “missions” in the last 30 years in various submersible crafts to get a glimpse of the mysteries that lay at the bottom of the sea, but we have only begun to scratch the surface. It is estimated that less than less than one-millionth of the sea’s darkness has been explored and seen by human eyes. It is truly a frontier in its infant stages of human discovery.

 

The average depth of the ocean is over two miles deep. It is estimated that of all the habitable regions on earth, including dry land and the vast oceans, that the deep sea regions (those two miles and deeper) make up 97% of habitable living space on the planet. If you add up all the people living today with all the other living organisms on land (plants, insects, animals, microorganisms), we account for less than one percent of all the biomass (the total mass of living organisms in a given environment) on the entire planet. Truly, the most successful habitat on earth, given the biomass it supports, is the deep sea. The bottom line is, as creepy and foreign as those bizarre deep creatures are to us, there are more of them living on this planet than us!

Deep Sea Trench - In a few places on the ocean floor there exist unusually deep zones. Nearly three times deeper than the average depth of the sea floor, these zones are known as deep sea trenches. The trench zones are characterized by complete darkness and unimaginable pressures of up to 16,000 pounds per square inch. Yet, despite the seemingly inhospitable environment of the deepest depths, life is inexplicably found thriving. It is in the Marianas Trench, of the Marianas Islands of the Southeast Pacific Ocean, where the deepest known place in the ocean was found.

Geography of the Ocean | Does Anything Live That Deep?