Como as águas mais quentes influenciam desde o sumiço das ostras à chegada precoce de baleias no Brazil

by Ana Menezes

 Pesquisadores apontam que o aumento da temperatura do mar já altera a migração de baleias, ameaça cultivos de ostras e impacta a pesca e o litoral catarinense

 

 O mar de Santa Catarina está mudando — e os impactos já começam a aparecer na economia, na biodiversidade e até em símbolos culturais do Estado, como as baleias-francas e as ostras cultivadas em Florianópolis.

 

Nos últimos anos, pesquisadores vêm observando o aumento gradual da temperatura das águas do Atlântico Sul e mudanças importantes no comportamento dos ecossistemas marinhos. Em Santa Catarina, especialistas alertam que os efeitos das mudanças climáticas já atingem a pesca, a maricultura, o turismo, a erosão costeira e os ciclos migratórios de espécies marinhas.

Em 2026, as primeiras baleias-francas chegaram ao litoral catarinense ainda em maio, antecipando novamente a temporada migratória. No mesmo cenário de mudanças no oceano, produtores de ostras enfrentaram perdas expressivas durante o verão devido à mortalidade dos animais provocada por altas temperaturas da água.

 

Pesquisadores apontam que os fenômenos ainda estão em estudo, mas que o aquecimento dos oceanos já provoca alterações perceptíveis na costa catarinense.

O que causou a morte das ostras?

 

Oceano absorve o calor do planeta

A oceanógrafa física e climatologista da Universidade Federal de Santa Catarina (UFSC), Regina Rodrigues, explica que os oceanos absorvem cerca de 90% do excesso de calor gerado pelas atividades humanas.

Segundo ela, estudos com dados de satélite analisados desde 1982 mostram uma tendência contínua de aquecimento no Atlântico Sul, incluindo o litoral de Santa Catarina.

— Estamos vendo cada vez mais períodos em que a temperatura do mar fica muito acima do normal — afirma.

 A pesquisadora explica que o aquecimento global atua junto de mudanças atmosféricas regionais. Entre elas, estão os chamados bloqueios atmosféricos, que reduzem a passagem de frentes frias, deixam o inverno mais seco e aumentam a incidência solar sobre o oceano.

 

— Santa Catarina está entrando mais no clima do Sudeste. Esses bloqueios, que antes eram mais comuns lá, estão se expandindo para o Sul — diz.

Fenômenos como o El Niño podem potencializar esse cenário, já que favorece a formação desses bloqueios atmosféricos e altera os padrões de chuva e temperatura no Sul do Brasil, conforme a pesquisadora.

Procurada pela reportagem, a Defesa Civil de Santa Catarina informou que não é possível afirmar uma relação direta entre o El Niño e o aquecimento das águas na costa catarinense.

Baleias-francas chegam mais cedo ao litoral

Os reflexos dessas mudanças também podem ser percebidos na migração das baleias-francas. A diretora de pesquisa do ProFRANCA, Karina Groch, explica que a chegada antecipada das baleias ao litoral catarinense ainda é estudada, mas que há forte relação entre alimentação, condições oceânicas e comportamento migratório.

 

As baleias-francas vêm para Santa Catarina principalmente para reprodução. As fêmeas chegam grávidas para dar à luz em águas mais abrigadas e permanecem na região até que os filhotes consigam retornar às áreas de alimentação próximas à Antártica.

Segundo Karina, a principal hipótese para a chegada antecipada desses animais envolve a disponibilidade de krill — pequeno crustáceo que serve de alimento para as baleias e depende do gelo antártico para se reproduzir.

— Quando está mais quente, há menos gelo e consequentemente menos krill. Isso influencia toda a cadeia alimentar — explica.

 Pesquisas do ProFRANCA indicam que alterações climáticas na Antártica podem gerar reflexos na população de baleias que chega ao Brasil até seis anos depois. A hipótese é que a espécie mais bem nutrida consegue completar antes o período de alimentação, iniciando a migração mais cedo.

 

— Tudo indica que o momento da chegada delas está relacionado à disponibilidade de alimento e às condições oceânicas — afirma Karina.

Ela ressalta, porém, que ainda são necessários anos de monitoramento para confirmar tendências e entender se a antecipação da temporada está diretamente ligada às mudanças climáticas ou a fenômenos específicos, como o El Niño.

 

Veja fotos das primeiras baleias-francas de 2026 no RS

Ostras sofrem com calor extremo

Enquanto as baleias antecipam a chegada, a maricultura catarinense enfrenta outro desafio: a mortalidade em massa de ostras provocada pelas altas temperaturas da água.

