When exploring the ocean, most of us are fascinated with the aquatic life that it holds in its waters, but have you ever wondered what’s lurking on the seabed?
The seabed, otherwise known as the ocean floor, seafloor, ocean floor, or ocean bottom, describes the bottom of the ocean. Regardless of the depth, consistency, and geography, all floors of the ocean are known as the seabed.
Below we will take a dive deep under the ocean to explore the dynamics of the seabed, what it consists of, its ecological importance, and how it plays a significant role in our larger environment, including those on the earth’s surface.
Geographical Features of the Ocean Seabed
The uppermost layer of the ocean’s tectonic plates is known as the oceanic crust.
Although the entire seafloor is considered part of the oceanic crust due to various geographical movements, such as tectonic plates colliding or moving apart, the ocean boasts a variety of topography across its bottom.
Approximate Ocean Floor Depths
| Depth Below Sea Level | Feature |
| 0 – 200 meters | Continental Shelf |
| 200 – 300 meters | Continental Slope |
| 2,000 – 4,000 meters | Continental Rise |
| 4,000 – 6,000 meters | Abyssal Plain |
| 6,000 + meters | Oceanic Trench |
Continental Shelf
The continental shelf forms the first part of the land that is covered by the ocean. Extending from the coastline, the continental shelf moves outwards towards deeper water, where it eventually drops off at a point known as the shelf break.
The size of a continental shelf differs around the world. For example, the largest continental shelf is the Siberian Shelf, which extends approximately 930 miles (1,500 km), while some of the narrowest continental shelves can be found along the coasts of South America, sometimes only between 12 and 37 miles wide.
Although the continental shelf is underwater, it is still considered part of the continent, which only changes after the drop-off when the shelf becomes a continental slope, which dives into the deeper layers of the ocean.
Continental Slope
Leading from the shelf break, the ocean floor takes a steep decline as it transitions into the continental slope.
The continental slope is a steeply sloping seabed that lies between the continental shelf and the deeper abyssal plain, which typically has a gradient of 2–5°, although this can be steeper in parts of the world.
The continental slope marks the boundary between the continental crust and oceanic crust at the point known as the continental rise.
Abyssal Plain
The abyssal plain usually begins at the base of the continental rise and is usually found at depths between 4,000 and 6,000 meters, forming some of the deepest parts of the ocean floor.
Approximately 50% of the seabed is an abyssal plain and forms the most unexplored areas of the ocean.
Abyssal plains are almost entirely flat and cover large areas that eventually meet up with other seafloor features such as mid-ocean ridges or trenches.
For example, the Sohm Plain alone covers 350,000 square miles.
Mid-Ocean Ridge
The mid-oceanic ridge, which forms the mid-Atlantic Ridge, is the largest and most extensive mountain range on Earth. More than 90% of its range lies underwater, rising from the deep ocean.
The mountain has an extensive chain that runs from the Arctic Ocean to the Southern Ocean.
Occurring along divergent plate boundaries (when two tectonic plates move apart), where seafloor spreading takes place, basalt escapes during volcanic eruptions, and magma solidifies, which forms these ridges.
Volcanic Islands
Similarly to the mid-oceanic ridge, volcanic islands are formed through tectonic movement and underwater volcanic activity.
Volcanic islands reach levels above water and are typically formed in the middle of oceanic plates or near subduction zones.
Many of these volcanoes form island chains like Hawaii, which continue to form as tectonic plates move over oceanic hotspots.
Volcanic islands form the tallest mountains on Earth, with Mauna Kea being the most notable, as the tallest mountain on the planet, reaching 33,500 feet from base to peak.
Volcanic islands are similar to seamounts but differ in their penetration of the ocean’s surface.
Seamount
Seamounts, similar to volcanic islands, are formed from volcanic activity, but unlike volcanic islands, they do not penetrate the water’s surface.
Seamounts are found in a variety of shapes, depending on the volcanic activity, which includes flat tops, conical, and irregular shapes.
Although seamounts are underwater mountains, it is possible for volcanic activity to build up enough and eventually bring the seamount to the ocean’s surface, which transforms it into a volcanic island.
Deep Ocean Trenches
Ocean trenches are long, narrow depressions on the seabed that form long canyons. These trenches form the deepest parts of the ocean and can be found in every oceanic basin.
That said, some of the deepest ocean trenches are found in the pacific ocean, forming the Ring of Fire.
The deepest point can be found in the Mariana Trench at Challenger Deep, which reaches a depth of 35,830 feet (10,920m) below sea level.
Oceanic trenches are formed by subduction, where one tectonic plate is pushed beneath another as its mantle cools.
Ocean Floor Composition
The composition of the seabed varies according to location and origin, from eroded land or sand to decomposing sea creatures and material from outer space.
As a general rule, there are four different types of sediment: Terrigenous, biogenous, hydrogenous, and cosmogenous, which sit on top of the oceanic crust.
Terrigenous Sediment
Terrigenous sediment is the most abundant sediment type found on the ocean floor and describes sediment from continents that have been eroded by rain, rivers, and glaciers, as well as sediment such as dust that has been blown into the ocean.
