More than 70 percent of the Earth’s surface is covered by water and it is sometimes referred to as “the blue planet.” Most original life forms evolved in the ocean, and to this day, the marine environment maintains a biodiversity not found in any other ecosystem. Humans are highly dependent on the ocean.
The expression “the seven seas” was used in the past by sailors who sailed across all the world’s oceans. These include the North Pacific Ocean, South Pacific Ocean, North Atlantic Ocean, South Atlantic Ocean, Arctic Ocean (Northern Ocean), Southern Ocean (Antarctic Ocean), and the Indian Ocean. The world ocean, also known as the oceans, is defined as the interconnected water area surrounding the Earth’s continents. The world ocean is divided into three oceans: the Pacific Ocean, the Atlantic Ocean, and the Indian Ocean, with the Pacific Ocean being the largest, covering over 30 percent of the Earth’s surface. Sometimes, the Antarctic Ocean is also considered a separate ocean. The three oceans include delimited seas or sub-seas. A sub-sea or semi-enclosed sea is a delimited part of an ocean. For example, the North Sea, the Arctic Ocean, and the Mediterranean Sea are sub-seas of the Atlantic Ocean.
Several of the world’s seas are relatively warm, but the average temperature of the world’s oceans is only around 3.5 degrees Celsius. This is because the large deep-water basins consist of cold polar water.
A large portion of the open sea areas does not belong to any individual country and is often referred to as the “high seas” or deep sea. These areas constitute almost half of the Earth’s surface, two-thirds of the world’s ocean area, and 95 percent of the world’s ocean volume. The deep sea is not subject to national laws and, in practice, belongs to everyone. The United Nations has long negotiated how these areas should be managed. After more than ten years of intense negotiations, the UN adopted a new binding treaty for the sustainable use of biodiversity in areas beyond national jurisdiction in 2023. This is a step towards fulfilling the global commitments of the international biodiversity agreement from 2022, where the goal is to protect at least 30 percent of the ocean by 2030.
Despite the ocean being a place where various organisms thrive, there are many extreme environments in the sea. From temperatures below freezing to near boiling points in hot underwater springs. Where the sea meets the land, the waves are powerful, UV radiation is high, and it is home to a large biodiversity. Some organisms utilize a wide range of habitats, while others specialize in a single type of environment.
The deep sea is a hostile environment for us humans. At a depth of 30 meters, most light is gone, at 70 to 80 meters, most of the oxygen disappears, and the pressure at the bottom is high. Therefore, very little of the deep sea has been explored. In fact, barely five percent of the ocean’s depths have been explored by humans. Researchers also know less than they would like about the organisms that can live in the deep sea. Moreover, they cannot be brought up and studied in aquariums or laboratories because they are adapted to withstand the high pressure in the depths of the sea.
To live in the depths of the oceans, where light does not reach, animals must adapt to life in darkness. Many have large mouths, light organs, or large and extra light-sensitive eyes. There is also a diversity of microorganisms living in this challenging environment. The fact that life can exist under such extreme conditions without oxygen or sunlight has led researchers to consider that there might be life on other planets that we have previously thought to be lifeless.
Although we still know very little about the organisms of the deep, it is known that overfishing and bottom trawling can also affect deep-sea animals. Many organisms are still undiscovered and therefore at risk of disappearing if fishing continues as it has done so far.
The Mariana Trench in the Pacific Ocean is the world’s deepest place in the sea. The maximum depth is Challenger Deep, which is approximately eleven kilometers below the sea surface. At the same time, the average depth of the world’s oceans is about 3700 meters. Sweden’s deepest point is 560 meters in Bratten in Skagerrak, and the Baltic Sea’s deepest point, Landsort Deep at 459 meters, is west of Gotland.
Ecosystem services
The world’s oceans and seas are a significant asset for us humans. The oceans provide us with a multitude of services. To remind us of the importance of the oceans and the need to protect them, June 8th has been designated as World Oceans Day by the United Nations. But there are more reminders of how important the ocean is in our daily lives.
World oceans give us more than just food. They produce more than half of all the oxygen in the atmosphere through photosynthesis, absorb greenhouse gases, and contribute to tourism. Some well-visited tourist destinations at sea include Gotland, the Koster Islands, and other archipelago areas.
Additionally, hundreds of millions of people depend on fish and other resources from the sea. More than 38 million people are employed in the fishing industry worldwide. The oceans are also widely used as transportation routes.
Coastal ecosystems such as coral reefs, seagrass beds, and mangrove forests are crucial places for the young. They are also significant for people living on the coast as they act as a protection zone against floods, storms, and can serve as wave breakers and erosion protection.