 

Santa Catarina é o maior produtor do marisco do Brasil, especialmente da espécie Magallana gigas, cultivada principalmente em Florianópolis. Mas a espécie, originária do Pacífico, é adaptada a águas mais frias.

Segundo o professor Rafael Diego da Rosa, do Centro de Ciências Biológicas da UFSC e coordenador do Laboratório de Biotecnologia e Saúde Marinha (LaBIOMARIS), o calor extremo registrado no verão provocou perdas expressivas na produção. No início do ano, produtores de ostras de Florianópolis enfrentam uma das maiores crises já registradas na maricultura local. A mortalidade em massa causada pelo aumento da temperatura da água do mar chegou a até 90% da produção, um índice considerado sem precedentes pelo setor.

O professor explica que o aumento da temperatura da água provoca estresse fisiológico nos animais e pode deixá-los mais suscetíveis à ação de vírus, bactérias e outros microrganismos.

Por conta disso, pesquisadores da UFSC, em parceria com instituições do Brasil, França e Chile, criaram uma rede internacional de pesquisa para investigar os fenômenos de mortalidade das ostras e a relação deles com as mudanças climáticas.

 

— Queremos entender se o que está matando as ostras é um fator ambiental, infeccioso ou uma combinação dos dois — diz Rafael.

“Ostras verdes” e novas florações

Outro fenômeno recente chamou atenção de pesquisadores e produtores: o

aparecimento

das chamadas “ostras verdes” em cultivos do Sul da Ilha.

O fenômeno ocorre quando uma microalga azul-esverdeada é filtrada pelos moluscos e pigmenta as brânquias dos animais. A mesma ocorrência já é conhecida na França, onde as ostras verdes são consideradas uma iguaria gastronômica.

Ostras esverdeadas despertaram curiosidade de produtores no Sul da Ilha (Foto: LaBIOMARIS, Divulgação)

Segundo Rafael, o evento já havia sido registrado em Santa Catarina há mais de 10 anos, mas voltou a aparecer recentemente. Pesquisadores agora tentam identificar se a microalga encontrada em Florianópolis é a mesma presente na Europa e quais fatores ambientais favoreceram a floração.

Embora essa microalga específica não apresente riscos à saúde humana, o pesquisador alerta que mudanças climáticas podem aumentar a frequência de florações de outras espécies tóxicas.

— Algumas microalgas produzem toxinas que podem inviabilizar cultivos e representar riscos para o consumo humano — explica.

Tropicalização da costa e impactos na pesca

O aquecimento do oceano também altera o comportamento de diversas espécies marinhas. Segundo Regina Rodrigues, da UFSC, pesquisadores já observam um

processo

chamado de “tropicalização” da costa catarinense: espécies típicas de águas mais quentes começam a migrar para o Sul, enquanto espécies tradicionais da pesca local podem se deslocar para águas mais frias, próximas ao Rio Grande do Sul, Uruguai e Argentina.

A mudança ameaça diretamente atividades econômicas ligadas à pesca artesanal.

— Já houve anos em que a tainha praticamente não apareceu em Santa Catarina, mas os pescadores relataram grandes cardumes mais ao sul — afirma Regina.

O NSC Total ouviu pescadores que relataram à reportagem que não sentiram diferença nos cardumes. Pelo contrário, a safra da tainha de 2026 já entrou para a história na Praia de Cima, na Pinheira, em Palhoça, por exemplo.

Em apenas um mês, o número de peixes capturados praticamente igualou todo o volume registrado ao longo da temporada de 2025. Somente em maio, foram pescadas cerca de 92.986 tainhas, segundo levantamento do grupo Informações da Pesca (IDP), de Florianópolis.

O resultado surpreendeu até os pescadores mais experientes do litoral catarinense. A expectativa inicial era de uma boa safra, mas a quantidade de cardumes que chegou às praias ficou muito acima do esperado.

 

— A Praia de Cima surpreendeu esse ano e ainda tem muita tainha chegando. Pelas informações das

embarcações

que trabalham no alto-mar, ainda existem muitos cardumes no litoral do Rio Grande do Sul subindo para Santa Catarina — afirma Marcelo Alcioni, do IDP.

Segundo Marcelo, as condições climáticas têm sido determinantes para o fenômeno. Isso porque o vento sul mais fraco estaria favorecendo a permanência dos peixes na costa catarinense por mais tempo.

— O vento sul não está sendo muito forte, então a tainha vai viajando devagarzinho e entrando nas praias. Se tivesse vento sul forte, como elas chegaram cedo, provavelmente já teriam passado por Santa Catarina rumo ao Paraná e São Paulo — explica ele.

