Our planet relies on the oceans as climate regulators. At the same time, the effects of our emissions are most evident in the oceans. Today, eutrophication, climate change, ocean acidification, and invasive species are some of the challenges the oceans face. The Ocean – A key player in climate
The oceans are already significantly impacted by human activity, making them sensitive to further influence from climate change. Habitats of species may disappear, shift, or shrink, while others gain access to new distribution areas. This can lead to a reduction in biodiversity, exacerbating the oceans’ resilience against, for example, climate change.
According to the International Panel on Climate Change (IPCC), over 90 percent of excess heat and between 20 and 30 percent of carbon dioxide emissions have been absorbed by the oceans. Carbon dioxide is absorbed by the oceans as the gas dissolves in water, and phytoplankton in surface waters take it up and bind it in organic material through photosynthesis. Phytoplankton are then consumed by zooplankton, which, along with other organisms, fall towards the ocean floor as marine snow when they die. This process allows large amounts of carbon from the upper layers of the ocean to reach deeper layers which is crucial for the organisms there. The transport of carbon to the bottom also ensures that it remains in the oceans much longer than if it were to stay in the surface layer, potentially leaking carbon dioxide back into the atmosphere.
One effect of increased emissions of greenhouse gases is ocean warming. When the oceans become warmer, the entire ecosystem is affected. Fish size may change, algal blooms and dead zones increase, and many species such as eelgrass, harbor seals, and mussels struggle to survive. Furthermore, as water becomes warmer, it becomes more challenging for the oceans to absorb carbon dioxide, potentially worsening climate change further.
The warming of the oceans is now the fastest in at least 11,000 years. Although it can be slowed down with powerful measures, the stored heat energy contributed so far will continue to warm our planet for hundreds or even thousands of years.
The oceans play a large role in how we experience the climate on our planet. Thanks to the Gulf Stream, Nordic countries for instance have a relatively mild climate in relation to their northern positions. Warming of the seawater leads to significant changes in ocean circulation and rising sea levels as the ice in the ocean’s melts. The decrease in ice is more pronounced in the northern hemisphere than in Antarctica, and research indicates that the ice will continue to melt for at least 100 years, regardless of the measures taken. However, the effects worsen with the more greenhouse gases we emit. Many scientists are concerned about how the Earth will be affected when the Arctic ice disappears, as it affects the climate by reflecting solar radiation.
Climate change will affect the salinity of the oceans. In areas near the equator, evaporation will increase, leading to an increase in salinity. In areas closer to the poles, such as the Swedish seas, salinity will decrease as precipitation and the influx of freshwater increase and polar ice melts.
Changes in salinity and temperature can, among other things, lead to increased oxygen deficiency. This is because the stratification of seawater in depth becomes clearer, preventing mixing and transport of oxygen-rich water to the bottom. Salinity and temperature also largely control the geographic distribution of species, meaning that climate change can have significant consequences for biodiversity.
The absorption of carbon dioxide by the oceans has almost doubled since the 1980s, but it has come at a cost. When carbon dioxide is mixed into the water column, the chemistry of the ocean changes. A higher concentration of carbon dioxide in the ocean increases acidity, a phenomenon called ocean acidification, sometimes referred to as the “evil twin of warming.” Like the effects of climate change, ocean acidification can lead to the extinction of species or shifts in ecosystems. Studies show that key species such as brittle stars in Gullmarsfjorden would not survive the acidification expected within a few decades. And since many species depend on them, it can have significant consequences for the entire ecosystem.
Ocean acidification affects various biological processes such as photosynthesis and calcification. Many marine organisms are affected by the fact that ocean acidification makes calcium less accessible, as they form shells and skeletons from calcium. Corals are affected by both calcium deficiency and increasing temperature. Coral reefs are one of the ecosystems with the highest biodiversity globally but are also most affected by climate change, leading to coral bleaching. Even the coral Lophelia in Kosterhavet National Park is affected by increased temperature and acidity.
Today, several marine areas, such as the Black Sea and the Baltic Sea, are affected by eutrophication. This is due to increased nutrient input, leading to the proliferation of fast-growing phytoplankton, cyanobacteria, and filamentous algae. This makes it difficult for other species to survive as much sunlight is blocked. When the algae sink to the bottom, bacteria use up the oxygen to break down the organic material. This has resulted in large dead zones in, for example, the Baltic Sea, where only bacteria and a few other microorganisms can survive in the oxygen-depleted environment. Eutrophication leads to overgrown bays, deteriorated water quality, and reduced biodiversity.
While some nutrient inputs occur naturally, human activities contribute significantly by adding extra nutrients in the form of nitrogen and phosphorus. Agriculture, sewage, industries, forestry, road traffic, and shipping all contribute to eutrophication. Because eutrophication in the Baltic Sea has been ongoing for so long, there are old sins in the form of nutrients bound in sediment. Internal loading is a process where these nutrients are released, mainly when there is limited oxygen at the bottom. Eutrophication thus creates a negative spiral where the system eventually feeds itself.
