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 Baltic Sea countries will strengthen the monitoring of underwater cables and ships. The Coast Guard will be the Swedish hub for sharing information and protecting cables. ‘Together, we will become sharper and more powerful in detecting and responding to various incidents, especially those related to cable security,’ says Lena Lindgren Schelin, Director General of the Coast Guard.
Ocean Devotion: Nuno Sá: ‘We need the sea’ Nuno Sá is one of the world's leading underwater photographers, with around twenty awards from the world's biggest nature photography competitions.
Tuna is usually caught using longlines, which the UN has classified as the fishing method with one of the highest levels of bycatch of all gear types. On average, bycatch in longline fishing accounts for more than a quarter (28%) of the total catch. Not only tuna are caught in the hooks, but also sharks, sea turtles, swordfish, seabirds, dolphins, juvenile fish, and other fish species. In the Azores, they have taken a different approach. By combining centuries-old craftsmanship with a large network of marine protected areas, they have managed to achieve both large catches and more fish remaining in the sea.
Since 2023, the fourth global mass bleaching event affecting the world's coral reefs has been underway. It is the most extensive and deadly one to date. And for those who have devoted years of their lives to try to preserve them, the devastation is difficult to cope with.
A few weeks ago, the British government released a report written by the country's intelligence service. They have assessed the consequences of the climate crisis and show how the impending collapse of ecosystems and loss of biodiversity pose a direct threat to Britain's national security. The report is addressed to the British government, but the security risks do not remain within any national borders.
Deep Sea Reporter examines bottom trawling in marine protected areas – part two. As a national park, Kosterhavet is covered by Sweden's strongest nature conservation laws. On paper. In practice, extensive bottom trawling for shrimp is taking place, a fishing method that is considered one of the most destructive in the world.
År 2025 blev det tredje varmaste året som registrerats. Det slår EU:s klimattjänst Copernicus fast i en ny rapport. För första gången har planetens medeltemperatur legat över 1,5 graders uppvärmning under tre sammanhängande år. En av platserna där det märks som mest är Antarktis.
Early in 2025, Holden Harris, Ph.D. was one of the hundreds of U.S. National Oceanic and Atmospheric Administration (NOAA) employees fired by the Trump regime. Almost one year later, Trump wants to slash budgets for scientific and climate change research. But Congress has pushed back, passing a package of bills to maintain most research funding. The deadline for a budget agreement is January 30th. This is Holden Harris’s story.
The Netherlands has failed to protect the inhabitants of the former colony of Bonaire from climate change, according to a ruling by the District Court in The Hague. ‘This gives island states a boost,’ says researcher Björn Ola Linnér.
It is well known that large amounts of rubbish float through Europe's rivers. But when researchers took a closer look at one of the continent's most important waterways, they made an unexpected discovery – the problem is much bigger than previously thought.
Three people, including two children, have been attacked by sharks in the waters around Sydney in a short period of time, according to the emergency services in the Australian city.
The Azores are a self-governing Portuguese enclave consisting of nine volcanic islands scattered across the Atlantic Ocean. Here, they have succeeded in creating something that very few countries have even begun to attempt: designating at least 30 per cent of the sea off their coast as marine protected areas. They have already achieved the UN's goal of protecting 30 per cent of their sea area.
Over 200,000 cod have died at a fish farm in Nordland, Norway. A new virus is behind the mass deaths.
The Norwegian Ministry of Energy has awarded shares in 57 new licences for oil and gas extraction on the Norwegian continental shelf, the authority writes in a press release.
The Kunming-Montréal Framework was adopted at CBD COP15 in Montréal in 2022. By COP16, all countries were to develop an action plan on how to implement the targets included in the biodiversity framework, including the target of protecting 30 per cent of nature in the oceans and on land. Three years later, Sweden still does not have such an action plan.
The ship Fitburg, which was seized by Finnish police last week, will be escorted out of Finland into international waters on Monday, according to the National Bureau of Investigation.
The strategic importance of the Arctic is only growing, according to NATO's Supreme Allied Commander in Europe, American General Alexus Grynkewich. And Sweden plays an important role there.
Several species of large whales in the North Atlantic carry a potentially deadly virus. This is according to a study in which researchers used drones to examine the exhaled air of these enormous animals.
Deep Sea Productions is currently working on a film series that will be shown on IMAX and Giant Screen theatres worldwide. The film work has required many long flights and taken the team along dangerous roads to remote locations. Packing for such an expedition must be meticulously checked; absolutely everything must be included from the outset. Far out at sea, it is not possible to call for a forgotten battery to be delivered, for example. Simon Stanford heads up film production at Deep Sea Productions. Come along as Simon takes you behind the camera – where it can sometimes be more exciting than in front of it.
Finland märker ingen minskning av rysk oljeexport genom Östersjön. Däremot har riskerna ökat när skeppen i ”skuggflottan” blir allt skraltigare, och sjönavigation störs ut i den trånga Finska viken. - Det värsta scenariot vore en kollision med en fullsatt Finlandsfärja, säger kommodor Mikko Simola ombord på bevakningsfartyget Turva.
More than 3,000 migrants died in 2025 while attempting to reach Spain, according to a report. According to the organisation behind the report, this is a sharp decrease compared to the previous year.
The term “Conservationist” is not a legally protected title like “lawyer” or “doctor” is, and that is a good thing. It allows for people like Hans Saleo to be recognized for the important work he is doing to protect the manta rays, even without the formal credentials.
A research project has engaged more than a thousand volunteers in a large-scale survey of plastic bottles on beaches along the Central and South American Pacific coast, as first reported by Mongabay. The researchers behind the study advocate the introduction of a deposit system.
For the first time in half a century, Sweden is investing in large modern warships. The new frigates cost billions and can hunt submarines, act as floating air defence and secure the vital sea route to Sweden.