A expectativa dos pescadores é de que os próximos dias possam registrar novos grandes lanços nas praias da região. Para Marcelo, o auge da safra ainda pode estar por vir.

 

Mais ressacas e erosão costeira

Por outro lado, os efeitos das mudanças climáticas também avançam sobre as cidades costeiras. Com temperaturas mais elevadas, aumenta a energia das tempestades, dos ventos e das ressacas, intensificando processos de erosão em praias catarinenses. Regiões como Armação, Campeche e Morro das Pedras, em Florianópolis, já convivem com episódios frequentes de avanço do mar.

Regina Rodrigues também faz um alerta sobre a ocupação urbana desordenada no litoral catarinense.

— Dunas, vegetação costeira e manguezais funcionam como proteção natural contra ressacas e erosão. Quando destruímos essas áreas, aumentamos nossa vulnerabilidade climática — afirma.

Record high ocean temperatures off southern California raise fears of prolonged marine heatwave

The waters of southern California historically warm every few years. But the marine heatwave that started last fall wasn’t caused by tropical currents. Photograph: Kevin Carter/Getty Images

by  Roque Planas

 Researchers warn the high-pressure conditions could disrupt marine life and ecosystems if it continues

For more than a century, shoreline stations operated by the Scripps Institution of Oceanography have measured water temperatures along the California coast. This year, they are flashing a warning sign.

Over the last three months, several stations have repeatedly posted record-breaking daily high temperatures – with the La Jolla station registering temperatures a full 10F above historical average at one point last month.

The waters of southern California historically warm every few years as tropical currents make their way north, a phenomenon known as El Niño. But the marine heatwave that started last fall wasn’t caused by tropical currents. Instead, a high-pressure atmospheric system – think of calm, sunny days – has perched above southern California, warming both air and sea above historic levels. The same phenomenon has helped fuel a ferocious California heatwave on land.

 

The extended ocean warming has drawn comparisons to “the Blob”, a three-year marine heatwave caused by similar prolonged high-pressure conditions a decade ago that devastated marine life. The next few weeks are likely to determine whether this marine heatwave fizzles out or evolves into something more Blob-like, scientists say.

“The biggest concern is how the year plays out,” Andrew Leising, an oceanographer with the National Oceanic and Atmospheric Administration, said. “We could be looking at much larger impacts next fall and winter, if it stays warm and then it’s followed by a strong El Niño.”

 

It’s typical in the spring for shifting atmospheric conditions to generate north-westerly winds that push warm surface water back out to the open ocean, allowing cooler water from below to rise to the surface – a phenomenon called upwelling. Upwelling brings nutrient-rich water from the depths to the surface, feeding the phytoplankton that play a crucial role in supporting much of California’s marine life.

Over the last few days, high water temperatures have cooled somewhat, raising the prospect that the heatwave may be dissipating already. It will take more time, however, to know for sure that the heat is clearing.

“The expectation right now is that likely the waters down to even southern California should start cooling a little bit into next month, but it’s not a guaranteed thing,” Leising said. “The concern is the sequence of events and how they unfold.”

Prolonged ocean heat has a devastating impact on phytoplankton and can cause harmful algal blooms. Those changes can wreak havoc on many forms of marine life, from sea lions and dolphins, to shore birds and halibut. The Blob years led to one of the worst Dungeness crab seasons in recent history, said Melissa Carter, a researcher at the UC-San Diego Scripps Institution of Oceanography.

Such heatwaves are becoming more common and lasting longer, partly because of the slow warming of the oceans driven by the climate crisis, and partly because of atmospheric changes that scientists are still struggling to understand.

“The question is what’s causing us to have these extreme warm temperatures?” Carter said. “What are the drivers? That’s what we’re trying to find out.”

 

What concerns Carter is that once these high-pressure systems establish themselves in an area, they create a “feedback loop” that tends to reinforce warm, calm conditions, making upwelling less likely to occur, she said.

“If these systems do become that strong and persistent, where they come every year, it can have the potential to shut down upwelling,” Carter said. “Everything we think of related to the health of the ecosystems of the west coast could be forever altered.”

The lingering ocean heat offers a few upsides, though they pale in comparison with the costs. The warmer water temperatures bring tuna far closer to shore, making it easier to fish for them. Surfers and swimmers have also enjoyed warmer water through the winter.

“I enjoy being in the water when it’s a marine heatwave,” Carter said. “But our ocean should not be a swimming pool. Nothing can live in a swimming pool. That’s not what we want.”