Although the eutrophication status is still poor in most parts of the Baltic Sea, improvements can be seen in the Gulf of Finland, Kattegat, and the Belts. According to the Helsinki Convention, HELCOM, nitrogen inputs have decreased by 19 percent, and phosphorus by 24 percent since the mid-1990s. To further reduce the impact of eutrophication, the main sources, namely agriculture and wastewater, should be controlled.
Many environmental toxins have decreased significantly since the 1970s. However, society’s extensive use of chemicals needs further reduction. History speaks clearly: actions make a difference.
Almost all toxic substances released into nature are considered environmental toxins. Some of these can harm animal and plant life even at low levels if they persist for an extended period. Environmental toxins often break down slowly, meaning their effects can be both long-lasting and spread over large areas. Some common environmental toxins include mercury, lead, cadmium, tributyltin (TBT), DDT, PCB, and dioxins.
Most organic environmental toxins are fat-soluble and therefore accumulate in the fat tissue of various organisms. Toxins accumulate to a greater extent the higher up the food chain you go. Therefore, top predators, often suffer more from environmental toxins than prey animals. When humans eat fish that have stored environmental toxins, they ingest these toxins. This has led to specific dietary recommendations for pregnant women, children, and young people when it comes to fatty fish.
White-tailed eagles and seals were heavily affected by environmental toxins during the 1960s and 70s because they are long-lived animals high up in the food chain. The white-tailed eagle was close to extinction because the chicks did not survive. Seals in the Baltic Sea struggled to reproduce, and in combination with hunting, environmental toxins led to only a few thousand seals remaining. After measures were taken to reduce the levels of environmental toxins, white-tailed eagles and seals in Sweden increased.
But despite the prohibition of PCB and many measures aiming at reducing the spread of environmental toxins, the levels are still relatively high. Some dioxins are considered some of the most dangerous environmental toxins as they can affect the development of our brain, immune system, nervous system, and the ability to have children. This is due to their long-lasting nature and the existence of emission sources that Baltic Sea countries have not yet addressed. Additionally, humans constantly introduce new chemicals that risk reaching the oceans.
A common pollution in the oceans today is plastic. In the oceans, more than around 150 million tons of plastic float, increasing by 5 to 13 million tons each year. Estimates show that 80–85 percent of marine litter in the EU consists of plastic. Of this, 50 percent are single-use products, and 27 percent are fishing-related items. Lost fishing gear, such as nylon nets, often float around as death traps for animals, known as ghost nets. Whales, seals, seabirds, and other animals can get entangled in these and die.
To try to reduce the problems of plastic waste in the oceans, the EU introduced a directive against single-use plastics in 2021, prohibiting the sale of plastic straws, among other items. Since it takes several hundred years for plastic to break down in the ocean, it instead slowly disintegrates into smaller parts, eventually becoming microplastics. Microplastics are also flushed into the oceans from wastewater treatment plants, often originating from fabrics made of synthetic materials and additives in hygiene products and cosmetics. About 10–30 percent of plastic particles elude capture by wastewater treatment plants and end up in the oceans. If animals ingest microplastics, they can be harmed or poisoned. Additionally, when they consume plastic, a false sense of being full occurs, leading to malnutrition. In water, plastic particles act as magnets for bacteria and environmental toxins, which animals ingest.
Although no significant risks for the environment and health have been found with current concentrations of plastics, knowledge gaps are significant. This currently prevents any conclusive statements about the risks of microplastics.
TEXT: Lina Mattsson
When this year’s seal hunt begins on Monday, 1,350 gray seals, 200 harbor seals, and 200 ringed seals may be hunted. That is more than last year, and the increased quota has outraged the Swedish Society for Nature Conservation, which believes the seal population is at risk in the long term.
In February 2026, historically low water levels were recorded in the Baltic Sea, in some places, the lowest in almost 100 years. This was mainly due to a stable high-pressure system and strong easterly winds over Scandinavia, which pushed water out of the Baltic Sea. There was hope that fresh, oxygen-rich and salty water would flow in from the North Sea to the heavily tested inland sea and its oxygen-depleted seabed – but that did not happen. Find out why in the news report.
Penguins in Argentine Patagonia can act as environmental monitors. In this way, researchers have discovered that PFAS – so-called ‘forever chemicals’ – are present even in this remote region.
From 3 April this year, commercial fishing is permitted within the Northeast Canyons and Seamounts Marine National Monument. The area, which covers a surface area as big as Connecticut, is located in the Atlantic Ocean off the US east coast and was established to protect and preserve these unique and pristine marine environments for future generations.
