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
The challenges of wrestling fifteen flight cases loaded with film equipment and dive gear from Stockholm to the Galapagos islands are forgotten the instant we emerge from the airport into the sunshine of Baltra island
Many Norwegian children probably cried themselves to sleep on Sunday 14 August 2022. In the early hours of the same morning, the popular walrus Freya was killed on behalf of the Norwegian authorities
For me, the sea has meant beautiful beaches back home in Brazil or a cold swim in Stockholm. Not much more. But my work for Deep Sea has given me a new perspective on the oceans
The manatee is a large marine mammal that lives in springs, rivers and shallow coastal inlets, including around Florida. Humans are the only serious threat to them and recent years have been difficult, with many animals killed in boat collisions and due to debris. Now, in addition, eutrophication in the sea is threatening their food, seaweed, so as an emergency measure they have started feeding manatees in the most vulnerable place.
Sharks and rays have long been considered "silent" fish - that is, unable to produce sound. Researchers from Sweden and Australia have now shown that this is a misconception, writes SLU (Swedish University of Agricultural Sciences) in a press release.
After five hectic days, the expedition has returned to the main island of Santa Cruz to exchange some scientists and crew. At the same time, the expedition is visited by journalists from CNN and Ecuador's Minister of the Environment, who will accompany them down in the expedition's submarine
An overwhelming majority of the world's glaciers are shrinking and many of them could disappear in the not-too-distant future, according to a series of new studies. This means that we may soon experience the same state as during the postglacial warm period 8,000-4,000 years ago
Most people associate walruses with the Arctic Ocean and eternal ice. So when the young walrus Freya was seen in a port on Smögen in March, many people opened their eyes. Two huge males have also been put near Stavanger and in Hammerfest on the northern tip of Norway. How unique is this?
The Faroe Islands will limit the number of dolphins that can be slaughtered, after the traditional hunting has been heavily criticised. Now no more than 500 white-sided dolphins may be killed per year
The Migration of mega shoals of sardine up the east coast of South Africa has been called the greatest shoal on earth. The wild coast on the east coast of
We are going to the northern Norwegian fjord Kvänangen approximately 20 miles north of the Arctic Circle. Fishing boats from all over the Norwegian west coast come to this particular fjord during some intense winter months to fish huge amounts of herring. But there are also other creatures that want the herring. In addition to a number of predatory fish and gulls, an unusually high number of killer whales and large humpback whales have also become increasingly numerous. Sometimes there may be conflict
Ørsted, the world's most sustainable energy company, is now planning the world's first attempt to support coral reefs by growing corals on the foundations of offshore wind turbines. Together with Taiwanese partners, the company will test the concept in Taiwan's tropical waters as early as this summer.
For decades, trawlers from Europe, China and Russia have been draining the sea off the coast of Senegal. With the fish running out, desperate poor people are scrambling to find new ways to survive. More and more people see Europe as a last resort. But that road is hard and expensive to take, and many times people end up back in Senegal again
The dumping of bottom sludge in the Sound has been defended on the grounds that it has only a negligible impact on the marine environment. But several Danish experts are now condemning the environmental impact assessment for the Lynetteholm project, which is based on a 40-year-old, American study, DR reports
Thousands of cod heads are hanging to dry on the quay off Husöy, a small island in the outer coastal strip of northern Norway. They are to be shipped to Africa, because
The Arctic and Antarctic have been 30-40 degrees warmer than normal this week, and heat records have been broken at at least one weather station. It's not a good sign when you see stuff like this happen," said University of Wisconsin meteorologist Matthew Lazzara
Mozambique plans to plant 100 million trees along its coast. The country in southeast Africa is severely beset by both tropical storms and rising water levels
Climate change is a major threat to coral reefs. But some coral species appear to be in a better position to withstand and survive in a warmer ocean – if global warming is limited to 2 degrees, according to a study published in the journal Scientific Reports
For the first time, we will now find out what happens during the winter, with carbon dioxide uptake and salinity and thus get more accurate data to put into different climate models to get more accurate predictions about the future
Two million tonnes of partially contaminated sludge and mud from the construction of the artificial island of Lynetteholm in Copenhagen are currently being dumped in the Sound. Now criticism is growing in both Denmark and Sweden where there is concern for the marine environment
Fishermen risk being left without income and with damaged fish stocks after the oil leak that occurred near the coast of rayong province in eastern Thailand on Tuesday
Plastics in various forms in the sea, and their effects on the environment, have been the subject of much research and debate. But nanoplastics - pieces so small we can't see them with the naked eye - are less well known. A research team that has investigated these particles can now conclude that plastic has been in the polar ice cap for a long time
Between 20 and 50 tons of crude oil have ended up in the ocean since a pipeline began leaking about two miles from popular beaches in Thailand, among other places
Penguins, sea lions and seabirds have died and fishermen have lost their income after an oil disaster in Peru - triggered by the eruption of a volcano in Tonga hundreds of miles away. 21 beaches on the Pacific coast have been polluted by the oil leak and an environmental emergency has been declared