‘Profound impacts’: record ocean heat is intensifying climate disasters, data shows. Oceans absorb 90% of global heating, making them a stark indicator of the relentless march of the climate crisis

 

The extra heat makes hurricanes and typhoons more intense, causes heavier downpours of rain and greater flooding, and results in longer marine heatwaves. Photograph: Michael Probst/AP

by Damian Carrington Environment editor

 

 

The world’s oceans absorbed colossal amounts of heat in 2025, setting yet another new record and fuelling more extreme weather, scientists have reported.

More than 90% of the heat trapped by humanity’s carbon pollution is taken up by the oceans. This makes ocean heat one of the starkest indicators of the relentless march of the climate crisis, which will only end when emissions fall to zero. Almost every year since the start of the millennium has set a new ocean heat record.

This extra heat makes the hurricanes and typhoons hitting coastal communities more intense, causes heavier downpours of rain and greater flooding, and results in longer marine heatwaves, which decimate life in the seas. The rising heat is also a major driver of sea level rise via the thermal expansion of seawater, threatening billions of people.

 

Reliable ocean temperature measurements stretch back to the mid-20th century, but it is likely the oceans are at their hottest for at least 1,000 years and heating faster than at any time in the past 2,000 years.

The atmosphere is a smaller store of heat and more affected by natural climate variations such as the El Niño-La Niña cycle. The average surface air temperature in 2025 is expected to approximately tie with 2023 as the second-hottest year since records began in 1850, with 2024 being the hottest. Last year the planet moved into the cooler La Niña phase of the Pacific Ocean cycle.

“Each year the planet is warming – setting a new record has become a broken record,” said Prof John Abraham at the University of St Thomas in Minnesota, US, and part of the team that produced the new data.

“Global warming is ocean warming,” he said. “If you want to know how much the Earth has warmed or how fast we will warm into the future, the answer is in the oceans.”

The analysis, published in the journal Advances in Atmospheric Sciences, used temperature data collected by a range of instruments across the oceans and collated by three independent teams. They used this data to determine the heat content of the top 2,000 metres of the oceans, where most of the heat is absorbed.

The amount of heat taken up by the ocean is colossal, equivalent to more than 200 times the total amount of electricity used by humans across the world. “Ocean warming continues to exert profound impacts on the Earth system,” the scientists concluded.

Ocean warming is not uniform, with some areas warming faster than others. In 2025, the hottest areas included the tropical and South Atlantic and North Pacific oceans, and the Southern Ocean. In the latter, which surrounds Antarctica, scientists are deeply concerned about a collapse in winter sea ice in recent years.

 

The North Atlantic and the Mediterranean Sea are also getting warmer, as well as saltier, more acidic and less oxygenated owing to the climate crisis. This is causing “a deep-reaching ocean state change in, making the ocean ecosystems and the life they support more fragile”, the researchers said.

“As long as the Earth’s heat continues to increase, ocean heat content will continue to rise and records will continue to fall,” said Abraham. “The biggest climate uncertainty is what humans decide to do. Together, we can reduce emissions and help safeguard a future climate where humans can thrive.”

Why the weirdest sea level changes on Earth are happening off the coast of Japan

Fishing boats sail toward a kelp harvest area in the Northern Territories, 3.7 kilometers off Nemuro, Hokkaido, Japan on June 2, 2018. Fish and kombu seaweed harvested in this region are crucial to Japan's food culture, but recent changes in a warm ocean current called the Kuroshio have damaged these fisheries.

The Asahi Shimbun/Getty Images

 

 By Chris Mooney, Yumi Asada

 

 

Bathtubs and pools mislead us about the ocean: Its surface is anything but flat.

Seas pile up in some spots, pushed by trade winds or pulled by gravity toward big things like ice sheets. Amid it all, at the western end of large ocean basins, the fastest surface currents — veins of warm water — race toward the poles, causing additional slopes at the surface.

The ocean is uneven to begin with, and its unevenness is also changing. Maps of recent changes show intricate patterns of watery hills and valleys, but also call attention to one extraordinary location. Off the coast of Japan, one region of the ocean has been rising by nearly an inch every year, right next to another where it has been falling even faster.

It’s the fingerprint of one of those surface currents changing its location, an event that has had dramatic repercussions. The Kuroshio, or “Black Current,” is one of the largest streams of water anywhere in the world, and its recent movement has triggered record-warm ocean temperatures and upended fisheries, an indelible staple of Japanese culture. Scientists say the warm waters have even amplified heatwaves on land and driven extreme rainfall. 

 

And while there are signs some of the changes are now waning, fishing communities say they aren’t yet back to normal. Meanwhile, scientists worry it could be a sign of more volatility to come.