Biogenous
Biogenous sediment is made up of the hard remains of ocean creatures, which consists mainly of phytoplankton and other crushed-up biologically produced material such as bone and shell.
Biogenous sediment makes up the second-largest composition of seafloor sediments. These sediments contain at least 30% biogenous material and are known as “oozes,” which are further broken into Calcareous oozes and Siliceous oozes.
Hydrogenous
One of the more uncommon ocean floor sediments, hydrogenous sediment, is created by chemical reactions that take place in the ocean with specific condition changes such as a rise or fall in temperature or pressure.
Hyrogenous sediments are formed from dissolved chemicals in seawater that precipitates out under changing conditions.
Many hydrogenous sediments, such as manganese nodules, have economic value.
Cosmogenous
The least common of the ocean bed sediments are those that come from outside of our planet.
Cosmogenous sediment includes material from comets, asteroids, and other space debris that have impacted Earth.
These sediments usually comprise of silicates and other metals, some of which are not naturally found on our planet.
Seabed Biodiversity and Ecosystems
The depths of the ocean floor can vary, and with this variation of depths comes a large array of biodiversity and oceanic life that inhabit some of Earth’s most outstanding landscapes.
Organisms that live on, in, or near the floor of the ocean, lake, or river are known as benthos, as they dwell in the benthos (the depths of the sea).
In other words, benthic animals can be described as “bottom dwellers.”
The biodiversity of the seafloor drastically changes as we move to deeper levels.
This is mainly due to the lack of light that is able to penetrate the deepest depths.
Along the intertidal zone and continental shelf tend to have a high diversity of oceanic life, including coral reefs and kelp forests, which host an array of bottom-dwelling fish such as flatfish like flounders and halibuts, mollusks, crustations, and invertebrates.
As depths increase, the type of life changes.
With less light, plants can’t photosynthesize, which greatly limits deep-sea species. That said, some organisms have adapted to living in these dark, cold environments.
Cnidarians, such as deep-sea jellyfish, deep-sea fish, such as anglerfish, gulper eels, tripod fish, and various types of worms, are more common in deeper parts of the ocean.
The diversity of the ocean bed and its benthic communities can vary depending on the seabed composition, location, depth, and temperature, but regardless, they play a crucial role in nutrient cycling and as a base for the greater food web.
Environmental Challenges on the Ocean Floor
Although so much of it is unexplored, and the life that it supports is crucial to the larger ocean ecosystem, the seabed still suffers from many of the environmental challenges that have plagued the rest of our planet.
Because the seafloor is largely unexplored and difficult to reach for prolonged periods, the condition of the ocean bed is a major concern.
Habitat Destruction and Loss of Biodiversity
Human activities, particularly unsustainable fishing practices such as deepsea fishing that involves trawling and dredging, have caused incredible amounts of habitat destruction on the ocean floor around the globe.
Trawlers rip up the deep ocean floor, regardless of what lives there. This can devastate a benthic community and often entirely wipes out sections of otherwise dense biodiversity.
The destruction of these habitats leads to a loss in biodiversity, which in turn affects the greater food web, whether it be due to a lack of food, nutrients, or safety.
Deep-Sea Mining
With the discovery of deep-sea minerals such as oil, gas, gold, silver, manganese, cobalt, nickel, copper, and zinc, large industrial operations n the ocean floor have increased, and with them, so have the levels of pollution and habitat destruction.
Deep seabed mining can lead to sediment plumes and chemical pollutants, which have devastating effects on the benthic ecosystem, as well as on the life of larger ocean-dwelling species.
Pollution and Marine Debris
All water eventually makes its way back to the ocean, and along with it comes all the pollutants of the land.
Chemical contaminants from households, which include heavy metals, pesticides, oil spills, and land sediments that find their way into the ocean, have a devastating effect on marine life.
Furthermore, plastic debris is a major concern for the ocean and its seabed.
Although the world is full of trash-cleanup projects, once plastic makes its way into the ocean, it becomes difficult to remove.
Once it reaches the ocean floor, it becomes near impossible.
It’s estimated that the ocean floor is covered in 14 million tones of microplastic, which is considered to be a conservative estimation that keeps rising.
Microplastics make their way into the diet of sea creatures, often suffocating or poisoning them.
Climate Change
Climate change is something that comes up every time we talk about the threats to the globe, and it affects the ecosystem of the seafloor just as much.
As the global temperature rises, along with it rises the temperature of the ocean.
This, along with altering sea levels, a change in ocean acidification, and changing currents, have profound effects on benthic life.
Coral bleaching is one major concern that arises from global change concerning the ocean floor, but changing conditions can quickly displace benthic communities as their favored habitats begin to degrade or shift.
Lack of Knowledge and Access
Although there have been major scientific advances in the exploration of the deep sea, much is still unknown about the seabed, which has made conservation difficult.
As we don’t understand the deep sea’s processes, it’s difficult to regulate our actions to best secure the life of the ocean’s benthos.