This is the story of what went on behind the scenes as we filmed our report on bottom trawling in Sweden’s Gullmarsfjorden. With the help of Voice of the Ocean (VOTO) and MidOcean, we ventured out into the fjord and filmed using both an ROV and deep-sea divers.
As far as we know, our planet is unique. Amongst other celestial bodies, a beautiful ‘blue ball’ floats there, where we – you and I and all living things on Earth – get to spend a short while. In the coming days, we will see beautiful new images sent back by the Artemis II lunar spacecraft. Artemis is, among other things, considered the protector of the wilderness in Greek mythology.
This is the extended version of the author talk with British writer Robert Macfarlane, who is described as the foremost nature writer of our time. In his latest international bestseller, *The River’s Life*, he urges us to fundamentally rethink our way of thinking. What happens if we shift our focus away from the prevailing anthropocentric view – that the Earth’s resources exist solely for our benefit?
The British author Robert Macfarlane is described as the foremost nature writer of our time.
From drones and smart cameras to biodegradable packaging, EU-funded researchers are working to remove plastic from rivers before it ever reaches the sea.
The European Commission is presenting new guidelines on how Sweden and other countries can tackle growing cormorant populations. “We are continuing to protect birds and fish, whilst providing farmers, fishermen, foresters and businesses with practical and balanced rules,” writes Environment Commissioner Jessika Roswall in a press release. ”Vi fortsätter att skydda fåglar och fisk och ger samtidigt bönder, fiskare, skogvaktare och företag fungerande och balanserade regler”, skriver miljökommissionären Jessika Roswall i ett pressmeddelande.
Sharks off the coast of the Bahamas have tested positive for caffeine, painkillers and even cocaine, according to a new study.
Few would say there is anything beautiful about an oil platform far out at sea. But if you dive beneath the surface, the picture is often quite different. Reefs may have formed around the platform’s foundations, teeming with soft corals, fish and other marine life. In 2018, two marine biologists from California, Amber Sparks and Emily Hazelwood, founded the Blue Latitudes Foundation to save these soft coral reefs.
Everything points in the wrong direction. Never before has the Earth’s climate been so out of balance, warns the World Meteorological Organisation (WMO).
Keep Sweden Tidy has been working with various partners in Finland and Estonia to remove abandoned fishing gear from the Baltic Sea. At the same time, it has been raising awareness of the problem of ghost nets, amongst other things, among recreational anglers and the general public. Over the three years the project has been running, nearly 9,000 metres of ghost nets and over two tonnes of lost fishing gear have been retrieved from the sea.
Every year, a climate barometer is commissioned by WWF to present the views of different social groups on specific election issues. An ongoing study in Lund and Örebro shows preliminary figures suggesting that young people have put the climate issue behind them. Deep Sea Reporter spoke to young adults in Stockholm about their thoughts on the ocean and climate.
For decades, the sea ice around Antarctica expanded every winter, only to shrink rapidly in 2015. Now, a study reveals what has caused this drastic change. Elephant seals have helped with the measurements.
As the oceans warm, it becomes harder for fish in mangrove forests to breathe. This is shown by a unique new study from researchers at the University of Gothenburg. ‘In some systems, conditions will become so extreme that only the most adapted species will survive,’ says the study’s lead author, marine chemist Gloria Reithmaier.
The Swedish Parliament has decided to ban bottom trawling in marine protected areas. The ban is due to come into force on 1 July this year. At the same time, they have made room for exceptions, and the Swedish Agency for Marine and Water Management (HaV) is now proposing that this should apply to Kosterhavet National Park.
It may be some time before the two vessels, which are suspected of being part of the Russian shadow fleet, are able to leave Swedish waters. ‘It will probably not happen quickly,’ says Mattias Lindholm, press officer at the Swedish Coast Guard.
President Donald Trump is calling on other countries to send warships to join the US in securing oil shipments through the Strait of Hormuz, which is under threat from Iran. Meanwhile, attacks on Iran – and Iranian counter-attacks – continue.
The search for sites in Sweden where carbon dioxide can be stored beneath the seabed has been underway for three years. Two potential sites have now been identified. ‘We've received some excellent samples and the results so far are very promising,’ says Sofie Lindström of the Geological Survey of Sweden (SGU).
Part three of our investigation into marine protected areas. Saltströmmen is world famous. It has the world's strongest tidal current, which has given rise to a rich fish life that has attracted recreational fishermen from all over the world. However, fish stocks have declined sharply, and this seems to be due to increased fishing pressure from recreational fishermen.
As the war between the United States and Iran enters its third week, it is clear that the intensified fighting is also having devastating consequences for the fragile marine life in the Persian Gulf and the Gulf of Oman.
Several ships have been subjected to suspected attacks in connection with the Strait of Hormuz, according to the British maritime security organisation UKMTO. French President Emmanuel Macron is calling on the G7 countries to restore traffic in the important strait ‘as soon as possible’.