The position of the current could keep fluctuating, said Bo Qiu, a leading Kuroshio expert at the University of Hawaiʻi at Mānoa. “It’s hard to predict the future, but given the data we have so far, I can only see the intensity becoming larger and larger,” he said. 

The Boso Peninsula forms the eastern edge of Tokyo Bay. Normally, the Kuroshio Extension banks away from Japan and heads into the Pacific near this spot. But in recent years, it's continued northward, bringing unprecedented warm water with it.

John S Lander/LightRocket/Getty Images

 

 

A river in the ocean

The deep, warm Kuroshio transports more than 200 times as much water as the Amazon River, traveling north from the equator and normally banking east around Japan’s Boso peninsula, near Tokyo. Here, it becomes known as the Kuroshio Extension as it heads into the open Pacific. 

 

But in recent years, the current has been behaving in anything but the usual way, and the Extension, in particular, made a major divergence along Japan’s coast. Its northern edge shifted as much as 300 miles farther poleward, leading to unprecedented warm waters in the surrounding region.

“I was so surprised I don’t even know if ‘surprised’ is the right word,” said Shusaku Sugimoto, an associate professor at Tohoku University in Sendai, Japan, a northern coastal city. 

 

When a major ocean current changed course, sea levels changed with it

Recent changes in a warm current called the Kuroshio have created some of the fastest rising seas on the planet — right next to seas that are falling even faster. 

Sugimoto led a study analyzing ocean temperatures off the coast in locations the Extension didn’t historically reach, but has in recent years. “The fact that the temperature rose 6 degrees (Celsius) off the Sanriku coast, and the elevated temperature persisted for two years, represents a level of water temperature rise we’ve never seen before,” he said. 

It’s not the only change.

In August of 2017, the Kuroshio current south of Japan settled into a “large meander” pattern, leaving the coastline and looping southward, taking its warm waters with it. This big shift in water temperatures south of Japan changes the distributions of fish species offshore.

Large meanders themselves are a well-known recurring feature of the current, explained Shinichiro Kida, an oceanographer at Kyushu University. Records of these events date back to the 1960s. During a lengthy meander event from 1975 to 1980, scientists saw a severe decline in anchovy in the Enshunada Sea, a major fishing region to the south of Japan’s main island of Honshu. The anchovy were replaced by sardines, which favor the warmer water the current brought to the region.

But no Kuroshio large meander that we know of has lasted as long as this one. In August, the Japan Meteorological Agency finally declared that it had ended after nearly eight years. But overall both changes have had a big effect on this country that is home to more than 100 million. 

 

The meander and the Extension shift are connected, Qiu said. He co-authored a new paper in the Journal of Climate arguing as much, and calling the configuration a “new dynamic regime.”

“I’ve been working on the Kuroshio Extension for more than three decades,” Qiu said. “I never expected this.”

As the Kuroshio powers along, it not only brings warmer water but also, depending on its location, higher sea level. There can be a several-foot difference between ocean heights on different sides of the current, thanks to its warmth and speed .

But because of these factors, any new movement of the current can have dramatic effects. 

 

The large meander, for example, triggered a sea level fall in one region and pronounced sea level rise — by as much as half a foot — along the coast of the island of Honshu south of Tokyo. In October of 2017, when Typhoon Lan struck the Shizuoka Prefecture along this coastline, the higher sea level amplified the damage, according to the Japan Meteorological Agency.

It is not only the height of the sea: As the Kuroshio is a warm current, and one traveling northward into cooler waters, its arrival in a new location has enormous effects on ocean temperatures.

The big question is how much the recent phenomena are part of a natural cycle, and how much it’s influenced by something else, like climate change. (And how much it’s both, combined.)

The impact of climate change on the large meander is unclear, because of its long history. But as far as the Extension shift goes, there are mounting reasons to implicate greenhouse gases and a changing climate.

When the tropics travel to you

To understand the recent changes in the Kuroshio is to understand how water moves through the world’s oceans, especially the large rotating “gyres” found in the world’s major ocean basins. 

 Five of these basins — North and South Pacific, North and South Atlantic, and Indian — feature a similar pattern. Warm water travels west along the equator, then turns toward the poles. The currents carrying the warm water north or south on poleward transits are called “western boundary currents,” and they include the Kuroshio and its four famed cousins: the Gulf Stream, the Brazil, the East Australian, and the Agulhas.

 

Japan has seen some of the world's most extreme ocean changes

In recent years, waters off Japan’s Pacific Coast have experienced some of the world’s highest rates of ocean warming, as well as extreme changes in sea level.

 

Scientists are now seeing most of these currents changing in a similar way — getting warmer and pushing even farther poleward.