TEXT: Lina Mattsson
Ecuador has extended the marine reserve around the Galapagos Islands to protect sharks, whales, turtles, rays and other species.
She has researched life under the Arctic's last intact ice – a place where no one has done research before. "We will map an unknown ecosystem," says marine biologist Pauline Snoeijs Leijonmalm
Every evening, as darkness descends upon the sea, millions of fish, crustaceans, and octopuses leave the ocean depths and rise to the surface, and when dawn comes, they return down into darkness. This is the largest known migration in the animal world. The cause, according to a new study, is fear of sharks, dolphins and other predators that hunt with the help of vision
The fossil of a giant sea reptile with a skull the size of a grand piano has been discovered in Nevada. The find is 246 million years old, which as far as we know it makes the creature the first giant animal on our planet
The Great Barrier Reef is larger than Finland, and it is still bursting with life. But climate change poses several kinds of threats to the future of coral reefs
After a protracted dispute over who will be allowed to fish what, an agreement for 2022 has been reached between the UK and the EU. The agreement is receiving criticism from environmental organizations who believe that short-term financial gains are more important than long-term consequences for the environment and fish stocks
Decisions have been made to protect the disputed coastal area of Exmouth Gulf in Western Australia, where humpback whales, whale sharks and dugongs, among others, have been threatened by planned construction projects. Instead of a salt plant and industrial port, it will be a nature reserve and a marine park
Underwater photography in Northern Norway heads below the surface to film killer whales and humpback whales eating herring. They also dive at night and meet other inhabitants of the Arctic Ocean
A new Danish research report shows that in recent years, 65% of all cod caught in trawlers' nets during lobster fishing have been discarded
EU fisheries ministers have agreed on fisheries in the Atlantic, including the North Sea, the Skagerrak and the Kattegat, next year. Environmental organizations are critical of parts of the agreement. France, Spain and Portugal in particular are singled out as irresponsible
In this second part of the reportage series from Northern Norway, we follow underwater photographer Johan Candert under the surface as he tries to film humpback whales, and he talks about what a challenge it is to capture the large fast animals with the camera during the few bright hours of the day
More than a thousand sea cows have died in Florida this year, many of them starving to death due to environmental degradation. Now a previously completely unthinkable measure is being considered – feeding the wild mammals with cabbage and lettuce in order for them to survive the winter
Scientists have established that some form of marine life lives in 90 percent of the larger plastic objects in the vast garbage area of the Pacific Ocean. They fear that it could have negative effects on marine ecosystems
Johan Candert had been diving and filming underwater for 25 years, but had never seen killer whales or whales in the oceans before. Recently, he returned from an expedition to the Arctic Ocean where he got to meet both species up close
On Tuesday night, researchers found that the corals send sperm and eggs into the Pacific Ocean to multiply. "It's gratifying to see the reef give life," said marine scientist Gareth Phillips
For 16 years, the puffin population has declined in Vestmannaeyjar, Iceland. Until this year. Now the scientist believes that the bad trend can reverse
At the forefront of climate change is Tonga – an island nation in the Pacific Ocean where rising sea levels, warmer waters and tropical cyclones pose an increasing threat. "The sea is everything to us. But it's on fire," the country's delegate Uili Lousi told TT [Tidningarnas Telegrambyra] at the climate summit
During an expedition in northeastern Greenland, we met arctic researcher Mie Winding. She studies the microscopic creatures that are necessary for all life in the oceans. Here she explains how the oceanic food chain works, and how the shrinking of the sea ice and the melting of the glaciers affect the entire ecosystem in the Arctic
Talks replace confrontation as France and Britain try to resolve the recent fishing dispute. New discussions await next week
Britain's stance on the fishing dispute with France remains unchanged after day two of negotiations on the issue
Britain's foreign minister is giving France 48 hours to withdraw its threats in the row over fishing licences in British waters that erupted after Brexit. France believes it has obtained too few licences and has threatened British fishermen with tighter controls and stops to unload fish in French ports
France threatens Britain with trade squabbles within days of brexit fishing permit dispute
About 30 percent of the world's undiscovered gas resources and 13 percent of the world's undiscovered oil resources are estimated to be north of the Arctic Circle. Sweden now leads meeting on ocean protection in the Arctic
Simon Stanford met climate researcher, professor Mikael Sejr of the Greenland Ecosystem Monitoring Program. He shared some of the insights into climate change he and his team have gained over the 23 years that have worked in this remote and sensitive environment