This lack of knowledge is largely due to a lack of prolonged access to many of these areas.
This lack of access has limited cleanup projects and other conservation efforts.
The Economic Significance of the Seabed
Sea depths of the ocean floor are inaccessible to most of us, but that has not stopped humans from taking advantage of its resources, both for recreation, as well as for the larger economy.
Although many of these processes have negative environmental impacts on the seafloor, they remain to be cornerstones in our global communities.
Oil and Gas
The discovery of oil and gas on the seabed has led to major offshore drilling and extraction projects. Oil and gas found in the ocean contribute to approximately ⅓ of the global oil and gas resources and largely contribute to global energy production.
Apart from these valuable resources, oil and gas companies generate large amounts of revenue, which in turn supports millions of jobs for industries that make use of the energy.
Mineral Resources
Manganese nodules, cobalt-rich crusts, polymetallic sulfides, and other valuable minerals are abundant along the ocean floor. These minerals are essential in various manufacturing processes, such as electronics and batteries.
The availability of these minerals not only allows for technological advances but creates job opportunities for an abundance of individuals as the products flow down the production and distribution lines.
Fishing and Aquaculture
The seabed provides a diverse array of aquatic life with commercial value, thanks to its expansive ecosystems.
Shellfish, crustations, corals, and reef fish are caught commercially and by local fishing villages, providing food and a livelihood for many who live along the coast.
With new technological advances and understandings in aquaculture, the nutrient-rich seabed is also used for fish farming, which sustainably supports the fishing industry.
Tourism and Recreation
Ocean tourism is a multi-billion dollar industry, and as technology advances, the industry gets bigger.
Whether it is simply playing in the intertidal zone, exploring through rock pools, snorkeling along a coral reef, or putting on SCUBA gear for some deeper ocean experiences, the seafloor has an abundance of activities for tourists and leisure speakers to enjoy.
Not only does recreational time bring us peace and fulfillment, but the industry itself supports jobs and livelihoods around the world.
Bioprospecting
The ocean floor is vastly unexplored yet rich in biological diversity, much of which has massive value to the pharmaceutical and biotechnological industries.
Bioprospecting refers to the exploration and discovery of potential resources that hold value to these industries.
As the seafloor is hugely unknown, it holds a lot of promise for its potential undiscovered uses.
Horseshoe crabs are one example of how life on the floor of the ocean has changed the pharmaceutical industry.
Submarine Cables
The seabed is host to a huge network of underwater cables that are essential for global communication.
Submarine fiber-optic cables laid on the seabed provide high-speed data transfer, which makes internet connectivity, international phone calls, and other similar services possible.
Renewable Energy
Offshore wind farms and tidal wave technologies are changing the way we produce our energy, providing a cheaper and more sustainable alternative to oil and gas.
The ocean floor works as a location to anchor many of these devices.
Although it’s not the seabed itself that provides the energy, without this safe, stable foundation, many of these renewable technologies would not be possible.
Regulations and Governance of the Seabed
The regulations and governance of the sea floor include a complex network of agreements between international parties such as organizations and governments, which includes national laws.
These laws are governed by the United Nations Convention on the Law of the Sea (UNCLOS) and administered by the International Seabed Authority (ISA)
The UNCLOS establishes the legal framework with regard to the ocean, including the seabed.
The ISA, on the other hand, deals with regulations such as seabed mining activities in international waters, issuing licenses, and promoting sustainable practices.
Research and Exploration
Research and exploration of the ocean floor have provided scientists with crucial knowledge and resources for understanding marine ecosystems, and larger geographical movements and have provided a plethora of resources below the earth’s crust that were once unknown.
Sonar systems (using echos), remotely operated vehicles (ROVs), deep-sea submersibles, and other innovative technology is used by biologists, geologists, oceanographers, and several other scientific disciplines to explore the ocean’s deepest environments.
Collaboration between global parties, including governments, educational institutions, and organizations, has brought a larger understanding of the ocean’s processes which guides conservation and sustainability efforts, as well as brings a sense of togetherness between the separate nations.
FAQs
Has anyone explored the ocean’s deepest seabed?
The first descent into The Challenger Deep (Mariana Trench) was made in 1960 by Jacques Piccard and Navy Lt. Don Walsh. Since then, several expeditions have been carried out using ROVs and other advanced equipment.
What lives on the deepest ocean floor?
Life at the deepest ocean bed is scarce, but according to the NOAA, even there, you can find tiny single-celled organisms called foraminifera, which is a type of plankton. Along with these, shrimp, marine worms, and sea cucumbers may also be found.
What is the most interesting thing discovered on the seafloor?
The seabed has been full of incredible discoveries, from coral reefs to ocean oil vanes. One discovery worth noting is that of hydrothermal vents, which are packed full of life and peculiar organisms.
What’s the biggest scientific discovery found on the seabed?
Exploration of the ocean floor has bought countless scientific discoveries, and along with those came evidence of tectonic plate movement theories, as well as bought groundbreaking discoveries in the medical industry.