This change is rooted in a phenomenon known as the Hadley Cell, a global zone of warm, rising air across the tropics. It’s now expanding due to climate change. 

 

“This expansion shifts not just rainfall patterns but also the zones of sinking air that anchor high-pressure systems, such as the Pacific High,” explains Brown University climate scientist Emanuele Di Lorenzo.

In the middle latitudes, these massive high-pressure systems are the driving force behind currents like the Kuroshio. So, when the winds move, the currents do too.

Both models and data suggest the Kuroshio Extension, in particular, has been moving north partly because of the atmospheric shift, Di Lorenzo explained.

Between 1993 and 2021, driven by wind changes, the northern edge of the Kuroshio Extension shifted north by about 130 miles, a recent study found. This was before an even larger shift in 2023 and 2024. 

 

The Kuroshio Extension’s leap in 2023 and 2024 was an extreme event. The northern edge reached nearly to the northern tip of Honshu, Japan’s largest island. In a different study, Sugimoto and colleagues with the Japan Meteorological Agency and the Meteorological Research Institute took oceanographic measurements in the Extension’s new location. They found water as much as 18 degrees Fahrenheit warmer than usual, extending to a depth of around 400 meters, or 1,300 feet.

The authors note that for an entire year and a half between April 2023 and August 2024, the region saw “intense marine heatwave conditions almost every day.”

And it was not just in the water: the Japan Meteorological Agency also found that the extreme ocean conditions contributed to record summer heat over land in northern Japan in 2023. Another group of scientists, meanwhile, linked the warm offshore current to extreme rainfall over Japan’s Chiba Prefecture, near Tokyo, in September of 2023. 

The first saury catch of the season is landed at a port in Nemuro on Japan's northernmost main island of Hokkaido on Aug. 15, 2025. This species has been particularly affected by changes in the Kuroshio.

Kyodo News/Getty Images

 

An uncertain future for fisheries

These ocean changes have altered the distributions of fish populations along Japan’s Pacific Coast, creating extreme impacts on Japan’s iconic fisheries. 

 

In central Japan, for instance, a major mackerel fishery was upended, and fishers say that even though the large meander has now ended, that doesn’t mean things can instantly go back to the way they were.

“Immediate recovery is not a reality, and while conditions may gradually improve, at present, there has been no recovery in catches,” said Osamu Nagai, executive director of the Mie Gaiwan (Outer Bay) Fisheries Cooperative Association.

“The catch has fallen to less than half of what it was 10 years ago — we’re now only catching about 20 to 30 percent of the mackerel. This is a major blow,” Nagai said.

Northeastern Japan’s Sanriku coast, known for its rich fisheries, is a different story, but still a bad one. Here, the southward flowing Oyashio current traditionally brings down cool waters and supports rich fisheries. But when the Kuroshio Extension moved northward into this region, it displaced the Oyashio, bringing on a stark change in ocean temperature. 

 

And it is not just fish species, like Pacific salmon and saury, that became harder to catch.

“What matters most is the foundation of Japan’s most important food culture, which is the flavor made out of Kombu seaweed — it can only be harvested in Hokkaido, near Japan,” said Yoshihiro Tachibana, a professor who specializes in climate dynamics at Mie University. 

 

Kombu kelp is laid in the sun to dry Wakkanai, Hokkaido, on July 15, 2012. This seaweed is a vital part of Japan's food culture and economy. But it's becoming harder to harvest.

Hiroaki Murata/The Yomiuri Shimbun/AP

 

 

“Kombu stocks are declining dramatically. Dashi (the fundamental Japanese soup stock) culture might collapse. It’s declining. We can’t get any at all. So I believe this has a tremendous impact on our food culture as well,” he said.

Recently, the northern edge of the Kuroshio extension has retreated a bit. It has moved back to around 37 degrees North Latitude, according to Qiu. That’s still a high location historically, but hardly as extreme as before. 

 

But the questions remain: what do these extreme ocean events mean, how they are linked to climate change? For at least one researcher, they’re an early sign of things to come.

“It’s a great opportunity to learn what the oceans will be like 100 years from now,” said Sugimoto, of Tohoku University in the northeastern region of Honshu, Japan’s largest island.

“An unprecedented ocean phenomenon is now occurring by chance in Tohoku,” he continued. “Understanding how this has altered the seas of Tohoku offers a chance to understand how the world’s oceans will change in the future.”

Elisabeth Doty contributed to this report.

Shifting Climate Alters Pattern of Atlantic’s Giant Seaweed Blobs. Blooms of yellowish-brown seaweed along the Equator are breaking records and defiling beaches, while a centuries-old patch farther north is disappearing.

Mexican National Guard members during a sargassum seaweed cleanup event in Cancun, Mexico, in June.Credit...Paola Chiomante/Reuters

 

By Eric Niiler

 

A 5,500-mile blob of seaweed in the Atlantic Ocean that has menaced beaches across the Caribbean and Florida in recent years is exploding in size, while a second patch farther north is declining rapidly, driven by rapid changes in the region’s climate.

A study published Thursday in the journal Nature Geoscience finds a big shift in the growth patterns of sargassum, a type of floating macroalgae that provides food and shelter for fish, turtles, seabirds and other marine life.

The southern patch, known as the Great Atlantic Sargassum Belt, has now reached 38 million metric tons, a 40 percent increase from its record year of 2022.

“Usually we have a 10 percent to 20 percent fluctuation year to year,” said Chuanmin Hu, a professor of physical oceanography at the University of South Florida and an author of the paper. “But this year was crazy, and we do not have an answer of why.”

 

Scientists hadn’t detected sargassum in this equatorial region before 2011.

Since then, winds and ocean currents have pushed blobs of sargassum west toward coastal waters in the springtime. Beaches along Mexico’s Yucatán Peninsula have suffered from smelly piles of seaweed, while the president of the Dominican Republic said in June that his nation faced a “regional emergency” from sargassum and called for action by the United Nations.

In 2023, about 13 million metric tons of sargassum covered some Florida beaches and decomposed into smelly piles before disappearing in the summer. A study that year in The Journal of Global Health by doctors on the island of Martinique reported respiratory ailments from decomposing seaweed that produces hydrogen sulfide gas.

While experts have not pinpointed the cause of the massive sargassum bloom, Saharan dust storms and smoke from African wildfires blowing west across the Atlantic are playing a role, scientists say. These tiny particles drift into the ocean and act as a kind of fertilizer for the sargassum, according to Brian Lapointe, principal investigator at Harbor Branch Oceanographic Institute at Florida Atlantic University and an author of the new paper.

Sully Sullivan, a graduate student at the University of South Florida College of Marine Science, collected sea samples in the Atlantic in July 2024.Credit...Sully Sullivan

 

 Runoff from the Amazon and Orinoco Rivers in South America and the Congo River in Africa also provide pulses of nutrient-laden water that feed the growth along the equatorial seaweed belt. After a two-year drought in the Amazon, Dr. Lapointe noted that big floods in the spring caused a corresponding boost in sargassum.

 

 

“The climate is having a very significant effect on this bloom, but there are many underlying drivers of climate change,” Dr. Lapointe said. “Everything from high temperature, extreme rainfall, droughts and rainfall events, and winds. ”

Dr. Hu and his colleagues used satellite imagery of the ocean surface as well as shipboard observations to document 25 years of sargassum movement. The rapid decline of the northern patch, known as the Northern Sargasso Sea, started in 2015. The Gulf Stream current system has carried seaweed from its nursery in the western Gulf of Mexico into the Northern Sargasso Sea for centuries. However, rising ocean temperatures and a series of marine heat waves have begun making the gulf too warm for Sargassum, Dr. Hu said.

In the past 20 years, the gulf on average has warmed 0.4 degrees Celsius, or 0.72 degrees Fahrenheit, he added.

“In the summer, the water is already warm, adding another 0.7 degrees is very bad,” Dr. Hu said. “Plus we have more frequent marine heat waves in the past 10 years, so that will add to more stress to native sargassum.”

Dani Cox, an independent marine microbiologist based in Miami, said rising ocean temperatures was just one of many causes for the decline of one patch and the explosion of the other, noting that some lab experiments found that sargassum thrive in warm water while others have found the opposite.

 

“There’s so much going on which is why everyone is not sold on one answer,” Dr. Cox said. “All of us can only look at one or two things at a time. I absolutely think the inundations will stay the same or get worse.”

As for next year’s seaweed invasion, Dr. Lapointe said beach-lovers should stay vigilant before booking a spring break vacation, noting that the Bahamas might be a safer bet than the Yucatán.

“I would be very careful in choosing a destination,” he said.

Mystery heatwave warms Pacific Ocean to new record

Mark Poynting and Matt McGrathBBC News Climate and Science

 

 

The waters of the north Pacific have had their warmest summer on record, according to BBC analysis of a mysterious marine heatwave that has confounded climate scientists.

Sea surface temperatures between July and September were more than 0.25C above the previous high of 2022 - a big increase across an area roughly ten times the size of the Mediterranean.

While climate change is known to make marine heatwaves more likely, scientists are struggling to explain why the north Pacific has been so hot for so long.

But all this extra heat in the so-called "warm blob" may have the opposite effect in the UK, possibly making a colder start to winter more likely, some researchers believe.

"There's definitely something unusual going on in the north Pacific," said Zeke Hausfather, a climate scientist at Berkeley Earth, a research group in the US.

Such a jump in temperatures across a region so large is "quite remarkable", he added.

The BBC analysed data from the European Copernicus climate service to calculate average temperatures between July and September across a large area of the north Pacific, sometimes known as the "warm blob".

The region extends from the east coast of Asia to the west coast of North America, the same area used in previous scientific studies.

The figures show that not only has the region been warming quickly over the past couple of decades, but 2025 is markedly higher than recent years too.

 

That the seas are getting hotter is no surprise. Global warming, caused by humanity's emissions of carbon dioxide and other gases, has already trebled the number of days of extreme heat in oceans globally, according to research published earlier this year.

But temperatures have been even higher than most climate models - computer simulations taking into account humanity's carbon emissions - had predicted.

Analysis of these models by the Berkeley Earth group suggests that sea temperatures observed across the north Pacific in August had less than a 1% chance of occurring in any single year.

Natural weather variability is thought to be part of the reason. This summer has seen weaker-than-usual winds, for example. That means more heat from the summer sunshine can stay in the sea surface, rather than being mixed with cooler waters below.

But this can only go so far in explaining the exceptional conditions, according to Dr Hausfather.

"It certainly is not just natural variability," he said. "There's something else going on here as well."

 

One intriguing idea is that a recent change to shipping fuels might be contributing to the warming. Prior to 2020, dirty engine oil produced large amounts of sulphur dioxide, a gas harmful to human health.

But that sulphur also formed tiny, Sun-reflecting particles in the atmosphere, known as aerosols, which helped to keep a lid on rising temperatures.

So removing that cooling effect in shipping hotspots like the north Pacific could be revealing the full impact of human-caused warming.

"It does seem like sulphur is the primary candidate for what's driving this warming in the region," said Dr Hausfather.

Other research suggests that efforts to reduce air pollution in Chinese cities has played a role in warming the Pacific too.

That dirty air did a similar job to shipping in reflecting sunlight away, while cleaning it up could have had the unintended consequence of allowing more ocean heating.

Possible impacts for the UK?

The north Pacific's marine heatwave has already had consequences for weather on both sides of the Pacific, likely boosting very high summer temperatures in Japan and South Korea and storms in the US.

"In California, we've seen supercharged thunderstorms because the warm ocean waters in the Pacific provide heat and moisture," said Amanda Maycock, professor in climate dynamics at the University of Leeds.

"In particular, there are things we call atmospheric rivers… bands of air, which contain very high amounts of moisture that fuel themselves from the ocean waters," she added.

"So if we have warm ocean waters… they can then bring a lot of moisture onto the land, which then falls out as rain, or in the wintertime can precipitate out as snow."

 

Long-term weather forecasting is always challenging, but extreme heat in the north Pacific has the potential to affect the UK and Europe in the coming months too.

That's because of relationships between weather in different parts of the world known as teleconnections.

"Although the current warm conditions are located in the north Pacific, these can generate wave motions in the atmosphere that can alter our weather downstream into the north Atlantic and into Europe," said Prof Maycock.

"That can tend to favour high-pressure conditions over the continent, which brings us more of an influence from the Arctic, where we have colder air," she added.

"That can be drawn over Europe and bring us colder weather in early winter."

A colder outcome is by no means certain, as this is a complex area of science. Several other weather patterns also affect UK winters, which are typically getting milder with climate change.

And a warm north Pacific appears to have different effects later in the winter, favouring milder and wetter conditions in some parts of Europe.

Emerging La Niña in the tropical Pacific

Another factor to throw into the mix is what's happening further south in the eastern tropical Pacific.

There, surface waters are unusually cool - a classic sign of the weather phenomenon known as La Niña.

 

La Niña, and its warm sibling El Niño, are natural patterns, although research published this week highlighted that global warming could itself impact the swings between them.

Weak La Niña conditions are expected to persist over the next few months, according to NOAA, the US science agency.

All else being equal, La Niña generally increases the risk of a cold start to winter in the UK, but also brings a higher chance of a mild end, the Met Office says.

"These two drivers in the north and tropical Pacific will be acting together this winter," said Prof Maycock.

"But since the La Niña is quite weak this year, the extreme warmth in the north Pacific could be more important for forecasting the winter ahead."

Additional reporting by Muskeen Liddar and Libby Rogers